Organic contaminants from industrial wastewater are making their way into the environment and threatening the health of humans and wildlife. Traditional wastewater treatment methods do not effectively remove refractory contaminants. To tackle this issue, Saint-Gobain and its academic partners have developed a new electrochemical advanced oxidation process that removes organic pollutants without the need for harmful chemicals. The secret to their system is their flexible, tunable TiOx anodes.
Virtually every industrial process produces wastewater. Dirty industrial water can contain an array of organic pollutants, from phenolic dyes from the textile industry to lignin from the paper industry.
Every day, we learn more about the risks of pollutants for the environment and our health. It is, therefore, crucial to remove these compounds from wastewater before they find their way into our water supplies. Regulations are beginning to reflect this need, with industrial wastewater treatment requirements becoming more stringent all the time.1
Traditional wastewater treatment is not efficient
Industrial wastewaters are treated using biological, thermal, and/or physiochemical processes. However, some organic compounds in wastewater, often called ‘micropollutants’ or dissolved organic carbons (DOCs), persist despite these efforts. They do not biodegrade, or breakdown in heat, and they aren’t removed by physiochemical processes.1,2
As a result, micropollutants remain in wastewater in very low concentrations and make their way into groundwater. These compounds have been found in rivers, lakes, oceans, and drinking water around the globe. Many of the molecules accumulate in the environment and can have devastating impacts on wildlife. Alarmingly, antibiotics can also become micropollutants, increasing the prevalence of problems associated with antibiotic resistance.3
New wastewater treatment solutions promise to eradicate more pollutants than ever before and help the industry meet the stringent requirements of enforcement agencies.4
Advanced oxidation technologies can meet the challenges of wastewater treatment
Advanced oxidation technologies are an attractive alternative to traditional wastewater treatment. They generate hydroxyl radicals, which have a very high oxidation potential, so they react with and eliminate most persistent organic molecules. As a result, advanced oxidation technologies provide rapid and complete degradation of micropollutants with no waste or sludge generated during the process. However, they can be expensive to install and run.1
There are several different advanced oxidation technologies, which employ different methods to generate hydroxyl radicals. Ozone, hydrogen peroxide, and/or ultraviolet light have all been used to generate the hydroxyl radicals needed to remove micropollutants. However, ozone and hydrogen peroxide are expensive and hazardous chemicals that should not be released into the environment, so care must be taken to remove any residues.1,5
Electrochemical advanced oxidation processes eliminate pollutants without harmful chemicals
Saint-Gobain and its academic partners have now developed a process that generates hydroxyl radicals by electrochemical oxidation using a titanium suboxide (TiOx) ceramic anode. The system doesn’t require any hydrogen peroxide or ozone, reducing running costs and environmental impact while improving safety.
Their system is flexible, and their anodes can be used with several types of electrochemical cell. For applications with low concentrations of pollutants, porous TiOx tubes with fine porosity can be used. For these cells, wastewater is injected into the gap between the anode and the cathode of the electrochemical system under a small amount of pressure. Some of the wastewater flows across the porous walls of the TiOx tube, and any organic contaminants present react with the hydroxyl radicals on the anode’s surface. The micropollutants in the permeate are eliminated, and the retentate is recirculated. Applications with higher pollutant concentrations may be better suited to using a similar system with a planar geometry and coarser pores, with no need for additional pressure.
Pilot tests prove the system’s viability
Saint-Gobain’s R&D team have set up a variety of pilot systems to test their TiOx anodes. In one example, they produced a TiOx anode tube with a porosity of 30% with an average pore size of 1.5-2µm. The team pumped a solution of a refractory dye called AO7 into the tank and applied a current of 1A, polarizing the anode. The concentration of the dye before it entered the tank was 175 mg/l, corresponding to a Total Organic Carbon (TOC) content of 77 mg/l. The resulting permeate, which was almost clear, had a TOC of 1 mg/l, demonstrating that the device had almost completely removed the dye and by-products formed by its degradation.
The team has also successfully tested the device with many other refractory pollutants. In another test, a pharmaceutical effluent was circulated through a cell with two cathodes and one anode, a treatment that almost completely eradicated organic contaminants.
The system is flexible; different combinations of cathodes and anodes can be arranged in planar or tubular configurations depending on the composition of the wastewater and the pollutant to be removed. What’s more, the current can be adjusted depending on pollutant concentration and flow rate.
Customized pore sizes for maximum efficiency
Unfortunately, wastewater with a lot of organic contamination can foul the porous anode of electrochemical advanced oxidation systems, reducing performance. To compensate for the potential effects of fouling, Saint-Gobain has developed a range of porous electrodes with varying porosity, from TiOx foams with small pores to meshes with apertures of several millimeters.
Saint-Gobain can tune the pore size of TiOx anodes to your specific application, to optimize the process efficiency, while avoiding the risk of fouling. What’s more, samples of your system’s effluent can be sent to the Saint-Gobain laboratory for testing. Using their laboratory cells, they can confirm the system will work for your specific application, estimate your electrode needs and predict the system’s energy consumption. As a result, you can be confident they have the right system before installation.
In conclusion, advanced oxidation processes are probably the best way to eliminate organic micropollutants. The electrochemical process designed by Saint-Gobain can provide lower running costs and environmental impact compared with other advanced oxidation technologies. What’s more, their system is flexible and can be tuned to your application for maximum efficiency. To find out more, visit their website.
References and further reading
- ‘Advanced Oxidation Processes for Wastewater Treatment: Emerging Green Chemical Technology’ — Ameta S, Ameta R, Academic Press, 2018.
- ‘What Are Micropollutants and How Can They Be Removed from our Water Supply?’ https://www.azocleantech.com
- ‘Occurrence, transportation, monitoring and treatment of emerging micro-pollutants in waste water — A review from global views’ — Jiang JQ, Zhou Z, Sharmab VK, Microchemical Journal, 2013.
- ‘Nanomaterials for Wastewater Remediation’ — Gautam RK, Chattopadhyaya MC, Butterworth-Heinemann, 2016.
- ‘Ground-level Ozone Pollution’