Abstract
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 (1.7 MHz) 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) (8–44 h) and mixed liquor suspended solids (MLSS) (6000–14,000 mg/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 (14,000 mg/L), was not considerable. It was concluded at MLSS of below 10,000 mg/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.Graphical
Highlights
Over recent years, various techniques such as physical, chemical and biological methods have been employed for wastewater treatment
The bioreactor was operated with mixed liquor suspended solids (MLSS) concentrations of 6000, 10,000 and 14,000 mg/L at three Hydraulic retention time (HRT) (8, 6 and 44 h)
As clearly displayed in the figure, the bioreactor indicated a stable behavior in relation to chemical oxygen demand (COD) removal throughout the design space, which means range of variables studied in this work, i.e., MLSS and HRT
Summary
Various techniques such as physical, chemical and biological methods have been employed for wastewater treatment. Membrane bioreactors (MBRs) have recently attracted many attentions from this point of view It has been documented in the literature an MBR, known as an amendment of the CAS process, employs membrane in place of clarifier to remove sludge from the treated water; thereby, suspended solids concentration within the bioreactor can be kept at a much higher level (Visvanathan et al 2000; Rhoida Eco Services Group 1998). This technology presents several benefits in comparison with the CAS system (Cicek 2003; Matošić et al 2009). Myriad studies have been conducted to lessen the relevant problems (Ghasemi et al 2016a, b)
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