Excess sludge produced in the process of wastewater treatment was rich in nitrogen and phosphorus, and phosphorus recovery from the excess sludge is an effective way to solve the growing lack of phosphorus resources. The release rule of phosphorus from the sludge is a prerequisite for phosphorus recovery in sludge. Therefore, a pilot model with 5 days of t sludge retention time was established, and the actual sewage sludge was studied in the system. Through analysis of the system parameters changes under anaerobic conditions, total phosphorus concentration and ammonia concentration in the supernatant were got, that is very important to provide conditions for the following sludge phosphorus recovery. The results show that, in the system of 5 days SRT under anaerobic conditions, microbial decay autolysis or decomposed in residual sludge, and intracellular substances was released, so the solid matter was changed into liquid, phosphorus, nitrogen and other related substances have been released. The concentration of total phosphorus and ammonia nitrogen in supernatant could reach 100 mg·L-1 and 40 mg·L-1, respectively. The concentration of nitrogen and phosphorus released was demanded to the minimum required to meet the economic requirements of struvite recovery method. The results provide important basis for nitrogen and phosphorus recovery using struvite method. SS and VSS were all found decreased, that were reduced more than 8.34% and 10.14%, respectively. The reduced mass of VSS was accounted for about 65%of the SS reduced mass. In additional, initial sludge concentration in anaerobic reaction system was great influence for releasing mass of nitrogen and phosphorus. Releasing mass of phosphorus and nitrogen was reached most under 6 300-7 200 mg·L-1of SS, that is 0.015 mg·mg-1 and 0.006 mg·mg-1 per unit dry sludge, respectively. The research results provide an important basis for the recovery of nitrogen and phosphorus in sludge.%污水处理过程中产生的剩余污泥富含大量的氮磷元素，从剩余污泥中回收磷是解决磷资源日益缺乏的一种有效途径。探寻出剩余污泥中磷的释放规律是实现剩余污泥中磷回收的首要前提。因此，以实际污水处理厂污泥为研究对象，建立污泥停留时间为5d的中试模型系统。通过系统分析5d停留时间的厌氧条件下污泥中污泥浓度、上清液总磷和氨氮浓度的变化情况，为后续的污泥磷回收提供支撑条件。研究结果表明，在中试系统污泥停留时间5d的厌氧条件下，剩余污泥微生物衰亡自溶或被分解，胞内物质释放，从而使固态物质转化为液态，污泥中磷及相关的氮等物质得到了较大的释放，污泥上清液总磷和氨氮质量浓度可分别达到100和40 mg·L-1以上。所释放出的氮磷浓度足以满足鸟粪石回收氮磷方法所需的最低经济性要求，为污泥进行厌氧消化后采用鸟粪石的方法回收释放的氮磷提供了重要的基础依据。研究中还发现5d停留时间下， SS和VSS都有不同程度的降低，二者分别减少8.34%和10.14%以上，其中VSS的减少量占SS减少量的65%左右。同时，进入厌氧反应系统的初始污泥浓度对于氮磷的释放有着较大的影响，反应系统的SS在6300~7200 mg·L-1的条件下，磷和氮的单位质量污泥释放量达到最佳，分别达到单位干污泥0.015和0.006 mg·mg-1。研究结果为剩余污泥中回收氮磷提供了重要的依据。
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