Dose disinfection by ozonation only inactivates pathogens?

In most aquatic environments, an increase in pathogenic load can be traced back to effluent discharge originating from Municipal Waste Water Treatment Plants (WWTP). Worse off, other Contaminants of Emerging Concern (CECs) have also been identified to instigate from the same. These two pollutants are a risk factor as they facilitate transmission of waterborne diseases to humans, are toxic, and have endocrine disrupting effects on aquatic organisms. Recently published literature has revealed that CECs are not efficiently removed in conventional wastewater treatment plants. Fortunately, current technological advances have refined ozonation (a water treatment technique deemed impractical owing to its prohibitive implementation cost when compared to UV and chlorination) to practical and financially acceptable technique. Ozonation method can inactivate bacteria, viruses and even the more resistant protozoan and has also been shown to remove CECs, which can result in treated water with lower toxicity.

To this effect, researchers at McGill University led by Professor Viviane Yargeau from the Department of Chemical Engineering thoroughly investigated the performance of ozone when used for disinfection of real effluents collected from three WWTPs. Their main motivation was to provide a feasible alternative that could effectively eliminate CECs and other contaminants, and was economically sound and practical for implementation in existing plants considering the imminent stringent regulations on effluents emanating from WWTPs. They anticipated that their technique would treat effluents to match the demands on the proposed regulatory requirements for wastewater from Environment and Climate Change Canada (This is the department of Government of Canada with the responsibility for coordinating environmental policies and programs as well as preserving and enhancing the natural environment and renewable resources). Their research work is currently published in Chemical Engineering Journal.

In brief, McGill scientists started their research with the selection of 16 CECs, based on their prevalence and appearance on priorities list of different countries, to be utilized to investigate the efficiency of ozone during the disinfection of three WWTP effluents. Next, the researchers collected, preserved and characterized the WWTP effluent samples. They then quantified CECs in the wastewater. The WWTP effluent samples were then subjected to ozonation followed by determination of disinfection levels. Lastly, they determined the chronic toxicity using Vibrio fischeri and endocrine activity using yeast estrogen screen assay and yeast androgenic screen assay.

The research team observed that wastewater disinfection using ozonation led to over 80% removal of CECs reactive towards ozone. In addition, the disinfection of wastewater was accompanied by significant removal of estrogenic and androgenic activity. The researchers also noted that the inherent anti-estrogenic activity was not affected during disinfection by ozonation. Lastly, modified in vitro high-throughput assays based on V. fischeri indicated a residual inhibition of less than 20% after disinfection.

In summary, the study by Viviane Yargeau and her research team presented the benefits of using ozonation as a wastewater effluent disinfection step and was demonstrated via its capacity to simultaneously overcome multiple risk factors. “In general, such results will ensure that investments in advanced wastewater treatment technologies for disinfection possess the added benefit of removing CECs and reducing their biological and toxicological impact” Said Viviane Yargeau, the lead author to Advances in Engineering in a statement. Altogether, the proposed technique protects the environment and provides safe and secure sources of drinking water.