Membrane bioreactors see longer runs and better cleaning with Neo WaterFX.

Membrane bioreactors, or MBRs, are a wonderful wastewater treatment process that produces high quality effluent. However, traditional coagulants for phosphorus removal can cause fouling that reduces run time, requires more frequent cleaning and subsequently lowers membrane life. This reduces operational efficiency and drives up costs both for energy, clean-in-place chemicals and ultimately, membrane replacement.

Maintaining membrane permeability is vital to MBR operation.

Membranes operate using a pressure differential to drive water through the membrane from the treatment side to the effluent side, leaving biomass and pollutants behind. This transmembrane pressure, the amount of pressure (and therefore, energy) that is required to move a unit of water across the membrane, indicates the permeability of the membrane. Low transmembrane pressure indicates high permeability, and water moves easily from the treatment side to the effluent side for energy efficient treatment. High transmembrane pressure indicates low permeability, and less water is able to move across the membrane per unit of energy expended.

The treatment process can foul the membranes. Daily backwashes, with and without air sparging, are used to reduce this fouling. But eventually the transmembrane pressure becomes too high and the filters must be removed for a “clean-in-place” chemical cleaning. The length of the filter run and how much water can be treated before a clean-in-place is required are key parameters in assessing MBR efficiency.

Typically, when a membrane is returned to service following a clean-in-place cleaning, the permeability is much better than prior to the cleaning, but still less than the “new” filter permeability, meaning the transmembrane pressure required for treatment is higher than that for a new filter. Eventually the transmembrane pressure following a clean-in-place cleaning is ruled too high, the energy required for treatment is no longer cost efficient per unit of effluent produced, and the filter must be replaced.

Traditional phosphorus removal coagulants increase fouling.

Many MBR plants also have phosphorus limits that require chemical coagulants. What these plants have found is that alum and iron-based coagulants tend to increase fouling on the membranes, requiring more frequent cleaning. This, in and of itself, lowers productivity and energy efficiency as more energy is required between cleanings for treatment and the shorter filter runs remove filters for cleaning more frequently. But perhaps the most important impact of this fouling is that post clean-in-place permeability is not restored to close to new filter permeability. As the cycle continues, the filter’s life span is shortened, and the filters require replacement.

MBR plants switching to Neo WaterFX for phosphorus removal show improved performance.

Many MBR plants are switching to WaterFX for their phosphorus removal. Initial reasons are often the usual – better pH control, reduced chemical sludge production, better compliance. But what they have found is that the switch makes a big difference in membrane performance.

Longer filter runs, reduced transmembrane pressure per unit of water, better cleaning.

Switching to WaterFX reduced fouling on the membranes, allowing for longer filter run times and better cleaning from the daily backwash cycles. This greatly improved the energy efficiency of the membranes. But the most important improvement was discovered after the clean-in-place.

Following clean-in-place, the operators found that the permeability had been restored to near new membrane levels. This meant that the switch had preserved the permeability of the membranes, and this will lead to longer life and more water treatment before the membranes have to be replaced. Combined with the longer filter runs and lower transmembrane pressure for better energy efficiency, the costs of operation are measurably reduced by switching to WaterFX.

Read about a specific customer who enhanced their MBR operation by switching to WaterFX.