Hydrothermal Aqueous Phase Research Articles

Sustainable bioenergy potential of peat-moss derived hydrothermal aqueous phase: Insights into methane production and organic transformation

Achieving Sustainable Development Goal 7 (SDG-7) by exploring bioenergy production from peat-moss derived hydrothermal aqueous phase (HAPs) through anaerobic digestion (AD). This study investigated six combinations of hydrothermal conversion temperature (HCT) and residence time (HCRT). Methane yields varied significantly, with the highest (256 mL/g COD) achieved at 200 °C:4h, while the lowest (97 mL/g COD) was at 320 °C:4h due to formation of toxic and refractory organics. Microtox analysis showed acute toxicity > 98 % for all HAPs. Notably, higher HCT and HCRT led to more complex and diverse organic patterns, promoting the formation of humus-like substances, ester, alkane alcohols, and aromatics. GC–MS analysis revealed a 23 % increase in aldehyde and ketone compounds at 320 °C:4h. Continuous experiments confirmed 29 % COD removal efficiency at 320 °C:4h and identified 13 refractory organics, highlighting challenges in biodegradability. These findings provided valuable insights for optimizing AD processes, enhancing bioenergy production, and advancing sustainable energy solutions in alignment with SDG-7.

The dynamic features and microbial mechanism of nitrogen transformation for hydrothermal aqueous phase as fertilizer in dryland soil

Hydrothermal aqueous phase (HAP) contains abundant organics and nutrients, which have potential to partially replace chemical fertilizers for enhancing plant growth and soil quality. However, the underlying reasons for low available nitrogen (N) and high N loss in dryland soil remain unclear. A cultivation experiment was conducted using HAP or urea to supply 160 mg N kg−1 in dryland soil. The dynamic changes of soil organic matters (SOMs), pH, N forms, and N cycling genes were investigated. Results showed that SOMs from HAP stimulated urease activity and ureC, which enhanced ammonification in turn. The high-molecular-weight SOMs relatively increased during 5–30 d and then biodegraded during 30–90 d, which SUV254 changed from 0.51 to 1.47 to 0.29 L−1 m−1. This affected ureC that changed from 5.58 to 5.34 to 5.75 lg copies g−1. Relative to urea, addition HAP enhanced ON mineralization by 8.40 times during 30–90 d due to higher ureC. It decreased NO3–N by 65.35%–77.32% but increased AOB and AOA by 0.25 and 0.90 lg copies g−1 at 5 d and 90 d, respectively. It little affected nirK and increased nosZ by 0.41 lg copies g−1 at 90 d. It increased N loss by 4.59 times. The soil pH for HAP was higher than that for urea after 11 d. The comprehensive effects of high SOMs and pH, including ammonification enhancement and nitrification activity inhibition, were the primary causes of high N loss. The core idea for developing high-efficiency HAP fertilizer is to moderately inhibit ammonification and promote nitrification.

In-Depth Identification of the Sources and Features of Organic Fluorescent Structures in the Sewage Sludge Hydrothermal Aqueous Phase

In-Depth Identification of the Sources and Features of Organic Fluorescent Structures in the Sewage Sludge Hydrothermal Aqueous Phase

Insights into aromatic methyl groups in the hydrothermal aqueous phase to enhance the efficiency of sludge gasification for hydrogen production

The present work studied the hydrogen production and transformation path of the gasification of domestic sludge with the hydrothermal aqueous phase (HTAP). The organic fractions of HTAP were found to significantly enhance the efficiency of sludge gasification for hydrogen production. FTIR and GC–MS were used to characterize the hydrothermal aqueous phase to further investigate the gasification pathways. Aromatics were found to be critical for the synergistic effect. The –CH3 bond dissociation energies in aromatics were calculated by the density functional theory (DFT) and compared with the preliminary dissociation enthalpy of the methane reforming process. The dissociation energies of –CH3 in the aromatics were much lower than that in methane. The contribution of the aromatics was mainly due to the disassociation of the side chain methyl groups. The dissociation of a large number of aromatic methyl groups in the HTAPs strongly promotes the reaction of methyl and water to produce hydrogen.

Enhancement of hydrogen production in steam gasification of sludge: Comparing different strategies for deeper conversion of hydrogen sources in biomass

Biomass has significant advantages in the gasification process but is frequently hampered by low hydrogen production. In this study, sludge and hydrothermal aqueous phase (HTAP) were selected as biomass substrates to provide a plentiful source of organic hydrogen for gasification, and different strategies for deeper conversion of hydrogen sources and higher hydrogen production were compared. Solid acid catalysts were used to alter the distribution of organic hydrogen sources in biomass substrates. Ni-ore-based catalysts were used to directly catalyze the gasification process. The results showed that nickel-ore-based catalysts exhibited a much higher contribution to hydrogen production. The solid acid catalyst resulted in the dissociation of methyl and methoxy on the side chain of HTAP, and the transfer of hydrogen source affects the subsequent hydrogen production. And Ni-ore-based catalysts efficiently can convert the hydrogen sources in tar into valuable gas. The Ni-ore-based catalysts achieved up to 62.07% increase in hydrogen production from gasification. This study elucidates the underlying mechanistic issues of the proposed strategies to produce hydrogen from gasification and provides a deeper understanding of the efficient utilization of hydrogen sources in biomass.

Coupling hydrothermal liquefaction and anaerobic digestion for energy valorization from model biomass feedstocks

Hydrothermal liquefaction converts food waste into oil and a carbon-rich hydrothermal aqueous phase. The hydrothermal aqueous phase may be converted to biomethane via anaerobic digestion. Here, the feasibility of coupling hydrothermal liquefaction and anaerobic digestion for the conversion of food waste into energy products was examined. A mixture of polysaccharides, proteins, and lipids, representing food waste, underwent hydrothermal processing at temperatures ranging from 200 to 350°C. The anaerobic biodegradability of the hydrothermal aqueous phase was examined through conducting biochemical methane potential assays. The results demonstrate that the anaerobic biodegradability of the hydrothermal aqueous phase was lower when the temperature of hydrothermal processing increased. The chemical composition of the hydrothermal aqueous phase affected the anaerobic biodegradability. However, no inhibition of biodegradation was observed for most samples. Combining hydrothermal and anaerobic digestion may, therefore, yield a higher energetic return by converting the feedstock into oil and biomethane.

Comparison of pyrolysis and hydrothermal liquefaction of Chlamydomonas reinhardtii. Growth studies on the recovered hydrothermal aqueous phase

The production of bio-oil by pyrolysis with a high heating rate (500 K s−1) and hydrothermal liquefaction (HTL) of Chlamydomonas reinhardtii was compared. HTL led to bio-oil yield decreasing from 67% mass fraction at 220 °C to 59% mass fraction at 310 °C whereas the bio-oil yield increased from 53% mass fraction at 400 °C to 60% mass fraction at 550 °C for pyrolysis. Energy ratios (energy produced in the form of bio-oil divided by the energy content of the initial microalgae) between 66% at 220 °C and 90% at 310 °C in HTL were obtained whereas it was in the range 73–83% at 400–550 °C for pyrolysis. The Higher Heating Value of the HTL bio-oil was increasing with the temperature while it was constant for pyrolysis. Microalgae cultivation in aqueous phase produced by HTL was also investigated and showed promising results.