Filtration Sequence Enables Water Reuse

Water scarcity and pollution are growing concerns. Not only are the droughts and overuse of natural resource problematic for drinking water supplies, they are causing production problems for manufacturers that need specific volumes of water for various processes.

A competitive environment and strong regulations drive industry to take actions that ultimately are more environmentally sustainable and economically feasible. For example, through the development of sustainable waste solutions and residuals management, industries adhere to the principles of green chemistry and seek alternatives to waste disposal that include source reduction and recycling.

Manufacturers that want to recover water from process and wastewater in their operations have a number of filtration technologies that enable them to do so (see Figure 1).

Figure 1  Many filtration and other technologies are applied to wastewater recovery, depending on the required purity of the water.

For example, polymeric adsorbents and selective ion exchange (IX) resins can be used to remove specific single contaminants such as dissolved heavy metals, aromatic and phenolic compounds, chromate, cyanide, mercury and volatile organic compounds (VOCs) in a cost-efficient manner.

Particle filtration removes high solids, particulates and fine particles from the wastewater; this helps downstream filtration technologies operate more efficiently and consistently. Similarly, ultrafiltration (UF) technology removes solids down to approximately 30 nanometers (nm).

Reverse osmosis (RO) technology removes dissolved solids and other persistent contaminants, such as small organic molecules.

Ultrafiltration and reverse osmosis allow manufacturers to determine the water quality that is suitable for their operation or applications–whether it is purified for reuse in a cooling system, or to a purity level that would make it suitable for drinking as a product ingredient or in a final wash parts station.

How the Filtration Systems Work 

Typically, membrane-based water reuse systems follows a sequence of filtration steps: Wastewater from the manufacturing process flows to a biological wastewater treatment system which does the core of the purification process by removing COD, BOD, suspended organic materials and nutrients in an activated sludge treatment, followed by a clarifier to separate sludge (solids) and treated wastewater. That solution then flows into a tertiary filtration or polishing with sand filtration and screening process with 100- to 300-micron safety screens and then through an ultrafiltration process, removing suspended particles down to 30 nm (see Figure 2).

Figure 2  Typically, membrane-based water reuse systems follow a sequence of filtration steps to achieve the desired water purity.

Finally, if further purification is needed to lower the total dissolved solids (TDS), it goes through a reverse osmosis filtration stage, which uses a very fine membrane to filter out dissolved solids and very small molecules such as dissolved organics.

How Much Water Can Be Recovered, Reused? 

Water recovery can be very high—greater than 96 percent at the individual process step. Most commonly, plant recovery levels are 70 to 90 percent. Notably some manufacturing locations operate in zero-liquid-discharge mode, meaning that no liquid waste is returned to the environment.

The process of filtering and screening the biologically treated wastewater to remove the largest particles to the smallest through progressively smaller and finer filter media—from filtration to ultrafiltration and then reverse osmosis. However end use applications for the reused water can vary from aquifer replenishment, discharge pollution limitation to industrial make up water to municipal water reuse such as irrigation, non-potable municipal uses.

Many industries, such as the textile industry in India and China and the coal-to-chemical industry in China are migrating towards zero liquid discharge. Because of the increased need for water conservation, there is a focus on reducing water consumption and pollution minimization at a regional level and other drivers can be industry or corporate sustainability efforts.

While the key technologies for advanced reuse are well-established, development continues at the individual component and application level. Water recovery systems’ component suppliers are concentrating R&D efforts on developing products that can handle harsh wastewater conditions better, drive efficiency, and improve the overall cost of operation. The establishment of certain technologies also has helped different industries leverage best practices of successful water-reuse installations which will drive others to adopt similar concepts.

One interesting development is collaboration among municipalities, industries, and public-private-partnerships, especially in terms of using municipal wastewater instead of raw freshwater as a feedsource for some industrial applications, such as cooling towers, process water, or boiler feedwater. This helps alleviate stress on the community’s potentially scarce freshwater source.

The concept of a circular economy using waste as a feed source is becoming a reality.

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Editor’s Note: Still thirsty? Read “Water reuse, recycling, conservation in manufacturing;”  and “How 5 manufacturers reduce water use”

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India Automaker’s Water Reuse Keeps Plant Humming; Zero Water Discharge

Maruti Suzuki India, Ltd. an automotive manufacturer in Gurgaon, India, was sourcing its water for production from a dedicated canal supply line. Per its agreement with local governmental bodies, Maruti Suzuki was to receive 7,200 square meters of water per day from the canal. However, competing demands on the canal resulted in Maruti Suzuki receiving only 2,000 sq. m per day–far below the water volume it needed. The lack of water adversely affected production and company revenues.

To help alleviate the water scarcity problems, Maruti Suzuki engaged Dow Water & Process Solutions to install a process water recovery system. A dual membrane system treats and recycles the plant wastewater mixture, or effluent, making up for the shortfall in raw water supply.

The system comprises an ultrafiltration system with 36 DOW™ SFP-2880 modules, that provides a robust pretreatment. The clarified water then feeds to a downstream reverse osmosis system, which reduces the dissolved solids and meets the water quality requirements of the automaker’s manufacturing process

The ultrafiltration system currently achieves water quality of silt density index (SDI) ≤ 3 and turbidity, or cloudiness of ≤ 0.1 nephelometric turbidity units (NTU), with a capacity of 120 sq. m per hour. An integral part of the company’s water treatment strategy, the dual membrane water recycling system has enabled the plant to achieve 62 percent reduction of water consumption per vehicle manufactured, and maintain a zero water discharge status.

This case is a prime example of using advanced filtration technologies to alleviate water scarcity at a regional level by reusing more wastewater within the industrial complex itself.

John Patrin is the global marketing director for the filtration business and Katariina Majamaa is the heavy industry marketing manager at Dow Water & Process Solutions, 5400 Dewey Hill Rd, Edina, MN 55439, 952-897-4200, [email protected], [email protected], www.dowwaterandprocess.com.

Infographic courtesy of Dow Water and Process Solutions.

Editor’s Note: Still thirsty? Read “Water reuse, recycling, conservation in manufacturing;”  and “How 5 manufacturers reduce water use”