Effects of sewage sludge and effluents from waste water treatment plants on heavy metals movement and content in soils, crops and groundwater

Heavy metals movement in soil profiles is a major environmental concern because even slow transport through the soil may eventually lead to the ground water contamination accumulation in soils and uptake by plants. The use of sewage sludge and effluents from waste water treatment plants for irrigation of agricultural lands is on the rise particularly in peri-urban areas of developing countries. Comprehensive research has been done to assess the long term effect of sewage irrigation on heavy metal content in soils, plants and groundwater. For this purpose, sewage effluents, groundwater, soil and plants samples were collected and analyzed mainly for metal contents and nutrients. Results indicated that sewage effluents contained much higher amount of P, Zn, Cu, Fe, Mn and Ni compared to ground water, but variation of Pb and Cd concentration in the two sources of water were within the permissible limits for its use as irrigation water. Soils receiving sewage irrigation for 10 years exhibited significant increases in Zn, Fe, Ni and Pb. The need for further investigation of the potential for water contamination from nitrogenous components and possible mechanisms to reduce the degradation potential of N is addressed. Acritical examination of fate of N, viruses, and fecal bacterial introduced into soils via application of sewage sludge and wastewater treatment plant effluents should be a priority research initiative. Heavy application s of liquid - Digested sludge on three types of soils showed an increased soil organic matter to a depth of 90 cm and forming acids, that lowered the soil pH, extractable Fe and Al increased to the 90 cm depth. Extractable Cu remained in top 30 cm and Zn in the top 90cm of the soil profile. Phosphorous (P) was significantly increased by sludge application and accumulated largely in the surface soil.