The Research On Ammonia-Oxidizing Bacteria During Agricultural Waste Composting

Composting is a technology which has been widely used in the disposing of agricultural waste. The lossing of nitrogen during the process of composting will result odor and reduce the quality of compost products. Studying the transfer and transformation of nitrogen during composting has important practical significance. The ammonia-oxidizing bacteria can conform the most reduced form of N(ammonia) into nitrate, and the process is the first step of nitrification, which play an important role in the nitrification. We choose the AOB as the object of the research, using the polymerase chain reaction-denaturing gradient gel electrophoresis technology to study the diversity and community composition of ammonia oxidizers in the composting, and explore the relationship between AOB species and composting parameters. The aim of this study was to provide theoretical guidance for optimizing the composting process.In this paper, aerobic composting was processed with agricultural waste such as straw. Composts were sampled during different composting periods. The changes of pile temperature, pH, moisture content, soluble NH4+-N and NO3--N were measured. The results showed that the pile was insulated and temperatures above50℃were maintained for8days. The highest temperature in the compost was55.6℃,which can reach the requirements to kill pathos. The pH ranged from6.59-8.76, which was beneficial for microbes. The content of NH4+-N raised from the initial composting, reaching the maximum at6d and then had a downward trend. The content of NO3--N gradually decreased from2d to12d with a short increase during the initial composting.The dynamic succession of ammonia-oxidizing bacteria(AOB)community during the agricultural waste composting was investigated using the polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE). DGGE results showed that the Shannon-Weaver index changed from2.58to2.02during the composting process, which reflected the diversity trends downward overall. Nitrosospira and Nitrosomonas were dominant species. Nitrosomonas eutropha, which was found throughout the whole composting process, was identified as a kind of well-tolerated species. Redundancy analysis(RDA)was applied to explore the correlation between the dynamic succession of AOB community and composting physic-chemical parameters. Compared with the slight change referring to its structure during the earlier phase of thermophilic period(4-9d), the AOB community experienced a more significant change during the later phase of thermophilic period(9-12d) as well as the following temperature falling phase(12-25d). Significant relationships have been found between pile temperature, soluble NH4+-N(p<0.01)and N03--N (p<0.05) with the dynamic succession of AOB community, which suggested those three parameters were likely to influence, or be influenced by AOB during the agricultural waste composting.