How to Treat Turbidity in Water
Table of Contents
What Causes Turbidity in Water?
Particulate matter causes water turbidity. When particles dissolve or suspend in water, they scatter light and give water a murky or cloudy appearance. Particulates can include:
- Algae
- Sand
- Silt
- Clay
- Precipitated iron
- Bacteria
- Fine organic matter
- Soluble colored organic compounds
Sediment sources can be natural or human-induced, and particles that cause water turbidity are usually microscopic and invisible to the eye. Natural sediment sources include erosion from stream banks, stream channel areas or high land areas. Human actions such as agriculture and development activities can quicken the erosion process.
Water movement through stream channels can release sediments in water, and algae that grow with nourishment from decomposition processes can also cause turbidity. Phosphorous sources such as cropland nutrient runoff, wastewater treatment facilities and other sources can cause algae growth, increasing water turbidity. Soil erosion, urban stormwater runoff and organic matter from sewage discharges also contribute to the sediment found in water.
Health Effects of Turbidity in Water
Turbidity in drinking water can provide shelter and nourishment for pathogens. Pathogen regrowth in drinking water can cause waterborne disease outbreaks. Many waterborne diseases can cause significant gastrointestinal illnesses with symptoms such as headaches, stomach cramps, diarrhea, nausea and vomiting. Turbidity does not guarantee the presence of a health risk, but there is a strong correlation between turbidity removal and protozoa removal.
Contaminants such as pesticides, metals and toxic organic compounds can attach to suspended particles in drinking water. When microbes attach to suspended particles, they can reduce their exposure to water distribution system disinfectants, which can help the microbes survive and cause illnesses.
Turbidity of water is also environmentally harmful. Suspended particles in streams, lakes and other bodies of water can reduce light penetration, decrease ecological productivity and affect habitat quality and recreational values. This effect can cause lakes to fill faster, and it can cause increased siltation and sedimentation in streams, which may harm fish and other wildlife habitats. Particles can also serve as attachment points for pollutants such as bacteria and metals.
Measuring Turbidity of Water
Turbidity is measured in Nephelometric Turbidity Units (NTUs). This measurement method examines how light scatters in a water sample compared to how light scatters in a reference solution.
A hand-held electronic meter or an instrument such as a Secchi disc measures turbidity. Turbidity meters shine a light into the water and report how much light reflects back to the sensor. Turbidity higher than 1 to 5 NTU can result in increased pressure drop in water filtration systems.
Some devices measure turbidity in Formazin Nephelometric Units (FNUs), which are similar to NTUs. Both units measure scattered lights at a 90-degree angle from the light beam. However, NTUs are measured with a white light source, while FNUs are measured by an infrared light source.
How to Reduce Water Turbidity
Reducing water turbidity can prolong a filtration system’s lifespan and prevent water contamination. The following turbidity filtration methods can help with the removal of turbidity in water:
Coagulation-Flocculation
The coagulation-flocculation treatment process destabilizes colloids in water, causing them to aggregate so they can be physically removed from the water. This process, combined with sedimentation and filtration, can reduce turbidity. Coagulation causes particulates to bind together, and flocculation is when particulates stick together visibly.
During the coagulation-flocculation process, a container collects water before a coagulant is added so turbidity can flocculate and settle. In large-scale water treatment processes, conventional coagulants include metal salts such as ferric sulfate, aluminum sulfate and ferric chloride. Coagulation dosing and efficiency depend on the water’s PH level. During sedimentation, particulates settle to the bottom of a container or basin before the resulting sludge is removed and the water can move on to filtration.
Settling and Decanting
During the settling and decanting process, water sits for two to 24 hours to allow particulates to settle at the bottom of a container. The clear water at the top of the container can then be decanted into an additional container, which separates the water from the particulates. This process requires minimal equipment, but it is more time-consuming than other methods.
Backwashing Filter
Water treatment filters collect and store water contaminants, which causes particles to stick to filter grain surfaces. The filtration process can cause particulates to fill open spaces between filter grains, resulting in flow resistance and increased pressure drops. Backwashing uses a reverse water flow at increased velocity to pass water back through a filter and remove clogged particles. The most common backwashing filters for turbidity reduction are sand or multimedia filtration. Other media may be selected based on the turbidity loading.
Reverse Osmosis Filtration
Reverse osmosis (RO) is a water filtration system that uses a semipermeable membrane to catch particulates and other larger molecules while allowing water to pass through. During the RO filtration process, high pressure pushes water through the membrane to remove contaminants in the following steps:
- Prefiltration: A pre-filter catches large particles such as dirt and dust.
- Reverse osmosis: The semipermeable membrane catches smaller, dissolved particles.
- Drainage: Removed contaminants are drained from the filtration system.
- Storage: Treated water is stored for future use.
Ultrafiltration
Ultrafiltration (UF) systems use hollow fiber membranes to remove suspended solids and finer particles from water to reduce turbidity. UF systems filter solid particulates on a microscopic level. They remove fewer types of contaminants than RO systems, so they retain minerals such as magnesium and calcium.
Industries Requiring Turbidity Filtration
Many industries handle products that come into contact with water or contain water, which is why turbidity filtration is important. Industries like these require turbidity filters for health and safety purposes:
- Food and beverage companies
- The pharmaceutical industry
- Medical facilities
- Plastic production companies
- Chemical production industries
- Pulp and paper production
The United States Environmental Protection Agency’s Surface Water Treatment Rules provides guidelines about turbidity levels and monitoring requirements.
Learn More About Our Water Filtration Services
Water turbidity can compromise your water source’s health and safety and your company’s efficiency. Maintain your current water filtration system or purchase new equipment to maintain efficiency and ensure water safety.
At Complete Water Solutions, we offer installation and maintenance services for all major manufactured water treatment systems. We provide turnkey installation of water treatment equipment, 24/7 customer service and free training for operating and maintaining your filtration system. Contact Complete Water Solutions to learn more about our water treatment system installation services.