Greetings dear friends of Hive.

In this opportunity I want to share information about the analytical determination of solids present in water, since undoubtedly when we talk about pollutants the solids content is one of its most important characteristics. Solids are the ones that mostly impart negative characteristics to water, and the determination of their concentration is an important part in the definition of the processes for their treatment.

Many substances can go unnoticed, but this is not the case with solids, which quickly alert us to the level of contamination in a given body of water. Water quality can be altered by natural causes or as a result of human activities derived from agricultural, industrial and domestic activities, so this type of analysis should be carried out regardless of the origin of the sample.

Its precise determination is an extremely important factor to establish the nature of the pollutants present and to have the necessary information to implement efficient water separation and purification processes, as well as to evaluate the operational efficiency of the treatment plants already in operation.

Solid contaminants are very common in water, and are present in various forms, so it is convenient to review the definition of each term and what are the conventional methods of analysis. Depending on their nature, solids can be classified into the following types: Total Solids, Suspended Solids, Dissolved Solids and Sedimentable Solids.

In this post we will begin the description of the method for the determination of total solids in water, I invite you to read.

Solids in water

Technically speaking, the word solid refers to any matter present in the water and which is solid when it is out of the water; thus, within this category fall from large particles such as debris and soil, to those that cannot be seen, such as fine particles of suspended sand or even dissolved salts, since out of the water they would be appreciated as solids[1].

But the garbage that floats or is sunk in a body of water is of a diverse nature, and the methods of separation can be very general and quite simple. Now, there are solids of smaller size that are more difficult to separate, so more rigorous procedures are resorted to in a laboratory, and these solids are used as control parameters in different industrial areas and to refer to environmental legislation.

Figure 1. Presence of solids in water samples: dissolved and suspended.
Source: @yusvelasquez

Solids are determined by gravimetric methods, which means that drying cycles are required until a constant weight is obtained, and they are expressed in amount of mass per volume of sample.
Among the solids we can find:

• Total Solids (TS): analytically, total solids are the resulting residual material obtained after evaporation of a sample and its subsequent drying in an oven at a defined and constant temperature[2]. In other words, they represent the total solids that are not retained by filtration and allow us to determine the amount of solids that enter a given process, regardless of their nature.

• Total Suspended Solids (TSS): are those that do not settle easily, are heterogeneous in nature and can be less than 0.01 mm, so they do not settle quickly; therefore, they represent all the solids that can be separated by mechanical means such as filtration or centrifugation, and are associated with the turbidity of the liquid[3].

• Total Dissolved Solids (TDS): is all the material that is dissolved in water and that is able to pass through a glass fiber or millipore filter, and that persist after evaporation and drying of the liquid.

• Sedimentable Solids: is the amount of solids that will separate from the sample by sedimentation after a certain period of rest, this determination is made by means of a special conical vessel called Imhoff cone. This is a parameter of great importance for treatment plants, since it determines the amount of sludge that will be separated from the wastewater stream.

Figure 2. Classification of solids. Source: @yusvelasquez

Total solids analysis method

The following procedure is based on the methods specified in the Standard Methods for the Examination of Water and Wastewater[4].

Figure 3. Methodology for solids determination. Source: @yusvelasquez.

Materials and equipment

• Porcelain capsules
• Mufla
• Drying oven
• Desiccator
• Analytical balance

Sampling and storage

Analysis should be performed as soon as possible, remove any large heterogeneous particles, either floating or submerged in the sample, and disperse visible fat and oil particles with a shaker in the sample brought from the field before taking the sample for analysis.

If the sample cannot be analyzed on the spot, it is recommended to store it at 4°C to reduce microbial spoilage as much as possible.

The sample should be taken in sturdy glass or plastic containers to prevent particles from adhering to the container wall.

Experimental procedure

• A porcelain capsule is placed in a muffle at 550 °C for one hour.

Figure 4. Drying of the capsule. Source: @yusvelasquez.

• It is removed and allowed to cool in a desiccator.

• The empty capsule is weighed and then a 50 mL volume of the sample is transferred to the capsule.
  

  
  Figure 5: Sample measurement. Source: @yusvelasquez.

• The capsule with the sample is taken to the oven calibrated at 98°C until all the liquid has evaporated.

• Once evaporated keep for one hour at a temperature between 103 and 105 °C.
  

  
  Figure 6. Sample drying. Source: @yusvelasquez.

• Then remove and let cool in a desiccator.

• Once the capsule is cooled, take it to be weighed.

• Repeat the drying process between 103 and 105 °C and weigh until a constant weight is obtained.

Figure 7: Solids weighing. Source: @yusvelasquez.

Expression of results

Total solids are calculated in ppm

Where:
A = weight of capsule with sample.
B = weight of the empty capsule

Conclusion and contribution

The determination of solids is a routine but indispensable procedure to know the quality of a given body of water, since solids influence many other characteristics such as color, turbidity and organoleptic properties of the water.

It is also a fundamental control parameter in any wastewater treatment operation. For example, Venezuelan environmental legislation, through Decree 883, establishes the maximum limits of solids in any effluent to be discharged directly or indirectly into any body of water. Therefore, the monitoring of this parameter is indispensable for any company operating a wastewater treatment plant.

So knowing the standard methods for solids characterization is essential for the chemistry student or professional who must ensure the discharge of treated water into a given water body.

This is the end of this post, I hope you find the information presented useful. Remember the importance of analytical methods in water quality control, see you next time!

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References

1. Microlab Industrial. Solids in water; manage your solids and improve your effluent.
2. INVEMAR. Manual of analytical techniques for the determination of physicochemical parameters and marine pollutants.
3. Wikipedia.com. Total suspended solids.
4. APHA.1998. Standard Methods for the Examinationof Water and Wastewater. Edition 20. APHA/AWWA/WPCF.