Efficiency And Membrane Fouling Characteristics And Its Control Of Membrane Distillation For Landfill Leachate Treatment

Landfill is one of the most important methods of urban waste treatment in my country,and the landfill leachate produced in the process of landfill is a major obstacle to the harmless treatment of waste.This high-concentration wastewater containing a large amount of organic pollutants,heavy metals,ammonia nitrogen,microbial metabolites and salt ions will inevitably cause serious damage to the surrounding ecological environment and water resources if it is not properly treated and directly discharged,thereby threatening human health.Membrane separation technology is widely used in landfill leachate treatment,however,the concentrated solution produced by membrane filtration is a major challenge in landfill leachate treatment.As an emerging technology in membrane treatment,membrane distillation has great potential in the treatment of landfill leachate and its concentrate.In this paper,direct contact membrane distillation technology is used to treat landfill leachate and membrane filtration concentrate in different periods.The study firstly selected two different membranes(PTFE and PVDF)for the treatment of landfill leachate of different ages(young and old),and evaluated the water purification efficiency of membrane distillation to treat landfill leachate.The results show that the water quality of landfill leachate with different ages is quite different.The COD of the leachate of young age is 3100mg/L,and the COD of leachate of old age is 320.5mg/L.The membrane fouling mechanism induced by different membrane materials is different.The young leachate will quickly block the membrane pores of the PVDF membrane and form an adhesive fouling filter cake layer on its surface.For the PTFE membrane,humic substances and metal ions in aging have a great influence on it,and the membrane crystallization pollution caused by these two plays a major role.On the whole,the performance of PTFE membrane is stronger than that of PVDF membrane,and the average removal rate of COD in landfill leachate treated by membrane distillation is stable above 99.5%.Secondly,the PTFE membrane is used in the membrane distillation technology to treat the landfill leachate concentrate.By changing the three operating parameters of the influent temperature,the influent flow rate and the influent p H,the membrane fouling and membrane moistening caused by the landfill leachate concentrate are explored.Wetness issues and conditions for ammonia nitrogen recovery.The results show that membrane distillation has a strong ability to remove organic pollutants,in which the removal rate of COD is over 99.5%,and the removal rate of metal ions is over 99%.p H=5 can effectively control the ammonia nitrogen in the effluent,so that the removal rate of ammonia nitrogen can reach more than95%.The research shows that the use of membrane distillation for ammonia nitrogen recovery is feasible.By adjusting the p H of the influent water to be alkaline,increasing the influent water temperature to 50 °C and the flow rate to 0.0333 m/s,the ammonia nitrogen flux can be effectively improved,and the ammonia nitrogen can be recycled at the effluent side.It is worth noting that increasing the influent temperature and flow rate will accelerate membrane fouling,and increasing the influent p H will increase the risk of membrane wetting.Therefore,ammonia nitrogen recovery has higher requirements on the membrane,requiring the membrane to be resistant to acid and alkali and not easily polluted.Finally,the combination of pre-coagulation and membrane distillation was used to treat the landfill leachate concentrate,and the effect of adding iron salt coagulation on the membrane fouling of the landfill leachate concentrate was investigated.The results show that the membrane pollution caused by landfill leachate is mainly humic acid and fulvic acid,and metal ions will combine with humus to cause pollution.Therefore,alkali cleaning in chemical cleaning can more effectively remove membrane pollution caused by landfill leachate,and simple pure water cleaning and physical cleaning are almost ineffective.Secondly,when the dosage is 0.3m M,the coagulation effect of potassium permanganate ferrous oxide on landfill leachate is not obvious.However,potassium persulfate strong ferrous ion has a good coagulation effect on landfill leachate,and increasing the dosage can effectively control membrane fouling.It can be used in pre-membrane pretreatment to improve the flux and water production efficiency of membrane distillation.In conclusion,membrane distillation has the advantages of high removal rate of organic pollutants,high ion retention rate and high removal rate of heavy metals in the treatment of landfill leachate and its concentrated liquid.However,ammonia nitrogen will pass through the hydrophobic membrane in gaseous form,so it needs to be controlled effectively before treatment.In this experiment,it is found that the amount of ammonia nitrogen passing through the membrane can be reduced by adding acid,and the ammonia nitrogen flux can be increased by adding alkali,so as to achieve effective recovery.Because the high inlet water temperature will accelerate the membrane pollution,low grade heat source can be used in practical engineering operation at low temperature.Premixed coagulation coupled membrane distillation can effectively alleviate the membrane pollution and improve the flux of water production.The study in this paper can provide important theoretical support for practical engineering applications.