Simultaneous removal of carbon and nitrogen using an entrapped-mixed-microbial-cell process

An entrapped-mixed-microbial cell (EMMC) process was investigated for its simultaneous removal of carbon and nitrogen in a single reactor which was operated on alternate schedules of aerobic, anoxic and anaerobic conditions. Two different size carrier cubes, with 20-mm (large) and 10-mm (medium) sides, were studied. The synthetic wastewater, with concentrations of 250 mg/liter of (SCOD) and 26 mg/liter of NH4+ -N was used as influent substrate. At 25° ± 2°C, both (SCOD) and nitrogen could be removed simultaneously at 96 and 84%, respectively, for the medium carrier operated at the hydraulic retention time (HRT) of 9 h and the ratio of aeration to non-aeration of 1:2. For the large carrier, removal efficiencies of SCOD and nitrogen of 96 and 76%, respectively, were achieved under the operation at the HRT of 9 h and the ratio of aeration to non-aeration of 1:1. The low-temperature (10°C) effect on the EMMC process (both carriers) for nitrogen removal (about 47–50%) was larger than the carbon removal (92–94%). The economic analysis indicates that the EMMC process has comparable net present worth (NPW) comparing activated sludge system and less operation and maintenance and land requirement than the conventional biological processes for removal of carbon and nitrogen. Therefore, the EMMC process is suitable to be used for replacement and upgrading of existing wastewater treatment plants were land is strictly limited.