Sunday B. Akinde, Micheal I. Nwachukwu, Young K. Umbu, Catherine C. Iwuozor
Sewage from nearshore and offshore oil production facilities in the Atlantic Ocean of the Gulf of Guinea are commonly treated in on-site WWTPs using aerobic biological and physical-chemical combined processes. This work evaluates the environmental compliance of treated sewage effluent from 3 nearshore houseboats and 3 offshore platforms WWTPs prior to discharge. ASTM, APHA and other international methods were adapted to determine pH, temperature, residual chlorine, BOD, TSS and DO while faecal coliform was enumerated using Most Probable Number (MPN) method. The evaluation made on weekly basis for 8 weeks revealed improved treated sewage effluent quality when compared with the raw sewage data and no significant variation (P>0.05) in the performance of all the WWTPs. The mean values of physico-chemical parameters of near-shore houseboats treated sewage effluent samples ranged between 0.12-0.60 mg l-1 for residual chlorine, 15.3-52.5 mg l-1 for BOD5, 53.9-62.4 mg l-1 for TSS, and 3.63-6.18 mg l-1 for DO. The average values of physicochemical parameters of offshore platforms treated sewage effluent samples ranged between 0.26- 1.39 mg l-1 for residual chlorine, 27.6-118 mg l-1 for BOD5, 77.1-243 mg l-1 for TSS and 4.82-5.55 mg l-1 for DO. Most of these magnitudes were higher than their respective specified DPR regulatory limits, which is an indication of probable cumulative anthropogenic contamination of the recipient Atlantic Ocean of the Gulf of Guinea. The mean faecal coliform range of 4.00-30.1 MPN/100 ml and 7.37-42.0 MPN/100 ml obtained for treated sewage effluent samples from nearshore houseboats and offshore platforms respectively were lower than 200 MPN/100 ml and 400 MPN/100 ml specified DPR limits for nearshore and offshore discharges. The faecal coliform results, therefore, gave an encouraging performance of the chlorination process in WWTPs with over 90% compliant to statutory DPR limits. Considering the growing volumes of sewage effluent that will be discharged into the Gulf of Guinea as a consequence of increased nearshore and offshore oil exploration and production activities, it is recommended that the WWTPs be optimally maintained and other disinfection processes such as UV radiation and nutrient removal be included. This will guarantee maximum reduction in waterborne pathogens that may pose direct hazard to public health and make the final effluent water re-usable.
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