Drinking water treatment
Clarifiers solve Quebec community's water quality need
The Quebec city of Victoriavil e's
potable water treatment plant has experienced many changes since
silica are added. Powdered activated car
mg/L, Color = 0, Iron = 0,005 mg/L, Man ganese = 0,03 mg/L and Turbidity = 0,02
bon is added to eliminate taste and odours.
NTU.
its construction in 1928.
The floes settle in the High-Rate Flocculator Clarifier. The water then passes through
Several problems had occurred earlier, leading the city of Victoriaville to review its entire treatment process and capabilities. In the early 1980s, a
On average, the city requires a flow of 31,000 mVd. In Victoriaville potable water comes from
current detector. Polymer and activated
two downflow sand and anthracite filters
three
sources: a potable wa ter treatment plant with an average yearly flow of 14,000 mVd; a radial collecting well with an average flow of 11,000 m'/d and a gravel-packed well with an average flow of 6,500 m7d. In 1990, adapting to a growing popula tion as well as indus
trial needs, the city
river dam located
upflow from the Pota 1. Raw water intet
ble Water Treatment
2. Vacuum chamber
Plant(PWTP)was de
3. Vacuum pump
stroyed because of ex cessive damage. It
4. Vacuum breaker valve
5. Raw water distribution conol
used to create a reser
6. Distribution iaterois
voir which provided the plant with a natu ral "pre-settling" tank
7. Parolfel plates
8. Sludge concentrator 9. Sludge extraction ppes
environment. The raw water was of ex
10. Sludge extraction volves 1. Clarified water collection laterals
ceptionally good qual ity and the static clari fiers produced satis factory water quality.
12. Tube settling modules
modified its static
clarifiers, capable of treating up to 18,000 mVd, to two dynamic
ÂŤ
When the dam was
destroyed, the water chemistry changed. Total suspended sol ids(TSS)content was higher and when it rained abundantly, the city was faced with levels: turbidity: 500-
clarifiers with a maxi
mum capacity of 30,000 mVd. The city was provided with a high-rate, sludge blanket, solids con
tacts system: the
1200 NTU; color
UltrapulsatorÂŽ. For the water treatment plant, the raw water comes from a reservoir created by a
and finally the water is chlorinated with the
dam on the Bulstrode river. Pre-treatment
preserve the aqueduct network. Clarifier sludge is pumped directly to the wastewater treatment plant. The water pumped from the wells by passes the treatment and is submitted only to disinfection (chlorination and corrosion inhibitor dosing) before it merges in the wa ter system. The water
consists of pre-oxidation with potassium permanganate, aeration and straining. The water is then pumped to the plant where a coagulant (alum when alkalinity is greater than 40 mg/L or P.A.S.S when alkalinity is less than 40 mg/L) is added by a streaming
addition of a corrosion inhibitor in order to
from the wells before
disinfection averages levels of Alkalinity =79 mg/L, Hardness = 108
AVERAGES FOR 1993 PLANT Characteristics
Alkalinity Aluminum
Colour Chlorine Hardness Iron
Manganese Nitrates
PH Fluorides rH Dissolved solids
Turbidity 34
RAW WATER
EFFLUENT
82,00 0,02 19,00
73,00 0,01 0,00 0,75 128,00 0,00 0,00 1,00 7,20 0,19 515,00 148,00 0,09
-
117,00 0,30 0,27 1,20 7,50 0,20 379,00 130,00 11,40
(mg/L) (mg/L) (Units) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (Units) (mg/L) (mV) (mg/L) (NTU)
>200PCU; alkalinity: 20-60 mg/L and ammoniac nitrogen: 0,20-0,65 mg/L. With these conditions, the static clarifiers no
longer performed well and changes were re quired. The High-Rate contact clarifier chosen by the city combines two techniques in sol ids contact flocculation: the recirculation of
sludge and the passage of coagulated water through a homogeneous sludge blanket maintained in suspension by periodic pul sations.
Recirculation of sludge is effected by a system of inclined plates with deflectors
AVERAGES FOR 1993 Chemicals used Activated silica Alum Activated carbon
Hydrated lime Chlorine
P.A.S.S.
Potassium permanganate Polymer Polyphosphate
Kg -
8724,00 2117,00 1753,00 866,00 5073,00 381,00 16,00 161,50
mg/L 2,50 45,00 8,40 9,00 3,70 35,10 1,60 0,10 0,77
Environmental Science & Engineering, June/July 1994