Lianpeng Sun,Yuhao Yang,Weifang Yuan,Xueya Wu,Zikun Cui,Hao Wang,Huanzhong Deng,Xinzhe Zhu,Ruohong Li
The practical phosphorus recovery process lacks a useful tool to predict the purity of struvite production, identify the precipitation species and evaluate the influence of impurities on struvite formation. This study developed an integrated struvite purity prediction process based on response surface methodology (RSM) and Visual Minteq combination. The integrated process combined the advantages of the RSM and chemical equilibrium model to predict the purity during the recovery of struvite and identify the impurities in the recovered products. The second-order polynomial models were established by RSM to predict the nitrogen and phosphorus removal efficiency, and struvite purity in the presence of calcium. Visual Minteq was used to simulate precipitation process of impurity groups based on 528 different reaction conditions. Each reaction condition was verified by the RSM results. The precipitation group including struvite, CaHPO 4 , MgHPO 4 , brucite, and Ca 8 H 2 (PO 4 ) 6
⋅ 5H 2 O, with the smallest Z-score root mean square error weighted mean (-0.43), was most suitable for predicting the formation of struvite. The importance of the 5 possible precipitation combinations is ranked. The integrated process reduces the deviation of the prediction results from the reality and provides a useful tool to predict and optimize the quality of recovered products in the field of practical phosphorus recovery process.
Egeria najas is a submerged aquatic plant, and the literatures on resourcification of submerged aquatic plant biochar remain limited. Until now, there has been no study on submerged aquatic plant biochar supported nZVI that is widely applied for removal of diversified contaminants in solution. In this study, an efficient approach to the preparation of Egeria najas- derived biochar supported nZVI composite is first developed for Cr(VI) removal in wastewater. The adsorption behavior and mechanism of Cr(VI) removal on the as-prepared Egeria najas- derived biochar/nZVI (EN@nZVI) composite were investigated. The results of FTIR and XPS indicate that the EN@nZVI surface had many functional groups such as R-COOH, R-OH, R-NH 2 and R-C-O-C, etc, which could provide active sites during the adsorption process. The BET results showed that the EN@nZVI had large specific surface area and average pore, which were 142.49 m 2 /g and 9.85 nm, respectively. EN@nZVI demonstrated high reactivity for Cr(VI) removal. Compared with nZVI, Cr(VI) removal efficiency by EN@nZVI is 50% higher than that of nZVI within 0.5 h. Furthermore, the maximum adsorption capacity of Cr (VI) was 56.79 mg/g and the energy of activation (E a ) was 31.30 kJ/mol. The adsorption process was well described by the pseudo-second order model and Sips adsorption isotherm model. The reaction mechanism of Cr(VI) removal was a multi-step removal mechanism, involving adsorption, surface complex formation, reduction and ion exchange reaction.
危险品化学品经营许可证（带存储）