How To Measure Total Suspended Solids(TSS) in Water
Natural water will produce turbidity when polluted. Therefore, the indicator of suspended solids can describe the level of water pollution when measuring the surface water, groundwater, domestic sewage, and industrial wastewater.
What are suspended solids?
Suspended solids refer to the solid substance suspended in water, including inorganic substances, organic substances, mud, clay, microorganism, etc., insoluble in water.
Generally, suspended solids in water refer to water samples after passing 63 um filter membrane and then passing through the pore diameter of 0.45 μm, which is retained on the filter membrane and dried to constant weight at 103 ~ 105 ℃, also known as non-filterable residue, unit: mg / L.
Suspended solids include settleable solid particles suspended in the water flow.
Relationship between turbidity and suspended solids
Turbidity is an optical concept, while suspended solids are a mass concentration concept. The relationship between turbidity and SS is different in different water sources, seasons, and temperatures. However, there is a certain connection between them.
Suspended solids and turbidity are a ratio relationship for the same kind of water under the same conditions. If we get the ratio relationship through experiments, we can directly calculate the suspended solids’ content by turbidity.
This relationship is commonly more accurate only under low turbidity. Generally, if the turbidity of water is high, its suspended solids index will also be high. Due to the complexity of the standard detection method of suspended solids, some laboratories use the turbidity result multiplied by the coefficient to get the suspended solids result, but the error is large.
Determination of Suspended solid method
Many determination methods of suspended solids in water, including spectrophotometry and gravimetric analysis.
Spectrophotometry pros and cons
Pros:
Simple operation and fast detection,
Cons:
- Need water quality detector.
- High cost
It is suitable for outdoor water quality detection or non-professional operation.
Gravimetric analysis pros and cons:
Pros:
No need water quality detector, low cost
Cons：
complex
It is suitable for professional laboratories.
Gravimetric determination of suspended solids in water
Suspended solids refer to the solid left on the filter material to constant weight at 103 ~ 105 ℃. It is to pass the water sample through the filter material and subtract the weight of the filter material from the weight, which is the suspended solid (total non-filterable residue).
Reagents and instruments
1) Reagent:
Distilled water o the same purity water
2) Instrument:
Oven, analytical balance, dryer, glass funnel, weighing bottle with an inner diameter of 30 ~ 50mm,
Filter membrane with a pore diameter of 0.45 μ m, corresponding filter or medium speed quantitative filter paper
Sampling and sample storage
1) Sampling
All polyethylene bottles or hard glass bottles must wash with detergent. Then wash it with tap water and distilled water in turn. Before sampling, wash them three times with the water sample. Then, Sampling 200ml representative water sample.
Note: floating or submerged uneven solid substances are not suspended solid. We should remove it from water samples.
2) Sample storage
The collected water samples should be analyzed and determined as soon as possible. If it needs to store, it should be stored in a 4 ℃ refrigerator, but not exceeding seven days.
Note: avoid adding no protective agent to prevent damaging the distribution balance between solid and liquid.
Steps
1. Put the filter membrane in the weighing bottle, open the bottle cap, dry it at 103 ~ 105 ℃ for 2h, take out the cooling cover and weigh the bottle cap until the constant weight (the difference between the two weighings is no more than 0.0005g).
2. Shake the water sample after removing the floating matter, measure a uniform amount of water sample ( suspended solid more than 0.5mg), and filter it through the filter membrane weighed to constant weight. Wash the residue with distilled water 3 ~ 5 times. (if there is grease in the sample, wash the residue twice with 10ml petroleum ether).
3. Carefully remove the filter membrane, put it into the original weighing bottle, open the bottle cap in the 103 ~ 105 ℃ oven for drying for 2h, cool the back cover, and weigh the bottle cap until the constant weight.
Calculation
C=（A-B）*10^6/V
C — concentration of suspended solids in water, mg / L;
A – weight of suspended solids + filter membrane and weighing bottle (g);
B – the weight of filter membrane and weighing bottle (g);
V – the volume of the water sample (ML).
Note:
- It should remove leaves, sticks, water plants, and other impurities from the water first.
- When the viscosity of waste water is too high, dilute it with 2 ~ 4 times distilled water, shake it evenly, and filter it after the sediment drops.
- If too many-suspended solids are retained on the filter membrane, it may carry too much water, which not only prolongs the drying time but also cause difficulties in infiltration. In this case, we can take fewer samples appropriately.
- If too little suspended matter is on the filter membrane, it will increase the weighing error and affect the measurement accuracy. If necessary, increase the sample volume. Generally, 5 ~ 100mg suspended solids are used as the practical range for measuring the sample volume.
Water quality Determination of suspended solids by Spectrophotometry
The absorption of light by substances is selective. There are different absorption bands for different substances. When the scattered light passes through the water sample, some wavelengths of light will be absorbed by the water sample.
At a specific wavelength, the concentration of the substance to be measured in the water sample has a specific proportional relationship with the intensity of light energy. In other words, it conforms to Lambert-Beer law. The water quality suspended solid SpectrophotometrySpectrophotometry is an instrument for quantitative analysis of water quality suspended solid by using the Lambert-Beer law.
Pros：
- convenient operation
- high accuracy
- easy implementation in the field or monitoring site
- rapid and continuous determination, and so on.
Instrument:
Suspended solid tester, power cord, 30mm optical path glass cuvette.
Step
Connect the power cord of the tester, turn on the switch of the tester, and preheat the instrument for 10 minutes in advance.
Add a 30mm optical path glass cuvette to 2 / 3 of deionized water, make a blank sample, put it into the instrument, and press the “blank” key.
Take another 30mm optical path glass cuvette, add the water sample to 2 / 3, put it into the instrument, press the “measurement” key, and the tester displays the measurement results.
Precision
Compared with the gravimetric method, the error range of the suspended solids concentration determination results is ≤ 5%.
Note:
- Keep the vessels clean.
- The water sample must be thoroughly mixed before determination and rapid finish the determination process.
- Ensure the water sample has no debris, floating objects, and particles easy to settle; avoid adding preservatives while preserving the water sample.
Centrifugal separation
It uses centrifugal force to separate the suspended solids before determination.
Pros：
Simple, relatively accurate.
It is a widespread method for the determination of suspended solids.
