Microbial Removal Sewage Treatment (Manchinchi Sewage Treatment Plant in Lusaka)

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Okeowo, Nsama Priscilla
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A series of microorganisms were detected from the Manchinchi Sewage Treatment Plant in the different levels of treatment. The samples analysed were :-raw sewage, secondary clarifier sewage and the maturation ponds effluent at the point where it is discharged into the receiving water body, the Ngwerere stream. Biochemical Oxygen Demand (BOD) and other physical and chemical parameters were analysed to determine the efficacy of the treatment. In all, 300 samples were analysed for total and faecal coliforms. Since the objective of Waste Water Treatment is microbial and organic reduction, comparisons were made in the levels of coliforms and protozoa between the raw sewage and secondary clarifier; between the secondary clarifier and the final effluent; finally between the raw sewage and the final effluent. In such a treatment plant it is impossible to totally remove all microorganisms. There is however, a limit given to the number of coliforms that can be discharged into a surface water body. In this study the numbers of coliform bacteria were reduced in one instance from 170 x 106 /100ml in the raw sewage to 71 x 106 /100ml in the secondary clarifier and 2 x 106 /100ml in the final effluent. The figure in the final effluent is still slightly high. This is due to the maloperation of the plant which is currently overloaded leading to inefficiency of some functions such as the vital trickling filters. Secondly, the excessive load is diverted to the maturation ponds leading to near eutrophication and this has contributed to the high bacterial count of the final effluent. Faecal coliforms recommended to be discharged into a water body should not exceed 5000 /100ml sample. The protozoan population is not a threat as such but as the method used is not very accurate, it is likely that the actual number could be a lot higher than what has been counted. Filtration after the entire treatment process would therefore be ideal for the removal of residual protozoa.
Microorganisms Treatment--Zambia , sewage disposal plants--ordour control--Zambia , Sewage--Purification