Heavy metals (Cr, Cd and Ni) concentrations in sewage sludge and bioaccumulation by Californian earthworms in the process of vermicomposting

Abstract

Sewage sludge treatment and utilization is an important issue for biodegradable waste management strategy. Heavy metals in sewage sludge complicates its use . One of the ways to improve characteristics of the sewage sludge and to reduce the residual concentrations of heavy metals at the same time is vermicomposting. Study of heavy metals (Chromium, Nickel and Cadmium) concentrations changes when vermicomposting sewage sludge was performed using Californian earthworms (Eisenia fetida). The bioaccumulation of these heavy metals in earthworms body tissues was studied throughout the whole vermicomposting process. For the study there were 60 kg of sewage sludge taken from the Vilnius city waste water treatment plant and 1.5 kg of Californian earthworms were inserted into it. Optimal conditions for earthworms to survive and to work (optimum temperature, moisture, pH) were maintained throughout all the time of the study. Duration of the study - 70 days, it was conducted in June - August and samples of sewage sludge and earthworms were taken every 10 days. The parametres of composting sewage sludge were monitored - total carbon, moisture, pH. Concentrations of heavy metals in sewage sludge and in body tissues of earthworms were measured using atomic absorption spectroscopy.