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VERTREAT™ is a high-rate activated sludge process. A compact, high-pressure reactor replaces the large open aeration basin commonly found in activated sludge systems. Vigorous mixing, high oxygen transfer, and high mixed liquor concentrations are critical design limitations in many conventional plants. The VERTREAT™ system has intensive mixing, high oxygen transfer, and high MLSS in a compact subsurface reactor, making it an efficient high-rate biological system. A VERTREAT™ system was selected for treatment of high-strength wastewater from a large dairy. The plant design consists of 3.2 million liters (850,000 gallons) of equalization capacity, two 2.75 m (9 ft) diameter 94 m (308 ft) deep bioreactors, and two rectangular flotation clarifiers. Influent is cooled to retain mesophilic conditions in the system.

During startup, 4- and 24-hour composite influent and effluent samples were collected and tested for TS, COD and pH. Highly variable loading from the dairy averaged 20,430 kg BOD5/day (45,000 lbs BOD5/day) and the flow averaged 2,320 lpm (613 gpm). These values far exceeded the design capacity of the plant, which is rated for an average load and flow of 7,300 kg BOD5/day (16,000 lbs BOD5/day) and 1,840 lpm (486 gpm), respectively. Peak 4-hour loading in the plant exceeded 25,000 lbs BOD5 – more than 5 times design. Despite BOD5 loading 3 times design, the system achieved an average BOD5 removal of 90%.

Despite an average oxygen transfer efficiency (OTE) in excess of 70% and a maximum OTE of 86% (conventional air activated sludge facilities achieve 8 – 10% OTE), oxygen was limited in the system due to the continuously overloaded conditions. With additional aeration capacity installed to design limits, the oxygen demand of the organic overload still exceeded the supply of oxygen. The flocculating ability and flotation of the microbes were invariably hampered – characteristics consistent with an ongoing organic overload.

This plant demonstrates the VERTREAT™ process is capable of treating a high-strength wastewater with a very small footprint facility. The 1,100 square meter (12,000 ft2) plant treated the BOD5 load of a 300,000 population equivalent during startup. It was demonstrated that the system has lower capital costs than competing technologies, as well as low variable and total operating costs – approximately .03 and .05 per lb BOD5 destroyed, respectively.
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Document Type: Research Article

Publication date: 01 January 2002

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