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The contribution of domestic sources to levels of key organic and inorganic pollutants in sewage: The case of Melbourne, Australia
~
Pergamon
. War. Sci. Tech. Vol. 34, No. 3-4, pp. 63-70,1996. Copynght © 1996 fA WQ. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved. 0273-1223/96 $15'00 + 0'00
PH: S0273-1223(96)OO557-4
THE CONTRIBUTION OF DOMESTIC SOURCES TO LEVELS OF KEY ORGANIC AND INORGANIC POLLUTANTS IN SEWAGE: THE CASE OF MELBOURNE, AUSTRALIA Philip J. Wilkie*, George Hatzimihalis**, Paul Koutoufides and Michael A. Connor* * Department of Chemical Engineering, University ofMelbourne, Parkville 3052, Australia ** Environautics, 222 Latrobe Street, Melbourne, 3000, Australia Melbourne Water, 625 Little Collins Street, Melbourne 3000, Australia
ABSTRACT For the purposes of regulating discharges by industry to Melbourne's sewer network, information was needed on the concentrations of key pollutants in sewage from purely domestic sources. Sampling sites around Melbourne were identified where sewage free of trade waste contributions could be obtained. The sites chosen spanned a range of geographical areas and residential area types. Samples from these sites were analysed for a wide range of components. Similar analyses were conducted on samples from domestic water supplies. The consolidated results of these analyses are presented. The results show that the water supply contributes substantially to levels of many pollutants in domestic sewage. Comparisons with data for sewage plant influents show higher than expected inputs, from domestic sources, of many pollutants often regarded as having a mainly industrial origin. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd.
KEYWORDS Composition; domestic; priority pollutants; sewage; wastewater. INTRODUCTION Melbourne is a city of three and a quarter million people located at the northern end of Port Phillip Bay. This Bay is a sizeable and almost landlocked body of water that connects with Bass Strait and the Southern Ocean through a relatively narrow channel; any pollutants discharged into the Bay therefore remain there for a long time before dispersing into the ocean proper. Wastewaters from the greater Melbourne area go mainly to one or other of two major treatment plants. The larger of these, the Western Treatment Plant (formerly known as Werribee Farm), is situated on 10850 ha of land on the western side of Port Phillip Bay. Presently it handles around 450 MIld of wastewaters drawn from the western and northern parts of Melbourne; since this region contains many of Melbourne's industries, the wastewaters reaching this plant contain a sizeable industrial contribution of around 17% by 63
64
P. J. WILKIE et al.
volume and almost 50% by load (BOD) (Sharples, 1992). These wastewaters are treated by a combination of land filtration, grass filtration and lagoon systems; the treated effluent discharges through four separate outlets into Port Phillip Bay. The second major plant, fonnerly called the South-Eastern Purification Plant and now known as the Eastern Treatment Plant, is located to the south-east of Melbourne. It is a conventional activated sludge plant handling around 380 MI of wastewater daily. Its catchment area includes fewer industrial areas but it nevertheless still receives 6% of its flow and around 20% of its BOD load from industrial sources (Sharples, 1992). The treated effluent from this plant does not enter Port Phillip Bay but is pumped to an outfall on Bass Strait and discharged into the ocean. Maximum permissible levels of environmentally significant components in the effluents from the two treatment plants are set by the Environment Protection Authority of Victoria (EPAV). These levels are reviewed regularly and new compounds are periodically added to the list of regulated substances. In recent years the trend has been for the limitations imposed by the EPAV to become progressively more restrictive; this trend is expected to continue. The implications of this trend were recognised some time ago by the organisation, presently known as Melbourne Water, that is responsible for the collection and treatment of Melbourne's sewage. For a number of years Melbourne Water has been working to develop strategies that will enable the levels of specified pollutants in treatment plant effluents and sludges to be kept within prescribed limits. An important part of these strategies has been regulation of the quantity and characteristics of wastes discharged by industries into the sewer network. This regulation is effected through Trade Waste Licences in which the permissible concentrations of specified pollutants in an industry's discharges are laid down. In setting these permissible concentrations the EPAV-imposed limits on treatment plant effluents are an important consideration. However there are also a number of other factors that have to be taken into account. These include (Sharples, 1992): (a)
the quality of sludges from treatment plants must confonn to EPAV-imposed standards.
(b)
the discharges should not be inhibitory or toxic to the treatment processes, should have no detrimental effect on the fabric or operation of the collection and treatment system, and should not threaten the health or safety of personnel.
(c)
it is desirable to increase opportunities for beneficial reuse of plant effluents and sludges.
(d)
it is potentially beneficial to encourage waste minimisation and recycling by industry.
From the perspective of a body like Melbourne Water, the more stringent the limits placed on industrial discharges, the easier it is to meet the above requirements. However there is a need to balance this against industry'S capacity to achieve the set limits without incurring disproportionately high costs. There is also a need for the limits set to not be unreasonable. For this reason it is Melbourne Water policy not to ask industries to achieve pollutant concentrations in their discharges that are lower than the relevant pollutant con~entr~tions in sewage of purely domestic origin. Imposing a limit of any greater stringency would ~chieve httle a~ ~ar as compliance with EPAV standards is concerned and could legitimately be regarded by mdustry as pumtive and unfair. The diffic~lty in implementing policies based on pollutant concentrations in domestic sewage is that these concentratIOns need to be known if compliance with limits set down in Trade Waste Licences is to be ~nforcea~le. And whilst much is known about the composition of sewages entering treatment plants, there is ht~e av.al1able, at least in Australia, on the quantities and compositions of wastewaters from purely resIdentIal sources. At the time the project described here was conceived, some work had been undertaken in Sydney (Copland, 1990) and Adelaide (Lock et ai., 1993; Lock, 1994) and a limited study undertaken at the
Contribution of domestic sources
65
Brushy Creek sewage treatment plant in the outer north-eastern suburbs of Melbourne (McCormick, 1991). No research covering a range of sites across Melbourne was then available. To fill this gap a project was initiated by Melbourne Water to ascertain the concentrations of selected organic and inorganic pollutants in sewage from a range of residential areas within the greater Melbourne area. The project was undertaken jointly by Melbourne Water and the Chemical Engineering Department at the University of Melbourne; the project's findings are reported in the following sections. RESEARCH PROGRAM Parameters to be measured Budgetary constraints precluded analysing sewage samples for all the chemicals regarded by the EPAV as priority pollutants. In selecting which chemicals should be placed on the list for analysis and which should not, factors favouring inclusion were as follows. (a)
limits on concentrations of the chemical concerned were already in place in Trade Waste Licences.
(b)
The chemical concerned had already been identified by Melbourne Water or the EPAV as a local problem, or potential local problem.
(c)
Significant levels of the chemical concerned had been detected in sewage samples at the Brushy Creek plant (McCormick, 1991) or in other relevant Australian studies.
(d)
Costs for analysis were not prohibitive.
The list of parameters finally selected for analysis was as follows. (a)
Basic wastewater characteristics: biochemical oxygen demand (BOD); chemical oxygen demand (COD); total organic carbon (TOC); oil and grease; total suspended solids (TSS); total dissolved solids (TDS); ammonia nitrogen; total nitrogen (TN); total phosphorus (TP); total oxidised sulfur; sulfate; sulfite; sulfide; total phenols; colour.
(b)
Elements (predominantly metals): aluminium (AI); antimony (Sb); arsenic (As); barium (Ba); beryllium (Be); boron (B); cadmium (Cd); calcium (Ca); chromium (Cr); cobalt (Co); copper (Cu); iron (Fe); lead (Pb); magnesium (Mg); manganese (Mn); mercury (Hg); molybdenum (Mo); nickel (Ni); potassium (K); selenium (Se); silver (Ag); sodium (Na); strontium (Sr); thallium (TI); tin (Sn); titanium (Ti); vanadium (V); zinc (Zn).
(c)
Phthalate esters: bis (2-ethylhexyl) phthalate; butylbenzyl phthalate; dibutyl phthalate; diethyl phthalate; dimethyl phthalate; dioctyl phthalate.
(d)
Chlorinated hydrocarbons; chlorobenzene; 1,2 dichlorobenzene; 1,3 dichlorobenzene; 1,4 dichlorobenzene; 1,2,3 trichlorobenzene, 1,2,4 trichlorobenzene; hexachlorobenzene; chloroform.
(e)
Polynuclear aromatic hydrocarbons (PAB's); acenaphthene; acenaphthylene; anthracene; benzo (a) anthracene; benzo (g,h,i) perylene; benzo (b) fluoranthene; benzo (k) fluoranthene; chrysene; dibenzo (a,h) anthracene; fluoranthene; fluorene; indeno (l,2,3-c,d) pyrene; naphthalene; phenanthrene; pyrene.
(f)
Amines: nitrosodimethylarnine; nitrosodiphenylamine; nitrosodipropylamine; 1,2 diphenylhydrazine.
(g)
Ethers: bis (2-chloroethoxy) methane; bis (2-chloroethyl) ether; bis (2-chloroisopropyl) ether; 3 bromophenyl phenyl ether; 4-chlorophenyl phenyl ether.
JWST 34:3/4-0
66
P. J. WILKIE el al.
Including basIc wastewater charactenstlcs on the list of measured parameters fulfilled two. purposes. It provided a means of checking that any sewage sample having unexpectedly high concentratiOns o~ some particular chemical was othenvise normal. It also made it possible to determine whether concentratiOns of any priority pollutants might correlate with levels of more commonly measured parameters. As the project progressed, the above list was amended several times. The amines wer~ deleted almost at once, as laboratory advice was that their rates of decomposition were too rapid for meanmgful results to be obtained from samples not analysed immediately. Later, once 33 samples had .been an~lysed, the ethers, PAH's and chlorinated aromatic hydrocarbons (CAH's) were removed from the hst. By thIS stage no ethers, no PAH's and just a trace of one CAH (I, 3 dichlorobenzene) had been detected in samples of purely domestic origin. For budgetary and other reasons, the BOD of the last sample and the colour of the last three samples were not determined. Location of sampling sites For Melbourne Water's purposes it was important that the mean concentrations of pollutants obtained be as representative as possible of conditions across the city as a whole. This meant that not only should the set of sampling sites chosen be widely distributed geographically but also that their catchments should encompass as diverse a collection of residential area types as possible. Aspects felt to be of relevance in characterising residential areas included a number of lifestyle-related factors: socio-economic status; cultural identity (in multicultural Melbourne many suburbs contain concentrations of residents from a single ethnic group); the age structure of the residents; and the residential density (lifestyles in low residential density outer suburbs are very different from those in high residential density inner-city apartment blocks). The age of a suburb was also felt to be important as it largely determines the types of materials used in sewer pipes and in household water heating and plumbing services. Further considerations included the desirability of avoiding low-lying areas where groundwater infiltration into sewers could distort measurements, and the need for easy and safe access to sampling points. Whilst the above aspects were all of importance, a majority of site catchment areas needed to be as free as possible of wastewater sources of other than a domestic nature. For each potentially suitable site, therefore, the exact catchment boundaries were determined using detailed computerised sewer maps; any licensed Trade Waste dischargers within the catchment were identified and their location marked on a street map of the area. The location marker was a coloured sticker bearing a number: the colour indicated whether the load (volume, strength or both) was high, medium or low; the number represented the magnitude of the risk posed by the discharge to Melbourne Water's operations (on a scale of I to 5, with I being potentially the most risky and 5 the safest). From such maps the number and type of non-domestic wastewater discharges could be seen at a glance and the relative suitability of different prospective sampling sites readily determined. The value of this exercise became clear when no inner-city site free of trade waste inputs could be found and a compromise site with as limited a non-domestic contribution as possible had to be chosen. Despite the emphasis placed on domestic sewage, there were obvious advantages in also sampling from sites where the sewage had a trade waste component. Data from such sites would be obtained at similar times and using the same sampling and analytical techniques as those used for the purely domestic sewage. For this reason they would be more relevant for comparative purposes than other published or plant data. Budgetary constraints, practical considerations such as distances between sites, and the need to satisfy the criteria discussed above led to the choice of 8 sampling sites. One was the Keilor wastewater treatment plant, a small plant in the western suburbs with a comparatively low trade waste component. Four sites, spanning the western, northern and eastern suburbs, had no licensed Trade Waste Dischargers in their catchments. One older suburban site, closer to the centre of Melbourne, received trade waste from an auto electrical servic~s company, a petrol station and a medical laboratory. The seventh site, originally thought to be a well est.abhshed suburban site receiving domestic sewage only, later proved to be receiving a moderate trade waste mput through a sewer connection shown on maps as closed off. The eighth site was on a main
67
Contribution of domestic sources
sewer receiving a substantial input from industry. Characteristics of the catchment areas for these sites are shown in Table 1. Table 1. Characteristics of sampling sites Site number 1 2 3 4 5 6 7 8
Suburb Box Hill North Warrandyte Croydon Hills Mooroolbark Camberwell Aberfeldie Keilor (Treatment Plant) Keilor
Trade Waste Input Moderate None None None Slight Substantial Moderate None
Area (ha) 138 225 155 301 343 2360 2168 263
Number of Tenements
Number of Residents
1500 880 540 1300 3600 18530 5550 675
3925 2880 1865 4200 9250 56740 20180 2487
Sampling program A total of seven separate sampling runs was undertaken. NATA - approved sampling protocols and analytical procedures were used in obtaining and analysing all the samples. Run 1 (25/3/94): This comprised a single sample taken from a site free of trade waste inputs in the southern suburb of Heatherton (details not shown in Table 1). This sample was used to evaluate the capabilities of the laboratory (Australian Laboratory Services Pty Ltd) which carried out all the analyses reported here. Run 2 (2/6/94): Samples were taken sequentially from sites 1,2,3,4,5,7,8,6 over the period 7.15 am to 2.38 pm. To test the consistency of sewage composition at a given site, two samples were taken, one after the other, at site 8. To these samples was added a sample drawn later in the afternoon from the inlet to the Western Treatment Plant. A composite sample of water drawn from garden taps adjacent to sites 1 to 6 and 8 was also submitted for analysis. The purpose of this was to ascertain how much of each pollutant in the sewage was present in the original domestic water supply and how much could be attributed to household activities; it is well established that the water supply is an important source of many sewage components (Klein et at., 1974; Lock et aI., 1993; Lock, 1994). Run 3 (17/8/94): This was similar to Run 2 except that: no sample was taken at site 6 (because of rain); the major treatment plant sample was from the Eastern Treatment Plant; and duplicates of the sample taken at site 7 were submitted to test the reproducibility of the analytical results. Run 4 (24/8/94): This was similar to Run 2 except that: the order in which sites were visited (7,8,6,5,4,3,2,1) was almost the reverse of that in run 2 (to compensate for time-related concentration changes); the major treatment plant sample was from the Eastern Treatment Plant; the sample for which duplicates were submitted was that from site 4. Run 5 (23/11/94): This run, conducted at site 3, was designed to determine the influence of the time of day on pollutant concentrations. The 23/11/94 was a Wednesday and therefore a typical working day; samples were taken at approximately the following times: 7,8,9 and 10 am, 12 noon, 2,3,4,5,6,7,8 and 10 pm. Samples were spaced most closely at times of greatest domestic activity. A composite water sample was taken and the sample at 6 pm duplicated. Run 6 (24/11/94-30/11/94): This run, also conducted at site 3, was designed to investigate the influence of the day of the week on pollutant concentrations. Samples were taken at 8 am and lOam on each day. These times were chosen as they represented the peak sewage flow periods for weekdays (8 am) and weekends (10 am).
P. J. WILKIE et al.
68
Run 7 (18/12/94): This run, also conducted at site 3, was designed to establish the nature of pollutant concentrations on a Sunday. as opposed to a weekday. In all other respects it was similar to Run 5. RESULTS The major purpose of the project described here was to determine representative values of the concentrations of key pollutants in sewage from purely domestic sources. To obtain the desired values the data from the 60 samples from sites 1,2,3,4,5,8 and the Heatherton site were combined to yield the results shown in Tables 2 and 3. To obtain truly representative results it was felt necessary to disregard unusually low or high values; if this had not been done there was a risk that an analytical error or an illicit discharge might exercise an undue influence on the results. The procedure followed was, for each pollutant, to determine the mean and standard deviation of all relevant values from the above-mentioned sites. Any points lying more than three standard deviations from the mean were then eliminated and the statistical parameters recalculated. The mean, minimum, maximum and standard deviation values given in Tables 2 and 3 refer to this latter, truncated set of values. The excluded values appear in the "outliers" column. Also included in the Tables are the means of the concentrations of each pollutant in the composite water samples. No entries appear in the Tables for a number of elements on the original list; of these beryllium, selenium and vanadium were not detected in any samples while antimony, mercury, molybdenum and thallium were found in very few samples and almost invariably only at levels close to the limit of detection. Table 2. Concentrations of selected pollutants in sewage ans the domestic water supply (basic wastewater characteristics) Concentration in domestic sewage (mg/L)
Component Mean Ammonia BOD COD TOC Oil & Grease TSS TDS TN TP Sulfate
36.2 203 505 173 22 266 375 57 7.3 46.4
Minimum
Maximum
12 38 265 89 1 132 124 24 2 27
73 432 820 262 47 492 596 114 16 69
Standard deviation
Outliers
14.8 88 110 43 10 85 94 22 3.7 10.9
120,128 950,950,870 388 61,69 138,155,185
Mean concentration in domestic water supply (mg/L)
Mean concentration in treatment plant influents (mg/L)
<1 3 14 15 1.5 4.9 92 3.7 <1
39 190 603 271 59 288 550 61 4.7
DISCUSSION AND CONCLUSIONS Sewage composition Noteworthy was the marked variability of measured values, reflecting the diversity of inputs to the sewer networ~, . even from households. This variability was emphasised by the significant differences in compos~tI~n. between the two samples .taken 15 minutes apart at site 8 on 2/6/94. Reassuring was the fact that vanablhty between results for duphcate samples was small (some variation was expected because of the heterogeneous nature of the TSS fraction). Comparison of t.h~ above ~esults with those from other cities served to show that local influences affect sewa~e compOSItIOn ~onslderably; levels of individual components were often of similar orders of magmtude but no consIstent trends were found.
69
Contribution of domestic sources
Runs 5,6 and 7 were undertaken at a single site to investigate whether obvious time-related trends were apparent. .Over the course of the week, the only obvious feature was a Sunday morning peak in concentratIOns and mass flows of components derived from basic human functions and activities. A more extensive sampling program is clearly needed if other, more subtle trends, are to be identified. Table 3. Concentrations of selected pollutants in sewage and the domestic water supply (specific pollutants) Concentration in domestic sewage
Component Mean
(~g/L)
Minimum
Maximum
Standard deviation
Outliers
Elements Aluminium Arsenic Barium Boron Cadmium Calcium Chromium Cobalt Copper Iron Lead Magnesium Manganese Nickel Potassium Silver Sodium Strontium Tin Titanium Zinc
745 2.3* 38 263 0.45* 9260 3.2* 1.28* 62 728 13 4925 48 4.2* 16780 0.94* 87280 50.0 4.69 <10 169
60 <1 2 10 <0.2 5000 <1 <1 35 <50 4 2600 17 <1 5000 <1 9900 30 <1 4 52
1560 4 90 860 1 15900 8 3 97 1770 31 9200 82 10 37500 3 163000 75 11 11 348
352 1.0* 17.7 206 0.21 * 2450 1.67* 0.90* 14.9 373* 6.8 1655 12.8 1.97* 7285 0.75* 28520 9.3 2.59* N/A 75.8
2060,2150,3250 6,24 115,117 1130 1.2,1.8,1.8 18900,21600 11,17,18,54,74,124 6,6,8,23 113,117,126,227
Phthalates Bis (2ethylhexyl) Butylbenzyl Oibutyl Oiethyl Dimethyl Oioctyl Chloroform
25.5 2.0* 3.2* 20 N/A N/A 7.2
5 <1 <1 5 <1 <1 1.3
68 5.7 8 49 3 43 13
15.33 1.64* 2* 10 N/A N/A 2.6
86,91,91,1500 7.6,12,15 43,61
633 17300,18200 114 11,32,137 5,6,6,8,19,42,56 84,105,117 14,17 20,49 468,733,766,1050 1050
N/A N/A
Mean concentration in domestic water supply
Mean concentration in treatment plant influents
(~g/L)
(~g/L)
131 <1 20 108 NO 7380 <1 NO 33 267 8.6 1660 7.1 2.1 580 NO 4250 24 ND <10 49
933 2.6 167 263 <1 17200 31 1.75* 77 1230 68 9900 218 14.3 22450 2.6* 137000 94.5 6.7 15.4 346
<20 NO NO <1 ND ND 19.4
66.7 <10 <10 21 <10 <10 3.7
*Mean and standard deviation calculated assuming that for samples reporting concentrations of less than a given detection limit the actual concentration was half that detection limit. NO = not detected; N/A = not applicable. Domestic water supply contributions The contributions of the water supply to pollutant concentrations in sewage were classified into 3 groups: dominant(>60%), substantial (25-60%) and small «25%). An interesting member of the first category is chloroform which has a substantially higher concentration in the water supply than in domestic sewage, and
P. J. WILKIE et al.
70
an even lower one in the influents to the major treatment plants. Its presence in the tap water samples is attributed to chlorination of the domestic water supply, its subsequent disappearance to evaporation. The remaining members of the first category are calcium and lead; the former's presence is attributable to upstream water treatment processes but the latter's is unexplained. In the middle group are barium, boron, copper, iron, magnesium, nickel, strontium and zinc. Many of these are common constituents of natural waters but several other possible sources suggest themselves. Magnesium and strontium are often associated with calcium and could be present as impurities in lime used at t;eatment works. In support of this, a peak in calcium concentrations at site 3 on 18/12/94 was associated with marked peaks in magnesium and strontium concentrations. In addition, copper, iron and zinc are widely used in water reticulation pipes and plumbing services and fittings; the significance of the contribution of household plumbing to concentrations of such metals in domestic sewage is well illustrated by Lock et al. (1993) and Lock (1994). For the third group it was noteworthy by how much the not insignificant amounts of potassium and sodium in the water supply were exceeded by the amounts derived from households. The fact that cadmium, silver and tin were not detected in the water supply serves to emphasise the importance of household practices and consumer products as contributors to levels of these metals in sewage. Treatment plant data Comparison of data from domestic sources with those from the 6 samples of wastewater treatment plant influents was enlightening. Whilst concentrations of many components were at or near their highest levels in the treatment plant samples, it was clear that domestic sources were a major contributor to final levels of many pollutants analysed for. Particularly surprising was the high domestic sewage TDS level, previously thought by Melbourne Water to have been much lower. These results suggest that if further reductions in levels of a number of priority pollutants in Melbourne's sewage are required, a much harder look will need to be taken at household activities and consumer products and how to make them more "sewer-friendly". ACKNOWLEDGMENTS The contribution made in the early stages of this project by the late Stewart Morgan is gratefully acknowledged, as is the help provided by Alan Bennett, formerly of Melbourne Water. Also acknowledged is the valuable assistance provided by Keith Evans in connection with sample analyses. REFERENCES Copland, B. (1990). Domestic Catchment Sampling Programme Report. Water Board, Sydney. Klein, L. A., Lang, M., Nash, N. and Kirshner, S. L. (1974). Sources of metals in New York City wastewater. 1. WPCF 46, 2653• 2662. Lock, W. H., Smith, K. E. and Thomas, P. M. (1993). Heavy metals and organics in domestic sewage. Proc. Australian Water and Wastewater Assoc. 15th Federal Convention 3, 753-758. Lock, W. H. (1994). Heavy metals and organics in domestic wastewater. Research Report No. 79, Urban Water Research Association of Australia, Melbourne. McCormick, M. J. (1991). Background toxicant levels in domestic sewage. Melbourne Water Report. Sharples, 1. (199?). Factors affecting the setting of limits for the discharge of trade-waste to sewer. M. App. Sc. project report, UnIversIty of Melbourne.
Pergamon
. War. Sci. Tech. Vol. 34, No. 3-4, pp. 63-70,1996. Copynght © 1996 fA WQ. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved. 0273-1223/96 $15'00 + 0'00
PH: S0273-1223(96)OO557-4
THE CONTRIBUTION OF DOMESTIC SOURCES TO LEVELS OF KEY ORGANIC AND INORGANIC POLLUTANTS IN SEWAGE: THE CASE OF MELBOURNE, AUSTRALIA Philip J. Wilkie*, George Hatzimihalis**, Paul Koutoufides and Michael A. Connor* * Department of Chemical Engineering, University ofMelbourne, Parkville 3052, Australia ** Environautics, 222 Latrobe Street, Melbourne, 3000, Australia Melbourne Water, 625 Little Collins Street, Melbourne 3000, Australia
ABSTRACT For the purposes of regulating discharges by industry to Melbourne's sewer network, information was needed on the concentrations of key pollutants in sewage from purely domestic sources. Sampling sites around Melbourne were identified where sewage free of trade waste contributions could be obtained. The sites chosen spanned a range of geographical areas and residential area types. Samples from these sites were analysed for a wide range of components. Similar analyses were conducted on samples from domestic water supplies. The consolidated results of these analyses are presented. The results show that the water supply contributes substantially to levels of many pollutants in domestic sewage. Comparisons with data for sewage plant influents show higher than expected inputs, from domestic sources, of many pollutants often regarded as having a mainly industrial origin. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd.
KEYWORDS Composition; domestic; priority pollutants; sewage; wastewater. INTRODUCTION Melbourne is a city of three and a quarter million people located at the northern end of Port Phillip Bay. This Bay is a sizeable and almost landlocked body of water that connects with Bass Strait and the Southern Ocean through a relatively narrow channel; any pollutants discharged into the Bay therefore remain there for a long time before dispersing into the ocean proper. Wastewaters from the greater Melbourne area go mainly to one or other of two major treatment plants. The larger of these, the Western Treatment Plant (formerly known as Werribee Farm), is situated on 10850 ha of land on the western side of Port Phillip Bay. Presently it handles around 450 MIld of wastewaters drawn from the western and northern parts of Melbourne; since this region contains many of Melbourne's industries, the wastewaters reaching this plant contain a sizeable industrial contribution of around 17% by 63
64
P. J. WILKIE et al.
volume and almost 50% by load (BOD) (Sharples, 1992). These wastewaters are treated by a combination of land filtration, grass filtration and lagoon systems; the treated effluent discharges through four separate outlets into Port Phillip Bay. The second major plant, fonnerly called the South-Eastern Purification Plant and now known as the Eastern Treatment Plant, is located to the south-east of Melbourne. It is a conventional activated sludge plant handling around 380 MI of wastewater daily. Its catchment area includes fewer industrial areas but it nevertheless still receives 6% of its flow and around 20% of its BOD load from industrial sources (Sharples, 1992). The treated effluent from this plant does not enter Port Phillip Bay but is pumped to an outfall on Bass Strait and discharged into the ocean. Maximum permissible levels of environmentally significant components in the effluents from the two treatment plants are set by the Environment Protection Authority of Victoria (EPAV). These levels are reviewed regularly and new compounds are periodically added to the list of regulated substances. In recent years the trend has been for the limitations imposed by the EPAV to become progressively more restrictive; this trend is expected to continue. The implications of this trend were recognised some time ago by the organisation, presently known as Melbourne Water, that is responsible for the collection and treatment of Melbourne's sewage. For a number of years Melbourne Water has been working to develop strategies that will enable the levels of specified pollutants in treatment plant effluents and sludges to be kept within prescribed limits. An important part of these strategies has been regulation of the quantity and characteristics of wastes discharged by industries into the sewer network. This regulation is effected through Trade Waste Licences in which the permissible concentrations of specified pollutants in an industry's discharges are laid down. In setting these permissible concentrations the EPAV-imposed limits on treatment plant effluents are an important consideration. However there are also a number of other factors that have to be taken into account. These include (Sharples, 1992): (a)
the quality of sludges from treatment plants must confonn to EPAV-imposed standards.
(b)
the discharges should not be inhibitory or toxic to the treatment processes, should have no detrimental effect on the fabric or operation of the collection and treatment system, and should not threaten the health or safety of personnel.
(c)
it is desirable to increase opportunities for beneficial reuse of plant effluents and sludges.
(d)
it is potentially beneficial to encourage waste minimisation and recycling by industry.
From the perspective of a body like Melbourne Water, the more stringent the limits placed on industrial discharges, the easier it is to meet the above requirements. However there is a need to balance this against industry'S capacity to achieve the set limits without incurring disproportionately high costs. There is also a need for the limits set to not be unreasonable. For this reason it is Melbourne Water policy not to ask industries to achieve pollutant concentrations in their discharges that are lower than the relevant pollutant con~entr~tions in sewage of purely domestic origin. Imposing a limit of any greater stringency would ~chieve httle a~ ~ar as compliance with EPAV standards is concerned and could legitimately be regarded by mdustry as pumtive and unfair. The diffic~lty in implementing policies based on pollutant concentrations in domestic sewage is that these concentratIOns need to be known if compliance with limits set down in Trade Waste Licences is to be ~nforcea~le. And whilst much is known about the composition of sewages entering treatment plants, there is ht~e av.al1able, at least in Australia, on the quantities and compositions of wastewaters from purely resIdentIal sources. At the time the project described here was conceived, some work had been undertaken in Sydney (Copland, 1990) and Adelaide (Lock et ai., 1993; Lock, 1994) and a limited study undertaken at the
Contribution of domestic sources
65
Brushy Creek sewage treatment plant in the outer north-eastern suburbs of Melbourne (McCormick, 1991). No research covering a range of sites across Melbourne was then available. To fill this gap a project was initiated by Melbourne Water to ascertain the concentrations of selected organic and inorganic pollutants in sewage from a range of residential areas within the greater Melbourne area. The project was undertaken jointly by Melbourne Water and the Chemical Engineering Department at the University of Melbourne; the project's findings are reported in the following sections. RESEARCH PROGRAM Parameters to be measured Budgetary constraints precluded analysing sewage samples for all the chemicals regarded by the EPAV as priority pollutants. In selecting which chemicals should be placed on the list for analysis and which should not, factors favouring inclusion were as follows. (a)
limits on concentrations of the chemical concerned were already in place in Trade Waste Licences.
(b)
The chemical concerned had already been identified by Melbourne Water or the EPAV as a local problem, or potential local problem.
(c)
Significant levels of the chemical concerned had been detected in sewage samples at the Brushy Creek plant (McCormick, 1991) or in other relevant Australian studies.
(d)
Costs for analysis were not prohibitive.
The list of parameters finally selected for analysis was as follows. (a)
Basic wastewater characteristics: biochemical oxygen demand (BOD); chemical oxygen demand (COD); total organic carbon (TOC); oil and grease; total suspended solids (TSS); total dissolved solids (TDS); ammonia nitrogen; total nitrogen (TN); total phosphorus (TP); total oxidised sulfur; sulfate; sulfite; sulfide; total phenols; colour.
(b)
Elements (predominantly metals): aluminium (AI); antimony (Sb); arsenic (As); barium (Ba); beryllium (Be); boron (B); cadmium (Cd); calcium (Ca); chromium (Cr); cobalt (Co); copper (Cu); iron (Fe); lead (Pb); magnesium (Mg); manganese (Mn); mercury (Hg); molybdenum (Mo); nickel (Ni); potassium (K); selenium (Se); silver (Ag); sodium (Na); strontium (Sr); thallium (TI); tin (Sn); titanium (Ti); vanadium (V); zinc (Zn).
(c)
Phthalate esters: bis (2-ethylhexyl) phthalate; butylbenzyl phthalate; dibutyl phthalate; diethyl phthalate; dimethyl phthalate; dioctyl phthalate.
(d)
Chlorinated hydrocarbons; chlorobenzene; 1,2 dichlorobenzene; 1,3 dichlorobenzene; 1,4 dichlorobenzene; 1,2,3 trichlorobenzene, 1,2,4 trichlorobenzene; hexachlorobenzene; chloroform.
(e)
Polynuclear aromatic hydrocarbons (PAB's); acenaphthene; acenaphthylene; anthracene; benzo (a) anthracene; benzo (g,h,i) perylene; benzo (b) fluoranthene; benzo (k) fluoranthene; chrysene; dibenzo (a,h) anthracene; fluoranthene; fluorene; indeno (l,2,3-c,d) pyrene; naphthalene; phenanthrene; pyrene.
(f)
Amines: nitrosodimethylarnine; nitrosodiphenylamine; nitrosodipropylamine; 1,2 diphenylhydrazine.
(g)
Ethers: bis (2-chloroethoxy) methane; bis (2-chloroethyl) ether; bis (2-chloroisopropyl) ether; 3 bromophenyl phenyl ether; 4-chlorophenyl phenyl ether.
JWST 34:3/4-0
66
P. J. WILKIE el al.
Including basIc wastewater charactenstlcs on the list of measured parameters fulfilled two. purposes. It provided a means of checking that any sewage sample having unexpectedly high concentratiOns o~ some particular chemical was othenvise normal. It also made it possible to determine whether concentratiOns of any priority pollutants might correlate with levels of more commonly measured parameters. As the project progressed, the above list was amended several times. The amines wer~ deleted almost at once, as laboratory advice was that their rates of decomposition were too rapid for meanmgful results to be obtained from samples not analysed immediately. Later, once 33 samples had .been an~lysed, the ethers, PAH's and chlorinated aromatic hydrocarbons (CAH's) were removed from the hst. By thIS stage no ethers, no PAH's and just a trace of one CAH (I, 3 dichlorobenzene) had been detected in samples of purely domestic origin. For budgetary and other reasons, the BOD of the last sample and the colour of the last three samples were not determined. Location of sampling sites For Melbourne Water's purposes it was important that the mean concentrations of pollutants obtained be as representative as possible of conditions across the city as a whole. This meant that not only should the set of sampling sites chosen be widely distributed geographically but also that their catchments should encompass as diverse a collection of residential area types as possible. Aspects felt to be of relevance in characterising residential areas included a number of lifestyle-related factors: socio-economic status; cultural identity (in multicultural Melbourne many suburbs contain concentrations of residents from a single ethnic group); the age structure of the residents; and the residential density (lifestyles in low residential density outer suburbs are very different from those in high residential density inner-city apartment blocks). The age of a suburb was also felt to be important as it largely determines the types of materials used in sewer pipes and in household water heating and plumbing services. Further considerations included the desirability of avoiding low-lying areas where groundwater infiltration into sewers could distort measurements, and the need for easy and safe access to sampling points. Whilst the above aspects were all of importance, a majority of site catchment areas needed to be as free as possible of wastewater sources of other than a domestic nature. For each potentially suitable site, therefore, the exact catchment boundaries were determined using detailed computerised sewer maps; any licensed Trade Waste dischargers within the catchment were identified and their location marked on a street map of the area. The location marker was a coloured sticker bearing a number: the colour indicated whether the load (volume, strength or both) was high, medium or low; the number represented the magnitude of the risk posed by the discharge to Melbourne Water's operations (on a scale of I to 5, with I being potentially the most risky and 5 the safest). From such maps the number and type of non-domestic wastewater discharges could be seen at a glance and the relative suitability of different prospective sampling sites readily determined. The value of this exercise became clear when no inner-city site free of trade waste inputs could be found and a compromise site with as limited a non-domestic contribution as possible had to be chosen. Despite the emphasis placed on domestic sewage, there were obvious advantages in also sampling from sites where the sewage had a trade waste component. Data from such sites would be obtained at similar times and using the same sampling and analytical techniques as those used for the purely domestic sewage. For this reason they would be more relevant for comparative purposes than other published or plant data. Budgetary constraints, practical considerations such as distances between sites, and the need to satisfy the criteria discussed above led to the choice of 8 sampling sites. One was the Keilor wastewater treatment plant, a small plant in the western suburbs with a comparatively low trade waste component. Four sites, spanning the western, northern and eastern suburbs, had no licensed Trade Waste Dischargers in their catchments. One older suburban site, closer to the centre of Melbourne, received trade waste from an auto electrical servic~s company, a petrol station and a medical laboratory. The seventh site, originally thought to be a well est.abhshed suburban site receiving domestic sewage only, later proved to be receiving a moderate trade waste mput through a sewer connection shown on maps as closed off. The eighth site was on a main
67
Contribution of domestic sources
sewer receiving a substantial input from industry. Characteristics of the catchment areas for these sites are shown in Table 1. Table 1. Characteristics of sampling sites Site number 1 2 3 4 5 6 7 8
Suburb Box Hill North Warrandyte Croydon Hills Mooroolbark Camberwell Aberfeldie Keilor (Treatment Plant) Keilor
Trade Waste Input Moderate None None None Slight Substantial Moderate None
Area (ha) 138 225 155 301 343 2360 2168 263
Number of Tenements
Number of Residents
1500 880 540 1300 3600 18530 5550 675
3925 2880 1865 4200 9250 56740 20180 2487
Sampling program A total of seven separate sampling runs was undertaken. NATA - approved sampling protocols and analytical procedures were used in obtaining and analysing all the samples. Run 1 (25/3/94): This comprised a single sample taken from a site free of trade waste inputs in the southern suburb of Heatherton (details not shown in Table 1). This sample was used to evaluate the capabilities of the laboratory (Australian Laboratory Services Pty Ltd) which carried out all the analyses reported here. Run 2 (2/6/94): Samples were taken sequentially from sites 1,2,3,4,5,7,8,6 over the period 7.15 am to 2.38 pm. To test the consistency of sewage composition at a given site, two samples were taken, one after the other, at site 8. To these samples was added a sample drawn later in the afternoon from the inlet to the Western Treatment Plant. A composite sample of water drawn from garden taps adjacent to sites 1 to 6 and 8 was also submitted for analysis. The purpose of this was to ascertain how much of each pollutant in the sewage was present in the original domestic water supply and how much could be attributed to household activities; it is well established that the water supply is an important source of many sewage components (Klein et at., 1974; Lock et aI., 1993; Lock, 1994). Run 3 (17/8/94): This was similar to Run 2 except that: no sample was taken at site 6 (because of rain); the major treatment plant sample was from the Eastern Treatment Plant; and duplicates of the sample taken at site 7 were submitted to test the reproducibility of the analytical results. Run 4 (24/8/94): This was similar to Run 2 except that: the order in which sites were visited (7,8,6,5,4,3,2,1) was almost the reverse of that in run 2 (to compensate for time-related concentration changes); the major treatment plant sample was from the Eastern Treatment Plant; the sample for which duplicates were submitted was that from site 4. Run 5 (23/11/94): This run, conducted at site 3, was designed to determine the influence of the time of day on pollutant concentrations. The 23/11/94 was a Wednesday and therefore a typical working day; samples were taken at approximately the following times: 7,8,9 and 10 am, 12 noon, 2,3,4,5,6,7,8 and 10 pm. Samples were spaced most closely at times of greatest domestic activity. A composite water sample was taken and the sample at 6 pm duplicated. Run 6 (24/11/94-30/11/94): This run, also conducted at site 3, was designed to investigate the influence of the day of the week on pollutant concentrations. Samples were taken at 8 am and lOam on each day. These times were chosen as they represented the peak sewage flow periods for weekdays (8 am) and weekends (10 am).
P. J. WILKIE et al.
68
Run 7 (18/12/94): This run, also conducted at site 3, was designed to establish the nature of pollutant concentrations on a Sunday. as opposed to a weekday. In all other respects it was similar to Run 5. RESULTS The major purpose of the project described here was to determine representative values of the concentrations of key pollutants in sewage from purely domestic sources. To obtain the desired values the data from the 60 samples from sites 1,2,3,4,5,8 and the Heatherton site were combined to yield the results shown in Tables 2 and 3. To obtain truly representative results it was felt necessary to disregard unusually low or high values; if this had not been done there was a risk that an analytical error or an illicit discharge might exercise an undue influence on the results. The procedure followed was, for each pollutant, to determine the mean and standard deviation of all relevant values from the above-mentioned sites. Any points lying more than three standard deviations from the mean were then eliminated and the statistical parameters recalculated. The mean, minimum, maximum and standard deviation values given in Tables 2 and 3 refer to this latter, truncated set of values. The excluded values appear in the "outliers" column. Also included in the Tables are the means of the concentrations of each pollutant in the composite water samples. No entries appear in the Tables for a number of elements on the original list; of these beryllium, selenium and vanadium were not detected in any samples while antimony, mercury, molybdenum and thallium were found in very few samples and almost invariably only at levels close to the limit of detection. Table 2. Concentrations of selected pollutants in sewage ans the domestic water supply (basic wastewater characteristics) Concentration in domestic sewage (mg/L)
Component Mean Ammonia BOD COD TOC Oil & Grease TSS TDS TN TP Sulfate
36.2 203 505 173 22 266 375 57 7.3 46.4
Minimum
Maximum
12 38 265 89 1 132 124 24 2 27
73 432 820 262 47 492 596 114 16 69
Standard deviation
Outliers
14.8 88 110 43 10 85 94 22 3.7 10.9
120,128 950,950,870 388 61,69 138,155,185
Mean concentration in domestic water supply (mg/L)
Mean concentration in treatment plant influents (mg/L)
<1 3 14 15 1.5 4.9 92 3.7 <1
39 190 603 271 59 288 550 61 4.7
DISCUSSION AND CONCLUSIONS Sewage composition Noteworthy was the marked variability of measured values, reflecting the diversity of inputs to the sewer networ~, . even from households. This variability was emphasised by the significant differences in compos~tI~n. between the two samples .taken 15 minutes apart at site 8 on 2/6/94. Reassuring was the fact that vanablhty between results for duphcate samples was small (some variation was expected because of the heterogeneous nature of the TSS fraction). Comparison of t.h~ above ~esults with those from other cities served to show that local influences affect sewa~e compOSItIOn ~onslderably; levels of individual components were often of similar orders of magmtude but no consIstent trends were found.
69
Contribution of domestic sources
Runs 5,6 and 7 were undertaken at a single site to investigate whether obvious time-related trends were apparent. .Over the course of the week, the only obvious feature was a Sunday morning peak in concentratIOns and mass flows of components derived from basic human functions and activities. A more extensive sampling program is clearly needed if other, more subtle trends, are to be identified. Table 3. Concentrations of selected pollutants in sewage and the domestic water supply (specific pollutants) Concentration in domestic sewage
Component Mean
(~g/L)
Minimum
Maximum
Standard deviation
Outliers
Elements Aluminium Arsenic Barium Boron Cadmium Calcium Chromium Cobalt Copper Iron Lead Magnesium Manganese Nickel Potassium Silver Sodium Strontium Tin Titanium Zinc
745 2.3* 38 263 0.45* 9260 3.2* 1.28* 62 728 13 4925 48 4.2* 16780 0.94* 87280 50.0 4.69 <10 169
60 <1 2 10 <0.2 5000 <1 <1 35 <50 4 2600 17 <1 5000 <1 9900 30 <1 4 52
1560 4 90 860 1 15900 8 3 97 1770 31 9200 82 10 37500 3 163000 75 11 11 348
352 1.0* 17.7 206 0.21 * 2450 1.67* 0.90* 14.9 373* 6.8 1655 12.8 1.97* 7285 0.75* 28520 9.3 2.59* N/A 75.8
2060,2150,3250 6,24 115,117 1130 1.2,1.8,1.8 18900,21600 11,17,18,54,74,124 6,6,8,23 113,117,126,227
Phthalates Bis (2ethylhexyl) Butylbenzyl Oibutyl Oiethyl Dimethyl Oioctyl Chloroform
25.5 2.0* 3.2* 20 N/A N/A 7.2
5 <1 <1 5 <1 <1 1.3
68 5.7 8 49 3 43 13
15.33 1.64* 2* 10 N/A N/A 2.6
86,91,91,1500 7.6,12,15 43,61
633 17300,18200 114 11,32,137 5,6,6,8,19,42,56 84,105,117 14,17 20,49 468,733,766,1050 1050
N/A N/A
Mean concentration in domestic water supply
Mean concentration in treatment plant influents
(~g/L)
(~g/L)
131 <1 20 108 NO 7380 <1 NO 33 267 8.6 1660 7.1 2.1 580 NO 4250 24 ND <10 49
933 2.6 167 263 <1 17200 31 1.75* 77 1230 68 9900 218 14.3 22450 2.6* 137000 94.5 6.7 15.4 346
<20 NO NO <1 ND ND 19.4
66.7 <10 <10 21 <10 <10 3.7
*Mean and standard deviation calculated assuming that for samples reporting concentrations of less than a given detection limit the actual concentration was half that detection limit. NO = not detected; N/A = not applicable. Domestic water supply contributions The contributions of the water supply to pollutant concentrations in sewage were classified into 3 groups: dominant(>60%), substantial (25-60%) and small «25%). An interesting member of the first category is chloroform which has a substantially higher concentration in the water supply than in domestic sewage, and
P. J. WILKIE et al.
70
an even lower one in the influents to the major treatment plants. Its presence in the tap water samples is attributed to chlorination of the domestic water supply, its subsequent disappearance to evaporation. The remaining members of the first category are calcium and lead; the former's presence is attributable to upstream water treatment processes but the latter's is unexplained. In the middle group are barium, boron, copper, iron, magnesium, nickel, strontium and zinc. Many of these are common constituents of natural waters but several other possible sources suggest themselves. Magnesium and strontium are often associated with calcium and could be present as impurities in lime used at t;eatment works. In support of this, a peak in calcium concentrations at site 3 on 18/12/94 was associated with marked peaks in magnesium and strontium concentrations. In addition, copper, iron and zinc are widely used in water reticulation pipes and plumbing services and fittings; the significance of the contribution of household plumbing to concentrations of such metals in domestic sewage is well illustrated by Lock et al. (1993) and Lock (1994). For the third group it was noteworthy by how much the not insignificant amounts of potassium and sodium in the water supply were exceeded by the amounts derived from households. The fact that cadmium, silver and tin were not detected in the water supply serves to emphasise the importance of household practices and consumer products as contributors to levels of these metals in sewage. Treatment plant data Comparison of data from domestic sources with those from the 6 samples of wastewater treatment plant influents was enlightening. Whilst concentrations of many components were at or near their highest levels in the treatment plant samples, it was clear that domestic sources were a major contributor to final levels of many pollutants analysed for. Particularly surprising was the high domestic sewage TDS level, previously thought by Melbourne Water to have been much lower. These results suggest that if further reductions in levels of a number of priority pollutants in Melbourne's sewage are required, a much harder look will need to be taken at household activities and consumer products and how to make them more "sewer-friendly". ACKNOWLEDGMENTS The contribution made in the early stages of this project by the late Stewart Morgan is gratefully acknowledged, as is the help provided by Alan Bennett, formerly of Melbourne Water. Also acknowledged is the valuable assistance provided by Keith Evans in connection with sample analyses. REFERENCES Copland, B. (1990). Domestic Catchment Sampling Programme Report. Water Board, Sydney. Klein, L. A., Lang, M., Nash, N. and Kirshner, S. L. (1974). Sources of metals in New York City wastewater. 1. WPCF 46, 2653• 2662. Lock, W. H., Smith, K. E. and Thomas, P. M. (1993). Heavy metals and organics in domestic sewage. Proc. Australian Water and Wastewater Assoc. 15th Federal Convention 3, 753-758. Lock, W. H. (1994). Heavy metals and organics in domestic wastewater. Research Report No. 79, Urban Water Research Association of Australia, Melbourne. McCormick, M. J. (1991). Background toxicant levels in domestic sewage. Melbourne Water Report. Sharples, 1. (199?). Factors affecting the setting of limits for the discharge of trade-waste to sewer. M. App. Sc. project report, UnIversIty of Melbourne.