MICRO:

Kimberly L. Ogden and Anthony J. Muscat, ; and Leah C. Stanley, Study results demonstrate the feasibility of employing immobilized bacterial cells to remove copper from wastewater. Among the challenges of using copper chemical-mechanical planarization (Cu-CMP) for IC metallization is compliance with the environmental regulations dictating that wastewater contaminated with heavy metals be treated prior to discharge. Copper concentrations in CMP and post-CMP cleaning effluents range from 1 to 25 mg/L and must be removed from the waste stream. To date, most of the removal options involve a combination of conventional operations such as chemical precipitation/flocculation, ion exchange, micro- or ultrafiltration, and reverse osmosis. Some fabs are using calcium fluoride precipitation, coprecipitating Cu(OH) ; however, state-level sludge generation and fluoride regulations make this technique undesirable in many areas. A phase-one study from Motorola and USFilter of a three-step process comprising oxidizer removal, solids removal, and ion exchange found that this method could remove more than 95% of the copper from simulated Cu-CMP wastewater. In another study, the copper content of actual Cu-CMP effluent samples was reduced from 38 to <0.1 ppm following coagulation and microfiltration. Despite these successes, the costliness of these traditional methods has led to considerable interest in such alternative treatment techniques as immobilized microorganisms, bacteria in particular. There are several advantages to using biosorption processes for treating effluents. Microorganisms are known to have the ability to remove metal ions from water through adsorption, metabolism, and/or transport. Biomaterials also are naturally abundant and can be inexpensively produced; their rapid binding rates make it possible to process large volumes of metal-bearing wastes in a timely manner, and the high selectivity of various organisms enables the removal and recovery of specific metal ions. The commercial use of cell walls for recovering metals from wastewater has been reported on elsewhere. After describing