Drinking water denitrification using a membrane bioreactor

A membrane bioreactor (MBR) was investigated for denitrification of nitrate (NO3−) contaminated drinking water. In the MBR, NO3− contaminated water flows through the lumen of tubular microporous membranes and NO3− diffuses through the membrane pores. Denitrification takes place on the shell side of the membranes, creating a driving force for mass transfer. The microporous membranes provide a high NO3− permeability, while separating the treated water from the microbial process, reducing carryover of organic carbon and sloughed biomass to the product water. Specific objectives of this research were to develop a model for NO3− mass transfer in the MBR, investigate the effect of shell and lumen velocity on NO3− mass transfer and investigate the effects of NO3− and organic carbon loading on denitrification rate and product water quality. A mathematical model of NO3− mass transfer was developed, which fit abiotic mass transfer data well. Correlations of dimensionless parameters were found to underestimate the overall NO3− mass transfer coefficient by 30–45%. The MBR achieved over 99% NO3− removal at an influent concentration of 200 mg NO3−-N L−1. The average NO3− flux to the biomass was 6.1 g NO3−-N m−2 d−1. Low effluent turbidity was achieved; however, approximately 8% of the added methanol partitioned into the product water.