By Gerard J. Lynch, PE
A staple of water and wastewater treatment systems, filtration has long been a tool to help improve the quality of water. Ancient texts outline practices for purifying water for drinking, including filtering it through sand and course gravel, primarily to improve its taste. Over the centuries, sand filtration became an important process and is one of the many filtration techniques still used today. The Greek doctor Hippocrates (c. 460 – c. 370 BC) also played a role in advancing filtration technology. He is credited for inventing a crude bag filter (also known as the Hippocratic sleeve) to purify water used for his patients. Of course, bag filters are also being used as part of some water treatment systems, albeit in a much more advanced form.
Today, filtration is used not only for drinking water but also by industry to remove and concentrate suspended solids and other contaminants from the water or wastewater stream. As pointed out by the American Filtration & Separations Society, filtration plays a key role in industries that touch all aspects of our lives: “Modern industries that are made possible, at least in part, by filtration and separation technology include: automotive, aerospace, chemicals, pharmaceuticals and diagnostics, medical devices, consumer electronics, food and beverage, pulp and paper, oil and gas, power generation in both public utility and battery scale processes, and environmental technologies that provide clean air, pure drinking water and wastewater treatment.”
Modern filters help address industries’ need for new and better solutions for wastewater disposal, water reuse and recycling, as well as recovery of valuable product from non-hazardous wastewater streams. They also play an important role in treating water for manufacturing processes and protecting industrial and commercial equipment by removing contaminants that could damage or cause it to malfunction. Commercial enterprises, from hotels to restaurants, also use filtration for a variety of applications.
Water and the food and beverage industry
An example is the food and beverage industry, one of the largest industrial and commercial users of water in the world. It is also an industry where advanced filtration and separation technology plays a critical role across its operations. According to GWI WaterData, the global volumetric demand for the food and beverage industry was 84.80 billion cubic meters of water in 2019; this number is expected to increase to 91.70 billion cubic meters in 2025. As a result, the food and beverage industry is faced with discharging large volumes of wastewater that typically require pretreatment for reuse or to ensure compliance with industrial discharge regulations. Discharge limits for food and beverage companies may typically apply to pH, fat-oil-grease (FOG), TSS, BOD, TDS and COD.
Advanced filtration in action
Companies in many industries require filtration solutions for their process water as well as their wastewater. Many considerations come into play when selecting the optimal filtration system. On the process water side, criteria include the impact on business efficiencies in production time, transportation, labor costs and product loss. In the food and beverage industry, for example, the filtration system must also be evaluated for its ability to protect the flavor of the product. In some cases, filtration systems may also be used to remove solids from those products. Until now, this was widely achieved by utilizing such equipment as bags, cartridges and centrifuges.
In the California Central Valley, for example, producers as well as processors struggle with high solids loading in both their process and wastewater applications. Both regulation and standard process procedures require high solids removal from their process streams. Rotary screens can fail to meet regulation standards as well as remove the required number of solids to avoid fouling downstream equipment. Filtration solutions, such as advanced automatic self-cleaning filters, can help both producers and processors bridge this gap in the process line.
As wastewater becomes more challenging, regulations are becoming more stringent. In January, for example, California’s State Water Resources Control Board approved an order to set up guidelines for wastewater processing at most of the state’s more than 3,600 bonded wineries, promising to bring at least 1,500 of those wineries into a regulatory framework for wastewater disposal for the first time. This development is expected to increase compliance costs for wineries. As a result, wineries must look to a new solution to reduce TSS and BOD. And the new requirements raise questions about potential impacts on wineries in other regions, as well as on smaller companies engaged in related industries, such as microbreweries and small batch distilleries, juice producers and so forth.
Management of high levels of solids in wastewater is an ongoing challenge for many producers, who are increasingly putting in place water reuse and recycling programs. Treatment of wastewaters can be challenging given that wastewater is generated by all areas of processing. In wastewater management, dewatering is important and the system must also be able to filter out impurities to meet regulatory standards. Concentrating solids in the wastewater stream also benefits industrial users by lowering disposal and regulatory fees. Producers may consider the process to be more separation than filtration. Recovered solids are not necessarily waste product; in some cases, they may become a nutrient-rich byproduct that can be sold to create an ancillary revenue stream.
For example, one manufacturer’s automatic self-cleaning filter is engineered for medium-to-high-flow, high-pressure, high-temperature applications and liquid/solids separation. It is designed to remove ultra-high and variable TSS (15,000 mg/L) from water and wastewater streams. Each filter contains a motor-driven, spiral-shaped brush that continuously cleans collected debris from inside the filter element. Solids collect at the bottom of the filter housing, to be expelled through an automatic purge valve or a continuous concentrate stream. This system does not require high pressures to operate and performs at very low differential pressure. No backwash cross flow or booster pumps are required.
It is a common misconception that businesses can satisfy their total filtration needs with a single piece of equipment. The truth is that most industrial water applications require a complex set of filtration steps to achieve the desired result, whether that result is total BOD reduction, TSS removal, clarification or simply nozzle protection. The array of filtration solutions starts with primary filters, such as a rotary drum. These are effective in removal of large solids, but problems can arise when a large number of finer particles pass through the drum filter and into a secondary filter, such as a dissolved air flotation (DAF) or clarifier system. To ensure continuous flow, manufacturers must typically invest in costly precautionary measures to prevent the system from being affected by an overload of solids.
Initial solids isolation becomes a crucial step toward making sure downstream efforts are not overextended to compensate for high-solids loading that remains in the system. Traditional solutions include centrifuges (which are expensive pieces of machinery and often require constant maintenance) and bags, cartridges and media filters that result in equipment redundancy, large footprints, expensive human resources and an unfavorable environmental impact.
Until recently, automatic self-cleaning filters had proven unable to handle high-solids loading or fats, oils and greases for an extended period of time without blinding off. New technology, however, such as the self-cleaning filter, solves this problem by immediately isolating high solids in a concentration chamber, which allows flowrates to be maintained throughout the filtration process.
A case in point is a raisin manufacturing company in the Central Valley of California that dehydrates and packages its product, in turn creating a high-solids wastewater stream that can’t be reused. The company was using a treatment system for its wastewater sump, which included a shaker bed and drum screen, before discharging the water to the local treatment plant. The company had tried solutions ranging from filter screens to a reverse osmosis (RO) system. Traditional automatic filters had plugged up and MF/UF/RO systems were too expensive to operate. Marginal improvements came with the implementation of a food processing shaker bed with a five-mm mesh to remove the coarse solids, followed by a rotary drum screen with a 250-micron mesh to remove finer solids. The drum screen, however, failed to provide the necessary TSS reductions.
A filter manufacturer assessed the situation and recommended installing its 25-micron automatic self-cleaning filter to follow the drum screen. Combined with a simple dewatering sack, the filter concentrated solids up to five percent by weight and can produce dewatered solids for fertilizer or landfill. In the first month of the filter’s operation, TSS levels dropped by 61 percent and BOD by 48 percent from the previous five months of operation.
What’s next in filtration?
The simple answer is that there is no silver bullet for water recovery and waste reduction. The answer lies in integrated solutions that incorporate advanced high-solids filtration and separation technology within a holistic framework. For example, small farms are faced with the challenge of reducing waste. One company has been working with dairy farms to treat wastewater streams and separate digestate that can then be resold as fertilizer. And as sustainable farming and the use of vertical farming increases, many growers are finding the value of automatic self-cleaning filters that concentrate more and waste less. Further development will continue to advance filtration and separation technology for commercial and industrial players in all sectors. If Hippocrates could see us now, he would be proud of where his invention has taken us.
About the author
President and CEO of Spiral Water Technologies, Gerard J. Lynch, PE, has extensive experience in filtration and separation technologies and advanced testing techniques with more than 30 years in filtration testing, design engineering and manufacturing operations. He has served as President of International Filter Testing Services, Inc. (IFTS), USA, an independent, non-profit center specializing in filtration and separation science, research and testing. Lynch has been a member of the American Filtration and Separations Society (AFS) since 1988. He served as the AFS National Chairman for 2006-2007 and has been an AFS board member since 1999. Lynch can be reached at email@example.com.
About the company
Spiral Water Technologies (www.spiralwater.com) develops and markets high-performance products for advanced high-solids filtration and concentration applications. The company’s patented automatic self-cleaning filtration technology delivers superior results, while reducing CapEx and OpEx for low Total Lifecycle Cost. Spiral Water products provide breakthrough performance in some of today’s most demanding applications, including water reuse and recovery; pre-filtration for DAF, MBR and RO/UF; industrial water filtration and concentration of valuable or resalable product from non-hazardous wastewater.