What happens in wastewater treatment?

By: James Greenwood on Sep 14, 2021

A growing number of commercial organisations are treating and re-using their wastewater in a bid to combat rising water supply and disposal costs and increasingly stringent discharge regulations.

By treating your wastewater you can significantly reduce your discharge costs. And if you can clean it up to domestic and industrial standards, you can start gaining long term value from your waste.

But what’s involved in the wastewater treatment process?

Three stages of wastewater treatment

There are three main stages in the wastewater treatment process: 

  • Primary
  • Secondary
  • Tertiary

1. Primary wastewater treatment

Primary treatment of wastewater involves the sedimentation of solid waste within the water.

The wastewater is temporarily held in holding tanks where solids settle to the bottom before being collected. Fats and oils are scraped off the top and the remaining liquid is discharged or moved through to a more thorough secondary phase of wastewater treatment. Meanwhile, leftover sludge can be treated separately and used for other commercial purposes (more on this later). 

Dissolved Air Flotation (DAF) is one primary treatment that can be used to concentrate and remove a wide range of suspended solids in wastewater, including fats, oils and grease. This technology is ideally suited to particles that are slow settling, of neutral density or buoyant. 

The Volute Dewatering Press machine is another important part of primary and secondary treatment cycles, as it enables both sludge thickening and dewatering. It is particularly popular in the dairy, food manufacturer, rendering plant, brewing, distillery and anaerobic digester sectors.

Both these processes can be used to remove contaminants that would negatively impact an industrial biological wastewater treatment system downstream.

2. Secondary wastewater treatment

The secondary phase of wastewater treatment works on a deeper level than primary and is designed to break the waste down into harmless substances.

Coagulants and flocculant chemicals are used for further solids removal, lime softening, sludge thickening and solids dewatering. Coagulants are added to destabilise the suspended particles while flocculants help them to bind together so they can be filtered out of the water more effectively. 

Water treatment with these chemicals and processes can result in up to 90% reduction in suspended solids and organic loads, thus reducing the strength and volume of the wastewater for discharge and, therefore, associated disposal costs.

3. Tertiary wastewater treatment

The aim of the tertiary phase of treatment is to raise the water quality to domestic and industrial standards or to meet requirements around the safe discharge of water into the environment.

Techniques include UV disinfection and chemical disinfection. UV treatment doesn’t affect the pH, appearance, taste or smell of water, but it does destroy microorganisms that may be harmful to humans and the environment. 

Read the blog: How does wastewater affect the environment?

The most commonly used chemical for disinfection is chlorine, an oxidising chemical that purifies the wastewater. Typical forms of chlorine used in wastewater treatment are elemental chlorine, hypochlorite and chlorine dioxide.

The treatment removes any remaining inorganic compounds and substances such as nitrogen and phosphorus, as well as bacteria, viruses and parasites that may be harmful to human life, including Giardia - a bacteria that causes stomach and intestinal illness.

Once this process is complete, the water is clean and safe to be re-used to discharged back to the environment.

Sludge treatment

So what to do with the sludge collected during primary wastewater treatment?

It can be put to good use.

The sludge collected can be used for:

  • Heat and power - Using a treatment called anaerobic digestion, the sludge is heated to encourage the bacteria to eat it. This creates biogas that can be turned into heat and used to generate electricity. Alternatively, the sludge can be dried into blocks (or ‘cakes’) which are then burned to generate heat.
  • Gas to grid - The biogas can also be cleaned to a higher standard (known as biomethane) and put back into the national grid.

Wastewater treatment can bring significant savings on daily running costs, enabling water re-use and waste to energy. In short, the process involves:

  • Separating water from contaminants
  • Breaking the waste down into harmless substances
  • Removal of pathogens 

WCS Group’s wastewater team provides specialist commercial and industrial water treatment knowledge which helps wastewater to be re-used. To find out more about how our solutions could help you, click here.

Wastewater Treatment

Topics: Wastewater

James Greenwood

Written by James Greenwood

James Greenwood as been working in the Water Treatment and Water Hygiene Industry for over 20 years. He is currently the Sales and Marketing Director for WCS Group the largest water hygiene and treatment Company in the UK. James has been instrumental in bringing significant innovations to the UK market over the years always focusing on enhancing client’s compliance and delivering true return on investment projects offering monetary and environmental savings.