Performance of a hybrid system combining constructed wetland and solar photo-Fenton for micropollutant removal in aquaculture farms

Abstract

One of the biggest threats to human society is the scarcity of fresh water. Approximately 40 % of world population does not have access to fresh water. Agriculture is the sector that uses the most, approximately 70 %. This is the reason why the reuse of water derived from aquaculture could be a solution for this big challenge. Aquaculture is based on the cultivation of aquatic organisms. Organic compounds such as antibiotics are commonly added to the medium to improve the production. Micropollutants are within these types of organic compounds and are found at low concentrations in aquatic environments used for aquaculture. Micropollutants are very difficult to remove by the conventional wastewater treatment plants. In this study, several micropollutants were evaluated such as antibiotics (e.g. sulfamethoxazole, ciprofloxacin and metronidazole), pesticides (e.g. acetamiprid) and the estrogen, estradiol. On the one hand, estradiol, metronidazole and ciprofloxacin are widely used in the aquaculture sector. On the other hand, acetamiprid and sulfamethoxazole have been found in river water. Constructed wetlands are spaces built by humans in which micropollutants can be absorbed under controlled conditions. However, they require an extensive land area and time. Contrary, advanced oxidation processes are a more efficient technology that removes these contaminants from wastewater. Although compared to constructed wetlands, they are more expensive and less environmentally friendly. This work aimed at finding a more effective, economic and sustainable process to remove micropollutants from wastewater. For this purpose, a hybrid system that combines advanced oxidation processes and constructed wetlands was evaluated. Among advanced oxidation processes, solar photo-Fenton at neutral pH using organic fertilizers as iron source was selected. For the constructed wetlands two different plants Phragmites australis and Cyperus haspan were chosen. Besides the effect of this hybrid system at different hydraulic retention times (e.g. 0, 2, 4, 7 and 14 days) was studied. A higher degradation of micropollutants was observed in the hybrid system when after 4 days in plants, the photo-Fenton method was applied using a concentration of 2.5 mg/L of iron and 25 mg/L of hydrogen peroxide as compared to the photo-Fenton method alone (using double the concentration of reagents). This degradation was also higher as compared to the use of the constructed wetland alone after 7 days without any additional treatment. Acetamiprid was the contaminant most difficult to remove. In the hybrid system, after 4 days in the constructed wetland and using the aforementioned concentrations of iron and hydrogen peroxide in photo-Fenton process, 79.10 % and 67.82 % of acetamiprd was removed in the presence of C.haspan and P.australis, respectively. The remaining pollutants were completely degraded under these conditions. The outcome of this study showed that a hybrid system is a more sustainable, efficient and economic process to reuse the water derived from aquaculture