Membrane bioreactors for communal waste water
Low cost and wide variety of use
Due to improved membranes, and therefore decreased investment and operation costs, this technology is now also an attractive option for municipal systems, especially if expanding an already existing WWTPlant or if space is limited. Another important decision criterion is the cleaning capacity which could turn the balance toward membrane filtration. Especially the higher cleaning performance is an important decision criterion and can be essential to use membrane filtration systems due to the significantly lower space requirements.
An economic alternative instead of a conventional and expensive extension was searched for a planned extension of the municipal WWTPlant in St.Peter near Judenburg, Austria, due to increased regulatory requirements. The “1.municipial membrane purification plant” started operation in April 2002. The know-how of more than a decade by now shows a great potential for the application of municipal membrane activated sludge processes.
Membrane technology for retrofit
The picture shows a setting pond which is reassembled with injectors for air ventilation to pre-degrade organic materials. The core pieces of the membrane purification plant in St.Peter are the membrane aeration basin and hollow fiber membrane (pore size 0.4 µm) modules which are submerged into the existing basin. In the membrane basin, which is after the setting pond, ammonium is oxidized and the remaining organic load is eliminated.
How it works
The modules are made of a stainless steel housing in which membrane fibres are incorporated. A single membrane fibre is manufactured to a length of about 40 cm and is fixed on both ends in ABS resin. Through the application of a low pressure permeate the waste water is sucked from the modified nitrification basin through the membranes to the pure water tank. The active biomass is held back in the system completely and consequently the purification rate is significantly increased. The sludge age becomes a control parameter; it ranges from 15 to 100 days.
Reliable results & output
Furthermore the membrane filtration marks a tight and save barrier for bacteria and germs. Coarse bubble aeration from the ground of the basin makes sure that the organic material is aerobically degraded and that sludge particles are sheared off the surface of the membrane. The cleaning capacity of this plant is characteristic for the capability of membrane filtration, the COD – total degradation rate has been > 95% during operating time. The concentration of ammonium and the total concentration of phosphor of the whole process fall considerably below the regulatory limits.