Abstract: In this article cattle farm biogas slurry was used as the research object to investigate the changes of biogas slurry composition under natural storage conditions in different seasons. The results showed that the temperature has an important effect on the composition of biogas slurry under natural storage conditions. Compared with autumn and winter（from October to January of the following year）, COD degradation was faster in summer（from June to September）. When the initial COD concentration was 6 975 mg/L, the COD concentration decreased to 3 158 mg/L and tended to be stable at the end of 60 days, and the degradation rate reached 54.7%, while the COD decomposition rate was only 27.0% in autumn and winter after 60 days. The available nutrients NH₄⁺-N and PO₄^3--P in biogas slurry decreased in different seasons, and the decrease rates were roughly the same. The decrease rates of NH₄⁺-N and PO₄^3--P were 27.5% and 55.4% respectively at the end of 60 days in summer, and that of NH₄⁺-N and PO₄^3--P were 26.5% and 49.1% respectively 60 days later in autumn and winter. The results of this article could provide a reference for the practical application of returning the cattle farm biogas slurry to the field.

Key words: biogas slurry, natural storage, temperature, composition change