Membranes have long been used to treat drinking water, but they are also increasingly being used to treat sewage. They can be utilised in tertiary filtration or as a pretreatment for reverse osmosis. Membrane bioreactor are used to treat wastewater and produce high-quality water that can be reused. This article examines the regulatory factors that have led to an increase in membrane usage today, various wastewater treatment applications and design factors, and the advancement of membrane technologies.


Drivers for Membrane Treatment


Restrictive effluent discharge conditions are one of many very good reasons to choose membrane treatment for wastewater. TMDLs and low effluent discharge requirements for nutrients like phosphorus are driving an increase in the prevalence of restrictive discharge limits. High-level waste water treatment is necessary under these circumstances, which membranes offer. For instance, the state of Washington’s Department of Ecology created a TMDL for the Spokane River’s dissolved oxygen levels that included one of the lowest in-stream phosphorus targets in the country—10 g/L. Combining treatment technology to 50 g/L with other phosphorus loading reductions will enable this limit to be reached.


The city of Coeur d’Alene, Idaho, where the Environmental Protection Agency set a 50 g/L effluent phosphorus limit, is also impacted by the Spokane River’s water quality conditions. All four systems were able to produce total phosphorus concentrations of less than 50 g/L during a recent pilot test of four advanced filtration technologies (including membranes) in Coeur d’Alene, but none of them could deliver effluent phosphorus as low than the 10 g/L in-stream target.


It is anticipated that future regulations will be even more onerous. The reference limits for both phosphorus and nitrogen in receiving waters are extremely low, and the EPA is prioritising a programme to establish numerical nutrient standards to reduce nutrient pollution. Membranes can be used as a pretreatment step for more sophisticated treatment techniques, like reverse osmosis, as well as a great stepping stone for future discharge requirements. Utility companies may want to build on this foundation as they develop future programmes that could involve indirect potable reuse and groundwater recharge.


Microconstituents, in addition to nutrients like nitrogen and phosphorus, have attracted widespread attention. Pharmaceuticals, cosmetics, and endocrine-disrupting chemicals are some of these substances. a Water Environment Research study According to a study by the Water Environment Research Foundation (WERF), these compounds are being eliminated through regular wastewater treatment procedures to a fair degree. However, due to increased solids capture and lengthy solids retention times (SRT) that are inherent to the membrane bioreactor (MBR) process, membrane systems typically have better removal performances.


Reuse programmes benefit greatly from the high-quality effluent that membranes produce, particularly satellite MBR installations that are positioned within the collection system. By extracting raw wastewater from the collection system and creating reuse-quality water, this distributed system can collect high-quality water close to the reuse demand.


Membrane technology’s benefit from compact facilities, particularly in the MBR format, makes membrane treatment an efficient solution for sites with limited space for facilities. Many compact treatment methods are advantageous in many rapidly expanding communities, including Coeur d’Alene, where space for treatment facilities is severely constrained.


Considerations for Design


Flux, transmembrane pressure, permeability, and recovery are the four crucial design factors to take into account when incorporating membranes into treatment plant design.


Flux, which is the filtration rate per square foot of membrane surface area, comes first. The surface area requirement and installation costs decrease as the flux design rate rises. The driving force or pressure required to push or pull the water through the membrane itself is known as transmembrane pressure (TMP). The price of maintaining the membrane rises as the transmembrane pressure does. The amount of water that passes through a membrane per square foot is what we refer to as permeability.