Control of Nanomaterials Used in Chemical Mechanical Polishing/Planarization Slurries during On-site Industrial and Municipal Biological Wastewater Treatment

Nanomaterials (NM) of silica (SiO₂), cerium (CeO₂), and alumina (Al₂O₃) are used in liquid slurries by a number of industrial applications, including chemical mechanical polishing/planarization (CMP) processes used multiple times during production of computer chips. These NM are designed to be dispersed in the CMP slurries, which are used once and subsequently discharged to sewers. The global production of these three NM CMP slurry materials exceeds 5000 ton/year, placing them among the highest nanomaterial production volumes worldwide. Industrial on-site treatment of NM is not part of most discharge permits, but some semiconductor facilities apply on-site treatment for other limits related to metals (e.g., arsenic, copper), turbidity, and/or biochemical oxygen demand. This chapter characterizes commonly used CMP NM, investigates removal efficiency using a representative industrial on-site treatment strategy (chemical softening and precipitation), and off-site treatment at biological wastewater treatment plants. We also demonstrate the use of techniques to characterize NM in liquid solutions, including the ability to separate dissolved from NM forms of silica. Overall, the results provide information on a large production volume NM waste stream that has the potential to enter the environment.