The Optimization Of Citrus Peel Composting Process And Its Microbial Community

Chongqing is one of the major citrus producing areas in China.The output of citrus reached 2.426 million tons in 2016 and about 600,000 tons of citrus peel was produced.The disposal method of citrus peel in domestic is buried.However,the high water content and low pH citrus peel in landfill will destroy the soil structure and pollute the water and air.In addition,citrus peel is rich in essential oils,pigments,flavonoids,pectin and other substances.The disposal problem of the waste residue produced by extraction of these substances has still not been properly solved.The research proposed that the resource utilization of organic fertilizer which was prepared from citrus peel fermentation.The compost inoculant suitable for citrus peel were prepared by combining the screened bacteria and purchased EM basic functional bacteria.The technological parameters of citrus pomace compost were optimized through orthogonal test,and the pilot-scale experiment was conducted based on the optimum conditions.Using high-throughput sequencing technology,the mechanism of citrus inoculum compost inoculant,the succession of microbial communities in compost and the relationship between compost community succession and changes in physicochemical parameters in the process of composting were also investigated.The main conclusions obtained are as follows.1.High-temperature compost samples and citrus orchard soils were used as raw materials to screen compound microorganism F through long-term high temperature limiting carbon source.Next,microorganism F and purchased EM were mixed in equal proportions to obtain compound microorganism J.Enzyme activity analysis and actual citrus peel composting pre-test were conducted.The compound microorganism J was proved to have good pectin and cellulose degradability by enzyme activity analysis and actual citrus peel composting pre-test.And it was also suitable for compost of citrus peel.2.Orthogonal optimization test was performed on the factors that had significant effects on the composting efficiency,including the water content,the C/N ratio,the lime quality and the microorganism dosage.The final total nutrient content was used as the index and the effect was ranked as C/N ratio> Lime quality > Microorganism dosage > Water content.The optimum parameters of citrus peel composting were 55% of water contents,25 for C/N ratio,10 g lime/kg and 3% of microorganism dosage.3.Based on the optimum conditions,the efficiency of pilot-scale experiment showed a comprehensive increase.The temperature and dewatering effect were significantly better than laboratory experiment.Moreover,the content of total nutrients had reached up to 6.48%,which was higher than 6.07% of the laboratory experiment.This shows that the fertilizer effectiveness after optimization has significantly improved and the optimization process has good reliability and stability.4.The high-throughput sequencing technology was used to illustrate the principle of citrus peel compost inoculum.Bacillus and Penicillium in compound microorganism J played a major role in the rapid degradation of pectin and promoted the success of composting.In addition,the changes of microbial communities in citrus peel compost were analyzed.Bacteria,Fungi,Actinomycetes and their dominant genuses in composting were constantly evolving.Bacillus,Penicillium,and Thermobifida dominated in the initial period.Sphingobium,and Sphingobium,Thermoascus and Nocardiopsis dominated later.The succession of compost microbial community structure was significantly correlated with the physical and chemical parameters.The effect was ranked as C/N>OM>WC >T>pH,where C/N,OM,and WC were positively correlated,while T and pH were negatively correlated.