Research Of Critical Technology In Engineering Application Of Landfill Leachate Treatment By DTRO

The DTRO?Disk Tube Reverse Osmosis?system was applied to treat landfill leachate in Southwestern China.The interaction among indexes such as membrane system operating pressure,temperature,leachate conductivity,desalination rate was analyzed over 10 months,and the optimization method was recommended.The main effect factors were determined,then the optimization experiment was designed.The concentration of COD,BOD₅,TP,TN,NH₃-N,SS of inlet and outlet were detected to test the performance of DTRO.For reducing the leachate salinity,improving the DTRO pollutant removal performance,the coagulation process and the parameters of Fenton oxidation were adjusted to optimized value;LFG output and calorific value of landfill were calculated to explore the feasibility of LFG reusing to improve the range of operating temperature;Membrane cleaning mechanism was optimized to improve membrane flux and extend service life.The DTRO,MBR,MVC were compared,the efficiency and economy of DTRO were studied.The results show:?1?The reverse osmosis membrane can selectively separate the ionic material.Thereby clean water achieving to be separated from the liquid mixture.It is the most accurate separation method at this stage.Treating landfill leachate with MBR,DTRO and MVC technology can meet the Landfill Control Standard?GB 16889-2008?.The DTRO process can be used to completely separate the leachate.It can also adapt to different water quality leachate,which can match another treatment method before or after the process.DTRO has advantages such as process combination flexibility,small size,easy to remove,processing size can be modularized,replacement of membrane failure is relatively simple.The construction and operating costs of DTRO are lower compared with other two processes when the capacity of all these three processes is 100t/d.DTRO also has some problems such as processing efficiency was affected by the environment temperature,leachate conductivity,osmotic pressure,and other issues.?2?The performance of DTRO in the process is mainly affected by salt concentration,environment temperature,transmembrane pressure,pH,membrane contamination,concentration polarization.The pollutant control indicators can always meet the standard during the operation.Landfill leachate conductivity kept on rising,from 16.14 mS/cm to 31.63 mS/cm.The operating pressure of the primary DTRO is also increased from 35.33 bar to 53.7 bar.The operating efficiency is related to temperature.The operating pressure enters the peak area when the leachate temperature is below 14?in winter.The highest pressure exceeds the normal range about 25%.In the pressure peak range,the first stage of DTRO's desalination rate reached 97.73%.COD,BOD₅,TP,TN,NH₃-N,SS,metal ions and other pollutants can be stable discharge and meet the standards.There was a positive correlation between pH value and COD removal rate.Adjusting the pH value of the solution is the most important influencing factor of the RO membrane on the main pollutant separation ability.If pH>7,it is conducive to COD,BOD₅,TP,SS removal.If pH<7,TN,NH₃-N removal effect is better.And it can effectively control the operating pressure.The pH of the solution should be adjusted to between 6 and 7 to achieve better operating economy and separating efficiency.?3?Pretreatment such as coagulation+Fenton process can effectively alleviate the effect of salinity accumulation on the leachate treatment system.The conductivity decreased from 18.62mS/cm to9.68mS/cm after pretreatment.And the operating pressure decreased about 3.2 bar.In the coagulation experiment,the pH value was adjusted to about 6.5.PFS dosage of 1.2g/L when the maximum COD removal rate of 46.82%.Vigorous coagulation 2min,slow coagulation 20min after precipitation 30min,coagulation removal effect is the best.In the Fenton oxidation experiment,the COD removal rate reached63.03%when the pH value was 4.From the economic point of view,H₂O₂ dosage of 8ml/L when the removal rate of 64.03%.The molar ratios of 1 to 2 are more appropriate.So nH₂O₂·nFe²⁺is set at 1.5:1.When the oxidation reaction time is 1 h,the removal rate reaches the maximum value.Using coagulation+Fenton pretreatment,the cost is about 14.82 yuan/t.Leachate per ton of processing costs increased by about 15 yuan.Integrated dosage and operating power consumption.After the pretreatment,the DTRO operating cost is about 43.79 yuan/t.?4?The dynamic viscosity and kinematic viscosity of the water in the leachate change with the temperature.Thus,the operating efficiency of the system is also affected.At an altitude of 2648 meters,when the leachate liquid temperature below 14?,DTRO operating pressure meets the peak area.In the elementary experiment,the leachate temperature increased from 14?to 22?.Then the primary DTRO operating pressure drops from 56.2 bar to 49.5 bar.The LFG is a kind of landfill waste.The untreated landfill gas calorific value is 19.2 to 22.5 MJ/m³.Equivalent to about 0.5m³ of natural gas calorific value.Which means it has higher recycling value.LFG gas production can be estimated by using the IPCC model.By calculation,the landfill treatment plant of the city of the experiment can produce about 5000m³/d of waste gas.LFG reuse combustion can produce about 105MJ/d of heat.The heating system can not only achieve low-temperature environment leachate heating but also run concentrated liquid dry evaporation system.Approximately about 3%of the residue is produced.The leachate can be completely harmless.The total cost is about 30.73 yuan/t?5?The operating pressure of the first stage DTRO kept on rising during the operation.Membrane flux increased from 15.6L/h·m² to 19.6L/h·m² after chemical cleaning.And running pressure also dropped.Chemical cleaning alternately with diluted H₂SO₄ and NaOH is the most effective way to clean the membrane.Membrane flux recovery faster when leaning time within 2h.The best cleaning time is about1.5²h for accounting for the clean economy.If the membrane flux after washing is unnormal rising,accompanied by a decrease in desalination rate.It means that the RO membrane inside has been damaged.Membrane flux interval to restore the fastest in 25²5?.The cleaning effect is poor when the temperature is lower than 15?.Membrane flux changes gentler when t>25?,and cleaning effect is not affected.The proposed cleaning temperature is 15³5?Under ordinary operating conditions.The leachate should be treated with coagulation+Fenton pretreatment to reduce the combined operating costs as far as possible before the landfill is closed.