Evaluation of the quality indices of the final effluents of two wastewater treatment plants in Buffalo City Metropolitan Municipality in the Eastern Cape Province

Abstract

Wastewaters can be sources of pollution to surface water and the environment with severe implications for public health. Most treatment plants in the Buffalo City Municipality in the Eastern Cape Province discharge their treated effluent into the surface waters which directly and indirectly impacts on the quality of surface waters in the region. The objective of this study was to determine the microbiological and physicochemical qualities of the final effluents of two wastewater treatment plants in the Buffalo City Municipality in the Eastern Cape Province of South Africa over a period of 12 months (September 2012 to August 2013). The qualities of the final effluents of WW-Ama Wastewater Treatment Plant with respect to phosphate (3.9 mg/l - 20.6 mg/l), free chlorine (0.05 mg/l - 0.71 mg/l), chemical oxygen demand (COD) (4.7 mg/l - 211 mg/l), and faecal coliform (0 - 2.92 × 104 CFU/100 ml) were not in compliance with the permissible limits set for effluent discharged to surface water by South Africa guidelines for effluent discharge. Other physicochemical parameters like biological oxygen demand (BOD) (2.2 mg/l - 9.0 mg/l), total dissolve solid (TDS) (253 mg/l - 336.3 mg/l) and turbidity (4.8 NTU - 43.20 NTU) with no SA regulatory set limits were compared to other regulatory standards and they do not comply with the limits. Also, at the second WWTP’s, the WW-Dim Treatment Plant effluent quality for free chlorine (0.06 mg/l - 7.2 mg/l), BOD (0.1 mg/l - 7.4 mg/l), and turbidity (4.02 NTU - 24.3 NTU) also did not comply. For microbiological qualities, counts of presumptive E. coli and Vibrio ranged between 0 - 2.92 × 104 CFU/100 ml and 0 - 9.93 × 103 CFU/100 ml for E. coli and Vibrio respectively at the WW-Ama plant and 0 - 1.86 × 104 CFU/100 ml for and 0 - 1.44 × 103 CFU/100 ml for E. coli and Vibrio respectively at the WW-Dim plant. About 41.7% of the samples analysed for E. coli and 16.7% for Vibrio for WW-Ama plant complied with the set limit of 1000 CFU/100 ml while 83.3% (E. coli) and 91.7% (Vibrio) of the WW-Dim samples complied in with the set limit. Also, DNA of the confirmed E. coli and Vibrio isolates were used for confirmation of their identities using species specific polymerase chain reaction (PCR) methods. About 300 confirmed E. coli and Vibrio isolates were pathotyped. The prevalence of the E. coli pathotypes were of the following orders: uropathogenic E. coli (9%), enteroaggregative E. coli (3.7%), neonatal E. coli (1.7%) and enteropathogenic E. coli (0.7%). None of the targeted Vibrio pathotypes i.e Vibrio parahaemolyticus, Vibrio fluvialis and Vibrio vulnificus were detected in either plant suggesting that the confirmed isolates are members of other Vibrio species besides those targeted. The incidences of enteric viruses in the final effluents were also investigated using real - time PCR. Target viruses included enteric viruses Adenovirus, hepatitis A virus (HAV), enterovirus, norovirus and rotavirus. Norovirus, enterovirus and hepatitis A virus were not detected in any sample from the treatment plants, while adenovirus and rotavirus were detected in all the plants with the WW-Ama plant having the highest detection rate and concentration of the viruses. The detection rate for Adenovirus was 67% for the WW-Ama Treatment Works and 17% for the WW-Dim samples; while for Rotavirus, the detection rate was 42% for WW-Ama and 17% for WW-Dim Sewage Treatment Works effluents. Antibiogram of the bacterial isolates were determined using the disk diffusion method. A total of 107 confirmed E. coli and 100 confirmed Vibrio spp. were used for this assay. Results of antibiotic sensitivity test revealed that 63.6% of the E. coli isolates were resistance to ampicillin while 49.5% were resistant to tetracycline and cephalothin. The least resistances were observed against gentamicin (3.7%) and cefotaxime (1.9%). No resistance was observed against meropenem. For the Vibrio spp, resistance was most frequently observed against tetracycline (38%) ampicillin (26%), chloramphenicol (16%), cefotaxime (14%), trimethoprim-sulfamethoxazole (13%) and the least resistance observed was against ciprofloxacin (1%). This study demonstrates that poorly treated wastewater effluent can be a source of eutrophic water with high nutrient levels and pathogenic bacteria and enteric viruses as well as antibiotic resistance determinants that could impact negatively on human health. The finding of this study also suggests that WWTPs have to be properly monitored and controlled to ensure compliance to set guidelines. This could be attained through the application of appropriate treatment processes, which will help to minimize possible dangers to public environment health.