Evaluation of additives for fouling reduction in MBRs
Traditional methods to limit fouling in membrane bioreactors (MBRs) are low flux operation and both, physical and chemical cleanings. An alternative strategy is the addition of fouling reducers. These are additives which modify the mixed liquor through mechanisms like adsorption, coagulation and flocculation.
Within AquaFit4Use activities, Eight products were selected: powdered activated carbon (PAC), 2 natural polymers starch and chitosan, ferric iron, 2 cationic polymers MPE50 and Adifloc KD452, and 2 novel synthetic flocculants provided by BASF (X1 and X2).
Batch experiments showed that the 4 synthetic polymers had a positive effect and high effectiveness on mixed liquor filterability. Both the reversible and the irreversible fouling propensity significantly decreased. PAC had no effect on reversible fouling, but decreased the irreversible fouling potential. This effect increased with increasing PAC dosage. The ferric salt had limited effect on the measured fouling indicators, while the natural polymers had adverse effects on irreversible fouling. The combination of PAC with MPE50 did not result in a much better performance than the sole use of MPE50.
The beneficial effects of MPE50 and X2 increased with increasing dosage. Since X2 exerted similar effects as MPE50 at lower dosage, this flocculant was selected as the most effective fouling reducer and further evaluated in a continuous MBR test. Two lab-scale MBRs were operated in parallel on BASF wastewater. After an acclimatization period, additive dosage was initiated in one of the MBRs, while the other one served as reference. The additive dosage was adapted to the (ir)reversible fouling potential measured by the MBR-VFM (VITO Fouling Measurement). X2 dosing had no adverse effects on biological reactor performance. It decreased both reversible and irreversible fouling, which corresponds to the results of the batch experiments. X2 dosing resulted in a significantly higher floc size and lower soluble foulant concentrations compared to the reference MBR.
Do you know that ...
• The impact of additives on mixed liquor can be measured in various complementary ways ranging from floc size determinations to soluble foulant measurements (extracellular polymeric substances, total organic carbon, UVA, ..), to fouling indicators (Time-to-filter, Capillary Suction Time, MBR-VFM, ..)?
• The MBR-VFM showed to be best suited for fouling monitoring in the continuous experiments because permeability was lowest at high reversible VFM values and showed the sharpest decline at high irreversible VFM values?
• Additives are usually dosed when upsets in fouling behaviour occur, instead of continuous dosing?
Heleen De Wever (VITO)
Based on internal report I5.2.1.4- Evaluating the use of additives for reduced fouling in MBRs
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