New Solids Separation System Features Immersed Membranes

USFilter's Immersed Membrane Bioreactor system (MBR) is a single-sludge activated treatment process designed to handle liquid/solids separation on a molecular scale. This integrated immersed microfiltration system emerged from the combined expertise of two USFilter companies that specialize in advanced wastewater treatment technology: USFilter Memcor Products, with years of experience in membrane systems, and Jet Tech Products with its expertise in aeration and mixing systems.

In the MBR process, wastewater is screened before entering a tank where the biological treatment process takes place. An aeration device at the bottom of the tank dissolves air into the process fluid to mix the tank contents and provide oxygen for the biological respiration.

Because the separation process relies on submerged membranes rather than clarifiers, sludge settleability is not an issue. This allows the biological process to operate at extremely high sludge ages (typically 25-100 days) and high mixed liquor suspended solids (MLSS) concentrations (typically 10,000 - 15,000 mg/L). High MLSS concentrations promote numerous process benefits, including stable operation, complete nitrification, and reduced biosolids production.

The submerged microfiltration membranes consist of polymeric hollow fibers bound together in clusters called modules using a unique dual-potting system. By applying a low vacuum to the inside of the hollow fibers, the fully oxidized and nitrified water is pulled through the membranes and filtered. Meanwhile, mixed liquor is continuously pumped uniformly with air into each membrane module fiber bundle. The resulting flow across the membrane fibers continuously scours and cleans the membrane surface.

Organics, bacteria, and most viruses which are not oxidized by the biological process are rejected by the membrane system and retained in the mixed liquor where they are expelled from the process with the waste activated sludge.

This separation process eliminates the need for clarifiers, weirs, and return sludge pumping. Eliminating the clarification process not only eliminates the maintenance associated with these processes, but also permits a much smaller, compact footprint. Without clarifiers, sludge settleability is no longer a concern so the biological process can be optimized for maximum treatment efficiency at minimum solids production.

The MBR process is suitable for a wide range of wastewater applications. The polymeric membranes provide a physical barrier to most sanitary wastewater pathogens.

One benefit of the immersed membrane technology is the lower operating pressure that is possible because of the large amount of membrane surface area in contact with the process fluid. Controlling the membranes' environment with an efficient fluid transfer mechanism also creates a stable operating environment and is key to successful operation of the system.

A variety of equipment variations, configurations, and options can be used with the USFilter MBR system, all of which are designed to provide the necessary treatment for each wastewater project. Equipment selection is dependent on effluent requirements, ease of maintenance and operation, power consumption, future expansion, and initial capital costs.