When municipal solid waste(MSW) with high content of food waste is landfilled, the rapid hydrolysis of food waste results in the imbalance of anaerobic metabolism in the landfill layer, indicated by accumulation of vo...When municipal solid waste(MSW) with high content of food waste is landfilled, the rapid hydrolysis of food waste results in the imbalance of anaerobic metabolism in the landfill layer, indicated by accumulation of volatile fatty acids(VFA) and decrease of pH value. This occurrence could lead to long lag time before the initiation of methanogenesis and to the production of strong leachate. Simulated landfill columns with forced aeration, with natural ventilation, and with no aeration, were monitored regarding their organics degradation rate with leachate recirculation. Hydrolysis reactions produced strong leachate in the column with no aeration. With forced aeration, the produced VFA could be effectively degraded, leading to the reduction in COD of the leachate effluent since the week 3. The CH_4 in the landfill gas from the column with aeration rate of 0.39 m3/(m3·d) and frequency of twice/d, leachate recirculation rate of 12.2 mm/d and frequency of twice/d, could amount to 40%(v/v) after only 20 weeks. This amount had increased up to 50% afterward even with no aeration. Most of COD in the recirculated leachate was removed. Using natural ventilation, CH_4 could also be produced and the COD of the leachate effluent be reduced after 10 weeks of operation. However, the persistent existence of oxygen in the landfill layer yielded instability in methanogenesis process.展开更多
To study the serious valve top gap cavitation of Datengxia high head single-lift ship lock,the 1:1 scale slice experiment is carried out,to truly reveal the gap flow characteristics,as well as the valve top gap cavita...To study the serious valve top gap cavitation of Datengxia high head single-lift ship lock,the 1:1 scale slice experiment is carried out,to truly reveal the gap flow characteristics,as well as the valve top gap cavitation characteristics and the anti-cavitation mechanism of natural aeration.Three kinds of cavitation,namely,the throat cavitation,the mainstream inner cavitation,and the valve plate cavitation,are determined and they are found to occur step-by-step in the gap section in the development of the cavitation.According to the anti-cavitation mechanism of the natural aeration,the pressure of the gap flow through the ventilation is increased,to avoid the mainstream inner cavitation and the valve plate cavitation,and to weaken the throat cavitation.The negative pressure zone in the gap section gradually extends with the development of the cavitation until the gap section is filled with a stable−10 m water head.When the natural aeration measure is employed,the pressure in the gap section approximately reaches the−2 m water head,and the cavitation disappears.The systematic tests reveal the quadratic polynomial relationship between the pressure in the gap and the ventilation per meter width.The pressure,which corresponds to the maximum value of the ventilation at the beginning of the gap,approximately reaches the−2 m water head,and the pressure and the ventilation reach the equilibrium state limit.When the pressure in the gap increases when the valve is opened,the ventilation gradually decreases until the natural aeration stops.The gap section length for the high head valves has a great effect on the natural aeration and should be long enough to maintain the stable negative pressure in the gap,whereas the throat width has a minimal effect.Results can be used for the anti-cavitation design of the high head lock valve.展开更多
基金The National Hi Tech Research and Development Program(863) of China(No. 2001AA644010 2003AA644020)
文摘When municipal solid waste(MSW) with high content of food waste is landfilled, the rapid hydrolysis of food waste results in the imbalance of anaerobic metabolism in the landfill layer, indicated by accumulation of volatile fatty acids(VFA) and decrease of pH value. This occurrence could lead to long lag time before the initiation of methanogenesis and to the production of strong leachate. Simulated landfill columns with forced aeration, with natural ventilation, and with no aeration, were monitored regarding their organics degradation rate with leachate recirculation. Hydrolysis reactions produced strong leachate in the column with no aeration. With forced aeration, the produced VFA could be effectively degraded, leading to the reduction in COD of the leachate effluent since the week 3. The CH_4 in the landfill gas from the column with aeration rate of 0.39 m3/(m3·d) and frequency of twice/d, leachate recirculation rate of 12.2 mm/d and frequency of twice/d, could amount to 40%(v/v) after only 20 weeks. This amount had increased up to 50% afterward even with no aeration. Most of COD in the recirculated leachate was removed. Using natural ventilation, CH_4 could also be produced and the COD of the leachate effluent be reduced after 10 weeks of operation. However, the persistent existence of oxygen in the landfill layer yielded instability in methanogenesis process.
基金Project supported by the National Nature Science Foundation of China(Grant Nos.51479124,51779151).
文摘To study the serious valve top gap cavitation of Datengxia high head single-lift ship lock,the 1:1 scale slice experiment is carried out,to truly reveal the gap flow characteristics,as well as the valve top gap cavitation characteristics and the anti-cavitation mechanism of natural aeration.Three kinds of cavitation,namely,the throat cavitation,the mainstream inner cavitation,and the valve plate cavitation,are determined and they are found to occur step-by-step in the gap section in the development of the cavitation.According to the anti-cavitation mechanism of the natural aeration,the pressure of the gap flow through the ventilation is increased,to avoid the mainstream inner cavitation and the valve plate cavitation,and to weaken the throat cavitation.The negative pressure zone in the gap section gradually extends with the development of the cavitation until the gap section is filled with a stable−10 m water head.When the natural aeration measure is employed,the pressure in the gap section approximately reaches the−2 m water head,and the cavitation disappears.The systematic tests reveal the quadratic polynomial relationship between the pressure in the gap and the ventilation per meter width.The pressure,which corresponds to the maximum value of the ventilation at the beginning of the gap,approximately reaches the−2 m water head,and the pressure and the ventilation reach the equilibrium state limit.When the pressure in the gap increases when the valve is opened,the ventilation gradually decreases until the natural aeration stops.The gap section length for the high head valves has a great effect on the natural aeration and should be long enough to maintain the stable negative pressure in the gap,whereas the throat width has a minimal effect.Results can be used for the anti-cavitation design of the high head lock valve.
