Experiment No. 3: Determination of Solids

This lab report details Experiment No. 3, focusing on the

Determination of Solids. This test is crucial in Sanitary Engineering for assessing water quality and treatment requirements.

OBJECTIVE:

To determine the concentration of suspended, dissolved, volatile and total solids in the given water/wastewater sample(s).

APPARATUS REQUIRED:

• Porcelain/crucible evaporating dishes of 150–200 mL capacity
• Steam bath
• Drying oven
• Desiccators
• Analytical balance
• Filter paper (preferably of glass fiber)
• Electric muffle furnace

THEORY/PRINCIPLE:

Solids in water occur in both suspended and dissolved forms. The classification of solids is based on their size, behavior during filtration, and mass lost or retained during heating. ‘Total solids’ is the term applied to the material left in the vessel after evaporation of a sample of water/waste water and its subsequent drying in an oven at a definite temperature. Total solids 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 550°C. The solid portion that is volatilized during ignition is called volatile solids. It will be mostly organic matter. Waters that are low in organic matter and total mineral content and are intended for human consumption may be examined under 103–105°C or 179–181°C. But water containing considerable organic matter or those with pH over 9.0 should be dried at 179–181°C. In any case, the report should indicate the drying temperature.

The sample is filtered and the filtrate evaporated in a weighed dish on a steam bath; the residue left after evaporation is dried to constant weight in an oven at either 103–105°C or 179–181°C. 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 pass through the filter and are 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 550°C. The increase in weight over that of the ignited empty vessel represents fixed solids in each instance. The difference between the total dissolved/total suspended solids and the corresponding fixed solids will give volatile solids in each instance. All the quantities should be expressed in mg/L.

Additional Specifications:

• Filter Paper: Glass microfiber (Chemlab) GF3 Grade filters were used, which have a nominal pore size of 1.2 µm.
• Guideline Values: For sewage/sludge, typical values for TSS in raw sewage range from 155–330 mg/L, while treated effluent is often regulated to < 30 mg/L.

PROCEDURE:

(a) Total solids

1. The clean evaporating dishes were ignited in the muffle furnace at 550°C for 30 minutes.
2. The dishes were cooled in a desiccator for 30 minutes and the empty weight of the dish (W₁) was noted down.
3. A measured portion (20 mL) of the well-mixed sample was poured into the dish and the contents were evaporated by placing the dish on a steam bath.
4. The dish was transferred to an oven at 103–105°C and dried for 1 hour.
5. The dish was allowed to cool in a dry atmosphere in a desiccator.
6. The dish was weighed as soon as it had completely cooled (W₂).
7. Weight of total residue = (W₂ – W₁) mg.

(b) Total fixed solids

1. The same dish used for determining total residue was kept in a muffle furnace for 1 hour at 550°C.
2. The dish was allowed to partially cool in air until most of the heat had dissipated, then transferred to a desiccator for final cooling in a dry atmosphere.
3. The dish was weighed as soon as it had cooled (W₃).
4. Weight of total fixed residue = (W₃ – W₁) mg.

(c) Total Suspended Solids (Modified for data)

1. A glass fiber filter paper was placed in a crucible and weighed (W₄).
2. A measured portion of the mixed sample was filtered through the filter paper.
3. The crucible with filter paper and residue was dried in an oven at 103–105°C.
4. Weight of suspended solids residue = (W₅ – W₄) mg.
5. W₄ = Weight of Crucible + Filter Paper (empty).
6. W₅ = Weight of Crucible + Filter Paper + Residue (after 103°C).

(d) Fixed Suspended Solids

1. The crucible used in determining total suspended solids was kept in a muffle furnace for 1 hour at 550°C.
2. The steps outlined in the total fixed solids procedure were repeated.
3. Weight of fixed suspended solids residue = (W₆ – W₄) mg.
4. W₆ = Weight of Crucible + Filter Paper + Fixed solids left after ignition at 550°C.

OBSERVATION:

Sl. No.	Item	Value
1	Sample Type	GC out
2	Volume of sample taken (V)	20 mL (0.020 L)
Total Solids
3	Weight of empty evaporating dish (W1)	46.194 g
4	Weight of dish + total solids (W2)	46.226 g
5	Weight of dish + fixed solids (W3)	46.205 g
Suspended Solids
6	Weight of empty crucible + filter paper (W4)	40.183 g
7	Weight of crucible + filter + suspended solids (W5)	40.206 g
8	Weight of crucible + filter + fixed suspended solids (W6)	40.188 g
9	Weight of filter paper alone	0.099 g

CALCULATIONS:

1. Total Solids (TS)

2. Total Fixed Solids (TFS)

3. Total Volatile Solids (TVS)

4. Total Suspended Solids (TSS)

5. Total Dissolved Solids (TDS)

6. Fixed Suspended Solids (FSS)

7. Volatile Suspended Solids (VSS)

8. Fixed Dissolved Solids (FDS)

9. Volatile Dissolved Solids (VDS)

RESULT

For the given water sample (GC out), different solid constituents can be tabulated as:

• Total Solids (TS) = 1600 mg/L
• Total Dissolved Solids (TDS) = 450 mg/L
• Total Suspended Solids (TSS) = 1150 mg/L
• Total Fixed Solids (TFS) = 550 mg/L
• Total Volatile Solids (TVS) = 1050 mg/L
• Fixed Dissolved Solids (FDS) = 300 mg/L
• Volatile Dissolved Solids (VDS) = 150 mg/L
• Fixed Suspended Solids (FSS) = 250 mg/L
• Volatile Suspended Solids (VSS) = 900 mg/L

DISCUSSION

The total solids content of the given sample is 1600 mg/L. The ratio of dissolved to suspended solids shows that Suspended Solids (1150 mg/L) are the major component, which suggests the presence of substantial particulate matter like silt, clay, organic debris, or microbial flocs. Dissolved solids are 450 mg/L, which may include minerals, ions, and inorganic salts.

The distribution of fixed (550 mg/L) and volatile (1050 mg/L) solids indicates a higher presence of organic matter (volatile portion), which is typical for “GC out” (Grit Chamber outlet) wastewater samples before biological treatment.

ENGINEERING SIGNIFICANCE

• Estimation of solids is essential for designing sedimentation tanks, coagulation–flocculation units, filtration systems, and clarifiers.
• Suspended solids greatly influence filter clogging rates and settling tank efficiency.
• Volatile solids indicate biodegradable organic matter, crucial for sizing bioreactors, aeration systems, and sludge digesters.
• Fixed solids help estimate sludge ash content and disposal requirements.
• Higher TDS affects hardness, conductivity, and corrosiveness of water.
• High dissolved solids can cause scaling in boilers and cooling towers.

PRECAUTIONS

• Use clean, dry, pre-weighed evaporating dishes to avoid systematic errors.
• Handle dishes with forceps or gloves to prevent contamination from fingerprints.
• Ensure constant temperature in oven and muffle furnace during drying and ignition.
• Allow dishes to cool in a desiccator, not in open air, to prevent moisture absorption.
• Mix the water sample thoroughly before taking the aliquot to maintain representativeness.
• Avoid splashing or loss of sample while evaporating on the steam bath.
• Use glass fiber filter paper for accurate separation of dissolved and suspended solids.
• Weigh the dishes immediately after cooling to maintain accuracy.
• Filter apparatus and funnels must be thoroughly cleaned before use.
• Record all weights up to three decimal places (mg level) for precision.