---
title: "Determining total, volatile, settleable solids"
subject: "Sanitary Engineering"
chapter: 5
key: "semester_6/sanitary_engineering:solids-determination-total-settleable"
source: https://www.bctengineer.com/q/semester_6/sanitary_engineering/solids-determination-total-settleable
site: BCT Engineering
---

# Determining total, volatile, settleable solids

Sanitary Engineering · Chapter 5: Characteristics and Examination of Wastewater

- Asked in: 2073 Bhadra, 8 marks
- Video: [Determination of all Solids in Wastewater/Water | TDS | TS | TFS | TSS | VSS | FSS | VDS | FDS | TSS](https://www.youtube.com/watch?v=WsRxE2IWVmk) — Vishnoo Spotlights
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/sanitary_engineering/solids-determination-total-settleable
- Whole chapter: https://www.bctengineer.com/md/semester_6/sanitary_engineering/chapter-5

## Question

How do you determine the Total Solid, Total Volatile Solid, Total Fixed Solid, Settleable Solid and Non-settleable Solids contained in a sewage sample?

## Short answer

Total solids by evaporation/weighing; volatile and fixed solids by ignition at 550°C. Settleable solids: one litre settled in an Imhoff cone for one hour, read volume in mL/L. Non-settleable solids = suspended solids minus settleable solids.

## Answer

All the solids are determined by weighing the residue after evaporation, filtration, settling or ignition.

#### Total solids (TS)
A well-mixed sample of 100 mL is poured into a clean, dried, pre-weighed evaporating dish (weight $W_1$). It is evaporated on a steam bath and dried in an oven at 103-105°C for 1 hour, cooled in a desiccator and weighed ($W_2$).

$$
TS\ (\text{mg/L})=\frac{(W_2-W_1)\times10^6}{\text{volume of sample (mL)}}
$$

#### Total fixed and volatile solids
The same dish with the residue is ignited in a muffle furnace at 550 ± 50°C for 15-20 min, cooled and weighed ($W_3$). Organic matter burns away.

$$
\text{Volatile solids}=\frac{(W_2-W_3)\times10^6}{V},\qquad \text{Fixed solids}=\frac{(W_3-W_1)\times10^6}{V}
$$

so $TS = \text{fixed} + \text{volatile}$.

#### Suspended and dissolved solids
A measured volume of sample is filtered through a weighed glass-fibre filter paper (Whatman GF/C). The filter with the residue is dried at 103-105°C and weighed. The weight gain gives the **suspended solids (SS)**. Then **dissolved solids = total solids − suspended solids**.

#### Settleable solids
One litre of well-mixed sample is poured into an **Imhoff cone** and allowed to stand for **1 hour** (after 45 minutes the sides of the cone are gently scraped or rotated to release the trapped matter). The volume of the solids settled at the bottom is read in **mL/L**. Settleable solids can also be found by weight:

$$
\text{Settleable solids}=SS_{\text{raw sample}}-SS_{\text{supernatant after 1 h settling}}
$$

#### Non-settleable solids
These are the solids which do not settle in 1 hour (colloids and very fine suspended matter):

$$
\text{Non-settleable solids}=\text{Suspended solids}-\text{Settleable solids}
$$

(or equal to the suspended solids in the supernatant after settling; some books also include dissolved solids in this term.)

```text
 Sample
   |
   +-- evaporate 103 C ---> Total solids (TS)
   |        '-- ignite 550 C -> Volatile / Fixed
   +-- filter ---> Suspended (SS) / Dissolved (DS)
   '-- Imhoff cone 1 h --> Settleable / Non-settleable
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How are suspended solids found?
   A. Filter through a weighed glass-fibre filter, dry at 103-105°C and weigh the gain
   B. Evaporate at 550°C
   C. Settle 1 h in Imhoff cone
   D. Total solids minus fixed solids
   Answer: A. The filter retains suspended solids. (Key point: Suspended solids)

2. How are dissolved solids obtained?
   A. Suspended minus settleable
   B. Total solids minus suspended solids
   C. Fixed minus volatile
   D. Volatile solids
   Answer: B. DS = TS - SS. (Key point: Dissolved solids)

3. How are settleable solids measured volumetrically?
   A. 100 mL for 1 min
   B. 1 L boiling
   C. 1 L in an Imhoff cone for 1 hour, reading mL/L
   D. 500 mL for 24 h
   Answer: C. Result is in mL/L. (Key point: Settleable solids)

4. How are non-settleable solids found?
   A. Total minus volatile
   B. Dissolved minus fixed
   C. Settleable minus suspended
   D. Suspended solids minus settleable solids
   Answer: D. They are colloids and fine matter that do not settle in 1 h. (Key point: Non-settleable)

## Related in Sanitary Engineering

- [Settleable solids; first-stage BOD](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asettleable-solids-first-stage-bod) — Sanitary Engineering, chapter 5
- [Why examine wastewater; solids procedure](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aexamination-necessity-solids-procedure) — Sanitary Engineering, chapter 5
- [BOD of Bagmati sample at 30°C](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Abod-thapathali-4day-30c) — Sanitary Engineering, chapter 5
- [Factors affecting sewage; calculating discharge](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Afactors-sewage-calculate-discharge) — Sanitary Engineering, chapter 2

## Related in other subjects

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- [Torsion of non-circular bars by Saint-Venant](https://www.bctengineer.com/question.md?key=semester_5%2Fmechanics_of_solids%3Asaint-venant-prandtl-stress-function) — Mechanics of Solids, chapter 9