Measurement of Solids in Water

Measuring solids in water is important as it is used for control of various treatment processes and for examination of water quality. The level of total suspended solids and total dissolved solids in water affect the quality of the water and how it can be used.

High levels of total suspended solids affect turbidity, increase water temperatures decrease dissolved oxygen (DO) and photosynthesis levels thereby reducing aquatic life.

Water with high amounts of dissolved solids is unpalatable for consumers and may be unsuitable for bathing or cleaning.

What are Total Suspended Solids (TSS)?

Total suspended solids (TSS) are harmful in excess and listed as a conventional pollutant as per statutory requirement indicating the quality of water.

It is useful in processes where suspended solids are present or are removed namely coagulation , flocculation, settling, clarification, precipitation, and filtration.

High levels of suspended solids can affect the performance of filtration systems, capital equipment and plumbing systems.

High amounts of suspended solids in lakes, reservoirs, rivers and streams have harmful effects on the ecological system.

TSS is measured when water is poured through a pre-weighed filter, the particulate matter that remains after the filter dries is classified as TSS. This type of measurement provides an actual dry weight of suspended solids.

TSS is calculated as follows:-

TSS (mg/L) = (Wfss – Wf)/Vs Where: Wfss: weight of filter with suspended solids Wf: weight of the filter Vs: volume of sample

ASTM D5907, EPA Method 160.2, Standard Methods 2540D or similar gravimetric method is used for measuring TSS.

What are Total Dissolved Solids (TDS)?

Dissolved solids ( Typically < 2 microns ) refer to any minerals, salts, metals, in the form of molecules, atoms, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that dissolve in water.

The TDS concentration is the sum of all filterable substances in water that can be determined gravimetrically. However, in most cases, TDS is primarily comprised of ions. TDS is mainly used in the studies of water quality in the natural bodies of water, including surface and ground sources.

TDS is not considered a primary pollutant, it is an indicator of water quality.


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