Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177
Aeration Treatment of Membrane Concentrates Of TMP Wastewater Unity Oviasogie* *Water Resources and Engineering Management Pfaffenwaldring 7, 70569 Stuttgart, Germany.
ABSTRACT The aim of this research paper is to investigate the chemical oxygen demand (COD), biological oxygen demand in 5 days (BOD5), suspended solids (SS) denoted as “food” (F) to biomass (M; microorganism) ratio (F/M), by targeting varying rate of influent stream. The experiment initially consisted of two acrylic cylinders with coneshape bottom with an inner diameter of 20 cm and 65 cm, respectively. The setup is fitted with a heater and aeration system. Temperature of wastewater range is maintained at 30 – 36 degree Celsius to promote the growth mesophilic microorganism. COD had its highest elimination rate on day 39 at 83% at an influent rate of 13.96 litres per day. COD mf result showed the highest elimination rate on day 39 at 78% with influent rate of 13.96 litres per day. Biological oxygen demand in 5 days (BOD 5; BSB5) result showed the highest elimination rate on day 43 at 94% with influent rate of 19.98 litres per day. The suspended solids (AFS; SS) result showed the highest elimination rate on day 39 at 98% with influent rate of 13.96 litres per day. The results attained from absorbance denoted as DFZ436, DFZ525, DFZ620 exhibits the highest elimination rate on day 44 at 72%, 78% and 59% respectively with a constant influent rate of 19.98 liters per day Keywords: Biological Oxygen Demand (BOD5); Chemical Oxygen Demand (COD); Continuous Biological Treatment (CBT); Suspended Solids (SS, AFS); Sequential Batch Reactor (SBR); Thermal Mechanical Pulping (TMP)
Directive 2008/1/EC on integrated pollution prevention and control covers industrial plants for the production of pulp and paper and cardboard with a production capacity exceeding 20 tonnes per day .The application of European Union (EU) policies on the pulp and paper sector and heighten awareness of the challenges waste management. The application of biological waste management process is common in the pulp and paper industry, but some drawbacks are associated with these methods. Challenges include, the large area required for the aerobic process, the difficulty in controlling the population of microorganisms and the rigorous control parameters i.e. pH, temperature, DO and nutrients. In addition to biological treatment process is the optimization of physical filtration of wastewater through the application of continuous pressure to drive water molecules through a membrane that is not permeable to the target substances. The application of membrane filtration by ultrafiltration (UF) and nanofiltration (NF) to pulp and paper manufacturing and treatment process reduces dissolved substances i.e. organic and inorganic, microorganisms and color. Ultrafiltration is considered an important treatment step in the hierarchy of conventional industrial thermal mechanical pulping wastewater treatment schemes. It is the main membrane process employed by the pulp and paper industry and serves as the primary steps in membrane treatment process . The effectiveness of ultrafiltration process is measured by its extraction of www.ijera.com
large molar mass of ligneous substances, a compound found in TMP wastewater. Nanofiltration removes most of the organic load and also the multivalent ions, such as calcium, iron, aluminum, silicon, magnesium and sulfate. . Nanofiltration is applied in the treatment of thermal mechanical pulping or TMP and Deinking wastewater in order to attain high retention of lignin before immediate continuous biological treatment by means of activated or aerated sludge in an aerobic environment. The efficiency gains can be attributed to the efficacy of ultrafiltration method in removing higher molar mass compounds and microorganism, thereby accelerating the efficiency of nanofiltration in the consequent filtration step. It is also widely believed that the choice of specific membrane filters and their design also have an influence on energy requirements and overall efficiency thereby removing problematic constituents of industrial wastewater from the pulp and paper. The aim of this paper is to investigate the efficacy of aerobic activated sludge system in the continuous biological treatment of TMP concentrate wastewater from the pulp and paper industry. i.
Membrane Resistance and Reduction of Efficiency The widespread application of membrane treatment processes has been very efficient in reducing toxic emissions to the water bodies. The tendency of the membranes to become fouled, or 171 | P a g e
Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177 blocked, by colloidal and other substances in wastewater is unavoidable. Fouling is not only limited to colloidal constituents. Biological fouling has steadily become an increasing issue in membrane treatment process. This occurs when various microorganisms can become deposited on membrane surfaces. The bioavailability of nutrients and alkaline environment may promote growth of microorganism and cause membrane fouling.  ii.
Continuous Biological Treatment (CBT) of TMP Membrane Concentrates with Aerated Sludge System The continuous biological treatment (CBT) system is continuously supplied dissolved oxygen as part and parcel of the activated sludge process. The wastewater in the aeration tank (see Figure 2) was provided oxygen at a minimum of 2 mg/min (peak aeration at 5mg/min) to meet the sludge demand and promote microorganism growth and BOD, COD degradation . The efficacy of activated sludge in industrial wastewater treatment is proving widely because of its effectiveness in reduction of measured wastewater parameters of interest in the effluent. Its high removal rate of toxic substances and efficacy has made the activated sludge treatment system an efficient means of emission reduction, water conservation and management. Aerobic treatment of activated sludge systems increases degradation of total, settled and soluble COD in the effluent with high organic loading rate and low nutrient levels .The high organic degradation during the course of aerobic treatment leads to an increase in the sludge production. It is best to monitor the sludge in the clarifier and withdraw occasionally to prevent excess suspended solids (SS) in the effluent. The continuous biological treatment (CBT) reactor (as seen Figure 2) is used in all the experimental runs. The CBT reactor is composed of a reactor (aeration tank), sedimentation tank (denitrification tank or clarifier) and reverse sludge recycling system. For example, mixed liquor suspended solids (MLSS) is the mixture of wastewater and microorganism in the activated sludge in the aeration tank until the adequate F/M ratio is reached. Continuous aeration by dissolved oxygen (DO) is used to promote microorganism growth through biological reaction. The MLSS is later separated to a liquid and solid phase in the sedimentation tank where the aeration is turned off to promote denitrification. The supernatant flows out of the top of the sedimentation tank as effluent while the settle solids at the bottom is recycled back to the aeration tank with the assistance of a vacuum pump. Volume recovery (VR) of wastewater is symptomatic after membrane filtration. Volume recovery factor in relation to membrane technology is characteristic of feed volume used to study the membrane performance during ultrafiltration and nanofiltration. For example, ultrafiltration process www.ijera.com
yields a VR of about 0.9 or 90% of permeate leaving 10% reject  .
MATERIALS AND METHOD
Two stage membrane filtration processes was used to obtain concentrated wastewater. Ultra filtration materials and methods were used to obtain 10% concentrated reject which was subjected to subsequent nanofiltration to attain 18% concentrated reject, and then stored separately. The treated influent was a mix of 10% and 18% permeate representative of the 2 stage filtration process as shown in Figure 1.
Figure 1: 2-Stage Membrane (UF-NF) filtration process The experiment was performed in a (CBT) reactor (Fig. 2) in a laboratory in WWTP Büsnau. The wastewater was delivered to WWTP Büsnau by Pulp and Paper mills around Baden Württemberg, Germany. The CBT apparatus consists of two 50 liters volume capacity acrylic cylinders with an inner diameter of 20 cm and 65 cm with cone-shape bottom, and attached to water heater and aeration system. The temperature of wastewater ranges between 30 – 36 degree Celsius and thermostat are used to continuously to maintain constant and optimal temperature to promote the growth of microorganism. Metabolic rate of all biological systems is affected by temperature. Biochemical reactions proceed more rapidly with increasing temperature. The treatment efficiency of anaerobic processes compared with aerobic processes is particularly sensitive to operation below optimum temperatures, because of the significantly lower substrate removal rate constants discussed above. Considering the relatively high temperatures of many pulp and paper mill process streams (50 to 85 degrees C), operation of anaerobic treatment systems in the optimum range of 55 to 60 degrees Celcius for thermophilic bacteria has been investigated, but as yet has not been found to be effective. Mesophilic temperature range (30-35 o C) was found to be most effective. Nutrients, phosphorus (P) and nitrogen (N) were added to influent wastewater prior to the onset each experimental run. Phosphorus was added in the form potassium dihydrogen potassium phosphate (KH2PO4) and nitrogen in the form of urea (NH2CONH2) at a dosing ratio 100C:5N:1P.  172 | P a g e
Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177 Nitrogen (N) and phosphorus (P) are essential nutrients required for the growth of microorganism which in turn synthesize new biomass. Beside the widely used nutrients, nitrogen and phosphorus. Microorganism also requires available macronutrients (S, K, Mg, Ca, Fe, Na, and Cl) and micronutrient (Co, Ni, Zn, Mn, Mo and Se) for growth. Nutrients in the form of ammonium NH2NH4 and di-hydrogen potassium phosphate KH2PO4 are added to the influent wastewater based on measured BOD5 concentration at the start of each run. Bulking, characterize by floating sludge blanket, is a commonly known operational problem in activated sludge plants treating pulp and paper wastewater. The best way to deal with bulking is longer adaptation time (long sludge age) which promotes optimal microorganism, and daily discharge through sampling of MLSS and MLVSS. This help in monitoring suspended solids (SS) in the system. The sludge volume index (SVI) was measured in 250-500 mL graduated glasses by settling samples, with known SS, for 30 minutes (German ATV DVWK131A 2002) as shown in Table 1. Total Suspended Solids (t ss) is defined as those solids which are retained by a filter paper and dried to constant weight at 103-105 degrees Celsius. A modification of filter paper was used to collect particulate and dried. The filter paper is left to dry for 24 hours and desiccated for 2-3 hours minimum then weighed.
Figure 2: Continuous Biological Treatment (CBT) TMP influent wastewater pH varied from 4 to 9. Therefore buffers were employed in regulation to desired pH of 6-9 value for each respective experiment. The acid and base buffers used are Sulfuric acid (H2SO4) 1M and Sodium Hydroxide (NaOH) 32%. Influent wastewater pH value of the was adjusted from 4 to range of 7-8 at the beginning of each experiment and readjusted as needed to maintain the optimal range through the experimental period Dissolved oxygen (DO), pH, and temperature in the reactors were measured typically on a daily basis. In the laboratory studies DO was measured using a YSI Jenway 9300 DO-meter, pH and temperature were measured using a Hanna Instrument 6028 pH meter. Dissolved oxygen (DO), pH and temperature were measured every experimental day and sample was taken before mixture at the start of each experimental day at the top of the aeration tank (reaction tank) for measurement of MLSS and www.ijera.com
MLVSS. The measurement of effluent parameters chemical oxygen demand (COD), soluble chemical oxygen demand (COD mf), biological oxygen demand (BOD5), suspended solids (SS, AFS), and absorbance (DFZ) was performed through sampling, at a minimum rate of three times every week. Table 1: German Standards ATV-DVWK-131A 2002 for Wastewater Analysis Parameters Abbrevia Uni DIN tion t mg/ DIN Chemical oxygen COD L 38409 demand Teil 41-2 mg/ DIN Soluble chemical COD mf L 38409 oxygen demand Teil 41-2 BOD mg/ DIN Biochemical 5 L 38409 oxygen demand in (BSB5) Teil 52 5 days (8-2) SS (AFS) mg/ DIN Suspended solids L 38409 Teil 2-2 (5.2) mg/ DIN Mixed liquor MLSS L 38414 suspended solids Teil 10 mg/ DIN Mixed liquor MLVSS L 38414 volatile suspended Teil 10 solids P tot mg/ DIN Total phosphorus L 38405 Teil 11 mg/ DIN EN Total Kjeldahl TKN L 25663 nitrogen pH DIN pH 38404 Teil 5 DO mg/ DIN EN Dissolved Oxygen L 25814 o T C DIN Temperature 38404 Teil 4 Influent parameter were taken 1 to 3 times per experimental period dependent on length of the experimental period and change in biodegradability of influent concentration, and the availability of staff to do the extra analysis. Total Kjelhdahl Nitrogen (TKN) and Total Phosphorus (Ptot) were sampled and at experimenterâ€™s discretion of F/M results and amount present in the effluent sample. Sampling of listed parameters was carried out 1-3 times a week and daily operation parameters were performed to ensure the functionality and integrity of the continuous biological treatment systems. The influent rate was monitored constantly and changed at authorâ€™s discretion. 173 | P a g e
Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177 III. RESULTS The growth of microorganism are seen in four phases; lag, log (growth), stationary and death phase with slight alteration based on varying chemical conditions in wastewater. The time needed to adapt to wastewater characteristics is the lag period, enzymes and it substrates to produce and sustain a growth phase (log). This is characterized by steady predation and succession of competing microorganism success in adaptation to changing wastewater parameters, substrate optimization and metabolism. This success of emerging species leads to decline in wastewater and death. An increase in the BOD of a sample due to the pretreatment would indicate its greater amenability to biodegradation. Thus, an increase in BOD/COD and BOD/TOC ratios after pre-treatment is indicative of improved biodegradability due to an enhancement in the proportion of COD or TOC amenable to biological mineralization. The relationship of BOD and BOD/COD or BOD/TOC are commonly used Kinetic studies based on Monod model have also been developed.  In aerobic treatment process, microorganism, through three main processes; oxidation, synthesis, and endogenous respiration uses organic matter (biomass) to produce energy. An example of this is exhibited by chemoautotrophs, Nitrosamines in the nitrification process. Microorganisms, in aerobic environment, ammonia are converted into nitrate in two steps: conversion of ammonia into nitrite, and then subsequent oxidation of nitrite into nitrate by Nitrobacteria. Chemo heterotrophs microorganism species involved in other conversions are bacteria, fungi, algae, protozoa and metazoans (flagellates or ciliates)  . Fungi and algae are competes for food , aerobic suspended growth process and lower pH gives fungi an advantage over algae at lower pH yielding lower algae in the process. Protozoan and metazoans like rotifers and nematodesâ€™ makes up the secession of the activated sludge process . The objective of these organisms revolves around solid formation, saprophytes, nitrification, predation and secession. A pH of 6-9 is optimal for carbonaceous removal. A constant pH range of 7-9 was maintained in all experimental phases. Although TMP and De-inking wastewater had a pH of 4 or lower; readjustment of pH was performed trough addition of Sodium Hydroxide (NaOH); consequently increasing the pH to increase microbial growth. An acidic wastewater characteristic drastically reduces microbial growth; therefore, antithetical to the activated sludge process because microorganism cannot survive under high acidic conditions. Increased secession by nuisance microorganism can be cause of sludge blankets, forming and excessive sludge bulking. During the course of the experimental work, experiences with nuisance microorganism in biological reactor led to www.ijera.com
longer adaptation periods and reduced influent rate. F/M ratio is the relationship of substrate removal to biomass is often termed the food-to-microorganism or food-to biomass (F/M) ratio. The influence of the F/M ratio on the COD load elimination and effluent COD concentration is to be considered. The F/M ratio is calculated by the following formula F/M = Where: F: M : food to microorganism ratio (g BOD5/g MLSS) V1 : liquid volume of the reactor, V1 = V in + Vs1 (liters) V in : volume of the influent (liters) V s1 : volume of the sludge fed in the reactor (L) BOD5, in : BOD5 concentration in the influent (mg/L) MLSS : mixed liquor suspended solids in the reactor (mg/L) SS in : suspended solids concentration in the effluent (mg/L) T : aeration time (days) MLVSS instead of MLSS may be more viable in estimation of the amount of substrate applied on the amount of active biomass. MLSS was chosen in accordance with the German Water Quality Standard (ATV-DVWK-131A, 2002). The carbonaceous organic matter removal capacity of the aerobic reactor is expressed by COD concentration elimination rate. It is calculated by the formula below: E=
Where: E : COD elimination rate (%) COD eff : COD concentration in the effluent (mg/L) COD R : COD concentration in the reactor (mg/L) COD R is calculated as follows: COD R = Where: COD in : COD concentration in the influent (mg/l) COD s : COD concentration in the sludge volume (mg/l) Sludge age is calculated according to the formula below: t = ss
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Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177 Where: T ss : sludge age (day) MLSS ES : mixed liquor suspended solid in the excess (mg/L) V ES : excess sludge flow (liters/day) V sample : sampling volume per day (liters/day) SS eff : suspended solids in the effluent (mg/L) V eff : clear effluent flow decanted from the reactor (liters/day) These studies were carried out in a continuous activated sludge system for short periods with variable feeds. Sludge Retention Time (SRT) characteristics are an estimate of the biomass growth yield on COD indicates slight decrease in yield at higher temperature operations. The possible explanation for lower cell yield at higher temperature is due to higher endogenous respiration which means more COD is used by cell bacteria for their cell maintenance (endogenous respiration) and less for cell growth. COD is the main parameter which is used to evaluate the carbonaceous organic matter removal capacity (see Figure 3). COD analysis was performed on the effluent of every experiment. COD mf was measured to assess the effect of SS content in the effluent on the COD elimination . COD mf analysis was performed in all stages of the experimental period and served as an indicator of true COD values. BOD5 was measured to evaluate whether the effluent was fully biodegraded after the experiment. And the analysis of Ptot and TKN (Figures not shown) was performed in order to check if the nutrients were sufficient for the microorganisms during the experiment. BOD5, Ptot and TKN were samples were measured randomly. Biomass can be found smaller or larger aggregates of free-living microorganism. SS in the form of aggregates would interfere with the treated wastewater effluent quality, as well as the production process and therefore have to be removed before reusing the water. The presence of free-living bacteria may not affect the product quality negatively, but a high number may decrease the drainage rate and therefore influence the efficiency of the treatment process. Therefore, the application of a functioning clarifier will most likely be needed in all cases for the optimum removal of SS. The removal efficiency and the final amount and character of the remaining suspended solids will probably differ from case to case.
Parameter DFZ436 DFZ525 DFZ620
Unit 1/m 1/m 1/m
www.ijera.com 1914 0.34 - 0.30 1230 1165 Influent 41.5 - 25.4 27.4 - 13.7 16.5 - 10.7
0.11 - 0.04 310 - 20
Effluent 92.1 - 32.8 64.9 - 17.1 35.6 - 13.4
TMP concentrate experiment by aerobic treatment was started on day 33 to 45 on the second experimentation phase of industrial wastewater treatment. The results of COD parameter showed the highest elimination rate on day 39 at 83 % with an influent rate of 13.6 liters per day. Meanwhile COD mf also experienced its highest elimination rate the same day at 78 % also with an influent rate of 13.6 liters per day as shown in Figure 4. 5. VARIABLES AND EQUATIONS All variables should be italic through the text. All equations should be placed on separate lines and numbered consecutively. The highest elimination rate within the experimental period was shown in the BOD5 parameter. Results as shown in Figure 5; exhibit the highest elimination rate on day 43 at 94 % with influent rate of 19.98 liters per day reinforcing the efficacy of biodegradability. Suspended solids denoted as AFS had the highest elimination rate on day 39 at 98% with influent rate of 13.96 liters per day as shown in Figure 6. This indicates that there was almost no suspended solid in effluent sample. The absorbance spectrum was analysed at three wavelengths 436, 525, 620 nm, respectively. DFZ436 (Figure 7) showed the highest elimination rate on day 44 at 72% with influent rate of 19.98 liters per day. The absorbance DFZ525 analysis results (Figure 8) shows higher elimination rate at a moderate wavelength on day 44 at 78%, and DFZ620 results (Figure 9) on the same day 44 at 59%.
Table 2: Analysis Results of Influent and Effluent Parameters of TMP concentrate-Aerobic treatment Parameter Unit Influent Effluent mg/L 6410 2460 - 639 COD 6320 mg/L 5000 2070 - 600 CODmf 4660 mg/L 2240 270 - 28 BOD5 www.ijera.com
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Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177
Figure 10: TMP Con-Ana-Aer Cod effluent
COD elimination rate
Influent Vol l/d
0.15 0.2 0.25 0.3 0.35 F/M (g BOD5/(g SS. D)
The food to microorganism (F/M) ratio was well targeted throughout the TMP concentrate experimental phase. The results shows that the highest influent rate at 19.98 liters per day influence a higher food to microorganism ratio and higher COD elimination rate.
Due to environmental regulation, the pulp and paper industry uses a lower volume of process water today, and recycles and reuses more water, and cleans water before releasing it to the environment. This treatment method is referred to as an end of pipe www.ijera.com
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Elimination rate (%)
Unity Oviasogie Int. Journal of Engineering Research and Application Vol. 3, Issue 5, Sep-Oct 2013, pp.171-177 technology non-distributed wastewater cleanup and treatment technologies. The treatments of concern are physical (dissolved air flotation) and a combination of physical and membrane treatment (i.e. ultrafiltration), which remove suspended solids from the effluent . This is made possible by the application of membrane technology in the treatment process. This practice is also a strategy in cost reduction which is primarily based on the amount of water consumed. The pulp and paper industry has made advancement in treatment techniques through the use of new and applicable technology to reduce its environmental impacts. The intermittent application of membrane technology in the treatment process also plays an important role in decreasing freshwater withdrawal but increases the toxicity of permeate retained; Hence, the necessity for efficacious activated sludge treatment. The activated sludge, used as inoculum, is collected from the return sludge of local municipal sewage treatment plant i.e. WWTP Busnau . TMP wastewater stream passing through one or more membranes and being concentrated in the stream permeate. The treated effluent is less concentrated. The experiment utilized the more concentrated reject. The results, as shown in Figure 3-9, show that the activated sludge system in combination with continuous biological treatment was very efficacious in removal of carbonaceous organic and inorganic matter. With elimination rate peaking at 98% for certain parameters, the author concludes that membrane concentrate of industrial wastewater from pulp and paper industry were biodegradable under certain optimal conditions i.e. long sludge retention time (SRT) or sludge age, constant maintenance of mesophilic temperature, DO, and daily operations parameters . One of the major problems encountered during activated sludge treatment of pulp and paper concentrate is poor sludge settling characteristics better known as bulking. Settling ability is dependent on the structure and type of sludge flocculation, which is in turn dependent on environmental conditions and process operating parameters. Therefore, the temperature effect on sludge settling and a better understanding of microbial flocculent also becomes important for improving the performance of these effluent treatment systems. All experimental parameters achieved high elimination rate after continuous biological treatment combine with activated “aeration” sludge system.
J. Nuortila-Jokinen, M. Mänttäri, T. Huuhilo, M. Kallioinen And M. Nyström; Water Circuit Closure With Membrane Technology In The pulp And Paper Industry; Water Science & Technology Volume 50 No 3 217–227 © IWA Publishing 2004 Industrial Waste Treatment Handbook Second Edition By: Woodard & Curran, Inc. © 2006 Elsevier Jutta Nuortila-Jokinen,Tina Huuhilo, and Marianne Nyström, Closing Pulp And Paper Mill Water Circuits With Membrane Filtration Ann. N.Y. Acad. Sci. 984: 39–52 (2003). © 2003 New York Academy Of Sciences. Nuortila-Jokinen, M. Nystron, Comparison of Membrane Separation Processes in the Internal Purification of Paper Mill Water. Journal of Membrane Science 119 (1996) 99-115 Ess Method 340.2: Total Suspended Solids, Mass Balance, Volatile Suspended Solids; Environmental Sciences Section Inorganic Chemistry Unit, Wisconsin State Laboratory of Hygiene, 465 Henry Mall, Madison, WI 53706 Revised June 1993 S. Contreras, M. Rodrıguez, F. Al Momania, C. Sansa, S. Esplugas; Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol; Water Research 37 (2003) 3164–3171 A.-S. Jönsson, O. Wallberg Cost estimates of kraft lignin recovery by ultrafiltration Desalination 237 (2009) 254–267 Goksen Capar, Levent Yilmaz, Ulku Yetis Reclamation of acid dye bath wastewater: Effect of pH on nanofiltration performance journal of Membrane Science 281 (2006) 560– 569 Anantha P.R. Koppol, Miguel J. Bagajewicz,, Brian J. Dericks, Mariano J. Savelski, On zero water discharge solutions in the process industry, Advances in Environmental Research 8 (2003) 151–171 Muhammad Afzal, Ghulam Shabir, Irshad Hussain, Zafar M. Khalid, Paper and board mill effluent treatment with the combined biological–coagulation–filtration pilot scale reactor; Bioresource Technology 99 (2008) 7383–7387 Vimal Chandra Srivastava, Indra Deo Mall, Indra Mani Mishra; Treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash Colloids and Surfaces; Physicochem. Eng. Aspects 260 (2005) 17–28
Commission of the European Communities Brussels, 30.7.2009 Sec (2009) 1111 Final Commission Staff Working Document European Industry in A Changing World Updated Sectoral Overview 2009 Section 26. Pulp, Paper And Paper Products
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