22    START-UP AND PERFORMANCE TESTING OF A FULL
SCALE UASB ANAEROBIC WASTEWATER
TREATMENT FACILITY
Derk Z. Maat, General Manager
Shashi S. Gorur, Process Engineer
Paques Lavalin
Willowdale, Ontario
Canada, M2J 5A6
INTRODUCTION
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 Netherlands,1'3 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 gas-
liquid-solids by using a three tiered baffle system (or settler) located at the top 4.5 ft of the overall 15
ft high reactor. This allows for not only maximum entrapment of the produced biogas (CH4, C02 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).
FULL SCALE PROCESS FLOW
Taystee Baking Company's production including bread only, cake only as well as a bread and cake
run results in a wide range of discharge characteristics. From a treatment point of view, the cake only
run poses the most difficult to treat situation as high fats, oil and grease (FOG) make up the plant
effluent. Table 1 summarizes the average and maximum expected wastewater characteristics.
The discharge criteria which Taystee Baking Co. must meet is listed in Table II.
In order to reduce the high influent TSS and FOG levels, a dissolved air flotation clarifier (DAF)
supplied by EIMCO is used for pretreatment. This is followed by the BIOPAQ process. Figure 1
shows the block process flow diagram for the effluent treatment.
Tank dimensions and normal HRT are given in Table III. A PA recycle stream (anaerobically
treated wastewater is pumped back to PA) is provided to dilute (if necessary) incoming COD to the PA
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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