B&V Awarded Contract to Study Membrane Residuals

May 3, 2005

Black & Veatch has been awarded a contract to study the impacts of membrane treatment residuals, such as concentrate and membrane cleaning wastes, on wastewater and advanced wastewater treatment plant operations and processes.

The research project is sponsored by the Joint Water Reuse and Desalination Task Force (JWR&DTF).

In addition to the WateReuse Foundation, which is managing the project for the JWR&DTF, funding partners include the U.S. Bureau of Reclamation, California State Water Resources Control Board, Awwa Research Foundation (AwwaRF), and Water Environment Research Foundation (WERF).

Membrane processes continue to gain in popularity for potable water treatment and water reclamation applications. Microfiltration, ultrafiltration and nanofiltration effectively remove disinfectant byproduct precursors, pathogens such as Cryptosporidium, and other undesirable constituents while reverse osmosis and electrodialysis are increasingly employed to desalinate seawater and brackish water.

Also growing, however, is the quantity and percentage of residual wastes from membrane filtration and cleaning that are disposed to community wastewater systems. Concern about how these concentrated contaminants affect wastewater and advanced wastewater treatment plant operations and processes is understandably rising as well.

"We realized that multiple organizations within the water industry needed to work together to identify and mitigate the impacts of membrane process residuals on treatment processes and effluent quality," said WateReuse Foundation Director of Research Programs Jeff Mosher. "Black & Veatch assembled a team with the membrane, reuse and residuals expertise necessary to provide both in-depth understanding and big-picture solutions for this complex issue."

Francis A. DiGiano, Ph.D. (University of North Carolina) and consultant Barnes Bierck, Ph.D. join Gary Hunter of Black & Veatch as research task leaders. The team will also rely on a small group of technical advisors representing utilities, academia, and engineering/consulting.

Membrane systems generate backwash discharges that contain raw water solids, pathogens, algae and possibly chemical residues; solids and sludge created by concentrating the solids removed from the raw water flow; and spent cleaning solutions with high levels of chlorine and other cleaning chemicals in addition to most of the raw water contaminants.

Over the next 12 months, the Black & Veatch-led project team will:

+Identify the concentrations at which constituents of concern can negatively impact wastewater treatment or treatment plant facilities;

+Identify critical gaps n knowledge that currently limit the assessment of negative impacts of these residuals; and

+Recommend and develop approaches for eliminating negative impacts of membrane process residuals on wastewater treatment as well as approaches for discharging residuals to wastewater systems in planning new membrane projects.

The research team has just launched a literature review and will develop a database to identify and catalogue the negative impacts of membrane residuals on wastewater treatment facilities that have currently been documented. Density impacts that result from mixing concentrate and wastewater and salt impacts to facilities, equipment and biological processes are just some of the many issues currently under investigation.

"An increase in total dissolved solids concentration entering wastewater systems can adversely affect settling, inhibit biological treatment and increase aquatic toxicity—which in turn can limit a utility’s disposal and reuse options," said Black & Veatch Principal Investigator Alan Rimer, Ph.D. "We are excited about this opportunity to develop recommendations that will enable utilities to improve effluent quality and keep their options open."

Following the literature review, the research team will conduct interviews with six utilities that process concentrate or other waste streams with high concentrations of total dissolved solids (TDS) at their wastewater treatment plants to gain insight into issues associated with such waste streams. The team will conduct a web-based survey of membrane facilities that discharge to wastewater systems. The resulting data, which will supplement previous work done by the Bureau of Reclamation, will assist in the development and validation of a concentration impact model. The research team will ultimately prepare a guidance manual to help utilities appropriately address issues associated with the discharge of various types of membrane residuals and high TDS waters into their treatment facilities.

Source: B&V