Phosphorus species transformation and recovery without apatite in FeCl3-assisted sewage sludge hydrothermal treatment

Phosphate substances transformation and vivianite formation in P-Fe containing sludge during the transition process of aerobic and anaerobic conditions

“…The recovery of phosphorus from sludge realizes sludge reduction and sustainable utilization of phos phorus resources. Therefore, phosphorus recovery from sludge is an important goal of sewage treatment research ( Li et al, 2020 ). At present, the main ways of recovery are struvite precipitation and calcium phosphate precipitation ( Zhang et al, 2020a ).…”

Phosphorus recovery from municipal sludge-derived ash and hydrochar through wet-chemical technology: A review towards sustainable waste management

“…Xu et al found that P extraction efficiency enhanced from 1% to 25% of total P in ash when NaOH concentrations increased from 0.01 M to 0.8 M (L/S = 25 mL/g, 2 h), while it only improved 5% when L/S increased from 25 to 200 mL/g (0.01 N, 2 h) [123]. It was suggested that limited P could be extracted from hydrochar at low pH (e.g., < 10% at pH = 10.5), while the extraction efficiency did not increase significantly at pH > 12 (L/S = 100 mL/g, 16 h) [97]. Sufficient contact time should be allowed to achieve maximum extraction efficiency.…”

“…However, it was reported that high incineration temperatures (700-900 • C) could prohibit the formation of pyrophosphates [101]. For hydrochar, Li et al and Shi et al also reported that orthophosphate was dominant (>90% of total P), and other forms of P (e.g., orthophosphate monoester and pyrophosphate) gradually disappeared with increasing hydrothermal temperature at 260 • C (4 h) and 320 • C (0.5 h), respectively [15,97]. Even at a low hydrothermal temperature (225 • C for 24 h), pyrophosphate can be totally converted into orthophosphate [103].…”

“…SS = secondary sludge, MPS = mixed primary and secondary sludge, AP = apatite P, NAIP = non-apatite inorganic P, OP = organic P, inorganic P = AP + NAIP. Data sources: Li1 [76], Li2 [49], Liang [62], Li3 [97], Shi [15], Xu [98], Zhai [96], Zhang [99], and Zheng [100].…”

“…( 12)) better than Pseudo-first-order (Eq. ( 13)) [97]. It indicates that the P desorption process is primarily controlled by chemisorption rather than diffusion, and the reaction rate is limited over time with the concentration of one or more substances [133].…”