When solids are referred to in terms of water treatment, it means any insoluble contaminants other than fats, oils and greases.

Solids are another parameter that will always appear on a trade effluent discharge consent which must be met to avoid potential prosecution and associated fines. They are also the third part of the MOGDEN formula – the method used to calculate your trade effluent charges when discharging to a water company – along with volume and COD.

Therefore, reducing solids to meet consent has a direct cost saving against the MOGDEN formula.

There are a number of different types of solids which may appear on your trade effluent consent to discharge:

  • Total Suspended Solids (TSS) – all solids present.
  • Settleable solids – solids that sink and do not appear in the top water when tested after the sample has been stood for 60 minutes.
  • Rapidly settleable solids – as above but the time frame is reduced to between 5 and 15 minutes.
  • Unsettleable solids – the solids that remain floating after a sample has been stood for 60 minutes.
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