Efficiency of Municipal Waste Water Treatment Plants in Kenya: A Case Study of Mombasa Kipevu Treatment Works

Abstract

This research study undertakes to establish the efficiency of Kipevu wastewater treatment works which is located in Mombasa County by analyzing the influent, effluent and storm water that runs adjacent to the treatment works. Sampling was done from August 2011 to February 2012. A total of thirty six samples were analyzed. The parameters studied included pH, Biological Oxygen Demand after five days (BOD5), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), oil and grease, total phosphorus, nitrates, heavy metals; chromium VI, cadmium (Cd), zinc (Zn) and Lead (Pb). Conformity to National Environmental Management Authority (NEMA) standards for wastewater and industrial effluents was determined. Results obtained were as follows: Influent and effluent pH values were 7.0 - 7.2 and 6.8 - 6.9 respectively. pH values for the storm water drain was 7.2 - 6.8. Percentage reduction efficiency of pH ranged between 4.23 and 1.43 percent. TSS concentrations for influent and effluent were 150 - 1200 mg/L and 21.8 - 1200 mg/L respectively. TSS percentage reduction efficiency ranged between 0 and 95.69. Concentrations of the storm water obtained were 24.6 - 500 mg/L. TDS concentration for the influent and effluent were 1000 - 1400 mg/L and 587 - 1117 mg/L respectively. TDS reduction efficiency ranged between 58.07 and 5.0 percent. TDS concentration in the storm water drain ranged between 670 mg/L and 2670 mg/L. The influent and effluent concentrations of BOD5 were 200 - 1200 mg/L and 85 - 260 mg/L respectively. Percentage reduction efficiency for BOD ranged between 35 and 83.33 %. Concentration of the storm water drain ranged between 50 and 300 mg/L. COD influent and effluent concentrations were 150 - 1800 mg/L and 80 - 520 mg/L respectively. Percentage reduction efficiency of COD varied between 98.89 and 5 %. Concentrations in the storm water drain were 80 - 640 mg/L. Influent and effluent concentrations for oil and grease were 79 – 331 mg/L and 39 - 117 mg/L respectively. Percentage oil and grease reduction efficiency was 12.50 - 66.67 %. Concentrations in the storm water drain ranged between 50 mg/L and nil. Influent and effluent concentrations were 7.93 - 13.46 mg/L and 11.19 - 3.59 mg/L respectively. Percentage reduction efficiency was 8.3 - 39.91 %. The storm water drain concentrations were 0.56 - 3.42 mg/L. Nitrates concentrations for the influent and effluent were 2.40 - 11.0 mg/L and 2.1 - 5.26 mg/L respectively. Percentage reduction efficiency ranged from 12.50 - 85.45. Concentrations of the storm water drain varied between 1.70 - 38 mg/L. During the period of study, Cr6+ and Cd2+ were not detected in the influent as their concentrations were below the detection limit of 0.02 mg/L. In December 2011, Pb2+ and Zn2+ had effluent concentration of 0.18 mg/L and 0.07 mg/L with reduction efficiency of 30.77 % and 97.71 % respectively. In January 2012, Pb2+ and Zn2+ had concentrations of 0.11 mg/L and 0.05 mg/L respectively with percentage reduction efficiency of 90.9 and 98.48 respectively. Pollution load for phosphorus and nitrates were 965 and 413.76 mg/s respectively. Heavy metals zinc and lead loaded 3.48 and 8.42 mg/s respectively into the Indian Ocean waters. BOD5 and COD had high pollution load of 2.27 × 104 and 3.34 × 104 mg/s respectively. The pollution loading of TSS and TDS into the ocean were 4.42 × 104 and 1.20 × 105 mg/s respectively. Oil and grease had a pollution load of 1.08 × 104 mg/s.