利用白云石回收污泥厌氧消化液中的磷

为经济有效地从污泥厌氧消化液中回收磷,构建了以白云石提供钙镁源的磷回收方法,探讨了磷回收的工艺条件与效果。通过盐酸酸化厌氧消化液以降低其碳酸盐含量,同时利用白云石溶于冷稀盐酸的特性使其钙镁缓慢释放到酸化的厌氧消化液中形成第一步磷回收体系,考察体系酸化pH、白云石与厌氧消化液的固液比以及反应pH对白云石的钙镁释放和磷回收效果的影响;第一步磷回收后的上清液为第二步厌氧消化液磷回收提供钙镁源,研究投加钙磷摩尔比对磷回收效果的影响。实验结果表明,当固液比为5.0时,在酸化pH为4.0～4.5且酸化溶出时间为10 h以及反应pH为9.0的条件下,第一步磷回收产物以磷酸钙盐沉淀为主,厌氧消化液磷回收率及回收产物含磷率（以P2O5计）分别达到99.43%和38.49%;第一步磷回收后的上清液按一定的钙磷摩尔比投加到酸化后的厌氧消化液中进行第二步磷回收,当投加钙磷摩尔比为0.20时,在反应pH为9.0的条件下,回收产物同时含有磷酸钙盐和磷酸铵镁,厌氧消化液中氮、磷回收率分别达到13.19%和90.90%,回收产物氮、磷含量（以P2O5计）分别为0.26%和39.58%;经XRD、XRF、ICP及SEM等分析表征,2步磷回收的产物以磷酸钙盐和磷酸铵镁为主要成分,杂质少。研究表明,利用白云石为钙镁源,通过分别构建不同的磷回收体系可以分步从污泥厌氧消化液中经济有效地回收磷,且磷回收率和回收产物含磷率高。

Phosphorus recovery from anaerobic digestion supernatant of sewage sludge using dolomite

In order to recover phosphorus from anaerobic digestion supernatant economically and efficiently, the method for phosphorus recovery was constructed by using dolomite to provide calcium and magnesium sources, and the process conditions and performances of phosphorus recovery were explored. Since the carbonate content could be decreased by acidification of anaerobic digestion supernatant with hydrochloric acid, in the meantime dolomite could be dissolved and calcium and magnesium in dolomite could be slowly released into the acidified anaerobic digestion supernatant by means of the characteristics that the dolomite could be dissolved in cold and dilute hydrochloric acid, the first-step phosphorus recovery system could be formed, and the effects of system acidification pH, solid-liquor ratio of dolomite to anaerobic digestion supernatant and reaction pH on phosphorus recovery were investigated. The supernatant after the first-step phosphorus recovery was used to provide calcium and magnesium sources for the second-step phosphorus recovery from anaerobic digestion supernatant, and the effect of the dosing Ca/P molar ratio on phosphorus recovery was studied. The experimental results showed that the first-step recovered product of phosphorus was mainly the precipitation of calcium phosphates, and phosphorus recovering rate and the phosphorus content (as P₂O₅) of product could attain 99.43% and 38.49%, respectively, when the solid-liquor ratio was 5.0, the acidification pH was 4.0~4.5 for 10 h of acidification and dissolution time, and the reaction pH was 9.0. The second-step phosphorus recovery was carried out when the supernatant after the first-step phosphorus recovery was dosed into the acidified anaerobic digestion supernatant according to a definite Ca/P molar ratio. When the dosing Ca/P molar ratio was 0.20 at the reaction pH of 9.0, the recovered product contained both calcium phosphates and magnesium ammonium phosphate, and nitrogen and phosphorus recovery rates of anaerobic digestion supernatant could reach 13.19% and 90.90%, respectively, and nitrogen and phosphorus contents (as P₂O₅) of recovered product were 0.26% and 39.58%, respectively. Based on the analyses and characterization by XRD, XRF, ICP and SEM, two-step recovered product mainly consisted of calcium phosphates and magnesium ammonium phosphate with little impurities. This research indicated that phosphorus could be economically and efficiently recovered from anaerobic digestion supernatant of sewage sludge based on two different phosphorus recovery systems established with dolomite as calcium and magnesium sources, and higher phosphorus recovery rate and phosphorus content could be achieved.