Anaerobic Membrane Bioreactors under Extreme Conditions

Abstract

Industrial wastewaters generated in chemical industries are often characterized by extreme conditions, such as the presence of complex, recalcitrant, and toxic aromatic compounds, high temperature, and high salinity. The mentioned conditions predominantly occur when chemical industries reduce process water use or strive for closing water loops. For wastewaters with extreme characteristics, conventional wastewater technologies have limitations. However, granular sludge-based or membrane-assisted anaerobic bio-treatment offers many advantages such as in-reactor augmentation of the required microbial species and long sludge retention times, ensuring high metabolic conversion rates per unit of reactor volume, besides low investment costs and low or negligible energy use. Frequently, auto-immobilization or stable anaerobic sludge granulation cannot be guaranteed under extreme conditions. Thus, the application of anaerobic membrane bioreactor (AnMBR) technology for pre-treating industrial wastewaters could offer an alternative solution with several advantages, such as full retention of specific and slow-growing microbial communities, effluents free of suspended solids, and system compactness. The purpose of this thesis is to investigate the applicability of the AnMBR technology for the treatment of chemical wastewater under extreme conditions by studying the impact of high and fluctuating salinity, and high temperature on the conversion of phenol. Phenol was selected as a model aromatic compound because it is commonly found in chemical wastewaters, while it is also a known inhibitor for the anaerobic conversion process. Moreover, this thesis provides additional understanding of the AnMBR operation, including assessment of membrane resistance to filtration, microbial population dynamics under the different conditions. Three laboratory-scale AnMBRs and one upflow anaerobic sludge blanket (UASB) reactor were used to carry out the experiments at varied salinity, phenol concentration and temperature. Different operating conditions were tested to determine the limitations and robustness of the AnMBR and UASB reactor configurations. The high salinity, expressed as sodium concentration, varied between 6 gNa+.L-1 and 37 g Na+.L-1. Influent phenol concentrations from 0.1 gPh.L-1 up to 5 gPh.L-1 were applied. The AnMBR operational temperature was mainly set to the mesophilic range at 35°C, but experiments were also performed in the hypermesophilic (40-45 ºC) and thermophilic (50-55 ºC) range...