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Final Activity Report Summary - MBR-TRAIN (Process optimisation and fouling control in membrane bioreactors for wastewater and drinking water treatment)

The scientific objective of MBR-TRAIN was to enhance process optimisation and fouling control in membrane bioreactors. MBR-TRAIN undertook dedicated efforts to characterise and investigate both biological and physico-technical aspects of this phenomenon and to develop strategies to control it.

The programme was structured in individual research projects which delivered 'training through research' to 21 fellows in total. Aiming at an improved understanding of fouling behaviour a number of full scale plants were systematically analysed by use of the Delft filtration characterisation method. This tool compared the filterability of activated sludge under standardised conditions. Measurement campaigns at European full scale and pilot membrane bioreactors (MBRs) as well as industrial plants showed good statistical correlation between measured filterability and the permeability of hollow fibre modules. The method could identify the hydraulic contact time as a relevant design parameter to assure good sludge filterability.

MBR-TRAIN also developed and assessed a new fouling indicator, which measured the transparent exopolymeric particles (TEP). It was demonstrated that the combination of this and three additional parameters was best suited to describe the fouling behaviour of MBR systems. Exploring new techniques, MBR-TRAIN applied metaproteomics for the functional characterisation of MBR biomass. A protocol to extract proteins was developed and applied to screen MBR and to monitor microbial dynamics during shock load events. Generally, the method could detect remarkable up-regulation and down-regulation of protein expression reflecting active adaptation to changing influent constituents and parameters as well as recovery behaviour.

Looking into the fate of micropollutants in MBR a comparative study found that MBRs did not exhibit remarkably better removal of pharmaceutical substances than conventional activated sludge systems when operated at realistic solid retention times (SRTs) with municipal wastewater. Further investigations concentrated on the analgesic diclofenac using radio-labelled compounds to better distinguish parent compound and degradation products. Though the substance was hardly further biodegraded in the beginning, several new metabolites were detected after one month of biomass acclimation.

In addition, various modelling activities investigated the hydrodynamics and degradation performance in MBR systems. MBR-TRAIN successfully described existing constellations in numerical models and worked towards characterisation of their behaviour. Amongst others we:

1. determined the aeration regime causing maximum shear stress at a tubular membrane
2. represented degradation processes in full-scale plants including phosphorus (P) removal effectiveness and predicted filtration performance having regard to fouling indicators and coarse air aeration requirements.

Approaches to optimise plants were practically implemented and concepts for operational improvements and cost savings were proven. MBR-TRAIN suggested for more efficient aeration and chemical dosage in full scale plants. We also tackled the operational challenges of a household MBR. Handling issues such as pH, sludge bulking and nitrification were identified as decisive for long-term stable operation within the effluent consents and without major maintenance efforts. In search for energetic more favourable configurations we investigated the feasibility of anaerobic MBR concepts for treating low loaded wastewater. The performances of suspended and granular anaerobic membrane bioreactors were compared to those of an aerobic MBR. Both anaerobic systems presented chemical oxygen demand (COD) removal of around 84 to 86 %. The energy required to control fouling compared favourably against the demand of aerobic MBRs. Modification of membranes through polyelectrolyte coating was effective in reducing fouling in short-term experiments; nevertheless under the price of reduced permeability. Moreover it changed the filtration performance of the membranes by lowering their molecular weight cut-off.

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