Coors brewery in Virginia expands low-rate anaerobic treatment system

By Shannon Grant and Robert Landine, ADI Systems Inc., and Albert Cocci, Paques ADI Inc.

Paques ADI Inc. recently constructed a second patented ADI-BVF^® anaerobic reactor at Coors’ Shenandoah Brewery in Virginia, US, on a design/build contract basis, with start-up and commissioning occurring in October, 2001. The first BVF reactor was constructed there in 1995. The decision to build another reactor was based on the expansion of the Coors production facility and the excellent performance of the original reactor.

The Coors Brewing Company’s Virginia facility is located between the beautiful Blue Ridge Mountains and the Shenandoah River, near the Shenandoah National Park. Treated wastewater from the plant is discharged directly into the environmentally sensitive South Fork of the Shenandoah River. The area is considered as Class I pristine for environmental permitting conditions.

Initially, the wastewater at this facility was treated directly with a conventional high-rate activated sludge system, which was started up in 1987. As is the case with many brewery wastewaters high in carbohydrates, but low in nutrients, direct treatment with activated sludge is problematic and sensitive to load changes. Treating this type of wastewater directly with an activated sludge type system is highly susceptible to filamentous bacterial growth.

Operators were continually challenged to keep the system sufficiently fine-tuned to meet effluent limits. Operating costs for energy use, chemical addition and sludge handling/dewatering were substantial. At that time there was also a concern for emission of volatile organic compounds (VOCs), which prevented further facility expansion.

Coors’ personnel undertook an analysis of the market place in the late 1980s and early 1990s to look for an appropriate technology to enhance the performance of the waste treatment system, reduce operating costs, and reduce VOC emissions. Various anaerobic and trickling filter technologies were investigated.

In the early 1990s, Coors entered into an agreement with ADI Systems Inc. to conduct a preliminary bench-scale pilot study of the anaerobic BVF reactor system to prove its adequacy in treating the Shenandoah facility’s wastewater. The low-rate BVF reactor offered the advantages of lower temperature operation, digestion of waste activated sludge (WAS), greater flow and load equalization, and easier procurement of seed sludge over high-rate anaerobic systems. Additional land use was not a significant factor in the decision. The pilot was successful and consistently achieved good removals, with an average of 87% COD removal at an operating temperature of 2°C.

ADI Systems was contracted in 1994 to design and build a 22,700 m³ capacity BVF reactor to treat the brewery wastewater at a design flow and BOD loading of 2,840 mVd and 6,400 kg/d, respectively. The reactor was also designed to digest the sludge produced in the existing activated sludge unit.

The original BVF reactor has performed very well. The improvement in the final effluent characteristics, and reduction in sludge generation, energy use, chemical addition, and operating costs have been significant (Heidt and Burke, 1996). Waste sludge yield has been so low in fact that Coors has not had to waste any biological sludge (anaerobic or aerobic) from the system in more than two years (at the time of writing in November 2001).

Design parameters and 2001 average operating results for the first BVF reactor (through September 2001 when the second reactor came on-line) are provided in Table 1. Average operating temperature of the reactor was 30°C for the time period reflected by the 2001 average results. During previous years the reactor typically operated 3-5°C cooler (based on the yearly average) before a new biogas boiler was installed in late 2000 to utilize biogas for heating the system.

Table 1 – Design Parameters and 2001 Average Operating Results for Coors’ First BVF Reactor

The BVF reactor is a proprietary technology which is classified by ADl as a low-rate upflow anaerobic sludge blanket system. The relatively large volume of the BVF reactor helps provide internal equalization, as well as sufficient sludge storage capacity to maintain significant sludge mass at long retention times. The large sludge inventory allows the system to operate at sub-optimum temperatures (the original BVF reactor operated at as low as 2°C for weeks at a time), allows aerobic sludge from the downstream process to be digested, minimizes overall sludge yield (and waste sludge generated), and provides for significant stability and resilience against shock loadings.

The new BVF reactor has a total volume of 45,400 m²; the original BVF reactor has a total volume of 22,700 m³ half the volume of the new reactor. The new design parameters for the two-reactor system are given in Table 2. Once the new design conditions are reached, the typical flow split between the reactors will be two-thirds/one-third, with the new BVF reactor taking the larger flow.

Table 2 – System Design Flow and COD Loading

The reactors at Coors are of earthen and concrete construction, with vertical concrete side walls constructed on earthen berms. The reactors are lined with an impermeable double-layer synthetic geomembrane.

Each reactor has a floating geomembrane cover with a layer of insulation attached to the underside. The covers are sealed gas tight to the concrete perimeter walls, thereby allowing collection of biogas, temperature control, and positive odour control. Access hatches and sampling ports are provided to allow inspection and monitoring.

A pair of effluent pumps for each reactor conveys effluent to the activated sludge system, based on operator-input ted flow settings. The cover and reactor designs for both systems allow level and volume fluctuations so that effluent flow can be kept constant for several hours, and even days. Allowable volume changes are 2,460 m³ and 4,920 m³ for the original and new BVF reactors, respectively. This built-in equalization is of significant benefit in terms of maintaining stable conditions for the down stream activated sludge and chlorination processes, allowing chemical addition (for polymer, chlorination, dechlorination, etc.) and recycle rates to remain constant for extended periods of time. The relatively long hydraulic retention time of the BVF reactors also means that influent BOD loading to the aerobic system remains very stable.

Sludge recycle piping and pumping allows sludge to be withdrawn from the effluent end of each reactor and returned to the influent end to provide greater contact with incoming wastewater. Interior baffles promote retention of sludge within the influent zone and discourage short-circuiting. The reactors have low-speed, high-flow mixers which operate on an interim basis to promote better substrate-biomass contact, reduce thermal stratification, reduce dead zones, and maintain sludge fluidity.

Piping is placed in the influent zone of the reactor in a design that promotes even distribution of influent beneath the sludge bed. Supernatant piping and pumping allows liquid to be drawn from near the top of the reactor and mixed with the influent wastewater to provide blending and buffering of pH, alkalinity, organic loading, and temperature, as well as transfer heat via the boiler/heat exchanger system.

Magnesium hydroxide slurry is typically added automatically to the influent to the anaerobic system to boost alkalinity and maintain a stable pH.

Biogas is generated on a continuous basis and is collected beneath the reactor cover automatically by a biogas blower and fed to the boiler for utilization; excess biogas is flared. A pressure transmitter is used by the control system to continuously monitor the cover pressure and control the biogas blower speed so as to maintain a desired pressure set point. The cover operates under a small negative pressure.

The computer control system provides continuous monitoring and outputting of system parameters such as flow, temperature, pH, cover pressure, etc. This data is trended graphically to aid in operator control and monitoring. System pumps, mixers, boiler, flare, and biogas blower are automatically control led by the PLC control system accord ing to fixed or operator-adjustable setpoints.

To start up the new reactor, sludge was pumped from the original reactor through common piping between the two sets of recycle pumps. Heating of the new reactor contents was accomplished using the boiler which burns biogas produced in the system. Since there was plenty of active sludge already acclimatized to the Coors wastewater to seed the new reactor, start-up proceeded quickly and smoothly.

At the time of writing, the new BVF reactor had been in operation for one month treating all the wastewater flow from the facility, which is currently about half the design flow/load for the new reactor.

The low-rate anaerobic BVF system has proven to be reliable, efficient, and has significantly reduced operating costs associated with aeration, nutrient addition, and sludge handling/dewatering/wasting at Coors Brewing Company in Virginia. Furthermore, the overall treatment plant has been much easier to operate since the first BVF reactor was added to the treatment train in 1995. The second BVF reactor allows for considerable future production expansion at the facility.