Removal efficency of a constructed wetland combined with ultrasound and UV devices for wastewater reuse in agriculture

This study evaluates the treatment efficiency of a chemical-free water treatment for treating the secondary effluent of amunicipal wastewater treatment plant with the aim of reusing the water for agriculture. Urban wastewater was treated bythree units run in series: a full-scale horizontal sub-surface flow constructed wetland, a small pond with an ultrasound (US)system and a UV device. The treatment efficiency was evaluated in terms of the Italian wastewater limits for irrigation reuse,water quality improvement (removal percentage) and algae bloom control. The tolerable infection risk, associated with theuse of wastewaters for irrigating crops, was also assessed by applying the microbial risk analyses proposed in the WHOguidelines for wastewater reuse. The constructed wetland was efficient in reducing physical-chemical and microbiologicalconcentrations, and its efficiency was very steady over the investigation period. The UV system significantly improved waterquality (p <0.05) in terms of pathogen concentration with a further average decrease from 0.35 to 1.23 log units, dependingon the microbiological parameter. The US device was able to prevent algae bloom on a free water surface and maintainChlorophyll-a concentration stable and low 2 months after activation.