Types of Solids | Activated Sludge Process | Wastewater Treatment Plant


 Types of Solids

Total Solids

  • Total dissolved and suspended organic and inorganic residue remaining after evaporation, expressed in milligrams per liter.
  • Total solids include dissolved as well as suspended materials.
  • Nonsettleable and settleable materials are both included in suspended solids.

Dissolved Solids

  • Solids that can be filtered using a standard glass fiber filter.
  • The weight difference between total solids and suspended solids is referred to as dissolved solids weight.
  • The suspended solids settle on the filter pad when a sample is filtered through a fine mesh filter (for example, a 0.45 micron membrane filter), while the dissolved solids remain in the water passing through the filter.
  • To calculate the weight of dissolved solids, take a sample of the water that has passed through the filter. To determine the weight of dissolved solids, evaporate the sample and weigh the residue.


Suspended Solids

  • Suspended solids are the solids captured on the filter pad, or the difference between the sample's total and dissolved solids content.
  • Solids that settle or float in a clarifier, as well as lighter nonsettleable (colloidal) solids.
  • The size, shape, and weight of suspended solids determine their classification.

Settleable Solids

  • Settleable Solids are a subset of the Suspended Solids.
  • Larger particles settle more quickly.
  • Before designing settling basins, sludge pumps, and sludge handling facilities, settleable solids are estimated.
  • Measuring settleable solids allows the basin efficiency of solids removal to be calculated.
  • The Imhoff cone measures solids in milliliters per liter.

Nonsettleable (Colloidal) Solids

  • Nonsettleable Solids are a type of suspended solids.
  • After the settleable solids have precipitated out, the colloidal solids will remain in suspension. The addition of a chemical flocculating agent or filtration is usually required to remove colloidal solids.
  • Subtract the weight of settleable solids from the weight of suspended solids to arrive at this figure.

Floatable Solids

  • Floatable solids are nonsettleable solids that float to the surface of a tank or stream.
  • There is no accepted method of measuring and evaluating floatable solids.
  • Scum is typically composed of fat or grease particles. Surface skimming equipment on the primary or secondary clarifiers is most effective at removing scum.
  • They are unappealing and unsightly, and they can emit odors.

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