Understanding and Managing Residuals of Industrial Wastewater Treatment

From power plants and chemical manufacturing facilities to beauty salons and residential housing, there are many sources of wastewater. Industrial facilities are tasked with treating wastewater before reusing it or sending it into the environment.

The Environmental Protection Agency (EPA) has placed limits on the concentration of contaminants that industrial buildings can release into the surrounding water. To avoid fines and other penalties, facilities typically treat the wastewater they produce.

During the treatment process, organic residues are removed from the wastewater to ensure most of the contaminants are filtered out. The types of residuals that can be taken out of wastewater include solid, liquid, and semisolid byproducts.

Businesses can use several different types of disposal methods, which include incineration and landfilling. The residuals can also be reused by creating fertilizer or compost. This guide offers an in-depth examination of the many residuals of industrial wastewater treatment.

Types of Residuals in Industrial Wastewater Treatment

When industrial wastewater is treated, it can leave behind many different residuals, including everything from biosolids and ash to landfill leachate and lime mud.

Biosolids

Biosolids are commonly produced during the wastewater treatment process. When this treatment occurs, solids are separated from the water. These materials can be treated chemically and physically to create a semisolid substance that’s referred to as biosolids. This product is rich in nutrients, which is why it has some beneficial applications.

If you want to use biosolids as a nutrient source for crops, you’ll need to adhere to specific state and federal requirements. If you’re able to apply biosolids to land, you can benefit from water reuse, improved soil structure, and nutrient addition. By applying biosolids to land, you’ll also be able to conserve landfill space and reduce demand for non-renewable resources.

Keep in mind that biosolids have a distinct odor that can change based on the process that’s used to treat the water. The compounds that typically cause these odors are amines and ammonia. Even though this product has a pungent odor, it’s not harmful to the environment or human health.

Ash

Ash is a substance that’s produced from combustion processes. When biomass combusts, heat and power are generated. This specific residual can be used as a substitute for lime to increase the pH in acidic soils. It can also serve as an alternative source of nutrients for plants.

Even though ash doesn’t consist of high levels of phosphorus or nitrogen, it alters the pH of soil enough to produce a synergistic fertilization effect that can be highly advantageous. If you’re searching for ways to manage or dispose of ash, your best option is to use it for beneficial applications. Reusing ash offers the following advantages:

• Product benefits like added durability and strength
• Economic benefits like lower disposal costs, higher savings, and more revenue when selling coal ash
• Environmental benefits like reduced landfill disposal, a more limited use of other materials, and lower greenhouse gas emissions

Food Processing Residuals

Food processing residuals are created whenever agricultural products are processed for animal or human consumption. These residuals can be obtained from the following processes:

• Conveying food materials
• Rinsing carcasses
• Cleaning slaughter areas
• Process wastewater sludges
• Seeds
• Pits
• Cheese whey
• Bone
• Fruit and vegetable peels
• Off-specification food products
• Feathers
• Hides
• Hair

These materials are naturally produced as the result of processing agricultural commodities, which means that you don’t need to mitigate this process. To properly dispose of food processing residuals, it’s highly recommended that you apply them to fields.

The purpose of soil conservation is to maintain the health of this substance, which occurs by increasing the amount of organic matter that’s present in the soil. Food processing residuals serve as beneficial organic matter.

By boosting the amount of organic matter that the soil has access to, the microbial population in this substance will be fed. Increasing the concentration of microbes in the soil allows for additional nutrient cycling and healthier soil. These residuals can also keep the soil from drying out, which ensures that beneficial nutrients don’t get swept away in runoff.

Pulp and Paper Residuals

Pulp and paper manufacturing also produces residuals. When wood is chemically or mechanically pulped, it creates a wastewater effluent stream that needs to be treated. The same occurs when recycled paper is processed. The most common treatment for raw effluent involves physically separating the wood fibers.

An additional treatment is often performed to add nutrients to the wastewater, which improves the removal rate of suspended solids. The main nutrients that are added during this process include phosphorus and nitrogen. Once these treatments are finished, the solids are recovered. These solids are known as pulp and paper residuals. Keep in mind that these residuals can also consist of short paper fiber, lime mud, and ash. There are several beneficial use opportunities for pulp and paper residuals, which include the following:

• You can use this substance as feedstock for fabricated soil, which allows it to be applied in leachate treatment, mine reclamation, and landfill closure applications
• It works as a barrier layer for landfill closures
• These residuals serve as soil amendments or fertilizers on land

The chemical and physical characteristics of these residuals allow them to be highly effective when used as soil amendments in reclamation and fertilization applications.

Water Treatment Residuals

When process and drinking water are treated in municipal and industrial facilities, water treatment residuals are created. The most common water treatment processes use coagulants to ensure organic matter is suspended, which means that only clean water will get through. The suspended matter is then collected as a dewatered solid or a thickened liquid.

These residuals contain ferric and aluminum oxides that you can use to moderate the concentration and movement of phosphorus in soils. You can either directly apply these residuals to the land or combine them with other residuals for a more potent product. These residuals can be used to effectively mitigate nutrient management challenges in places with too many available nutrients.

Some facilities choose to discharge these residuals to water treatment facilities or landfills. However, land application is the most beneficial use for them. Water treatment residuals mainly consist of water and iron or aluminum. However, they can also hold trace amounts of suspended solids, biological particles, organic chemicals, and metals.

Landfill Leachate

Leachate refers to any liquid that extracts suspended or soluble solids when it passes through matter. This term is regularly used in environmental science applications to describe a liquid that contains substances that are harmful to the environment. While leachate can be produced from industrial waste, it has its origins in landfill operations.

Leachate that comes from a landfill can be highly varied in composition. The factors that determine the makeup of leachate include the type of waste and the age of the landfill. This substance typically consists of suspended and dissolved materials. Most landfill leachate is caused by precipitation moving through the waste that has been sent to a landfill.

Once water comes into contact with solid waste that’s decomposing, it will become increasingly contaminated. If the water flows out of the waste, it will become leachate. Keep in mind that the decomposition of landfill waste can also produce many other materials, which include the following:

• Carbon dioxide
• Alcohols
• Simple sugars
• Aldehydes
• Organic acids
• Methane

Landfills can limit the risks associated with leachate production by properly engineering and designing their sites. For example, building a landfill on geologically impermeable materials can significantly reduce the amount of leachate that’s generated from waste.

It’s also possible to install impermeable liners that are made from engineered clay or geomembranes. Keep in mind that these linings are now required in the European Union, Australia, and the United States. You’re only allowed to bypass these requirements if the waste in your landfill is considered inert.

Today, most harmful and toxic materials are excluded from entering landfills. Even though restrictions have been put in place to mitigate the damage caused by leachate, many landfills disregard these requirements. Some household products can also produce leachate when disposed of in a landfill.

While modern standards help reduce the amount of leachate that enters the environment, landfills that were built before 1992 don’t need to adhere to these guidelines. High concentrations of leachate continue to be produced by older landfills. This leachate flows directly into the surrounding groundwater, which means that the substance can eventually make its way to nearby springs.

Leachate often has a black color and is highly deficient in oxygen. Once oxygen is introduced to the substance, it will turn yellow or brown. Over time, the leachate develops a type of bacterial flora that contains Sphaerotilus natans. This organism is regularly associated with polluted water.

While leachate is harmful to the environment, it can be used in specific soil and plant systems that have been fabricated with biosolids. These residuals can enhance the growth of short-rotation willow plants and hybrid poplar crops. When leachate is discharged from this type of system, it will be much improved because of the new nutrients it contains.

Waste Lime or Lime Mud

Lime mud is a type of byproduct that’s often produced in pump mills when wood chips are turned into pulp to create paper. Pulp mills cook wood chips with a sodium hydroxide solution to separate the wood fibers from the lignin that effectively glues the wood together. The sodium hydroxide turns into sodium carbonate, after which the pulp mill adds some calcium oxide to it.

This substance converts the carbonate into sodium hydroxide, which allows it to be reused. When this occurs, calcium carbonate forms. Calcium carbonate is one part of ground agricultural limestone. While lime mud mainly consists of calcium carbonate, it can also contain a small amount of magnesium carbonate. Keep in mind that these residuals are also produced from mining and cement manufacturing applications.

Wood Waste

During forestry operations and wood processing applications, wood waste is naturally produced. This is the second largest type of construction and demolition debris. Around 10% of the material that enters landfills every year is wood waste. When a building is demolished or a wall is torn down to make way for a renovation, wood waste is generated. During demolition operations, the wood becomes contaminated with other materials.

Feedstock can consist of scrap wood that comes from wood frame construction, shipping crates, or warehouse pallets. Since it’s difficult for these materials to be reused, the best option for disposing of them is to recycle the waste to create mulch, compost, bedding material, or biomass.

Challenges in Managing Wastewater Residuals

There are many challenges associated with managing wastewater residuals. If your facility produces wastewater sludges during standard operations, you’ll need to manage the streams to properly address issues like:

• Variations in residual composition
• Production increases and volume fluctuations
• Reduced solids loading and thickening processes
• Dewatering deficiencies and additional treatment needs
• Chemical treatment requirements

It’s also crucial that you maintain your facility’s infrastructure to minimize the environmental impact of the wastewater effluent.

Role of Waste Management Services

When you treat the wastewater that’s produced by your industrial facility, you’ll likely generate residuals that can be used for beneficial applications. It’s highly recommended that you obtain waste management services to handle these residuals. When you request this type of service, the company you hire will manage your wastewater treatment needs. Companies that offer this service can manage concentrations of:

• Cyanide
• Suspended solids
• Organic matter
• Acids
• Bases
• Metals
• Water-based paints
• Petroleum-contaminated water
• Used oil
• Tank rinse
• Industrial process wastes

You may also be able to request turnkey services that are more personalized. Make sure the company you hire accepts industrial wastewater by tanker truck, container, or rail.

Services Provided

When you obtain waste management services, you’ll benefit from the following:

• Mitigation of maintenance outages and episodic events
• Long-term solutions for any issues that arise
• Consultative approach to high-volume and high-cost waste streams
• Zero capital requirements pertaining to design, build, operate, and maintain applications
• Waste reduction programs
• Evaluation of your facility’s dewatering technologies
• Custom-engineered oil recovery and dewatering solutions

If the company you hire offers dewatering solutions, make sure they take an unbiased approach when they evaluate your existing technologies.

NEIWPCC Residuals Workgroup

Throughout the years, several groups and agencies have been established to promote better and more environmentally friendly residuals management. For example, the NEIWPCC is a regional commission that has been a leader within the wastewater industry since its formation in 1947. They perform scientific research, engage with water quality professionals, and provide educational materials and outreach.

In 1993, they established the NEIWPCC Residuals Workgroup to enhance interstate communication on residuals management. They focus on the residuals that are produced from on-site sewage disposal and wastewater treatment. This workgroup meets twice every month and consists of staff from the EPA, NEIWPCC, and state environmental agencies. Residuals coordinators from all NEIWPCC member states are part of this group. The South Carolina, New Jersey, Michigan, and Minnesota environmental agencies also send representatives.

Activities and Focus Areas

The goal of the NEIWPCC Residuals Workgroup is to promote compatibility with federal and state sludge management programs. The NEIWPCC website houses a forum that accommodates interstate discussion, coordination, and technical assistance. Some of the topics of discussion that occur when the workgroup meets include sludge technologies, long-term stressors that impact the region’s sewage sludge management system’s capacity, and polyfluoroalkyl substances (PFAS).

PFAS substances are a group of contaminants that have emerged in recent years. The group has been paying more attention to these contaminants because of their mobility and durability. These man-made chemicals are harmful to human health and have been present in common household products since the 1940s. Today, they are found in air, fish, water, and soil in varying concentrations.

The National Institute for Health (NIH) indicates that more than 9,000 different PFAS compounds have already been identified. Because of how many there are, it’s challenging for the EPA to study and regulate these compounds. PFAS was listed as one of the five main areas of concern in the 2020 Water Program Priorities document that the NEIWPCC workgroup put together. They aim to investigate the effects that these chemicals have on aquatic life and human health.

Sludge End-Use and Disposal Report

The NEIWPCC Residuals Workgroup created a Sludge End-Use and Disposal Report in 2022 to identify more beneficial ways to reuse wastewater sludge.

2022 Report Overview

A large portion of this report contains data on the disposal and reuse of almost 800,000 tons of sewage sludge. While the report was published in 2022, the data is from 2018. This report includes some state-specific metrics that show how much sludge was sent to a landfill or incinerated.

The data includes information about the amount of sludge that was set aside for beneficial reuse. Later in the report, key pressures and issues facing resource recovery facilities were outlined. These issues were mainly focused on biosolids and sludge management.

Biosolids Sampling Guide

The Biosolids Sampling Guide was published by the NEIWPCC in 2006 but is still relevant today.

2006 Guide Overview

The purpose of the Biosolids Sampling Guide was to provide wastewater treatment plant operators with comprehensive guidance on sludge sampling plans. At the time, most sampling guidance documents gave more surface recommendations that had significant limitations.

The 2006 guide created by the NEIWPCC was made to be highly specific while providing operators with adaptable appendices and worksheets that can help them craft effective sludge sampling plans. The many subjects that are covered in this manual include sample collection, documentation procedures, handling, data reporting, and laboratory considerations.

Conclusion

Industrial wastewater residuals are created during food production, paper manufacturing, and water treatment applications. With modern technologies and comprehensive waste management plans, it’s possible to reuse these residuals for beneficial purposes. You can more effectively adapt to the latest environmental requirements by adopting proper management strategies and innovative solutions. Explore additional resources and guidance for best practices in residuals management.