The fate of heavy metals (Zn, Cu, Pb, Cd and Cr) in an integrated wastewater treatment plant: Two phase anaerobic reactor (RAP) ‐ high rate algal pond (HRAP)

Abstract

Removal of heavy metals (Zn, Cu, Pb, Cd and Cr) by an integrated wastewater treatment system, Two Phase Anaerobic Reactor (RAP) ‐ High Rate Algal Pond (HRAP), was investigated. Results indicate a good reduction of these micro‐pollutants by this system. Global elimination rates of treatment system are 80%, 87%, 38%, 60% and 63%, respectively for Zn, Cu, Pb, Cd and Cr. Primary treatment (RAP) was not involved in this reduction. Metal concentrations detected in RAP effluent are higher than those detected in raw wastewater. However, the essential metal removal was ensured by the HRAP and the two maturation ponds. Sedimentation of metals adsorbed on suspended matters is the principal factor that intervened in metal elimination by these ponds. Indeed, metal analysis of wastewater dissolved and particulate fractions showed that the majority of these cations was in particulate fraction, notably for Zn, Cu, Cd and Cr. Their distribution between these fractions evolved towards their solubilization, during the treatment. Otherwise, metal sediment analysis of different ponds showed that sludges accumulate important quantities of metals, especially in RAP sludges. Thereafter, Zn, Cu and Cd concentrations increased in HRAP sludges, but Pb and Cr contents decreased. However, in maturation pond sludges metal quantities are lower. On the other hand, metal contents in sludges are variable from upstream to downstream of each pond.