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Membrane Bioreactors for Wastewater Treatment.
| Date post: | 10-Jan-2017 |
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Environment |
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Membrane Bioreactors for Wastewater
Treatment.
MBR is the combination of a membrane process like microfiltration or ultra filtration with a suspended growth bioreactor, and is now widely used for municipal and industrial wastewater treatment with plant sizes up to 90,000 population equivalent.
MBR(Membrane Bio Reactor) is an Advanced technology is now widely used for municipal and industrial wastewater treatment plant. Most important aspect of MBR technology is production of very high quality Treated Water consistently.
Process of MBR:
When used with domestic wastewater, MBR processes can produce effluent of high quality enough to be discharged to coastal, surface or brackish waterways or to be reclaimed for urban irrigation. Other advantages of MBRs over conventional processes include small footprint, easy retrofit and upgrade of old wastewater treatment plants.
Two MBR configurations exist: internal/submerged, where the membranes are immersed in and integral to the biological reactor; and external/ sidestream, where membranes are a separate unit process requiring an intermediate pumping step.Internal/submerged : The filtration element is installed in either the main bioreactor vessel or in a separate tank. The membranes can be flat sheet or tubular or combination of both, and can incorporate an online backwash system which reduces membrane surface fouling by pumping membrane permeate back through the membrane. External/side stream :The filtration elements are installed externally to the reactor, often in a plant room. The biomass is either pumped directly through a number of membrane modules in series and back to the bioreactor, or the biomass is pumped to a bank of modules, from which a second pump circulates the biomass through the modules in series. Cleaning and soaking of the membranes can be undertaken in place with use of an installed cleaning tank, pump and pipe work.
Sequential batch reactors (SBR) are a type of activated sludge process for the treatment of wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. Oxygen is bubbled through the mixture of wastewater and activated sludge to reduce the organic matter (measured as biochemical oxygen demand (BOD) and chemical oxygen demand (COD)). The treated effluent may be suitable for discharge to surface waters or possibly for use on land.
There are five stages in the treatment process:FillReactSettleDecantIdleThe inlet valve opens and the tank is being filled in, while mixing is provided by mechanical means (no air). This stage is also called the anoxic stage.
During the fourth stage the outlet valve opens and the clean supernatant liquor exits the tank.
The various stages in the sequence are as follows:Stage 1: FillingDuring this stage the SBR Tank is filled with the influent wastewater. In order to maintain suitable F/M (food to microorganism) ratios, the wastewater should be admitted into the tank in a rapid, controlled manner. This method functions similarly to a selector, which encourages the growth of certain microorganisms with better settling characteristics.Stage 2: ReactionThis stage involves the utilization of biochemical oxygen demand (BOD) and ammonia nitrogen, where applicable, by microorganisms. The length of the aeration period and the sludge mass determines the degree of treatment. The length of the aeration period depends on the strength of the wastewater and the degree of nitrification (conversion of the ammonia to a less toxic form of nitrate or nitrite) provided for in the treatment.
Stage 3: SettlingDuring this stage, aeration is stopped and the sludge settles leaving clear, treated effluent above the sludge blanket. Duration for settling varies from 45 to 60 minutes depending on the number of cycles per day.Stage 4: DecantingAt this stage of the process effluent is removed from the tank through the decanter, without disturbing the settled sludge.Stage 5: IdlingThe SBR Tank waits idle until it is time to commence a new cycle with the filling stage.Stage 6: Sludge Wasting Excess activated sludge is wasted periodically during the SBR operation. As with any activated sludge treatment process, sludge wasting is the main control of the effluent quality and microorganism population size. This is how the operator exerts control over the effluent quality by adjusting the mixed liquor suspended solids (MLSS) concentration and the Mean Cell Residence Time (MCRT).
