Research On Aerobic Composting Technology Of Kitchen Waste With Spend Mushroom Substrate As Amendments And Its Mechanism

Kitchen waste (KW) has the largest quantities in municipal waste, it has the characteristic of high moisture, high organic content, easy corruption and difficulty in collection. Composting is one of the economical and practical methods in the treatment of such waste. The unique characteristics of kitchen waste make the conventional composting unfeasible, advanced technology for composting needs to be carried out. In this study the feasibility and merit of addition of waste mushroom into kitchen waste were investigated to overcome the problems occurred in composing by kitchen waste. Furthermore, other existing difficulties in composting such as odor pollution, low fertilizer efficiency and long operation period were also studied based on microbial technology and engineering methods. Technology on odor removal and nitrogen storage, screening and application of high-temperature cellulose degradation bacteria for composting with kitchen waste were performed in this study.The physical and chemical properties for spend mushroom substrates (SMS) such as the particle size, bulk density, water content, C/N and pH, showed SMS could be regarded as a kind of good amendments for kitchen waste composting. Composting with KW and SMS had a faster warming speed, and maintained a high temperature period of 9 d, reached the composting standard for aerobic composting of municipal solid waste (CJJ T52-93); compared with corn straw as the amendments, after the first fermentation, moisture decreasing ratio in composing with KW and SMS increased 3.66 percent, organic degradation ration enhanced 6.7 percent, germenation index increased 15.8 percent, it demonstrated that the addition of SMS could hasten the treatment speed for kitchen waste. The release pattern of NH₃ for kitchen waste composing showed that the release of NH₃ mainly occurred from 7 to 12 days, occupiied 53%-54% of the total amount, thus the phase could be regarded as the key period for NH₃ control. On the other hand, the NH₃ release in KW and SMS was 36.49% of those in KW and straw, the odor reduced significantly, thus the utilization of SMS had odor removal and nitrogen storage effect. Electron microscopy analysis showed that the structure of SMS was rough, porous, it was more favorable for NH₃ adsorption and microbes growth than the strawThe ammonia contained waste water obtained from biotrickling filter (spray liquid source) were used for composting with kitchen waste. After composting, the accumulative dry weight in spray treatment was 12.9 percent less than the control, the germination index for spray liquid treatment was 16.3% higher than the control, which showed that the spray liquid could improve the maturity of composting and had a good reduction effect.Furthermore, compared with control, the nitrogen removal in spray treatment was 16 percent less, thus the spray liquid could help to decrease the nitrogen loss in composting. The total nitrogen amount during spray treatment was 6.644g, that meant 34.3% of exogenous nitrogen was able to remain in the compost system. Microbial flora analyze showed all the microbes decreased during high-temperature phase, the number of bacteria was larger than fungi the whole time. the nitrifying bacteria were sensitive to th etemperatue, they could not be detected druing high-temperature phase and 50℃culture. PCR-DGGE analysis showed that the ammonia oxidation bacteria was abundant in the beginning, when the composting reached the high-temperature phase, ammonia oxidation bacteria decreased sharply and only resumed at the latter phase of composing, thus in the high-temperature phase, the nitrification effect was trivial, mainly were volatile and microbial assimilation.A strain which could decrease cellulose effectively at high temperatures was screened in kitchen waste composing with SMS. It was identified as the genus brevibacillus sp and named as Brevibacillus sp. FA2, shortform as FA2. This strain had a better reduction effect for straw and filter paper, the reduction ratio could reach 25.8% and 48.2%, respectively.Compared with control strain of B. licheniformis, the FA2 had a higher reduction ratio for straw and filter paper of 17.0 and 35.7%; scanning electron microscopy observation of the microstructure for the straw and filter paper showed that FA2 could damage the micro-structure of the substrates, made its dispersion and flocculation. The biological characteristics for FA2 showed it could grow in the range of 30℃-60℃, the optimum temperature was 60℃, it was a heat-resistant bacteria; FA2 had a wide suitable pH value ranged from 6 to 8.5; it had a low requirement of oxygen; it could grow with the salt content less than 10%. The utilization of FA2 in composting system showed that: in the non-sterilized condition, the treatment with FA2 inoculation had a organic degradation ratio of 31.26%, 10.43% lignocellulose degradation rate, seed germination rate was 61.67 %, compared with control, increased 4.49,5.09 and 3.65 percent respectively.In summary, the use of SMS as amendments for KW composting could improve the material properties, prevent odor and storage nitrogen. The utilization of spray liquid from ammonia removal by biotrickling filter into the composting system could not only improve the nitrogen content, but also provided deodorization technology for continuous ammonia removal in biotrickling filter. Analysis for ecological mechanism of micro-organisms during composting and the acquisition of high efficient cellulose degradation bacteria could contribute to further understanding of the composting mechanism, what's more, it could provide technology and strains resource for composting process in the future.