Microconstituents – What is a Typical Municipal Wastewater Treatment Plant Designer to Do?

Abstract

Microconstituents, emerging containments, endocrine disrupting chemicals, pharmaceuticals and personal care products (PPCPs), and other natural and manmade substances pose a new challenge to traditional municipal wastewater treatment plant designers. These various contaminants and compounds are receiving increasing attention as trace concentrations are being detected in waters worldwide. As federal and state agencies begin to consider regulatory options, municipal wastewater treatment facilities and facility designers need to develop options as typical facilities are designed for 20-30 year build-out conditions.According to the U.S. Environmental Protection Agency (EPA) published documents, "Sewage systems are not equipped for PPCP removal. Currently, there are no municipal sewage treatment plants that are engineered specifically for PPCP removal or for other unregulated contaminants. Effective removal of PPCPs from treatment plants varies based on the type of chemical and on the individual sewage treatment facilities. The risks are uncertain and the numbers of PPCPs are growing."Ongoing research suggests that existing facilities are capable of treating some microconstituents, forcing treatment plant designers looking to upgrade or expand a facility to evaluate what mechanism or technology is most effective to treat these compounds. Cost implications and reliability of treatment are inherent to this discussion. With unknown risks and the number of detected microconstituents growing, a pragmatic design approach is required.With this perspective in mind, a preliminary literature investigation was conducted with the objective of determining what is being removed in current treatment processes, the percent removal, and the technology performing the removal. The goal was to develop an approach to estimating the extent of PPCP removal to be expected based on treatment technology applied. The investigation focused on data and information available through industry organizations and research foundations. The data and information from the various sources were consolidated into a table that focused on 32 compounds and attempted to determine the mechanism/technology within the treatment train responsible for removal. The review of the data and information produced some interesting results. It was noted that there is limited work on conventional technologies. Furthermore, because a large percentage of the work to date has focused on removals across the entire treatment train, there is limited information on the performance of individual technologies. . Based on information available, the table was broken into the following technology focus areas:• Primary clarification • Activated sludge at a solids retention time (SRT) less than five days • Activated sludge at a SRT greater than five days • Membrane bioreactor