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Entrapped Mixed Microbial Cell Process for Combined Secondary and Tertiary Wastewater Treatment

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Abstract:

An entrapped mixed microbial cell (EMMC) process was investigated for simultaneous removal of carbon and nitrogen from a synthetic wastewater in a single bioreactor. The influent had a soluble chemical oxygen demand (SCOD)/nitrogen ratio varying from 4 to 15 and an alkalinity of 140 and 230 mg/L as calcium carbonate. An alternating schedule of intermittent aeration was used for two sizes of carriers: 10 × 10 × 10 mm3 and 20 × 20 × 20 mm3. The medium carrier (10 × 10 × 10 mm3) was found to achieve higher removals of nitrogen, chemical oxygen demand, and 5-day biochemical oxygen demand of 92, 95, and 97%, respectively. These higher removal rates occurred at a 12-hour hydraulic retention time (HRT), an aeration/nonaeration ratio of 0.5:2 hours, and an SCOD/nitrogen ratio of 15 in the influent.

Influent alkalinity concentrations of 140 and 230 mg/L as calcium carbonate were found to have minimum effect on the removal of carbon and nitrogen. However, the oxidation-reduction potential, ranging from – 100 to 400 mV (during air-off period), provides better nitrogen removal efficiency to maintain the total nitrogen (nitrate, nitrite, and ammonium) less than 10 mg/L when an SCOD/nitrogen ratio of 10 or 15 is maintained in the influent. Nitrogen removal efficiency increased with increasing ratios of SCOD/nitrogen in the influent (i.e., SCOD/nitrogen ratio of 15 > 10 > 7 > 4.0). The results of actual wastewater operation based on a study of synthetic wastewater show that organics removal efficiencies (94.6 and 94.2%) and nitrogen removal efficiencies (61.0 and 60.9%) are similar for reactors packed with medium and large carriers, respectively, when they are operated with a 9-hour HRT, an air on/air off ratio of 1 hour:2 hours and an SCOD/nitrogen ratio of 4.6.

Keywords: ALKALINITY; BIOCHEMICAL OXYGEN DEMAND REMOVAL; CELLULOSE TRIACETATE; CHEMICAL OXYGEN DEMAND REMOVAL; DISSOLVED OXYGEN; DOMESTIC WASTEWATER; ENTRAPPED CELL PROCESS; NITROGEN REMOVAL; OXIDATION-REDUCTION POTENTIAL; SECONDARY TREATMENT; SYNTHETIC WASTEWATER; TERTIARY TREATMENT

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/106143002X139947

Publication date: May 1, 2002

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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