Internally fed rotary screens solve clogging problems for a craft brewery

Chances are the last beer you drank was a craft beer. With more than 4,000 craft breweries in the U.S. and nearly two more opening every day, craft beer is on tap for more and more Americans. The country has not seen a surge in locally owned and operated breweries since the 1880s. The tremendous popularity of craft beer is evident from the IPAs, locally crafted hefeweizens, and even sour beers served up at bars and available on the shelves of grocery stores across the nation. One look at the current brewery and beer landscape, and you can see this trend is here to stay.

Resurgence of the “farm-to-table” mentality opened the door for small, independent brewers to find more secure footing in a market that, just decades ago, was nearly nonexistent. 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 every 1 gallon of beer produced, 6 to 8 gallons of water are required. While some of that water ends up in bottles, cans or kegs as steam during the sanitation process, more than half of it ends up as wastewater. Unlike what is typically found in municipal waste streams, the waste enzymes that result from beer brewing cause considerable disruption to the entire sewer system. Beer waste is made up of sugar, yeast and complex proteins that, in significant 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, such as hops and spent grains, before they reach the anaerobic digester is critical for optimal system functionality and assists the digester with further successful breakdown of the organic materials.

Internally fed rotary screening systems are an economical, reliable pretreatment solution for medium-to-large breweries. They help eliminate suspended solids from the waste stream. Anaerobic digesters are then able to function at full productivity while more-solid waste is compacted, dried and 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 with the knowledge to more successfully manage their wastewater and focus on their craft.

Adding screens to the brewery mix

To grasp how rotary screening systems become an integral, beneficial component of a large-scale brewery operation, the brewing process must be broken down. 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 the 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 per year, that ends up being a large amount of spent hops in need of disposal. If left within the system, that grain can cause significant damage to the brewery process equipment and other facilities, pumps and pipelines within the wastewater system farther downstream of the brewery.

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 cannot handle the increased BOD levels. While rotary screening systems do not impact 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.

Operation

Internally fed rotary screens are designed for the high-flow rate/low-solids content of brewery wastewater but are also ideal for 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 in which the flow energy is dissipated and 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 s 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 (see Figure 1).

Matt Brewing Company case study

Matt Brewing Company in Utica, New York, is a picture of sustainability in the craft brewing community and uses several energy-saving methods within its brewing process. An on-site 200,000-gallon equalization tank normalizes the flow of the wastewater and preconditions it before it enters 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 and carbon dioxide.

Nearly 900 gallons of wastewater, which includes tough, gritty spent hops, flow through the system every minute. To protect the heat exchanger before the digester, the company used 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 the team 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 drier, more compact discharge. Since the installation, Matt Brewing Company eliminated costly downtime caused by filter maintenance and has not experienced any issues related to spent hops or grains with its anaerobic digester.

Industrial pretreatment’s future

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

Screening beyond the brew

Industrial wastewater debris comes in all shapes and sizes — and so do pretreatment screening systems. Wastewater engineers should consider four key aspects to determine the right screening product for the industrial application.

1. Type of wastewater contaminants

Understanding what contaminates are in the wastewater is critical in selecting the proper screen and will heavily influence the screening efficiency. Some variables to consider are the size of the particulates and particle size distribution; the shape of the particles such as granular or striated; whether the particulate is soft or hard and organic or inorganic; and whether the particulate has stickiness that will cause it to adhere to the screen’s surface. The presence of fats, oils or grease (FOG) is also an important consideration. This is a common byproduct of many industrial applications, and FOG in the waste stream will promote the filling of the screen opening. Proper steps in the design of the pretreatment screen can deal with most of these variables.

2. Flow rate

Screening decisions should be made based on the maximum flow rate possible for optimal effectiveness. Engineers should identify variations in the industrial process that can cause significant changes in flow. Often some surge controls or equalization can be designed into the process to normalize either low- or high-flow conditions. Improper selection of a high-flow screen for a low-flow application can lead to problems as well, such as debris settling.

3. Solids loading

The screen selection will depend on the solids concentration and percentage of solids that are captured or rejected. If the process is variable in both flow and solids concentration, then typically the screen selection is based on the point of maximum solids loading.

4. Treatment scheme

Understanding the complete treatment requirements will determine the selection of the type of screen unit and screening element. The screen determination will be a factor of the maximum-sized particulate that can be accepted at the succeeding stages of all individual treatments. It will also be a factor in the costs of disposing the byproducts of treatment and the cost or cost recovery associated with the screened materials. Screen placement is also a consideration in the overall treatment system design scheme. When installing screens in industrial plants, putting them as close to the wastewater source as possible is important. This prevents the natural breakdown of solids and makes screening the solids from the waste stream easier.

Bob McGowan is the industrial sales manager for JWC Environmental. He may be reached at [email protected].

Stacy Peshkopia is global product manager for commercial and industrial products at JWC Environmental. She may be reached at [email protected].

For more information about the internally fed rotary screens discussed in this article, visit http://jwce.com.