Study On The Control Of Landfill Pollutants Using A Bio-bin System In The Northwest Loess Region

The treatment of domestic waste in the northwest loess region is mainly based on sanitary landfill technology.The region has low rainfall,long sunshine hours and high evaporation,and the total amount of landfill leachate generated is small and the treatment cost is high,while the amount of landfill gas generated is also small and lacks collection and utilization value.Combining with the regional characteristics,this paper carries out a study on the use of bio-bin system to control landfill pollutants,taking the resource-rich loess around the landfill as the main component of the filter media of the bio-bin system,introducing active substances by recharging leachate,improving the physicochemical properties of the loess biofilter media,and creating suitable conditions for the growth of microorganisms.At the same time,the leachate absorbed by the filter media can be reduced by evaporation through local climate characteristics,and the landfill gas can be oxidized and decomposed by microorganisms in the filter media to reduce its emission.In order to realize the control effect of the bio-bin system on the pollutants in the landfill,firstly,it is necessary to have a comprehensive understanding of the characteristics of domestic waste in the landfill and the generation of pollutants;secondly,the loess in the area is generally wet-submerged,which will collapse under the recharge of leachate and affect the stability of the bio-bin system;furthermore,the natural loess around the landfill is infertile,which is not conducive to the growth and development of microorganisms.Finally,field tests are needed to further verify the control effect of the bio-bin system on landfill pollutants.To address the above situation,this paper investigated the characteristics of domestic waste in the northwest loess region through basic research,laboratory studies and field tests;explored the infiltration and sedimentation patterns of loess biofilter media in the bio-bin system,the changes of chemical properties of loess biofilter media under leachate watering,and the changes of methane oxidation capacity and microbial community of loess biofilter media;and analyzed the field test data to evaluate the efficiency of bio-bin system on landfill gas removal.The efficiency of landfill gas removal by the system was evaluated.The results of the study are as follows:（1）Taking Lanzhou New Area as an example,the main components of domestic waste are food waste,rubber and plastic waste and paper waste,with the percentages of the three being 52.90%,21.73%and 10.58%respectively;the moisture content of domestic waste ranges from 48.09%to 58.79%,with an average value of 53.11%;the bulk weight ranges from 205.47 to 278.79 kg/m³,with an average value of 238.52 kg/m³.The cumulative gas production of the first phase of the Lanzhou New Area Landfill was23,918,900 m³ and the cumulative gas production of the second phase was 35,768,500m³,with the total cumulative gas production of the two phases being 59,687,400 m³.（2）Comparing the loess biofilter media composed of 100%loess by volume,50%loess+50%fine sand and 50%loess+50%cinder,it was found that the 50%loess+50%cinder loess biofilter media had the best liquid holding performance,infiltration performance and settlement inhibition performance,with tightly connected particles,smooth surface,small porosity and no large pores and cracks formed,compared to the other two combinations,50%loess+50%cinder was the most suitable loess biofilter media.（3）The adsorption of COD,ammonia nitrogen and total phosphorus in the leachate was significantly enhanced by the loess biofilter media with 50%loess+50%cinder by volume compared to 100%loess;under the conditions of long-term watering of the leachate,the p H,conductivity,organic matter and total nitrogen content of the loess biofilter increased significantly relative to the initial state,while the ammonia nitrogen content decreased and the total phosphorus content did not change significantly.The average evaporation of distilled water was 3.38 mm/d and the evaporation of leachate was 2.89 mm/d.The average soil evaporation for the three test groups was 0.21 mm/d,0.29 mm/d and 0.35 mm/d,giving a total annual leachate reduction of 766.5 L/m²,1058.6 L/m² and 1277.5 L/m² respectively.（4）The adsorption of methane by the loess biofilter under leachate watering was particularly effective,with the adsorption pattern conforming to a pseudo-second order kinetic equation.Domestication tests in a methane-rich environment showed that the peak methane oxidation activity of loess biofilter media under leachate watering was5.93μg·g^-1·h^-1,which is 3.24 times higher than the methane oxidation activity of loess biofilter media under long-term watering with distilled water,and that the methane oxidation activity was dependent on temperature,oxygen concentration and methane concentration.In terms of bacterial community,long-term watering of loess biofilter media with leachate significantly increased the relative abundance of Gamma-proteobacteria,and inhibited the relative abundance of Alpha-proteobacteria and Actinobacteria.In terms of the methane oxidizing bacteria community,type I methane oxidizing bacteria（83.36%）consisting of Methylocaldum and Methylococcus were predominant,and their relative abundance was 4.3 times higher than that of type II methane oxidizing bacteria（15.72%）.（5）Field tests have shown that the bio-bin system has a significant reduction and control effect on methane and malodorous gases escaping from the gabion pilot wells,with removal rates ranging from 93.51%to 100%for methane,97.4%for ammonia,99.6%for hydrogen sulphide and 93.99%for malodorous gases overall.