Abstract

The physicochemical characteristics of effluents from industries, wastewater treatment plants as well as stream water in Blantyre city were assessed in order to determine their impact on water quality of streams near industrial activities. The effluents and stream water at selected points were analysed for dissolved oxygen, pH, alkalinity, electrical conductivity, temperature, suspended solids, oil and grease, biochemical oxygen demand, chemical oxygen demand, chlorides, sulphates, nitrates, phosphates, and the metal ions (Ca, K, Pb, Mn, Ni, Cd, Zn, Fe, Cu, and Cr). The results showed that effluent quality discharged by the twenty eight industries in Blantyre, Malawi, varied greatly in both composition and potential to pollute the natural environment. The mean levels of sulphates, nitrates, phosphate, biochemical oxygen demand, suspended solids, electrical conductivity, alkalinity, cadmium, nickel, lead, chromium, copper, iron calcium and potassium in the industrial effluents differed significantly between the seasons (p<0.05) whereas the levels of chlorides, chemical oxygen demand, dissolved oxygen, temperature, pH, zinc, oils and grease did not differ significantly in both seasons(p>0.05). However, levels of chlorides, cadmium, copper, iron and nickel were below the public sewer discharge limits set by Blantyre City Assembly, Cape Town, Nepal, Singapore and India, while levels of chromium(56.12 mg/l), zinc (30.83mg/l), lead (2.60 mg/l), Biochemical Oxygen Demand (1570.32 mg/l), Chemical Oxygen Demand (26784.33 mg/l), oil and grease (650.00 mg/l) were observed to exceed the public sewer discharge limits in some of the industries. Assessment of efficiency of pretreatment plants in industries revealed that the overall order of efficiency of treatment plants in removing pollutants was as follows; BOD >SS, O&G> COD >Cl-> PO43-, Alkalinity> SO42->EC >NO3-. For metals the best efficiency was observed at an oil interceptor treatment system where removal percent ranged from 7.24% for manganese to 100% for Copper. In the major wastewater treatment plants being managed by the local authority the efficiency for metals varied from 0.51% for calcium to 100% for zinc and copper. Removal efficiencies for the other parameters ranged from 4.02 % for chlorides to 97.55 % for oil and grease. However, some parameters like chlorides, sulphates, phosphates, nitrates and few metals (Zn, Cu, Mn) survived the treatment systems indicating the possibility of pollutants passing through the treatment system without being reduced and some increasing in the process.v Characterization of the wastewater at the major treatment plants revealed that metals such as lead, cadmium, nickel were conspicuously absent whilst other metals were sparse. The presence of COD, BOD and suspended solids was detected in all the wastewater treatment plants. The water characteristics of streams passing through the industrial areas showed that the impairment of water quality depended on the type of industry in its vicinity and stateof sewerlines which conduits the wastewater from the source to the designated Blantyre City Assembly wastewater treatment plants. Most of the parameters such as pH, conductivity, chlorides, sulphates, temperature, Oil and grease, calcium and potassium were below the acceptable limits set by Malawi Bureau of Standards and World Health Organization for surface water meant for drinking. However the levels of phosphates, nitrates, COD, BOD and cadmium were observed to exceed the limits set by the regulatory bodies. It was generally observed that the effluents from industries in Blantyre City have a high potential of polluting the water bodies and if they are not properly managed by good wastewater treatment systems, they could result into gross impairment of water quality of streams in Blantyre City. It was therefore suggested that Blantyre city Assembly and other environmental regulatory bodies such as Environmental Affairs Department, Water Resources Board, should be more aggressive and effective in environmental monitoring, assessment and enforcement of environmental laws and regulations so as to preserve the water resource from further degradation. Further more, it is recommended that effluents from industries should be treated to acceptable levels by the industries before discharging to either rivers or sewerlines.

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School	: School of Natural and Applied Sciences
Issued Date	: 2007

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