Study On The Redox Buffer System And PH Buffer System In The Landfill Leachate Plume

With the growing prosperity of the world economy and the rapid development of industry and agriculture, Industrial waste, waste water, waste gas and municipal solid waste contaminate environment, especially groundwater, which has become a prominent global environmental problem. In addition, with the accelerated process of urbanization, more and more solid waste is generated, and municipal solid waste is arbitrary dumped or not to be properly managed, which will lead to groundwater pollution, particularly harm caused by landfill leachate.There are lots of control and restoration technology against underground environment pollution, such as extraction treatment, PRB treatment, etc. However, these methods are difficult to implement and need too much money. For China's current situation, these methods are very difficulut be applied. In the early 1990s, some scientists'studies have shown that Natural underground environment have a certain restoration potential for internal pollutants. Thus, the natural attenuation, as a method of soil and goroundwater restoration, was in-depth study.Considering the situations of domestic and foreign recent research, the study which simulated underground experiment polluted by landfill leachate was constructed to investigate redox buffering system, pH buffering system and relation between the two systems.Results of experiment indicated that: (1) Sulfate reduction zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone existed in the columns filled with sand soil or clay loam, and neighboring redox zones weren't completely sepatated. In sand soil column, sulfate reduction zone was distributed in the iron reduction zone which occupied around 2/3 of the whole column. (2) In the liquid environment of three simulation columns, oxidation capacity (OXC) gradually increased from 12cm to 84cm. At the same time, reduction capacity (RDC) gradually reduced. OXC and RDC behaved gentle in the two ends of the columns, but in the columns'middle part, the change of OXC and RDC was rapid. In addition, the fastest parts happened in iron reduction zone. In the sedimentary face of three simulation columns, the average OXC of each redox zone gradually increased, while the average RDC of each redox zone gradually reduced from sulfate reduction zone to oxygen reduction zone. In sedimentary face of column 3, the spatial variation of RDC first increase and then decrease from 12cm to 84cm, which dued to the spatial distribution of NH4+ concerntration. In a word, the spatial gradient variation of OXC and RDC in liquid environment was faster than that of sedimentary face, especially in sandy simulated columns.(3) In the liquid environment of sandy or clay loam simulated columns, between 12cm and 84cm, SO₄^2- which accounted for the largest proportion in OXC was main electron acceptor; NH4+ and TOC were main electron provider. The proportion of NH4+ in RDC was lager than that of TOC. In sedimentary face, Fe³⁺ was main electron acceptor in plume upstream of column 1, while in plume downstream, SO₄^2- was main electron acceptor. In the whole column, NH4+ and TOC were main electron provider. In column 2, Fe³⁺ was main electron acceptor, and NH₄⁺,TOC and Fe2+ were main electron provider.(4) In the liquid environment of simulated columns, SO₄^2- concerntration gradually decreased from sulfate reduction zone to oxygen reduction zone. The spatial variation of SO₄^2- in clay loam and sandy simulated columns were respectively 3068.071mg/L and 2492.267 mg/L, which showed that SO₄^2- played an important role in redox buffer process. In the sedimentary face of simulated columns, Fe³⁺ concerntration gradually decreased and Fe2+ concerntration gradually increased from oxygen reduction zone to sulfate reduction zone. Fe³⁺ palyed very important role during the redox buffer process, especially in sandy simulated columns. In sandy simulated column, iron reduction zone was main place of biological degradation, and Fe³⁺ will play a major role in long term natural attenuation. In the plume, the migration pcocess of dissolved Fe2+ and the sedimentation process of dissolved Fe2+ with sulfide coexisted.The special changement of TOC and biological activity which showed a declining trend were almost similar. In the overlapping areas of neighboring redox zone of liquid environment, TOC and biological had minor fluctuation, which probably owned to the outcome of ultima electron acceptor's replace. The concertration of NH4+ was higher levels in the columns, especially in the plume upstream. In sedimentary face of sandy simulated columns, the concertration of NH4+ firstly increased and then recreased.(5) In clay loam simulated column, the pH buffer capacity which gradually increased from oxygen reduction zone to sulfate reduction zone was less than that of original samples. In sandy simulated column, the pH buffer capacity whose variment had no rule in each redox zones was more than that of original sand soil.In the pH buffer system of columns plume, secondary buffer system accounted for largest proportion, followed by calcium carbonate buffer system. From oxygen reduction zone to sulfate reduction zone, the concertration of calcium carbonate gradually increased, and the corresponding buffer capacity also gradually increased in the sedimentary face. The fluctuation of cation exchange and the exchangeable base was violent in space, which was the same with the corresponding buffer capacity. Portland buffer capacity had no significant change in entire plume.(6) In the landfill leacheat plume, the physical and chemical properties of soil, and the concertrition distribution of TOC, humic acid, biological activity, SO42- and NH4+-N affected pH buffer capacity and redox buffer capacity, which was consistent with the theory.