| With adjustment of the agriculture structure and the development of its industrialization, large-scale and intensive livestock farm has rapidly developed. The dimension is from small to large, and the area is from point to surface, which makes the country economy improve. Because of the poor management of the livestock farm and its disjointing with agriculture, a large amount of the livestock wastes are disposed at random, which pollutes the water, soil and air, effects the health of people, destroys the biological environment, and disturbs the further development of the livestock industry.Composting is one of ways to handle the wastes, which is a fermentation process under the conditions with appropriate moisture, C/N ratio, and oxygen. During the process the organic materials will be turned to the stable humus, which can be used as fertilizer and amend for the plant soil. Thus the pig manure changing into the organic fertilizer is important way to protect biological environment and promote the sustainable development of the agriculture.Oxygen is an important factor in composting. The optimization of oxygen supply can increase the decomposition of organic matters and reduce the duration of composting and the emission of odor. The consumption rate of oxygen can be used as an indicator of maturity of composting. More intensively studies on oxygen processes in composting should be done in future. According to the study of the rule of the changing of oxygen during the composting, this paper has some parts as follows:First, effect of different bulking agents on aerobic composting of swine feces was studied in a plastic greenhouse. Three kinds of organic compost were manufactured from pig feces with sawdust, rice hull and rice germ respectively. The change of temperature, pH, water content and the content of main nutrient element N, and O2 consumption were measured. The results showed that the highest temperature of the compost namely pig feces + rice germ is only 38℃, which indicated that the rice germ isn' t fit for composting bulking agent. And the temperature of the two types of compost namely feces + sawdust and feces + rice hull were relatively high. The former' s compost temperature was lower than the latter, the time when its temperature decreased under environment temperature was much longer, and the time when its temperature maintained above 55℃ was shorter than the latter.The sawdust has good humidity absorption, thus the water loss of 'feces + sawdust' was bigger. The change of organic matter of both composts were basically same. But the 'feces + sawdust' compost had more organic matter than the 'feces + rice hull' compost, for the sawdust has plenty of lignin which decomposes difficultly. The changes of T-N of the two composts were basically same too, but the compost with sawdust increased more than with rice hull at last .which indicated that compost with rice hull isn' t goodfor conserving nutrient element N. T-N increased .which was the symbol of composting maturity and quality promotion. Each of the two kinds of bulking agents has pros and cons.Second, pig manure was composted with 10% of bulking agent. The oxygen consumption rate was measured at every sampling time. And the oxygen concentrations were measured at 0, 5,10,15 and 20 minutes later after the stopping ventilation, respectively. In order to study the oxygen dynamics, the oxygen concentrations were monitored at the same time every several days, and the measured data were used to analyze the oxygen variation during the composting process.The oxygen consumption rate during the composting process decreased firstly, influenced by moisture efficiency, then increased to a maximum, decreased slowly at last. In whole composting process, the oxygen concentration showed increasing tendency, and increased faster in mid-process and late process. The oxygen decreasing speed in the pile was fast during the first 5 minutes and then decreased slowly. The four piles showed different characteristics under different aeration quantities. After analyzing, the optimized aeration volume is 0. 35mVmin.Third, the variation of oxygen concentration at different stages of pig manure composting was analyzed . The result showed that in a short time after ventilation at different composting stages, the oxygen concentration increased by 15% or more, and the oxygen consumption rate at temperature increasing stages and at the beginning of high temperature stage could reach up to a very high level, while decreased at the stages of high temperature and of dehydration as the composting process going on . In the last period of composting, the rate of oxygen concentration slowed to 0. 2AO2%/min . A ventilation strategy was proposed based on the analyses which was that at temperature increasing stage, ventilation time was shorten and its frequency was increased, at high temperature stage, ventilation volume was increased properly to control temperature and at mature stage, few ventilation was needed because of the ceasing of microbes action. |
