Every community produces both liquid and solids waste and air emissions. Wastewater collected from municipalities and communities ought to be ultimately returned to receiving waters, land, or potentially reused. Wastewater contains numerous pathogenic microorganisms that dwell in the human intestinal tract. Other contaminants include biodegradable organics (measured as biochemical oxygen demand “BOD” and Chemical oxygen demand “COD”) which can lead to depletion of natural oxygen resources, nutrients (such as nitrogen and phosphorous) which can stimulate the growth of undesirable aquatic life, and may contain toxic compounds that may be mutagenic or carcinogenic. For the aforementioned reasons, the immediate removal of wastewater from its source of generation, followed by treatment, reuse, or disposal into environment is necessary to protect public health and the environment.
Membrane Bioreactor Technology
Membrane bioreactor (MBR) technology is an integration of biological treatment and membrane filtration into a single process, in which microorganisms are responsible for organic and nitrogen removal, while membranes capture biomass and suspended solids physically from the mixed liquor. The MBR process utilizes microfiltration (MF) or ultrafiltration (UF) technology ranging from 0.05 to 0.4 µm to enable complete retention of bacterial flocs and suspended solids. MF membranes are responsible for removing suspended solids, algae, protozoa, and bacteria, while UF membranes can additionally retain small colloids and viruses.
There are two main MBR process configurations: submerged or immersed (iMBR), and sidestream (sMBR). iMBRs are generally less energy intensive than sMBRs, as implementing membrane modules in a pumped sidestream crossflow significantly increases energy demand due to high pressures and volumetric flows imposed. sMBRs typically operate at higher flux and hence tend to experience higher fouling propensity (i.e., lower permeability) than iMBRs. As such, the current trend in MBR design encourages submerged over sidestream configurations.
The configuration of membrane plays a crucial role in determining the process performance. There are mainly three types of membrane configurations that are being used in MBR technologies: 1) plate-and-frame/flat sheet (FS), 2) hollow fiber (HF), and 3) multi tubular (MT). In FS membranes, the fluid flows from the membrane’s coated side towards the permeate side. In MT module, fluid flows from inside towards outside the tube (lumen to shell-side), whereas in HF configuration fluid flows from outside towards inside (shell to lumen-side).
How does a wastewater treatment plant work?
In general, wastewater treatment plants are built to treat waste water and cleanse sludge so that each could be returned to the environment. As these plants eliminate suspended solids, contaminants, and organic material from purified water, the oxygen composition is restored. These results are attained through four divisions of treatments named preliminary, primary, secondary and sludge.
The pretreatment phase involves filtering large waste materials from the water. The rate of water inflow is also monitored in order to separate organic materials such as sand, glass, and stone.
After pretreatment, the process of aeration is used to supply oxygen to bacteria for purifying and preserving the wastewater. This development allows for biodegradation, which dissolves the organic substances that contain carbon into smaller compounds to form CO2 and water.
Primary treatment consists of the usage of equipment to break down large contaminants. Afterwards, extracting these contaminants is undertaken through the use of sedimentation. Secondary treatment is usually used alongside the primary method for the purposes of further removing organic matter, and sludge that were not caught during the primary treatment process.
Chlorination dosing and UV purification systems are widely used methods to remove harmful microorganisms in water. Chlorine has gained its popularity due to its effectiveness in eradicating disease-causing bacteria. It does this by attacking the biological components of bacteria. As for UV purification, these systems depend on the intensity of the UV radiation, and the duration of time the microorganisms visible to the radiation. If the treated wastewater or reclaimed water will be used in water recreation parks, swimming pools, or for drinking applications, then a reverse osmosis or ultrafiltration system must be used as a final polisher.
How membrane bioreactor works?
A membrane bioreactor MBR utilizes a bioreactor in which microbes remove organic material, nitrogen, and suspended solids. Membranes are designed to absorb and separate biomass and suspended solids (TSS) from the water. Both of these processing steps can be made to run in succession with a reuse of some of the divided sludge to the bioreactor. Membrane bioreactors are now the preferred wastewater treatment process for municipal and industrial applications.