STARTUP OF A FULL-SCALE VERTREAT? WASTEWATER TREATMENT PLANTAT A CHEESE PRODUCTION FACILITY

摘要

VERTREAT? is a high-rate activated sludge process. A compact, high-pressure reactor replacesthe large open aeration basin commonly found in activated sludge systems. Vigorous mixing,high oxygen transfer, and high mixed liquor concentrations are critical design limitations inmany conventional plants. The VERTREAT? system has intensive mixing, high oxygentransfer, and high MLSS in a compact subsurface reactor, making it an efficient high-ratebiological system. A VERTREAT? system was selected for treatment of high-strengthwastewater from a large dairy. The plant design consists of 3.2 million liters (850,000 gallons) ofequalization capacity, two 2.75 m (9 ft) diameter 94 m (308 ft) deep bioreactors, and tworectangular 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 testedfor 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 exceededthe design capacity of the plant, which is rated for an average load and flow of 7,300 kgBOD5/day (16,000 lbs BOD5/day) and 1,840 lpm (486 gpm), respectively. Peak 4-hour loadingin the plant exceeded 25,000 lbs BOD5 – more than 5 times design. Despite BOD5 loading 3times 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 of86% (conventional air activated sludge facilities achieve 8 – 10% OTE), oxygen was limited inthe system due to the continuously overloaded conditions. With additional aeration capacityinstalled to design limits, the oxygen demand of the organic overload still exceeded the supply ofoxygen. 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-strengthwastewater with a very small footprint facility. The 1,100 square meter (12,000 ft2) plant treatedthe BOD5 load of a 300,000 population equivalent during startup. It was demonstrated that thesystem has lower capital costs than competing technologies, as well as low variable and totaloperating costs – approximately $.03 and $.05 per lb BOD5 destroyed, respectively.