Some people may have heard the term CECs, referring to Contaminants of Emerging Concern. These are chemicals, usually anthropogenic in origin, that are starting to appear in natural waters at levels approaching those that might cause issues with human and environmental health. Pesticides, hormones, and other compounds found in agricultural and personal care products are having impacts on susceptible populations, such as aquatic wildlife. Recently, the EPA has undertaken a screening of potential endocrine disrupting compounds (EDCs) to determine their risk level and make a decision on monitoring and regulation of these compounds.
In the context of drinking water, why are we worrying about contaminants that are at levels below human concern? The answer is that, in the foreseeable future, these contaminants may no longer exist at innocuous levels. Water scarcity is putting pressure on municipalities across the country to devise new methods of supplying potable water. The answer to that problem in many cases is to implement processes for water reuse. In fact, many cities already conduct a certain level of de facto water reuse as treated wastewater from upstream areas makes its way to drinking water sources. This method of reuse is considered indirect potable reuse (IPR)–the case where water enters a natural water body, such as a lake, river, or aquifer, before being extracted again for drinking water treatment. On the other side is direct potable reuse (DPR) where treated wastewater is sent directly to advanced treatment processes for the creation of potable water. While current technologies are sufficient for DPR, it receives the biggest pushback from the public.
So how are water reuse and trace contaminants related? The issue with water reuse is that the loop between water consumption, treatment, and re-consumption is getting smaller, and trace contaminants need to be removed in order to avoid buildup and concentration of contaminants. DPR processes typically involve a high rejection membrane to ensure removal of unwanted chemicals. One of the hurdles in DPR implementation is the ability to verify removal efficiency before discharge of treated water to consumer taps. IPR instead relies on dilution and bioattenuation to prevent an increase in contaminant levels. A paper entitled Direct potable reuse: A future imperative by Leverenz, Tchbanoglous, and Asano (2011) covers many of the topics related to water needs and water reuse.
In my research, I am working on a unit process employing small size activated carbon to efficiently remove these trace contaminants. If successful, this process can be added to a treatment train for lower cost removal of contaminants that are not removed in conventional treatment trains, removed inefficiently with larger size activated carbon, and/or require costly processes for removal. My research direction is to investigate how these high performing small size carbons can be removed from the finished water after treatment using microfiltration membranes. We’re making good headway and hope to be able to tell you about our published reports soon. Plus, we’ll be talking about it in a couple of presentations at the Water Quality Technology Conference (WQTC) in Salt Lake City this November.