Demonstration study of bypass multipond wetland system to enhance river water quality.

This study focused on the water quality of a river in Wuhan City, China, which is surrounded by ponds that were transformed into a bypass multipond wetland system to improve river water quality. The bypass multipond wetland system included surface-flow artificial wetlands, modified partition ponds, aeration reoxygenation ponds, ecological ponds, and other processes. After the stable operation of the process, the water transparency was higher than 60 cm and the dissolved oxygen (DO) was higher than 5 mg/L, while the ammonia nitrogen (NH3-N) concentration was less than 1.0 mg/L, total phosphorus (TP) was lower than 0.2 mg/L, and chemical oxygen demand (COD) was lower than 20 mg/L, achieving the treatment target. After monitoring the results of each process, the process which best enhanced the water transparency enhancement was the surface-flow of the artificial wetlands and ecological ponds. The aeration reoxygenation pond had the best effect on DO enhancement. The processes that most affected NH3-N and TP removal were the surface-flow artificial wetlands and ecological ponds. The modified parthenogenic pond had the greatest effect on COD removal. The bypass multipond wetland system not only improved the river water quality but also enhanced the river landscape, and can act as a reference for similar river water quality improvement actions.

Demonstration study of bypass stabilization pond system in the treatment of eutrophic water body.

This study involved a comprehensive renovation of fish ponds to improve the water quality of a eutrophic river in Dongguan City. The abandoned fish ponds were transformed into three different types of stabilization ponds: facultative, aerated biological, and submerged plant stabilization ponds. The water of the eutrophic section of the river was pumped into the facultative stabilization pond and discharged into the Haizai River through an aerated biological pond and a submerged plant pond. In the aerated biological pond, secondary treatment was carried out using plant zoning and artificial floating island aeration system. The submerged plant pond used fountain-type aeration and an underwater forest for tertiary treatment. After four months of monitoring the water quality of the stabilization pond and the river, the ammonia nitrogen (NH3-N), total phosphorus (TP), and chemical oxygen demand (CODCr) levels in the raw sewage reduced from 6.53 mg/L to 1.13 mg/L, 1.76 mg/L to 0.29 mg/L, and 63 mg/L to 22 mg/L, respectively; the transparency of water increased to 45 cm, and dissolved oxygen (DO) level increased to 5.32 mg/L. This study provides a reference for the ex-situ treatment of urban eutrophic waterbodies.

Case study of the in-situ restoration of black-odorous water by combined process of forced aeration and biological contact oxidation.

Black and odorous water bodies are an extreme phenomenon that impair ecological integrity, adversely affect the lives of residents and the town's image, and cause unpleasant sensory experiences. Herein, we consider a black and smelly river in Heshan City, Guangdong Province, as a case study. The proposed comprehensive governance process combines the use of pollution control and interception, sediment remediation, aeration oxygenation, a high-efficiency biological contact oxidation/denitrification pond, and ecosystem construction. The project operation results showed that the combined process can effectively improve water quality. The water quality of the river improved to the Class V standard. All indicators met the requirements of the 'China Surface Water Environmental Quality Standard' (GB3838-2002). River water quality indicators, monitored for four months, revealed that water transparency and dissolved oxygen increased by 5.9 times and 24.5 times, respectively. Dichromate index (CODcr), total phosphorus (TP), and ammonia nitrogen (NH3-N) were reduced by 5.8, 4.17, and 5.17 times when compared to the values observed before treatment. The black-odor and eutrophication of the river were successfully eliminated, and the water quality improved significantly. In general, the combined process exhibits a high technical feasibility for implementation, providing a specific reference value for the treatment of black and odorous water bodies in urban settings.