REFINERY WASTEWATER TREATMENT UTILIZING THE VERTREAT™ PROCESS
Abstract: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 vertical effluent treatment system was selected for treatment of wastewater from the Chevron Canada Ltd. petroleum refinery in Burnaby, British Columbia, Canada. The process wastewater contains FOG (Free Oil and Grease), BTEX (Benzene, Toluene, Ethyl Benzene, and Xylene), MTBE (Methyl tert-Butyl Ether), NH3 (Ammonia), H2S (Hydrogen Sulphide), and other volatile organics and inorganics. The flowrate is of the order of 2650 m3/day (700,000 US GPD) with a typical BOD concentration of 250mg/l and a COD of 500mg/l. The stream fluctuates widely in flowrate, BOD, and in particular pH, as the refinery is subject to a variety of upsets.
The unit processes include secondary treatment using a vertical subsurface reactor (1.8m diameter, 105m deep), fixed-media, down-flow biofilters to remove residual suspended solids and refractory compounds, a vertical ‘U’-tube mesophilic aerobic digester placed within the reactor, and an up-flow, fixed-media biofilter to treat waste off-gas. The reactor is operating under mesophilic conditions (27-32°C [80-90°F]). The plant at Chevron occupies 697m2 (7500ft2) and operates on 56kW (75hp) at peak load. By comparison, a traditional aerobic system would require a land area of 3485m2 and consume 112kW – that is approximately five times the land space requirement and double the operating cost.
Since start-up in 1996, the performance of the system has been excellent. The plant routinely achieves an effluent having a BOD/TSS of 15/15 or better and virtually eliminates VOCs (including BTEX) and NH3 from the off-gas stream. This paper focuses upon aspects of the design specially suited to handling the broad pH and flow swings and towards mitigation of air emissions and effluent toxicity in a compact, economic and cost-effective manner.
Document Type: Research Article
Publication date: 2003-01-01
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