Nitrogen Transformation And Related Enzyme Activity Research In Vermicomposting With Different Temperatures

The treatment and disposal and utilization of sludge has become a worldwide seriousenvironmental problems. Sludge composting and land use are important ways to achieve itsharmless and resources purpose. Vermicomposting is a new way of composting developed onthe basis of traditional compost. Sludge was mixed with earthworms before it was pretreated,and it was degraded through their activities and the joint action of earthworms andmicroorganisms. The compost can be directly used for farmland and green space, and it canalso be used as a soil remediation agent and soil fertility, relieve excess sludge environmentalpollution problems. In earthworm composting process, nitrogen and other nutritionalingredients lost with the degradation and transformation of organic matter, so understandingthe nitrogen forms during composting earthworms transformation and enzymes changes in theregulation of composting conditions can improve quality and compost efficiency, it isimportant.In this thesis, after simple process of fresh crushed dry for pure raw sludge as compost,sludge was introduced a certain density Eisenia foetida, set15℃,20℃,25℃threeexperimental groups at different temperatures, regular daily manual turning by seven days fora period of42days for a total of six periods of composting. The composting process wasstudied under different temperature conditions within each period pile physicochemicalproperties of different nitrogen forms and related changes in enzyme activity changes, themain conclusions as follow:Basic physical and chemical properties of compost was no significant difference underthree temperature test group.Composting organic matter content of experimental group was obviously influenced bytemperature changes. The15℃group at each stage of sludge organic matter degradation rateis the slowest and the rate of the reduction is also the smallest,20℃and25℃, theexperimental group at each stage of sludge organic matter degradation rate reached the samemagnitude almost.The pH increased at first and then decreased composting process,15℃and25℃groupdecreased more significantly than20℃group. The pH became from the initial faintly neutralto acidic.The pile EC were increased first and then decreased after the experiment, EC values arequite different at different temperatures between,20℃group>25℃group>15℃group.After the experiment, TN content of the different temperature groups was decreased, theorder of magnitude25℃group>15℃group>20℃group, the25℃group TN suffered themost severe loss. The NO₃^--N content showed an upward trend, in the end NO₃^--N content of20℃group>25℃group>15℃group throughout the process; NO₄^-N contents of20℃and 25℃group in the first and the fourth week ending reached periodically peak,15℃group NO₄^-N concentration reached the maximum at the end of the second week, and thereafter nolonger increased, the minimum amount of nitrogen losses, but the lowest rate of degradationof organic matter.Different temperatures,20℃and25℃group NO₂^--N content in two obviousammonification phases increased rapidly in the latter half of compost nitrification had reduced,15℃group extent changed unclearly, at the end of experiment NO₂^--N content20℃group>15℃group>25℃group; after approximate estimate, organic nitrogen in the whole processeda downward trend,20℃group>25℃group>15℃group, but NO₂^--N content value was verylow and the contribution to nitrogen loss small can be ignored.Protease activity at different temperatures set significantly decreased at the first fourstages of the composting process, then leveled off gradually after two stages. It can beinferred that protease activity was positively correlated with organic matter content from theorganic nitrogen degradation curve. The different temperatures differences betweenexperimental groups combined with organic matter degradation curve can also reflected thisconclusion.Urease activity increased in the first two period and then decreased under differenttemperature conditions, but significantly higher than the latter four stages. Urease activity andorganic matter content may be positively correlated changes from organic matter degradationrate curve and the conductivity curve, temperature was also the important factor affecting theurease activity, the urease activity was positively correlated with the level of temperature.