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

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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.
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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

Publication date: 2002-05-01

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  • Water Environment Research (WER) is published monthly, including an annual Literature Review. A subscription to WER includes access to the latest content back to 1992, as well as access to fast track articles. An individual subscription is valid for 12 months from month of purchase.

    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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