Improving Performance And Life Expectancy Of Mbr Membrane

By Author: Rohan Mehra
Total Articles: 23
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Membrane replacement is the third-largest contributor to the operating and maintenance cost of a membrane bioreactor (MBR) or ultrafiltration/microfiltration (UF/MF) plant. Membrane life is of the utmost importance to membrane technology practitioners. Budgeting for membrane replacement is a tough issue: renewing the membranes for an entire installation is a little pricier than a couple of IBCs of hypochlorite for membrane cleaning.

Just like anything else in the world, membranes get old and their performance does not remain optimal throughout their life. This manifests itself in two ways: permeability and integrity.

Permeability is defined as the flux per unit pressure. It shows how irrecoverably fouled the membranes have become- irrecoverable fouling means the membrane cannot be cleaned by mechanical or chemical processes.

Integrity refers to the extent to which the membrane has become physically damaged which impairs the rejection of key contaminants in the water. In MBRs the key contaminants that are directly rejected by the membrane are micro-organisms.

Hence, when membranes ...
... become irrecoverably fouled, it is so because colloidal and other material gets trapped in the pores or the pores themselves have collapsed. This leads to an increase in selectivity but reduces the permeability. On the other hand, with a loss of membrane integrity, selectivity decreases.

How to increase the life of a membrane?

While all membranes will degrade over time and will eventually need to be replaced, with proper care and maintenance of the MBR system, one can prevent fouling and maximize cost-effectiveness for the system as a whole by extending the life of the membrane.

One of the downsides of membrane bioreactor units is that they require quite an effort for operations and maintenance. They require a regular cleaning regimen that includes both physical cleaning and chemical cleaning. Physical cleaning removes all of the solids attached to the membrane surface, while chemical cleaning removes more tenacious substances.

Normally physical cleaning is performed by ‘backflushing’ that may be enhanced by combining air. Backflushing is done by reversing the flow back through the membrane.

Chemical cleaning uses sodium hypochlorite (NaOCl) in combination with mineral and organic acids (like citric acid). This can be done without removing the membrane from the tank. If chemical cleaning is combined with physical cleaning or backflushing, it is referred to as a ‘chemically enhanced backflush’ or CEB. CEBs are carried out routinely on a weekly or monthly basis for most membrane bioreactors for wastewater treatment plants.

Physical cleaning has several advantages over chemical cleaning like: more rapid, demanding no chemical, does not produce any chemical waste, and is less likely to degrade the membrane. However chemical cleaning may be required at some points as even after physical cleaning, there might remain a residual resistance or ‘irrecoverable fouling’ that may develop over some time and decrease the membrane life.

On the other hand, chemical cleaning aims to recover permeability and therefore requires higher reagent concentrations and longer contact times. A precise cleaning and maintenance schedule is key to increasing the lifetime of your membrane. This includes routine weekly cleanings and deep cleaning cycles a few times a year. The other methods to extend the service life of your membrane bioreactor are:

1. Effective pretreatment of material liquid

Effectively pretreating the feed liquid to improve the water quality of the membrane module inlet water will greatly affect the membrane life. Methods such as pre-flocculation, pre-filtration, or changing the pH of the solution to remove solutes that can affect the membrane negatively must be adopted.

2. Improvement of membrane materials and optimization of the membrane modules

The material of the membrane, its pore size, and the hydrophobicity of its surface all affect the rate of membrane fouling greatly. The most common materials used in an MBR membrane are polypropylene resin, polyolefin, etc.

3. Placing membrane modules appropriately

The membrane module must be properly placed. The distance between the membrane module and the wall of the aeration tank, between the membrane module and the air diffuser, the membrane module, and the liquid level of the reactor must be taken into consideration.

Final thoughts

While buying membrane bioreactors, it must be bought from one of the top membrane bioreactor manufacturers in India. Expert engineers keep making improvements in each generation of products, and designers update their techniques and methods of designing the plants so that they need less looking after.

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I have been writing informative and high-quality article on Water Treatment Plant. In the above articles have covered topics such as top membrane bioreactor manufacturers in India, membrane bioreactors for wastewater treatment, membrane bioreactor