A large-scale installation of a modular constructed wetland sewage treatment system has been completed in Nanjing, China, in what the constructed wetland specialists involved believe is a world first.
The installation features a system developed by Sino-Europe Constructed Wetland Research and Development Center (SECWR&DC) of Jiangsu Hippo Co Ltd. It is being used to treat wastewater treatment plant effluent and has been installed in Xingdian Town, in Nanjing City’s Pukou District.
The modular constructed wetland incorporates patented variable ‘box’ units from Jiangsu Hippo. The Nanjing plant has been constructed using previous practice of a smaller-scale modular system developed by the SECWR&DC. The specialists say that, to the best of their knowledge, the plant is the first large-scale project of its kind in the world.
According to the specialists, constructed wetlands offer advantages of lower investment and easier maintenance and management, while delivering considerable benefits for the environment. They note that constructed wetlands have been used increasingly in China, including in ‘sponge city’ construction.
They see that constructed wetlands can also deliver the benefits of intensive and large-scale application, consistent with China’s green infrastructure development, but say that implementation so far has suffered from lack of professionalism during construction, along with substrate clogging during wetland operation.
According to the specialists, the modular approach as used in Nanjing can break through the current traditional model of large-scale constructed wetland construction. The technology allows directional flow of water, and features such as factory production of parts and construction site assembly combine to speed up construction.
The Nanjing installation is treating effluent from kitchen waste and domestic sewage mixed wastewater treatment, with a capacity of around 800m3/day. It consists of a multi-stage hybrid system covering a net wetland area of about 1,600m2. The installation uses a combination of mixed substrate packing and, according to the specialists, the approach prolongs the life of wetland. The specialists add that use of the system saved around 3,200m2 compared with a conventional constructed wetland, and that land has been reserved for later stage development.
Item based on information received from Professor Yaqian Zhao of the Xi’an University of Technology, and Mr Minwei Zhou, Engineer and Deputy Manager, and Mr Yunfeng Wei, Chief Engineer, both at SECWR&DC. Professor Zhao is a Fellow of IWA and Regional Coordinator for China of IWA’s Specialist Group on Wetland Systems for Water Pollution Control.