剩余污泥焚烧灰分磷回收及其技术进展

焚烧渐渐成为剩余污泥终极处理、处置方式，而焚烧产生的污泥灰分中又包括了污水中绝大部分（>90%）的磷.因此，从焚烧灰分中回收磷也为污水磷回收提供了最佳位点.从污泥灰分中回收磷已存在一些适用技术，但灰分中重金属含量对工艺选择有重要影响，这可能会限制灰分直接用作农作物肥料的可行性与价值.因此，磷提取并纯化是灰分磷回收的重要技术步骤，同时也需兼顾工艺经济成本与环境影响.为此，本文从磷提取与磷纯化角度总结了目前灰分磷回收技术的国际研发进展，涵盖生物法、湿式化学法和热化学法；分析比较了不同方法在技术经济、环境影响及适用灰分方面的差别.生物法行之有效、环境影响小，但完成磷回收时间漫长；湿式化学法研发、应用最为广泛，但对环境影响较大；与污泥焚烧统筹合建可使热化学法更具经济性.然而，3类不同技术工艺并不具有相互替代性，需根据灰分成分进行合理选择.此外，前端污水处理以及中端污泥前处理也应与末端灰分磷回收相结合，尽量避免过多化学药剂投加带来的污泥灰分金属含量增加.污泥单独焚烧亦是决定灰分磷回收效率的关键.欧洲政策已明显支持污泥焚烧并从灰分中回收磷，政策和做法值得我国借鉴、学习.

Advances of phosphorus recovery from the incineration ashes of excess sludge and its associated technologies

Incineration has gradually become the ultimate treatment and disposal method of excess sludge, and the resultant incineration ashes contain >90% of phosphorus from the influent. Thus, sludge incineration ashes could become a most favorable site for phosphorus recovery from wastewater. Currently, there are some applicable technologies for recovering phosphorus from sludge incineration ashes, but the content of heavy metals in the ashes would put some impacts on selected processes, which may limit the feasibility of direct utilization of the ashes as fertilizers. For this reason, phosphorus extraction and purification from the ashes are very important, in which both economic cost and environmental impact have to be considered. As such, this article summarizes the technical progress of phosphorus recovery from the ashes in terms of extraction and purification, including biological method, wet chemical method and thermochemical method; the technical, economic and environmental impacts are also discussed and analyzed. The biological processes work well and the associated environmental impacts can be minimum, except time-consuming; the wet chemical processes have been widely developed and employed, but there are some adverse environmental impacts; the thermochemical processes associated with sludge incineration could be more economical and sustainable. However, the three-types processes are not mutually substitutable, which should be selected according to the characteristics of the ash compositions. Moreover, wastewater treatment and sludge pretreatment should be also coupled with phosphorus recovery from sludge incineration ashes, to avoid introducing more heavy metals due to dosing chemicals. The mono-incineration of excess sludge is also a key determining the efficiency of phosphorus recovery from the ashes. European policies have clearly promoted sludge incineration and phosphorus recovery from the ashes, and the European experience worth being studied by China.