What is pH?
pH refers to a substance's hydrogen potential, or, to put it another way, the quantity of hydrogen atoms present in a solution. The pH scale, which ranks solutions from 0 to 14, is used to describe it. Acidic solutions have a pH of 0–6 (high number of hydrogen ions), while basic solutions have a pH of 8–14 (low number of hydrogen ions). On the pH scale, a solution with a pH of 7, or that of pure water at 25°C, is regarded as normal.
Why is pH important?
pH levels between neutral and slightly alkaline are ideal for bacteria and other organisms that actively engage in wastewater treatment (7 to 8).
There should be sufficient alkalinity in the effluent to neutralize acids generated by active biomass during the treatment of waste, especially nitrification, in order to maintain these ideal pH conditions for biological activity. Alkalinity is essential to the wastewater treatment process because it allows for the maintenance of the ideal pH in the wastewater as it is being processed.
pH Adjustment in Wastewater Treatment:
We can eliminate heavy metals and other hazardous substances from water by altering its pH. Metal and other toxins are typically dissolved in runoff or wastewater and do not clear out. The positively charged metal ions will create bonds with the negatively charged hydroxide ions if we increase the pH and the quantity of negative hydroxide ions. As a result, a dense, insoluble metal particulate is produced, which can either naturally filter out of wastewater over time or be removed directly using a filter press.
The two electrodes that are used most frequently in digital measurement are the reference electrode and a glass measurement electrode through which the solution being measured travels. An accurate pH number is produced by the electrodes' voltage difference, which is directly proportional to the solution's pH level. Modern measurement systems can perform measurements continuously and are increasingly adding extra features like fieldbus compatibility and explosion-proof construction that are tailored especially for industrial applications.
What Justifies pH Control in Wastewater?
The pH of water can be utilized for killing off microbes in wastewater in addition to the treatment. Most of the bacteria and organic matter we come into touch with on a regular basis prefer a neutral or slightly basic environment. A cell's growth is slowed or completely stopped at an acidic pH where the extra hydrogen ions start to make bonds with and destroy the cell. Following a wastewater treatment cycle, the pH needs to be brought back to neutral by adding additional chemicals, otherwise it will keep harming any living cell it comes into touch with.
How to control the pH in primary treatment in ETP plant?
Prior to controlling pH, determine which components—the pollutants or impurities—exist in the effluent. Once those pollutants have been identified, decide on a particular treatment method and the starting and ending pH values. Then decide which chemicals will work the best for the recommended therapy.
The treatment process is largely determined by the pH values at the beginning and conclusion. For the pH to be adjusted as necessary during effluent treatment, there must be residence or contact time. When compared to a broader pH range, a very narrow pH range (7.0 to 8.0) needs less contact or residence time (i.e., 7.0 to 10.0).
Due to different reaction periods, which impact pH control and adjustment, chemical choice is crucial. Therefore, the choice of treatment chemicals affects the residence or contact duration of the apparatus.
The pH cannot be immediately altered. The rate of change is influenced by chemical reaction times, which are related to tank capacity, mixing intensity, and other treatment-related factors. Even after the wastewater has left the treatment tank, the pH can frequently alter. When that happens, response time is longer than residence or contact time.
Adjusting the pH:
A substance called a pH adjuster or neutralization is used to change the pH or potential hydrogen level. You can lower pH by introducing a pH reagent, such as an acid. You can raise pH by using a caustic or another alkaline material.
Sodium hydroxide (50%) and sulfuric acid (98%) are the two compounds that are most frequently used to neutralize acids or bases. Ammonium hydroxide, calcium hydroxide (lime), magnesium hydroxide, sodium carbonate (soda ash), and calcium hydroxide (lime) can also be used to increase the pH of an acidic substance. In addition to sulfuric acid, other acids such as phosphoric acid, hydrochloric acid (HCI), nitric acid, or carbon dioxide can be used to decrease the pH of a basic liquid. All these substances work well to change pH.
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