Optimization Of The Food Waste Degradation System And Research On Characteristics Of Its Microbial Community Structure

The disposal of the huge amounts of municipal solid waste (MSW) generated with the acceleration of urbanization, is becoming a severe challenge in China nowadays. At present, the most prominent problem of domestic refuse disposal is the lack of reduction and classification in situ. A large amount of perishable food waste (PFW) with high moisture collected into the MSW system caused a series of subsequent disposal problems. In view of these factors, scavenging PFW in situ by biodegradation systems is a feasible way to deal with the disposal problem of MSW. The food waste biodegradation in a disposer is a process of aerobic respiration of the microorganisms with the PFW as substrates. The key points of improving the efficiency of a biodegradation system are applying the functional strains with high degradation ability and creating the proper aerobic condition in the biodegradation system. The aerobic degradation condition depends on not only the ventilation system of the equipment but also the permeability and water absorbing capacity of the carrier in the degradation system. In this paper, a series of PFW degradation experiments were conducted for optimizing the combines of functional strains or the carrier material in the degradation system and for improving the ventilation system of the degradation equipment, by the means of molecular biology methods based on our previous work. Here are the main results.(1) Based on three rounds of PFW degradation experiments with different combinations of carrier material, an optimized carrier with mulberry branch powder and turf in the ratio of 4:1 was selected for the small capacity food waste disposer. The waste biodegradation efficiency was increased and running duration of the biodegradation system kept to 3 months when this optimized carrier adopted and matrix moisture content maintained within 25%?30%. The significant positive correlation was observed between the enhanced temperature of the matrix and the intensity of microbial respiration in the biodegradation system, which indicated that the biodegradation efficiency could be characterized by temperature of the matrix.(2) The degradation efficiency and the duration of temperature rising of matrix as well as the system running time were obviously increased after refitting ventilating system of the small capacity food waste disposer from the exhaust mode into the inlet mode. However, they are not significant changed when heating mode of this disposer was refitted. As a consequence, improving the ventilation system of the equipment and creating favorable aerobic environment rather than heating the system can consolidate aerobic microorganism respiration intensity, which in turn raises the degradation efficiency.(3) Based on the consequences of (1) and (2), a PFW degradation experiment with two food waste degradation agents was carried out. The result indicates that the gross degradation rates of both the two systems are higher in late stage than early stage. Moreover, the degradation rate in the system of agent 2 is higher than agent 1 in the early stage and both close to each other in the late stage. Under the inlet mode, the range of suitable moisture content of matrix is 30%-35% and their upper and lower limits are both increased about 5 percent points compared with the exhaust mode, which implied that the matrix still keeps the favorable aerobic condition even the moisture content was as high as 35% rather than the undesirable anaerobic condition under the exhaust mode. The analysis results based on the DGGE profiles of matrix shown that Bacillus subtilis F2 could be the dominant bacteria strain in the biodegradation systems and the similarity coefficients of matrix microbial community structure between two systems increased as the system running time goes by, indicating that the microbial community structures of both systems became similar to each other at the late stage.(4) Two rounds of PFW degradation experiments with different combinations of carrier material were conducted in a large capacity food waste disposer which was trial manufactured. The result illustrated that the degradation efficiency and the extents of enhanced temperature after food waste added in the system with mulberry branch powder and organic fertilizer in the ratio of 4:1 as carrier was higher than that with mulberry branch powder and turf in the ratio of 4:1. The microbial community structure changed from the early stage to the late stage in the same degradation system. In later stage of the system, the microbial community structure of matrix become more complicated, the evenness index increased which means that all microorganism individuals became more homogeneous. Once more, it was also observed that the microbial community structures of two systems became similar to each other at the late stage.(5) The dynamics of matrix temperature in two detecting cycles at 0h,3h,17h and 24h after PFW added during the steady running period of the system were monitored and at the same time, the matrix was sampled to measure the activities of 3 kinds of hydrolase and T-RFLP profiles of matrix DNA digested by Hhal and Hae?. A meaningful phenomenon was observed in both monitoring cycles that all the detected properties including enhanced temperature, activities of three hydrolase and the peak areas of predominant fragment in T-RFLP profiles showed a similar dynamic trace with the highest value at 17h. Furthermore, the significant positive correlations between these properties were also discovered. It suggests that a strong food waste degradation process happened and there was a dominant bacteria in the degradation system. According to the closeness of the predominant fragment length between matrix samples DNA and pure cultured functional strain DNA digested by the same restriction endonuclease and the high correlation between the predominant fragment peak areas of matrix DNA digested by Hhal and Hae?, it is again inferred that Bacillus subtilis F2 may be the dominant bacteria in the biodegradation system.