Phosphorus Transformation in Hydrothermal Pretreatment and Steam Gasification of Sewage Sludge

Abstract

Sewage sludge is an important pool of phosphorus (P), while thermal disposal results in the enrichment of P into a final solid product. Hydrothermal treatment combined with steam gasification is an effective method to produce high-quality syngas from sewage sludge. This study discussed the transformation of P during this integrated thermochemical process based on thermodynamic calculation and the Standards, Measurements and Testing Programme analysis of solid products. The results showed that P was enriched in hydrochar with the concentration above 14 mg/g. By the hydrothermal pretreatment, organic phosphorus (OP) was significantly removed from the solid as a result of destruction, while inorganic phosphorus (IP) was mostly recovered. Part of OP was converted to IP in disposal from 220 to 240 °C. At 260 °C, destructed OP was emitted to the gaseous phase in the form of phosphorus oxide and, thus, not captured by minerals. In addition, inorganic phosphorus associated with oxides and hydroxides of Al, Fe, and Mn (NAIP) tended to be transformed into Ca-associated forms (AP) with the increase of pH, and CaO addition significantly promoted this transformation. In the gasification process, OP was completely removed, while IP was almost recovered with the substantial conversion from NAIP to AP. The highest total P recovery (84.92%) was achieved from gasification ash of hydrochar pretreated at 200 °C with CaO addition, while P was the most concentrated in gasification ash of hydrochar pretreated at 240 °C (30.39 mg/g). This study provided basic data for P recovery from sewage sludge using thermochemical conversion.

Feedstock-Dependent Phosphate Recovery in a Pilot-Scale Hydrothermal Liquefaction Bio-Crude Production

“…Moreover, IP consisted mainly of AP (97 wt% and 65 wt% for HTL-PSS-SP and HTL-SPR-SP, respectively). The phosphate form distribution was in line with those in previous studies of phosphate behavior under hydrothermal conditions [70][71][72][73]. The higher percentage of AP in the HTL solid phase from PSS could relate to the higher level of calcium in PSS (Table 1) compared to in SPR [73].…”

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

“…Besides, one study also suggested that gasification can be coupled with P recovery through thermochemical conversion. It was reported that P 2 O 5 could be completely converted into gas phase after 600 °C, and a total P recovery of over 80% can be achieved (Feng et al, 2018).…”

“…Favored by the low melting point of P 2 O 5 (340 °C), P in hydrochar can be vaporized under heated conditions, and thus recovered in the form of settled ash (Ahn et al, 2020). So far, only Feng et al evaluated the feasibility of P recovery through thermochemical process, steam gasification of hydrochar derived from waste activated sludge (Feng et al, 2018). It was found that phosphorus oxides can be completely converted into gas phase after 560 °C, and AP was the primary form in the gasification ash.…”

“…The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. a HTP = hydrothermal processing; HTC = hydrothermal carbonization; HTL = hydrothermal liquefaction; HTG = hydrothermal gasification; references (Aida et al, 2016;Aragón-Briceño et al, 2017;Berge et al, 2011;Couto et al, 2018;Danso-Boateng et al, 2015;Escala et al, 2013;Fakkaew et al, 2018;Fei et al, 2019aFei et al, , 2019bFeng et al, 2018;He et al, 2019He et al, , 2013Huang et al, 2013Huang et al, , 2014Huang and Tang, 2016;Inoue et al, 1997;Khoshbouy et al, 2019;Lee et al, 2019;Leng et al, 2018Leng et al, , 2015bLi et al, 2010Li et al, , 2012M. Liu et al, 2017;Liu et al, 2018;Liu et al, 2019;Ma et al, 2019aMa et al, , 2019bMishra and Mohanty, 2020;Molton et al, 1986;Nazari et al, 2017;Ovsyannikova et al, 2020;Paneque et al, 2017;Parmar and Ross, 2019;Peng et al, 2016;Qian et al, 2020;Ren et al, 2017;Saetea and Tippayawong, 2013a;Shah et al, 2020;Shao et al, 2015;…”

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

“…4. Chemical compositions of phosphate rock and sludge-derived ash and hydrochar: (a) typical compositions of phosphate rock from various countries [6,48]; (b) mean values and (c) violin distribution of ash compositions [6,31,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]; (d) mean values and (e) violin distribution of hydrochar compositions [14,15,22,23,28,32,45,[68][69][70][71][72][73][74][75]. EU = European Union (data from Belgium, Denmark, Germany, Poland, Spain, Sweden, and Switzerland).…”