DESIGN IMPLICATIONS AND OPERATING IMPACTS WHEN A POTW TREATS SEMICONDUCTOR CMP WASTEWATER

Chemical Mechanical Planarization (CMP) is in essence a wet grinding operation using slurries composed of uniformly sized particles of silica dioxide or other materials typically in the 0.1 to 0.2 micron range that many semiconductor facilities are incorporating into the their production systems. The slurry solids are so small that they form a stable colloidal dispersion in water that will not settle by gravity. This study focused on one silica slurry. The purpose of this study was to evaluate the impact of these colloidal silica solids on the activated sludge process. Specifically the study focused on the degradation rates for BOD and ammonia oxidation, the effect of the silica solids on primary clarifier solids capture efficiency, the settleability of MLSS, and impact on secondary effluent quality. Preliminary tests were performed on effluent sand filtration. Both batch and continuous pilot tests were performed. Batch testing was used as a screening tool to narrow the variables to be studied in the continuous pilot tests.