Introduction

The term “solids” is generally used when referring to any material suspended or dissolved in water or wastewater that can be physically isolated either through filtration or through evaporation. Solids can be classified as either filterable or non-filterable. Filterable solids may either be settleable or non settleable. Solids can also be classified as organic or inorganic.

Total Solids is the term applied to the material residue left in the vessel after Evaporation of a sample and its subsequent drying in an oven at a defined temperature. Measurement of Solids can be made in different water samples (industrial, domestic and drinking water) and it is defined as residue upon evaporation of free water. Thus, Total solids are nothing but summation of total dissolved solids and total suspended solids.

Principle:

Suspended and dissolved impurities are commonly present in surface water. A well-mixed sample is filtered through standard whatman No.1 filter and filter is evaporated to dryness in evaporating dish, dried at 103 –

105 ^oC. Increase in weight of dish represents “Total dissolved solids”. The residue on filter paper is dried at 120 ^oC. Increase in weight of filter paper represent “Total suspended solids” in water.

Requirements

1)    Water sample

2)    Buchner filter Assembly

3)    Dessicator

4)    Whatman filter paper no-1

5)    Evaporating dish (Crucible)

6)    Hot air oven

7)    Analytical Balance

Procedure

·       Preparation of crucible or evaporating dish: Heat clean dish to 180^o C for 1 hour in hot air oven. Store in a dessicator until needed.

·       Set Buchner filter assembly.

·       Take about 10 ml sample and filter through Watman filter paper No.1.

·       The dissolved solids are filtered out and go to the filtrate.

·       Take about 10 ml filtrate in a pre weighed crucible.

·       Place the crucible in hot air oven preset at 180^o C.

·       Dry the sample for at least 1 hour in an oven.

·       Cool in a desiccator for at least to balance temperature and weight.

·       Repeat drying cycle until a constant weight is obtained or weight change is less than 4% of previous weight or 0.5mg whichever is less.

·       Calculate TDS/lit of given water sample.

Advantages of total dissolved solids

Total Dissolved Solids (TDS) is a measure of the concentration of dissolved substances in water. While high TDS levels in drinking water can indicate potential water quality issues, there are also some advantages to having a certain level of TDS in water:

Mineral Content: TDS often consists of essential minerals like calcium, magnesium, and potassium. These minerals contribute to the taste and overall quality of water, making it more palatable. Drinking water with some mineral content can also provide trace elements necessary for human health.

Flavor Enhancement: In some cases, moderate TDS levels can enhance the flavor of water, making it more enjoyable to drink. Many people prefer the taste of water with a slight mineral content.

Potential Health Benefits: Consuming water with moderate TDS levels can provide some health benefits. For example, calcium and magnesium in water can contribute to your daily intake of these minerals, which are important for bone health and muscle function.

Hydration: Water with a moderate TDS level is still effective at hydrating the body. In fact, the minerals in water can aid in maintaining electrolyte balance, which is essential for proper hydration.

Reduced Corrosion: Very low TDS levels in water can be aggressive and corrosive, potentially damaging plumbing and infrastructure. Having some dissolved solids in water can reduce this corrosive potential.

Enhanced Brewing: In industries such as brewing and winemaking, TDS can influence the taste, texture, and quality of the final product. Brewers and vintners often pay attention to TDS levels to achieve desired outcomes.

Indicator of Water Quality: While high TDS levels may indicate water quality issues, monitoring TDS can be a useful tool for assessing the overall quality of water sources. It can help identify contamination or salinity problems in water supplies.

It's important to note that the advantages of TDS are generally associated with moderate levels. Extremely high TDS levels, especially in drinking water, can be a sign of pollution or excessive mineral content, which may have health or taste-related disadvantages. Therefore, the ideal TDS level in water can vary depending on its intended use and local water quality standards.

Limitations of total suspended solids

Total Dissolved Solids (TDS) is a measurement used in water quality assessment that quantifies the concentration of dissolved inorganic and organic substances in water. While TDS can provide valuable information about water quality, it has certain limitations and considerations to keep in mind:

Lack of Discrimination: TDS does not provide information about the specific constituents present in the water. It only gives a cumulative measurement of all dissolved substances. Therefore, it cannot differentiate between harmful pollutants and essential minerals.

Limited Organic Compound Detection: TDS primarily focuses on inorganic ions and minerals. It may not detect certain organic pollutants, volatile organic compounds (VOCs), or synthetic chemicals that can be harmful to human health and the environment.

Variable Impact on Water Quality: The impact of TDS on water quality depends on the specific constituents present. High TDS levels can be due to beneficial minerals like calcium and magnesium or harmful contaminants like heavy metals or industrial pollutants. Therefore, interpreting TDS values requires additional information about the water source and constituents.

Seasonal and Geological Variability: TDS levels can vary seasonally and geographically due to factors such as precipitation, evaporation, and geological formations. This makes it necessary to establish baseline values for specific regions and times of the year.

Taste and Aesthetic Issues: High TDS levels can lead to undesirable taste, odor, or scaling in drinking water. While these issues are not necessarily indicative of health risks, they can affect consumer acceptance and water utility operations.

Incomplete Water Quality Assessment: Relying solely on TDS measurements may provide an incomplete picture of water quality. It's essential to consider other water quality parameters like pH, turbidity, specific ions (e.g., chloride, sulfate), and microbiological contaminants (e.g., bacteria, viruses) to comprehensively assess water quality.

Health Guidelines and Regulatory Compliance: TDS is not typically regulated as a primary drinking water standard. Instead, specific maximum contaminant levels (MCLs) are established for individual constituents within TDS, such as arsenic, lead, or nitrate. Compliance with these individual MCLs is crucial for ensuring safe drinking water.

Environmental Impact: Elevated TDS levels in natural water bodies can harm aquatic ecosystems, leading to decreased oxygen levels, impaired reproduction of aquatic organisms, and altered habitats. It is essential to consider the ecological impact of TDS in such cases.

In summary, while TDS is a useful parameter for assessing water quality, it should be used in conjunction with other measurements and information to gain a comprehensive understanding of water quality and potential health and environmental concerns. Specific constituent analysis and compliance with regulatory standards are necessary for a complete assessment of water safety.

Reference

•         Clesceri L.S., Greenberg A.E., Eaton A.D. (1998) Satandard methods for the examimnation of water and waste water. 23^rd edition APHA.

• Kulkarni P.D. Laboratory manual in environmental engineering. Jaico Publishing House. Bombay.