Raw, untreated sewage is a serious hazard to the environment as well as to the nearby population. However, through proper treatment, wastewater facilities can keep up with demand, reduce pathogenic risks, and reintroduce clean water back into the environment. Learn more about the role of sludge treatment in improving wastewater processing.

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oxygen bubble in dirty sewage water treatment in factory pond.

Sewage Sludge

When municipal wastewater treatment centers process wastewater, they generate sewage sludge as an unwanted byproduct. This semi-solid sludge is made up of chemicals, plant nutrients, organic material, and inorganic waste. This material is also full of bacteria and pathogens, making it dangerous to process and store without the right tools and procedures in place. Treatment is one of the most important parts of wastewater processing, as it alters the sewage sludge to minimize environmental hazards as well as safety and health concerns.

Sludge Treatment Process

The sludge treatment process incorporates these four stages:

1. Sludge Thickening

One way to help control sewage sludge is to thicken it. This can help control the flow of semi-solid fluid, reduce its overall volume, and make the material easier to process. 

Before sludge thickening occurs, many systems add clarifying agents and mix them into the fluid. After reaching primary or secondary clarifiers, the sludge is then stirred to help the material settle and thicken. A gravity thickener reduces the final volume of the material. In the primary stage, the sludge is between 8 and 10 percent solids. Secondary sludge can contain up to 4 percent solids after thickening.

2. Sludge Digestion

Now that the sludge is more compact and easier to handle, wastewater treatment plants can start to address the pathogens and bacterial hazards in the sludge. Sludge digestion processes break down the material so it decomposes and turns into stable components. The dangerous pathogens are digested, and the lingering solids lose mass. After this stage, treatment facilities can dewater the sludge without worrying that pathogens will adversely affect the environment.

Let’s take a closer look at the sludge digestion process, which usually involves two stages:

  1. Heating and Mixing: The sludge is mixed in a closed tank to break down the material. It is also heated to encourage the growth and activity of bacteria that anaerobically eat the pathogens in the sludge. Certain acid-forming bacteria can consume the lipids and proteins in organic waste to produce water-soluble, less hazardous byproducts. Those byproducts, in turn, become fatty acids.
  2. Gas Production: Treatment facilities move the sludge into a second tank, where aerobic digestion takes place. Gases start to separate from the sludge as more bacteria break down the sludge. While the resulting CO2 is often a waste product, the facility can collect the methane to provide power for the digestion tank and other functions.

3. Dewatering

Once the treatment process has collected the methane for power applications, the sludge can move to the dewatering stage, which separates salvageable water from the material. Up to 85% of the volume of sludge can be water. When facilities dry and dewater the sludge, they can both safely reintroduce water to the environment and significantly reduce the total volume of remaining waste. 

Next, the sludge passes through a centrifuge, which uses centrifugal forces to press the water out of the sludge and isolate the dried, solid remainder of the sludge for disposal. Some treatment facilities use a filter press instead to press all the water out of the sludge and compress the remaining solids.

Two of the most common processes for drying sludge are depositing the material along sludge-drying beds and processing the sludge in solid-liquid separators (thermal dryers). 

4. Disposal

Now that water has been removed from the sludge, the remaining cake can be disposed of through:

  • Landfill
  • Incineration and coverage
  • Use as a fertilizer (depending on the makeup of the sludge)

Benefits of Wastewater Treatment

Proper wastewater treatment has several benefits, ranging from easier and safer waste disposal to the formation of useful byproducts. Consider these crucial benefits:

Waste Reduction

By treating and releasing water from sewage sludge, facilities significantly reduce the total volume of remaining waste. This reduces adverse environmental effects and also reduces the total disposal cost of sewage sludge cake.

Energy Production

By collecting methane, facilities can power the digestion tanks and other processes in their treatment stations. This lowers the total energy consumption and can even make some wastewater treatment processes self-sustainable. In the event that the sewage sludge produces excess methane and generates extra electricity, that power can be sold to the regional or national grid.

Fertilizer Production

Safe, biodegradable material in dried sewage sludge can be used as a fertilizer, increasing agricultural production and decreasing sewage storage demand.

An infographic explaining the benefits of wastewater treatment

Contact ELODE for the Right Sludge Treatment Process

By investing in wastewater processing that includes sludge treatment processes, you can reduce negative environmental effects, increase energy efficiency, support sustainable processes, and more. Wastewater processing produces positive short-term and long-term effects that help combat water shortages and other crises around the world. Contact our team today to learn more about how ELODE is developing and innovating sludge treatment processes.

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