Additive-free Wastewater Treatment Method

By Annel K. Greene, PhD, Center Director
Clemson University Animal Co-Products Research and Education Center

Wastewater treatment additives currently employed in the food and rendering industries increase the difficulties in recovering proteins and quality fats. However, such industries rely on these additives for conventional methods of wastewater cleanup. New research being conducted by Clemson University Professor Dr. Scott Husson and his students is showing great promise for elimination of water treatment additives. Husson’s lab has developed a new procedure for modifying filtration membrane surfaces thereby allowing great resistance to fouling. The modified membranes resist accumulation of rejected dissolved solids, suspended solids, and other components on the membrane surface. They are designed to be used for treatment of water with high solids loading and can be cleaned using a chemical-free water rinse step.

The goal of Husson’s current project is to test membrane performance on rendering plant wastewater without addition of the additives used in conventional treatment methods. Using wastewater collected from a Valley Proteins, Inc. rendering plant in South Carolina, Husson and doctor of philosophy graduate student Daniel Wandera are measuring the productivity of the membranes. Productivity is defined as the volume of water that can be filtered per unit area of the membrane per unit of time. They also are measuring the capacity, which is the total volume of wastewater that can be processed per unit membrane area before the membrane must be cleaned. Additionally, the two are measuring the effect of the membrane on the effluent water quality by measuring chemical oxygen demand (COD), total solids, and pH.

In the first four months of the study, Husson and Wandera generated preliminary laboratory results indicating a greater than 99.8 percent reduction in rendering plant wastewater turbidity, greater than 80 percent reduction in COD, and greater than 91 percent reduction in total solids in the permeate during a five-day filtration run with no intervening cleaning steps. In the proposed project, Husson aimed to develop and optimize membrane-cleaning protocols using cold water rinsing. However, in a very promising development, the researchers have been unable to foul the membranes sufficiently during short-term testing in order to need to clean them. If fouling can be achieved in long-term tests, future work will be conducted to determine the effectiveness of cleaning by measuring the productivity recovery following the cleaning protocol, and visualizing the membrane surfaces using scanning electron microscopy. The nature of the fouling components will be studied using infrared spectroscopy. At the completion of the study, the researchers will provide a preliminary cost analysis for using the chemical additive-free membrane process versus chemical treatment using dissolved air flotation (DAF) processes.

Membrane technology is an economically competitive alternative or addition to traditional wastewater treatment technologies in a number of industries. Distinct advantages of membrane technology include high quality permeate, the possibility of total recycled water systems, small space requirements, moderate capital costs, ease of operation, and insensitivity to fluctuations in feed concentrations. Unlike DAF, membranes are used as a barrier to reject solids and allow reduced solid permeate to pass. Membrane separations thus have the advantage of not requiring added chemicals used in DAF processes. Thus, fluctuations in the feed concentration will not require process or chemical adjustments.

The chemicals currently used in DAF processes include pH adjusting agents and ferric-based compounds that can greatly enhance free fatty acid formation and quicken fat degradation. In addition, polyacrylamide is used as a coagulant agent to facilitate the separation. Polyacrylamide is a recalcitrant molecule that causes numerous problems for rendering systems, including coating of cooker surfaces and downgrading of products. Elimination of treatment chemicals and use of the membranes is expected to have cost benefits and will reduce hazardous chemical storage.

Husson’s work is oriented to modification of existing commercially available membranes. His laboratory has developed a special procedure to coat the surface of these membranes with an extremely thin polymer film that improves their resistance to fouling by organic compounds in water and allows them to be cleaned by a chemical-free water rinse step. The polymer coating is bound to the membrane by chemical reaction and does not leach off the surface.

Limiting membrane fouling will reduce energy costs for pumping and decrease the frequency of cleaning. The system allows for constant trans-membrane pressures so pumping rates can remain constant. The absence of harsh chemicals being used for cleaning the membranes means the membrane lifetime is longer than for other types of filtration systems. Approximately 50 percent of total operational costs typically include membrane filtration systems, membrane replacement, energy usage, and cleaning. Therefore, for Husson’s membranes, longer membrane life, lower energy, and simple cleaning with chemical-free water will all reduce wastewater treatment costs.

The next step of the project is to evaluate the use of nanofiltration and reverse osmosis as a final polishing stage for purifying the water in a completely additive-free, membrane-based wastewater treatment process. As anticipated, the membranes used to reduce turbidity and COD did not stop low molecular weight organic compounds or salts from passing into the water. The membranes used by Husson are designed for initial purification and not for salt rejection. A polishing step such as nanofiltration or reverse osmosis is necessary to complete the water treatment to yield clean water for direct discharge or beneficial use.

In the next phase of the study, Husson and Wandera will evaluate commercial nanofiltration and reverse osmosis membranes for final polishing of rendering wastewater to yield high purity water. The envisioned overall process would use a combination of membrane steps: ultrafiltration followed by nanofiltration or reverse osmosis. The use of membrane combinations (cascades) is common, and seawater desalination is one example where ultrafiltration followed by reverse osmosis is used in practice.

Upon completion of laboratory studies, the next phase will be scaled up for use in a plant wastewater treatment operation. If successful, this technology will eliminate the need for treatment chemicals and the many problems induced by addition of ferric-based compounds, pH adjustment compounds, and polyacrylamide for wastewater treatment to produce clean water for direct discharge or beneficial use.

Husson is a professor of chemical and biomolecular engineering and a member of the Clemson University Animal Co-Products Research and Education Center team. His research group develops advanced membranes for use in a wide variety of applications, including water purification. Husson earned his bachelor of science degree from The Pennsylvania State University and his PhD from the University of California at Berkeley in chemical engineering. He has earned a number of major awards including a National Science Foundation (NSF) Presidential Early Career Award for Scientists and Engineers (2000), an NSF New Century Scholar (2000), Byars Prize for Excellence in Teaching (2003), Clemson University Board of Trustees Award for Faculty Excellence (2001, 2004, 2009, 2011), Murray Stokely Award (2007), Fractionation Research, Inc./John G. Kunesh Award from Separations Division of the American Institute of Chemical Engineers (2010), and the Prince Award for Innovation in Teaching (2011).

Husson was co-chair of the 2009 American Membrane Society meeting and now serves on the board of directors and as treasurer of the executive committee for the organization. He also serves on the board of directors for the Separations Division of the American Institute of Chemical Engineers, and directs a NSF summer research experiences program for undergraduates on advanced functional membranes. Husson is also associate editor for the Journal of Separation Science and Technology.

June 2012 RENDER | back