The physico-chemical properties of sewage sludge processed for agricultural use from the Nyeri-Kangemi wastewater treatment plant, Nyeri county, Kenya

Abstract

This study was conducted to assess the physico-chemical properties and changes that occur in the composting process between raw sewage sludge inflow at the sludge tank and the composted end product in the dry beds used for agricultural application at the Nyeri-Kangemi wastewater treatment plant in Nyeri County, Kenya. Sludge samples were collected between June and October in different stages of the sludge treatment process; the sludge tank received from the primary and secondary wastewater treatment processes and the composted sludge from the dry beds. Results showed the final composted dry sludge had a pH ranging from 5.53 to 6.52. The mean values were; EC was 3.77 ± 0.05 mS/cm, TOC of 2.03 ± 0.05 per cent, ON of 0.19 ± 0.01 per cent, TOP 88 ± 1.6 mg/L, Temperature 21.03 ± 0.06 °C, particle density of 2.30 ± 0.02 g/cm³, Bulk density of 0.24 ± 0.02 g/cm³, 90.7 ± 0.01 per cent pore space, moisture content of 11.3 ± 0.70 per cent, TS of 53.40 ± 8.82 per cent and VS of 29.79 ± 9.94 per cent. The concentrations of Fe, Ca, Mg, Mn, K, Na, Zn and Cu were 1896.15 ± 106.2 mg/l, 266.42 ± 27.55 mg/l, 190.52 ± 4.82 mg/l, 139.3 ± 0.29 mg/l, 114.38 ± 4.81mg/l, 84.61 ± 0.71 mg/l, 39.18 ± 0.36 mg/l and 5.65 ± 0.12 mg/l respectively. This study recommends the need to do more research on how to improve and stabilise the physico-chemical parameters in the sludge treatment before agricultural use.