Managing chlorate levels is critical to ensuring the safety of water. While the Drinking Water Directive regulates chlorate levels, many operators are still getting to grips with what is required from them. Here, Ryan Flood, global product manager at Evoqua Water Technologies, discusses evolving regulation and what plant managers can do to meet their obligations and maintain the efficiency of their plant.
As the topic of chlorates becomes an industry focus, we are seeing the introduction of tighter regulations and more data about their toxicity. Currently, the World Health Organisation (WHO) specifies a chlorate limit of 0.7 mg/L (700 µg/L). Recently, in 2019 however, the European Food Safety Authority (EFSA) revised this down to just 3 μg/kg of body weight, equivalent to around 0.25 mg/L at the tap. Today, the new Drinking Water Directive aims to address concerns about the high concentrations on human health and with a growing body of research outlining hazards, understanding and managing chlorates is essential for plant managers.
In the water, chlorine acts as a strong oxidising agent, inactivating harmful pathogens and providing residual disinfection, ensuring the water remains safe for consumers and has been used in this way for more than 100 years. Chlorates are a salt formation of chlorate anions and are by-products of water disinfection formed in the synthesis of sodium hypochlorite, calcium hypochlorite or chlorine dioxide.
Thanks to the success and broad adoption of chlorine and chlorine compounds as water disinfectants, the presence of chlorates is widespread, commonly affecting drinking water, aquatics centres and water reuse, as well as the food and beverage industry. While tolerated at the safe levels outlined above, significant exposure can be particularly harmful to infants, toddlers and pregnant women.
To that end, it is vitally important that the concentration of chlorates is controlled and does not exceed recommended levels ‘at the tap’. Currently, many plants use bulk hypochlorite, which is both expensive and can create operational challenges around safety and sustainability. Furthermore, it generates additional risks for both plant workers and consumers and has the potential to degrade in storage. Fortunately, there are alternatives.
If we are to maximise effective water treatment and, equally, the safety of the water throughout a municipality, there is a greater need for precision and plant self-reliance. Fortunately, just as chlorate regulations evolve, we are seeing innovations and technology developments that enable plants to better manage chlorates while also improving operational efficiencies and sustainability.
There is a growing trend of plants investing in on-site electrochlorination as preparation to meet future requirements. Not only does it eliminate many of the challenges, uncertainty and risks of bulk hypochlorite decomposition, but it promotes facility independence and provides the ability to match varying demands.
On-site electrochlorination is a proven and effective disinfection process that minimises health risks to operators and downstream users. There is no handling of dangerous chemicals – only salt – and the process only requires salt, water and electricity. Critically, as it is co-located with the treatment plant, there are no transportation, handling, safety or security risks associated with it, unlike conventional processes.
Overall, the process is incredibly efficient with electrochlorination able to scale output to meet demand with minimal storage requirements. Eliminating the need for disinfectant storage and purchase means that the systems are repaid quickly, with additional cost savings possible via off-peak production. Additionally, without bulk hypochlorite or gaseous chlorine, there are no significant risk management planning costs.
The process is reliable too, with hypochlorite solution at stable concentration always available. This ensures the minimal decomposition of active chlorine in solutions and a significant reduction of by-products, with greater accessibility to raw materials for disinfection.
With a firm commitment to safety – of both plant operators and end consumers – Evoqua’s R&D team has conducted hundreds of field and lab tests in the development and evaluation of the global Evoqua OSEC® systems. With industry-leading efficiency, the OSEC system is able to produce stable sodium hypochlorite as needed, on-site to deliver cost and efficiency improvements.*
With just the salt to be handled, risks are minimised and there is no need for large storage capacity as the sodium hypochlorite can be made as needed. Costs are substantially less than repeated bulk hypochlorite deliveries, resulting in a rapid return on investment and yet another reason why plant operators are shifting to on-site production. Water disinfection is also better controlled, with precisely the right quantities of sodium hypochlorite delivered to the system to ensure water quality throughout its journey while minimising chlorate levels for end consumers.
Supporting OSEC systems, Evoqua’s team has developed a guide for best sampling practices to ensure accurate and rigorous testing in line with the latest industry requirements and legislation. The OSEC system itself is supported by a predictive model for chlorate formation and Evoqua has put together a global guide on chlorate production to increase industry awareness and keep plant operators informed.
*Evoqua OSEC® systems are designed to produce 0.65-1% sodium hypochlorite under normal operating conditions. With less than one minute of contact time, the OSEC®-produced concentration range (6,500-10,000ppm) is significantly higher than the concentration requirements to meet industry standards for microorganism inactivation and disinfection. Specific disinfection rates depends on dose, concentration and time (CT value), pH, and water temperature. Performance limitations depend on feed conditions, overall installed system design, and operation and maintenance processes; please refer to Operations Manuals. For more information: Contactus@boxmi.cn
