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

Abstract

Microalgae (Spirulina) and primary sewage sludge are considerable feedstocks for future fuel-producing biorefinery. These feedstocks have either a high fuel production potential (algae) or a particularly high appearance as waste (sludge). Both feedstocks bring high loads of nutrients (P, N) that must be addressed in sound biorefinery concepts that primarily target specific hydrocarbons, such as liquid fuels. Hydrothermal liquefaction (HTL), which produces bio-crude oil that is ready for catalytic upgrading (e.g., for jet fuel), is a useful starting point for such an approach. As technology advances from small-scale batches to pilot-scale continuous operations, the aspect of nutrient recovery must be reconsidered. This research presents a full analysis of relevant nutrient flows between the product phases of HTL for the two aforementioned feedstocks on the basis of pilot-scale data. From a partial experimentally derived mass balance, initial strategies for recovering the most relevant nutrients (P, N) were developed and proofed in laboratory-scale. The experimental and theoretical data from the pilot and laboratory scales are combined to present the proof of concept and provide the first mass balances of an HTL-based biorefinery modular operation for producing fertilizer (struvite) as a value-added product.

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

“…One study found that oxalic and sulfuric acids can effectively extract P from hydrochar with 80-95% of P leached, but no further precipitation of solid fertilizer was conducted (Acelas et al, 2014). Several studies have performed struvite production with acidic leachate from hydrochar and ammonium-rich HTP aqueous phase (320-2,970 mg/L) (Becker et al, 2019;Ovsyannikova et al, 2020;Zhai et al, 2014b). A high P recovery rate (82-98%) can be reached in batch scales.…”

“…The low overall recovery rate was attributed to the dispersion of P-containing particles into the biocrude (Ovsyannikova et al, 2020).…”

Evaluating the Struvite Recovered from Anaerobic Digestate in a Farm Bio-Refinery as a Slow-Release Fertiliser

“…Research on the liquid fraction of digestates has rapidly intensified in recent years, covering struvite recovery [15], ammonia stripping, vacuum evaporation [16], and microalgae or duckweed cultivation [17]. The research primarily focuses on determining the effectiveness of particular recovery processes [18][19][20]. It is necessary, however, to valorise and assess their suitability, including the fertiliser value of the recovered products, e.g., struvite or ammonium sulphate.…”

Bio-Crude Production Improvement during Hydrothermal Liquefaction of Biopulp by Simultaneous Application of Alkali Catalysts and Aqueous Phase Recirculation

“…The major proportion of P present in the biomass was recovered in the solid phase in all cases. With the introduction of the alkali catalysts, the concentration of multivalent metal ions (e.g., Ca 2+ , Al 3+ , Fe 2+/3+ ) in the solid phase increased, which led to the higher concentration of P in the form of phosphate salts in the same phase [57,58]. Based on the results presented in Table 4, the molar ratio of Ca/P in the solid residue is 1.3 to 2.4, which, in most cases, meets the required amount of Ca to form hydroxyapatite.…”