Chlorine dioxide (ClO₂) is one of the most widely used disinfectants in drinking water treatment: it acts on a wide range of microorganisms, maintains its efficacy even at high pH, penetrates biofilms better than traditional chlorine, and avoids the formation of the potentially carcinogenic halogenated byproducts (such as trihalomethanes and haloacetic acids) associated with classical chlorination. But there is one question that until now the scientific literature had not systematically answered: do all methods of ClO₂ production have the same environmental impact? Or does choosing one synthetic route over another really make a difference?
To answer this question, we conducted the first comparative Life Cycle Assessment (LCA) of ten industrial ClO₂ production processes, following international standards ISO 14040 and 14044 and using the ecoinvent v3.8 database. The reference unit is 1 kg of ClO₂ produced, and we evaluated six impact categories: climate change, freshwater ecotoxicity, human toxicity, water consumption, acidification, and eutrophication.
The results show that the choice of process matters, and a lot. The carbon footprint varies by 35 percent between the best and worst method (3.86 to 5.20 kg of CO₂ equivalent per kg of ClO₂), while human toxicity can vary up to 6.6 times. Processes based on hydrochloric acid are the most toxicologically impactful, while the electrochemical route and the chlorine and sodium chlorite (Cl₂ + NaClO₂) based route are the most favorable in terms of climate emissions.
An interesting fact emerges from the analysis of the contributions: in most cases, it is not the actual synthesis of ClO₂ that weighs most on the environment, but the upstream production of the precursor reagents (chlorate and sodium chlorite), which alone explains 85-97% of the overall climate footprint. It means that the most effective environmental leverage lies not so much in reactor optimization but in decarbonizing upstream chemical supply chains.
Then there is a particularly relevant result from an application point of view: the electrochemical route, while being the “cleanest” on paper, is highly dependent on the energy mix of the power grid. We have identified a critical threshold of about 0.35 kg CO₂ per kWh: below this value, typical in countries such as Norway, France or Switzerland, electrochemistry is the best choice; above (e.g., in coal-dominated grids) its climatic advantages vanish. Electrochemistry also consumes more water than alternatives, an aspect that should not be overlooked in contexts of water scarcity.
In summary: there is no “clear winner” method. The best choice depends on the context, local energy mix, water availability, regulatory constraints on inorganic byproducts (chlorite and chlorate), type of pathogens to be treated. For chlorine-resistant microorganisms such as Giardia and Cryptosporidium, for example, ClO₂ remains a functionally excellent choice even at slightly higher production impacts.
This work provides water utilities and regulators with a concrete quantitative tool to guide technology choices according to sustainability criteria, and confirms how central it is, for a company like ours engaged in the development of instrumentation and metering systems, to reason about the overall life cycle of the technologies we propose to the market.
Those who wish to learn more will soon be able to read the full article in the Journal of Ecological Engineering, authored by Andrea Macchia, Angelino Ermini, Irene Angela Colasanti, Mauro Francesco La Russa and Silvestro Antonio Ruffolo – the result of a collaboration between EMEC S.r.l., YOCOCU APS, University of Calabria and University of Rome Tor Vergata, entitled “Environmental performance of industrial chlorine dioxide production methods: A life cycle assessment” More info: https://www.jeeng.net/Environmental-performance-of-industrial-chlorine-dioxide-production-methods-A-life,220575,0,2.html
Andrea Macchia
, R&D Special Project
