Study of two approaches for the process water management from hydrothermal carbonization of swine manure: Anaerobic treatment and nutrient recovery

Hydrothermal carbonization (HTC) is a promising alternative to transform biomass waste into a solid carbonaceous material (hydrochar) and a process water with potential for material and energy recovery. In this study, two alternatives for process water treatment by conventional and acid-assisted HTC of swine manure are discussed. Process water from conventional HTC at 180 °C showed high biodegradability (55% COD removal) and methane production (∼290 mL STP CH4 g−1 CODadded) and the treatment in an upflow anaerobic sludge blanket reactor allowed obtaining a high methane production yield (1.3 L CH4 L−1 d−1) and COD removal (∼70%). The analysis of the microbiota showed a high concentration of Synergistota and Firmicutes phyla, with high degradation of organic nitrogen-containing organic compounds. Acid-assisted HTC proved to be a viable option for nutrient recovery (migration of 83% of the P to the process water), which allowed obtaining a solid salt by chemical precipitation with Mg(OH)2 (NPK of 4/4/0.4) and MgCl2 (NPK 8/17/0.5), with a negligible content of heavy metals. The characteristics of the precipitated solid complied with the requirements of European Regulation (2019)/1009 for fertilizers and amendments in agricultural soils, being a suitable alternative for the recycling of nutrients from wastesTED2021-130287B-I00, PDC 2021-120755-I0

Strategies to improve swine manure hydrochar: HCl-assisted hydrothermal carbonization versus hydrochar washing

The work focuses on the study of hydrochar upgrading from hydrothermal carbonization (HTC) of swine manure by HClassisted HTC or washing with HCl or acetone, as a post-treatment to conventional HTC. Conventional HTC of swine manure yields a low-quality hydrochar (C content~ 38 wt.%, higher heating value (HHV)~ 15 MJ kg−1, and ash content up to 32 wt.%). HCl-assisted HTC (0.5 M HCl at 230 ℃) substantially reduced the ash content up to ~10 wt.% in the hydrochar and increased the C content to 58 wt.%, reaching a HHV of 23 MJ kg−1. However, the N and S contents remained at values similar to those of the swine manure. Washing post-treatment of conventional hydrochars with HCl or acetone signifcantly improved the C content and the HHV in the range 47–58 wt.% and 19–25 MJ kg−1, respectively, as well as the ash removal with values 7-11 wt.%. Washing the hydrochar with acetone signifcantly reduced the N and S contents, obtaining a carbonaceous material with properties suitable for solid biofuel according to ISO/TS 17225–8, (N17 MJ kg−1; and ash<10 wt.%). Hydrochars obtained by HCl-assisted HTC and HCl/acetone washing post-treatment yielded higher thermal stability, as well as better reactivity and low ash agglomeration indexes than compared to conventional hydrochars. Washing post-treatment with acetone proved to be the best strategy to obtain improved hydrochars from swine manure for industrial use as a solid biofuelAuthors greatly appreciate funding from Spain’s MICINN (PID2019-108445RB-I00), MINECO (PDC2021-120755-I00 and TED2021-130287B-I00), Madrid Regional Government (Project S2018/EMT-4344), and Grupo Kerbest Company. R.P. Ipiales acknowledges the fnancial support from the Community of Madrid (IND2019/ AMB-17092) and Arquimea Agrotech Compan