Electrochemical Analysis and pH Control in Wastewater Treatment

Posted in: Applications, Electrodes

Author: Matt O’Reilly

Date Posted: 04/04/2024

Any wastewater produced in industry must be analysed, treated and decontaminated before it can be reused or released. It is important to set limits on the water quality to ensure that legislation is adhered to. Electrochemical analysis and pH control of wastewater pre and post treatment is needed to ensure that the treatment has had the desired effect, and the waste is safe to discharge.

How you treat wastewater really depends on the contaminants and their concentrations. A range of tools are available for quick in-lab or inline electrochemical analysis of water such as conductivity, pH and various different target ions can be measured using ISE. By using a selection or maybe just one of these electrodes you can take a more targeted approach to wastewater treatment allowing you to use the correct chemicals in the correct volumes to treat the contamination, ultimately reducing costs.

Batch or continuous pH monitoring and control?

Most water treatment systems are integrated into existing industrial facilities and need to be constantly adjusted based on environmental, operational and legal factors. As such, continuous monitoring control measures must be implemented at all times. This can be either done manually by qualified technicians or by automated instrumentation. Manual control measures involve testing the pH levels in water at least once a day and making any manual adjustments accordingly. Some facilities where the pH levels must be kept at a certain level at all times, precise automatic monitoring systems need to be used. Sentek produce a range of sensors suitable for inline monitoring these are specifically designed to withstand high pressures and temperatures so that they are suitable for CIP procedures. By using continuous monitoring, a system can automatically dose the wastewater to allow effluent to be safely withing the desired range at all times and can automatically alert operators when outside of defined limits to ensure that legal limits aren’t breached, and the facility is safe at all times. By using a feedback loop a facility can dose a precise amount to constantly stay within range minimising waste chemicals. Long term data monitoring can also give the operators the opportunity to analyse wastewater trends and optimize water treatment.

pH control in wastewater

Measuring pH levels in wastewater is one of the simplest and most common ways to determine the quality of the water and the best way to treat it. pH is measuring specific ions; either H+ or OH- in water. In the UK, drinking water must be between pH 6.5 and 9.0, this can be quickly measured either inline or by an operator using a pH electrode. Using pH measurement can take the guess work out of how to treat waste streams. You can deliver an exact amount of chemicals to balance the pH that is safe to dispose of. Water can be treated by manipulating the pH to remove certain impurities, for example a range of heavy metals can be removed by adjusting the pH of solution into a basic range to form metal hydroxides; these are insoluble compounds which can be easily filtered out before then adjusting the waste stream back into an acceptable range.

Chemical treatment efficiency – Many chemical processes used in wastewater treatment, such as coagulation and flocculation, depend on specific pH levels to work effectively. For instance, certain coagulants will work best at specific pH levels to aggregate and settle out contaminants.

Achieving optimal biological activity – Wastewater treatment often relies on beneficial microorganisms to break down contaminants. These microorganisms have an optimal pH range where they are most active. If the pH deviates significantly from this range, the microbial activity can decrease, leading to reduced treatment efficiency. By adjusting the pH to acid levels, you can quickly kill bacteria and inhibit further growth of organic matter until you are ready to adjust back to safe levels for disposal.

Infrastructure Protection – Maintaining the right pH level can help protect wastewater infrastructure. Highly acidic or basic wastewater can corrode pipes, tanks, and other system components, leading to premature equipment failure and increased maintenance costs.

Dissolved Oxygen Electrodes

The biological oxygen demand (BOD) and chemical oxygen demand (COD) is used to estimate the impact discharging the waste stream will have in the short term to the receiving body of water. These can be rough indicators on the quality of the water and whether or not it is safe to discharge. BOD is a measure of the oxygen used for all of the metabolic activity of the microorganisms in the water and this is often used as a measure of how polluted a river system is. A higher polluted waste stream may have more organic material for biological life to grow on which in turn will consume more oxygen. A pristine river is considered to have a BOD at 1mg/L or less whilst untreated sewage is 600mg/L or higher. So, by measuring the BOD the effectiveness of water treatment can be analysed. This is monitored by measuring the dissolved oxygen in a sample and incubating in a sealed container for 5 days before remeasuring the dissolved oxygen content.

COD similar to BOD as both measure the relative oxygen demand of the waste stream however, the COD is a measure of the amount of oxygen that is consumed by reactions occurring in the water. This can be tested by measuring the dissolved oxygen content before oxidising all of the organic matter into carbon dioxide using strong oxidisers in highly acidic conditions then remeasuring the dissolved oxygen content.

ISE (ion selective electrodes)

Ion selective electrodes work similarly to pH electrodes and will allow the user to measure specific ion concentration in their effluent stream. By continuous measurement of target pollutants or treatment reagents the effluent treatment efficiency can be monitored. There are a range of ions that are considered pollutants by environmental agencies which can be detected and measured directly using our electrochemical sensors.

Conductivity electrodes

Conductivity is an extremely simple low maintenance method to determine contamination levels of your water. Conductivity cannot give you the concentration of specific ions except in some very well controlled experiments but will give an indication of the overall ion concentration. By measuring the conductivity of a solution this will give us a good overall picture of what is dissolved in the water. An increase in conductivity indicates an increase in ions or charge conducting solids in the waste stream.

ORP/ redox electrodes

Oxidation reduction potential (ORP) is the measure of a solutions ability to accept or donate electrons. An oxidiser will readily donate electrons whilst a reducer will readily accept electrons. An ORP electrode is a low maintenance electrode that can be used to measure the overall oxidation/reduction potential of an effluent stream. Chlorine for example is a very common cleaning agent it is also a very strong oxidising agent by measuring the oxidation potential you can see how much of the chlorine has reacted in the solution and if further dosing is required. Another example could be Ferric (III) sulphate, this is a common coagulant used in water treatment; this is also a reducing agent so the dosage can be monitored and controlled using an ORP electrode.

Choosing an electrode

To get the most accurate measurement of the quality of water there are several electrodes you could choose:

  • pH electrodes – This is the most common way to measure water quality. The electrode tests how acidic or alkaline the waste stream is. Often a waste stream can be treated entirely by adjusting this parameter.
  • Redox electrodes – These measure the relative oxidising or reduction potential of a sample. This can be useful in measuring disinfection techniques and how effective they are.
  • Conductivity electrodes – This electrode measures the ability of the water to conduct an electrical current. Higher quality water, the lower its ability to conduct a charge, a high conductance is an indication of ions or conducting solids.
  • Ion selective electrodes – Used to measure the concentration of specific ions in water. By using a range of these ISE, you could potentially detect particular ions present in your manufacturing stream that are making it through into your wastewater.

Contact our technical team today and find out if we have any electrodes for you.

Choosing the right electrode for analysis of wastewater and treatment is a combination of understanding the specific challenges of your industry and matching them to the features and specifications of available electrodes. Once a suitable set of electrodes or chosen, these will allow you to monitor your specific wastewater to ensure environmental compliance. Regular maintenance, calibration, and periodic evaluations ensure that the chosen electrode provides accurate and consistent results over time.

These electrodes and other bespoke options are available to purchase from Sentek. Download our water and wastewater treatment brochure, or view electrodes online that are suitable for electrocheimcal analysis and pH conrol in wastewater treatment.

Not sure what you need, or want to know more about pH analysis in wastewater treatment? Get in touch with us today to speak to a specialist.


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