Chemical mechanical planarization (CMP) wastewater emanating from semiconductor processing contains copper (II) ions and either alumina and/or silica nanoparticles with an average size of 100 nm. The efficiency of biotreatment schemes to remove copper before water recycling or disposal is improved when the nanoparticles are removed before biotreatment. Therefore, coagulation of nanoparticles and filtration were studied in order to identify the most viable and optimal way to employ coagulants using common methodologies for wastewater treatment.

It is difficult to separate nanoparticles from CMP wastes through settling and conventional filtration. Chemical aggregation of nanoparticles was found to enhance the settling and filtration characteristics. The efficiency of five chemical coagulants was evaluated, and reagents were based on aluminum and iron salts, natural coagulant and polyelectrolytes with different electrical charge. Optimal operating conditions such as coagulant dosage, pH, type of coagulant, and sedimentation time were established. These parametric studies demonstrated the viability of coagulants to reduce the amount of particles in wastes. Over 95% turbidity reduction was achieved and less than 5 NTU (the recommended value for good quality water) was realized. Filtration characteristics of aggregated particles were also established. To realize the goal of water recycling, it was imperative to develop a rapid and efficient technology taking into account the characteristics and complexity of this waste as well as the interactions between coagulants and nanoparticles.