Turbidity, What It Is and How It’s Successfully Mitigated

With the right combination of knowledge and technology, treatment plants can keep turbidity low and properly disinfect both municipal and industrial wastewater prior to discharging, in addition to delivering safe, clean drinking water.

Turbidity is simply a measure of how clear water is (or isn’t). It’s a simple and intuitive property of water and one of the few that can be observed without instruments. However, as easy as it may be to observe turbidity, the relationship between turbidity and water quality is not straightforward. This article will clarify the essential aspects of turbidity, how it can affect human health, and how best to measure and mitigate it.

What Is and Is Not Turbidity

Turbidity is caused by high concentrations of particulate matter that affect the transparency of water, such as dirt, minerals, proteins, oils, or microorganisms like algae. While some water sources are naturally more turbid than others, turbidity levels can change over time. Stormwater or agricultural runoff, erosion, and other factors can cause source water to become more turbid.

In the case of drinking water, although turbid water is likely to taste different due to the suspended particles, that doesn’t necessarily mean it’s harmful. Similarly, new or unwanted odors can manifest in both clear and turbid water, yet it’s also possible for turbid water to have no telltale smell.

Turbidity is also distinct from color. Color is generally the result of dissolved organic material or high concentrations of certain minerals, such as iron oxide. Similar to taste and odor, contaminants that cause turbidity can also cause coloration and vice versa. However, the two are technically different.

Perhaps the most important relationship to understand is between turbidity and total suspended solids (TSS). Higher TSS almost always correlates to increased turbidity. However, the relationship isn’t one-to-one. Different types of solids will have a greater or lesser impact on overall turbidity. Still, when instrumentation shows higher-thanacceptable levels of turbidity, it means that TSS has likely also increased.

The Role of Turbidity In Drinking Water

While turbidity-causing matter is not always harmful to drink, it can provide food for pathogens, including bacteria, viruses, and protozoa such as Cryptosporidium and Giardia lamblia. This allows such pathogens to reproduce to potentially dangerous levels.

In addition, turbidity can reduce the effectiveness of disinfection efforts in a number of ways. Firstly, the sediment can provide shelter to pathogens, preventing disinfection molecules (i.e., chlorine) from reaching and killing them. Secondly, a portion of the disinfectant molecules may react with sediment particles instead of pathogens. Thirdly, if the turbidity-causing particles are organic, they may form disinfection byproducts such as trihalomethanes, which themselves can be harmful to humans.

How To Effectively Reduce Turbidity

Many filtration systems that remove particulate matter can reduce turbidity. Larger water treatment plants (WTPs) may use sedimentation and flocculation tanks. Smaller WTPs can achieve good results with pleated cartridge, sand, or other media filters.

Chemical treatment is an excellent method for dealing with turbid water. Flocculant and Coagulation polymers are used to aid in the removal of solid particles. Flocculants separate solid content in the wastewater from the liquid content. A coagulant combines small particles to form larger chain particles. These polymers change the charge of the particles so that they will combine rather than repel other particles. The resulting long chain polymers will form a thick sludge and settle to the bottom.

Blue-White’s FLEXFLO® M4 Peristaltic Metering Pump will deliver smooth, gentle and consistent chemical dosing that does not damage long chain polymers. Operators will always know they are dosing the correct amount of chemical with the highly responsive and easy to read 5” touchscreen display. The LCD screen features easily recognizable icons and is as simple to operate as a smart phone. The M4 is equipped with the latest Communication Protocols and is designed to be fully field upgradeable.

How To Measure Turbidity

There are several turbidity measurement instruments on the market.

Guidelines include, the U.S. EPA standardizes turbidity measurement under Method 180.1, Determination of Turbidity by Nephelometry. Nephelometric technology measures light scatter at a 90-degree angle from the initial light path. Turbidity is represented using nephelometric turbidity units (NTU). The EPA rules require that water from any individual filtration line maintain a turbidity reading of < 0.15 NTU (although WTPs often aim much lower than this), with any exception lasting no longer than 15 minutes. The final effluent stream must maintain a turbidity reading of < 0.30 NTU, without exception.

In closing, Turbidity is a simple concept that is, more often than not, simple to measure and address. With the right combination of knowledge and technology, operators can keep turbidity low and deliver properly remediated discharge water and safe, clean drinking water to their customers.

Written by:
Blue-White® Industries
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