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Acid Drainage Control and Its Limitations
Published in V. P. (Bill) Evangelou, and Its Control, 2018
The schematic diagram in Figure 5.4 shows that rock phosphate may also react with Fe(II) thus, forming vivianite (Fe3(PO4)2·8H2O) a relatively insoluble compound which in the presence of O2 converts to water-insoluble FePO4 solid.
Recovery of phosphorus from wastewater: A review based on current phosphorous removal technologies
Published in Critical Reviews in Environmental Science and Technology, 2023
Yulin Zheng, Yongshan Wan, Yue Zhang, Jinsheng Huang, Yicheng Yang, Daniel C. W. Tsang, Hailong Wang, Hao Chen, Bin Gao
Iron salt is one of the common precipitation/coagulation chemicals for removing P from wastewater to meet stringent P discharge standards (Zhang et al., 2013). These metals could remain in SS and bind with P to form low-soluble minerals, which further reduce the P recovery efficiency in the route to struvite product (Wu et al., 2019). In the SS, several biological activities take place, where Fe3+ is reduced to Fe2+ by dissimilatory metal-reducing bacteria and organic phosphorus is converted to phosphate by anaerobic microorganisms under reducing environments with rich presence of organic matter (OM). Iron(II) phosphate (vivianite) could be formed with the presence of organic matter, microorganism under reducing condition. Vivianite formation is a complex process and is influenced by various factors, such as iron source preferred pH (6.0 − 8.0) and the concentration of sulfate, due to competing reaction with formation of FeS (Wu et al., 2019). On the one hand, vivianite can be recovered from sludge via magnetic separation. On the other hand, many studies indicate sulfide can be used to effectively release P from SS with high content of vivianite (Wilfert et al., 2018). Phosphate recovery from vivianite is efficient because sulfide reacts directly (1:1) with Fe(II) to form FeSx, without Fe(III) reduction (Liu et al., 2018). However, the release of recoverable P might be sacrificed by the decrease in sludge dewaterability (Wilfert et al., 2020). To further recover the lock-up Fe-P minerals, microbial fuel cell (MFC) was also implemented to extract P from digested sludge via the redox reaction driven by the electron transfer and electrical current, where the P-rich supernatant was used to form struvite (Fischer et al., 2011).