Experimental Research On Microbial Degradation Of Food Wastes

The quantity of municipal solid waste (MSW) is sharply increasing, alongwith the economic development and the living standard improvement in China.According to the National Environment Report, the quantity of MSW was134,704,000 ton in 2001, among which the food wastes made up about 40%. Therecycled of MSW is being picked up out and the food wastes are the most of it,even more in restaurant, hotel and eatery.Food wastes are leftover, ort, vegetable root and leaf, peel, scraps of animaltissue etc generated in kitchen and eatery, mostly including moisture, carbohydrate,protein, fat, salinity etc. The food wastes are large in amount, dispersed, decayedeasily, stinks. If the food wastes do not be treated in time, it will pollute road,atmosphere and river system, moreover propagate insects and rats.After simply heated, the food wastes in the restaurant, hotel and eatery usuallyare collected to feed pigs by raisers. For pathogenic pollution and food safety, thefood wastes have been banned to feed animal legally in Beijing etc. The most of thefood wastes are mixed with MSW to be treated by the methods of landfill andincineration. But because the moisture of the food wastes is about 70%, themoisture of MSW mixed with the food wastes is increasing greatly. It not onlyincreases the quantity of MSW, aggravates dustman's labour intensity, but alsobrings difficulty to landfill and incineration.The food wastes can be degraded into organic fertilizer with microbialdegradation timely, rapidly, efficiently. The equipments would be laid up in theeatery, restaurant, residential area and house. It not only can avoid pollutingenvironment, but also can decrease the disposal quantity and cost of MSW. It willbe an ideal disposal method of the food wastes which can make the food wastesinnocuity, reducing and recycling, moreover intending direction in future. It hasvery important social significance, enormous economical benefit andenvironmental benefit that implementing classified system of domestic wastes andresearching disposal process and equipment of the food wastes. .Supported by Social and Technology Develop Program of Changchun(Research on Microbial Degradation of Food Wastes, project serial number:05SF11), on basis of collecting much information, the experimental research andproductions has been expatiated as follows:1. The food wastes has been tested for a long term. Then its physical, chemicaland biological properties have been made clear. It provides the foundation for thefuture research.(1) The food wastes were composed of vegetable, meat/fish, grain and else,their contents were respectively 42.47%, 10.47%, 26.61%, 25.46%. The proportionof composition was 4:2:1:3;(2) The density and viscidity of the food wastes were respectively 1045 kg/m3,1.81Pa·s;(3) The contents of moisture, protein, fat, carbohydrate and salinity in the foodwastes were respectively 73.03%, 12.16%, 6.22%, 4.16%, 1.24%.(4) The dry moisture, dry volatilization, total carbon, ash content and calorificvalue of the food wastes were respectively 5.55%, 97.97%, 42.88%, 5.37% and2203.0945 kcal/kg.(5) The biological degradation and pH of the food wastes were respectively36.50% and 6.8.2. The treatment process has been researched with the small-scale experiments.The influence rules of temperature, original containing moisture, inoculum andreaction time on treatment effect have been made clear.(1) The influence with temperatureAlong with temperature increasing, the degradation of starch and protein inthe food wastes changed evidently, and respectively over 70%, 53%. But thechange of temperature effected on the degradation of fat indistinctively, and thedegradation of fat was over 49%.(2) The influence with inoculumAlong with inoculum increasing, the degradation of starch, fat and protein infood wastes changed evidently. When the inoculum was 10%, the degradation ofstarch, fat and protein in food wastes were respectively over 70%, 48% and 53%.(3) The optimum combinationThe degradation of the food wastes related with A (temperature), B (inoculumof sludge), C (reaction time) and D (original containing moisture). In order todefine the optimum combination of the aerobic degradation, the thesis hasresearched the single factor test and L16(45)cross test and educed distinct factors,the optimum combination and the maximal degradation.1) The results of cross test of the degradation of starch in the food wastesshowed the sequence of these 4 influence factors was B>C>A>D, the optimumcombination of these factors was A=30℃, B=7%, C=18d, D=50%,and themaximal degradation was 73.43%.2) The results of cross test of the degradation of fat in the food wastes showedthe sequence of these 4 influence factors was B>C>A>D, the optimumcombination of these factors was A=50℃, B=7%, C=21d, D=50%,and themaximal degradation was 44.78%.3) The results of cross test of the degradation of protein in the food wastesshowed the sequence of these 4 influence factors was C>B>A>D, the optimumcombination of these factors was A=50℃, B=10%, C=21d, D=40%,and themaximal degradation was 48.87%.4) The results of cross test of the gross degradation of the food wastes showedthe sequence of these 4 influence factors was B>C>A>D, the optimumcombination of these factors was A=50℃, B=10%, C=21d, D=50%,and themaximal degradation was 50.26%.3. The isolation, screening and domestication of strainsThe sample of soil has been collected and applied to the corresponding culturemediums to isolate and screen the microbe. The effects of degrading protein, fatand starch were made a note. It has provided the foundation for enlarging cultureand making multiple strains that the research of domesticating microbe to the foodwastes.(1) The bacterium, actinomyces, microzyme and mould have been isolatedfrom soil, and observed the status of growth and the quantities of colony.(2) The starch, fat and protein have been degraded by the microbe in soil. Andthe effects of degradation were evident.(3) According to the theory of domestication, the isolated strains have adaptedto the degradable environment of the food wastes, and shortened the time ofmicrobial degradation.(4) The food wastes have been disposed with strains domesticated, anddegraded entirely after 10d. The volume and weight of the food wastes wererespectively 15% and 16.99%.4. The components of product have been analyzed after microbial degradation,and compared with the Standard of Organic Fertilizer in China (NY525-2002).(1) The organic matter, total nitrogen (TN), total phosphorus (TP), pH, density,salinity and moisture in the production after microbial degradation wererespectively 27.53%, 11.78%, 0.228%, 7.3, 1.184 g/mL, 3.45%, 29.14%;(2) The contents of organic matter and TP were below the standard. Thecontent of moisture was over the standard. The content of TN and pH met thestandard. In the standard, organic matter ≥30%, TP ≥4%, moisture ≤20%, TN ≥4%,pH 5.5～8.0.(3) The content of salinity in the production was 3.45%. The salinity wouldresult in the terrene depravation, affect the growth of crop and make soil to desert.So the question needs to be researched for the future.The research on microbial degradation of the food wastes involves manyscience and technology fields. The contents of research are abroad and complicated.Except for the researches of this thesis, many works need to be researched andexplored as follows:1. The exploitation of special, high-efficiency and multiple strains;2. The development of the equipment on microbial degradation of the foodwastes;3. The automatic test and control of equipments;4. The experimental research of equipments;5. The research of practicality and conditions of process on microbialdegradation.