Biological treatment also removes colloidal and dissolved substances from wastewater. Bacteria oxidize organic substance to carbon dioxide, build up (metabolize) biomass and attach (adsorb) matter on their surface. In addition, some bacteria eliminate the nutrients nitrogen and phosphorus under certain process conditions
A particularly efficient process for biological wastewater treatment is performed in membrane bio-reactors (MBR). Large clarifiers, needed in conventional activated sludge processes for removal and recirculation of activated sludge, are replaced by membrane filters. In this way the biomass concentration in activated sludge tanks can be increased by a factor of three to four, and much smaller tanks are sufficient for removal of the same freight. Effluent (permeate) that is drawn through the membranes is free of solids. Ultra-filtration membranes even retain all bacteria and produce a virtually pathogen-free (disinfected) effluent.
Membrane bio-reactors are preferably used where space is insufficient and the plant needs to have a small footprint and/or where effluent of exceptionally good quality is required, e.g. where it is discharged into sensitive water bodies or where it is reused as service water, e.g. for irrigation.
HUBER Vacuum Rotation Membrane VRM® Bioreactor
Our VRM® Bioreactor is a membrane filter for use in membrane bio-reactors. Its special characteristic is that flat membranes are applied on both sides of vertical plates that are arranged as a rack on a slowly rotating horizontal shaft. Scouring air is introduced along the shaft. Air bubbles rise within the gaps between the plates and remove biomass from the membrane surfaces due to the turbulence they generate. In this way we prevent formation of biomass layers on the membranes' surface, which would reduce water flux through the membranes. Rotation of the membranes through the scouring air flow provides the following advantages:
A narrow, but intensive stream of air bubbles is sufficient for reliable scouring of the membranes' surface
The scouring air is introduced with low pressure at half the water depth
Power consumption for air scouring is low
The membranes, while they rotate, are subject to swelling water pressure and are thus periodically relaxed
The need for backwashing of the membranes is avoided
The permeate quality complies with the requirements of the European Bathing Water Directive. VRM® membrane filters are certified according to California Title 22.