Heavy Metal Biosorption Efficiencies of Expanded Bed Biofilm Reactor and Sequencing Batch Biofilm Reactor

Abstract

Conventional physico-chemical processes for removing heavy metals from industrial effluents are high in chemical usage and produce large amounts of chemical sludges, which in turn needs secure disposal. Biological processes to overcome these problems have been developed for treatment of wastewaters containing heavy metals. Heavy metal biosorption efficiencies of an expanded bed biofilm reactor and a sequencing batch biofilm reactor were studied, using zinc and copper containing wastewaters. Without adding any precipitant, the processes could achieve Zn removal of 60-95 and 50-80 %, respectively for expanded bed biofilm reactor and sequencing batch biofilm reactor and Cu removal of 50-70 % by using sequencing batch biofilm reactor. Metal biorecovery carried out in this study achieved 84.5 and 82.0 % metal recovery for Cu and Zn, respectively. This shows a promising potential for bio-recovery via this low cost anaerobic process, which becomes also a means of reducing sludge volume and weight. This bio-recovery prevents discharge of metals to the environment and conserves these nonrenewable resources. The processes used were operated in continuous mode (expanded bed biofilm reactor) and sequencing mode (sequencing batch biofilm reactor). Thus the Monod growth model could be used, with biomass measured during aeration stage for the sequencing batch biofilm reactor. The kinetic parameters obtained for the processes for μ_H, K_H, d_H and Y_H are 0.230 d^-1, 482.998 mgL^-1, 0.038 day^-1 and 0.076 mg/mg for the expanded bed biofilm reactor and for sequencing batch biofilm reactor system: 0.235 d^-1, 73.190 mgL^-1, 0.008 d^-1 and 0.020 mg/mg for Zn removal and 0.092 d^-1, 284.590 mg L^-1, 0.003 d^-1 and 0.312 mg/mg for Cu removal. Compared to a conventional physico-chemical process, treatment of a cubic meter of wastewater with Zn would require about 1390 mg of chemical and would generate 1736 mg of chemical sludge. No chemical is required here and no chemical sludge is generated instead 545 mg of metal is recovered.