Reuse of Sludge from Wastewater Treatment Plants in Agriculture: Problem of Heavy Metals in Moshi Municipality Wastewater Treatment Plant

Abstract

Municipal wastewater treatment plants (WWTPs) have the potential to play a significant role in a circular economy by adopting the principles of reduce, reuse, and recycle (3R). While the primary goal of a WWTP is to decrease the pollution in sewage, this process also produces various potentially valuable byproducts such as treated effluent, biogas, and sludge. The challenge in recycling beneficial nutrients from sludge to agricultural soil primarily arises from the presence of heavy metals, partly due to their toxicity and environmental persistence. This study aimed to examine the concentrations of specific heavy metal contaminants (Cd, Zn, Fe, Cu, and Cr) in sludge from the Moshi municipal WWTP, which is slated for use as fertilizer. The samples underwent analysis using an Atomic Absorption Spectrophotometer (AAS). The examination of sewage sludge revealed a pH average indicating an acidic condition at 5.93 ± 1.05, while iron averaged at 53.32 ± 3.66 mg/kg and copper varied between 0.10 and 3.43 mg/kg, with an average of 1.63 ± 1.18 mg/kg. Environmental assessment involved the application of three pollution indices—Contamination Factor (CF), Index of Geo-accumulation (Igeo), and Pollution Load Index (PLI). These indices collectively confirmed the absence of contamination in the sludge regarding these elements. However, ensuring the elimination of environmental risks and evaluating potential impacts on human and animal health regarding the use of sludge from treatment plants necessitates comprehensive studies across various treatment facilities in the country, considering the chemical composition of these sludges.