Evaluation of direct removal of nitrate with entrapped mixed microbial cell technology using ethanol as the carbon source.

Abstract

Biological denitrification from simulated contaminated groundwater using ethanol as an external carbon source was investigated with an entrapped mixed microbial cell (EMMC) system. Ethanol was used as an external carbon source to serve both as the energy source for the nitrate removal reaction and substrate for microorganisms in the system. The hydraulic retention time and chemical oxygen demand (COD)/nitrogen ratio significantly affect nitrate removal performance and, therefore, must be monitored carefully to achieve high rates of nitrate and COD removal. The effect of packing ratios of carriers in the reactor on nitrate removal performance was also investigated. The removal of nitrate and COD in reactors with various carrier packing ratios (12, 22, and 35%) is not significantly different during steady-state operation. However, the start-up periods in these three reactors are significantly different. The highest packing ratio can result in a fast removal of nitrate during the start-up periods. Results of solids retention time (SRT) analysis indicate that a long SRT in the EMMC system contributes to the stable removal of nitrate and to fast start up of the system. The increase of SRT is related to the increase in days of operation, SRT is maintained at a level of more than 200 days.