Study On Water Quality And Ecological Toxicity Of Landfill Leachate Under Dynamic Ion Exchange

The landfill leachate,as a kind of highly-concentrated organic wastewater,seriously affects the steady operation of sanitary landfill and its surrounding ecological environment.It is essential to develop a feasible and efficient treatment technology of leachate to promote the healthy developmet of sanitary landfill and reduce the ecological risks of leachate pollution.In this paper,the feasibility of ion-exchange technology to treat the leachate were evaluated by utilized of the conventional physical and ecological toxicity assessment.The main contents are as follows:1.Na OH was used to induce the self-flocculation of leachate to reduce the pollution of leachate to resin.The results show that the optimal flocculation effect is achieved when adjusting the p H value to 12.00-13.00,and the removal rate of turbidity and hardness can reach 97.38% and 93.91% respectively.In addition,the self-flocculation process could also remove the CODCr,NH3-N,T-N and T-P by 10%-20% each.2.The treatment efficiency of leachate by cation and anion resin under static and dynamic operational modes was studied.The results show that cation resin is beneficial to the removal of salt,and the anion resin to the removal of CODCr,and the treatment efficiency under dynamic exchange is better than the static exchange.Further analysis of the effluent from the anion and cation resin exchange showed that cation resin and anion resin were selective for pollutants,and the cation resin mainly removed the positive pollutants,such as NH3-N and salt while the anion resin could reduce the chroma,CODCr and T-P.3.The optimal operational conditions containing influent load,exchange sequence,exchange order and resin dosing ratio were further investigated.The results show that the highest removal rates of colorness,CODCr,NH3-N,T-N and T-P of 100.00%,92.70%,99.46%,96.61%,59.76% and 98.25% respectively were achieved under the influent load of 4 m L/min and dosage ratio of anion/cation resin of 1.43:1.00 with the leachate flowing through the anion and cation resin columns from bottom up.After a further secondary exchange,the effluent quality can reach the discharge standards of leachate pollution.In addition,in order to solve the problem of high or low p H value of cation/anion or anion/cation effluent,this project adopts the method of mixing two kinds of water exchange sequence for the first time to adjust the p H value without introducing new impurities.4.HCl and Na OH solutions were used to dynamically elute the failed cation and anion resins.The optimal concentration and folw rate of regeneratin solution and the effect of ion exchange times to the regeneration efficiency were studied.The results show that the regeneration efficiency of cation and anion resins can reach 95.96% and 90.70% respectively at the regeneration solution concentration of 7% and the flow rate of 4 m L/min.The regeneration efficiency of cation and anion resin was reduced to 92.56% and 83.75% respectively after five recycling experiments.5.The ecotoxicity of leachate and the effluent treated by new and regenerated resins to maize seedlings were studied.The results showed that:(1)the leachate could inhibit the growth of maize seedlings at high concentrations,while promote the growth at low concentration;(2)the water quality of leachate was improved significantly after ion exchange,but still exhibited ecotoxicity to maize seedlings,and the effluent from secondary ion exchange was the least toxic to the growth of maize seedlings;(3)the growth of maize seedlings was negatively correlated with the p H value,conductivity,chroma,CODCr,NH3-N,T-N,T-P and total salt content of leachate;(4)the variety and content of organic compounds in the leachate decreased after resin exchange.However,due to the complex components of pollutants in the leachate effluent,it still shows inhibition effect on maize seedlings with the extension of exposure time.In conclusion,the results of this study show that the ion exchange technology can be used to treat the landfill leachate efficiently,and reduce the ecological risk of leachate.