Occurrence and Fate of Nanoscale Particles in Water Reclamation Processes

The primary objective of wastewater treatment plants (WWTPs) is to remove contaminants composed of a complex mixture of particulate and soluble organic and inorganic constituents. However, treatment efficiency is typically measured in terms of chemical oxygen demand (COD) or biological oxygen demand (BOD) while particle characteristics are not taken into account. Currently, correlations between nanoparticle characteristics and treatment efficiency are unknown. It was hypothesized that nanoparticles not removed during primary treatment will significantly increase the energy demand of an activated sludge process and the energy footprint of tertiary processes (i.e. membrane fouling). Nanoparticle characteristics were investigated throughout the entire treatment process at two local treatment plants for an entire year and bench-scale membrane fouling experiments were conducted.;Before conducting this experiment, fractionation methods were evaluated to determine changes in particle characteristic. The results showed that optimal fractionation methods included centrifugation followed by membrane filtration. In addition, dilution experiments showed a linear relationship between the concentration of wastewater and particle count for all samples tested. Temporal analysis of particle characteristics showed that particle concentrations correlated with COD removal, indicating that nanoparticle concentrations can be analyzed for monitoring activated sludge performance. The energy burden of particles larger than 450 nm was significant but the burden of nanoscale particles (1-450 nm) was not significant. The COD contained in nanoparticles was less than 10% of the total biodegradable COD and nanoscale particle concentrations were insignificant compared to particles larger than 450nm. Thus, the energy to remove this particle fraction (1-450 nm) in secondary treatment is insignificant. Yet, the scenario shifts dramatically if these organic nanoparticles are afforded the possibility to hydrolyze hence contributing to the truly soluble COD, which is the main driver of the overall process energy footprint. Therefore, our study on the use and effectiveness of coagulant to alter the nanoparticle size distribution showed key information to maintain the organic nanoparticles in the particulate form thus curbing energy wastage. Furthermore, our membrane analysis indicated that higher nanoparticle concentrations rapidly foul tertiary microfiltration membranes, suggesting that a balance is required between secondary and tertiary processes in order to lower overall treatment energy costs.