The impact of inadequate wastewater treatment on the receiving water bodies – Case study : Buffalo City and Nkokonbe Municipalities of the Eastern Cape Province

The performance of four wastewater treatment plants that serve the Buffalo City (Dimbaza, East London) and Nkokonbe (Alice, Fort Beaufort) Municipal areas in the Eastern Cape Province of South Africa was investigated for the removal of microbial and chemical contaminants. Statistical evidence showed a relationship between the quality of the final effluent and that of the receiving water body and the relationship was such that the better the quality of the final effluent, the better the quality of the receiving water body. The quality of both the effluents and the receiving water bodies was acceptable with respect to the temperature (mean range: 16.52 to 23.33°C), pH (mean range: 7.79 to 8.97), chemical oxygen demand (COD) (mean range: 7 to 20 mg/l) and total suspended solids (TSS) (mean range: 161.43 to 215.67 mg/l). However, in terms of the nutrients (orthophosphate mean range: 3.70 to 11.58 mg/l and total nitrogen mean range: 2.90 to 6.90 mg/l) the effluents and the receiving water bodies were eutrophic. The dissolved oxygen (DO) (mean range: 3.26 to 4.57 mg/l) and the biological oxygen demand (BOD) (mean range: 14 to 24 mg/l) did not comply with the EU guidelines for the protection of the aquatic ecosystems. The general microbiological quality of the effluents discharged from all the plants did not comply with the limits set by the South African authorities in respect of pathogens such as Salmonella, Shigella, Vibrio cholera and coliphages. The effluents discharged from the Dimbaza, East London, Alice and Fort Beaufort wastewater treatment plants were identified as pollution point sources into their respective receiving water bodies (Tembisa Dam, the Nahoon and Eastern Beach which are part of the Indian Ocean; the Tyume River and the Kat River).


INTRODUCTION
South Africa is a water-scarce country, and the demands on this resource are growing as the economy expands and the population increases.For the country to continue to develop economically, while meeting the wide-ranging needs for water, urgent steps must be taken to protect the quality of the resource.It is well known that water sources are subjected to frequent dramatic changes in microbial and chemical qualities as a result of the variety of activities on the watershed.These changes are caused by discharges of municipal raw waters or treated effluent at a specific point-source into the receiving waters such as streams, rivers, lakes, ponds etc (1).Point-source pollution problem not only increases treatment costs considerably, but also introduces a wide range of potentially infectious agents to waters that may be supplied to many rural and urban communities, thus resulting in incidences of waterborne diseases with far reaching socioeconomic implications (2).
Pathogens such as Shigella, Salmonella, Vibrio cholera and enteric viruses have been known to cause severe diarrhea, in children and adults, which can lead to morbidity and mortality, as experienced in South Africa recently with outbreaks of Shigella dysenteriae and Vibrio cholera that resulted in 13 and 288 fatalities, respectively (3,4).Also, typhoid fever remains endemic to many parts of South Africa, including Kwazulu-Natal, Northern Transvaal and the Transkei (5), with a recent outbreak occurring in Delmas, Mpumalanga.In this province, health spokespersons reported that there were 380 cases of diarrhea, 30 suspected cases of typhoid fever and nine confirmed cases (6).The outbreak originated in the town's water supply, suspected to have been contaminated with human faeces.Hepatitis A virus, caliciviruses, adenoviruses, rotavirus, and enteroviruses have the greatest effect on public health.A large number of epidemics due to the presence of these viruses in the environment have been reported (7,8,9).
Wastewater treatment plants discharge significant amounts of faecal pollution indicators and pathogenic microorganisms leading to a reduction in the quality of water (10,11).The Buffalo City and Nkonkobe Municipalities of the Eastern Cape Province are obligated to provide safe drinking water, to address public health risks of polluted environmental water affecting the entire community, and to comply with stipulated standards.The poor operational state and inadequate maintenance of most of these municipalities' sewage treatment works i.e. design weaknesses, overloaded capacity, faulty equipment and machinery, has resulted in major pollution problem and impacts on the quality of water resources, with marine water quality standards consequently not meeting regulatory standards.In this paper, we report the impacts of discharged effluents of some wastewater treatment plants located in the Eastern Cape Province of South Africa on their respective receiving waterbodies.

Study site
Four wastewater treatment plants that serve the Buffalo City (Dimbaza and East London) and Nkonkobe (Alice and Fort Beaufort) Municipal areas in the Eastern Cape Province of South Africa were used in this study.The wastewater treatment plants are located in rural areas (Alice and Fort Beaufort Sewage Treatment Works), semi-urban (Dimbaza Sewage Treatment Works) and in urban (East Bank Reclamation Works) areas.The activated sludge system is the biological wastewater treatment used in all four plants, followed by chlorination of the final aqueous effluent.
The Alice wastewater treatment plant is situated on the banks of the Tyume River, which is also used as the receiving water body for the final effluent from the plant.The final effluent from the Fort Beaufort Sewage Works is discharged into the Kat River.The Dimbaza wastewater treatment plant discharges its final effluent into a stream that empties into the Tembisa sewerage dam.The final effluent from the East Bank Reclamation Works is discharged into the Indian Ocean between Nahoon and Eastern Beach at Bats Cave and into a pond for the irrigation of a nearby golf course.Supernatant liquor from the sedimentation tanks is channeled into a fishpond located within the plant premises.
Wastewater samples were collected between 6th August 2003 and 24th March 2004 and between the 25th of October and 25th of November 2004 from the raw influents, the final effluents and the receiving water bodies of the four plants.Samples for microbial analyses were aseptically collected in sterile 2L glass bottles (for chlorinated final effluents, the sterile glass bottles contained c. 17.5 mg/L sodium thiosulphate).For chemical analyses, thoroughly cleaned non-sterile 2L glass bottles were used according to the standard procedures described elsewhere (12,13).The samples were then placed in coolers containing ice packs and transported to the base laboratory at the University of Fort Hare for analyses within 2-4 h after collection.

Physico-chemical analysis
Temperature and pH were determined on-site with a mercury thermometer and a pH meter, model 2000 (Crisson Instruments).The concentrations of free chlorine residual in the treated effluent samples were determined using a multi-parameter ion-specific meter (Hanna BDH-laboratory).The concentrations of orthophosphate as P, total nitrogen (Nitrate + Nitrite as N) and chemical oxygen demand (COD) were determined by the standard photometric method ( 14) using the Spectroquant NOVA 60 photometer (Merck Pty Ltd).Samples for COD analyses were digested with a Thermo reactor Model TR 300 (Merck Pty Ltd) and then analysed by the Spectroquant NOVA 60 photometer (Merck Pty Ltd).Biochemical oxygen demand (BOD 5 ) was determined using the Oxitop WTW BOD meter (Merck Pty Ltd).The incubation period for BOD determinations was 5 days.Dissolved oxygen (DO) was measured with the Merck DO meter, Model Ox 330 (Merck Pty Ltd) while total suspended solids (TSS) were estimated according to standard methods (14).

Microbiological analysis
Raw influent, final effluent and receiving water body samples were analysed for the target microorganisms using internationally accepted techniques and principles (14).The isolation of Salmonella and Shigella were done by enrichment in tetrathionate broth (Merck) in accordance with established method (14).Isolation of Vibrio was done by enrichment in alkaline peptone broth (pH 8.5) for 6-8 h at 37°C, after which the cultures were diluted and plated on Vibrio diagnostic agar (VDA) (Biolab) and incubated aerobically for 24h at 37°C as described elsewhere (15).
For the coliphage analyses, wastewater samples were passed through filters (25 mm, 0.45 µm Millipore filters) into sterile 250 mL flasks.The filters were pretreated with 10 mL of sterile 1.5% beef extract to minimize phage adsorption to the filters.The filtrates were then serially diluted in antibiotic-free peptone-saline within the range of 10 -1 to 10 -5 .Enumeration of Somatic coliphages and F-RNA coliphages was done on double-agar-layer plaque assay ( 16) using E. coli strain C (ATCC 13706) nalidixic acid-resistant mutant WG5 and Salmonella Typhimurium WG 49 nalidixic acid-resistant mutant as hosts respectively, and inoculum culture was prepared as described elsewhere (17).

Identification of bacterial isolates
The individual bacterial colonies from the different stages of the wastewater treatment plants were randomly selected from various plates (XLD, VDA and Chromocult agar) and subcultured onto the corresponding recovery media.The colonies were further purified by the same method for at least three times using nutrient agar (Biolab) before Gram staining.Oxidase test was then conducted on those colonies that were gram negative.The API 20E kit was used for the oxidase-negative colonies and the strips were incubated at 37ºC for 24 h.The strips were then read and the final identification was secured using API LAB PLUS computer software (BioMérieux, Marcy l'Etoile, France).

Concentration of chlorine residual in the final effluent
Table 1 illustrates the free chlorine residual concentrations in the final effluents of the wastewater treatment plants during the study period.Chlorine residual concentration ranged between 0.05 and 3.50 mg/l throughout the sampling period, with overdosing observed during the months of August 2003 in Dimbaza and September 2003 in Fort Beaufort (Table 1).A regular acceptable concentration of free chlorine residual was noted in the East London plant while low concentrations were noted in Alice plant during the study period.
Although the 1996 South African Guidelines do not specify any standard for the concentration of free chlorine residual in the treated effluent, this study considered those for domestic water supplies which recommend ranges of 0.3 -0.6 mg/L as ideal free chlorine residual concentration and 0.6 -0.8 mg/L as good free chlorine residual concentration with insignificant risk of health effects (18).The mean concentration of the free chlorine residual in the final effluents complied with the 0.3 mg/L recommended for domestic water supplies.

Physico-chemical characteristics of the wastewater samples
For all four wastewater treatment plants, the values obtained for COD, TSS, temperature, pH and total suspended solids in the effluents and receiving surface water bodies were well within the recommended limit of no risks (Figure 1, 2).The BOD, DO, total Nitrogen and Phosphate concentrations are shown in Figure 3. BOD indicates how much oxygen is needed by the water to completely oxidize its organic pollution load.There is no South African guideline for BOD in the effluent.For the protection of fisheries and the aquatic life, the EU guidelines stipulate the BOD target limits of 3.0 to 6.0 mg/L (19).The BOD levels recorded in all effluents and receiving water bodies are much higher than those indicated in the EU guidelines.Consequently the high levels of BOD in both effluents and receiving water bodies disqualify these water sources for use as aquatic ecosystems.Dissolved oxygen is an important parameter used for water quality control.The effect of waste discharge on a surface water source is largely determined by the oxygen balance of the system, and its presence is essential to maintaining biological life within a system (20).Dissolved oxygen concentrations in unpolluted water normally range between 8 and 10 mg/l (24).Concentrations below 5 mg/l adversely affect aquatic life (20).The concentrations of DO in the effluents and receiving water bodies (with the exception of the receiving water bodies in East London and Fort Beaufort) are less than 5 mg/L (Figure 2).Consequently, these water sources would not be suitable for use of aquatic ecosystems.
The mean total nitrogen (Nitrate + Nitrite as N) levels showed a gradual decline from the influents to the effluents in each wastewater treatment (Figure 3).However, the South African guidelines for total nitrogen (Nitrate + Nitrite as N) in drinking water for domestic use is <6.0 mg/L as N ( 18) and the target water quality range for total nitrogen in water for full contact recreational purpose is 6.0 to10 mg/L as N.The World Health Organization safe limit for nitrate for lifetime use is 10 mg/L as N.The total nitrogen levels obtained during the study period did not exceed the regulatory limits and thus total nitrogen is not considered to pose a problem to communities when the receiving water bodies are used for the domestic and recreational purposes.However, it is important to note that the total nitrogen levels in the final effluents could be a source of eutrophication for the receiving water bodies as the values obtained in all wastewater treatment plants (and especially in the Alice wastewater treatments) exceeded the recommended limits for no risk of 0 to 0.5 mg/L as N (21).
Although the levels of phosphate in influents varied from one plant to another, a gradual removal of phosphate was noted from the influent to the effluent in each wastewater treatment plant (Figure 3).The mean levels of phosphate in effluents were 6.2 mg/L in Alice, 5.4 mg/L in Dimbaza, 5.9 mg/L in East London and 11.6 mg/L in Fort Beaufort.The levels of phosphate in receiving water bodies varied in accordance with those recorded in effluents (Figure 3).In receiving waterbodies, the levels of phosphate averaged in the range of 3.1 to 6.8 mg/L (Figure 3) and differ significantly (p<0.05)compared to the effluents as higher phosphate levels were found in effluent zones than in receiving water bodies.The South African guidelines do not specify the target water quality ranges for phosphate in water for domestic use and recreational purpose (18).However the level of phosphate in water systems that will reduce the likelihood of algal and other plant growth is 5µg/L (21).Other investigators have pointed out that eutrophication-related problems in temperate zones of aquatic systems begin to increase at ambient total P concentrations exceeding 0.035 mg P/L.In warm-water systems, the values range between 0.34 and 0.70 mg P/L (22) and the associated N concentration would also range between 0.34 and 0.70 mg N/L.These represent nutrient threshold levels beyond which there will be a corresponding increase in the risk and intensity of plant-related water quality problems (23).Based on these limits (21,22), the nutrient levels obtained in the present study are exceeded in both effluents and receiving water bodies.This is due to inadequate removal of nutrients by the Alice, Dimbaza, East London and the Fort Beaufort sewage treatment works.Their respective final effluent discharges are therefore considered as main sources of phosphate in Tyume River, Tembisa Dam, Nahoon and Eastern Beach (which are part of the Indian Ocean) and Kat River respectively.

Microbiological characteristics of the wastewater samples
In general, a gradual removal of presumptive bacterial pathogens was observed in the different zones of the wastewater treatment plants.Although, there were variations with regards to both the patterns and the efficiency of each plant for the removal of the target pathogens, about 71% of the total influent samples contained presumptive Salmonella, while only 50 and 33.5% of the effluent and receiving waterbody samples were observed to contain presumptive Salmonella (Figure 4).Similar observations were made for presumptive Shigella and Vibrio pathogens with decreasing incidences of the pathogens from influents to the receiving waterbodies (Figure 4).The presence of these presumptive pathogens in the enriched cultures is indicative of the presence of at least one cell per 100 ml of the wastewater samples.Hence, the microbial qualities of the effluents in all locations exceeded the maximum safety limit for effluent discharge by the South African General and Special Standards of nil faecal coliforms/100mL.
A total of 21 culturable bacterial species were identified in the wastewater samples.The number of species isolated from specific treatment stages in all the plants ranged between 6 and 10 (Table 2), but their distribution does not appear to follow any regular pattern.However, the presence of potential pathogens such as Aeromonas hydrophila and Escherichia coli in the effluent is a cause for concern as most people in the rural Eastern Cape region use these surface waters for drinking and recreational purposes.Previous report (24) has shown that the impact of waterborne diseases in the rural Eastern Cape province of South Africa is significant as a result of drinking water sources with poor microbiological quality.The preponderance of A. hydrophila in the final effluents is an indication of the inefficiencies of the wastewater treatment plants for the removal of the presumptive pathogens, and a consequence of inadequate disinfection practices and inadequate maintenance of the infrastructure as suggested elsewhere ( 25 The four treatment plants contained high densities of both somatic and F-RNA coliphages.The densities of the somatic coliphages in the influent samples ranged between 5.6 log 10 to 6.5 log 10 pfu/100ml, being least at the East London plant and highest at the Alice plant.Treatment processes reduced the somatic coliphage densities in all treatment plants to between 3.2 log 10 and 5.5 log 10 pfu/100ml in the effluents (Figure 5), with the % reduction (log 10 ) being 28.1, 13.5, 31 and 41% for Alice, Fort Beaufort, Dimbaza and East London plants respectively.A further reduction in somatic coliphage densities was observed at all receiving waterbodies, and is probably a consequence of the dilution effect of the receiving waterbodies.It would appear that the East London plant was most efficient in the removal of somatic coliphages.

Figure 1 .Figure 2 .
Figure 1.Mean value of COD and TSS in the influent, effluent and the receiving water bodies of the individual wastewater treatment plants.

Figure 3
Figure 3 Mean values of BOD, DO, total nitrogen and phosphate in the influent, effluent and the receiving water bodies of the individual wastewater treatment plants.

Figure 4 .
Figure 4. Cumulative proportions of the wastewater samples containing different presumptive bacterial pathogens.

Table 1 .
Concentrations of free chlorine residual in the final effluents from during the sampling period (ranges and means) Samples collected between the 25th of October and 25th of November 2004 *