| In recent years,underground Wastewater Treatment Plants(WWTPs)have developed rapidly and became an important choice of urban sewage treatment facilities,because they are environmental friendly,land saving,etc.In this paper,comprehensive and systematic research and practice in the fields of land-saving treatment technologies,operation and maintenance,and construction mode were carried out based on my over 20underground WWTPs projects.The aim of this paper was to solve the problems of underground WWTPs as follows:high investment,lack of standard specifications,simplex ground space utilization,etc.and achieve overall promotion and sound development of underground WWTPs.Improvement of biochemical treatment technologies and secondary sedimentation tank were studies in order to reduce the land occupation and investment of underground WWTPs.A new process(multilevel AO+secondary sedimentation tank+high density sedimentation tank+filtration)was proposed based on the mainstream biological processes used in underground WWTPs,and engineering practices using the new process were carried out.The lab scale and pilot scale experiments of high filler filling rate FBBR(Fixed Bed BioReactor)process were developed,and the results showed that FBBR had a good performance in removal of COD,SS,ammonia and total nitrogen,and can connect with advanced treatment process with the secondary sedimentation tank omitted.Surface load of FBBR process was higher than AAO process according to a WWTPs project of 3×10~4 m~3/d.The design of peripheral-feed and peripheral overflow(PFPO)secondary clarifier was optimized by means of the combination of numerical simulation and pilot experiment,in order to improve the treatment performance.Optimized rectangle PFPO secondary clarifier had a good performance and its surface load could reach over 1.5m~3/(m~2·h)according to real projects.A series of problems that have a great influence to underground WWTPs such as sand removal,ventilation,deodorization and lighting,have been investigated.Compilation of technical code for underground WWTPs was explored base on above research.Fine sand removal efficiency was increased by 10.3%and influence to biological process was reduced through gas-water ratio optimation of aerated grit chamber.The odor concentration underground and on the ground surface while the ventilation and deodorization system was under normal operation and shutdown was investigated systematically,which gave instructions to the design and accident management.The lighting demands in different areas of underground WWTPs were systematically investigated.Natural light band and light reflection system were presented and used,which led to 41.7%of energy consumption of lighting system reduced according to engineering practice.The quantitative characterization of regional and watershed comprehensive value of underground WWTPs was explored in order to enrich ground space utilization forms,which provide basis for the formation optimation of ground space.Influence to land value of WWTPs and undergournd WWTPs in Beijing was evaluated using Differences-in-Differences estimation method.Quantitative analysis of comprehensive economic advantages of underground WWTPs arrangement in watershed was carried out combining with the Nanming river watershed comprehensive management project.Two new models of application and promotion of WWTPs:urban ecological complex cosist of public service functions and regional industry cooperative development with ground space,were presented and practiced based on above research,which provides guidance for the full utilization of the ground space and the promotion of the comprehensive value of underground WWTPs. |
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