Study On The Design Of Double Anaerobic Units Multiple Constructed Wetland Sewage Treatment System And Its Aplication On The Purification Of Piggery Wastewater

Livestock and poultry breeding industry have been developing quickly in recent years in China, resulting in the production of large amount of livestock wastewater with high levels of organic material, nutrients, especially ammonia and heavy metals such as copper and zinc, which has been a great threat to our environment. Traditional treatment processes are not suitable for the treatment of this kind of wastewater either because the load is too high for the system or because the cost is too high. A sewage treatment system with double anaerobic units followed by multiple constructed wetlands is developed here and it is applied to treat piggery wastewater.The double anaerobic units-multiple constructed wetland sewage treatment system includes two anaerobic units followed by a series of multiple constructed wetlands. The main function of the anaerobic units is to lower the organic concentration. Two anaerobic units are included to separate the different bacteria in the anaerobic digestion processes to improve operation stability and efficiency. The constructed wetlands units perform further purification of the wastewater with the filtering of padding material, bio-chemical processes of microorganism and the obsorption by the plants grown in the wetlands. The construted wetland part includes the surface flow constructed wetlands followed by subsurface flow constructed wetlands. This design can prevent effectively the clog problem in the subsurface flow constructed wetlands and improve treatment efficiency. The layout of the combined constructed wetlands can be arranged flexibly according to the wastewater load and specific space conditions. So, this system combines anaerobic treatment technology and constructed wetland technology. The specific and flexible design can not only guarantee each unit to perform one or two main functions but also adapt to different wastewater and location conditions.The double anaerobic units-multiple constructed wetland sewage treatment system was applied to treat piggery wastewater form a small fig farm with150pigs and the designed flow rate was1.5m3/d. The results showed that the average removal efficiencies of CODcr, BOD5, TN, NH3-N, TP, Cu and Zn were about96%,97%,75%,82%,89%,82%and86%, respectively. And the effluent concentrations were11.5mg/L,33.4mg/L,168.3mg/L,63.5mg/L,7.8mg/L,0.32mg/L and0.67mg/L, respectively.The water quality can meet the discharge standard of pollutants for livestock and poultry breeding (GB18596-2001) in terms of organic material and nutrients and can reach the I series standard of Integrated Wastewater Discharge (GB8978-1996) in terms of Cu and Zn.The double anaerobic units-multiple constructed wetland sewage treatment system is cost effective both in construction and in running. The management and maintenance are simple and convenient. The system can be also suitable for the treatment of sewage from small and medium-sized towns and rural area.