Complete guide on how to Detect, Test & Treat Turbidity in Water

Turbidity in water is a phenomenon caused by the impurities in water. Many a times you may have faced issues related to bad water quality in form of cloudiness or haziness. The physical dissolved impurities in water cloud the water. The light that was supposedly able to cross the otherwise transparent water get scattered by the impurities and due to the light they disperse, appear hazy to us.

The obvious question that may arise in your mind is, aren't these impurities suppose to dissolve or settle down under the force of gravity?

Actually these impurities are particles of varying size and density. The heavier ones tends to settle at the bottom of the container but the low dense particles remains afloat. These low dense particles appears to us as haze in otherwise transparent water. This haze in water is caused by the presence of suspended solids (impurities) in it.

Turbidity in water is an optical water parameter and can be identified through naked eye. It is measured in NTU or Nephelometric Water Turbidity Units. 

But if all these particles as an individual are so small to even defy gravity and individually remain invisible to the human eye, how do they together appear indistinctly hazy to us in otherwise transparent water?

The answer lies in the amount of light that is scattered by these particles in water when light ray travel through the impure water medium. Higher the amount of particles in water, greater would be the intensity of scattered light and hence more distinct would be the haze in water that you observe.

TSS is the undissolved solid particles suspended in water. The dry weight of these particles give the exact amount of TSS suspended in water. TSS is reported in milligrams of solids per litre of water or mg/L. Another unit to represent it is ppm or parts per million.

TDS is the total solid particles dissolved in water. It consists of all dissolved organic and inorganic components in water.
It can be expressed in both mg/L and ppm.

Measuring the relative clarity of water defines the turbidity. Classifying these impure particles into TDS and TSS help us understand the water quality. Knowing the amount of turbidity in water helps explains:

Suspended solids are good absorbent of heat. They block the sunlight and absorb its heat. This raises the temperature of water which ultimately affects the metabolism of the organisms living in it.

As we know, suspended solids being good heat absorbent raises the temperature of water. The solubility of gases in water decreases with the rise in water temperature. Hence with increase in the amount of TSS, the water temperature may rise decreasing the dissolved oxygen level in water.

Knowing the TDS and TSS in water indicates the presence of pathogens and chemicals present in it if any. Turbidity in water shield the pathogens from disinfectant and sunlight. Thus eliminating turbidity is of utmost importance before you move onto treat the pathogens in water.

The organic and inorganic impurities in water could alter the pH of water. If the pH of water eg. oceans falls down the scale from alkaline to acidic, can have a devastating impact on its inhabitants. 

Ocean Acidification is one such challenges facing the humans as a result in the change of pH.

Natural calamities such as landslides, storms and floods, often raises the turbidity of surrounding water body. This is because the eroding ability of water increases with the speed of its flow. High speed of a rivers erodes the sand and soil around its embankments thus rapidly dissolving more of the sand, minerals and organic compounds in its way.

Impurities generated through human activities such as mining, construction enter the surface water as in rivers, lakes through rainwater runoffs. Water penetration into the groundwater through leaching also cause water pollution and raise the level of suspended solids.

Runoffs from agriculture farms using Pesticides, Unsafe disposal of biomedical wastes, etc could end up dissolving into the water body and polluting it.

Water is called a universal solvent because of its ability to dissolve a large number of elements. Water on reacting with the carbon dioxide forms a weak carbonic acid. Carbonic acid is even a better solvent than water. When water under pressure flows in rivers, it passes through many types of rocks and soil. During this process minute quantities of calcium and magnesium gets dissolved in water and is carried away to our urban water supply.

The reaction between water, carbon dioxide and calcium carbonate results into:

     CaCO₃  + CO₂ + H₂O ⇌ Ca²⁺ + 2 HCO3⁻

^{The end products are free Calcium ion cations and weak carbonic acid. This release of free calcium ions increases the level of calcium in water. Thus hardness level increases in water along with the level of Calcium.}

The color of the below four different samples of water indicates the amount of turbidity in water (expressed in NTU). High turbid water tends to remain more hazy and less transparent than their lesser counterparts.

The otherwise odorless water with turbidity has a foul smell in general but it may varies depending on the type of impurities suspended in it. Eg. A rotten egg smell in water indicates the presence of hydrogen sulphide in it.

A turbidity meter measures the amount of particles present within the medium. It does so by a combination of two basic things:

Flasher- for sending a light wave into the medium to be tested for turbidity.
Sensor- which measures the amount of light that is reflected back when light travels through a medium and collides with the particles( impurities ) present in the medium.
These sensors could vary as per usage ranging from conductivity sensors for electrical conductance to temperature.

Turbidity meter is a very accurate turbidity measuring device in the market.

Check out the turbidity meter available.

Tubidity Meter check out in the market.

Sedimentation and Decantation
Chemicals and Filters in tanks - household water supply purification

It is a physical process of removing impurities from water. As the name suggests it consists of two processes:

Sedimentation : Sizable sediments in water under the force of gravity settles down onto the bottom of the container containing the impure solution
Decantation: The upper layers of water is then extracted without disturbing the solution and the impurity at the bottom is separated.

Is the chemical process for purifying water in household and commercial water supply.

Filters : The filters come in various shapes and sizes. They are used to trap the fine impure particles in water.
Chlorine : The excess impurity in water which escapes the filter could be removed by adding chlorine to the water. This chlorine is used up to oxidize the organic impurities in water.
Activated Charcoal: is one such type of filter used for household tanks. It is known for its ability to not only absorb inorganic impurities in water such as hydrogen sulphide but also organic impurities. Besides, it absorbs any leftover chlorine in water which was used for oxidizing organic impurities. Most remarkable feature of activated charcoal filter is that it not only removes the impurities but also their odor in water thus providing the aesthetic water quality. 

RO or Reverse Osmosis Technology makes use of a narrow semi-permeable membrane through which impure water under pressure is made to pass through. This semi-permeable membrane blocks chemicals and ions from entering the channel thus separating impurities from clean water.

Certain natural phenomenon such as landslides or heavy rainfall flood the water body thus increasing its turbidity. This results in increase in suspended solids in water which not only blocks the sunlight penetration but also raises the temperature of water. This results in blocking the process of photosynthesis. It not only lower the water dissolved oxygen content but have a devastating impact on the entire aquatic food chain.

This turbidity is followed by excessive sedimentation under gravity thus causing habitat destruction in most of the freshwater ecosystem. The impurities also host a number of harmful pathogens and shields them from sunlight that could seriously affect the aquatic life of that water body.

The only good good thing about these natural calamities are that they do not occur very often and their effect is generally short-lived. In due time most of the sediment settles down under gravity.

The impurities often host a number of harmful pathogens which could cause a number of diseases most common being gastrointestinal in humans. Not only does these impurities hosts pathogens but also shields them from the disinfectants that you apply to treat them.

The run-offs during heavy rainfall often wash away the minerals and chemicals (as in pesticides) from the land surface to the water body. This runoff in ponds and lakes results into Eutrophication which completely kills the entire ecosystem of the area.

USGS - Water Turbidity

Wikipedia - Water Turbidity