Study On The Relationship Between Pollutants Attenuation And Microbial Activity In The Landfill Leachate Contaminated Sites

In recent years, soil and groundwater pollution caused by random dumping or poor management of municipal solid waste has become global environment problem. Transportation, transformation and attenuation of landfill leachate pollutants such as organics, heavy metals in underground environment could change soil environment and groundwater quality, which arouses a serious threat to the agriculture production and drinking water supplying. Therefore, it is necessary to further understand natural attenuation process and mechanisms of landfill leachate pollutants in underground environment. Because of microorganisms play a significant role underground in the natural attenuation process, we can study on the relationships between pollutants attenuation and microbial activity as the theoretical basis of controlling and treating the landfill leachate contaminated sites.In the underground condition, microbial activities have significant influences on groundwater chemical composition, rock surface characteristic and chemical substance transportation and transformation and so on. Meanwhile, the using of matters, energy and nutrition by the microorganism also alters the underground surroundings'chemical composition, pH and Eh condition. As to the sites contaminated by landfill leachate, the participation of underground microorganisms directly affect the pollutants decomposition. The microorganisms oxygenate organic pollutants and transform inorganic substance through aerobic metabolism, fermentation and anaerobic respiration. As the result, parts of the products migrate or are obstructed, and others are utilized by the microorganism for the synthesis metabolism. The way of degeneration not only depends on how much energy can relatively be produced, but also influenced by organic matters and the validity of final electronic acceptor and so on.Considering the situations of domestic and foreign recent research, this study mainly investigated the rule of pollutants'spatial-temporal variation, which contained in the leachate and the sediments. Simultaneously, it discussed how the microbial activity influenced the transportation and transformation of the pollutants. A series of simulating soil columns and sorts of static experiments were conducted. The purpose of the study was to provide the theory basis for the enhanced natural attenuation in landfill leachate contaminated sites and the pollution risk assessments to groundwater resources and so on.Results of experiment indicated that: (1) Microbial activities in liquid can evidently indicated different stages of microbial growth, and also reflected the outflow bio-availabilities. When the value of microbial activity in outflow was more than 0.04(A), it could be approximately reckoned as a higher bio-availability; The COD concentrations of discharge had prominent correlation with the microbial activity. We found that the microorganism in stabilized stage had stronger metabolized ability, which caused COD decreased by the rate of 500mgO2/d in the younger landfill sites. Compared with the younger sites, organics could be difficult utilized by the microorganisms in the old landfill sites; Ammonium attenuation in short term not mainly depended on biological processes. We calculated that the absorption capacity of sands to ammonium is 0.85g/kg, from which it could be reckoned that the sand column contaminated by the younger landfill leachate would be saturated adsorbed by ammonium for 15 days. After the phase of saturated absorption, ammonium was attenuated mainly by microorganisms.(2) In the different underground medium contaminated by the same leachate, the growth of microorganisms was alike. As for the younger landfill leachate contaminated sites, microorganisms went through a prohibitive–adaptive stage, and then came the logarithm growth stage in 5 days for soil and sand medium, 20 days for clay medium. During the logarithm growth stage, the microbial activity increasing in different types of underground medium such as soil, sand and clay at the rates respectively of 0.15(A)/d,0.013(A)/d,0.013(A)/d, and then went into stabilized phase in 10d, 18d and 28d. After the stabilized stage (about 5~7d in the three medium), microbial activity decreased at a rate of 0.015(A)/d in the different medium, when came the declining stage; As for the old landfill leachate contaminated sites, microorganism activity increased nearly at the rates of 0.05(A)/d, and went into stabilized stage in 5d for different mediums. Microorganisms had a longer stabilized stage for soil and sand medium, nearly 15d, and then decreased at the rates of 0.03(A)/d, but only 0.005(A)/d in clay medium. In the old landfill leachate contaminated sites, microorganisms of longer generation periods were in activity and there existed some evidences of the nitrification, by which we speculated on that autotrophic bacteria were the main biotype in that case. Compared with the old landfill leachate contaminated sites, there mainly existed the heterotrophic bacteria in the younger sites. (3) Soil medium had a high ability for obstructing the organic matter, and the distribution of organic matter was closely related with the microbial activity. It was obvious that the content of organic matter in soil medium>>in sand medium>in clay medium, and it was decreased with time. As for the soil medium contaminated by the younger landfill leachate, organic matter mainly decayed in the microbial stabilized and declining stages, and its average decreasing velocity was nearly 1.03(g/kg)/d. As for the sand medium, organic matter mainly decayed in the microbial logarithm growth stages, and its average decreasing velocity was nearly 0.45(g/kg)/d; As for the clay medium, organic matter mainly decayed in the microbial stagnant and logarithm growth stages, and its average decreasing velocity was nearly 0.24(g/kg)/d. The distribution of humus was more or less the same as organic matter. As for the soil medium contaminated by the young and old landfill leachate, the average decreasing velocities of humus were respectively 0.6(k/kg)/d,0.53(g/kg)/d. The velocity of humification process in the old landfill leachate contaminated sites was evidently slow.(4) The main modality of Al in sediment substance was bound to organic matters, and the oxidation processes were along with the activation and transportation of Al;The main modality of Fe and Mn in sediment substance was bound to Fe-Mn oxides, and the activity of deoxidized bacterium was propitious to the activation and transportation of the oxides of Fe and Mn. Furthermore, the acidification process influenced by pH condition was the dominantly factor of the activity and transportation of Fe-Mn oxides;The influence of underground medium type and pH condition on the transportation of Zn was unapparent, and the process of organic matter utilized and degraded was the main factor in strengthening the transportation ability of Zn;The dissolved and complex action of exchangeable Cu in sediment substance played a main role in its transportation, and the exchangeable modality was dominating in the process of Cu used by microorganism;As mainly was bound to Fe-Mn oxides as existing in sediment substance, and the type of soil had the obvious effect on As's transportation. The action of exchanging adsorption and acidification and deoxidization and oxidation could affect the transportation and distribution of As in some degree;The main transportation part of Cr and Ni was exchangeable, and the transportation of Cr was less influenced by the microbial redox, but mainly by the pH condition, what had less influences on the transportation of Ni. The complex action could enhance the transportation character of Ni prominently, and the deoxidization and oxidation could also affect the transportation and transformation of Ni in different degree; The bound to Fe-Mn oxides was the main modality of Pb and Cd existing in the sediment substance. The transportation of Cd was mainly influenced by adsorb-complex process, however, the microbial process, such as acidification, deoxidization and oxidation, was inconsiderably. As for Pb, it had a low microbial availability, and there was little effect to its transportation and transformation of different processes.