How to Reduce Volatile Suspended Solids From Wastewater

Removing suspended solids from wastewater is essential for maintaining environmental and human health. Volatile suspended solids (VSS) are the organic particles that help make up total suspended solids (TSS), and they pose serious health risks. VSS can also reduce oxygen levels in streams, lakes and rivers, threatening ecosystems and the aquatic life they support.

Choosing the right wastewater treatment method and equipment can help treatment plants reduce VSS efficiently, releasing safer water back into surrounding communities while decreasing operating costs.

Importance of Reducing Volatile Suspended Solids in Wastewater

VSS are organic or biological particles, such as microorganisms, that can settle in water. They differ from fixed suspended solids (FSS), which are inorganic particles, such as silt or undissolved salt crystals. Together, VSS and FSS make up the total suspended solids in water or wastewater.

Anaerobic and aerobic wastewater treatment processes produce VSS — or sludge yield — because organic material converts to biomass, water and carbon dioxide in wastewater. The wastewater treatment process involves steps that reduce sludge volume and pathogenicity, but amounts of sludge remain in dry mass after treatment.

Reducing VSS from wastewater is essential for the following reasons:

Safety

VSS can consist of organic matter or live bacteria, posing serious health risks to surrounding communities. Removing VSS from wastewater prevents bacteria exposure and potential health effects such as gastrointestinal illnesses.

Healthier Ecosystems

Natural bodies of water, such as streams, lakes and rivers, rely on adequate dissolved oxygen concentration to sustain aquatic life. If treated wastewater is high in VSS when it reaches a natural water body, microorganisms consume more oxygen to decompose suspended solids. As the microorganisms work hard to decompose and oxidize the solids, they deplete the water’s oxygen, which plants and aquatic animals need to thrive.

Biochemical oxygen demand (BOD) measures the amount of oxygen microorganisms and bacteria consume to decompose organic matter, and chemical oxygen demand (COD) measures the amount of oxygen microorganisms use to oxidize organic matter. Reducing total volatile solids in wastewater helps lower BOD and COD levels, making the water safer for ecosystems when it returns to natural water bodies.

Greater Water Clarity

Water with a high turbidity level is cloudy and lacks transparency, blocking sunlight from reaching aquatic life. Reducing organic solids or VSS in wastewater helps reduce its turbidity, making it clearer when it returns to the ecosystem so sunlight can reach aquatic life easily.

Higher Wastewater Treatment Efficiency
Reducing VSS in wastewater can help a treatment plant boost efficiency, reducing costs and saving time on treatment processes. The fewer suspended solids in water, the less sludge it produces and the lower a plant’s sludge handling and disposal costs are. Reducing VSS also reduces the amount of chemicals necessary in a wastewater treatment process, helping the equipment last longer.

Reduce Volatile Suspended Solids From Wastewater

State and Federal Regulatory Compliance

State and federal governments enforce effluent regulations to protect people and the environment from pollution. VSS reduction is a crucial part of TSS removal, helping treatment plants comply with Environmental Protection Agency (EPA) standards and protect public health.

Clear Pipes and Filters

Organic solids can clog and scour pipes and filters in wastewater treatment systems. Reducing VSS reduces the solid particles entering pipes, helping a plant’s equipment last longer and perform better.

Improved Budget

Because reducing VSS can help a treatment plant comply with EPA standards and extend equipment life spans, it can also decrease costs. By properly removing VSS from wastewater, plants typically experience fewer maintenance costs and avoid EPA fines.

Factors That Increase VSS in Wastewater

The following factors increase VSS in wastewater:

Algae growth
Food waste
Increased BOD
Human pollution

TSS Removal Methods

Since volatile suspended solids are a part of total suspended solids, understanding how TSS removal methods work is important. Common TSS treatment methods are:

Oxidizing

The oxidizing wastewater treatment method uses oxygen to destroy TSS. This process produces a chemical reaction, increasing the sizes of suspended solids so equipment can remove them easily. A treatment plant may choose one of the following oxidizing solutions if they choose the oxidizing method:

Aeration
Ultraviolet
Hydroxyl radical
Ozone generators

Physical Filtration

Physical filtration methods separate suspended solids using depth filtration, sediment filters, strainers and screens. Facilities that treat wastewater with small particles and high TSS levels typically prefer the depth filtration method. If a plant uses this method, it’s best to opt for rotary valves because they prevent solid materials from rubbing against O-rings and spacers.

Chemical Precipitation

Chemical precipitation is also known as coagulation and flocculation. This process reduces TSS using chemicals known as polymers. Polymers gather small solid particles together, forming larger particles that are easier for equipment to filter. After the coagulation and flocculation process clumps particles together, a plant can filter them using one of the following types of equipment:

Dewatering bags
Auto strainers
Filter presses

Anaerobic and Aerobic Treatment

Biological wastewater treatment processes, such as aerobic and anaerobic methods, use microorganisms to break down suspended solids. Aerobic treatment depends on oxygen and high-quality equipment to effectively break down solids, while anaerobic treatment is effective with or without oxygen.

Aerobic and anaerobic treatment processes convert the organic material in wastewater to biomass, water and carbon dioxide.

Anoxic Treatment

Anoxic treatment is another type of biological wastewater treatment. This method mixes wastewater with sludge in an anoxic tank where microbes gain energy from nitrate and release nitrogen gas. The microbes also release oxygen as they break nitrogen down, so they work without additional oxygen.

How Wastewater Treatment Processes Can Reduce Sludge

The wastewater treatment process a plant uses can impact the amount of sludge that is produced. In some situations, combining aerobic, anaerobic and anoxic treatment processes can help decrease sludge production, and alternating cycles can reduce conventionally activated sludge’s sludge yield by approximately 50%.

How to Reduce VSS From Wastewater After Treatment

When biological treatment processes produce VSS, treatment plants can thicken the solids and utilize them as compost amendments or move them off-site. A plant can remove VSS from wastewater in the following steps:

Thickening

Thickening is typically the first stage in the sludge treatment process. During this phase, the primary or secondary sludge stirs and mixes with clarifying agents, creating larger solid clumps.

Dewatering

The dewatering phase of the sludge treatment process consists of reducing water content through one of the following processes:

Centrifugation: Centrifugation is a rapid process that separates liquids and solids using a rotating cylindrical bowl. The bowl’s fast rotating motion separates liquids and solids based on their densities, forcing solids to the bottom of the bowl while liquids move to the top.
Filtration: A filtration process forces water through sludge using a filter press, belt filter press or a screw press.
Evaporation: Evaporation is a process that increases a solute’s concentration using heat. Condensing steam produces heat that vaporizes water from sludge.

Treatment plants handle sludge as a solid material if it contains 50% to 75% water. If it contains over 75% water, plants handle the sludge with further treatment.

Digestion

During the digestion phase of the sludge treatment process, a treatment plant reduces the amount of organic matter and microorganisms in solid sludge. This process takes place in one of three methods:

Aerobic digestion
Anaerobic digestion
Composting

Disposal

In the final stage of the sludge treatment process, dewatered sludge moves to disposal sites. A plant may use one of the following methods to transport sludge to a designated disposal site:

Landfill
Reclamation
Incineration
Land application

Meeting VSS Wastewater Standards

The EPA establishes and enforces effluent guidelines or wastewater discharge standards that vary by industry. The EPA creates these standards based on the highest pollutant reductions possible for an industry based on the following factors:

Discharge characteristics such as flow variability, stormwater or pollutants
Practices, technologies or equipment a plant uses to treat discharge
Economic factors
Industry practices

To determine the greatest pollutant reductions economically possible for an industry, the EPA identifies the best wastewater treatment solutions or technology. The organization then bases its regulatory requirements on how well the technology performs. While the EPA doesn’t require a treatment plant within an industry to use the best solution or technology, it does require the plant to meet the regulatory standards that are based on the most effective technology.

Most Effective VSS Reduction Solutions

Some treatment methods work better than others at removing organic organisms such as bacteria from wastewater. Choosing the right wastewater treatment solution can help plants meet EPA standards, save money and reduce energy consumption.

The most effective VSS reduction methods are:

Moving Bed Biofilm Reactor

A moving bed biofilm reactor (MBBR) system is a biological treatment process that uses small organisms to help decompose waste. A biological process uses natural cellular processes and the organic matter in wastewater to break waste down into smaller particles and consume it. The microorganisms involved also turn complex waste materials into simpler substances that are easier for wastewater treatment equipment to filter out. A biological treatment system can operate independently, but it most often works as part of a more comprehensive system.

An MBBR system is one of the most effective biological treatment processes, making it a popular option for wastewater treatment plants. It decomposes organic organisms using the following components:

Aeration tank: An MBBR process takes place inside an aeration tank or basin featuring an open top that lets in plenty of oxygen. Wastewater enters this basin and can exit into a second basin for additional MBBR processing or further treatment.
Media: Thousands of biofilm-covered plastic chips occupy up to 50% to 70% of an aeration tank. Media may be in the shape of discs or wheel-shaped pasta, and they move freely in the tank, providing plenty of surface area for bacteria to grow and thrive. Bacteria grow on the media in multiple layers, allowing the MBBR system to self-regulate and recover faster than other processes if a pH change occurs.
Sieve: A sieve is a mesh material that allows water to exit the tank while keeping media inside.
Aeration grid: An MBBR system’s aeration grid is a fan that helps media move throughout the tank so they can collect waste effectively and efficiently.

The bacteria on an MBBR system’s media digest the organic material present in wastewater and convert soluble material into biomass. A solid separation system then removes the biomass downstream. The type of microorganisms a treatment plant introduces into its MBBR system depends on the type of waste it needs to remove. For example, a plant would introduce denitrifiers such as Alcaligenes, Paracoccus or Pseudomonas to convert nitrate into nitrogen gas — a process also known as denitrification.

Integrated Fixed Film Activated Sludge System

An integrated fixed film activated sludge (IFAS) system is similar to the MBBR system because it uses biofilm growth to enhance wastewater treatment technology’s effectiveness and reduce VSS. The IFAS process combines biofilm carriers with an activated sludge basin or a mixture of water and activated sludge.

During the IFAS process, wastewater flows into an aeration tank containing high oxygen levels that aid microbial growth and organic waste decomposition. The water then exits into a settling tank that separates the remaining waste from the water.

How Diffused Aeration Enhances Activated Sludge and MBBR Systems

Aeration is a crucial part of an activated sludge or MBBR process because it pushes oxygen into the tank via diffusers. A diffuser features tiny slits that create bubbles when the air comes in contact with the water. These bubbles feed the microorganisms used in an MBBR or activated sludge process, increasing the system’s speed and efficiency.

The air that diffusers add to a tank also mixes wastewater, helping solids remain suspended to prevent excess sludge buildup.

Improving VSS Reduction With Effective Equipment and Materials

The aeration process can consume approximately 60% of a treatment plant’s energy. Choosing the right equipment can significantly reduce energy consumption and overall operating costs.

Fine and Coarse Bubble Diffusers

Fine bubble disc and plate diffusers disperse oxygen via small bubbles, while coarse bubble diffusers produce large bubbles. Fine bubble diffusers are more efficient because they have a higher oxygen transfer rate.

Polytetrafluoroethylene Aeration Diffuser Membranes

Some diffusers feature a polytetrafluoroethylene (PTFE) surface, which can slow scaling and fouling and decrease energy consumption in an aeration tank. PTFE diffuser membranes can help reduce operating costs and maintenance frequency, increasing equipment uptime. PTFE membranes also typically last longer than other types of membranes because they maintain their flat shape longer.

Reduce VSS With SSI Aeration’s Wastewater Treatment Solutions

Reducing VSS in wastewater is crucial for the environment, human health and regulatory compliance. While several methods can help reduce VSS in wastewater, finding the right solution can significantly reduce operating costs, boost system longevity and increase equipment uptime.

SSI Aeration carries high-quality wastewater treatment solutions such as MBBR systems, aeration systems, IFAS systems, fine bubble diffusers and coarse bubble diffusers. You can also depend on SSI Aeration for proper installation, design and engineering services, and lab testing to ensure your system provides peak performance. Contact SSI Aeration to learn more about available wastewater treatment systems and equipment and how to choose the right option.