The Research On Leachate Recycle Of Bioreactor Landfill

Municipal solid waste (MSW) buried in sanitary landfill accounted for more than sixty percent of all the solid waste in the past. Although landfill has appropriately lost at present some of its percentage in the array of solid waste management technologies to those of 3Rs (reduce, reuse, recycle), it is still the primary means of disposal of MSW. Conventional landfill (CL) is always regarded as a 'bomb' because of its high pollution potentiality to environment, especially the soil and the groundwater. Therefore, there is a growing inclination to bioreactor landfill (BL). This can be easily achieved by leachate recycle. In practice, however, a lot of process problem hover over operators. In an anaerobic system, the first phase named hydrolytic and acidogenic stage is critical in that process. However, high concentration of VFA produced in this stage will probably inhibit both hydrolysis and methanogenesis. This thesis introduces three methods to remove (minimize) the influences of VFA on process, and enhance biodegradation in BL: two-phase biologic treatment, altering recirculating frequency and pH buffers (lime and ash). Through series of experiments we get the following conclusions:1) BL can enhance biodegradation efficiently as a method of MSW land disposal. Moreover, we can approach BL simply by leachate recycle. The proper humidity is maintained, the biodegradation is enhanced, and the microorganisms are well cultivated. In the proceeding, organic pollutants decrease rapidly. Initially the COD of leachate is about 4000mg/L, falling to 1000mg/L after two months. The experiments simulate the process of stabilization of sanitary landfill, which is in the same condition. In a word, leachate recycle is economical and practicable from the point of MSW stabilization.2) Taking the form of 'mixing biologic treatment' (aerobic& anaerobic), aims at removing (minimize) the negative effect brought by descent of pH value in the acidogenic stage of MSW digestion. It was achieved in experiment. The acidogenic stage never appeared if we aerated at the time when otherwise that stage should exist. In aerobic conditions the stabilization of MSW was faster than in anaerobic environment. But after the cessation of aeration COD of the leachate remained constantly even if the recycle was continuing, the results seeming ironical. In addition, phase-separation that is what we want is equivocal in the conditions. Except convincing data are provided with experiments, this kind of treatment should be evaluated carefully before in practice.3) Recycling frequency is an important parameter in the process. It was tested by experiment that reactor performance could be improved by varying the leachate recirculation rate. Optimum conditions for biowaste digestion can be reached at a low leachate recirculation rate at the start and at a higher recirculation rate as the process progresses. It was also favorable that we adopted interim recycle in acidogenic stage. After that stage, the higher frequency should be applied. For the landfills already existed in our country, the technique of aeration is more or less difficult so the improvement of anaerobic reactor seems to be very helpful. The critical phase of biowaste digestion is the first phase hydrolysis and acetogenelysis. In the phase we should minimize recycle frequency, which is to say that we should control the rate of liquid flow down.4) For the removal of disadvantageous effect brought by VFA, pH buffers could be added into the leachate. It is established that we can do it by using white lime and ash. It is evident effectively and small quantity by using lime as a pH buffer. Pozzolanic reaction perhaps occurs where the alkaline accumulate to a certain extent. Clogging raised by Pozzolanic reaction will probably hinder the process of biodegradation. Ash can also be used as a buffer and the quantity needed is large. In this condition, we should consider the problem of movement of ash and block of outlet. On the other side, we can adjust pH value with some methods in wastewate...