Biosorption Of Lead(Ⅱ),Copper(Ⅱ)and Cadmium(Ⅱ) By Aerobic Granular Sludge

Aerobic granular sludge is a novel type of biosorbent for lead, copper, and cadmium ion removal from wastewater. Aerobic granular sludge is a by-product of the municipal wastewater treatment process, and it can serve as an abundant and cheap source for an adsorbent. On the other hand, aerobic granular sludge can be cultured by inexpensive techniques for using in the removal of heavy metals. The metal removal capacities of aerobic granules were six times higher than of activated carbon, especially the cadmium removal capacity was very high.The potential of aerobic granule sludge in removing Pb2+, Cu2+and Cd2+ions were demonstrated through a series of batch and continuous column studies.In the batch studies, the adsorption process obeys the pseudo first-order and second-order model. However, the pseudo first-order model was more suitable to describe the biosorption kinetic process accurately. Langmuir and Freundlich models were found to describe well the adsorption of heavy-metal ions on to the aerobic granule sludge. The optimum pH value for the uptake of metals on biomass was a range of4.0-5.0, and the time need for equilibrium sorption process about20-30minutes.The uptake capacity of the viable aerobic biomass was higher than that of the non-viable aerobic biomass. However, the viable biomass, if pretreated with Calcium hydroxide (Ca-biomass) showed little difference for its sorption capacities for the metal ions. The maximal uptake capacities (mmol/g DW) of Ca-biomass were0.84,0.92and1.50for Pb2+, Cu2+and Cd2+respectively.In the continuous flow, column packed studies. The sorption of heavy metals on aerobic granular sludge was shown to be highly effective and very easy for wastewater treated application. The both Thomas and New model were fitted well to describe the adsorption process of Pb2+, Cu2+and Cd2+on Ca-biomass bead column. In multi metal ion sorption systems, the affinity order of non-viable biomass for the three metals under study has been established as:Pb2+>Cu2+>Cd2+. Adsorbed metal ions can be eluted out from beads in continuous column studies by using of0.1N HC1, and the regenerated beads can be reused to adsorb metal ions again. The regenerated beads can be reused for at least four cycles of sorption.Carboxylate, amine, and phosphate functional groups present in non-viable aerobic biomass were found to be the main biosorption sites for Pb2+, Cu2+and Cd2+ions. The uptake of heavy-metal ion by non-viable aerobic biomass was followed three mechanisms, including ion-exchange, complexation and micro-precipitation. Ion exchange was identified to be the dominant mechanism for the sorption of Pb2+, Cu2+and Cd2+.