Features - Membrane operation

Channel clogging in membrane bioreactors

Clogging can take place within MBR module channels as a thick deposit which fills the channel (‘sludging’ or ‘localised dewatering’). Sometimes long rags or braids can develop in the tank itself which wrap around the membrane tank infrastructure (‘ragging’ or ‘braiding’). Chemical cleans are largely ineffective since they can only attack the foulants on the membrane surface, so leaving the clogged material filling the membrane channels largely unaltered. Cranfield University and Qatar University have completed work on this largely neglected research area.

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Membrane operation

The disinfection capability of MBRs: credit where credit’s due

Disinfection by MBRs. Unlike regular physical membrane filtration, virus removal by MBRs is not limited to simple size exclusion. Adsorption onto the sludge solids and the membrane cake layer (as well as the membrane itself) represent important removal mechanisms, as well as removal by predation (the feeding on the pathogens by other higher organisms).

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Membrane operation | Process biology | Water quality and treatability

The impact of biofouling on surface membrane properties in MBRs

MBR membranes are prone to fouling generally, and biofouling in particular, by organic matter originating from the microbial cells. These biofoulants vary in concentration with the activated sludge characteristics, such as the mixed liquor suspended solids (MLSS) concentration and solids retention time (SRT) (and so the food/microorganism (F/M) ratio), as well as the feedwater chemistry.

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Membrane operation | Process biology

Reducing process aeration energy consumption in MBRs

MBRs use more energy compared with classical activated sludge (CAS) because the aeration requirements are greater. Aeration is needed both for the biological and membrane tanks for degrading the organics and scouring the membrane respectively. Typically, aeration energy consumption accounts for 70–80% of total energy used for the municipal wastewater treatment process, with 40–60% consumed by the process biology.

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Membrane operation | Process biology | Feasibility, optimisation and costs

Kunming Underground MBR: a Chinese case study

China features many of the largest municipal wastewater MBRs in the world. Apart from their capacity, some also are ambitious in their construction. The below-ground installation at Kunming City, commissioned in 2012, is one such example. At an ADF (average daily flow) capacity of 150,000 m3/d and a peak daily flow of 195,000 m3/d, it is a substantial plant.

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Membrane operation | Feasibility, optimisation and costs | Pre-treatment and post-treatment | Water quality and treatability

MBR OPEX − the theory of running costs

Operational costs in MBRs are marginally higher than those of conventional activated sludge (CAS). Firstly, permeating water through a membrane demands energy. In the case of the immersed technologies (iMBRs) this means that the overall specific aeration demand (SAD) is higher, since air is needed both for maintaining the process biology in the aeration tank and scouring the immersed membrane.

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Membrane operation | Process biology | Feasibility, optimisation and costs