采用厌氧发酵和冷冻微波联合处理剩余污泥并回收氮磷

Recovery of nitrogen and phosphorus from excess sludge pretreated by anaerobic fermentation and freezing microwave

为了实现从剩余污泥中高品位回收鸟粪石(MAP, MgNH4PO4·6H2O),本研究考察了厌氧发酵、冷冻+微波两种污泥预处理方式促进污泥中氮、磷的释放及回收效果.试验结果表明:污泥厌氧发酵在温度30℃、pH=12、发酵时间4 d时,PO4^3——P和HN4^+-N的最大释放量分别为224.50 mg·L^-1(即7.24 mmol·L^-1)和278.17 mg·L^-1(即19.87 mmol·L^-1),PO4^3——P物质的量浓度远小于HN4^+-N物质的量浓度.冷冻+微波联合预处理在冷冻温度-20℃、冷冻时间48 h、微波初始pH=3、微波时间9 min时,PO4^3——P和HN4^+-N的最大释放量分别为1011.84 mg·L^-1(即32.64 mmol·L^-1)和220.82 mg·L^-1(即15.77 mmol·L^-1),PO4^3——P物质的量浓度高于HN4^+-N物质的量浓度.根据污泥上清液中的氮、磷含量,将厌氧发酵与冷冻+微波两种污泥预处理后的上清液按体积比1∶9进行混合,使Mg∶N∶P物质的量比为1.6∶1.4∶1时,PO4^3——P的最高回收率为99.11%,HN4^+-N的最高回收率为73.46%.X射线衍射(XRD)结果显示,回收的沉淀物主要为鸟粪石晶体.将两种污泥预处理后的上清液进行混合,有效地解决了污泥上清液中由于氮、磷比例失衡所导致的回收率下降的问题,从而实现以鸟粪石的形式高效回收剩余污泥中的氮、磷.

To achieve high-grade recovery of struvite(MAP, MgNH4PO4·6 H2O), two pretreatment methods of anaerobic fermentation and freezing microwave were investigated to promote the release and recovery of nitrogen and phosphorus from the excess sludge. The results showed that the maximum release of phosphorus and ammonia nitrogen reached 224.50 mg·L^-1(7.24 mmol·L^-1) and 278.17 mg·L^-1(19.87 mmol·L^-1), respectively, at the fermentation temperature of 30 ℃, the pH of 12 and the fermentation time of 4 days. In the anaerobic fermentation supernatant the molar concentration of phosphate was much less than that of ammonia nitrogen. When the freezing temperature of-20 ℃, the freezing time of 48 h, the initial pH of microwave of 3 and the microwave time of 9 min, the release of phosphorus and ammonia nitrogen was 1011.84 mg·L^-1(32.64 mmol·L^-1) and 220.82 mg·L^-1(15.77 mmol·L^-1), respectively. Contrastively, in the frozen + microwave supernatant the molar concentration of ammonia nitrogen was much lower than that of the phosphate. According to the content of nitrogen and phosphorus in the supernatant, the optimal mixed volume ratio of the supernatant with anaerobic fermentation and frozen + microwave was 1∶9. When the molar ratio of Mg∶N∶P was 1.6∶1.4∶1, the highest recovery efficiency of phosphorus and ammonia nitrogen was 99.11% and 73.46%, respectively. The result of X-ray diffraction(XRD) showed that the recovered precipitate was mainly struvite crystal. Mixing the supernatant of two sludge pretreatment methods effectively solved the problems of low recovery resulted from the imbalance of nitrogen and phosphorus. And thus nitrogen and phosphorus from excess sludge could be efficiently recovered in the form of struvite.