Abstract
The influence of ultrasound (US) irradiation applied for membrane fouling control of a membrane bioreactor (MBR) over the physico-chemical and biological characteristics of the activated sludge was analysed. Three parallel MBR modules coupled to a sonicator which provided US irradiation at 20, 30 and 40kHz (fixed power 0.5W/L) were evaluated. The modules were fed with activated sludge from a conventional MBR. Particle size distribution (PSD), exopolysaccharide substances, soluble microbial products, biomass concentration and kinetic and stoichiometric parameters were assessed. The combination of 2s US pulses every 3min of filtration with 1min of backwashing with 3s of coarse bubble aeration achieved good results in membrane fouling control. A slight worsening of the effluent quality was observed for the sonicated MBR modules with respect to a conventional MBR, mainly for the 20kHz module, which showed the worst transmembrane pressure control. A slight activated sludge PSD displacement towards larger sizes was observed for all frequencies, but the characteristics of the activated sludge was not significantly altered, so the worsening of the effluent quality or membrane fouling were not related to the effect of US irradiation on biomass. Alteration in the biological activity was not relevant.
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