Turbidity v. suspended solids. What’s the difference?

Turbidity and suspended solids are two different terms each with their own specific meaning. However, they are both intrinsically linked and regularly used to measure the quality of water and wastewater.

What is turbidity?

Turbidity refers to the transparency of water. If there are suspended particles in water, they will have a direct effect on its transparency. The more suspended particles there are in the water, the darker it will appear. So, water with a high turbidity will be quite cloudy or murky and could potentially be of low quality.

What causes turbidity?

Several parameters can affect the turbidity of water including sediments, waste discharge, algae, urban run-off and phytoplankton.

What are suspended solids?

Suspended solids are solid particles that are floating or drifting in the water. To be counted as a suspended solid, the particle must be 2 microns or larger. Anything smaller than that is considered a dissolved solid.

Suspended solid particles can be organic or inorganic. This could include sand, silt and clay, which can be carried along in the flow of water. This is why flood water or fast moving rivers often looks cloudy. If the flow becomes low, much of these can settle on the bottom and become settled solids, improving the clarity of the water. Those particles too small or light to settle will remain suspended in the water. Small particles from decomposing animals and plants can also become suspended solids such as bacteria,  algae and plankton. The amount of suspended solids contained in any body or sample of water will indicate how cloudy that water actually is.

the difference between turbidity and suspended solids sensors

Typically, turbidity is measured for clean water with low level suspended solids. Many turbidity sensors will monitor in the region of 0-1000 NTU. Suspended solids sensors typically measure higher suspended solids ranges in the region of 1000 mg/l – 8% solids. Understanding the typical solids range of a process helps determine the appropriate instrument to monitor turbidity and/or suspended solids.

Detectronic has a turbidity sensors and suspended solids sensors for a variety of different applications. Our team of experts is available to discuss your application and help you choose the right equipment.