Membrane bioreactor

Membrane bioreactors are combinations of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. These technologies are now widely used for municipal and industrial wastewater treatment. The two basic membrane bioreactor configurations are the submerged membrane bioreactor and the side stream membrane bioreactor. In the submerged configuration, the membrane is located inside the biological reactor and submerged in the wastewater, while in a side stream membrane bioreactor, the membrane is located outside the reactor as an additional step after biological treatment.

A Membrane Bioreactor (MBR) is an advanced wastewater treatment technology that integrates biological degradation processes with membrane filtration for solid–liquid separation. In contrast to conventional activated sludge systems that rely on secondary clarifiers, MBR systems employ microfiltration or ultrafiltration membranes to retain suspended solids and biomass within the bioreactor.

This configuration allows operation at higher mixed liquor suspended solids (MLSS) concentrations and extended sludge retention times (SRT), which can enhance organic matter degradation and nitrification efficiency. The elimination of a secondary clarifier results in a smaller treatment footprint and consistently high effluent quality, making MBR systems particularly suitable for water reuse applications.

However, membrane fouling remains a critical operational challenge, influencing transmembrane pressure (TMP), energy consumption, and maintenance frequency. Fouling control strategies include air scouring, backwashing, chemical cleaning, and optimization of hydraulic retention time (HRT) and flux rates.

Due to their compact design and superior effluent quality, MBR systems are widely implemented in municipal and industrial wastewater treatment plants where stringent discharge or reuse standards apply.

Water scarcity has prompted efforts to reuse waste water once it has been properly treated, known as "water reclamation" (also called wastewater reuse, water reuse, or water recycling). Among the treatment technologies available to reclaim wastewater, membrane processes stand out for their capacity to retain solids and salts and even to disinfect water, producing water suitable for reuse in irrigation and other applications.

A semipermeable membrane is a material that allows the selective flow of certain substances. In the case of water purification or regeneration, the aim is to allow the water to flow through the membrane whilst retaining undesirable particles on the originating side. By varying the type of membrane, it is possible to get better pollutant retention of different kinds. Some of the required characteristics in a membrane for wastewater treatment are chemical and mechanical resistance for five years of operation and capacity to operate stably over a wide pH range.

There are two main types of membrane materials available on the market: organic-based polymeric membranes and ceramic membranes. Polymeric membranes are the most commonly used materials in water and wastewater treatment. In particular, polyvinylidene difluoride (PVDF) is the most prevalent material due to its long lifetime and chemical and mechanical resistance.