Acetonitrile wastewater treatment enhanced by a hybrid membrane-aerated bioreactor containing aerated and non-aerated zones.

Acetonitrile (ACN) is a very volatile, toxic and nitrogen-rich organic compound. To enhance ACN wastewater treatment, a novel hybrid membrane-aerated bioreactor (MAB) containing aerated and non-aerated zones was established. A polypropylene hollow fiber membrane module (HF) and a silicone rubber membrane module (SR) were separately used as the bubble-free aeration diffuser and the biofilm carrier, and the non-aerated zones of these two types of reactors were packed with ceramsite. When the influent ACN loading was 1.200 kg/m3·d, under aeration pressures of 20 kPa in the HF-MAB and 40 kPa in the SR-MAB, ACN removal loadings of 1.116 kg/m3·d and 1.004 kg/m3·d, respectively, were achieved, and the TN (total nitrogen) removal loadings were 0.267 kg/m3·d and 0.246 kg/m3·d, respectively. In the MABs, different stratified biofilm structures of the two zones and the diffusion and counter-diffusion of oxygen synergistically promoted ACN degradation, nitrification and denitrification.

Simultaneous p-nitrophenol and nitrogen removal in PNP wastewater treatment: Comparison of two integrated membrane-aerated bioreactor systems.

The chemical p-nitrophenol (PNP) is a priority pollutant, and PNP wastewater is highly toxic and resistant to biodegradation. The traditional physical and chemical methods (adsorption, extraction, and oxidation) for treating PNP wastewater have the disadvantages of complicated processes, high costs and secondary pollution generation. In this study, two integrated membrane-aerated bioreactor systems (RA and RB) with anoxic and aerated zones were constructed to enhance PNP biodegradation. The results showed that a helical silicone rubber membrane module displayed a high oxygen supply rate under a low membrane aeration pressure, and the hydraulic flow state of the reactor approached ideal mixing. At an influent PNP concentration of 500 mg/L, the average removal rates of PNP, chemical oxygen demand (COD) and total nitrogen (TN) reached 95.86%, 89.77%, and 94.81%, respectively, for RA and 89.48%, 74.26% and 64.78%, respectively, for RB, indicating efficient simultaneous PNP and nitrogen removal. Compared with that of RB, the pre-anoxic zone in RA not only performed detoxification pretreatment but also enhanced PNP degradation and denitrification effects, which relieved the biological treatment burden of the subsequent aerated zone. Based on these comprehensive analyses of reactor performance, the hydroquinone pathway might be the main route in the aerobic degradation of PNP.