Membrane filtration is widely used in the treatment of water and wastewater, because it is more efficient and effective than conventional water treatment technologies.
The four primary membrane processes are microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). The separation ranges of these membranes are as follows: The range is 100–1000 nm for MF, 5-100 nm for UF, 1–5 nm for NF, and 0.1–1 nm for RO. Let’s understand more about the benefits of MBR technology for water and wastewater treatment.
Benefits of MBR technology for water and wastewater treatment
The advantages of membrane bioreactors over alternative wastewater treatment systems, are generally regarded to include:
· HRT and SRT are controlled separately
· High-quality effluent
· A minimal environmental impact
· Improved bio-treatment
1: HRT and SRT are controlled separately
The bioreactor's full containment of the biological solids, mixed liquid or sludge, makes it possible to manage the solids retention time (SRT) separately, from the hydraulic retention time (HRT). The flocculant solids (also known as "flocs"), which are essentially biomass in the conventional activated sludge process, must be allowed to develop in size until they can be sorted out in the secondary clarifier.
The HRT and SRT are thus linked in CAS; when the HRT rises, the flocs must expand, which then raises their settleability.
2: High-grade effluent
The treated effluent has a very high purity and a substantially lower pathogen concentration, compared to the conventional activated sludge procedure since the membrane pores of the MBR are much smaller.
The effluent is of a high enough standard to be released into bodies of water, or used for purposes like urban irrigation or toilet flushing. Additionally, it can be fed straight into a reverse osmosis system, to produce a permeate with even better water quality.
3: A minimal footprint
Due to CAS's high HRT, a greater plant size is needed. The footprint is lower in MBRs because the same total mass of solids is stored in a smaller container, due to greater concentrations being achieved.
4: Improved biotreatment
Since, nitrifiers and other slower-growing microorganisms are encouraged to proliferate, MBRs with higher SRT tend to give superior overall bio-treatment. Because of this, MBRs are particularly good at biologically removing ammonia, also known as "nitrification".
What drawbacks are there to MBRs?
The operating process complexity and expense are the main drawbacks of an MBR system. The price of the membrane has a significant impact on both the flow of membrane life, and the rate of membrane air scour energy.
In general, the following factors have a significant impact on MBR:
Net permeate flux (product flow/unit area), accounting for downtime and the use of product water for membrane cleaning, membrane cost/m2 membrane surface area, and membrane specific aeration demand in Nm3/m2
The difference between conventional activated sludge (CAS), and the Membrane Bioreactor (MBR) technologies
The following may be required by CAS in order to produce effluent with water quality, comparable to that of the MBR:
1: Increased chemical dosing to achieve high phosphorus (P) concentration post-treatment, with either a multi-media filter (MMF) or ultrafiltration/microfiltration (UF/MF), to achieve a comparable treated water quality to the MBR, with reference to suspended solids (SS) and microorganism concentration.
2: Increased tank sizes and therefore a large sized land area for extended HRT.
3: The amount of space available will determine whether current plants may be retrofitted with an MBR. This enables raising the flow capacity or enhancing the treated water quality, albeit at a cost to energy.
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