Membrane Bioreactor MBR
it is one of the newest rapidly growing sewage treatment technologies in this industry. Ultrafiltration (UF) MBR membranes replace sedimentation, sand filtration and disinfection methods that were used in traditional methods of activated sludge (CAS) active sludge for separating suspended matter. MBR submerged modules locate in a biological tank (active sludge) or in a lateral tank, under vacuum operation, while the biomass remains behind the membrane, .Water passes through and out of the membrane and the module. MBR systems, in addition to their high output quality, occupy less space than traditional systems, and are more resistant to input shocks.
MBR technology makes a biological process with a long life of sludge (usually between 20 and 100 days) and an increase in MLSS concentration in the range of 8000-15000 mg / l. High concentrations of MLSS and high SRTs will result many benefits, including stabilizing activated sludge, full nitrification, and reducing excess sludge production. High concentration of MLSS also reduces the amount of aeration required by 30 to 50 percent compared to the traditional method.
Bioreactor:
In a wastewater treatment process, a bioreactor is specifically-designed chamber to support a biologically active environment, namely where bacteria and protozoa (the so-called biomass) can grow and consume some (or all) the substances within the raw wastewater.
They can be aerobic (to remove organic matter and oxidize ammonia to nitrate), anoxic (to remove nitrogen from nitrates to nitrogen gas) or anaerobic (to remove organic matter), depending on the presence of oxygen and nitrates or their absence. Typically, membranes are installed after aerobic or anaerobic bioreactors (respectively, the MBR and the An MBR processes).
There are three types of bioreactors:
- Suspended growth bioreactors, where the biomass grows into flocs;
- Attached growth (or biofilm) bioreactors, where the biomass grows attached to carriers;
- Hybrid bioreactors, which combines suspended and attached growth.
Membranes:
In the MBR process, membranes act as a solid-liquid separation device, keeping the biomass within the bioreactor before discharging the treated effluent to the nature. Basically, they take the place of clarifiers used in the conventional activated sludge (CAS) process.
Both micro- (MF) and ultrafiltration (UF) membranes can be used in MBR applications. Typically, UF membranes are the preferred choice because of their superior separation characteristics (thus, being able to remove some colloids and viruses as well) and lower fouling tendency (because of the smaller pore size, they have a lower risk of pore clogging).
There are three types of membrane geometries used for MBRs:
- Hollow fibre (HF)
- Flat sheet (FS)
- Tubular (or multi-tubular, MT)
Features :
- Above information is based on Inlet BOD : 300 mg/l , Outlet < 5 mg/l
- Discharge of 150 liter/person/day
Advantages:
- Smaller footprint or higher hydraulic throughput
Large clarifiers no longer are needed. A smaller often rectangular shaped chamber, fitted with the membrane cassettes replaces the secondary clarifier whose size is governed by hydraulic and solids loading. On top, because of the higher biomass concentrations that can be sustained within the bioreactors, the same total mass of solids is stored in a smaller tank, resulting in up to 50% smaller footprint.
- High-quality effluent, free of bacteria and pathogens
In comparison to the activated sludge (CAS) process, the effluent is free of suspended solids and reduced bacteria and viral content. Therefore, minimum disinfection is required.
Therefore, the MBR process easily allows the treated effluent to be discharged to sensitive receiving bodies or to be reclaimed for applications such as urban irrigation, utilities or toilet flushing. Meanwhile, it is also of high quality for feeding directly to a reverse osmosis (RO) process.
This is becoming increasingly crucial in the view of the strict effluent quality requirements imposed by local regulations taking effect during the recent years and in the near future.
- Higher automation capabilities
The operation of the MBR system can be fully automated, minimising operators intervention that are typically required for conventional treatment plants. This means that the MBR process can be easily implemented also in decentralized sites.
- High operation and capital costs (membranes)
- Membrane complexity and fouling
- Energy costs