Experimental Study On Evaporative Concentration Of The Landfill Leachate Reverse Osmosis Concentrate

In recent years,new membrane separation technology has been widely used in China's landfill leachate treatment field in order to better meet the requirements of municipal solid waste landfill pollutant control.Reverse osmosis(RO),as one of the typical processes of membrane separation technology,produces membrane filtration concentrates during operation.Concentrate owns the characteristics of complex composition of pollutants,high concentration and conductivity,thus needs to be further handled properly.At present,there are some kinds of concentrated liquid treatment methods,which exist advantages and disadvantages respectively,and the combination of some methods can play the biggest advantage,to make up for the disadvantages of each method.Based on the requirements of the combined methods to treat the concentrates,the concentrates is evaporated and re-concentrated,and the contaminants are separated from the water to facilitate the final harmless treatment.In this paper,we focus on the separation of water and pollutants during vacuum evaporation of concentrated liquid.The concrete work and conclusions are listed as follows:(1)Taking the leachate reverse osmosis concentrate of Chang An landfill in Chengdu as the research object,the water quality index and physical characteristics were measured.The results show that the concentrate has the characteristics of high conductivity,high organic pollutants concentration and low ammonia content,and the physical properties are close to those of water.(2)Select and design evaporation equipment appropriately according to the above characteristics of water quality.The single-effect forced external circulation evaporator is selected as Evaporator,crawler-type electric heater is selected as heating device,and the device assembly connected to the evaporation system by choosing plate heat exchanger for the condenser.(3)Analyze the variations of condensate water quality,and determine the appropriate evaporation time.The results shown that the COD value of the condensate increased slightly with the increase of time,and the ammonia nitrogen,pH value and conductivity value decreased gradually.The results shown that the COD value of the condensate increased slightly with the increase of the pH value at 70?,0.07MPa and the pH value of 7.58.The value of each indicator in the condensate reaches to stabilization after 12 min.Thus,12 min is determined as the appropriate evaporation time.(4)Research the main control factors on the impact of pollutant separation,and determine the best operating conditions.Results shown that the vacuum(temperature)and the pH value of the stock solutions are the main controlling factors affecting the water quality of the condensate.By using the minimum significant difference method,it is found that the optimal operating conditions of negative pressure vacuum evaporation are as follows:the best vacuum degree is 0.085MPa,the pH is 7.58.In this paper,the effective separation of pollutants and water from reverse osmosis concentrate was achieved by negative pressure vacuum evaporation test.The optimum operating conditions of condensate water quality were obtained,which provided a strong reference for the practical application of reverse osmosis concentrate.