TSS/Turbidity
Total suspended solids (TSS) are defined as solids in water that can be trapped by a filter. The removal of TSS is typically achieved through physical treatment processes such as sedimentation, filtration, and flotation. Sedimentation involves allowing the suspended solids to settle out of the water by gravity, while filtration involves passing the water through a filter media to remove the solids. Flotation is a process in which air is introduced into the water to create bubbles, which attach to the suspended solids and carry them to the surface where they can be removed.
TSS is an important water quality parameter measure for wastewater treatment operations and environmental health. Wastewater contains large quantities of suspended organic and inorganic material that must be removed through screening, filtration or settling/flotation methods prior to environmental discharge. TSS will also have adverse affects on UV disinfection blocking/scattering UV light bound for pathogen disinfection or alternatively requiring higher intensity for proper disinfection, increasing energy costs.
If TSS is not removed properly through treatment, high concentrations can lower the water quality in the receiving environment. The suspended solids absorb light, causing increased water temperature and decreased oxygen which creates an unfavorable environment for aquatic life.
Turbidity provides the amount of fine particulate in the water. Turbidity is defined as the degree to which light is scattered by particles suspended in a liquid. There are several different units for turbidity depending on the wave length of the light source and the incident angle. Nephelometric turbidity units (NTU) are based on white light (400–680 nm) and 90° incident angle.
Turbidity in wastewater treatment describes the clarity or haziness of a wastewater sample. The level of cloudiness or the presence of suspended particles in the wastewater sample is usually measured in FTU. FTU stands for Formazin Turbidity Unit.
One common method to measure wastewater turbidity is called Nephelometry which uses scattered light. ISO 7027 and E-P-A 180.1 allow only infra-red 860nm or white light 500nm as light sources for the test.
When the light source hits the wastewater sample, suspended particles will reflect the incoming light. Depending on the shape, density and size of the particles the light will be scattered in different directions. Smaller particles tend to reflect light into perpendicular direction whereas bigger particles scatter light in more directions.
Sensors around the wastewater sample can measure how much light was reflected and in which direction it was scattered. This allows to determine the sample turbidity but it also provides information on amount of total suspended solids and particle sizing.