Study On Strain Screening Of Microbial Fertilizer And Fermentation Research

Low-value aquatic product is the general name for low-value fish and aquatic product processing scrap, which is rich in nutrients and functional active substances. With the rapid development of aquatic products processing industry and fishery industry, a large number of low-value aquatic products were left. At present, people have made some preliminary processing on aquatic products.In China,the processing technology is not perfect and the processing method is simple and extensive.This lead to the utilization of low-value aquatic products is low.For example, most fish scraps were made into the feed fish meal,in which the value is not high. Some factories even discarded or buried the low-value aquatic products directly,resulting in a great waste of resources and environmental pollution at the same time. So in this article,we use low-value aquatic products culture medium to screen strains with high efficient decomposition of low-value aquatic products from a class of unknown commercial compound strains. And explore an effective fermentation strain formulation and a set of optimal fermentation technology.This not only can improve the utilization rate of low-value aquatic products, solve the problems of resources wasting and environmental pollution, but also laid a solid foundation for the industrialization production of microbial fertilizer.The main work and results of this study are as follows:1. Using low-value aquatic products to prepared culture medium. Preliminary study showed microbial growth well in this medium without any additions and the best concentration of aquatic products was 2%. Four typical bacterial colonies were obtained from a class of unknown commercial compound strains by using dilution plate culture method and crossed purification method. Two of them were bacteria, the other two were fungi. According to the characteristics of morphology, physiology and biochemistry tests and the comparison of 16 S r DNA,18 Sr DNA sequence,the strains were classified. Result showed two fungi were candida tropicalis and cryptococcus laurentii,two bacteria were Bacillus subtilis and Bacillus cereus.2. Abilities of phosphate-solubilizing, potassium solubilizing, nitrogen fixation were investigated by using organic phosphate medium, inorganic phosphate medium, silicate bacterial medium and nitrogen-free medium. The content of free amino acids was indicator of fermentation by single strain and mixed strains combination experiment. Finally,according to characteristics of fermentation feedstock and target product requirement,selected the optical strain formulation. The result showed that a combination of strains(candida tropicalis + Bacillus subtilis+Bacillus cereus) obtained the best fermentation of low-value aquatic products. The total content of free amino acids was 12.365g/L,significantly higher than other single and combination fermentation.3. Studied the single factor experiment for inoculation proportion, speed,solid-liquid ratio, inoculum size, fermentation temperature, fermentation time.According to the results of single factor experiment and practical feasibility of operation,response surface methodology was applied to optimize the fermentation of mixed strains for the content of free amino acid nitrogen.The result showed that the optimal conditions were as follows: inoculation proportion was 1:1:1, speed was 205.17 rpm, inoculum size was 5.13%,temperature was 30.30℃, time was 5 days and solid-liquid ratio was 1:8. Under these conditions, the theoretical content of fermentation was 13.9243g/L. The experimental result was similar with theoretical result, which proved this model could fit true value and kept a high credibility.4. Amplification test in 5L scale were conducted to validate the optimized technical parameter achieved from the shake flask optimization experiment. According to the compound microbial fertilizer standard NY/T798-2004,fermentation products were detected. The result showed that the content of free amino nitrogen was reached more than13.8g/L and the test was successful. Each indicators of fermentation products conformed to national standards, it can be considered to produce microbial fertilizer by the optimum fermentation process.