CP-1998-05
Entrapped mixed microbial cell process for combined secondary and tertiary wastewater treatment
Yang, P.Y., and K. Cao
An entrapped-mixed-microbial-cell process was investigated for the simultaneous removal of carbon and nitrogen in a single bioreactor with influent COD/N ratios varying from 4 to 15 and with influent alkalinity concentrations of 140 mg/l and 230 mg/l as CaCO3. The alternated schedules of the intermittent aeration was operated for two different sizes of carriers (i.e., medium carrier is 10x10x10 mm3 and large carrier is 20x20x20 mm3). It was found that the medium carrier achieved higher removal of nitrogen, COD, and BOD5 at 92%, 95%, and 97%, respectively. This was under the operation of a hydraulic retention time of 12 hours, 0.5 hour of aeration/ 2 hours of nonaeration, and a COD/N ratio of 15 in the influent. The influent alkalinity concentration of 140 and 230 mg/l as CaCO3 has minimum effect on the removal of carbon and nitrogen. However, the oxidation-reduction potential, ranging from -100 to 300 mV, provides better nitrogen removal efficiency to maintain the total nitrogen (NO–3-N, NO–2-N, and NH+4-nitrogen) at less than 10 mg/l when a COD/N ratio of 10:15 is maintained in influent. The higher ratio of COD/N in the influent performs better nitrogen removal efficiency; i.e., COD/N of 15>10>7>4. It is apparent that the EMMC process is technically feasible for the simultaneous removal of carbon and nitrogen under the operation of an alternated aeration/nonaeration schedule in a single bioreactor. Ultimately, it can replace or upgrade the existing combined secondary and tertiary wastewater treatment plant in one bioreactor and provide simple maintenance and operation.