Removal of trace organic contaminants by submerged membrane bioreactors

Laboratory scale experiments were conducted to investigate the removal mechanisms of trace organic contaminants using a submerged MBR system. The system was equipped with a Zenon ZW-1 membrane module. Bisphenol A and sulfamethoxazole were selected as model trace organics representing endocrine disrupting chemicals (EDCs) and pharmaceutically active compounds (PhACs), respectively. Results obtained from this study demonstrate an excellent performance of MBRs regarding basic water quality parameters such as turbidity, TOC and TN. However, removal efficiency of specific trace organic contaminants was found strongly dependent on their physicochemical properties. Approximately 90% removal of bisphenol A was recorded, while under the same condition, the removal efficiency of sulfamethoxazole was only about 50%. Both biodegradation and adsorption to the sludge were thought to be responsible for the removal of bisphenol A, which is a relatively hydrophobic organic compound. In contrast, the latter mechanism was absent for sulfamethoxazole as this compound is rather hydrophilic. Results reported here indicate that it may be possible to predict the removal efficiency of trace organic contaminants by a submerged MBR system based on their physicochemical properties. This would lead to better selection of subsequent complementary treatment processes prior to indirect potable water reuse.

This study demonstrates a superior performance of MBR regarding the removal of basic water quality parameters such as turbidity, TOC and TN. QSAR analysis was found to be a useful qualitative tool for the prediction of trace organic removal. However, removal efficiency of specific trace organic contaminants was also found strongly dependent on their log KOW as well as their speciation behaviour. Approximately 90% removal of bisphenol A was recorded, while under a similar condition, the removal efficiency of sulfamethoxazole was only about 50%. Both biodegradation and adsorption to the sludge were thought to be responsible for the removal of bisphenol A, which is a relatively hydrophobic organic compound. In contrast, the latter mechanism was absent for sulfamethoxazole as this compound exists predominantly as negatively charged species under the experimental condition of this study. Results indicate that physicochemical properties of the trace organic contaminants should be taken into account when assessing their removal efficiency. Furthermore, this prediction ability would lead to better selection of subsequent complementary treatment processes prior to indirect potable water reuse.