Impacts Of Earthworms On Acidic And Alkaline Buffer Capacity And Ammonia Oxidation Process Of Dewatered Sewage Sludge In Vermicomposting

Municipal sewage sludge(MSW)is the inevitable product of the urban sewage treatment,in which the rich organic matter,the high nitrogen and phosphorus and humic acids make it possible to be a soil conditioner and fertilizer.But it is easy for sludge to corrupt and large amount of harmful gases such as ammonia,mercaptans and hydrogen sulfide,is released from sludge,especially under anaerobic condition,which brings about lots of environmental pollution problems related.Vermicomposting is a very attractive sludge treatment in all aspects by which stabilized dewatered sludge not only is no longer smelly,but also has the ability to adsorb odor.Although vermicomposting include effects of both earthworms and microorganisms,as the main force of the degradation of organic matter,microbes are affected by many factors,including ways of composting,environmental factors and oxygen conditions.One important factor for holding the stability of MSW is to ensure the balance of acid-base production and consumption.In the same time,lower carbon-nitrogen ratio of sludge(when compared to other composting)makes mineralization of organic nitrogen become severe factor in changing acid-base environment in sludge.In this paper,we use physical and chemical indicators and denaturing gradient gel electrophoresis(PCR-DGGE)technology to study the pH buffering capacity,organic nitrogen mineralization and ammonia oxidation process aiming to understand the pH changes in composting process and the key factors affecting the strength and sludge ammonia oxidation process.The main results are as follows:Dewatered sludge has a lower ratio of carbon and nitrogen,so concerning a series of changes in mineralization of organic nitrogen is helpful to understand the vermicomposting stabilization process.With the help of research the organic nitrogen mineralization of dewatered sludge,especially in its core areas-ammonia oxidation process,the understanding of stabilization path and physicochemical properties in vermicomposting are as following:(1)Choosing sludge samples from Qilihe-anning sewage treatment plant in Lanzhou as a research sample,pelletized for vermicomposting.In the early period,it was controlled by the acid which was produced by the degradation of organic carbon,and in the post period,the pH buffering capacity increased with processes that a large number of weak acid and weak base were produced and consumed in organic nitrogen ammonification,nitrification and denitrification,so that the fluctuations of acid and alkaline were not violent in sludge environment because of its large buffer capacity pH.Earthworms advance sludge ammonification,improve nitrification and promote the generation of weak acid and weak base in the matrix thereby increasing the pH buffering capacity.That the PH fluctuations in earthworm treatment group are lower than in the control group,and ABC,ALBC and pHBC are higher than in the control group in the whole process shows that the more stable pH and higher pH buffering capacity are matched;vermicomposting changes ammonia oxidizing bacteria community structure,increases the diversity of ammonia-oxidizing bacteria,at the same time,earthworms inoculation can significantly improve the micro-environment pH stability,which is conducive to the efficient play of microbial activity.(2)Vermicomposting temperature was raised from 15? to 25?,but this cannot change the start time of the ammonia oxidation,which means that rise of temperature does not affect the ammonia oxidation process.But the increase in temperature can significantly strengthen organic nitrogen mineralization,and strengthen the degree of positive correlation with temperature.Among the proper temperature range of earthworms,rise temperature can significantly affect the pH change.At the end of vermicomposting,pHBC,ABC,ALBC is high,and increasing the temperature bring the turning point of ABC ahead of time,the proportional matching the degree of temperature increase.By controlling the temperature it can ahead ammonification and strengthen the nitrification process which is benefitted in improving ABC,ALBC and pHBC.At higher temperatures(25?),vermicomposting can significantly improve the stability of acid-alkaline environment and compost texture.(3)Research found that factors affect ammonia oxidization contains intianal organic matters,environment temperature diameter of pelletized dewatered sludge and inoculation of earthworm.Higher organic matter content of pelletized dewatered sludge means that vermicomposting organic matter reaches a stable longer,while its nitrification start time will be a corresponding rearward,the temperature can affect the rate and start time of nitrification of sludge,but not affect its nitrification start time in vermicomposting.Size of pelletized dewatered sludge can significantly affect the process of nitrification sludge,which means small particle size has stronger reaeration ability.Small pelletized dewatered sludge enjoys large specific surface area and a relatively faster degradation of organic matter,stronger reaeration ability is the core reason that it can begin nitrification earlier.