Advanced Wastewater 95


Employs a bed of highly permeable media such as crushed stone or plastic to which are attached microcosms for treating sewage sprayed on the media by a mechanical arm.

The conventional secondary treatment process incorporates chemically enhanced primary clarification and/or innovative biological treatment processes to increase the removal efficiency of suspended solids, BOD, and total phosphorus. Sludge production is typically increased overall as a result of the chemical enhancement of primary clarification and biological processes. Effluent concentrations of BOD5 range from 10 to 30 mg/L and processes included to remove ammonia and phosphorus in excess of effluent levels typical for secondary treatment.

Advanced wastewater treatment (AWT), or tertiary treatment, facilities are designed to achieve high rates of removal of nutrients (nitrogen or phosphorus), BOD, and suspended solids. Nitrogen removal is achieved by enhancement of the biological processes to incorporate nitrification (ammonia removal) and denitrification (nitrate removal). Phosphorus removal is accomplished by either chemical or biological processes. Addition of high doses of metal salts removes phosphorus while biological processes are dependent on the selection of high-phosphorus microorganisms. Additional removal of nutrients and organic carbon can be accomplished using processes such as high lime, granular activated carbon, and reverse osmosis. Effluent BOD5 is generally less than 10 mg/L, and total-N removal is more than 50 percent.

Note: Readers desiring more technical details about these processes should review standard engineering reference texts (e.g., Metcalf & Eddy, 1991) or technical reports on wastewater treatment (e.g., NRC, 1993). Effluent removal efficiency and effluent concentrations are taken from the 1978 USEPA Needs Survey (USEPA, 1978).

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