water pH tester

Wastewater Treatment and pH Adjustment

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Having a wastewater treatment plant is an important regulation that every industrial plant has to follow. Not complying with environmental regulations can have financial and other consequences such as suspensions and terminations. Clarifying wastewater requires certain chemicals. The following are the three categories of chemicals used in this job:

  1. Chemicals to adjust of pH of water 
  2. Coagulant chemicals 
  3. Flocculent chemicals 

Chemicals to adjust of pH of Water 

In wastewater treatment, chemicals are used to adjust the pH. This modifies the ionic charge. A water pH tester is a device used to measure the pH level of wastewater. pH expresses the intensity of the basic or acidic nature of wastewater. Water or any other solution can have pH from 0 to 14. Neutral solutions have a pH of 7.0. An acidic solution has pH below 7.0 and a basic solution has a pH above 7.0. Wastewater also contains solids. Wastewater treatment often requires changing the solubility of these solids. This is the reason why the ionic charge of wastewater is changed. Solids get attracted by other solids. 

Different chemicals are used to adjust the pH of the wastewater. The chemical makeup dictates the selection of chemicals. When using these chemicals for pH modification, a water pH tester is used to test the acidic or basic nature of wastewater. The following alkaline or basic chemicals raise the levels of wastewater: 

  • Mg (OH) (magnesium hydroxide)
  • Ca (OH) (calcium hydroxide) 
  • MgO (magnesium oxide)
  • CaO (calcium oxide or lime)

These chemicals are used because they are affordable, easily available and effective. Sodium hydroxide (NaOH) is an expensive chemical that is commonly available, controllable and convenient. This is the reason why it is used for occasional applications or small applications. The following two concentrations of caustic soda in liquid form are available:

  1. 25% NaOH
  2. 50% NaOH

As 50% NaOH crystallizes at 12℃, it requires proper storage or dilution before using. 25% NaOH crystallizes below freezing temperature. The dry (solid, ground, flake, or powdered) or anhydrous state of caustic soda at 100% concentration is also available. The dilution process generates considerable heat. It is required to carefully control the dilution rate and cooling method. This is done to ensure that there is no splattering or boiling. Wastewater pH is lowered using certain acidic chemicals. Sulfuric acid is most commonly used as it is easily available and most affordable. It is oily, dense, strongly corrosive and dark brown or clear. There should be no heavy metals.

Muriatic acid or hydrochloric acid is slightly yellow or clear, pungent, fuming. This poisonous chemical contains arsenic or iron.  

The gaseous forms of sulfur dioxide or carbon dioxide are also applied when available. Certain industries neutralize alkaline water using flue gas that is economical and easily accessible. Instead of using any of these chemicals, low or high pH waste streams can also be used to modify wastewater treatment. A water pH tester is used to measure pH level while modifying wastewater pH. 

Coagulant Chemicals 

These chemicals adjust pH and coagulate solids. Wastewater’s chemical makeup determines the selection of coagulant chemicals. The following chemicals are used to coagulate solids:

  • Aluminum Chloride (AlCl3)
  • Ferric Chloride (FeCl3).  
  • Aluminum Sulfate [Al2(SO4)3]

 Coagulant chemicals can also play a role in pH adjustment. They can also supplement chemicals used to adjust the pH of the wastewater. 

Flocculant Chemicals

These chemicals don’t adjust the pH of the wastewater. They flocculate and separate solids. It is important to consider the chemical makeup to select flocculant chemicals.   

It is important to make controlled use of these chemicals. This is the reason why it is important to check wastewater pH using a water pH tester.  

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