Physico-chemical Characterization of Domestic Sludge of Hawassa Industry Park and evaluation of its potential use as fertilizer

Abstract

Using domestic sewage sludge on cultivated soils may increase agricultural yield in developing countries; nevertheless, the environmental damages must be properly examined and addressed before application. This research was undertaken to determine the physical and chemical characteristics of domestic sludge from Hawassa Industrial Park in Ethiopia and assess its potential applicability as organic fertilizer for crop production and hence to reduce environmental problems related to their disposal. For this purpose, five domestic sewage sludge samples were collected over five consecutive days in a week and the samples were then analyzed at the College of Agriculture soil laboratory of Hawassa University for physical and chemical properties. Descriptive statistics were conducted to describe the physico-chemical properties of the domestic sewage sludge. The results revealed that organic carbon, total nitrogen, and available phosphorus contents were higher in all domestic sludge samples than conventional organic fertilizers. The bulk density of the sludge samples was low and the water holding capacities were high. These results indicated that the domestic sludge could improve the soil's physical and chemical properties. The analyses also revealed that the sludge is slightly alkaline (pH>7.4) and with low electrical conductivity (EC, 2.06 mS/cm). The analyses of concentrations of heavy metals (Zn, Cu, Cd, Pb, Ni, and Cr) showed that concentrations in the domestic sewage sludge are below the Ethiopian standard and FAO limits. In general, the majority of the physical and chemical properties revealed that the sewage sludge is potentially suitable for use as a fertilizer. However, further research should be conducted on the effect of the sewage sludge on crop growth. Also, the biological characteristics of sludge and the content of polychlorinated byphenyls (PCB) should be studied for a solid recommendation.