Experiment: Determination of Total Solids in Water Sample

• Porcelain evaporating dishes

• Whatman No. 41 filter paper

• Filtration apparatus (Funnel, Conical flask, Stand)

• Beakers

• Drying oven

• Desiccator

• Analytical balance

• Steam bath

• The representative water sample to be tested

Background

Solids present in water can be classified as either dissolved or suspended. Total Solids (TS) is the term for all material left as residue after a water sample has been evaporated and dried at a specific temperature. This residue is further divided into:

• Total Suspended Solids (TSS): The portion of total solids that is retained by a filter. These are non-filterable particles like silt, clay, and microorganisms.

• Total Dissolved Solids (TDS): The portion that passes through the filter. These solids result from the solvent action of water on minerals, salts, and organic matter.

Working Principle

This experiment employs the gravimetric method, which relies on the physical separation and weighing of solids to determine their concentration.

Significance

The determination of solids is a crucial test in sanitary engineering. It provides a direct measure of the pollution load and the overall quality of water. High concentrations of solids can affect the taste of water, interfere with industrial processes by causing scaling and corrosion, and indicate the presence of contamination.

A) Determination of Total Solids (TS)

1. A clean, dry porcelain evaporating dish was weighed using an analytical balance. This initial weight was recorded as W₁.

2. A well-mixed sample of 25 mL of water/wastewater was poured into the dish.

3. The dish was placed in an oven at 103-105°C to evaporate the water to dryness (approximately 1 hour).

4. The dish was cooled in a desiccator to room temperature to prevent moisture absorption.

5. The dish was then weighed again, and the final weight was recorded as W₂.

6. The Total Solids (TS) in mg/L was calculated using the formula:

B) Determination of Total Suspended Solids (TSS)

1. A clean Whatman No. 41 filter paper was dried in an oven, cooled in a desiccator, and weighed. This initial weight was recorded as W₃.

2. A well-mixed 25 mL sample was filtered through the filter paper using a funnel and conical flask.

3. The filter paper containing the residue was carefully removed and dried in an oven at 103-105°C for approximately 1 hour.

4. The dried filter paper was cooled in a desiccator and then weighed again. This final weight was recorded as W₄.

5. The Total Suspended Solids (TSS) in mg/L was calculated using the formula:

C) Determination of Total Dissolved Solids (TDS)

1. The filtrate obtained after the TSS procedure was used for this test.

2. A clean, dry evaporating dish was again weighed (if not already) to ensure accuracy (W₁ reused or freshly determined).

3. 25 mL of the filtrate was added to the dish.

4. The filtrate was evaporated to dryness over a steam bath or heated directly in the oven.

5. The dish was placed in an oven at 103-105°C for 1 hour.

6. After cooling in a desiccator, the final weight was recorded as W₂.

7. The Total Dissolved Solids (TDS) was determined by:

(Note: The final values are taken directly from the provided observation sheet. The TSS value is calculated from the difference in filter paper weights, and the TDS value is from the difference in crucible weights, both adjusted for the sample volume.)

The experimental results show a Total Suspended Solids (TSS) concentration of 2380 mg/L and a Total Dissolved Solids (TDS) concentration of 3060 mg/L. When compared with established guidelines, both values are exceptionally high for potable water.

Comparison with Guidelines: The World Health Organization (WHO) and Nepal Drinking Water Quality Standards (NDWQS) recommend a TS level below 500 mg/L for drinking water. The measured TDS of 3060 mg/L far exceeds this limit. While there isn’t a specific numerical guideline for TSS in the provided documents, drinking water should be clear, and a TSS value this high indicates extreme turbidity, making it aesthetically unacceptable and unsafe.

Implications: Such high levels of solids indicate significant contamination of the water source. The high TSS suggests heavy pollution from surface runoff, soil erosion, or discharge. The elevated TDS points to a high concentration of dissolved salts and minerals. This water is unsuitable for drinking without extensive treatment, as it can harbor pathogens and cause gastrointestinal issues. It is also unfit for most industrial applications due to the high risk of scaling and corrosion.

The water sample analyzed is heavily contaminated, with concentrations of both suspended and dissolved solids that are significantly above the permissible limits for drinking water set by the WHO and NDWQS. The total solids content of 5440 mg/L confirms that the water is of very poor quality and requires comprehensive treatment to be considered safe for domestic or industrial use.

To address the high solids content in the water source, the following mitigation measures should be considered:

• Erosion Control: Implement practices such as planting vegetation and creating buffer strips around the water body to reduce soil erosion and runoff.

• Sedimentation: Install silt fences, sediment traps, or larger sedimentation basins to capture suspended particles before they enter the main water body.

• Source Management: Identify and manage potential point sources of pollution, such as industrial or agricultural discharges.

• Advanced Treatment: For TDS reduction, advanced treatment methods like reverse osmosis, ion exchange, or distillation would be necessary.

• Continuous Monitoring: Regularly monitor the TSS and TDS levels to assess the effectiveness of implemented measures and track the water quality over time.

• Use clean and calibrated equipment to avoid contamination and ensure accuracy.

• Handle chemicals and water samples with care to avoid health risks.

• Ensure proper drying of samples to constant weight to avoid error due to moisture.

• Wear gloves and safety goggles when handling chemicals or contaminated water samples.

• Handle hot equipment, like porcelain dishes and crucibles, with tongs or heat-resistant gloves.

• Keep the workspace clean and organized to avoid contamination and ensure smooth workflow.

• Calibrate the analytical balance regularly to ensure accurate weighing.

• Avoid touching the filter paper or evaporating dish with bare hands to prevent contamination.

1. What is the application of determination of settleable solids?

The determination of settleable solids is primarily used in the design and operation of sedimentation tanks (clarifiers) in water and wastewater treatment plants. It helps predict the volume of sludge that will accumulate and allows for the calculation of the clarifier’s removal efficiency.

2. Explain the significance of determination of total solids in sanitary engineering.

The determination of total solids is significant because it provides a comprehensive measure of the overall quality and pollution level of water. This data is critical for selecting appropriate treatment processes, assessing the efficiency of treatment plants, and ensuring the water is suitable for its intended use (e.g., drinking, industrial processes). High total solids can lead to issues like unpleasant taste, pipe scaling, and interference with other treatment steps like disinfection.

3. How will the volatile solids affect the strength of sewage? Why?

Volatile solids, which are primarily organic matter, directly affect the strength of sewage. Sewage strength is often measured by its Biochemical Oxygen Demand (BOD), which is the oxygen required by microbes to decompose organic waste. Since volatile solids represent the organic fraction, a higher concentration of volatile solids means there is more biodegradable material present. This leads to a higher BOD, indicating a “stronger” sewage that requires more oxygen and a more robust biological treatment process for stabilization.

4. Why do you determine the fixed solids by igniting at 550°C? How will the result be affected if it has magnesium carbonate content?

Fixed solids are determined by igniting the sample at 550°C because this temperature is high enough to oxidize and drive off most organic (volatile) matter but low enough to prevent the decomposition of most inorganic salts. This provides a reliable separation of the organic and inorganic fractions. However, if the sample contains magnesium carbonate (MgCO₃), the result will be affected. MgCO₃ can decompose at temperatures as low as 350°C. During ignition at 550°C, it would break down, releasing carbon dioxide gas. This weight loss would be incorrectly measured as volatile solids, leading to an underestimation of the true fixed solids content.

5. What significant information is furnished by the determination of volatile solids?

The determination of volatile solids provides a valuable estimate of the amount of organic matter present in a water or wastewater sample. In the context of wastewater treatment, this information is crucial for assessing the strength of the sewage, designing and operating biological treatment units (e.g., activated sludge, anaerobic digesters), and estimating the amount of biological sludge that will be produced.

6. What is sludge volume index?

Sludge Volume Index (SVI) is a key operational parameter in the activated sludge process that measures the settling characteristics of the sludge. It is defined as “the volume in milliliters occupied by 1 gram of activated sludge after settling the aerated liquor for 30 minutes.” It is calculated as:

A low SVI (e.g., 50-150 mL/g) indicates a dense, compact, and well-settling sludge, whereas a high SVI (>200-250 mL/g) indicates a poorly settling or “bulking” sludge.