Determination of Solids in Water-Total Solids,Fixed and Suspended Solids

Solids refer to matter suspended or dissolved in water or wastewater. The determination of solids in water is very important in assessing the suitability of water used for drinking and industrial purposes.

The solid analysis in water can be characterized in many ways such as total solids, suspended solids, dissolved solids fixed solids, volatile solids and settleable solids

Principle of total solid analysis in water

These tests can be used to determine the physical and chemical properties of water.

Total solids is the term applied to the material left in the vessel after evaporation of a sample of wastewater and its subsequent drying in an oven at a definite temperature.

Total solids analysis include “total suspended solids” the portion of total solids retained by a filter and “total dissolved solids” the portion that passes through the filter.

Fixed solids are the residue remaining after ignition for 1 hour at 550oC. The solid portion that is volatilized during ignition is called volatile solids. It will be mostly organic matter.

Water that are low in organic matter and total mineral content and are intended for human consumption may be examined under 103-105oC or 179-181oC.

But water containing considerable organic matter or those with pH over 9.0 should be dried at 179-81oC. In any case, the report should indicate the drying temperature.

The sample is filtered and the filtrate evaporate in a weighed dish on a steam bath, the residue left after evaporation is dried to constant weigh in an oven at either 103-105oC or 179-181oC.

The increase in weight over that of the empty dish represents total dissolved solids and includes all materials, liquid or solid, in solution or otherwise, which passes through the filter and not volatilized during the drying process.

The difference between the total solids and the total dissolved solids will give the total suspended solids. The dishes with the residue retained after completion of the tests for total solids and total dissolved solids are subjected to heat for 1 hour in a muffle furnace held at 550oC.

The increase in weight over that of the ignited empty vessel represents fixed solids in each instance. The difference between the total solids and the fixed solids will give volatile solids.

All the quantities should be expressed in mg/L. Settleable matter in surface and saline water as well as domestic and industrial wastes may be determined and reported on a volume basis as milli litre per litre.

Determination of Solids in Water
Determination of total Solids in Water

Measurement of solids in water

a) Determination of Total Solids

  1. Ignite the clean evaporating dish in the muffle furnace for 30 minutes at 550oC and cool in a desiccator.
  2. Note down the empty weight of the dish (W1)
  3. Pour a measured portion (50 to 100 ml) of the well mixed sample in to the dish and evaporate the contents by placing the dish on a steam bath
  4. Transfer the dish to an oven maintained at either 103-105oC or 179-181oC and dry it for one hour.
  5. Allow the dish to cool briefly in the air before placing it while still warm, in a desiccator to complete cooling in a dry atmosphere.
  6. Weigh the dish as soon as it has completely cooled (W2).
  7. Weight of residue = (W2-W1) mg
  8. W2 and W1 should be expressed in mg.

The below video shows measurement of total solids in water

b) Determination of Total fixed solids

  1. For the determination of total fixed solids in water.Keep the same dish used for determining total residue in a muffle furnace for 1 hour at 550oC.
  2. Allow the dish to partially cool in air until most of the heat has dissipated, then transfer to a desiccator for final cooling in a dry atmosphere.
  3.  Weigh the dish as soon as it has cooled (W3).
  4. Weight of total fixed residue = (W3-W1) mg
  5. W3 and W1 should be expressed in mg.

c) Determination of Total suspended solids

  1. For the determination of total suspended solids in water.Filter a measured portion of the mixed sample (50 or 100 mL) through a filter paper which is previously dried and weighed (W4 mg).
  2. Dry the filter paper in an oven at 103-105oC for one hour
  3. Note the weight of the filter paper with dried residue as W5 mg.Weight of suspended solids = (W5-W4) mg.



Determination of Solids in Water

The below video shows the measurement of suspended solids in water

d) Determination of Total dissolved solids

For determination of total dissolved solids in water

  1. Total dissolved solids= Total Solids –Total Suspended Solids.

e)Determination of Total volatile solids

For the determination of total solids in water.

  1. Total volatile solids= Total Solids –Total Fixed Solids

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