Formatted Title
Pilot-Scale Removal of Emerging Contaminants from Graywater: Overcoming the Barriers to Reuse
Background/Objectives
Water security is a growing concern with physical and economic scarcity occurring due to increased freshwater demand and lack of infrastructure investment. With greater regulatory scrutiny on water resources, micropollutants (MPs) or personal care and pharmaceutical products (PCPPs) are emerging contaminants as many of these compounds are not quantitatively removed by tertiary treatment. As many of these MPs can permeate reverse osmosis (RO), post-treatment media filtration may be required to ensure safe use or environmental discharge.
Approach/Activities
In this 10 GPM pilot study, ultrafiltration (UF) and reverse osmosis (RO) membrane technologies with ultraviolet (UV) disinfection were evaluated for the treatment of low strength graywater from shower facilities over a six-month period. With >100,000 gallons of source separated graywater treated, this is one of the largest and most comprehensive graywater treatment events to date. Although not specifically mentioned in reuse or discharge guidelines, if graywater is to be reused, the occurrence and removal of these MPs must be investigated. Sources of the detected MPs were predominantly from personal care products, flame retardants, and human waste biomarkers. In general, the system effectively removed most MPs encountered (with removal efficiencies from 31% to 82%) but RO is not an absolute barrier and MPs have proven difficult to remove in other similar treatment systems and will require additional media filtration. Although activated carbon (AC) is the leading adsorbent in the water treatment industry, graphene nanoplatelets (GNP) offer targeted opportunities to increase performance of micropollutant adsorption.
Results/Lessons Learned
While AC is limited to diffusion, surface area, and hydrophobic interactions, GNPs offer the added benefit of π-π electron donor-acceptor system as an important mechanism to selectively target micropollutants. π-π interactions are a driving force for graphene adsorption of MPs which provides significant improvements in kinetics though reduced equilibrium time. The use of GnP as a sorbent for micropollutants shows a higher sensitivity compared to commonly used GAC, suggesting its potential to use in environmental conditions with source water chemistry with background organic matter. Notably, non-selective adsorptive media remove a wide range of organic compounds present in the water being treated. Therefore, tuning the selective π-π interactions provides an alternative mechanism for MP removal that will not be negatively impacted through competitive adsorption with reduced residence times for more efficient filtration applications.