GUIDELINES FOR THE RE-USE OF TREATED WASTEWATER: PUBLIC HEALTH PROTECTION OR DENIAL OF ESSENTIAL RESOURCES? ABSTRACT

Transcription

1 Presented at WISA 2000 Biennial Conference, Sun City, South Africa, 28 May 1 June 2000 GUIDELINES FOR THE RE-USE OF TREATED WASTEWATER: PUBLIC HEALTH PROTECTION OR DENIAL OF ESSENTIAL RESOURCES? M Steyn and P Jagals Centre for Health and Environment Research and Development. Technikon Free State, Private Bag X20539, Bloemfontein, 9300 South Africa. msteyn@tofs.ac.za and jagals@tofs.ac.za ABSTRACT Treated wastewater (TWW) reuse in South Africa is historically limited to irrigation of recreation facilities (sports fields, urban parklands). In rare instances, uses of these waters are allowed for food-related activities such as fodder production. Environmental health practitioners discourage reuse of TWW for aquaculture and production of edible crops for fear of adverse health effects. However, South Africa is a semi-arid county with erratic rainfall patterns. Demands from communities in and around urban areas to use treated wastewater for food production in small-scale farming practices are rapidly increasing. The Department of Health applies the South African Guidelines for the Permissible Re-Use of Treated Sewage Effluents (1978) to help regulate reuse of treated wastewater. The Guideline approach appears to favour the treatment method - and configuration that produces the effluent - as a benchmark for decision-making rather than the actual quality of such effluent. Reuse applications that involve more elaborate treatment facilities (primary, secondary and tertiary treatment processes within the configuration) would generally be favourably considered for purposes of food production and recreation-related applications. Applications for the reuse of effluent from waste stabilisation pond systems (WSP) are generally discouraged - regardless of the effluent quality. To illustrate this discrepancy a study was undertaken over a period of twelve months to assess the levels of faecal coliform bacteria in the effluent of two system categories. ➀ Two fully configured waste stabilisation facilities. ➁ Two waste stabilisation ponds, each consisting of a series of an initial anaerobic pond followed by several facultative ponds and ending with maturation ponds. There were no statistical significant differences in the effluent quality. Further discrepancies are illustrated in another study undertaken over the same period that compared the levels of faecal coliform bacteria in the effluents of the abovementioned system categories to that of a public stream receiving polluted urban surface runoff. There were statistically significant differences in the quality, with higher levels of faecal coliforms in the stream. Yet, unrestricted irrigation of food crops could be undertaken from the public stream. In practice this implies that the Guide (1978) does not provide the public health protection desired, nor suitable discretionary measures that may conditionally permit the reuse of treated wastewater regardless of the system producing the effluent. Officials would therefore tend to implement an absolute precautionary principle thereby denying poor communities the sustainable use of a valuable resource. KEYWORDS Treated wastewater, reuse, faecal coliforms, waste stabilisation ponds, public health, irrigation, polluted urban run-off, edible crops INTRODUCTION Treated wastewater (TWW) reuse in South Africa is historically limited to irrigation of recreation facilities (sports fields, urban parklands) and commercial horticultural and agricultural activities such as the cultivation of instant lawn and animal fodder. In rare instances, uses of these waters are allowed for food-related activities such as grazing pasture maintenance for dairy and meat animals. Public health practitioners actively discourage reuse of TWW for aquaculture and the production of edible crops because of fear of adverse health effects that may be caused by pathogenic microorganisms in such water. South Africa is a semi-arid country with erratic rainfall patterns (Kriel, 1992). Although the annual rainfall had been reported to be between mm p.a., many areas would report rainfall of between mm p.a. In fact the South African climate have an annual water deficiency because evaporation exceeds rainfall (Snyman and Fouchè, 1991). Because of low rainfall and non-perennial surface water resources as well as periodic droughts, community farming of edible crops becomes difficult. Optimal use of water therefore becomes critical

2 (Republic of South Africa, 1997). Demands from communities in and around urban areas to use treated wastewater for food production are rapidly increasing. Despite large-scale urbanisation, intensive efforts are made in South Africa to collect and treat wastewater from all urban areas before discharge into public watercourses. Substantial water resources are therefore generated with accessible infrastructure such as waste stabilisation and maturation ponds that would otherwise not be available. Urban farming communities are beginning to develop a perspective that these water resources should be made available for crop production especially in smaller urban areas. Persons or instances who wish to use treated effluent for agricultural purposes are, in terms of Section 21 of the National Water Act (Act 36 of 1998), required to apply for a conditional water-use licence under the Act. The Department of Water Affairs and Forestry (DWAF) processes applications for any type of treated effluent re-use. If the intended re-use involves public health issues such as the production of food, or sports facilities that promote probable direct contact with surfaces irrigated with treated wastewater, the provincial Departments of Health (DOH) become involved. To protect public health, officials of DOH recommend issue or refusal of such licence applications to DWAF on the strength of the South African Guide for the Permissible Utilisation and Disposal of Treated Sewage Effluent (Department of National Health and Population Development, 1978). The 1978 Guide classifies treated effluents according to the type of treatment by which it was produced and also includes a microbiological indicator organism parameter (numbers of E. coli per 100 ml). Specific guidelines for the release of nematode concentrations are not included, which is contrary to international norms (WHO, 1989; Blumenthal et al., 1999). This guide therefore only offers environmental health officials (EHO s)a dual approach for decision-making on licence applications. The treatment method - and configuration - that produces the effluent is the primary benchmark with the E. coli criterion to support the evaluation. This is then a case of first considering the type of treatment before considering the quality of the effluent. In practice this often implies that licence applications that involve effluents from more elaborate treatment facilities would generally be preferred for purposes of food- and recreation-related applications on the strength of system sophistication regardless whether the system actually produces a realistic health-related microbiological effluent quality. There is good reason for this. Effluent from a well designed and maintained treatment system, which could effectively reduce the numbers of E. coli in raw sewage to the level required for the effluent used for crop irrigation would not require frequent monitoring of its microbiological quality. Unfortunately, permutations of treatment class, as well as crop and irrigation type in the 1978 Guide indicate strong prejudice against reuse of effluent from waste stabilisation pond systems (WSP) regardless of the effectiveness of design and effluent quality. This becomes a dilemma as many smaller South African communities who wish to use treated effluent for crop production are serviced by WSP to dispose of raw sewage. The practical application of the South African Guide (1978) by officials of the two Departments might presently be denying these communities of an essential development resource rather than protecting health. To illustrate this, a study was undertaken over a period of 12 months to investigate the numbers of faecal coliform bacteria in the effluent from two different categories of wastewater treatment facilities. Both these categories of facilities were in areas where the local communities had indicated that they want to use the water for agricultural purposes especially including the production of crops that may be eaten uncooked. These facilities discharge into receiving waters that also receive faecally polluted urban surface run-off.

3 These communities therefore have a choice of licence application. They may either apply to extract irrigation water directly from the river, or extract from the final effluent discharge points, which are closer to the arable land they wish to use. In cases for the former application mentioned above, environmental health practitioners (EHP s) from DOH would not be involved regardless of the health-related quality of the river s water. They would however, have to consider the latter type application. Previous studies in the vicinity (Jagals, 1997) indicated that urban surface runoff into receiving waters in this particular area often contained numbers of faecal coliforms of the same order of magnitude than that of raw sewage. For this study these levels of faecal coliforms in the river was also compared to the levels of faecal coliforms in the final effluents. METHODOLOGY Test Systems The quality of the final effluent from the following 2 categories of treatment facilities were assessed: Fully staged systems. The 1 st of these have a fixed medium bioreactor with primary and secondary sedimentation and a sequence of maturation ponds with a 2-week retention capacity before discharge (PS & MP). The 2 nd has a suspended medium bioreactor with secondary sedimentation and chlorination as tertiary treatment (PS & Cl). Waste stabilisation pond systems. Two waste stabilisation ponds, each consisting of one initial anaerobic pond followed by several facultative ponds and ending with maturation ponds with a minimum of 7 days retention (WSP 1 & 2). WSP #1 was an older system serving a community that had extended its sanitation facilities such as wastewater conservancy tanks and water borne systems to the extent that the treatment facility has reached it s full capacity. WSP #2 was a newly built facility of which the influent was below its design capacity. Polluted public waters. 30 samples from a stream that receives microbiologically (faecal) polluted urban surface run-off were also compared with the combined effluent quality from the fully staged (FS) and WSP systems shown in Table 2. The 30 samples of the urban runoff included 15 samples of run-off taken from stormflow discharging from non-point sources. The indicator This study was based on the faecal coliform indicator concentrations in the final effluent at the point of discharge into the receiving waters. Although faecal coliforms have shortcomings for indicating the presence of resistant organisms such as pathogenic viruses and protozoa, it is a reliable indicator for the possible presence of mainly bacterial pathogens such as Salmonella that may be present in water (Grabow, 1996). Faecal coliforms were enumerated with the membrane filter technique using M-FC Agar (Difco ) in triplicate on 65-mm petri dishes. The plates were inverted and incubated at 44.5 C ± 0.2 C, for 24 hours ± 2 hours. Faecal coliform colonies were identified as colonies in various shades of blue or partial blue (Standard Methods, 1998). All counts were expressed as the average of tests done in triplicate. RESULTS AND DISCUSSION Table 1 shows the combined results of the 2 system categories, while Figure 1 illustrates the individual performance. The geometric mean is an acceptable central value for presenting

4 microbiological data (Standard Methods, 1998) and is presented in Table 1 to provide a realistic perspective of the quality effluent discharged by the various systems. However, the resistant mean (median) is not easily influenced by outliers and is therefore used as an estimation of the true mean when applied to the log transformed data that follows the geometric mean in Table 1 (Helsel and Hirsch, 1995). Table 1: Faecal coliform concentrations in effluents discharged from the 2 wastewater treatment categories. Fully configured treatment system + maturation ponds (PS & MP) Fully configured treatment system + chlorination (PS & Cl) Waste stabilisation pond system #1 Waste stabilisation pond system #2 Geometric Mean 1.57 x x x x 10 1 n-values Log Data Median % Confidence Interval Lower 95% CL Upper 95% CL The differences in the median values among the faecal coliform levels in the final effluent of the fully-configured facilities and the two waste stabilisation pond systems were not great enough to exclude the possibility that the difference is due to random sampling variability. There was not a statistically significant difference (P = 0.487). Faecal coliform concentrations log / 100 ml PS+MP PS+Cl WSP1 WSP2 Wastewater treatment systems FIGURE 1: Faecal coliform concentrations in various wastewater treatment systems Of the two fully configured systems, the system using chlorination as a tertiary treatment process produced effluent containing less faecal coliforms than the system using maturation ponds. However, the results for the chlorinated system showed greater variance at the 25 th and 75 th percentiles of the boxes presented in Figure 1, indicating that this system was prone to intermittent interruptions in its final pathogen barrier e.g. chlorination system breakdown. The maturation ponds ensured more stable results but generally allowed a larger number of indicators through in the final effluent.

5 Of the two waste stabilisation pond systems, the newer system (WSP#2) allowed the smallest numbers of indicators through, indicating the effectiveness of a system to stabilise raw sewage if operated within its design capacity. The older system (WSP#1) showed the typical symptoms of an overloaded system by intermittently discharging high levels of faecal coliforms, although it generally produced the better microbiological quality overall. The South African 1978 Guide is dominated by treatment systems as denominator of effluent quality assurance and does not favour the use of effluents from WSP for crop irrigation regardless of the WSP system design or effluent quality. By contrast, the international community recognises the effectiveness of waste stabilisation ponds to produce effluent of quality suitable for crop irrigation (Mara and Cairncross, 1989; Blumenthal et al., 1999). The WHO (1989) also supports the wider use of properly designed waste stabilisation pond systems and their effluents rather than relying so strongly on costly sophisticated systems that can often not be afforded by smaller communities. The results in Table 1 and Figure 1 show that, based on faecal coliforms as indicators, there is little to choose between the health-related bacterial qualities of the effluents discharged from any of these systems. This is in agreement with the WHO s (1989) view that there is sufficient evidence that properly designed WSP systems are effective to achieve public health protection. However, as a stronger safeguard, the WHO (1989) as well as Blumenthal et al. (1999) include a nematode criterion to indicate the presence of pathogenic parasites - something that lacks for the South African Guide (1978). In practice, the South African 1978 Guide proposes measures to control microbiological health hazards in the reuse of treated domestic wastewater through the following: Treatment method. Microbiological effluent quality based solely on the levels of E coli per 100 ml. Some crop restriction Irrigation type regulation While this is a comprehensive set of criteria, it appears to be a combination of being stricter than what is necessary to avoid health risks in the process discouraging more liberal use and being too lenient in the sense of not using a nematode indicator criterion. When considering that databases of microbiological effluent quality of numerous facilities are often not comprehensive or simply available especially in many smaller areas, the Guide (1978) does not provide suitable discretionary measures for EHP s to use that could effectively permit the safe reuse of treated wastewater regardless of the system producing the effluent. The practitioners would therefore tend to implement an absolute precautionary principle of not recommending the effluent to be used - thereby denying the sustainable use of a potential valuable resource to communities. The Guide (1978) is confusing when crop and irrigation types are to be considered. It clearly does not provide for aquaculture nor does it make provision for newer agricultural practices such as hydroponics where certain edible crops are cultivated without the vegetable touching the water. It is proposed that the South African 1978 Guide should be reviewed and adapted to encourage a wider scale use of WSP as well as provide realistic guidelines for the healthrelated reuse of the effluents from any of the systems. This will greatly enhance crop security in small-scale community farming practices. Urbanisation in South Africa added another dimension to the use of surface waters for irrigation, especially in and around urban areas. It was found by Jagals (1997) that the

6 microbiological qualities of surface water runoffs from urban areas are often comparable to raw sewage. Persons wishing to irrigate crops from public waters would need water-use licences in terms of Section 21 of the Act (Act 36 of 1998). Environmental health practitioners are not involved in the consideration of this category licence, because of the non-existence of guidelines for the health-related microbiological quality of general surface waters in public streams used for irrigation. Applications for a licence to irrigate directly from rivers and streams receiving run-off are therefore not subjected to the South African Guide (1978) or to any other health-related considerations. To illustrate this discrepancy, the quality of faecally polluted urban surface runoff was compared with combined effluent quality from the fully staged (FS) and WSP systems shown in Table 1. Table 2: Faecal coliform concentrations in WWT effluents as well as in polluted urban runoff. Fully configured treatment system + tertiary treatment Waste stabilisation pond systems Polluted urban runoff Geometric Mean 1.35 x x x 10 3 Log Data n-values Median % Confidence Interval Lower 95% CL Upper 95% CL There were still no statistically significant differences (P = 0.329). The faecal coliform levels in the urban runoff were, however, significantly higher than those from the treatment systems (P 0.001). Faecal coliform concentrations log / 100 ml FS WSP PUR Wastewater treatment systems FIGURE 2: Faecal coliform concentrations in wastewater treatment system effluents and in polluted urban runoff Figure 2 illustrates the microbiological water quality from the 2 systems as well as the urban discharges.

7 These urban discharges contained higher levels E. coli within the band of faecal coliforms than the 1000 E. coli per 100-ml maximum proposed by the South African Guide (Department of National Health and Population Development, 1978). Yet these waters could be used without restriction for agriculture and aquaculture. From a health-related microbiological water quality perspective, the public health protection that the 1978 Guide is supposed to offer appears now to be in danger of becoming quite redundant. CONCLUSION The demand for reuse of treated wastewater, as well as pollution pressures on receiving waters in South Africa, requires comprehensive yet readily applicable guidelines to enable the use of all types of treatment system effluents while, at the same time, serve as guidelines for public health protection. This study had shown that quality based on faecal coliform numbers in effluents discharged from properly designed waste stabilisation ponds, as well as from more sophisticated wastewater treatment systems, were not different and that these effluent were of a better quality than that of a stream receiving faecally polluted urban run-off. What is needed are more comprehensive guidelines that offer, to agriculture and aquaculture, wider application as well as discretion for public health protection from polluted discharges, be it from point sources such as treated wastewater discharges or other polluted diffuse sources such as urban runoff. Recent advances in epidemiology have shown that past standards for hygiene in waste reuse, which were based solely on potential pathogen survival, are stricter than is necessary to avoid health risks (Blumenthal et al., 1999). In the light of these and other recent studies as well as other pressures, which include increasing public demands for using these waters globally, Blumenthal et al. (1999) are currently reviewing the WHO Guidelines for Wastewater Reuse in Agriculture and Aquaculture (1989). This provides the ideal opportunity as well as some benchmarks to review the applicability of the present South African Guide (1978) as well as the South African Water Quality Guidelines (1996). Such a review should assess the suitability of the various guidelines to address and express health risks related to the use of treated wastewater as well as other potentially polluted water sources for various agricultural and aquacultural activities. This should include to what extent the safe use of these waters by communities can be accommodated, encouraged and guided. ACKNOWLEDGEMENTS The assistance of the National Research Foundation is hereby acknowledged. REFERENCES BLUMENTHAL, U., PEASEY, A., RUIZ-PALACIOS, G. and MARA DD (1999) Guidelines for wastewater reuse in agriculture and aquaculture: recommended revisions based on new research evidence. Water and Environmental Health at London and Loughborough. Task No: 68 Part 1 DEPARTMENT OF NATIONAL HEALTH AND POPULATION DEVELOPMENT (1978). South African Guidelines for the Re-Use of Treated Sewage Effluents. Pretoria. GRABOW, WOK (1996) Waterborne diseases: Update on water quality assessment and control. Water SA. Vol. 22 (2) HELSEL, DR and HIRSCH, RM (1995) Statistical Methods in Water Resources. Elsevier, Amsterdam.

8 JAGALS P (1997) Stormwater runoff from typical developed and developing South African urban developments: definitely not for swimming. Water Science & Technology. Vol. 35(11-12). KRIEL, JP (1992) Die jaarlikes reënval, afloop en verhoging in afloop met verhoogde reënval in die Vaalrivier opvangsgebied by die Vaaldam. (The annual rainfall, runoff and increase in run-off with increased rainfall in the Vaal River catchment at the Vaal Dam) Water SA. Vol MARA, DD. and CAIRNCROSS, S (1989) Guidelines for the safe use of wastewater and excreta in agriculture and aquaculture. WHO and UNEP, Geneva. REPUBLIC OF SOUTH AFRICA (1997) White Paper on a National Water Policy for South Africa. Department Of Water Affairs and Forestry (DWAF): Directorate Communication Services. Pretoria. REPUBLIC OF SOUTH AFRICA (1998) Water Act - Act No 36:1998. Govt. Notice No: Vol Office of the President, Pretoria. SHUVAL, H., LAMPERT, Y. and FATTAL, B (1997) Development of a risk assessment approach for evaluating wastewater reuse standards for agriculture. Water Science and Technology. Vol. 35 (1ll12) SNYMAN, HA and FOUCH, HJ Production and water-use efficiency of semi arid grasslands of Southern Africa as affected by veld condition and rainfall. Water SA. Vol. 18: CLESCERI, LS, GREENBERG, AE and EATON, AD (1998) Standard Methods. For the Examination of Water and Wastewater. 20 th Edition. United Book Press, Inc. Baltimore, Maryland. WHO Scientific Group (1989) Health guidelines for the use of wastewater in agriculture and aquaculture. Technical Report Series 778, World Health Organisation, Geneva.