Bioavailability of trace metals in lime-mud stabilised anaerobically digested sewage sludge substrate

Abstract

On-land disposal of waste materials containing trace metals (TM) can give rise to accumulation of these potentially toxic elements in the topsoil, following adverse effects on plant growth and crop quality. Sewage sludge (SS) on-land application poses a great concern because soil acts as a transferor, and due to bioaccumulation TM can appear in a food chain (Castro et al., 2009). As terrestrial plants are the first step of food chain, it is important to have good knowledge about their capacity to accumulate toxic metals and ability to pass them on to animals and humans (Khan et al., 2010). On-site chemical immobilization of TM can be carried out by using specific additives, which tend to form with metal-ions stable, non-mobile, poorly soluble compounds. Such stabilisation techniques help to immobilize TM in the soil, so that they cannot be easily taken up by plants. Hydroxides, oxides, phosphates, carbonates, ferric salts or even industrial by-products can be used in-situ as metal immobilizing agents (Hartley et al., 2004; Paulauskas et al., 2006). Furthermore, industrial waste usage can significantly reduce the cost of the immobilization process (Kumpienė et al., 2007). The objective of the present study – to evaluate bioavailability of the selected TM (Cd, Cu, Pb and Zn) in lime-mud stabilised sewage sludge substrate by carrying out the vegetative pot experiment with romaine lettuce (Lactuca sativa). Seeking to predict mobility as well as potential bioavailability of TM in the sludge, sequential extraction procedure has been applied before/after SS anaerobic treatment.[...]