Selection And Purification Efficiency Of Compound Substrate Of Constructed Wetland In Cold Climate Regions

With the development of economy and accelerated urbanization process of China, population of villages and towns increases remarkably, which makes the increasing discharge of wastewater. It is a growing problem which impacts the whole fresh water environment of China. Constructed wetland treatment technology needs low investments, low operating costs, low level of regulatory requirements, and high treat efficiency, compared to traditional technology. So, constructed wetlands (CWs) are suitable for domestic sewage of small towns and non-point pollutions of rural areas. However, under the cold climate of northern regions, constructed wetlands show low efficiency in winter, which impacts the application of them in Northern China.Based on the characteristic of Northeastern China, we choose decontamination effective, cheap and easy-getting materials such as natural soil, zeolite and slag as substrates of constructed wetlands. We construct vertical-subsurface flow biological filter bed, with different substrates/substrate ratio filled; discuss the solution of the operation of CWs in winters in north areas, aiming at providing sound technique support for its application.We choose static experiments for the research on adsorption properties of the fillers, focusing on adsorption kinetics and isotherm. We fit the data of the experimental results; conclude some indicative index such as their adsorption capacity, equilibrium time and adsorption stability; evaluate the fillers'adsorption performance, and discuss their adsorption principles. We also structure six vertical sub-surface flow filter beds, whose sizes are all 35cm×25cm×20cm, aim to simulate the performance of CWs without plants in winter. The ratio of fillers is gravel 5cm, the main filler 10cm, and natural soil 5cm. The condition of running are: operation cycle is 24h, including inflow, 8h stay and outflow, 16h stay, hydraulic loading is 0.114m3/ (m3·d). The changes of main pollution index of water are considered, comparing the decontamination capability of different filter beds and under different temperatures. We also make analysis on microbial indicators, in order to explore the purification mechanism of the system.The experimental results show: zeolite indicates fine capacity on ammonia adsorption; natural soil and slag have good adsorption on phosphorus and nitrogen. Beds with zeolite, slag, and zeolite/slag mixed packed all show good purification capacity for domestic sewage. Among these three kind of filter beds, zeolite bed shows better performance of nitrogen removal, with average removal rate 82.7%, and under low temporary, its efficiency is high for total nitrogen; and slag bed shows better capacity of decontamination of phosphorus and organic matter, the removal rates of whom are 94.1% and 80.8%, respectively. Removal capability for organic compounds is impacted under low temperatures, while nitrogen, phosphorus and suspended solids removal rates are less affected by temperature. There are a large number of microorganisms accumulating in the reactors. Microbial biomass and biological activity are significant higher in the surface soil than in the lower filler layer; and the biological index could indicate the mechanism of decontamination of wastewater to a certain extent.