The Mitch Laboratory
RESEARCH BACK
Engineering Sustainable Wastewater Recycling
| The shortage of clean water represents a critical challenge for the next century, and has necessitated the recycling of wastewater, even for indirect potable reuse. The practice of wastewater recycling has skyrocketed in California, the desert Southwest, Texas, and Florida, the states where most Americans live. Population growth has fostered wastewater recycling projects in non-arid regions as well (e.g., the Washington, D.C. area). We seek to understand ways of engineer this process in ways to minimize harmful byproduct formation. Currently, we are focusing on two areas. |  |
Minimizing Harmful Disinfection Byproduct Formation
Despite all of the potential chemical contaminants in wastewater (hormones, pharmaceuticals, consumer personal care products), Water Factory 21, the nation's oldest indirect potable wastewater reuse plant operated without problems for 30 years until NDMA, a potent carcinogenic nitrogenous disinfection byproduct was discovered in 1999. The plant was taken offline until pending the installation of an expensive, and energy intensive UV treatment system. We seek to understand how the chemical forms so we can re-engineer the disinfection process to prevent its formation and avoid UV treatment. Click for more information.
Sustainable Reuse of Membrane Concentrates
Advanced membrane treatment systems (e.g., reverse osmosis) are becoming the treatment technique of choice for the recycling of municipal wastewater effluents for indirect potable reuse. Because a full accounting of all of the trace organics that might occur in municipal wastewater effluents is not feasible, these systems are favored because they remove a wide range of contaminants. Unfortunately, membrane treatments also generate waste brines that are currently dumped in surface waters in inland arid regions. There are increasing concerns about the effects of the concentrated contaminants in these brines on organisms in receiving waters. Because wastewater recycling is practiced in arid regions and the brines can constitute 30% of wastewater recycling plant flows, there is interest in beneficial reuse applications for the brines. Due to the elevated salt concentrations, aquaculture is one potential application, but the organic contaminants must be removed to prevent adverse impacts to fish and the consumer.
Advanced oxidation processes (AOPs) that generate highly oxidative hydroxyl radicals (OH*) have traditionally been employed to remove trace organics that might pass through membranes in wastewater recycling plants. Although less efficient than treatment of permeates, AOP treatment of brines may be more efficient and sustainable than brine disposal. The chief limitation may be scavenging of OH* by halides. Halides scavenge OH*, but in the process form halogen radicals. On the positive side, these radicals may aid in the contaminant destruction process, enhancing process efficiency. However, these radicals may also form toxic halogenated byproducts. Our research seeks to understand these tradeoffs.
Grebel, J.E.; Pignatello, J.J.; Mitch, W.A. Effect of halide ions on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes. Environ. Sci. Technol., 2010, 44, 6822-6828. (Full Text)