Development of filtration/biotreatment schemes to recycle CMP wastewater

Environmentally benign processing is a concept geared towards reducing the release of pollutants into the environment while maximizing the industrial recyclables. It has been demonstrated that effluents, especially at the critical chemical mechanical polishing (CMP) step in the semiconductor industry, are effectively treatable via filtration/biotreatment schemes and CMP wastes are recyclable. CMP wastes were characterized to study multiphase and multicomponent interactions and in order wastes were treated to remove copper (II) ions via biosorption and to remove abrasive nanoparticles via filtration. The treated CMP effluents not only comply with discharge requirements, but they provide the added benefit of CMP reuse in raw CMP slurry dilutions. The samples used in this study were samples prepared from raw CMP slurries diluted with ultra pure water (UPW) with/without copper, surrogate CMP samples, copper-in-UPW (Cu-UPW) samples, and the University of Arizona tool-room effluents. A protocol for characterization of the various samples was developed based on EPA and other analytical standards.;The efficiencies of two filtration/biotreatment schemes at removing copper were compared. The schemes being: filtration followed by biotreatment; and biological filtration in which the bacterium cells were grown on the filter matrix to combine filtration and biotreatment into a single step (biofilter). The results of copper-particle interactions and biosoption studies revealed that particles limit the efficiency of biosorption and, thus, the need to implement filtration/biotreatment schemes. The biotreatment studies were conducted with two bacterium strains known for biosorption of copper (II) ions: Staphylococcus Soil Y5 and Thriothiox A1. The continuous column experiments were conducted using Staphylococcus Soil Y5 grown on KaldnesRTM biocarriers in free medium to maximize bacterial biofilm surface area.;Biological filtration studies involved seeding the high efficiency depth filter with Soil Y5 bacterium and the results revealed the effectiveness of simultaneous removal of particulates and copper from the waste. It was found that approximately 86% of the copper was removed from Cu-UPW samples without nanoparticles; and the treatment of un-diluted Cu-CMP (269.23 PPM Cu) and 75% diluted Cu-CMP (201.71 PPM Cu) samples in biofilter removed more than 95% of the copper. The studies demonstrated overall the efficacy of filtration/biotreatment schemes to treat CMP wastes and reuse treated CMP effluents.