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A total of 330 wastewater treatment plants located in the northwestern United States responded to a survey about their treatment processes. Exemplary facilities of the top four processes being used were asked to complete more detailed questionnaires about plant operations. Process descriptions are provided along with a brief discussion of unique features of each exemplary facility.

Operating data is quantified so that the advantages and disadvantages of lagoons, oxidation ditches, sequential batch reactors, and selector activated sludge can be determined. Issues such as land area, effluent quality, electrical power, labor, operating cost, sludge processing, and capital cost for construction are compared.

Partially aerated lagoons have the advantage of ease of operation and reduced sludge production. Oxidation ditches provide simple, stable operation that may result in excellent quality. Selector activated sludge can also achieve excellent effluent quality and may provide the greatest flexibility. Sequential batch reactors eliminate the need for both primary and secondary clarifiers.

Noted disadvantages for lagoons include large land requirements and poor effluent quality if advanced treatment is not included at the facility. Energy efficiency and ammonia removal may not be optimized with oxidation ditches. Selector activated sludge may require greater operator control and laboratory testing. Finally, sequential batch reactors need large aeration basins and have more complex controls than alternative technologies.

Document Type: Research Article


Publication date: January 1, 2002

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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