Suspended solids in water are particles with diameters roughly between 0.1 um and 100 um, visible to the naked eye. These particles consist mainly of silt, clay, protozoa, algae, bacteria, viruses and high-molecular-weight organic matter, and are usually suspended in the flowing water. The turbidity of water is also caused by such substances.

Solid particles that can remain suspended in seawater for a considerable time are sometimes also called suspended solids or suspended colloids. They comprise two major fractions: organic and inorganic. The organic fraction consists mostly of detrital particles composed of carbohydrates, proteins and lipids. The inorganic fraction includes terrigenous mineral detritus (such as quartz, feldspar, carbonates and clay) and authigenic marine minerals (such as precipitated silicates including glauconite and phillipsite, and carbon).

The particle size of suspended solids generally ranges from a few to several hundred micrometers. To study their chemical composition, they are usually separated from seawater using filter membranes with a pore size of 0.45 um. Suspended solids contain two categories of components, organic and inorganic:

(1) Organic components. These are mainly biological remains, excreta and decomposition products, composed of carbohydrates such as cellulose and starch, proteins, lipids and chitin.

(2) Inorganic components. These include mineral detritus of continental origin such as quartz, feldspar, carbonates and clay, as well as silicates formed during chemical processes in seawater. [1]

1. Suspended solids refer to solid matter that cannot pass through a filter. A filter paper pre-dried to constant weight is placed in a Buchner funnel, the water sample is filtered through medium-speed quantitative filter paper, and after drying at 103-105 degrees C to constant weight, the total non-filterable residue (suspended solids) content is obtained (see the test method below for details).

2. Suspended solids refer to water-insoluble sand, clay particles and the remains of plant and animal organisms. Impurities in water are highly detrimental to boiler maintenance and steam evaporation, readily forming scale that causes metal corrosion and overheating, and leading to foaming and carryover.

3. Suspended solids refer to clay minerals, silt, humus and hydrated iron and aluminium oxides contained in soil extracts. Organic and inorganic substances undergo a series of migration and transformation processes at the suspended solid-water interface, such as adsorption, desorption, and precipitation-dissolution.

4. Suspended solids refer to solid matter retained on a filter and dried at 103-105 degrees C to constant weight. Suspended solids present in surface water make the water body turbid, reduce transparency, affect the respiration and metabolism of aquatic organisms, and may even cause channel blockage. Therefore, measuring suspended solids has particular significance in water and wastewater treatment.

5. A membrane filter with a pore size of 0.45 um retains suspended solids and most bacteria in water. Consequently, the fraction passing through a 0.45 um filter is conventionally defined as "dissolved" and "soluble", while the retained fraction is termed suspended solids.

6. Impurities in natural water can be divided into three categories according to particle size: the largest are suspended solids; next are colloids; and the smallest are ions and molecules, i.e. dissolved substances. Suspended solids have relatively large particles, are unstable in water and are easy to remove. Turbidity in water is mainly caused by such substances.

This standard specifies the determination of suspended solids in water.

This standard applies to surface water and groundwater, as well as to the determination of suspended solids in domestic sewage and industrial wastewater.

Suspended solids in water quality analysis refer to the matter retained on a membrane filter with a pore size of 0.45 um and dried at 103-105 degrees C to constant weight.

Collected water samples should be analysed as soon as possible. If they must be held, they should be stored in a refrigerator at 4 degrees C for no longer than seven days.

1. Common laboratory apparatus plus the following equipment.

2. All-glass microporous membrane filtration apparatus.

3. GN-CA membrane filter, pore size 0.45 um, diameter 60 mm.

Polyethylene or hard glass bottles must be washed clean with detergent, then rinsed successively with tap water and distilled water. Before sampling, rinse them three times with the water to be sampled. Then collect a representative sample of 500-1,000 mL and cap the bottle tightly.

Note: Floating or submerged non-homogeneous solid matter is not classified as suspended solids and should be removed from the sample.

Distilled water or water of equivalent purity.

Note: No preservative may be added, to avoid disrupting the partition equilibrium of substances between the solid and liquid phases.

Using flat-tipped smooth forceps, place the membrane filter in a weighing bottle previously dried to constant weight, transfer it to an oven and dry at 103-105 degrees C for half an hour, then remove and cool to room temperature in a desiccator and weigh. Repeat drying, cooling and weighing until the difference between two successive weighings is <= 0.2 mg. Place the membrane, now at constant weight, correctly on the filter support of the membrane filtration apparatus (4.1), fit the matching funnel and secure it with a clamp. Wet the membrane with distilled water and apply continuous suction.

Measure 100 mL of thoroughly mixed sample and filter under suction so that all the water passes through the membrane. Wash three times consecutively with 10 mL of distilled water each time, and continue suction to remove traces of water. After stopping suction, carefully remove the membrane bearing the suspended solids, place it in the original weighing bottle at constant weight, transfer to an oven and dry at 103-105 degrees C for one hour, then move to a desiccator, cool to room temperature and weigh. Repeat drying, cooling and weighing until the difference between two successive weighings is <= 0.4 mg.

Note: Excessive suspended solids retained on the membrane may entrain too much water, which not only prolongs drying time but may also make filtration difficult; in such cases the sample volume may be reduced as appropriate. Too little suspended matter on the membrane increases weighing error and reduces measurement accuracy, in which case the sample volume may be increased. Generally, a suspended solids mass of 5-100 mg is the practical range for selecting the sample volume.

The suspended solids content C (mg/L) is calculated using the following formula:

Where: C - concentration of suspended solids in water, mg/L;

A - combined weight of suspended solids + membrane + weighing bottle, g;

B - combined weight of membrane + weighing bottle, g;

V - sample volume, mL. [2]

Suspended solids are the most common pollutant in water and an important water quality indicator. A membrane filter with a pore size of 0.45 um retains suspended solids and most bacteria in water, so the fraction passing through a 0.45 um filter is conventionally defined as "dissolved" and "soluble", while the retained fraction is termed suspended solids. The quantity of suspended solids is expressed as the mass contained per unit volume of water, i.e. mass concentration, usually in milligrams per litre (mg/L).

Suspended solids in water bodies include both inorganic and organic matter. Inorganic suspended solids include particulate matter such as dust, silt and fine metal fragments suspended in wastewater, mainly originating from domestic sewage and stormwater. Organic suspended solids include fibres, plastic products, branches and wood chips, mainly originating from domestic sewage and industrial wastewater.

The harm caused by suspended solids mainly consists of blockage, siltation and abrasion of channels, pipelines and pumping equipment; respiratory difficulties for aquatic organisms; turbidity in water supply sources; and interference with the operation of wastewater treatment facilities and recovery equipment. Some suspended solids are also toxic to a degree. Almost all wastewaters contain varying amounts of suspended solids, so their removal is a fundamental task in wastewater treatment.

Removing suspended solids from wastewater at a treatment plant is a solid-liquid separation process. In the primary treatment stage before biochemical treatment, physical methods are mainly used and can remove most suspended solids - for example, installing coarse and fine screens or using mesh to intercept non-dissolved solids; separating suspended solids by air flotation; and using the gravity of suspended particles for grit removal and sedimentation. During biochemical and advanced treatment stages, chemical flocculation and sedimentation are typically used, dosing coagulants so that colloidal suspended solids and dispersed particles form flocs of greater size and mass that then settle. To further improve effluent quality, filtration methods can be applied for advanced treatment, such as biofilm filtration and activated carbon adsorption [3].