Sustainable wastewater treatment solutions for industries with high discharge rates

Dealing with wastewater can be a costly but necessary enterprise for industrial facilities—especially for those dealing with large volumes of wastewater. Facilities must contend with both the costs and environmental risks of handling their waste streams responsibly, so it’s important to find a wastewater treatment strategy that minimizes wastewater volumes, environmental risks, and costs. Here, we’ll look at some common wastewater treatment strategies for achieving these goals.  

Chemical-physical treatment for solids removal

High levels of suspended solids in wastewater can mean higher discharge costs. Industries that produce wastewater with high solids content often turn to chemical-physical treatment to ease the burden on downstream treatment and reduce the total volume of liquid waste that ultimately gets discharged. Chemical-physical separation processes like coagulation, flocculation, and sedimentation are tried-and-true methods for separating out solid wastes, but they have their drawbacks, particularly when it comes to environmental impacts.

Chemical-physical treatment is a multi-step process. It typically begins with coagulation, which is a process that uses chemicals known as coagulants to instigate the process of suspended solids to combining into small particles. Coagulants work by neutralizing the electromagnetic charges of solids so that they clump together. The specific coagulant chemicals used for an application must be selected based on the charges of the solids present, but common coagulants include aluminum sulfate, ferric chloride, ferric sulfate, and other metal salts.  The stream may also be agitated with mixers to further encourage coagulation.

Next, the stream will be treated with a chemical known as a flocculant. Flocculants work by binding the small particles together into larger “flocs” that can be easily removed through physical separation. The most common flocculants are long-chain synthetic polymers (polyacrylamide). Finally, the solids will be removed through a physical separation process, such as sedimentation, which uses gravity to settle out solid wastes, or filtration, which uses a physical barrier to catch larger solids while allowing water to pass through. Following chemical-physical treatment, a facility is left with sludge that is typically disposed of as a solid waste, and a liquid water stream that may be routed for further treatment onsite or at a receiving facility, or discharged to a local waterway. Industrial facilities considering this approach should weigh the pros and cons of chemical-physical treatment:

• Benefits: By removing excess solids, coagulation and flocculation help to reduce the environmental impact of wastewater and costs associated with disposal. They also improve the efficiency of downstream treatment processes. For this reason, it is often used in zero and minimal liquid discharge systems ahead of more sensitive equipment like reverse osmosis or ion exchange.
• Drawbacks: Compared to other separation technologies, like membrane filtration, chemical-physical separation can be a slow and complex process. In addition, coagulants, flocculants, and other treatment chemicals can be costly to source and store, and they can also add further complexity to downstream treatment. Treatment chemicals can also pose health, safety, and environmental risks if discharged to a sewer or to local waterways. Depending upon wastewater chemistry, facilities may be able to use alternative chemicals, like natural chitosan or starch-based flocculants, which may be safer for both the environment and human health.

Direct discharge to the environment

Industrial facilities that release wastewater into the environment are known as direct dischargers. In most regions throughout the world, such wastewater releases are strictly regulated to ensure that harmful pollutants don’t make their way into the environment. In the US, releases to rivers, streams or other waterways must be done under a National Pollutant Discharge Elimination System (NPDES) permit and other local regulations. As such, facilities must typically install and operate their own wastewater treatment facilities to ensure adequate removal of all regulated pollutants. Industrial facilities considering this approach should weigh the pros and cons of direct wastewater discharge:

• Benefits: The advantages of direct discharge can depend upon several variables, but compared to discharging to a publicly owned treatment works (POTW), facilities may appreciate greater control of their wastewater treatment processes, flexibility, and potential long-term cost savings over user fees paid to a POTW.
• Drawbacks: Capital costs for building an onsite wastewater treatment facility can be high. Additionally, failure to comply with regulatory standards can lead to fines and other penalties, and discharging wastewater to local waterways can risk public trust and reputation.

Indirect discharge to a POTW

Many industrial facilities opt to discharge their wastewater to a publicly owned treatment works (POTW). This practice is also called indirect discharge, and it can be a sensible wastewater management strategy for some industries. However, since most POTWs are primarily intended to treat household sewage, they simply aren’t designed to treat the wide scope of pollutants that might be found in industrial wastewater. For that reason, indirect dischargers must comply with pretreatment requirements to protect the receiving facility’s equipment and processes and ensure that toxic contaminants don’t make their way into the environment. In the US, the Environmental Protection Agency (USEPA) developed a national pretreatment program to regulate industrial discharges to POTWs. Industrial facilities considering this approach should weigh the pros and cons of discharging wastewater to a POTW:

• Benefits: Wastewater quality standards are generally less stringent for POTWs than they would be for direct discharge to a local waterway, meaning that industrial facilities may be able to invest less of their own resources into onsite wastewater treatment, which can save space, as well as capital and operational expenses.
• Drawbacks: POTWs place limits on the volume of wastewater they accept from industrial users, which can hamper growth. Additionally, facilities will generally still need to invest in some level of wastewater treatment to meet POTW discharge standards, and they generally must pay user fees and potentially surcharges to the POTW.

Minimal and zero liquid discharge (MLD/ZLD)

MLD and ZLD are wastewater treatment processes that are designed to drastically reduce the amount of liquid waste that ultimately gets released by a facility, producing mostly solid waste residues instead.  MLD and ZLD are typically used together with a water reuse strategy, with the recovered water being recycled for other applications within the facility.

• Benefits: MLD/ZLD systems offer many advantages. By recovering upwards of 80% of wastewater for reuse, MLD/ZLD can cut the amount of water a facility takes in. In addition, they allow facilities to recover valuable materials from waste streams. Finally, MLD/ZLDs help facilities reduce—or even eliminate—wastewater discharges. This can help a facility meet ambitious water stewardship goals, which can boost their public image and reduce risks associated with regulatory compliance.
• Drawbacks: MLD/ZLD systems carry high capital and operational costs. Additionally, excess energy consumption may cancel out environmental benefits that MLD/ZLD might otherwise have generated in terms of water use or carbon emissions.

Water reuse and reclamation

Water reuse and reclamation refers to the practice of capturing process water streams and recycling them for use in the same process, or in other processes. Reuse applications can be as simple as recirculation of cleaning solutions, rinse water, or cooling water, or they can be more elaborate, requiring segregation of streams for different processes, sometimes with various forms of water treatment prior to reuse. Industrial facilities considering this approach should weigh the pros and cons of water reuse and reclamation:

• Benefits: Water reuse and reclamation can help facilities cut down on water use and discharge, which can generate cost savings on sourcing fresh water and discharging wastewater. In so doing, water reuse can help companies meet sustainability goals.
• Drawbacks: The simplest water reuse systems may be quite affordable, so cost isn’t necessarily a drawback. But complex applications and treatment needs can drive up capital and operational costs, so facilities need to carefully consider technical feasibility before proceeding with a reuse project.

How can SAMCO help?

SAMCO has over 40 years of experience designing, engineering, and building process separation and wastewater treatment systems. Whether it’s building a new system from the ground up, or upgrading existing equipment, we offer a comprehensive range of services to engineer, design, fabricate, and install custom solutions for any application. We can also help you to maintain your current systems, or provide rental equipment or modular solutions to solve temporary challenges.

Have a specific question? Contact us to learn more about SAMCO’s engineering, design, lab tests and pilot studies, fabrication, installation, and ongoing support services. You can also visit our website to set up a call with an engineer, request a quote, or click on over to our blog to learn more about process purification and separation systems, wastewater treatment systems, industrial water conservation strategies, and more.