Pilot plant biosorption in an integrated contact-settling system: application to Cu(II) removal by anaerobically digested sludge

Surplus biological sludge can be used as a low-cost adsorbent in the remova l of heavy metal from wastewater. A three-zone contact-settling pilot plant was designed and operated to maintain continuous sludge-metal solution con tact and subsequent separation of solid-liquid phases, all in the same vess el. Mild agitation was used to ensure good contact between Cu(II) and sludg e without impairing solid-liquid separation. Heavy metal removal efficiency was largely unaffected by an increase in the Cu/sludge feed ratio as long as metal binding sites in the sludge remained unsaturated. Maximum metal up take (75 mg Cu(II) g(-1) of total solids in the sludge) was found for Cu/sl udge feed ratios greater than or equal to 90 mg Cu(II) g(-1) of total solid s. Pilot plant metal sorption uptake at different operational conditions co rrelated well. with the calculated values from batch equilibrium adsorption isotherms. The amount of Cu(II) adsorbed on sludge influenced the degree o f clarification due to the flocculating effect of Cu(II). Under operational conditions, a high degree of heavy metal removal and efficient clarificati on were achieved. Pilot plant operation at a Cu/sludge feed ratio around 90 mg Cu(II) g(-1) of total solids allowed efficient use of the biosorbent an d high heavy metal removal efficiency in addition to a good quality metal-f ree effluent in terms of low total suspended solids content. (C) 2001 Socie ty of Chemical Industry.