Natural Mineral Flocculation Pretreatment Of Landfill Leachate Reinforcement Effect

With the continuous development of our economy,the living standard of the people is increasing day by day,and a large amount of garbage is produced.Landfill leachate has gradually received extensive attention from researchers at home and abroad.Landfill leachate refers to a kind of high-concentration organic wastewater formed from the moisture contained in the garbage itself in the landfill,the rain and snow water entering the landfill and other moisture,excluding the saturated water capacity of the garbage and the overlying soil layer,and passing through the garbage layer and the overlying soil layer.There have been relevant studies on the treatment of landfill leachate,but relatively little attention has been paid to the treatment of landfill leachate combined with natural mineral flocculation,and there are still many deficiencies in the understanding of the flocculation process of landfill leachate.Aiming at the landfill leachate with high pollutant concentration and complex components,this paper uses natural minerals for environmental protection,economic benefits,no secondary pollution,and a large number of particulate colloid will be produced in the added solution to help the flocculation sedimentation method solve the problems of loose flocs and difficult settlement in the process of landfill leachate flocculation,so as to achieve efficient flocculation and rapid settlement.The strengthening effect of three kinds of natural minerals on flocculation pretreatment of landfill leachate was studied in this paper.Chemical Oxygen Demand(COD),ammonia nitrogen and turbidity were the target pollutants.Through single factor experiment and orthogonal experiment,the influences of flocculant dosage,natural mineral dosage,p H value,stirring speed,standing time and other factors on the flocculation effect were investigated,and the optimal flocculation process conditions were determined,and the strengthening mechanism was explored by combining the fractal dimension of floc,three-dimensional fluorescence spectrum analysis and UV-visible spectrum analysis.In this paper,the experimental research on landfill leachate is carried out from three aspects.(1)Flocculant experiment.In this experiment,the leachate from the regulation tank of a landfill in Lanzhou City was selected as the experimental water sample,and the water quality in the actual treatment plant was treated experimentally.The influent water COD concentration is 15376.4 mg/L,the ammonia nitrogen concentration is 479.2 mg/L,and the turbidity is 596.5 NTU.Polyaluminum chloride(PAC),polydimethyldiallyl ammonium chloride(PDMDAAC)and chitosan(CTS)were used as flocculants to treat landfill leachate.Single factor experiment and orthogonal experiment showed that flocculant dosage,p H,stirring speed and standing time were the main factors affecting the flocculant experiment.The results show that the order of COD removal effect is PDMDAAC > PAC > CTS.The optimal experimental conditions for the treatment of 300 m L landfill leachate by PDMDAAC are as follows: dosage of PDMDAAC with concentration of 0.01 g/L is 1.5 m L,p H value is8.0,stirring speed is 320 r/min,and standing time is 60 min.Under these conditions,the COD concentration after flocculation is 7792.12 mg/L,the ammonia nitrogen concentration is419.57 mg/L,the turbidity is 111.2 NTU,and the removal rates of COD,ammonia nitrogen and turbidity are 49.32%,12.45% and 81.36%,respectively.(2)Enhanced flocculation experiment of natural minerals.Attapulgite,bentonite and diatomite were used as coagulants to enhance the flocculation treatment of landfill leachate,and the influence of natural mineral dosage on the experimental results was investigated by single factor experiment.The results show that the order of COD removal effect is attapulgite > bentonite > diatomite.The optimal dosage of 300 m L landfill leachate treated with attapulgite enhanced flocculation is 2.5 g.When the dosage of attapulgite and PDMDAAC were 2.5 g and 1.5 m L respectively,the removal rates of COD,ammonia nitrogen and turbidity in the supernitant reached 67.10%,35.07% and 97.25%,respectively.The addition of natural minerals can effectively promote the flocculation effect.When the dosage of attapulgite and PDMDAAC is 2.5 g and 1.5 m L respectively,the COD of attapulgite decreases from 7792.12 mg/L to 5058.88 mg/L compared with no addition.The turbidity of the supernatant decreases from 111.21 NTU to 16.4 NTU.The change of floc from floating form to rapid settling is more conducive to the subsequent separation and biochemical treatment.(3)Characterization analysis.The fractal dimension was used to characterize the physical structure of the floc of the water sample after the flocculation of the leachate,and the change of the microstructure and the dynamic change of the floc growth were analyzed.The results showed that the floc after the enhanced flocculation of attapulgite had the largest fractal dimension,the floc structure was dense,the sedimentation rate was fast,and the flocculation and precipitation effect was good.The composition characteristics of organic matter in leachate were studied by means of continuous chemical extraction and three-dimensional fluorescence spectrum analysis.The results showed that,on the whole,the fluorescence signal of the landfill leachate decreased after coagulation treatment,indicating that DOM components in the leachate were removed to varying degrees,and the removal effect of tryptophan was more significant,while the removal effect of humic acid and tyrosine-like substances was poor.The absorbance curve of the leachate before and after treatment was observed by UV-visible spectrum analysis technology.Although the substance structure of the leachate before and after treatment was relatively complex,the absorbance value of the water sample after flocculation was significantly reduced,indicating that some pollutants were removed during the flocculation process and the tryptophan in the leachate was significantly reduced,which was consistent with the conclusion of three-dimensional fluorescence spectrum analysis.In this paper,the optimal treatment parameters under different conditions were determined by experiments.The research results are helpful for the treatment of landfill leachate with high concentration and complex components by flocculation precipitation method,and can provide reference and support for the treatment of landfill leachate.