Effects Of Feed Modes On Nitrogen Removal Efficiencies In Constructed Rapid Infiltration Systems

Constructed rapid infiltration system (CRI system) is a new sewage treatment technology which is based on the traditional rapid infiltration (RI). As adopting better artificial infiltration media replacing the natural soil, it could effectively decontaminate wastewater through controlling the dose of sewage. Though the development history of CRI system in our country is short, this system has obvious advantages in treating rural sewage because of its characteristics of small floor area, high hydraulic loading, flexible design and low operating cost. As a new technology, little information is available about the effects of environmental factors and operating parameters on the treatment efficiency. Furthermore, the removal mechanisms of pollutants are also insufficient in CRI system, which seriously affect its engineering application. Towards these problems, the effects of feed modes on the removal efficiencies of nitrogen in CRI system were investigated. Furthermore, the microbial community in CRI with step-feed mode by PCR-DGGE also was investigated. The main results were summarized as follows:System3(steel slag) and system5(zeolite) were operated with step-feed mode. The removal efficiencies of ammonia nitrogen increased with increasing step feed ratios from1:1to3:1. When the step feed ratio was2:1and step feed position was at a depth of600mm below the surface, the TN removal efficiencies of system3and system5reached50.90%and45.93%, respectively, increasing by12.45%and12.23%compared with the normal flooding pattern. And the best removal efficiency of CODMn Was obtained at the step feed ratio of3:1.Compared with the normal flooding pattern, the removal efficiency of ammonia nitrogen can be effectively increased under integrated vertical flow and up flow. But the TN removal efficiencies cannot be improved under integrated vertical flow. System1(bank sand) and system4(activated carbon) were operated with up flow. Compared with normal flooding pattern, the TN removal efficiency can be effectively increased in system1, while no obvious influence was observed in system4. Fourthermore, increasing the hydraulic loading can also enhance the removal efficiency of nitrogen. DO is one of the important factors affecting the removal efficiency of nitrogen in CRI system. Under the experimental conditions, the high DO content with the depth range0-600mm below the surface was benefit for nitrification, resulting in the conversion of ammonia into nitrates. While low DO content within the bottom layer enhanced denitrification process, eliminating nitrate from wastewater in CRI system.Nitrogen removal efficiency can be improved by shunt distributing wastewater in CRI system. Toward a further understanding the relation between nitrogen removal and the microbial community structure, the diversity of bacterial community in system3and system5were studied by PCR-DGGE. The result shows that, the diversity of bacterial community was the highest in upper layer of CRI system. The dominant bacteria were the same in different layers of system3, while there were obvious differences in system5. The high population similarity for the same layer between system3and system5suggested that media material had little influence on microbial community structure. The diversity of bacteria community in the bottom of CRI system could be increased under step feed mode to some extent.