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Municipal Wastewater Effluent Characterization and Loadings

Municipal Wastewater Treatment Plants

Characterization

Effluents from MWTPs are derived from both household and industrial sources and consist of suspended solids, microorganisms, debris, and about 200 chemicals (Environment New Brunswick 1982; Birtwell et al. 1988; OMOE 1988).  While municipal wastewater effluent (MWWE) contains a wide variety of constituents, they can generally be described by the following categories: solids; suspended and dissolved substances that exert a biochemical oxygen demand; nutrients; pathogens; organic chemicals; metals; oil and grease; and, plastics and floatables.  Of these, total suspended solids (TSS), biochemical oxygen demand (BOD) or chemical oxygen demand (COD), nutrients in the form or phosphorus (P) and/or nitrogen (N), pathogenic bacteria, and plastics and floatables are the primary targets for removal through wastewater treatment. Concentrations of these conventional parameters are given in Table 3 for selected Canadian cities and different treatment types.

In addition to conventional substances, recent surveys (OMOE 1988; Rutherford et al. 1994; Golder Associates Ltd. 1995a,b) have shown that toxic substances including metals and organic chemicals are present in MWWEs across Canada (Tables 4 and 5). In particular, a wide variety of synthetic organic chemicals have been found in MWWEs in Canada (Table 6).  While their concentrations might not be very high, many of these organic chemicals are toxic and persistent in the environment.  In Ontario, for example, a study of 37 MWTPs with various types of treatment reported up to 24 base/neutral and acid extractables, seven dioxins and furans, 30 pesticides and herbicides, and 19 volatiles, along with 15 metals and cyanide (OMOE 1988).  Effluents from two MWTPs in Edmonton contained 19 metals and 3 to 7 organic compounds (Golder Associates Ltd. 1995a,b) whereas up to 48 organic chemicals including detergents, solvents, chlorinated compounds, plasticizers, fecal-derived compounds such as dihydrocholesterol, and miscellaneous compounds such as caffeine and nicotine were found in effluent from four Nova Scotia MWTPs (Rutherford et al. 1994).  Industries are often a significant source of metals and organic compounds; however, some of the metals and organic compounds in MWWE are derived from household waste.  For example, metals such as copper, zinc, iron, cobalt, manganese and molybdenum are essential elements in human nutrition. Consequently, small concentrations of metals and other toxic chemicals that are by-products of human physiological functions will always be found in municipal wastewater. In addition, aluminum can be introduced from cooking ware and antacids, tin can be introduced from canned foods, while household cleaning agents can introduce a variety of  chemicals. Thus, U.S. EPA (1986) found that approximately 20% of metals in U.S. wastewaters are from domestic sources.

Table 3.  Concentrations (mg/L) of conventional parameters and annual discharge (x 106m3) for selected municipal wastewater treatment plants in Canada. (Blanks indicate data are not available; sample years given in brackets after parameter value if different from year(s) given in “Date” column.)
Location and MWTP typeDateBODCODTotal Suspended SolidsAmmoniumNitriteNitrateTotal PhosphorusEffluent Discharge
1Hamilton and North 1986 8 EVS Consultants 1992; Taylor et al. 1995
2Charlton and Bayne 1986 9Rutherford et al. 1994, except discharge from Environment Canada 1986  
3 Anderson et al. 1986 10 OMOE 1988
4 Golder Associates Ltd. 1995a,b 11CUM 1994; Deschamps et Ceijka 1993; PAHs and PCBs from Pham and Proulx 1996 
5 Chambers 1996; Chambers and Mills 1996 12 Saskatchewan Environment and Public Safety 1989
6 Environment Canada 1992 13 City of Saskatoon records
7 French and Chambers 1995; City of Prince George records (BOD values are carbonaceous BOD (CBOD); CBOD and TSS from 1991-1994)
14 Enns and Soprovich 1995 15 Environmental Management Assoc. & Hydroqual Laboratories  Ltd. 1993
Alberta
Calgary secondary1
Calgary secondary + P removal2
Goldbar Edmonton secondary3
Goldbar Edmonton secondary4
Capital Region Edmonton tertiary4
Grande Prairie primary5
1980
1985
1982-83
1980-93
1980-93
1988-93


16

22

 8.6


65

38


14


9
5


16


20
0.6





0.5
0.4		 
3.5
<13.
7
3.1
5.4
5.0


132

 90
114
17
4

British Columbia
Iona Island Greater Vancouver primary6 Annacis Island Greater Vancouver primary6
Lulu Greater Vancouver primary6
Prince George secondary7
Macaulay Point Victoria primary8
Clover Point Victoria primary8
1985
1985
1985
1985-91
1992
1992
81
156
139
197
224
192		 
57
71
64
307
320
186
8.8
16
20
26
28
18



1.2



1.6
2.9
4.5
5.3
5.0
170 (1987)
107 (1987)
15 (1987)
11 (1993-94)
} total 36x106 m3 for both outfalls
Nova Scotia9
2 secondary
Eastern Passage primary
Lakeside tertiary
fall 1991
fall 1991
fall 1991
<5-50
80
<5		 
25-45
31
12
<0.14-28
18
2.0		   

4.4 (1986)
0.5 (1986)
Ontario10
7 primary
28 secondary
1 tertiary
1987
1987
1987
48
21
25
109
53
99
30
10
32
10
3.9
18
0.00
0.22
0.05
0.05
2.33
0.14
1.34
0.68
1.56
291
1044
16
Quebec11
Montreal primary + physical/chemical  treatment with ferric chloride
1993
38
105
20
5.9		  
0.5
412
Saskatchewan
Saskatoon primary
Saskatoon primary + P removal13
Saskatoon secondary13
1985-89
1993-95
1996
8313
78
44		 
7413
24
19
19 (1987)12		  
5.213
0.96
1.12
32 (1987)12
34
30
Yukon14
Carmacks secondary
Oct 93
18
56
10
0.2
0.11
27		 
0.03
Table 4.  Metal concentrations (µg/L unfiltered total, unless otherwise indicated) for selected municipal wastewater treatment plants in Canada. (Footnotes as for Table 3.  Blanks indicate data are not available; nd is below detection limits.)
Location and MWTP typeDateAlAsCdCrCoCuFePbHgMnMoNiSeAgZnSr
Alberta
Calgary secondary1
Calgary secondary + P removal2
Goldbar Edmonton secondary3
Goldbar Edmonton secondary4
Capital Region Edmonton tertiary4
1980
1985
1982-83
1980-93
1980-93


60

60a
76a


1


0.8
1


<1


2
2


48

21
9


2

1
1


21


5
10


115

110
89


18

3
4
3





0.1
0.1


34

43
54
75





10
3
8

2
22
8



0.2
0.2



20
20


114

53
53
85

 
British Columbia6
Iona Island Greater Vancouver primary
Annacis Island Greater Vancouver primary
Lulu Greater Vancouver primary
1985
1985
1985

799
2789		 


1.7
nd
nd
150		 
101
141
160
889
1799
2692
43
41
58		 
60
99
90		 
nd

150		  
120
171
340		 
Nova Scotia9
2 secondary
Eastern Passage primary
Lakeside tertiary
fall 1991
fall 1991
fall 1991
280-12000
320
340		        
20-120
20
30		          
Ontario10
7 primary
28 secondary
1 tertiary
1987
1987
1987
550
102
1252
nd
17
Nd
2.5
2.1
6
11
9
69
6.5
6.4
9
18
13
55		 
21
17
56
0.05
0.03
0.17		 
7
7
11
9
22
26
17
17
nd
6.4
6.9
6.6
70
53
960
305
341
1171
Quebec11
Montrealprimary + physical/chemical treatment with ferric chloride
1993
1009
1
1.8
8		 
26
2000
7		   
14		 
1.8
58		 
Saskatchewan12
Saskatoon primary + P removal
spring92
summ92
fall 92		 
0.5
<.5
3.2
<1
<1
<1
11
5
14
<1
<1
<1
33
44
51		 
<5
9
<5
0.09
0.31
0.16		 
13
5
21
4
26
4
2
2
<1
2
1
3		  
Yukon14
Carmacks secondary
Oct93
690		    
90
510		  
210		    
160
390

a Extractable

Table 5.  Concentrations of organic contaminants for selected municipal wastewater treatment plants in Canada. (Footnotes as for Table 3.  Blanks indicate data are not available; and is below detection limits.)
Location and MTWP typeDate

Chlorinated Solvents

 (µg/L)

PCB

(ng/L)

PAHs

(µg/L)

Phenols (µg/L) 
  TetrachloroethyleneTricholoroethylene  ChlorinatedNon-Chlorinated
a all phenols; bbenzo(a)anthracene; c pyrene; dpentachlorophenol; e for 13 PCBs; f for 21 PAHs.
Alberta
Goldbar Edmonton secondary3
Goldbar Edmonton secondary4
Capital Region Edmonton tertiary4
1983
1992-93
1992-93

1.5		   
16a
13a
8a
British Columbia
Iona Island primary Greater Vancouver6
Annacis Island Greater Vancouver primary15
Lulu Greater Vancouver primary6
1985
1993
1985

5.9

1.5		  
30a
51a (1985 data4)
39a
Ontario10
7 primary
28 secondary
1 tertiary
1987
1987
1987
4.39
1.18
3.50
1.71
1.12
1.26
30
20
50		 
ndb  ndc
1.08b   1.61c
1.29b   1.85c		 
ndd
2.71d
3.10d
1.78
1.65
1.99
Quebec11
Montrealprimary + physical/chemical treatment with ferric chloride
1993		   
1.10e
0.00b  0.03c
0.66f 
nd
12
Table 6. Organic chemicals detected in municipal wastewater treatment plant effluents.
(1,1'-Biphenyl)-2-ol 1Benz(a)Anthracene 2
1,1,1-Trichloroethane 2,3Benzo(k)Fluoranthene 2
1,1-Dichloroethane 2Beta-hexachlorocyclhexane 2,4
1,1-Dichloroethene 2Bis(2-Chlorethoxy)Methane 2
1,2,4-Trichlorobenzene 2Bis(2-Chloromethyl)Ether 2
1,2-Benzenedicarboxylic acid, diethyl ether 1Bis-2-ethylhexylphthalate 4
1,2-Benzenedicarboxylic acid dibutyl ester 1Bromodichlorobenzene 2
1,2-Benzenedicarboxylic acid, bis(2-ethylhexyl) ester 1Butylbenzylphthalate 2,4
1,2-Dichlorobenzene 3Caffeine 1
1,2-Dichloroethane 2Carbon tetrachloride 2
1-Methyl-5-(3-pyridinyl)-2-pyyrolidinone 1Chlorobenzene 2
1-Octene 2Chloroform 3
2,4,5-Trichlorophenoxyacetic acid 2Chlorodibromomethane 2
2,4,6-Trichlorophenol 2Cholest-5-en-3-ol 1
2,4-D-propionic acid 4Cis-1,2-Dichloroethylene 2
2,4-Dichlorophenol 2Cyclododecane 1
2,4-Dichlorophenoxyacetic acid 2Cyclohexadecane 1
2,4-Dichlorophenoxybutyric acid 4Decanoic acid 1
2,4-Dimethylphenol 2Di-N-butylphthalate 4
2,4-Dinitrotoluene 2Di-N-octylphthalate 3
2,6-Dinitrotoluene 2Diacetin 1
2-(2-Butoxyethoxy)-ethanol 1Dichlorobenzoic acid 1
2-(Methylthio)benzothiazole 1Dichlorodifluoromethane 2
2-Butoxy ethanol 1Dichlorophenol 1
2-Butoxy, phosphate ethanol 1Dieldrin 2
2-Butyl-phosphate ethanol 1Diethyl Ether 2
2-Chlorophenol 2Dihydroxycholesterol 1
2-Ethyl-1-hexanol 1Dimethyl Phthalate 2
2-Methyl-3-hydroxy-2,4-trimethyl propanoic acid 1Dimethyl-(methylethyl)benzene 1
2-Methyl-4,6-Dinitrophenol 2Dimethylethylbenzene 1
2-Nitrophenol 2Dodecanol 1
3-(1-Methyl)-2-pyrrolodinyl) pyridine 1Endosulphan I 2
4-Nitrophenol 2Endosulphan II 2
9-Hexadecanoic acid 1Endosulphan sulphate 2
9-Octadecenoic acid 1Endrin 2
Alpha-Chlordane 2Ergost-5-en-3-ol 1
Alpha-Chlorotoluene 2Ethylbenzene 2
Alpha-hexachlorocyclhexane 2Ethyl methylbenzene 1
Alpha-terpineol 1Fluorene 2
Androsterone 1Gamma-Chlordane 2
Atrazine 1Gamma-hexachlorocyclohexane 2,4
Benzeneacetic acid 1Heptachlor 2,4
Benzeneethanol 1Heptachlorodibenzodioxin 2
Benzenemethanol 1Hexachlorobenzene  4
Benzenepropionic acid 1Hexachlorocyclopentadiene 2
Hexachloroethane 2o-Xylene 2
Hexadecanoic acid 1Octachlorodibenzodioxin 2
Hexadecanoic acid hexadecyl ester1Octachlorodibenzofuran 2
Hexadecanol 1p-Chloro-m-Cresol 2
Hexadecenoic acid 1PCB (total) 2
Hexanoic acid 1Pentachlorophenol 2
Hydroxybenzoic acid 2Phenanthrene 2
m- and p-Xylenes 2Phenol 2
m-Cresol 2Phenoxyethanol 1
Methoxychlor 2,4p,p’-DDD 2,4
Methyl(methylethyl)benzenes 1p,p’-DDE 2
Methyl-(methylethyl)cyclohexanol 1p,p’-DDT 2
Methyl-(methylethyl)cyclohexen-1-ol1Pyrene 2
Methylbenzoic acid 1Silvex 2
Methylene chloride 3Stigmast-5-en-3-ol 1
Methylphenol 1Styrene 2
Mirex 2Tetrachlorodibenzofuran 2
N,N-bis(hydroxyethyl)dodecanamide1Tetrachloroethylene 2,3
N,N-Diethyl-3-methylbenzamide 1Tetradecanoic acid 1
N,N-Diethylmethylbenzamide 1Tetradecanol 1
N-Nitroso-di-N-propylamine 2Tetramethylbenzene 1
Naphthalene 1,2Toxaphene 2
Nicotine 1Trans-1,3-Dichloropropene 2
Nitrobenzene 2Trichloroethylene 2
Nonanoic acid 1Trimethylbenzene 1
o-Cresol 2Trimethylpentanediol 1
1 Rutherford et al. 1994
2 OMOE 1988		3 Golder Associates Ltd. 1995a,b
4 Orr et al. 1992

In addition to chemicals introduced from domestic and industrial sources, chemicals in MWWE may also be derived from the treatment process.  For example, strontium, aluminum and ferric chloride are used as chemical precipitants and are consequently high in effluents receiving these types of treatment (e.g., strontium and aluminum in many Ontario effluents, iron in the Montreal effluent; Table 4).  Another example is total residual chlorine (TRC) which is a measure of the amount of chlorine remaining in the final effluent after chlorination treatment for disinfection (Table 7). 

Concentrations of chemicals in MWWE can differ considerably, despite similarities in treatment (Tables 3, 4 and 5)  While the degree of pollutant removal often increases from primary to secondary to tertiary treatment (particularly for conventional parameters such as BOD and TSS), it is difficult to characterize the chemical content of MWWE on the basis of treatment type as concentrations depend upon many factors, including domesticvs. industrial sources, types of industries, surface area served, and  volume treated.  In addition to variability in effluent characteristics among MWTPs, there may be temporal (e.g., daily, weekly and seasonal) variability in effluent within a plant. At three Ontario MWTPs, effluent variability was associated with daily rhythms in raw sewage characteristics: organic substances, particularly phenolics, exhibited the greatest degree of variability in effluents; metals were the next most variable and conventional parameters the least variable (OMOE 1991).  Variability may also be related to seasonal use of certain treatment processes (e.g., chlorination) or to different operating conditions between winter and summer (e.g., Table 7 for wintervs. summer TRC concentrations for eight MWTPs in Ontario). 

Table 7.  Concentrations (µg/L) of total residual chlorine (TRC) and annual discharge (x 106m3) for selected municipal wastewater treatment plants that use chlorine for disinfection. (Blanks indicate data are not available.)
Location and MWTP typeDateTRCEffluent Discharge
1 Rutherford et al. 1994, except discharge from Environment Canada 1986
2Orr et al. 1992 - 1989 TRC data, 1988 discharge
3Saskatchewan Environment and Public Safety 1989
Nova Scotia1
2 secondary
Eastern Passage primary
Lakeside tertiary
fall 1991
fall 1991
fall 1991
5-850
250
120

4.4 (1986)
0.5 (1986)
Ontario2
Bracebridge secondary
Huntsville secondary
Walkerton secondary
Stratford secondary
Toronto North secondary
Toronto Highland Creek secondary
Midland secondary
Wallaceburg secondary
1989
1989
1989
1989
1989
1989
1989
1989		summer:
70
530
40
6
310
5
260
81		winter:
9
950
nd
nd
190
46
nd
190
0.9
1.4
1.7
8.1
12.7
55.3
4.1
2.2
Saskatchewan3
Saskatoon primary
summer 1987
1892
32

Loadings

Comparison of effluent load (effluent concentration x effluent discharge) to the load of the receiving water provides an estimate of the long-term potential for an effluent to affect the receiving water, especially for persistent and bioaccumulative substances which can cause cumulative impacts. For conventional parameters, a 1991 study of 387 Ontario MWTPs found that the highest load was for BOD (41,000 tonnes/yr) (OMOE 1993). For metals, strontium (1.3 tonnes/d), aluminum (0.8 tonnes/d), and zinc (0.2 tonne/d) were the greatest contributors to loadings among all treatment types in a study of 37 Ontario MWTPs (OMOE 1988). Ten other metals had smaller loads (less than 0.5 tonne/d) but are more toxic (e.g., cadmium, copper, chromium, lead, nickel). Cadmium loadings from 37 Ontario MWTPs totalled less than 10 kg/d and mercury loadings totaled less than 150 g/d. Three Greater Vancouver MWTPs (Environment Canada 1992), two Edmonton MWTPs (Golder Associates Ltd. 1995a,b) and a MWTP in the Yukon (Enns and Soprovich 1995) showed a similar pattern in metal loadings with high aluminum (up to 233 kg/d) and zinc (up to 56 kg/d) and low cadmium and mercury loadings.

Although numerous organic pollutants have been detected in MWTP effluent (OMOE 1988; Rutherford et al. 1994; Golder Associates Ltd. 1995a,b), total loadings of organic chemicals are generally lower than for metals.  Total loadings averaged 132 kg/d for base/neutral and acid extractable organics, 107 kg/d for volatile organic compounds, 1.4 kg/d for pesticides, 0.082 kg/d for PCBs and 0.004 kg/day for dioxins and furans for 37 MWTP in Ontario (OMOE 1988). Theaverage load of all 21 PAHs in Montreal MWTP effluent was 1.2 kg/d, while the load for the sum of 13 PCBs averaged 2.5 g/d (Pham and Proulx 1996).  In the case of PCBs, this represented only 1% of the PCB load measured in the St. Lawrence River at Quebec City.  Although the loadings of PCBs and other organic pollutants are relatively small, they are a cause for concern because they are persistent and have the potential to bioaccumulate and biomagnify in the food chain. 

Stormwater, CSOs and MWTP bypasses

Characterization

Stormwater and CSOs have not been routinely monitored because the diffuse and intermittent nature of these sources makes large-scale monitoring programs prohibitively expensive. However, some information is available for Ontario because of work done in support of the Canada/US and Canada/Ontario Agreements respecting Great Lakes Water Quality and for British Columbia because of the Fraser River Estuary Management Plan. Stormwater and CSO discharges are characterized by high flows during or shortly after periods of wet weatheror during periods of snowmelt, high quantities of suspended solids, and significant quantities of nutrients, toxic substances (e.g., heavy metals, chlorides, hydrocarbons) related to traffic and road maintenance, and microorganisms.

The main pollutants of concern in stormwater are suspended solids, nutrients (particularly P), heavy metals, hydrocarbons, and fecal bacteria.  A recent review by Makepeace et al. (1995) of 140 studies mostly from the USA, several European countries and Canada identified the 28 most important contaminants in stormwater that have the potential to affect aquatic life and human health, mostly through contamination of drinking water supplies (total solids, TSS, Al, Be, Cd, Cl, Cr, Cu, Fe, Pb, Mn, Hg, N, Ag, Zn, DO, PCBs, bis(2-ethylhexyl) phthalate,d-BHC, chlordane, heptachlor, heptachlor epoxide, total PAHs, benzo(a)pyrene, tetrachloroethylene, fecal coliforms, fecal streptococci, enterococci). Concentrations of water quality constituents reported in Ontario, British Columbia and Calgary, Alberta stormwater are listed in Table 8.

The chemical composition of CSOs has been studied much less than for stormwater, in part because CSOs are more difficult to monitor than stormwater.  During the early phase of a runoff event, when sewage sludge may be scoured from the sewer bottom by high flows.

Table 8. Typical concentrations of various constituents found in stormwater and annual stormwater discharge.
ParameterOntarioCalgary, Alberta
(meand)		Lower Mainland,
British Columbia(meane)
 Stormwater
(mean or range)		CSOa(meanUrban RunoffUrban RunoffCSO

MPN = Most Probable Number; numbers in brackets indicate sample size; NA = Not Available

aWaller and Novak 1981 d Hamilton and North 1986
bMarsalek and Ng 1989                      eEnvironment Canada 1992 from Greater Vancouver Regional District 1988a
cMarsalek et al. 1992

      
total suspended solids        (mg/L)   170a19016914859
biochemical oxygen demand   (mg/L)                                   14a41171460
chloride (mg/L)                    230-340b 7  
ammonia (mg/L)                   0.30-0.75b 0.740.153.8
total phosphorus (mg/L)    0.35a1.41.520.11.9
total nitrogen (mg/L)                          3.5a836.83  
cadmium (µg/L)1.5-6.8b  4.83.2
copper  (µg/L)                      43.4-47.2b 334077
iron (µg/L)                                           5710-6960b 22300  
lead (µg/L)                                           97-233b 4585589
mercury  (µg/L)29-104b    
nickel (µg/L)                                        28-39b 9  
zinc (µg/L)                                           234-307b 1709881
oil and grease (mg/L)                          2.14-5.37b    
PAHs (µg/L)                        2.1-9.1b    
benzo(a)pyrene (µg/L)       0.3b             
fecal coliform  (MPN/100 mL)12000 - 51000c1000000 2043390000
E.coli (MPN/100 mL)800 - 61000c    

CSO composition resembles or even exceeds pollutant concentrations in raw sanitary sewage. After this first flush, pollutant concentrations in CSOs subside. The main parameters of concern are suspended solids, BOD, nutrients (N and P), fecal bacteria and possibly some other chemicals originating from local municipal and industrial sources. Concentrations of water quality constituents reported in Ontario and British Columbia CSOs are listed in Table 8.  In comparison to stormwater, constituent concentrations in CSOs are similar for TSS (Marsalek et al. 1993), but greater for BOD (Marsalek et al.1993), total N and total P (Marsalek et al. 1993), and generally smaller for unconventional pollutants, including heavy metals, PAHs and some other trace organic contaminants released from industrial sources (Marsalek and Ng 1989).

Loadings

Loadings from stormwater and CSOs depend on the drainage area, land-use activities in that area and, in the case of CSOs, the nature of the sewage generated in the area.  One of the more extensive summaries of stormwater loadings was published for the Canadian Great Lakes basin (Marsalek and Schroeter 1988).  Here, annual loading was greatest for TSS (108 kg/y), followed by oil and grease (105 - 106 kg/y), inorganics (mostly heavy metals, 102 - 105kg/y), PAHs (100 - 102 kg/y), and some trace organic contaminants (10-1 - 101 kg/y). 

For CSOs, conventional pollutant loadings in the Canadian Great Lakes basin were estimated to be 17,400 tonnes/y for TSS, 3,700 tonnes/y for BOD, 760 tonnes/y for total N and 130 tonnes/y for total P (Waller and Novak 1981).  These estimates are consistent with more recent studies of CSOs in Sarnia and Windsor (Marsalek and Ng 1989) which gave the combined annual CSO discharge from both municipalities as 6.2 x 106 m3/y and corresponding annual loads of 1200 tonnes/y TSS, 51 tonnes/y total N, and 8.7 tonnes/y total P. These loads represent about 7% of the total estimated loads of TSS,  total N and total P to the Great Lakes basin, which is consistent with the fact that Sarnia and Windsor represent about 9% of the basin population assumed by Waller and Novak (1981) in their calculations. 

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