New discharge permit standards require wastewater treatment facilities to achieve lower concentrations of pathogenic microbes, bacteria, and environmentally hazardous nutrients in their effluent. In order to meet these regulatory demands, some wastewater treatment plants are retrofitting their facilities with membrane separation filters. These membrane filters act as a physical barrier to suspended solids and replace the large round settling tanks used in conventional plants.

Advantages
Membrane filters remove solids by filtration rather than settling, so the clarification process is much faster than conventional treatment methods, and can operate with a much higher concentration of suspended solids and micro-organisms. This process filters a higher concentration of solids and micro-organisms and breaks down the organic matter more completely. The end result is a cleaner effluent with significantly less sludge.

Because the membranes provide much faster treatment than a conventional plant, raw wastewater does not sit as long in the equalization tank; which dramatically reduces wastewater-related odors that can emanate from the facility. In addition, membrane systems are compact offering a significant advantage when retrofitting to an existing location or in instances where space is at a premium.

How It Works
The membrane filter consists of a series of membrane "cassettes." Each cassette contains thousands of loose-hanging membrane fibers. Operators immerse the entire membrane filter into the wastewater and apply a slight vacuum to the end of each membrane cassette. This suction causes the membrane fibers to draw water through microscopic pores and into the hollow fibers. The fibers act as a physical barrier and their microscopic pores are small enough to filter out very small particles; including pathogenic microbes, bacteria, and environmentally hazardous nutrients.

Operations and Maintenance
The system operates at the touch of a button. To clean the system, operators simply reverse the operations process and force water or high-pressure air back through the fibers. This cleaning process dislodges any particles that may clog the pores or adhere to the fibers. Over time, the membranes will clog and reduce water filtration below the specified level. When this occurs, operators can clean the system with special chemicals to retain the system's optimum performance.

Cost
Thanks to advances in membrane manufacturing and a better understanding of its applications, this technology costs a fraction of what it did 10 years ago. Today, membrane filtration operates in hundreds of water and wastewater treatment facilities across North America.