Ozonation of wastewater in facultative sewage lagoons can improve the quality of effluent in small communities. Injecting ozone into wastewater reduced levels of contaminants like ammonia and organic matter. The toxicity of the treated wastewater decreased for some organisms, but not for others. Most emerging contaminants decreased in concentration after ozonation, but some remained stable. Overall, ozonation of small volumes of wastewater in lagoons can be an effective method for enhancing wastewater quality.