Study On Screening Of Food Waste Degrading Strains

Food waste refers to food residues including rice,noodles,vegetables and other substances produced by enterprises and public institutions,families and catering industry.The main chemical components of food waste are cellulose,starch,oil,protein,inorganic salt and trace elements.Food waste is an important part of urban solid waste,and causes environmental pollution due to its higher contents of moisture,organic matter,inorganic salt and oil of food waste.Recently,studies on the resource utilization of food waste in China mainly focuse on aerobic decomposition,aerobic composting and anaerobic decomposition.As a new technology,aerobic decomposition has the advantages of short cycle and significant effect in the application of food waste degrading.Therefore,the application of aerobic decomposition method can provide a new techinque for food waste utilization.In this study,bacteria and yeasts isolated and purified from the natural environment were added to the food waste for aerobic decomposition,and the strains with better overall decomposition effect on food waste were screened out.These strains were combined with Aspergillus fumigatus(Z5)in the laboratory,and the optimal combination was found by comprehensively evaluating the test results with the indexes of odor,p H,number of culturable microorganisms,solid infiltration rate,solid decomposition rate and light transmittance.Subsequently,the optimal combination of different proportions of the study and the final comprehensive effect of a better ratio were determined in order to provide experimental basis for effective decomposition of food waste in a short period of time.The main research results are as follows:1.Thirty-six strains of bacteria and sixteen strains of yeast were screened from natural environment,and ten strains were screened out for identification under the culture condition at 37℃.The ten strains are CM1(Bacillus altitudinis),CM2(Bacillus tequilensis),CM5(Bacillus paralicheniformis),CM12(Bacillus paralicheniformis),CM18(Bacillus licheniformis),CM22(Bacillus subtilis),CM24(Bacillus subtilis),RS8(Pseudoxanthomona suwonensis),RS11(Bacillus aryabhattai),RS12(Komagataella phaffii).The results of the degradation ability of starch,cellulose,oil and protein identification showed that: CM2,CM12,CM18,CM24,RS8,RS11 and RS12 can degrade starch effectively,with RS12 showing the strongest ability to degrade starch;CM1,CM5,CM12,CM18,CM24,RS11 and RS12 can degrade cellulose effectively;CM24 and RS12 can degrade fat effectively;CM1 and RS11 can degrade protein effectively.Interestingly,CM24,RS11 and RS12 can degrade three of cellulose,starch,oil,protein effectively.CM1,CM2,CM12,CM18 and RS8 can degrade two of cellulose,starch,oil,protein effectively,and CM5 and CM22 can only degrade fiber effectively.2.In order to make better use of strains,the p H of food waste needs to be adjusted.Hydrated lime was used to adjust the p H of food waste,as food waste is strongly acidic.As the amount of hydrated lime increases,the p H of the food waste increases.4.0-4.5‰(w/v)hydrated lime was added to the food waste to adjust its p H value to 5.5-6.0 to facilitate its decomposition.The results of food waste degrading strains optimization showed that the odor of food waste of RS12,CM22 and CM24 was minimal on the third day,and the total cultivable bacteria of these 3 strains was always higher than that of CK during the experiment,so RS12,CM22,and CM24 were selected for the combined experiment.3.Subsequently,RS12,CM22 and CM24 was combined with Aspergillus fumigatus(Z5)that has been validated in the laboratory to find the best combination with the odor,p H,number of cultivable microorganisms,solids infiltration rate,solids reduction rate and OD.The results of the strain combination experiment showed that the p H of each processed food waste basically reached a stable value of about 7.5 on the 8th and 9th days,so 9 days can be regarded as optimal for food waste degradation cycle.The combination CM22+CM24+Z5 and the combination CM22+CM24+RS12have a better overall effect.According to the number of cultivable microorganisms,p H,OD and focusing on visual indicators such as odor,solids infiltration rate and solids reduction rate,3%CM22+5%CM24+5%RS12 and 5%CM22+5%CM24+3%RS12 are obtained.The overall effect of the ratio is good,and the reduction rate of solids in the food waste is as high as 80.6% with 3% CM22 + 5% CM24 + 5% RS12.In summary,the application of 3%CM22+5%CM24+5%RS12 and5%CM22+5%CM24+3%RS12 for aerobic decomposition of food waste can reduce the smell effectively after 9 days,promote the reduction of solids,and reduce food waste.