Water Journal October 1994

AUSTRALIAN WATER & WASTEWATER ASSOCIATION

Volume 21, No 5 October 1994 Editor EA (Bob) Swinton

CONTENTS

Editorial Correspondence 4 Pleasant View Crescent Glen Waverley Vic 3150 Tel/Fax (03) 560 4752

ASSOCIATION NEWS From the Federal President From the Executive Director Association Meetings

2 3 7

FEATURES Contracting Overseas •

Australia Inc? Asia: A Shangri-la for Australian Contractors

15

Peter Gebbie, PWT •

South East Asia: Experiences and Prospects

17

Peter Gilchrist, Chairman ~quatec-Maxcon •

Expansion into New Areas

18

John Polich, Manager Warman Project Engineering Group •

Exporting a New Technology

19

Tony MacCormick, General Manager Marketing Memtec •

Joint Venture in Manufacturing

21

Peter Becker, Marketing Services Manager Vinidex Tubemakers •

Trade Diplomacy, or Otherwise?

22

John Towns, Chief Executive ANI-Kruger •

Some Recent Contracts

Nutrient Removal in Intermittent Cycle Plants

23

24

RI Siebert Nitrogen and Phosphorus in Laboratory Scale Models

33

42

Australian Water & Wastewater Inc ARBN 054 253 066 PO Box 388 Artarmon NSW 2064

REPORTS

Federal President 36

David Dixon IAWQ Budapest Water Quality in America

38 40

Mike Chapman Drought and Disaster Planning

41

David Watson

DEPARTMENTS Industry News International Affiliates Products Books Meetings

ACT - Alan Wade Tel (06) 207 2350 Fax (06) 207 6084 New south Wales - Mitchell Laginestra Tel (02) 412 9974 Fax (02) 412 9876 Northern Territory - Ian Smith Tel (089) 82 7244 Fax (089) 41 0703 Queensland - Leon De W Henry Tel (07) 233 1611 Fax (07) 233 1649 South Australia - Phil Thomas Tel (08) 259 0244 Fax (08) 259 0228 Tasmania - Jim Stephens i;el (002) 31 0656 Fax (002) 34 7334 Victoria - Mike Muntisov Tel (03) 600 1100 Fax (03) 600 1300 Western Australia - Alan Maus Tel (09) 420 2465 Fax (09) 420 3178

WATER (ISSN 0310- 0367)

P Haines, J Nielsen, B Druery, J Ball

IAWQ Flotation Conference

Branch Correspondents

is published six times per year February, April, June, August, October, December by

J Brodsky, FE Grey The Salmon-Q Water Quality Model:A Murray Darling Application

F R Bishop, Chairman B N Anderson, G Cawston, M R Chapman P Draayers, W J Dulfer, GA Holder M Muntisov, P Nadebaum, JD parker A J Priestly, J Rissman

30

D H Abeysinghe, C A Borthwick The Economics of Wilderness Areas

Margaret Bates Tel (02) 413 1288 Fax (02) 413 1047 A\Y/WA Federal Office Level 2, 44 Hampden Road Artarmon NSW 2064

Editorial Board 14

Damian Ryan, AUSTEMEX •

Advertising Sales & Administration

4

12

46 47 48

OUR COVER Solomon Islands, one of the countries that have received aid from the Australian

International Development A ssistance Bureau (A /DAB). Photograph - Norman Plant AIDAB/OIB

Richard Marks

Executive Director Chris Davis Australi an Water & Wastewater Association assumes no responsibility for opinions or statements of facts expressed by contributors or advertisers and editorials do not necessarily represent the official policy of the organisation.

Display and classified advertisements are included as an informational services to readers and are reviewed by the Editor before publication to ensure their relevance to the water environment and to the objectives of the Association.

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Subscriptions Water is sent to all members of the AWWA as one of the privileges of membership. Non members can obtain Waier on subscription at an annual subscription rate of$35 (surface mail).

TECHNOLOGY

NUTRIENT REMOVAL IN INTERMITTENT CYCLE PLANTS RI Siebert*

PART 1 COMPUTER SIMULATION Summary The presence of Poly-P organisms in the Woolgoolga Sewage Treatment Plant indicated that biological phosphorus removal may be achieved in intermittently decanted extended aeration (IDEA) sewage treatment plants. Through the use of a dynamic computer simulation of IDEA sewage treatment plants a number of operating regimes and configurations were trialled to determine which would give the greatest propensity for the biological removal of phosphorus. It was found that two configurations achieved significant biological phosphorus removal. They are an intermittent feed configuration and a configuration utilising an anaerobic reactor.

This paper deals with the computer simulations. A later paper will summarise the results of pilot plant trials.

Introduction At present the Woolgoolga Sewage Treatment Plant (in north eastern New South Wales) is dosed with alum to achieve phosphorus removal to a level not greater than 1 mg/L as required by the Enviromental Protection Authority. As part of the licence conditions the effluent is monitored for phosphorus on a weekly basis. It was found that during winter when the influent to the plant was colder the effluent phosphorus levels decreased from close to 1 mg/L to below 0.2 mg/I. Staining and microscopic examination of the sludge from the plant showed that there was growth of Poly P organisms and as such it was assumed some biological removal of phosphorus was occurring. Sludges from plants at Coffs Harbour and Sawtell were examined in the same manner and Poly P organisms were also found in these sludges. As with Woolgoolga it was assumed that some biological phosphorus removal was occurring.

Ho et al (1993) reported on the performance of laboratory scale intermittently operated biological nutrient removal activated sludge processes and found that biological phosphorus removal was achievable.

It was stated that phosphorus removal occurred in systems fed either continuously or intermittently provided that the basic 24

requirements such as a COD:TKN ratio greater than 10: 1 and an influent concentration of RACOD greater than 50 i'ng/1 were met. Ho et al (1993) also stated that over-aeration adversely affects both nitrogen and phosphorus removal as simultaneous nitrification and denitrification was required during the aeration cycle to achieve biological phosphorus removal.

Bliss et al (199 3) investigated and reported on the biological removal of phosphorus in the intermittently decanted extended aeration activated sludge process using data from plants at Bathurst, Urunga and Port Macquarie . The investigations centered on the use of anaerobic reactors up stream of the intermittent decant extended aeration (IDEA) process to provide an environment suitable for the biological removal of phosphorus. The report indicated that biological phosphorus removal could be achieved with the use of an anaerobic reactor and mixed liquor suspended solids (MLSS) recycle.

Anecdotal data from a number of operators also indicated that with aeration equipment failure and subsequently long periods of little or no aeration IDEA plants exhibited a phosphorus release. When aeration was re-commissioned the plants achieved low levels of effluent phosphorus.

This could indicate a level of phosphorus release and uptake as seen in biological phosphorus removal plants.

Two studies were proposed on biological phosphorus removal in intermittent cycle plants at Coffs Harbour to determine operating regimes which would maximize the biological removal of phosphorus.

They were the simulation of intermittent cycle plants, using a dynamic computer model , to evaluate theoretically various operating regimes, and the operation of a pilot plant constructed by Aeration and Allied Technology Pty Ltd. This paper deals with the dynamic computer simulation.

Dynamic Simulation The computer model was developed using a model similar to that proposed by the IAWPRC (1986) and Wentzel et al (1989).

The model operates on 17 substrates listed in Table 1.

The fate of each of these substrates as used in the development of the dynamic

model is presented in Figure 1 in a matrix format as described by IAWPRC (1986), and the equations are discussed below.

It should be noted that the model does not consider the nondegradabl e so luble COD. It also only considers the nondegradable particulate COD as part of the inert sludge. These two items were not considered further as they do not take part in reactions on the model.

Notwi thstanding, the model can be modified to include these two substrates.

The model does not consider the nondegradable fractions of nitrogen and phosphorus as these also play no part in the biological reactions. These substrates could be added to the model if required.

Reactions Hydrolysis of SBCOD to form ISCOD. In the model the SBCOD undergoes hydrolysi s by heterotrophs to form Table 1~ Substrates and acronyms considered Slowly biodegradable chemical oxygen demand Readily biodegradable chemical oxygen demand Internally stored RBCOD Poly B hydroxybutyrate Organic Nitrogen Ammonia Nitrogen Oxidised Nitrogen Organic Phosphorus Soluble Phosphorus Poly phosphate Alkalinity Imaginary Salt Dissolved oxygen Heterotroph concentrations Nitrifier concentrations Poly - P concentrations Inert sludge

SBCOD RBCOD IS COD PHB Org-N NH 4 NOX Org-P PHO PPH ALK SALT

DO XBH XBN XBP XI

Table 2. Influent parameters.

Substrate

Influent mg/L

200 200

SBCOD RBCOD Org-N

13

42

TH 4

Org-P PHO

2

10 270 100

ALK XI

pH

7.4

1500 kL

ADWF

*Coffs Harbour City Council WATER OCTOBER 1994

!ism. The energy from the catabolism provides the energy for heterotroph growth or anabolism.· The steps of the conversion of RBCOD to Acetyl CoA, the energy transfer for anabolism and the anabolism were not used in the model as the conversion as described by Wentzel et al (1989) is less than the rate of removal of ISCOD and RDCOD to form heterotrophs as described by IAWPRC (1986 ), Metcalf and Eddy ( 1991 ), and others. The model would therefore have had an inordinately slow heterotroph growth rate. Also there was no published information on the rates of anabolism from energy produced. The rate used for the combined reaction is consistent with the rate of heterotroph growth published by Metcalf and Eddy (1991 ) and others. In the model the ISCOD is utilized in preference to the RBCOD. The figure used in the model for yield in the growth of heterotrophs Yh is given

by WRC (1984), Wentzel et al (1989 ), IAWPRC (1986) and others. The figure used is 0.67 g heterotrophs as COD per g COD removed.

Using the composition of cells as given

by Metcalf and Eddy (1991 ):

RBCOD which is stored in the heterotrophic biomass as RBCOD (ISCOD).

The ISCOD is then available 'for the reactions of aerobi c heterotroph growth and anoxic heterotroph growth using oxygen and nitrate as electron acceptors repectively. The ISCOD produced in this reaction is transferred immediately into the cell. It is therefore not available for uptake as PHB by Poly-P organisms.

This hydrolysis also releases into solution the nitrogen and phosphorus bound in organic matter producing ammonia nitrogen and soluble phosphorus. This reaction also includes the conversion of the released nitrogen to ammonia and the utilization of the hydrogen ion.

In the model the hydrolysis is assumed to occur in aerobic, anoxic and anaerobic conditions. This is consistent with the findings of Wentzel et al (1989). The rate of hydrolysis is as given by IAWPRC (1986) as 3.0 g SBCOD per day per g het erotrophs (as COD) and is temperature dependent.

Aerobic growth of heterotrophs.

The model for the growth of heterotrophs is simplified in that it addresses the growth of heterotrophs using ISCOD and RBCOD as a singular reaction. In reality ISCOD and RBCOD must reduce to Acetyl CoA or a similar substrate prior to it being utilized as the substrate for catabo-

C6o Hs1

0 23 N12

The rate lior heterotrop h growth is given by IAWPRC (1986) as 5.0 g cells per day per g cells at pH 7.2 and is affected by pH and temperature, and the concentrations of RBCOD, oxygen and so lubl e phosphorus.

Anoxic growth of heterotrophs.

The anoxic growth of heterotrophs occurs using nitrate as an electron acceptor. In the model this reaction occurs at a rate equal to 80% of the aerobic reaction reaction rate (after IAWPRC 1986). This equates closely to the rates described by Barnard in Barnes and Gttenfield (1986) and Griffith (1993) as Kdn. l plus Kdn.2 which occur when both RBCOD and SBCOD are available. The three rates usually quoted were not used in this model as the model includes the hydrolysis reactions and the lysis of biomass. The slower rates of 0.101 (Kdn.2) and 0.072 (Kdn.3) are on ly applicable to the combined reactions of hydrolysis of SBBOD then utilization of ISCOD/RBCOD, and lysis of cell matter then hydrolysis to ISCOD/RBCOD then utilization of the ISCOD/RBCOD respectively.

Based on an electron balance l g of nitrate is equivalent to 2.857 lg of oxygen.

In the model the nitrate removed is equated to an equivalent ISCOD/RBCOD removed as follows:

P

it can be determined that, for cell growth: Per g ISCOD or RB COD removed: 0.0155Yh g of soluble phosphorus, 0.084Yh g of ammonia nitrogen and 0.3Yh g of alkalinity are utilised and the oxygen demand is I - Yh g.

(I - Yh) NOX removed= ,- - - 2.8571

x RB COD removed

Figure 1 Matrix S BCOO RBCOD ISCOD

Hydrolysis of BOD toRDB

.,

PH13

0'1-N

NH.

NOX

Org-P

XBH

XDN

XDP

XI

ALK

Reaction rates DO •

.... G- - -

BODIXBH~J

..

Tl<N /800 ,.. 1bcMt

+l.571 4

+I

.,

.,

Anoldc growth of heterotrophie biomass

- 0.°'4• Y,

OPH/BOOKabov-e

+I

-0.01551

v,

.,

- (1 - YJ

-,...-

0..) IV,

Y,

-0.0155 1

v,

( I . YJ

...

l.5714 1

v,

~t · l~ooj •~Jt '- X ROB ~

Y.

it

.,

1 - 0.0..11

v.

Kda

B

-0.01 55 11 Y,

0.4'44

I

Aerobic growth of Poty-P biomass

•(7. 1411 - -(4.57 U O.JV.) Y.)

Y,

~~ ~ •TKN

k.,,•00

J~

+ O.N7J

1' 0.0IJ4

O.l1:l.4J

+ O.N 12

+ 0.0114

Ux1.4J

+ 0.067J

+ 0.0U4

I

., .,

Deacy of Poty-P biomass

.,

Release of Poty-P

.?;-

:5~ "-0

~~

""'

UJ -0

WATER OCTOBER 1994

81 L

UJ-o

( I • V.)

b.., x fn (temp)

,.,

b,. x ln(temp)

,.,

b.x ln(temp)

~

:0

-0

-0

-0

::>

::>

C

..0

11....C:

k,.o·OO

j

x ln (pH)x ln (temp)x XBP

b.x ln (temp)

::, ..8 >. co ~ u C =~ 8-0 'rJ ~ !lC: ...Si .Q~ 0 >-. ~g -

x ln{lemp)J X8H

b. x ln(temp)

., .?;-

~

NOX1w,tch • NOX

j

k.-,-PHB/XBP

,.,

..

I

>.

-0.J 1 V,

Y,

Decay of nitrifying· biomass

:So ]o 1o ... o ~o ';;;Q :;U :.u ;U - u "'3~ - ... :§~

NOX •~"h

1'

~-PHBIXBP - - , ~-DO -

jo.015SV,

O.lxJ .4J

I

, fa(pH) ,fa~,mp), XBH

.. tn(pH) .. tn{lemp) xXBH

II

--:;:

11_.,ROB., _00,~"h __ OOswitch • 00

-0.4144

...

- 0.0M• Y,

-I

Release of PHB

NOX j k.,.•NOX

k.,,•00

~

,I

fnlPH) ifn{temp)x XBH

11,. • ROB_

( I - VJ

Aerobic growth of nitritying biomass Sequestering of ROB to PHB

1 ln(temp) .. xBH

It,• 800/XBH

Hydrolysis of organic P to soluble phosphorus

Decay of heterotrophic biomass

PPH

"

Hydrolysis of TKN toNH 4

Aerobic growth of heterotrophlc biomass

PHO

o ·c:

2

-~

C E "'0

C

£~

..8"' "t' ~

.i::: ~

2 t~ -~-g_ :0::>"' -a e .Qo

El g .f~ Z< zz at 00"'

~

0

C

"'0

-0

-o o.i:::

Cl) 0.

o~ -

.;;~

E 0 l5

(.)

:aP. 0

ti"' 0

~

.; ,.:: ·5

"'~

E 0 l5 ~

i5 t ::C:l5 z ~

"' :2 0 "' t:

"' .E

0

:s ]

<

C

"'00 I<'

0

v,, c Helerolroph gro/'1h rale ""' • Nilrffier grOW1h rate 11, • Poly-P growth rate k, • Rate or hydrolysis k,, • 1/2 ra te for hydrolysis Ii;. • Substrate 112 rate for he1erotroph k.,." • DO 112 rate for aerobic heterotroph k, • rate of sequeslering ~- rate of lysis or cells Y • yield

25

Similar to the aerobic growth of heterotrophs 0.015 5Yh g of phosphorus is removed per g ISCOD/RBCOD removed.

The grams of alkalinity produced in the reaction (in terms of CaCO 3) can also be calculated from the grams of ISCOD/RBCOD removed as: 3.5714 x (I - Yh) - - - -- x RB COD removed 2.857 1

The rate for anoxic growth of heterotrophic biomass is affected by pH and temperature, and the concentrations of ISCOD/RBCOD, oxygen, nitrate and soluble phosphorus.

Aerobic growth of nitrifiers. As with the oxidation of ISCOD/RBCOD the model is simplified in that the reactions to convert soluble nitrogen to ammonia are not considered. It is assumed that entrapped available organic nitrogen is converted directly to ammonia nitrogen during hydrolysis.

Figures for yield in nitrifier growth Yn are again given by WRC (1984), Wentzel et al (1989), IAWPRC (1986) and others.

In general the figure used is 0.15 g nitrifiers as COD per g ammonia nitrogen nitrifi ed. The oxygen and other substrate demand for cell growth can then be determined as: Per gram ammonia nitrogen nitrified: 4.57 13 - Yn g oxygen 0.0155Yn g of soluble phosphorus 7.1428 - 0.3 Yn g of alkalinity.

I - 0.084Yn g of nitrate are produced.

The rate for nitrifier growth using ammonia as the substrate is taken as 0.35 g cells per g cells.day at pH 7.2 and is affected by pH and temperature, and the concentrations of oxygen, ammonia-nitrogen and soluble phosphorus .

Sequestration of PHB. Only the readily degradable RBCOD in solution is available for sequestering to form PHB .

The sequestering of RBCOD to form PHB is a first order reaction. After Wentzel et al (1989) it is proposed that Poly-P cells will sequester 1 g of RBCOD for the release of 0.4844 g of stored phosphorus. This phosphorus is released to form part of the available soluble phosphorus substrate. The figure of 0.4844 is derived from the production of ADP from ATP per mole of RBCOD converted to Acetate and taken up to form PHB. Growth of Poly-P organisms. A figure for yield of Poly-P biomass Yp is given by Wentzel et al (1989) as 0.639 g Poly-P per g PHB removed. The substrate demands for cell growth can then be determined as: Per g PHB removed: I - Yp g oxygen 0.0155Yp g of soluble phosphorus, 0.084Yp g of ammonia nitrogen, 0.3Yp g of alkalinity.

0.9 to 1.1 g phosphorus are taken up and stored as Poly-P (Wentzel et al,1989) (a figure of 1 is used in the model).

26

The rate for Poly-P biomass growth is given as 1.0 g cells per day per g cells and is affected by pH and temperature, and the concentrations of oxygen, PHB and soluble phosphorus.

Decay of biomass. The model assumes endogenous decay or lysis of the biomass which both removes active biomas s from the reactors and produces SBCOD, Org-N and Org-P. For the model it is also assumed that 0.2 of the biomass remains as undegradabl e nonactive or endogenous mass after lysis.

The lysis of 1 g of biomass produces: 0.8 g of SBCOD as COD 0.0 124 g of organic phosphorus 0.0672 g of organic nitrogen and 0.2 g of inert mass as COD ¡

In the decay of Poly-P biomass the stored PHB is released to form RBCOD and the stored Poly-P is released to form soluble phosphorus.

The rates of endogenous decay or lysis of the biomass are given for the different types of biomass as: 0.24 per day for heterotrophs 0.04 per day for nitrifiers 0.04 per day for Poly-P biomass

The rate of lysis is temperature dependent. pH Control. The pH of the reactions was modelled by assuming the presence of a buffer salt as described below.

In the presence of a buffer Salt pOH = pKb + logl0( - - .- ) Alkali

This can be rewritten as pH = 14 + Logl0(

Kbx C CO 3 ) a Salt x 50000

As Kb, 14, and 50000 are constants the equation may be used in the form Salt pH = -Log l0( - - - ) CaCO 3

Variations in alkalinity in the form of CaCO 3 due to chemical and biological reactions will give rise to variations in pH. Dissolved oxygen. The dissolved oxygen (DO) is modelled in terms of power consumed. A transfer of 1.5 Kg oxygen per Kw .hr at a DO of 0 mg/Lis assumed. The modelling of DO is therefore: 1.5 x Power DO = DO 0 + - - - -- x (DO,at - DO 0) Volume x DOsat where DO 0 is the DO at time 0 and DO," is the DO at saturation

Sludge settling. In the settling cycle the settlement of sludge is modelled using the equation V = Vo e-kX

as described by White and Vesiland in White (1975). In the model the sludge settles to a concentration defined by the stirred settled volume index (SSVI) of the sludge. Again this is a simplification as compression of the sludge or Type IV settling are not considered.

Although SSW. can be modelled, using the parameters of F:M ratio, DO:biomass ratio and the active fraction of the biomass, the model used in the preparation of this paper assumed an SSVI of 150 ml/g

Format of model The model is a time step integrating model. That is, at the start of a time period the model adds the influent volume and mass of substrates to each reactor or portion of a reactor and subtracts the flow out of the reactor or portion of a reactor. The model then does .a mass balance of substrates in each reactor or portion of a reactor assuming they are completely mixed.

After the initial concentrations in the reactor have been determined, the model then undertakes the calculations associated with the physical, biological and chemical reactions in the reactor or portion thereof. It then uses the calculated substrate concentration at the end of this step to undertake the next mass balance for the next time step.

In the settling and decanting periods the soluble substrates report to the supernatant phase, as the suspended biological floe settles as a sludge blanket..

To maintain stability in the model, primarily associated with the transfer of oxygen and oxygen utilization, a time step of 15 seconds was us~d. In continuous models based on the same format a time step of 1 to 2 minutes can be used.

The model then graphed the concentrations of~ oluble phosphorus, dissolved oxygen, oxidised nitrogen and ammonia nitrogen in the suspended solids, i.e. in the mixed liquor during aeration and in the settled sludge during settling and decanting.

Operation of the model Initial set-up of model. The model was configured to emulate the standard design sewage treatment plant as constructed at Woolgooolga. The plant in the model was assumed a volume of 2.7 ML at bottom water level giving the plant a hydraulic capacity of 1.8 days or 43.2 hours. The actual plant at Woolgoolga has a capacity of 2.77 ML at bottom water level.

The influent data to the model was based on typical influent data to the Woolgoolga sewage treatment plant but in the first instance diurnal variations in flow and concentrations were neglected. (The model could be adjusted to cater for these).

There was a difficulty in that no instrument for measuring RBCOD (or RACOD) was available. At Woolgoola, the influent BOD 5 ranges from 290-330 mg/L, and total COD ranges from 480-600 mg/L. Filtered COD ranges from 200-230 mg/L. Bridger and Townsey ( 1993 ) had WATER OCTOBER 1994

~ubstrate Effluent (Typical) mg/L

IC-CF Configuration 20 ~ - - - - - - - - - , - - - - - - - - - - - - , - - - - - - - - - -

15

30

60

90

120

150

180

Time (minutes)

Figure 2 Substrate Concentrations in suspended solids of IC-CF IC-IF Configuration 20 . . - - - - - - - - - - - - - - - - - - - - - - - - - - - -

15

~

= 0 u

SETTLING

AERATION

~

DECANTING

10

PHO

30

60

90

120

150

180

Time (minutes)

Figure 3 Substrate concentrations in the suspended solids phase of IC-IF

found a high degree of correlation between RACOD and BOD 5, and a lesser degree of correlation between RACOD and filtered COD. For the purposes of the model, it was assumed that the RBCOD was equivalent to the lowest figure for filtered COD, ie 200 mg/L. Table 2 lists the parameters used in the model.

It should be noted that the total biodegradable COD is split between SBCOD and RBCOD. The total nitrogen is split to Org-N (organically bound nitrogen) and NH 4 (ammonia). A similar split was undertaken for phosphorus.

The model was used to simulate one year of operation of various plant configurations. At the end of the simulated year the plants were considered to be operating in a steady state mode. The results of the simulation are given below.

WATER OCTOBER 1994

The model operated, in general, on a cycle of 90 minutes aeration, 60 minutes settling and 30 minutes decanting. Sludge withdrawal was assumed to occur during the aeration period where 1/SRT of the volume at bottom water level was removed during the aeration periods of one day.

All model configurations were operated with a power, for aeration, of 35 kW. The oxygen transfer assumed was 1.5 kg of oxygen per Kw into mixed liquor. Where denitrification reactors and anaerobic reactors were used the volume of those reactors was 2.5 hours of AD\XIF. The recycle rate used was 2 x AD\XIF and was assumed to operate continuously. This may not be practical as operation during settling and decanting would disturb the sludge blanket.

Intermittent cycle continuous feed (IC-CF). The IC-CF configuration

produced the following effluent:

SBCOD+RB COD NH 4 NOX PHO PH

5.27 0.33 10.53 9.23 7.04

Th e concentrations of DO, PHO , NOX and NH 4 in the suspended solids phase during the period of a cycle are shown in Figure 2. The model also showed that PHB was present at the start of aeration indicating that Poly-P biomass growth could occur. Similarly if a mass balance for phosphorus is determined, considering the phosphorus utilized in the growth of XBH and XBN and the pho sphorus in the endogenous mass after lysis of the biomass, it can be shown that luxury biological phosphorus uptake occurs. However, the extent of this luxury uptake is small.

This is consistent with observation of sludge at the Coffs Harbour, Woolgoolga and Sawtell sewage treatment plants.

The DO during aeration showed profiles typical of plants at Coffs Harbour and Woolgoolga. Notwithstanding, the DO during and at the end of aeration in the model (about 3 mg/L) was higher than that measured in the treatment plants (about 2 mg/L).

The effluent NH 4 was 0.33. Typical figures from the Coffs Harbour, Woolgoolga and Sawtell sewage treatment plants, where tb,ere is large variation in diurnal flow, range from 0.5 to 0.8 mg/L. Initial figures from the constant flow pilot plant are 0.3 mg/L The effluent NOX was higher than anticipated at 10.5 mg/L whereas the plants at Coffs Harbour, Woolgoolga and Sawtell usually produce levels below I 0 mg/L. This may be explained by the higher levels of DO in the model during and at the end of the aeration cycle thus reducing the denitrification during aeration and delaying denitrification in the settling period. This may be corrected by reducing the rate of oxygen transfer.

Intermittent cycle intermittent feed (IC-IF). The IC-IF configuration

introduced sewage into the reactor only during the periods of settling and decanting. The flow rate into the reactor was altered to ensure the reactor received 1.5 ML /day as with the continuously fed plant. This configuration produced the followip.g effluent: Substrate Effluent (Typical) mg/L SBCOD+RBCOD NH 4 NOX PHO pH

5.95 0.48 5.86 6.13 7.10

The concentrations of DO, PHO, NOX and NH 4 in the suspended solids phase during the period of a cycle are shown in Figure 3. The model also showed that the PHB at the start of aeration was about 10 mg/L, higher than for the IC-CF 27

configuration, indicating that a greater Poly-P biomass growth could occur. This is evidenced in the lower phosphorus concentration in the effluent.

Watching the PHB and phosphorus levels over a period of time indicated there was very slow Poly-P growth. This is due to the very brief time period during which nitrates were at a minimum and PHB production was subsequently limited.

It is also noted that where denitrification in the sludge blanket is more complete than that in the IC-CF, the alkalinity of the sludge is maintained at a level higher than that in the IC-CF causing a higher pH and subsequent increase in the rate of nitrification. This leads to a lower NH 4 at the end of aeration .The effluent NH 4 is greater than the IC-CF configuration due to the wash through of influent NH 4 during the settling period ..

As there is a gre ater amount of RBCOD and NH 4 available at the start of aeration the DO levels remain depressed for a longer period from the start of aeration. This gives a greater period of simultaneous nitrification and denitrification. As denitrification is greater there is a higher DO at the end of the aeration cycle with it reaching a peak of about 4.0 mg/L. From the graph it can be seen that the NOX level in the sludge blanket approaches O mg/L at the end of decanting. From this it can be assumed that an extension of the settling period would result in anaerobic conditions in the sludge blanket and subsequent phosphorus release and uptake.

Operating the model with an extended settling period showed high rates of phosphorus release and uptake at levels similar to those achieved using an anaerobic reactor.

This resulted in low effluent phosphorus.

Similarly control of aeration such that the DO did not rise above 2 mg/L produces NOX levels of O mg/L prior to the end of decanting. This produces an anaerobic period at the end of the decanting period and subsequently conditions suitable for phosphorus removal.

Intermittent Cycle Continuous Feed with Anaerobic Reactor (IC-CF-

AN). The IC -CF-AN configuration introduced sewage into an anaerobic reactor which received return sludge from the main intermittent reactor. The recycled flow was set at 2 x ADWF and operated continuously. This configuration produced the following effluent:

IC-IF-AN Configuration

15

SETTLING

AERATION

DECANTING

PHO

30

60

120

90

150

180

Time (minutes)

Figure 4 Substrate concentrations in suspended solids phase of IC-CF-AN

IC-CF-AN Configuration 20

+------------------------------,

15

AERATION

SETTLING

DECANTING

NO

60

90

120

150

180

Time (minutes)

Figure 5 Substrate concentrations in suspended solids phase of IC-IF-AN IC-Cf -DE Configuration 20-.-----------------------------,

15 AERATION

SETTLING

DECANTING

Substrate Effluent (Typical) mg/L SBCOD+RBCOD 8.66 NH 4 0. 27 NOX 5.90 PHO

0. 14

pH

7.09

Th e co ncentrations of DO, PHO , NOX and NH 4 in the suspended solids during the period of a cycle are shown in Figure 4. The model also showed that the PHB at the start of aeration was over 150 mg/L indicating that greater Poly-P biomass growth could occur and the plant. could accept shock loads of phosphorus.

28

30

60

90

120

150

Time (minutes)

Figure 6 Substrate Concentrations in suspended solids phase of IC-CF-DE WATER OCTOBER 1994

This was also reflected in the levels of PPH in the sludge and in the effluent.

It can also be seen on the graph that the phosphorus released in the anaerobic reactor leads to a steep rise in PHO level in the sludge during settling.

The DO at the end of aeration is less than that in other configurations. This is due to the greater sludge mass in this configuration. The greater sludge mass also resulted in the lower NH4 effluent concentration but a greater effluent RBCOD. Intermittent cycle intermittent feed with anaerobic reactor (IC-IFAN). The IC-IF-AN configuration introduced sewage into an anaerobic reactor which received return sludge from the main intermittent reactor. The influent to the reactor was set as in the IC-IF configuration. The recycled flow to the anaerobic was set at 2 x ADWF and operated continuously. This configuration produced the following effluent: Substrate Effluent (Typical) mg/L SBCOD+RBCOD NH4 NOX PHO pH

6.28 0.32 5.47 0.24 7. 10

The concentrations of DO, PHO , NOX and NH 4 in the suspended solids during the period of a cycle are shown in Figure 5. The model also showed that PHB at the start of aeration was over 200mg/L indicating that a great degree of Poly-P biomass growth could occur and the plant could accept shock loads of phosphorus. The configuration seemed to offer little advantage over the IC-CF-AN configuration with the exception of lower nitrates. The DO at the end of the aeration cycle was about 4.3 mg/L and as such the IC-IF-AN configuration appeared to use less oxygen than the IC-CF-AN configuration. This is consistent with the IC-IF configuration.

Intermittent cycle continuous feed with RAS denitrification (IC-CFDE) .The IC-CF-DE configuration produced the following effluent: Substrate Ef!luent (Typical) mg/L SBCOD+RDCOD NH 4 NOX PHO PH

5.24 0.43 9.77 9.15 7.05

The concentrations of DO , PHO , NOX and NH 4 in the suspended solids during the period of a cycle are shown in Figure 6.

The effluent NOX was less than the IC-CF configuration but greater than that in all other configurations. The NOX concentrations in both the RAS denitrification reactor and in the main reactor remained high. This limited the phosphorus release and subsequently the production of PHB .

The model also showed that the PHB at the start of aeration was less than 10 mg/L indicating that Poly-P biomass growth. could occur but not at a rate which would WATER OCTOBER 1994

produce significant biological phosphorus removal.

Conclusions The ability of the model to simulate plants appears to be good when compared to the sewage treatment plants at Coffs Harbour, Woolgoolga and Sawtell. The simulation is to be verified with the operation of the pilot plant in a number of configurations.

In the models the level of substrates in the plant effluent were in the range s expected. The dynamic models showed that biological phosphorus removal should be achievable in intermittent plants using one of two methods. The methods are (1) Intermittent feed (2) Use of an anaerobic reactor The configuration including the RAS denitrification reactor showed little propensity for the removal of phosphorus.

There appeared to be no advantage with the IC-IF-AN configuration over the ICCF-AN configuration for the removal of phosphorus.

As can be seen in all the graphs the DO levels at the start of aeration were very low but at the end of aeration were in mo st cases well in excess of 2 mg/L. There are problems related to low DO such as sludge bulking, but running plants at a high DO is usually a waste of power. The models indicate that plants would operate much better in re spect to ammonia, nitrates, phosphorus and power consumption if aeration was controlled such that the DO rose quickly to a set level of 1.5 to 2.0 mg/Land stayed at that level through the aeration cycle.

All the models indicate that the intermittent cycle plants are robust providing aeration is adequate and controlled. As such, operators, should be encouraged to try different operating parameters to try and improve the plants' performance in re spect to nitrogen and phosphorus removal. Alternatively this can be done with an appropriate dynamic model on a computer.

Acknowledgements I thank P.A. Jelliffe for his tolerance in reading drafts of this paper , Ms B. Wad leigh of the Coffs Harbour City Council who found the Poly-P organisms, and Robert Shaw of Aeration and Allied Technology Pty Ltd who provided me with the ideas assoc iated with an anaerobic reactor and provided a sounding board for my ideas.

References Barnard J.L. , (1976}. A Review of Biological Phosphorus Removal in the Activated Sludge Process. Water S.A. Vol 2 No 3.

Barnes D.B. and Greefield P.F., (I 986). Nutri ent Removal from Wa stewater Streams , (Shor t Course).

Barnes D. and Bliss P.J., (! 983). Biological Control of Nitrogen in Wastewater Treatment. E & F.N.

Spon.

Bliss P.J., Harris S., Jackson A., Kaye R.B. , (1993).

Final Report on Biological Phosphorus Removal in the In termi tt ently Decanted Extended Aeration Activated Sludge Process. Final Draft 16/06/93 Breck W.G., Brown R.J.C., and McCowan J.D., (1981 ). "Chemi str y for Science and Engineering. " McGraw Hill Ryerson.

Bridger J.S. and Townsey E.R., (I 993). Instrumental Measurement of Readily Assimilable COD in Sewage. Proceedings 15th Federal Convention A\Y/WA Catundra P.F.C . and Haande l A.C . van ., (! 992).

Activated Sludge Settling Part I. Wa ter S.A . Vol 18No 3.

Catundra P.F.C, and Haandel A.C. van. , ( ! 992 ) Activated Sludge Settling Part II. Water S.A. Vol 18 No 3.

Clayton J.A., Eckema G.A, Wen tze l M.C. , and Marais GvR (1991), Denitrification Kinetics in Biological Nitrogen and Phosphorus Removal Activated Sludge Systems Treating Municipal Wastewaters. Water Science and Technology Vol 23.

Comeau Y. , Hall K.J. , Handcock R.E.W., and Oldham W.K. , (1986). Biochemical Model for Enhanced Biological Phosphoru s Removal.

Water Research Vol 20 No 12.

Gaudy A. and Gaudy E. , ( ! 981 ). Microbiology for En vironmental Scienti sts and Eng in eers.

McGraw Hill.

Ho Kin-man, Greenfield P.F., Blackall L.L., Bell P.F. , Krol A. , (1993). Performance Evaluation of Variable Vo lum e Intermittently Operated Biological Nutrient Removal Activated Sludge Processes. Proceedings 15th Federal Convention AWWA IAWPRC, (1986). Act ivated Sludge Model Nol. IAWPRC. Jennings J. ,Pulbrook C. and Griffiths P., (! 993 ).

Bendigo Biological Nutrient Removal Plant Startup and Commissioning. Proceedings 15th Federal Convention A'/i.TWA. Nutrient,.Control. Manual of Practice FD-7, (1983).

Water Pollution Control Federation, Washington D.C. Metcalf and Eddy, (I 99 1). "Wastewater Engineering, Treatment, Disposal and Reuse. " McGraw Hill.

Wentzei M.C., Dold P.L., Eckema G.A. and Marais GvR (1988). Enhanced Polyposphate Organism Cultures in Activated Sludge Sys tems Part I. WaterS.A. Vol 14 No 2.

Wentzel M.C., Dold P.L., Eckema G.A. and Marais GvR (I 989). Enhanced Polyposphate Organism Cultures in Activated Sludge Systems Part II. WaterS.A. Vol 15 No 2.

Wentzel M.C., Dold P.L., Eckema G.A. and Marais GvR (! 989). Enhanced Polyposphate Organism Cultures in Activated Sludge Systems Part III. WaterS.A. Vol 15 No 2.

Wentzel M.C., Dold P.L., Eckema G.A. and Marais GvR ( I 990). Biological Excess Phosphorus Removal - Steady State Process Design. Water S.A. Vol 16 No I. White M.J.D., (1975). Instruction Manual for WRC Settling Apparatus for Activated Sludge. WRC. WRC (1984). Theory, Design, and Operation of Nutri ent Removal Activated Sludge Processes.

Water Research Commision Pretoria.

Author Rob Siebert graduated B. Eng from RMC Duntroon in 1975, and remained in the Force until 1985. He has worked as District Engineer for the Kosiusko National Park, then as an engineer with CMPS&F. Since 1992 he has been the Manager, Sewerage, for Gaffs Harbour City Council. He has a Graduate Diploma in Municipal Engineering and M.Eng Sc in Waste Management.

29

RESEARCH

NITROGEN AND PHOSPHORUS IN LABORATORY SCALE MODELS D H Abeysinghe *, CA Borthwick Many research programs have addressed nutrient enrichment problems.

Most of these problems involve laboratory scale modelling of ecological or treatment processes. Nutri ent analysis, which is a vital part of most water inves tigation s involves determination of ammonia, nitrite, nitrate and phosphorus. Most of the chemical nutri ent method s currently in use require at least 100ml of sample. In laboratory scale model s, a small er samp le is preferable to minimise effects on loading and flow rates. Reduced sample size also saves on chemicals.

Another factor affecting nutrient analysis is the time involved in carrying out the test in replicates. If automated analytical methods are used , sa mpl e size can be reduced to 1ml and duration of the test to a few seconds. Automated analytical methods are faste st, but the capital cost is extremely high. Therefore, a quicker, low cost nutri ent analysis method that consumes minimal sample volume is needed.

A low cost variation of the standard colorimetric method has been developed for the analysis of nitrogen and phosphoru s. It involve s a singl e wave length microplate reader as the main instrument.

Materials and Methods Spectrophotometry. The most often used instrumental technique in analytical chemistry is spectrophotometry. Th e amount of light absorbed (or transmitted) by a solution depends upon the concentration of the solution and its ¡pathl ength.

Thi s relation ship is expressed by th e Lambert-Beer law, which is the mathematical basis for the spectrophotometric determination of concentration. The amount of light absorbed is directly proportional to the solution concentration but is exponentially related to the pathlength through which light passes. This exponential relationship occurs because each layer of equal thickness absorbs an equal fraction of the light that passes through it. Path length is defined as the distance the light beam travels through th e ab so rbin g so lu tion.

Absorbance is usually expressed in terms of a standard cell of 1cm path length.

Microplate reader. Microplate readers are microproces sor controlled spectrophotometers designed to measure the absorbance of sample s in microplat es .

They are ideally suited to all colorimetric, agglutination and turbidometric applica30

tions. They offer fast reading rates eg. as little as 1.7 seconds in single wave length mode for an entire 96 well microplate.

Rapid operation is essential for accurate and reliable determination of kinetic functions.

The path length through solution in a microplate well is less than 1cm. Nevertheless, accurate values of absorbance can be obtained, providing all blanks, standards and samples are of equal volume.

Standard Methods . The new method is based on the standard methods described in Standard Methods for the Examination of Water and Wastewater, 18th edition 1992: Phosphate test is based on 4500-P E Ascorbi c acid method , Nitrat e test is base d on 4500-N03 E Cadmium reduction method and Nitrite test is based on 4500 - NO2 B Colorimetric method. The ratios of reagents to samples were as specified in standard methods. A different volume of sample (200 ÂľL compared to 25mL in stan dard methods ) results in smaller overall volumes.

The basis of the analysis is the comparison of the extent of absorption (or transmittance) of radiant energy at a particular wavelength by a soluti on of the sample with that of a series of standard solutions treated identically.

Assay development. Soluti ons of 0.2mg/L and 2.0mg/L nitrite N were prepared. These values were chosen to represent the upper and lower concentration limits in use . Absorbance valu es we re obtained at different wave lengths for both solutions, and are plotted against wavelengths.

The peak range was observed to be 475nm-600nm. The range at which peak absorbance was similar for both 0. 2 mg/L and 2 mg/L, indicating, as expected, no dependence of wavelength on concentration. The wavelength corresponding to the highest variance of absorbance for the two concentrations (highest sensitivity) was observed to be 530 nm . The microplate reader has specific wavelength filters. The nearest wavelength filter was chosen at 570nm.

By constructing a graph of absorbance versus concentration the extent of linearity for the specifi c tes t co mpound can be established. Although the amount of light absorbed is lin early proportional to the soluti on concentration this relationship does not hold for higher concentrations. It

was established that for nitrite measurement at 570n m wave len gth, a goo d (r 2>0 .9 5) linear relationship exists for 0.05-2.0mg/l nitrite N. Similar procedures were carried out to establi sh th e optimum wave length and concentration range for pho sphate.

Optimum wave leng th was found to be 850nm. For phosphate measurement at 850nm wavelength, in 0.05-5 mg/I range, an extremely good (r2>0. 98) linear relationship was observed between absorbance values and the solution concentration.

Precision and Accuracy When an entirely new method is developed or an existing method is modified to meet special requirements, the method should be evaluated for comparable precision and accuracy. This method involves deviations from standard procedures, and therefore, va lidati on of the method is required. Synthetic samples (n=8), containing nitrite and phosphate dissolved in de-ionised water were analysed with the following results.

The method of known additions was used to verify the absence of interferences.

Recovery of known additions was found to be 85% - 115%. This recovery range is well within the acceptable limits specified in the Standard Methods. It is advisable to have at least a one known addition to verify the absence interferences for each analytical run, if the sample contents are unfamiliar or unknown .

Conclusions A low cost method has been developed for the analysis of nitrogen and phosphorus. The results indicate the method produces precise and accurate results. This method can be adopted where the test is co nstrain ed by sample size, numb er of samples and the cost of analysis. However1 great care is required to maintain equal volumes of samples, blanks, standards.

Table 1 Precision and Accuracy of Results Concentration mg/I

Precision mg/I

Bias mg/I

Bias %

nitriteN

0.2 2.0

0 602 0.2

+0.0 15 +0.028

+7.5 +1.4

phosphate P

0.5 5

0.064 0.15

-0.02 +0.29

+5 .8

-4

*Schoo l of Civi l Engi neering, Queensland University of Technology, Brisbane WATER OCTOBER 1994

MANAGEMENT

THE ECONOMICS OF WILDERNESS AREAS J Brodsky, F E Grey* Abstract Water managers, like natural resource managers and governments everywhere, are being confronted by the need to appraise environmental values. This need is an important part of making the best choices for society at large. This paper is an example of this process. It examines the complex multi-resource, multi-use and multi-value choices involved in evaluating the Shoalwater Bay Military Training Area, located north of Rockhampton, QLD. The paper, based on a larger work, introduces an approach, with the ungainly title of 'sustainability-bounded total economic value', as a method of evaluating options which have significant environmental values.

The Economist Blues There is a fair bit of grumbling going on these days in the media, when the subject switches to economists and the influence they are having on range of critical issues - particularly those to do with valuing the natural environment. Members of the public, conservationists and various high-profile academics have been scathing about the narrow profit-centred approach used by "economic rationalists" to assess areas rich in natural resources. They are right in some ways, but they are also wrong when you consider that the properlydefined role of economic analysis is to ensure that the scarce resources of society are deployed to provide the greatest benefit for both people living now, and those who will be there in years to come. This is the true expression of the neo-classical economic tradition. So-called economic rationalist views expressed by certain private think-tanks in Australia are distortions of economic theory, as taught to students around the Anglo-Saxon world. Were such think-tankers to return to university, they would find that their analysis would earn a "fail" in even the most conservative economics courses.

Still, never underestimate the power of wrong ideas, and of well-funded interest groups!

Too Many Uses Can Overwhelm Market-Based Allocation Recently, the Australian Conservation Foundation provided an assessment of how the Shoalwater Bay Training area in Queensland could be valued - bearing in mind that the area is currently relatively unspoilt bushland, and that apparent WATER OCTOBER 1994

multi-billion dollar options such as tourism and recreational industries pose both opportunities and dangers to this environmental status quo (Grey & McDonald 1993) .

Other competing interests in the Shoalwater arena are established users of the area (defence training) and prospective users, eg the mining industry. The exercise presented the perfect platform for cultural, non-financial, financial and alternative financial values to be placed in what we call an "integrative economic framework".

Each value is assessed, with a view toward preserving the ecological sustainability of the Shoalwater area.

Traditionally, Australian society relies on the processes and outcomes of the market to obtain an efficient allocation of resources. A problem arises, however, when experts assume that there are only limited options for the use of natural resources; and when (in the cases of some resources) benefits to the community cannot be delivered, because of a conflict between monetary and cultural expectations which is not solved by the usual reliable market mechanisms. It is in these instances that the government must step in to determine the best allocation of those resources.

Total Economic Value: Trying to Give All Values Equal Weight Much as "economic rationalism" is a dirty phrase in the minds of many, there is in fact "rationality" in the way that ecologically sustainable development can be put to worthwhile use. Because resources are limited, and because good economic analysis should assume that there is always more than one "use" for these resources, we bring into the equation the concept of "Total Economic Value" (TEV).

Human beings naturally attach a range of values, both material and emotional, to most objects. This is as true of wilderness areas as it is of purchasing a car, or making a business decision. For example, an individual will impute a range of these values to an object at any one time, which forms the TEV of that object. He/she might love the bush because the atmosphere is green and peaceful, there are animals and birdlife to observe, it's an inexpensive Sunday outing for the family, the air is invigorating and cooling. Equally, a community or Australian society will attach a spectrum of values to that same object (the bush), ranging from pleasure that the bush exists in its pristine state, to

the contemplation of its raw potential in terms of hidden coal reserves. In both cases, this collection of values indicate Total Economic Value.

Values ca.n, of course, be positive or negative. Thus choices need to be made about whether the use of an object is going to cause negative value (eg de-foresting the area), and whether uses and seeming nonuses of the bush can be combined to form an outcome which has more positive value for both individuals and the community.

There is a whole list of values which can be attached to an area like the Shoalwater Bay. These include financial (eg commercial enterprises op·erating· there), traditional use (people living there because they like the ambience of the bush), biodiversity (the area is rich in this), mineral (there are prospective sites for mineral resources), visual (it is a beautiful area), cultural (it is a way of life), heritage (the area is rich in indigenous history), social, environmental quality, defence training (this i; of use to the military), the fact that it exists (existence value) and combination value (ie it is a combination of the lttlove which makes the area special).

Some of these values have direct "use" appeal - eg Shoalwater is a training site for the military, and it boasts a number of commercial enterprises - but other nonuses (such as the ambience of the bush, its visual beauty) attract an equal level of importance. Making a decision to, say, mine or deforest the area, could be a mistake, if the other so-called non-use values (or "externalities") have not been sufficiently taken into account.

Thus, any seasoned assessment of the area's options sets out to create a number of differing scenarios - each taking into account: • the range of values people are likely to attach to the area, • examining which uses create what values, and • weighing the likely impact (negative and positive) that' a scenario is expected to create Such an approach to economic decision-making sounds unbelievably straightforward, but is raPely adopted when it comes to advice about "natural capital" (a term used by economists Pearce and Turner 1990) as opposed to the short-term goodies proffered by financial capital.

* Francis E Grey, Economist at Large & Assoc, PO Box 256, Noble Park Vic 3174 33

The Role of Sustainability in Total Economic Value People have objected to the "economic rationalist" (or to put it more accurately, neo-classical) model, when it comes to environmental deci sio ns, becau se it assumes that there is reversibility of choices, and that there exists an informed approach to future options (no matter how far off they might be).

Reality dictates otherwise. An economic analysis which, in the interests of quick financial gain, fails to take account of slowly depleting natural stocks (eg the destroying of bush habitat and wildlife), is inherently 'irrational". It endangers the future welfare of generations not-yet living, not to mention the natural environment which exists now.

The idea of sustainable development has been coined to assist decision-making, and to avoid the prospect of irreversible and potentially dangerous choices. In this context, a person (or industry or government body) having to evaluate limited information and knowing that A is an irreversible choice, proceeds to B which is reversible. He/she then sees that C is more valuable, and reverses the choice that led him to B, and consequently, starts to discover the best path under the circumstances.

Of course, reality is harsher on those who make mistakes. Lack of information and the danger of choice irreversibility are similar to standing in a fog-shrouded, unknown area which can lock agents into sub-optimal choices. The task for policy analysts is to identify a strategy that will steer choices through the "foggy ground" of decision-making, avoiding lock-in and maximising benefits to society in all time periods.

The recent work of economists such as Pearce & Turner (1990), and Bishop (1978) advocates the setting aside of environmental resources for sustainable use only. Accordingly, a development benefit would have to significantly and demonstrably exceed preservation benefits to justify development. Pearce and Turner's argument is that there are sound, economic reasons - imperatives - for conserving natural stock ("natural capital"), because to do otherwise is to kill the goose that lays the golden eggs (ie making irreversible decisions that lock us in).

Steve Burrell, Economics Editor of the Financial Review, recently acknowledged (November 24 1993) the significance of irreversibility in the work of two American economists Dixit and Pindyke. The significance of irreversibility was that its presence requires that corporate investment options must provide a far larger investment return than previously expected, if they are to proceed. This recent awakening to the realities of human choice has long been acknowledged in environmental economics literature, which is why leading economists in this area have advocated the setting aside of any option which involves irre34

versible changes. This is an intuitively appealing method for dealing with economic decision-making under conditions of uncertainty.

A fishery works in this way. No economist would advocate the "mining" of a fishery in order to put the money in a bank account. The depleting of fish stock, without allowing for the rates of regeneration, is akin to an irreversible, and hence, economically and environmentally stupid decision. What we, and the above-mentioned economists, are advocating is that the sustainability rule of thumb - so common to fisherie s - need s to be applied when it comes to the management of other natural resources. Where a natural resource displays the characteristics of uncertainty, non-substitutability, multi-functionality and irreversibility, it makes good, economically rational and wealth-maximising sense to conserve and sustain it as natural capital - which should not be destroyed.

Sustainability, Total Economic Value and Shoalwater Bay Armed with this approach, we consider the values of Shoalwater Bay. We know that a proper assessment of the area has to consist of defining all values present (financial and non-financial), examining the total economic value of each combination of values, assessing the risks and tradeoff in each scenario, and establishing the boundaries of sustainability for resources in the area.

The Shoalwater Bay Inquiry listed a number of different potential uses for the area: fishing, tourism/recreation, mining and mineral processing, water production, residential, agriculture, forestry, horticulture, conservation/wilderness, craft industries, traditional use, research use, and defence training.

What the uses of each listed area will entail depends on what the TEV scenario consists of. For example, if the TEV says that all other uses will be limited by mining, then scientific use would be limited, defence could be disrupted, conservation compromised, water production halted .

Where uses are limited by sustainability and wilderness objectives, then mining would not occur, biological prospecting as an economic activity is possible, defence training is proscribed, and tourism is limited to wilderness experience.

Then what must be decided is how and whether some values outweigh or exist alongside others. Any particular perceived use of a resource consists of several value components, such as direct use (which can be financial or ecological), option value (where a society is willing topay to maintain the option of enjoying a particular visual amenity), existence, stewardship (rights of other species), or combination and bequest.

Trade-offs Between Values Put more simply, we can consider the intervalue trade-off between the visual amenity of Shoalwater, and a proposed

mining site . If mtning is given the goahead, the visual amenity value will decline (as would the ambience). And there are potential intervalue trade-offs between different financial values, too . What spells "resource security" for one industry could mean resource insecurity for other industries, such as tourism. Understanding the intervalue trade-offs is critical to an analysis of any area rich in natural resources, because there can be unexpected and unwanted outcomes, which can cause significant economic and environmental losses ( the two must be considered in the same light). Spoiling the water in the region as a result of deforestation can have a direct impact on fishing and touri sm potential - which as industries, may bring more returns to the region than does the forestry industry. The relation ships between these different values must be clearly understood for the best possible economic projections to take place prior to the event.

Taking the analogy further, it is common for project proponents to sell an idea to a community, based on estimates of the project's financial value. The start-up cost of a project, it may be claimed, is $200 million. But did any other assessments take place? Could it be that the start-up of one project may undermine the fishing industry in the region, for example? What must be ensured in any worthwhile assessment of a region, such as Sboalwater, is that all industries are compared on a similar basis, preferably using discounted cash-flow analysis.

...

Trade-offs Between Industries {Financial Values) Then, it should be asked, have any comparable alternative projects - such as the creation of a national park - been considered? The creation of the national park may result in a rapid expansion of the tourist industry, as hundreds of agents invest in expanded accommodation and other infrastructure. It may be that tourism in Shoalwater Bay is likely to offer a financially handsomer prospect than a mining site. Even so, we would need to assess the intervalue trade-offs with conservation use, defence, mining and mineral processing, environmental quality, etc . How much does tourism contribute to Australian economic welfare? In Shoalwater Bay, we would need to determine the net increment (financial, employment and investment) to the regional economy. But there can also be losses such as social change, ecological impact and a range of other key values that make up the Australian set of values. Only social preferences and socially - acceptable "rules of thumb" (eg s~stainability) can determine the correct balance between thefinancial benefit of tourism and its negative impact.

Then, what sort of tourist attraction is being envisaged? Will it be resort developm en t, capitalising the environmen ta! amenity values into the project's asset WATER OCTOBER 1994

value? This could po se two problems.

Such a development could cause the environmental amenity of the site to dissipate.

Secondly, there is potentially a huge loss of value to the Australian community with the onl y wilderness area left on the Queensland coast being turned into a se ries of resorts. It amount s, in other words, to privatisation of the public's environmental amenity, which requires that all Australians, present and future , be compensated for their lo ss of the amenity's environmental existence value. There would nee d to be an evaluation of the Australian public's willingness to be compensated for the loss of Shoalwater as a wilderness area. Assessing resort developers' financial preparednes s to pay thi s degree of compensation would be interesting, to say the least.

The probable way to go would be to maintain the area's environmental qualities in the form of a national park arrangement, in a manner similar to Kakadu . Then the values of this area are protected for the benefit of all visitors, and all those who know of its existence. There would be no need for compensation, all development would take place outside the park boundaries in designated locations which fit in with the requirement to maintain other values. Developers would still receive a financial windfall produced by the setting up of such a park, because they could provide facilities in nearby towns. This would attract a wider pool of developers, both small and large , while encouraging a healthy competitiveness, and ensuring that the ultimate source of their capital value, the national park, is being protected for all time.

We would consider the economics of water production in a similar way. In the case of Shoalwater Bay, sand-mining of the dunal system would destroy the source of fresh water for towns such as Byfield. This would force Byfield to purchase water at great expense from another catchment nearby, and cause an irreversible loss to the region. A smart economist would point out that if the mining were so valuable , the miners ought to be able to compensate Byfield for the $50 million cost of changing its water source (and supply). Secondly, this smart economist would also note that under common law, it's highly likely that Byfield's right to the water precedes that of the miners to the dune system, and hence compensation would be required. Thirdly, any attempt by government to override the rights of Byfield to its water would fly in the face of the principles of neo-classical economics as established over 200 years.

The Choice Set: 'Sustainable' Options Only, Compare Values In sum, it is economically logical to avoid irreversible choices in environmental decisions. This has been proved, according to the strong principles of neo-c lassical economics. What follows from this is that sustainability is a major criterion in utilisWATER OCTOBER 1994

ing the environment, and that unsustainable options are ruled out - unless they return a financial reward of fantastic proportions. And no reward of that stature is likely to be worth it, when an irreplaceable ecosystem or environmental amenity is destroyed forever.

Going beyond this, sound economic analysis recognises that any object provides a suite of values, and that the aggregation of these values under different potential uses needs to be thoroughly compared - if the fundamental dictum of economics is to be satisfied . That is, the maximisation of social we lfare in the community at all points in the future. The significance of Total Economic Value (TEV) analysis is that it points out the importance of anal ys ing th e trade -offs within and between non-financial values, financial values and alternative financial values.

In particular, the significance of tradeoffs between the financial value of mining and the financial value of activities such as water production, fishing and tourism are crucial for the financial - let alone the environmental - future of Australia. After all, what sort of economic irrationalist would grant resource security to one industry, undermining the investment certainty of environment-dependent industries which are potentially more financially beneficial?

References Grey F E and McDona ld R (I 993 ) Shoa lwa ter Econom ics: 'Getting it Right' . Au stralian Conservation Foundation, Melbourne.

Pearce D \VI and Turner R K (1990) 'Economics of at ur al Re so urce s and the Env ironm ent.

Harvester \V/heatshef, London.

Bi shop R C ( 1978 ) Enda ngered Species and Uncertain ty: The Econo mi cs of a Safe Minimum Stand ard. Amjnl Ag,· Economics 60, 1, pp 11-1 8.

Authors Juliette Brodsky is a freelance journalist who has worked mainly in radio. She was the presenter of the "Undercurrent Affairs" program on Community radio, and is currently working for the ABC;s "7. 30 Report". She produced the recent documentary on Urban Water Quality for the "Green and Practical" program on Radio National.

Francis Grey gained his degrees in economics and in politics from ANU. He worked in the Commonwealth Treasury and in the financial market before setting up his own consultancy in 1989. As well as other projects he is involved in a number in the area of the water indusuy, including a submission to EWMESS on behalf of CSIRO, and financial incentives to improve farm run-off

On 2 September Federal Cabinet, after intense debate, decided to repeal the mining leases and maintain Shoalwater Bay area as a Defence Force Training Zone. This was a victo1y for the environment movement and the local councils. Economic analysis had demonstrated that the value of sand mining was less than the future value of this area, which, because it had been responsibly tended, represented a relatively untouched area of wilderness.

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3(

MANAGEMENT

THE SALMON-Q WATER QUALITY MODEL: A MURRAY DARLING APPLICATION *P Haines) Abstract Recently, sophisticated water quality models have been introduced in Australia.

These computer-based numerical models are commonly used overseas as water quality management tools. Water quality models have had very little use in Australia, and their full potential is on ly now being realised. This paper describes the use of the SALMON-Q water quality model as a catchment management tool, with specific reference to the Murray-Darling Basin.

Excellent correlation between computer prediction and measured nutrient levels have been obtained for a 200 km reach from the Hume Dam to Yarrawonga Weir.

Introduction Water quality management Needs.

Catchment management has become an important issue over recent years, with authorities becoming more aware of their responsibilities. Water quality is a fundamental component of catchment management, and due to its extreme diversity, is one of the hardest components to manage.

The catchment of the Murray-Darling River covers an area of over one million square kilometres including parts of New South Wales, Victoria, Queensland, South Austra lia and the Australian Capital Territory. The large size and diversity of the catchment in both natural environment and land-use practices makes it extremely difficult to manage. Extensive blue-green algae blooms have dominated the river's water quality during the last few years, highlighting the importance of catchment management and the need for an effective catchment management plan.

The Blue-Green Algae Task Force (BGATF) was formed by the NSW Government to address catchment management issues relating directly to the development of blue-green algae blooms.

Their recommendations are outlined in their final report (BGATF, 1992). The major recommendation was the implementation of a Nutrient Contro l Strategy.

Management of water quality, and in particular nutrients, requires a three-tiered approach.

Firstly, the exact problems need to be identified, and the causes of the problem determined. As there may be many interactive causes to each problem, a good understanding of the total riverine processes is 42

J Nielsen) B DrueryJ J Ball

essential. This stage requires extensive field and laboratory work to establish the water quality of the system and determine important point and non-point sources. Much of this work has recently been carried out for the Murray-Darling Basin by Gutteridge Haskins and Davey (GHD, 1992). GHD found that point and diffuse sources contribute approximately equally to nutrient levels in the Murray-Darling River. Point sources include sewage, industrial effluent, irrigation drainage and urban stormwater drains. Diffuse sources refer to general catchment runoff or groundwater sources and their magnitudes often depend upon farm management practices, such as pasture, crops and forests.

Secondly, various measures for reducing or eliminating the nutrients need to be assessed, and the best options determined.

Many interactive and often conflicting factors need to be considered when assessing nutrient mitigation measures, including environmental, social and economic effects. These have proven to be difficult to analyse and integrate as methods for assessing cumulative environmental impacts on aquatic systems have been limited. Mathematical models are ideal tools for assessing mitigation measures, as they can incorporate many complex environmental interactions.

The third stage in water quality management involves the implementation of preferred nutrient mitigation options and the development of a plan aimed at maintaining reduced nutrient levels in the future. Acceptance by the community is fundamental to the success of any water quality management plan.

Water quality models as catchment management tools Computer-based models, such as SALMON-Q, are ideal tools for assessing proposed mitigation options, as they can be used to investigate a variety of proposed developments and water quality mitigation measures, producing results quickly and at a minimal cost. The level of detail in a model can vary considerably from a general pilot model to a detailed model, and depends entirely on the application and requirements of the user. The size and level of detail of a model will control its complexity, and hence the computer runtime and overall cost of using the model.

Potential management uses of water quality models include: • Assessing the relative importance of different pollutant sources, including point and diffuse sources; • Providing an understanding of the major water quality processes of a system; • Assessing the importance of other environmental factors in a system, such as flow, temperature and turbidity, and their interactive effects; • Determining levels of pollution that do not result in unacceptable in-stream water quality condition • Determining the effects of natural or man-induced changes to the aquatic environment, such as new sewage treatment plants or upgrades, regulation of river discharges, construction of physical structures (eg., weirs and tidal barrages), effects of in-stream works (eg., dredging) and increasing sali'nity of a system; • Assessing the effectiveness of various catchment management measures, such as sediment controls, wetland filters and gross pollutant traps; • Providing input to strategic planning for urban expansion and/or new areas of land development; • Developing water quality monitoring programs which minimise the data collection requirements whilst maximising the benefits of the data.

By use of dynamic graphical displays, models, such as SALMON-Q, can be used as demonstration tools to help explain the effects of complex and interactive processes to the general public. It is possible to demonstrate the probable effect of various pollution reduction measures and the extent of these measures in improving the general health of aquatic environments.

Description of the SALMON-Q Water Quality Model The SALMON-Q water quality model has been developed by Hydraulics Research Ltd.(HR Wallingford, Oxfordshire, U.K) over the past 20 years and has been successfully applied 1 to many river systems overseas and in Australia, including the Nepean-Hawkesbury River system in New South Wales (PBP, 1993) . SALMON-Q is a one dimensional mathematical model of *Patterson Britton & Partners Pty Ltd. PO Box 515, North Sydney 2059.

WATER OCTOBER 1994

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unsteady flow, salt intrusion, mud transport, oxygen balance and primary productivity in channel networks of various sizes.

It uses a six point implicit finite difference scheme to solve partial differential equations representing the Saint Venant equations of one dimensional flow.

Water quality processes in the model are simul ated simult aneously with the hydrodynamic processes, and are governed by various equations representing the natural interactive effects of the aquatic environment. For example, the decay of organic materials and the nitrification of ammonia nitrogen are modell ed as first order kinetics, whereas primary productivities of water-borne algae, macrophytes and benthic algae are calculated using MichaelisMenten (Monod) type equations. Many years of model development by Hydraulics Research Ltd. have demonstrated that the adopted equations are the most appropriate mathematical expressions for representing the complex water quality processes.

On-going development will enable further model refinements.

There are several interacting water qu ality var iables, whic h are tracked throughout the system in both the water WATER OCTOBER 1994

column and the bed (fluffy layer and consolidated mud layer) . A large number of variables are incorporated in the model, as listed in Table 1.

The growth of algae is dependent on many environmental factors, such as water temperature, light intensity and nutrient availability, all of which are incorporated in the model. The model allows simultaneous simu lations of the dominant groups of water-borne algae (blue-green algae, green algae and diatoms), as well as macrophytes (rooted plants) and benthic algae. This allows time-dependent changes in the composition of the main algal groups to be simulated. Furthermore, the model is able to simu late water-sediment interactions, which are particularly important for phosphorus availability, and transport of nutrients in sediment pore water. BGATF found that the transformation of phosphorus attached to sediment to dissolved phosphorus was a contributing factor to the formation of the algal blooms on the DarlingBarwon River. The adsorption of phosphorus onto sediment surfaces is included in the model and is described by a Langmuir adsorption isotherm.

A SALMON-Q water quality mod, was set-up for a 200 kilometre reach of th Murray River as part of a Master c Engineering Science degree (Hainei 1993). The simulated reach extends fror the Hume Dam, approximately 20 kilome tres upstream of Albury, to the Yarrawong Weir pondage, approximately 50 ki lo metre s downstream of Corowa, an, includes the main river channel, sever~ anabranch channels and a small section C the Kiewa River.The model was based o hydrographic and water quality data pro vided by the Rural Water Commission c Victoria, and the Murray Darling Basi1 Commission, respectively. Thirty-thre, nodes, 40 reaches and over 250 individua elements ranging in sizes from 400 metre to over 1000 metres were used to rep res en the river system. Point source inputs int, the model were the Albury Sewag, Treatment Works (STW), the new and ol, Wodonga STWs, and the Kiewa River The hydrodynamics of the model were cal ibrated by simulating recorded flood event and adjusting channel roughness as neces sary. A subsequent verification confirme c the appropriateness of the adopted channe roughness . The flood events employed ir the calibration and verification representec a wide range of measured flows, whid would only be exceeded for approximate!)

10% of the time. Hence, the model is con· sidered to be calibrated for the vast majorj. ty of flow conditions experienced by th< river. Hydrodynamic calibration results an shown in Figure 1.

A preliminary water quality calibratior for the algal nutrients phosphate, nitroger and silicate was performed for low flo~ conditions in the river. Low flow conditions were used in the water quality simulations because algae blooms generally dominate during these flow conditions, and the in-stream water quality is not complicated by unmonitored inputs from local irrigation drainage and other diffuse sources. By adjusting values for the appropriate process parameters in the mode l, a good fi t between predicted and measured nutrient concentrations was achieved, as shown for phosphate concentrations in Figure 2.

Process parameters that required adjustment included the nutrient to carbon ratios in algae, nutrient uptake rates for the algae, and nitrification and ammonification rates.

However, a lack of suitable algae data for Table 1. Variables considered in SALMON-Q Fast dissolving BOD Slow dissolving BOD Fast organic nitrogen Slow organic nitrogen Ammonia nitrogen Oxidised nitrogen Dissolved oxygen Salinity Temperature

Suspended soli ds Fast particulate BOD Slow particulate BOD Algal carbon Detrital carbon Dissolved phosphorus Particulate phosphorus Silicate Coliforms 43

this stretch of the Murray River prevented calibration of algal levels.

Simulations for Catchment Management Purposes Two additional simulations of the Murray River model were performed to demonstrate the capabilities of SALMONQ as a catchment management tool.The first simu lation demonstrated how the model could be used to assess proposed nutrient mitigation mea sure s, such as upgrading sewage treatment plants discharging into the Murray River. For this simulation, the phosphate loads from the Albury and Wodonga STWs were reduced by 75%. As a result of these reductions, the model demonstrated that the in-stream phosphate concentrations wou ld be reduced by approximately 65%, and the downstream algal carbon concentrations would also be reduced substantially, as shown in Figure 3. Without a model, it would be hard to ascertain the potential reduction of in-stream algal concentration.

As a result of the modelling, we can now say that the water quality in thi s stretch of the river is dominated by the Albury and Wodonga STWs during periods of low flow. Hence, any improvement to the quality of the sewage effluent would result in a reduced potential for algal formation within the river, and a general improvement of river water quality.

The second simulation demonstrated the use of SALMON-Q to predict water quality changes in response to an increased flow from Hume Dam. The model showed that a five-fold increase in the flow from Hume Dam would only result in in-stream nutrient concentrations being halved, as shown for phosphate in Figure 4. Instream concentrations wou ld not be reduced five-fold because of the other inputs into the system, such as the Kiewa River, which, based on this assessment, would certainly require consideration in any water management plan.

The simulation also showed an increase in the nutrient concentrations at the higher flow directly upstream of Mulwala Reservoir, within the last 40 kilometres of the modelled reach. A lower residence time in the river means that algae do not have as much time to grow and use dissolved nutrients. These unused nutrients are flushed further downstream, where they accumulate, finally discharging into the Mulwala Reservoir. The implications of an increased nutrient load in the Mulwala Reservoir could be significant, possibly resulting in eutrophication of the waterbody.

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"' Figure 4 Phosphate concentration: Sensitivity to volume released from Hume dam. regarded as only being calibrated to a preliminary level. Neverthel ess, the model results demonstrate the power of a model in simultaneously including the effects of over 20 hydrodynamic and water quality processes in predicting river water quality.

Models can therefore be used as powerful management tools for predicting the water quality effects ofhuman developments and catchment management changes. These varying effects can be compar~d in a relative sense for a model which is only calibrated to a preliminary level , or in an absolute sense for well calibrated and verified models.

Models also allow the effects of specific hydrodynamic and water quality processes to be examined, and consequently are very useful in interpreting water quality and hydrodynamic data. They can also be used to define data requirements for various management purposes, including sampling locations, water quality indicators to be measured, and the sampling frequency.

References Conclusions

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Distance from Yarrawonga W eir Pondage (km)

Blue Green Algae Task Force (BGATF)( l 992 ) "Blue-Green Algae- Final Report of the New South Wale s Blue-Green Algae Task Force " ISBN 0730578860 Gutteridge Haskins & Davey (1992) "An investig-

l

ation of nutrient pollution in the Murray-Darling River System" Unpublished report prepared for MDBC Ref. #311/1048/0504.

Haines PE, Druery BM, Nielsen JS, Deen A, Fisher I (1993) "Water quality modelling on the NepeanHawkesbury River" Proc. WATERCOMP '93, Melbourne pp351-356.

Haines PE (1993 ) "A Numerica l Water Quality Modelling Study of the Murray River" MEngSc thesis, UNSW Patterso n Britton & Partners (I 993 ) "Nepean & Hawkesbury River water quality mode ls.

Preliminary Calibration of Beta SALMON-Q models" unpubli shed report to Sydney \Xlater Board

Authors Three authors are members of Patterson Britton & Partners Pty Ltd. Philip Haines is an Engineer, specialising in river and water resources engineering.

He gained his M.Eng.Sc. in Water Engineering from the University of New South Wales.

Dr Jeppe Nielsen, an Associate Director, is a leading authority in water quality processes.

Bruce Druery is a Director, and has had over 20 years' expaience in river and coastal engineering.

Dr James Ball is a Senior Lecturer in the School of Civil Engineering at the University of New South Wales with many years' experience in numerical modelling.

WATER OCTOBER 1994