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28 June 2019

Uses of sludge from wastewater

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Wastewater treatment plants (WWTP) around the world operate to remove contaminants from municipal wastewater. This is mainly comprised of household sewage, however, some contaminants come from industrial wastewater.

These contaminants are removed using biological, chemical and physical processes resulting in treated water (or effluent) that is safe for release back into the environment. As a result, a residue called sludge (sometimes referred to as biosolids) is formed. This article looks to discuss the different uses of the residual sludge from wastewater, along with the processes involved in its production.

NCH Asia Pacific provides a number of wastewater treatment solutions to help with the reduction of sludge build-up, contaminant levels, and more.

What is wastewater sludge?

Sludge is a by-product of wastewater treatment processes, usually presenting itself as a semisolid slurry classified as either primary sludge or secondary sludge.

  • Primary wastewater sludge is typically captured by a clarifier in the primary treatment process. Gravitational sedimentation is used to filter out the suspended solids and organics in the wastewater. This removes approximately half of the solids that enter at this stage.
  • Secondary wastewater sludge is created using an accelerated biological process in which naturally occurring microorganisms breakdown the biodegradable organic matter. The wastewater then flows to a secondary clarifier where the residual biomass settles to the bottom and can be removed.

What is the residual sludge from wastewater used for?

There are a number of uses for wastewater sludge - most requiring highly technical treatment processes to stabilize the matter. This is due to its hazardous pathogen content. Stabilizing processes include:

  • Thickening
  • Dewatering
  • Anaerobic digestion
  • Aerobic digestion
  • Alkaline stabilization
  • Composting

Once the sludge has been stabilized it can be referred to as biosolids. These biosolids can either be safely disposed of or go on to be recycled for use in a number of applications. Due to the strain put on landfills around the world, more solutions are being sought to reintroduce sludge back into the environment.

Recycling sludge in land applications

  • Recycling sludge as soil fertilizer looks to reintroduce the organic matter and plant nutrients back to agricultural lands.
  • This application returns the nutrients in the biosolids back into the soil so they can be used to produce crops.
  • This is particularly beneficial in soil with depleted organic matter due to continuous cropping.
  • Biosolids can also be subjected to further processes which enable them to be sold to agricultural, landscaping, and nursery markets.

Benefits of using sludge as fertilizer

  • The nutrients contained in the sludge at this stage act as a substitute for inorganic fertilizers.
  • When applied properly, the potential for loss of nutrient content through leaching or runoff is lower than with inorganic fertilizer.

Risks of using sludge as fertilizer

  • Any pathogens or pollutants remaining in the biosolids will be fed into the soil, which could adversely affect the health of humans and animals.
  • Soil quality and plant growth may also be affected by contamination.

Recycling sludge for building materials

  • Stabilized sludge, or biosolids, can be used in the production of building and construction materials.
  • The reuse of wastewater sludge as construction materials offers a feasible alternative for costly sludge disposal.
  • Building materials that can be produced using sludge include bricks, concrete, and aggregate.

Disposal of sludge

High concentrations of toxic materials from industrial processes may make the sludge unsuitable for the applications above. This is where disposal of the sludge, either through thermal destruction or landfill site, becomes necessary.

To find out more about sludge solutions for your business, contact NCH Asia Pacific today.

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