Effect Of Humidification And Dehumidification On Landfill Leachate Treatment

With the rapid development of China’s society,the output of domestic and industrial waste is rising rapidly,resulting in more and more serious landfill leachate problem.In order to use waste heat of waste incineration plant more efficiently,humidification and dehumidification technology developed rapidly in the field of seawater desalination has gradually entered the field of sewage treatment.In this study,humidification and dehumidification technology was proposed to treat landfill leachate,and the pollutant removal performance of the technology under different operating parameters was explored.In addition,（Up-flow Anaerobic Sludge Bed/Blanket）UASB and（Sequencing batch activated sludge reactor）SBR series were used to conduct in-depth treatment on the humidification and dehumidification condensate,and the pollutant removal performance under the process was explored.Finally,the heat and mass transfer characteristics of the device under different operating parameters are analyzed to provide ideas for process optimization.The contents and conclusions of this study are as follows:（1）In this study,parameters such as inlet temperature,inlet flow rate and circulating wind speed were optimized for the treatment of landfill leachate by the humidifier and dehumidifier.The optimal parameter values were determined by comprehensive consideration of the removal efficiency of conventional pollutants,heavy metal and water production efficiency.The results of temperature optimization show that the pollutant removal and water production efficiency are best at 60℃in the range of influent temperature from 40℃to 80℃（with 10℃as gradient）.The concentration of COD,NH₄⁺-N,NO₃^--N,TN,TP and salinity values in effluent are 1850 mg/L,118 mg/L,2.44 mg/L,127 mg/L,0.21 mg/L and 0.023%,respectively.The corresponding removal rates were 94%,91%,98%,92%,98%,97%,respectively.The effluent Cu,Cd,Pb and Zn are 0.36 mg/L,0 mg/L,0 mg/L and 0 mg/L.The water yield was 468 m L/h.The effluent conductivity was 732 us/cm,which was significantly lower than that of influent 20.9 ms/cm.The results of wind speed optimization show that the pollutant removal and water production efficiency are best when the circulating wind speed is at 2.0 m/s in the range of influent wind speed between 2.0 m/s to 4.0 m/s（with 0.5 m/s as gradient）.The concentrations of COD,NH₄⁺-N,NO₃^--N,TN,TP and salinity values in effluent are 1515 mg/L,102 mg/L,1.45 mg/L,105 mg/L,0.12 mg/L and 0.024%,respectively.The corresponding removal rates were 95%,92%,98%,93%,99%,97%,respectively.The concentrations of Cu,Cd,Pb and Zn in effluent are 0.23mg/L,0mg/L,0mg/L and 0mg/L.The water yield was 705 m L/h.The effluent conductivity was 602 us/cm,which was significantly lower than 19.8 ms/cm of influent conductivity.The results of flow rate optimization show that the pollutant removal and water production efficiency are the best when the influent flow rate is at 100 L/h in the range of influent flow rate between 60 L/h to 100 L/h（with 10 L/h as gradient）.The concentrations of COD,NH₄⁺-N,NO₃^--N,TN,TP and salinity values in effluent are 1578 mg/L,118 mg/L,1.39mg/L,125 mg/L,0.42 mg/L and 0.027%,respectively.The corresponding removal rates were95%,91%,98%,91%,98%,97%,respectively.The concentrations of Cu,Cd,Pb and Zn in effluent are 0.20 mg/L,0mg/L,0mg/L and 0mg/L.The water yield was 762 m L/h.The conductivity of outlet water was 884 us/cm,which was significantly lower than that of inlet water,21.3 ms/cm.At the same time,the orthogonal analysis results show that the influence degree of the influencing factors of the system is as follows:inlet temperature>inlet flow>circulating wind speed.（2）In order to seek appropriate system operating parameters,the heat and mass transfer effects of the humidification and dehumidification system under different operating conditions are explored by establishing a data model,The results show that the outlet temperature and the water production capacity of the system are increased with as the inlet temperature rises.When the inlet temperature is 60℃,the SYSTEM（gained output ratio）GOR reaches 0.86,（specific thermal energy consumption）STEC reaches 438 KW·h·m^-3,and the water production rate is 468 m L/h.When the circulating wind speed is 2.0 m/s,the SYSTEM GOR is 0.88,STEC is 430 KW·h·m^-3,and water yield is 705 m L/h.When the inflow flow is 100L/h,the SYSTEM GOR reaches 0.93,STEC reaches 401 KW·h·m^-3,and water yield is 762m L/h.（3）The effluent from the humidifier and dehumidifier contains relatively high concentration of volatile pollutants,such as NH₄⁺-N and volatile fatty acids.In this study,the up-flow anaerobic sludge bed（UASB）and sequential batch activated sludge reactor（SBR）were used in series to treat the effluent from the humidifier and dehumidifier,and the pollutant removal efficiency is investigated.The results show that under the UASB+SBR process,the concentrations of COD,NH₄⁺-N and TN in influent are 1698 mg/L,114 mg/L and121 mg/L,respectively.The concentrations of COD,NH₄⁺-N and TN in effluent are 30 mg/L,14 mg/L and 29 mg/L,respectively.The corresponding removal rates were 98%,87%and76%,respectively.After the landfill leachate is treated by humidification and dehumidification device UASB+SBR,the concentrations of COD,NH₄⁺-N,TN,TP,Cd,and Pb in effluent meet the standards listed in Table 2 of Domestic Waste Landfill Control Standard GB 16889-2008.