Ultrasound-induced settleability and membrane filterability of activated sludge treating milk processing wastewater

In practice, established operation of activated sludge treatment system with high biomass concentration is restricted because of difficulty in settling the sludge in clarifiers. Membrane bioreactor is a modified form of activated sludge, and despite the superior advantages, its widespread application is restricted by the membrane fouling. Therefore, in this research, to improve the sludge sedimentation at high biomass concentration in the activated sludge system, high-frequency ultrasound (1.7MHz) was exerted in clarifier of activated sludge system and its performance was compared with a bioreactor followed by an antifouling ultrafiltration membrane. The antifouling ability of NH2-functionalized multiwall carbon nanotubes (NH2-MWCNTs)-modified nanocomposite UF membrane during filtration of mixed liquor-activated sludge was investigated. Hydraulic retention time (HRT) (8-44h) and mixed liquor suspended solids (MLSS) (6000-14,000mg/L) were chosen as the operating variables to analyze the process. The biological process showed high COD removal efficiency throughout the experiments (>96%). The membrane and high-frequency ultrasound had no effect on the system performance in terms of COD, TKN, TN, TP removal. However, the HRT and MLSS indicated an increasing impact on flux. The effect of ultrasound on the sludge properties, i.e., sludge volume index, sludge settling velocity and height of sludge at high MLSS concentration (14,000mg/L), was not considerable. It was concluded at MLSS of below 10,000mg/L, about 40% water recovery was obtained. As a result, activated sludge equipped with ultrasound showed a promising performance; however, its industrial development needs further examinations to attain the design criteria. [GRAPHICS] .