Internally Fed Rotary Screens on Tap for Craft Brewing Success

Industrial wastewater debris comes in all shapes and sizes — and so do pretreatment screening systems. Here are tips to ensure proper screen selection.

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Internally Fed Rotary Screens on Tap for Craft Brewing Success

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The craft brewing industry hit an incredible milestone at the end of 2015 — there are now over 4,000 craft breweries in the United States, and about two more open every day. But this growth comes with increased challenges for the less glamorous side of beer production — the wastewater created by the brewing process. 

Brewing beer is water-intensive. About 6 to 8 gallons of water are required for every 1 gallon of beer produced, more than half of which 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 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 drum screening systems present an economical, reliable pretreatment solution for medium to large breweries to help eliminate suspended solids like spent hops and grains from the waste stream. Anaerobic digesters are then left to function at full productivity, while more solid waste is compacted, dried and altogether eliminated from the wastewater thanks to the screening system. This means overall waste output is reduced, so breweries pay fewer fees for landfill transport, while maintaining the integrity of their other equipment. 

By understanding the cost- and energy-saving benefits of screening systems, brewery owners can equip themselves to more successfully manage their wastewater and focus on their craft. 

Adding screens to the mix

Breweries that produce over 50,000 barrels a year, end up with 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, but also to the 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 take 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 drum screens are designed for the high flow rate and 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. Splashguards 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 fitted with a bank of spray nozzles.

The following case study shows how one such brewer employed an internally fed rotary drum screen within their operation, protecting the equipment and allowing their anaerobic digester to function at full capacity. The result is a more streamlined system, and elimination of unscheduled maintenance for filter screening. 

Case in point: Matt Brewing Company

Matt Brewing Company in Utica, New York, is a picture of sustainability in the craft brewing community, using several energy-saving methods within their brewing process. An on-site 200,000-gallon 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. 

Approximately 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 drum screen removes the solids from the wastewater stream, and compresses them for dryer, more compact discharge.

Since the installation, Matt Brewing Company 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

As craft brewing continues to surge in popularity, and existing craft breweries expand their operations, a more careful look at pretreatment options will be crucial to limiting the impact of waste on both sensitive process equipment, and also 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 biggest cost savings and productivity benefits of the screening solution.

Screening beyond the brew

Industrial wastewater debris comes in all shapes and sizes — and so do pretreatment screening systems. To determine the right screening product for a specific industrial application, engineers should consider five aspects of their wastewater to ensure proper screen selection:

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 particulate and particle size distribution; shape of particles such as granular or striated; whether the particulate is soft or hard, organic or inorganic, and whether it has a “stickiness” that will cause it to adhere to the surface of the screen.

The presence of FOG is also an important consideration in screen selection. 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 max size particulate that can be accepted at the succeeding stages of all individual treatments. It will also be a factor in the costs of disposal of the by-products of treatment and the cost or cost recovery associated with the screened materials.

5. Screen location: Screen placement is also a consideration in the overall treatment system design. When installing screens at industrial plants, it is important to screen as close to the wastewater source as possible. This prevents natural breakdown of solids and makes it easier to screen out the solids from the waste stream.



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