Effect of toxic heavy metals at downstream irrigation of wastewater treatment plant

Abstract

For several years, domestic wastewater from Addis Ababa's seven sub-cities has been treated at Kality domestic wastewater treatment plant. Despite being designed to treat domestic waste, certain industrial wastes were discharged into the treatment plant system via point and non-point sources, causing a number of problems. The effluent from the treatment plant was primarily used for irrigation by local farmers in the Akaki-Kality sub-city. To identify and quantify heavy and toxic heavy metals in treatment plant effluent, irrigated soil, and vegetable plants, as well as to determine how they affect human health downstream, α cross- sectional study design was used. Liquid samples were collected at the Up flow Anaerobic Sludge Blanket reactor (UASB) inlet and outlet, trickling filter and secondary clarifier outlets, a soil sample from a cultivated field, and plant samples such as habesha gommen and kosta grown using the effluent. The presence and concentration of heavy and toxic heavy metals were determined in the samples, and the ability of unit processes such as the UASB, trickling filter, and secondary clarifier to remove toxic heavy metals was assessed. The laboratory tests revealed that majority of the toxic heavy metals were present in the samples analyzed (chromium, cadmium, arsenic, copper, lead, and manganese) and the unit processes were inefficient to remove these metals.