Integrated ozonation as a strategy for enhancing treatment of municipal wastewater in facultative sewage lagoons

Facultative sewage lagoons are widely used to treat domestic wastewater in small and remote communities, but the wastewater discharged is often out of compliance. Novel, affordable and scalable methods are needed to improve the quality of effluent. Ozonation of wastewater in these lagoons to enhance natural treatment may be an effective method. In facultative sewage lagoons operating in two Indigenous communities, we injected ozone into wastewater pumped from the lagoons to treat approximately 15% of the volume and monitored wastewater quality. In the first study, there were significant reductions in total ammonia, cBOD and cBOD/COD. Based on Vibrio fischeri, the toxicity declined post-ozonation, but there was no evidence of a similar decline in toxicity to freshwater mussel (Lampsilis fasciola) larvae (i.e., glochidia). Among 14 contaminants of emerging concern monitored, the concentrations of most compounds declined but the concentrations of others, especially 17a-ethinylestradiol remained stable. In the second study, significant decreases were observed post-ozonation in cBOD, cBOD/COD, total and unionized ammonia, but in this case, the toxicity to V. fischeri did not decline. The parameters in this lagoon were below the regulatory limit for cBOD by 4 weeks after ozonation and below the regulatory limit for unionized ammonia after 6 weeks, which is earlier then the historical dates for reaching compliance in this lagoon. Overall, the results in operational facultative lagoons, for which no comparable data are available at that scale, indicate that ozonation of small volumes of wastewater in lagoons may be an effective method for improving wastewater quality.