Complexation of heavy metals by extracellular polymers in the activated sludge process

TLDR

Heavy metals in industrial and domestic wastewater pose significant ecological and public health risks, necessitating their removal before discharge to protect receiving waters, especially where water reuse is common. The study aims to evaluate how wastewater treatment can help maintain surface water quality as regulatory standards become stricter. Primary sedimentation removes up to 40 % of metals, while soluble metals are subsequently retained by absorption into activated sludge biomass during biological treatment.

Abstract

Raw industrial and domestic wastewaters are likely to contain persistent anthropogenic pollutants, one group of which, the heavy metals, is particularly hazardous. Therefore, these ma terials must be removed prior to effluent discharge to reduce the potentially harmful effects to both the ecosystem of the receiving watercourse and the public health.1 Englande and Reimers2 have stressed that adequate dilution capacity of receiving waters is important to minimize the adverse effects of effluents, especially in areas where water reuse is practiced. In the U.K., during the low flow period of 1976, 40% of the River Derwent consisted of effluent, mainly from industry3; in other areas with extensive water reuse, almost 90% of surface flow could be from wastewater effluents.4 Because of the nature of wastewater treatment processes, accumulation of mineral content is inherent in water reuse2; thus, considerable environ mental concern has focused on these nonbiodegradable and toxic heavy metals.5 By whatever method water quality control standards are used, the movement to reduce and ultimately eradicate aquatic pollution is likely to require increased restrictions on the discharge of metal-laden and other effluents.6 To comply with the standards, industrial effluents could be diverted from direct discharge to sewers, which could cause treatment plant perfor mance to deteriorate but which would improve the condition of receiving water. Thus, as standards are raised, wastewater treatment will contribute significantly to the maintenance of surface water quality. Particulate and precipitated material is removed by primary sedimentation, which generally accounts for up to 40% of the initial metal load.7'8 Forms of metal entering the biological treatment stage are predominantly soluble.9 Biological removal of soluble metals is critical because their overall retention depends on absorption by the activated sludge biomass.