Internally-fed rotary screening systems: Economical pretreatment solutions for brewery wastewater

There’s a good chance that the last beer you drank was a craft beer. With more than 5,000 craft breweries in the United States and nearly two more opening every day, craft beer is on tap for more and more Americans. The country hasn’t seen a surge in locally owned and operated breweries since the 1880s. Yet with this growth in demand for craft brews comes an increase in challenges for the less glamorous side of beer production — the wastewater created by the brewing process.

Brewing beer is water-intensive. For just one gallon of beer produced, six to eight gallons of water is required. While some of that water does end up in bottles, cans or kegs as steam during the sanitation process, more than half of it ends up as wastewater. Unlike what’s typically found in municipal waste streams, the waste enzymes that result from beer brewing cause considerable disruption to the entire sewer system. Waste from beer comprises sugar, yeast and complex proteins that — in significant enough quantities — can dramatically change the microbial makeup of the waste stream. To reduce the biological oxygen demand (BOD) from these compounds, some forward-thinking breweries have chosen an anaerobic digester to combat these waste disposal issues. However, pretreatment of the brewery wastewater to remove coarse solids, like hops and spent grains, before they reach the anaerobic digester is critical for optimal system functionality, and will assist the digester with further successful breakdown of organic materials.

Internally-fed rotary screening systems are an economical, reliable pretreatment solution for medium to large breweries. They help eliminate suspended solids, like spent hops and grains, from the waste stream. Anaerobic digesters are then able to function at full productivity, while more solid waste is compacted, dried and altogether eliminated from the wastewater thanks to the screening system. In the end, overall waste output is reduced, so breweries pay fewer fees for landfill transport, while maintaining the integrity of their other equipment.

Understanding the cost- and energy-saving benefits of screening systems equips brewery owners to more successfully manage their wastewater and focus on their craft.

Adding screens to the mix

To grasp how rotary screening systems are an integral, beneficial component to a large-scale brewery operation, you need to break down the brewing process.

Beer is made from barley malt that is ground and mixed with other grains to fuel the fermentation process. These ingredients are mixed with water and mashed so that the grain starches are converted to smaller carbohydrates, mostly fermentable sugars. This mash is separated into a clear liquid called wort, which contains the sugars and other grain-derived components, and the non-soluble spent grains.

The wort and hops are boiled in the brew kettle to extract the hop resins and oils. The boiled-out spent hops are usually added to the spent grain. For breweries that produce more than 50,000 barrels a year, that ends up being an enormous amount of spent hops in need of disposal. If left within the system, that grain can cause significant damage to both the brewery process equipment and other facilities, pumps and pipelines within the wastewater stream further down the line.

Some of the nation’s largest craft breweries spend millions of dollars transporting their process wastewater to cities with more robust treatment systems, because their own municipalities simply can’t handle the increased level of BODs. While rotary screening systems don’t make an impact on BOD reduction, eliminating the damage from spent hops and grains to an anaerobic digester mitigates unscheduled maintenance costs, and allows brewers to dispose of that waste more effectively.

Method of operation

Internally-fed rotary screens are designed for the high-flow rate/low solids content of brewery wastewater, but are also ideal at managing other municipal and industrial wastewater. The cylindrical drums are mounted horizontally on four shaft-mounted trunnions that are supported on pillow block bearings. The influent — in this case, brewery wastewater — enters an engineered headbox, where the flow energy is dissipated and is evenly distributed onto the interior sidewalls of the drum. The spent hops and grains are retained on the screen surface, and the wastewater flows radially through the screen openings. Splash guards direct the liquid filtrate to a central drainage area, and the spent hops and grains are transported axially, by flights, to the open end of the drum. The rotation of the drum allows the entire screening surface to be continuously or intermittently washed by a fixed, external, spray bar.

Matt Brewing — Utica, N.Y.

Matt Brewing Co., which makes the Saranac brand of craft beer, is a picture of sustainability in the craft brewing community, using several energy-saving methods within their brewing process. An on-site 200,000 equalization tank normalizes the flow of the wastewater and preconditions it before entering the company’s digester units. The wastewater is pumped from the equalization tank to five anaerobic digester tanks, located 50 to 150 feet away. The 40,000-gallon digester tanks can be operated in parallel or in a series. Organics in the digester tanks are treated by a mixture of anaerobic bacteria that create biogas composed of methane gas and carbon dioxide.

Nearly 900 gallons of wastewater flow through the system every minute, which includes tough, gritty spent hops. To protect the heat exchanger before the digester, the company was using a two-dimensional filter to capture this material. However, the spent hops regularly clogged the filter, and operators had to clean it manually each time. After dealing with this hassle for years, the executive team conducted research on alternative screening products. This led them to choose an internally fed rotary screen, which catches the spent grain but allows the yeast to flow through to the digester. The rotary screen removes the solids from the wastewater stream, and compresses them for dryer, more compact discharge.

Since the installation, Matt Brewing eliminated costly downtime due to filter maintenance, and hasn’t experienced any issues with their anaerobic digester as related to spent hops or grains.

The future of industrial pretreatment

If lovers of craft beer have anything to say about it, craft breweries are here to stay, which means their wastewater challenges will continue to persist as well. As the industry continues to grow, and existing craft breweries expand their operations, examining pretreatment options will be crucial to limiting the impact of waste on both sensitive process equipment, and the entire wastewater system of the municipality. Engineers who evaluate pretreatment screens based on the debris makeup, flow rate and end use for the screenings will be poised to gain the greatest cost savings and productivity benefits of the screening solution.

Bob McGowan, Industrial Sales Manager at JWC Environmental, and Stacy Peshkopia, Global Product Manager for commercial and industrial products at JWC Environmental.