Wastewater Treatment

Treatment of wastewater prior to discharge may be required in order to comply with conditions of consent to discharge or an operating permit under IPC/IPPC legislation.

Treatment of effluent prior to discharge will also reduce the costs imposed by the water company (if discharge is direct to the sewers) or the Environment Agency (if discharge is direct to controlled waters).

An overview of some of the techniques available is outlined below (source: Effluent Management On-line)

Preliminary Treatments include:

• Coarse screens located at source
  

• Flow and load balancing to cope with the variability of effluent streams liberated from an installation
  

• Corrective treatment such as pH control and chemical conditioning of effluent
  

• Gravity settling

Primary Treatment involves the removal of particulate solids or gross contaminants such as fats oils and greases this can be achieved by:

• Screening
  

• Sedimentation
  

• Dissolved air flotation
  

Secondary Biological Treatments involve the removal of biochemical oxygen demand (BOD) by

Aerobic systems

• Conventional activated sludge processes

• Sequencing batch reactors

• Membrane bioreactors

• Fixed film processes

• Hybrid systems

or

Anaerobic systems - breakdown organic matter in the absence of oxygen with the production of methane that may be re-used as a fuel source

• Up flow anaerobic sludge blanket

• Expanded granular sludge blanket

• Internal circulation reactor

• Hybrid anaerobic system
  

Secondary Chemical Treatment

• Neutralisation and precipitation

• Flocculation and coagulation

• Oxidation and reduction

Tertiary Treatment - often seen as a top-up treatments following secondary biological treatment and is often required to achieve a consent to discharge to controlled waters. Treatments include:

• Sand Filtration

• Carbon Filtration

• Membranes

• Disinfection techniques such as chlorination, UV light and ozone

Sludge Treatment and Disposal - sludge's produced in the primary and secondary treatment stages can be thickened and dewatered using

• Belt thickeners

• Filter Presses

• Centrifuges
  
  
  

Effluent Management On-line is a web site funded by Envirowise (a Government programme providing practical environmental advice for business) providing news and views on all aspects of effluent management and a forum for registered companies to exchange experiences. In order to get full access to the site potential users must first register by completing an on-line registration form.

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