Study On Improvement Of Membrane Separation Performance Of Biologically Treated Leachate From Municipal Solid Waste Incineration Plant By Ozonation

The leachate from an incineration plant for municipal solid waste(MSW) is a kind of wastewater that has black stunk, complicated organic pollutants and high content of ammonia nitrogen. The harmful substances in leachate will cause serious environmental pollution if improperly handled, and then endanger human beings’ health. However, the leachate needs high technology in actual operation process, in industry it is usually pretreated by biological process, but after the pretreatment, the wastewater also has high proportion of COD and ammonia nitrogen, thus the deep processing is required.The biologically treated leachate being treated by Ca(OH)2 flocculation and then oxidized by ozone in the Ca(OH)2 flocculated leachate, and finally the ozonated leachate was treated by RO and NF membrane,respectively. The experimental results indicated that Ca(OH)2 flocculation can effectively remove a large fraction of organic pollutants like humic acids, and strongly catalyze O3 oxidation to remove the rest refractory organic small molecules in wastewater, and its mechanism might be timely remove carbonate ions generated in the reaction system. Further study showed that Ca(OH)2 flocculation processing could effectively remove the heterocyclic compounds in the biologically treated leachate and then improve the membrane flux of NF in wastewater treatment. The COD concentration in the flocculated leachate can be further reduced after the ozonation process, but NF membrane flux was not improved. The reason could be that the siloxane compounds generated by the ozonation process caused the fouling of NF membrane. Compared with RO treatment process, ketone compounds, amines and amides compounds, heterocyclic compounds present in the biologically treated leachate can pass through the NF membrane, as a result the NF permeate COD was increased by 100 mg·L-1 to 160 mg·L-1. Besides, the increases of NF average flux could lead to a slight increase of permeate COD. Membrane fouling is not obvious after the NF treatment of the biologically treated leachate and its pretreated samples. The COD and Ca2+ and Mg2+ concentration in the flocculated leachate can be further reduced after the ozonation process. The RO membrane flux of the ozonated leachate was raised by 25~35 % compared with that of the biologically treated leachate, and RO membrane fouling is obviously reduced.The present work deals with lime flocculation, O3 oxidation process parameter optimization, and the performance and mechanism of the RO and NF membrane process, exploring the feasibility of combining the lime flocculation, ozonation and RO/NF process to treat the biologically treated leachate. It’s valuable for the application of MSW incineration technology and complex wastewater treatment.