Research On Space And Time Conversion Rate Of Microcell Bioreactor Landfill

Landfilling process has been considered as one of the most important final disposal alternatives with respect to its economical and environmently-friendly features for MSW treatment,however it is facing unprecedented development bottlenecks arising from two primary problems including its poor atmosphere pollution control in the process of operation and its nature of occupying much land.In order to solve the above problems,the author puts forward a novel recycling and sustainable landfilling system comprised of three features:enhancing coverage technique to restirict odor gases emission,dividing bioreactor landfill sites into micro cells to speed up stabilization rate,exploiting "urban mine" to reuse resources.The aim of this research is to highlight the effects of accelerated stability of microcell bioreactor landfill.According to the concept of "transformation of time and space",the author plans to study MSW stabilization process when humus daily cover,pretreated leachate recirculation and anaerobic + aerobic joint operation mode are adopted.Based on the lab-scale contrast experiments of microcell bioreactor landfill(ML)and conventional bioreactor landfill(CL)simulators,the evolution of gas generation,solid waste stabilization and leachate degradation were analyzed to deduce the stabilization rate constants respectively,and finally comprehensive assessment method determined as "space-time conversion rate" for ML was established.In addition,in order to gain insight into the landfill stabilization more intuitively,it was studied that a convenient and fast aerobic characterization method of biodegradable organic matter content in the solid waste.The feasibility and rationality of determining respiratory index(RI)with BOD analyzer were assessed and the standardized measurement procedure was attempted to be established.The results indicated that:Based on the determination results of four typical food waste components,such as rice,vegetables,lean and fat,it was found that it is feasible a certain extent to determine the respiratory index(RI)with BOD analyzer.In the process of determination,the total amount of oxygen supply for the sample in the environment is fixed,so sample weight becomes the main factor restricting the accuracy of determination results.Surplus coefficient is defined as the ratio of oxygen demand of the solid sample if completely mineralized to oxygen consumption range of the instrument,and it should be 0.2-0.8.According to the aerobic fermentation characteristics of four typical components,it was found that the ratio of the cumulative oxygen consumption in the previous four days to ten days(AT4/AT10)was 0.7-0.8 and the fat organics was slightly lower(0.6-0.7).Therefore the test time is set to be four days,which takes into account both the need for improving efficiency and ensuring accuracy.RImax was highly affected by the hydrolysis rate of organic substrates,which could not reflect the actual situation in the process of aerobic degradation.RI24h was closely correlated with AT4,both of which could effectively reflect the biological stability of organic matter.ML featured as humus daily cover,pretreated leachate recirculation and anaerobic + aerobic joint operation mode,compared with CL,exhibited better performance in terms of landfill gas composition,MSW biological stability and leachate characteristics.The lag phase of CL and ML were 0.35 yr and 0.32 yr respectively,which meant ML switched into the methanation stage earlier.The stabilization rate constant of CL in the anaerobic stage was 3.40 yr-1,while that of ML in the anaerobic stage was 4.36 yr-1 and that of ML in the aerobic stage was 20.84 yr-1.The space-time conversion rate of microcell bioreactor landfill was 1.28,which indicated that it could make full use of landfill space more efficiently and dispose more MSW in a certain period of time.Aerobic bioreactor landfill(AL)was prominent in the removal of leachate COD and ammonia nitrogen.It is suggested that AL should be adopted in the late stage of landfill operation because it is impossible to utilize the biomass energy and the energy consumption is high.The leachate COD,total nitrogen and ammonia nitrogen of CL,ML and AL landfill simulators showed a rapid decrease and then decreased gradually after reaching the maximum value,which accorded with the exponential decay law.The COD degradation rate constants of CL,ML and AL were 0.017 5 d-1,1.024 6 d-1 and 0.057 1 d-1,respectively.The degradation rate of COD in aerobic environment was higher.ML adopted humus cover and pretreated leachate recirculation,which were beneficial to accelerate the degradation of leachate COD.The total nitrogen degradation rate constants of CL and ML,were 0.0053 d-1 and 0.0269 d-1,respectively.The leachate of ML was pretreated with an anaerobic device,and a large number of acclimated bacteria in humus could effectively degrade nitrogenous organic matter through nitrification and denitrification.Due to the presence of humus and crushed concrete gravel,leachate could be distributed more evenly across the various sections of ML simulator.Higher intensity of leachate recirculation could accelerate the dissolution of small molecules.Contaminants in the leachate could be efficiently degraded from both inside and outside of the reactor because of the large amount of bacteria in the humus and leachate anaerobic pretreatment.Therefore,the biological stability of MSW in ML was higher than CL.GB21 of solid sample in ML on day 154 was close to the limit value in German ordinance(20 L·kg-1 D/W).Since aerobic stabilization process could greatly promote the biodegradation of organic matter,the biological stability of MSW in AL was higher than ML.AT4 of solid sample in AL on day 280 was close to the limit value in German ordinance(5 mg O2·g-1 DW).The above results showed that microcell bioreactor landfill technology could make full use of time and space to promote the rapid stabilization of MSW,which laida solid foundation for construction of recycling and sustainable landfilling system characterized by the transformation from the final "dry tomb" to "cradle" reused as"urban mining".