Study on the application of integrated eco-engineering in purifying eutrophic river waters

Eutrophication has become the primary water quality issue for most of the freshwater in the world. An integrated ecological engineering was applied to treat the eutrophic water of the Shuangqiao River (SQ River), one of the most heavily polluted rivers inflowing to the Chaohu Lake, China. A multi-pond constructed wetlands system was built up to treat the external loading of wastewater. Meanwhile, an in situ purification system consisted of sediment dredging, hydrophytes restoration and artificial floating islands was constructed to purify the internal loading and the river course water. By monitoring the river water quality and analyzing the samples of sediments and plants, the treatment effects and efficiencies of single and integrated ecological technique were studied. Our results indicated that the implement of ecological project notably enhanced the river’s capacity of reducing total phosphorus (TP), total nitrogen (TN) and potassium permanganate index (COD), which had increased from 2.49, 33.69 and 40.32 tons per year to 3.75, 58.28 and 74.36 tons per year, respectively. As a result, the concentrations of TP, TN and COD in the river water were dropped by 10.5%, 11.8% and 8.2% respectively. The monitoring data also showed that the removal efficiency of the in situ purification system varied with the seasons, while that of the wetlands system remained at a high level throughout the year, indicating the feasibility of a combination of different techniques to reduce the impact of season on water purification. In summary, this research indicated that single ecological technique produced no satisfying results due to the limits of technique features and environmental conditions, while the integrated engineering techniques could overcome those restrictions and had the potential to remediate heavily polluted rivers.