Pharmaceuticals Removal And Mechanism In A PAC Enhanced MBR

With the development of instrumental analysis techniques, pharmaceutical pollutants were gradually detected and drew attention due to its potential, long-term, harmful characteristics.The aim of this study are to investigate the removal efficiencies of five Pharmaceuticals from synthetic domestic wastewater under different influent pH and SRT condition in the membrane bioreactor (MBR).Batch experiments were conducted to explore the contributions of sludge adsorption and biodegradation for pharmaceuticals removal.PAC enhanced MBR was used to investigate the persistent pharmaceuticals removal efficiencies. In this process, sludge characteristics and microbial communitywerecompared with the MBR process. And the mechanism of pharmaceuticals removal in the PAC enhanced MBR were demonstrate.Notable difference of those pharmaceuticals removal efficiencies was observed, at about92.2,90.0,55.4,38.5and3.2%for acetaminophen,17β-Estradiol, naproxen, diclofenac sodium and carbamazepine, respectively. The form of pharmaceuticals exit and the electronic attraction between pharmaceuticals and sludge were influenced by influent pH. And it influented the pharmaceuticals removal. Higher removal efficiencies were obtained at the extened SRTcondition. Results of batch adsorption experiments via sterilized sludge showed that the removal efficiencies of five pharmaceuticals by sludge adsorption were7.9,68.2,60.1,40.1and71.5%, respectively, which were positively correlated with their octanol-water partition coefficients. Results of batch experiments via activated sludge showed that acetaminophen,17β-Estradiol and naproxenwere mainly achieved by biodegradation, diclofenac sodium was mainly achieved by sludge adsorption and neither sludge adsorption nor biodegradation is effective for its removal. Pharmaceuticals properties taken effect on its removal, especially, functional groups (electronic donating group/electronic withdrawing group) mainly affect their biodegradation removals.Powdered activated carbon (PAC) enhancedMBR on pharmaceuticals removal exhibited higher average removal efficiencies for carbamazepine, diclofenac sodium, naproxen and sulfamethoxazole about22%,12%,19%and14%than the one without PAC.In the PAC enhanced MBR, specific oxygen uptake rate was20%higher than the MBR, which benefit the pharmaceuticals removal.Particle size distribution was lower than the MBR which exhibit larger specific surface area and favored for pharmaceuticals removal.Soluble microbial byproducts, humic substances and aromatic protein were the main components of sludge extracellular polymeric substances (EPS). But the content and proportions of protein and polysaccharide were differentbetween the two processes. Microbial communities of the two processwere analyzed. At the beginning, the microbial species of the two systems were similar. After eight months of the operation, microbial species in both two processed increased and more pharmaceuticals biodegradation bacterium such as sulfamethoxazole biodegradation bacterium were found in the PAC-MBR process. Therefore the pharmaceuticals removal efficiencies were improved.The products of pharmaceuticals in contact with activated sludge were investigated, and results showed that the electronic donating groups are readily oxidizable functional groups. The electronic withdrawing groups break weak bonds.