What are the various solids present in waste water?
Solids are the parts of a liquid or slurry that remain after the water is removed. The quantity of solids in wastewater and manure impacts nutrient content, handling procedures and treatment processes.
Solids and moisture content:
The Total Solids (TS) substance of a sample is the mass of solids left after drying in a 103oC oven for 24 hours divided by the original mass of the sample. The TS content of thick slurries is expressed as a mass percentage (%). TS is commonly expressed as mass per volume, most commonly mg/l, for dilute slurries and liquids.
As the TS concentration rises and slurries begin to behave as semi-solids, the method of expressing mixture solid/liquid relationships shifts from solids content to moisture content.
The moisture content of a semisolid material is defined as the mass of water divided by the wet mass of the material. As long as the solids and moisture content are calculated on a wet mass basis, the two quantities add up to 100:
Moisture content (%) = Solid content (%) = 100
Solid fraction:
Total solids indicate the amount of solids in a liquid or slurry. It doesn't say much about the type of solids present. Total solids are divided into seven fractions based on two criteria:
1. Are the solids in the liquid suspended or dissolved?
2. Are the solids organic or inorganic in nature?
1-Suspended/ dissolved solids:
TDS (Total Dissolved Solids) appear as solid material only after the sample has been dried. Solid salt (NaCl) and sugar, for example, dissolve in water and appear to be invisible. When the sample is dried, the crystals reappear. Total Suspended Solids (TSS) are solids that do not dissolve when mixed with water.
The distinction between TDS and TSS is actually a little more complicated. A particle is considered dissolved (TDS) if it can pass through a 1.5 micron (1/17,000 inch) opening filter. If a particle is stopped by the 1.5 micron filter, it is said to be suspended (TSS). This may appear arbitrary, and many particles smaller than 1.5 microns are unquestionably not dissolved. This distinction between dissolved and suspended at 1.5 microns, on the other hand, is quite practical. Given the density of natural materials, a particle with a diameter of 2 microns is the smallest size that can be easily removed by mechanical means.
2-Organic and inorganic solids:
To the uninitiated, organic matter is defined as material that is alive or was once alive. Chemists use carbon content to determine whether a substance is organic or inorganic. The organic component of wastewater or manure solids is what burns.
Total Fixed Solids (TFS) is the portion of TS that remains after heating at 550®C for 1 hour; Total Volatile Solids (TVS) is the portion that is lost during heating (TVS).
The fixed solids content is also known as the Ash Content. Volatile Solids is a measure of the organic matter content of a liquid or slurry, but it is important to note that most organic materials contain some ash. Fresh manure, for example, is typically 80 percent volatile and 20% fixed.
Units of solid content:
The solids content of liquids and slurries can be expressed as a volume or as a mass.
-milligrams per litre on a mass per volume basis: The mass of solids contained in a sample is divided by its volume. The most common units are mg/l, though g/l units are sometimes used in extra-thick slurries.
-Parts per million on a mass per mass basis:If the sample density is assumed to be 1,000 g/l (the density of water), then units of mg/l directly convert to ppm – there are 1 million mg in a litre of water. These units may not be applicable to slurries because the density of the slurry may exceed 1,000 g per litre.
-percent solids on wet basis (% wb): The mass of solids in a sample is divided by the sample's original weight and multiplied by 100. This is usually the more accurate method for reporting slurries' solids content. A simple formula to remember is: percent wb = ppm x 10,000.
-percent solids on dry basis (% db): These units are sometimes used when reporting a sample's volatile solids content. Because the dry content of the sample is, by definition, TS, this gives the percentage of TS that is volatile.
For more information, contact Netsol Water.
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