What is Wastewater Treatment?

Mike Froom

Wastewater is water that is no longer needed or no longer suitable for use. It arises from many domestic activities such as bathing, flushing toilets and rainwater run-off. It’s also created in many industrial processes where water might be used for cooling or other process applications. This wastewater is often contaminated with bacteria, toxins and chemicals. Wastewater treatment refers to the processes used to convert this wastewater into water that is safe to be discharged back into the environment.

What is Municipal Wastewater?

Municipal wastewater is derived largely from human habitation in municipal areas. Urban wastewater is defined as the mixture of domestic waste water from kitchens, bathrooms and toilets along with the wastewater from industries discharging to sewers and rainwater runoff from roads and other impermeable surfaces such as rooftops and pavements.

Although untreated wastewater is still primarily water (generally containing less than 0.1% solid material) without treatment it would cause significant damage to the environment. It also presents potential health risks from water-borne pathogens if discharged into environments used for recreational activities, such as swimming and canoeing. Untreated wastewater contains sewage litter and sewage solids which can smother river beds and adversely affect wildlife.

Water Pollutant Categories

Liquid wastes contain a variety of suspended and dissolved pollutants which fall into the following defined categories.

  • Oxygen demanding wastes (Biodegradable organics)
  • Disease-causing agents (pathogens and parasites)
  • Nutrients
  • Synthetic organic compounds
  • Inorganic compounds and minerals
  • Sediment
  • Radiation
  • Heat

Municipal wastewater presents a number of challenges to remove various contaminants.

How is Wastewater Treated?

The broad objectives of wastewater treatment are:

  • To protect the water environment for animals and plants that live in and around water
  • To make water safe for recreation.
  • To make water that is safe for use as a resource for drinking water, sanitation, industry and commerce.

The selection of wastewater treatment methods depends on the contaminants present.

Wastewater treatment plants tend use multiple levels of water treatment.

  • Primary treatment: This allows suspended solid matter, mainly organic, to settle.
  • Secondary treatment: This stage involves biological break down to reduce residual organic matter.
  • Disinfection and release: Disinfection by chlorination is carried out.
  • Sludge digestion: Anaerobic sludge digestion and sludge drying.

How to Treat Industrial Wastewater

So far we’ve looked at the treatment of municipal and urban wastewater. But what about the wastewater that’s created by various industries? For example, the mining and mineral processing industries which use lots of water for all aspects of their operations. Or the petrochemical industries which use vast amounts of water in cooling tower systems and other applications and often have to deal with oil based contaminants along with inorganic chemicals in the wastewater.

Effective industrial wastewater treatment can be very challenging. Differing industries and operational practices influence the type of wastewater produced so there is no single industrial wastewater treatment process that is right for all applications. Here are just a couple of examples.

Detergent Manufacturing Industry

A detergent and disinfectant manufacturer was spending a significant amount each month to have an external service provider collect their wastewater for offsite disposal. The manufacturing plant produces a significant volume (6 cubic metres per day) of wastewater which could not be discharged directly to the sewage system without appropriate treatment. Their aim was to implement a wastewater treatment system which could cope with their wastewater volume and the highly variable effluent they produce, allowing it to be discharged directly to the main sewers.

The solution for them was devised based upon a worst case scenario for the effluent quality. This involved the implementation of an evaporator system which accelerates the natural evaporation process producing a distillate that is well within the required limits for biological and chemical on demand (BOD and COD) consent. This resulted in full approval from the local water authority and SEPA, allowing the discharge of the majority of their processed wastewater to the main sewage system. This saved them the monthly bill they had been paying to have their wastewater taken offsite for treatment.

Food and Beverage Industry Wastewater Treatment

Another contrasting solution was required for a food processing plant generating as much as 500 cubic metres of wastewater per day. Their intention was to apply advanced wastewater processing technologies and renewable energy solutions to showcase sustainable development.

The solution for them was an Anaerobic Membrane Bio-Reactor (AnMBR) which produces extremely high quality effluent that can be reused or discharged directly to the drainage system, while maximising renewable energy production. The biogas produced by the reactor was to be used as fuel for onsite plant, contributing to their aim to be the first zero carbon facility of this type in the UK.

These two examples demonstrate how how industrial wastewater treatment will often require a bespoke solution to meet specific aims and objectives.

What is Wastewater Management?

Our worldwide water resources are under continuing pressure due to rapid industrialisation, urbanisation, population growth and food production. Water related diseases account for high levels of infant mortality in some parts of the world. The management of wastewater plays an important role in establishing and improving healthy water supplies for human populations, supporting the needs of industry and protecting the environment.

The primary goal of wastewater management is to clean wastewater of contaminants and protect our water resources. Water needs to be clean enough to be released into waterways, rivers and oceans without causing any environmental impact. And it needs to be clean enough to be used by people, for drinking and domestic uses. It also needs to be clean enough to be used in industrial and agricultural applications.

Urbanisation and human migration are having a significant impact on wastewater production. Wastewater management therefore faces some serious challenges in the collection, treatment and safe reuse of wastewater.