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The clean-up process

The 'how' and 'why' of Wastewater Treatment Works

Put simply, a Wastewater Treatment Works (WwTW) receives soiled water from the sewers and cleans it up so that it's fit to go back into the natural environment, usually via rivers to the sea. Wastewater Treatment Works (WwTW) have a large 'footprint' and typically require lots of open space.

Both the design and operation of WwTWs are highly skilled activities, calling for the most able engineers and operators. The larger the town or city, the more 'works' it will have, sited usually on the outskirts and geographically lower than the main developed areas to take engineering advantage of the natural drainage.

WwTW are categorized by their processing capacity. Depending on the relative population it serves, a WwTW will typically be one of two types:

  1. Activated sludge works – sophisticated, high-tech, expensive (normally service large towns and cities).

  2. Oxidation ponds (lagoons) – simple, basic, inexpensive (typically found in country towns).

For an in-depth look at both systems, click on Types of WwTW.

From sewer to stream

The inlet works receives raw sewage (COD often 2,500-5,000ppm), which is then passed over screens designed to strain it. Solids such as rags, plastic and other litter are retained while the sifted effluent is allowed to pass into the plant. Here it is processed (using bacteria) to remove the pollutants, sanitised and then discharged back into the environment in a healthy condition (COD approximately 100ppm).

Common WwTW problems

  • The efficacy of a WwTW is often hindered by toxic shock. Typically this is caused by large amounts of industrial waste (such as solvents, old oil or abattoir waste) being dumped into the system. Large numbers of latent bacteria in the WwTW are killed off as a result, reducing the effectiveness of the plant.
  • Poor 'settling' (of sludge) can result when there is very little bacterial activity in the works.
  • Organic overload occurs when the WwTW receives more sewage than it is designed to treat.
  • Hydraulic overload occurs during heavy rain when storm water finds its way into sewers. The sudden surge can cause organic 'wash out' in the works and sewage pollution with its associated health hazards in watercourses and rivers.

The BIO-SYSTEMS solution

BIO-SYSTEMS SA has a selection of products that are highly effective in remedying problems associated with the degradation of effluent in WwTW. These products include:

  2. BIO-SYSTEMS B220 - degrades grease deposits in pipes, sump boots and tanks. It can be used in gravity sewer lines, high grease food processing facilities and WwTWs. It is suitable for seeding into reactors, aeration basins and ditches where it enhances Chemical Oxygen Demand (COD) removal.
  3. BIO-SYSTEMS B500 - maintains high performance in bio-digestors and trickling filters (also known as bio-filters). It can also be used in rotary biological contactors and anaerobic ponds.
  4. BIO-SYSTEMS B600 - reduces sludge in any type of secondary biological treatment system. Use it in wastewater treatment lagoons, oxidation ponds and maturation rivers. It performs very well in cold weather.

  Wastewater Treatment Works before BS product  Wastewater Treatment Works before BIO-SYSTEMS treatment



Wastewater Treatment Works after BIO-SYSTEMS treatment  WwTW after BS product

The reason these products work so well

BIO-SYSTEMS products improve and balance the bacterial activity in specific sections of the WwTW. Being naturally-occurring consortia, selected and concentrated for their ability to degrade human sewage and associated effluents, they rapidly adapt to the conditions within a WwTW. By using small regular seedings of a combination of the above products, we have been successful in 'buying back' capacity in plants running up to 120% of design capacity, achieving discharge quality to DWAF Standard. Once the enhanced activity has been established, routine weekly seeding by the plant operator will enable the works to run optimally.

How is effluent transferred to the WwTW? Click on Sewage conveyance.

For a complete list of BIO-SYSTEMS products and their target pollutants click on our Product table. Also visit our Case histories.

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