Start-Up and Performance Testing of a Full Scale UASB Anaerobic Wastewater Treatment Facility
Anaerobic wastewater treatment using high rate digesters, namely the upflow anaerobic sludge blanket (UASB) process, is rapidly becoming the choice of industry for organic reduction to meet governmental discharge criteria for effluent. The UASB process, developed by Lettinga and coworkers at the Agricultural University of Wageningen in The etherl lands,'.' is marketed in North America by Paques Lavalin under the registered trade name BIOPAQ. It is a two stage treatment system consisting of a preacidification (PA) tank followed by the UASB reactor. The PA tank allows for sufficient retention of incoming wastewater to ensure natural acidification. It also provides for addition of nutrients (urea for nitrogen and phosphoric acid for phosphorus) for microbial growth as well as sodium hydroxide (NaOH) for pH control. Thus, the ideal feedstock for methanogenesis (in the UASB) is provided for in the PA tank. The UASB portion of the BIOPAQ two stage process is unique in configuration from other UASB type systems. It provides maximum separation of gasliquid-solids by using a three tiered baffle system (or settler) located at the top 4.5 ft of the overall IS ft high reactor. This allows for not only maximum entrapment of the produced biogas (CH,, CO2 and H2S) but also optimizes the zone beneath the settlers for granular anaerobic sludge to occupy. Furthermore, the highly efficient settler units ensure that solids retention time (SRT) is much greater than the hydraulic retention time (HRT) thus maintaining high biomass concentrations within the bed. This is critical since anaerobic bacteria are characterized by slow growth rates.4 As a result, sufficient concentrations (3-6 ft deep at 60-80 g VS/L) must be maintained to ensure proper treatment and discourage process upsets. Many factors can, however, induce washout of the dense granular sludge bed including high total suspended solids (TSS) as well as fats, oil and grease (FOG) incoming to the UASB reactor. To minimize this, a properly functioning pretreatment stage is necessary. A full scale BIOPAQ facility is now in operation to treat effluent from a baking process. Taystee Baking Co. located in North Kansas City, Missouri, first discharged effluent to Paques Lavalin's system on July 1988. The facility consists of pretreatment using a dissolved air flotation (DAF) clarifier supplied by EIMCO followed by anaerobic treatment by the two stage BIOPAQ system. A successful start-up followed by a steady operation period was attained. Some process upsets were encountered. This chapter will summarize the operation of the facility from start-up (July 1988) to the present (April 1989).