Zhi-Wu Wang

Hydrothermal liquefaction (HTL) of lignocellulosic biomass produces multiple product fractions, including solid residue (SR), heavy bio-oil (HBO), aqueous phase (AP), and light bio-oil (LBO). This study mainly applied principal component analysis (PCA) and regression modeling to predict AP solution weight, LBO weight and fuel characteristics, and HTL wastewater biodegradability, as well as to improve prediction accuracy for SR and HBO under various operating conditions (temperature: 250–350 °C, residence time: 5–60 min, and the combined solid loading of three batches: 15–45 g). A complementary relationship between SR and AP weights found in PCA enabled the estimation of AP weight based on predicted SR values in a regression analysis. A modified partition coefficient was introduced to link LBO weight with the carbon content of AP and was predicted, enabling accurate LBO yield estimation. Although LBO fuel characteristics could not be modeled reliably, those of SR and HBO were predicted with improved accuracy over prior kinetic models. The concentration of catechol in HTL wastewater (HTL-WW) was also modeled from operating conditions and linked to half-maximal inhibitory concentration (IC₅₀) of R. jostii and A. niger as a biodegradability index. This work demonstrates the feasibility of predicting underrepresented HTL outputs using statistical approaches.

In this manuscript, we report niche differentiation among important groups of organisms involved in phosphorus and nitrogen cycling, and the interplay between relevant metabolic pathways carried out by these key organisms. We employed nanopore-based long-read and Illumina-based short-read sequencing techniques for metagenomics and metatranscriptomics, respectively, on samples collected from an integrated fixed film activated sludge (IFAS) bioreactor run in the conventional A²O mode under low dissolved oxygen (DO) conditions. Among the recovered metagenome-assembled genomes (MAGs), >90 MAGs from each community were high-quality, including 39 and 30 MAGs that were close-circularized, from the floc and biofilm communities, respectively, with no or minimal contamination. Some Candidatus Accumulibacter strains encoded for either full or partial denitrification. Ca. Accumulibacter were very efficient in aerobic and anoxic inorganic phosphorus (Pi) uptake, while the second highly enriched Ca. Accumulibacter was as competitive for denitrification metabolism. The potential of nitrous oxide (N₂O) emissions in both the floc and biofilm communities was nearly 20 times higher in the aerobic zone than in the anoxic zone. As opposed to our initial hypothesis that slow growers will mostly reside in biofilms, the expression of ammonium monooxygenase (amoABC) was higher in flocs than in biofilm communities.

Although hydrothermal liquefaction (HTL) is the leading technology in converting wet biomass into bioenergy, the treatment of its toxic‐laden aqueous phase wastewater presents a major challenge on its path toward commercial viability. This study presents the first‐ever assessment of sewage sludge‐fed HTL wastewater (SS‐HTLWW) treatment and toxic compound removal using municipal activated sludge (AS) by optimizing its cultivation condition. It was found that AS with optimized pretreatment can remove up to 91.2% of the soluble chemical oxygen demand (sCOD) in SS‐HTLWW, of which up to 82% can be attributed to biological mineralization and adsorption of sCOD by AS. Conventional bioprocess optimization techniques, including overliming, elevated temperatures, and nutrient supplementation, were found to raise the maximum rate of sCOD utilization (R _m ) of AS treatment by 44%, 67%, and 45%, respectively. The variation in the maximum degradation potential (D _max ) after 23 days of treatment across all groups was negligible. Adjusting the SS‐HTLWW dilution factor from 20× to 10× resulted in no significant difference in R _m or D _max values due to the counteracting effects of high substrate and inhibitor concentrations. Additionally, AS was able to eliminate almost all N ‐heterocycles, phenolic compounds, and organic acids found in SS‐HTLWW. This suggested that AS can both survive in and mitigate the high level of toxicity associated with SS‐HTLWW; however, the high levels of recalcitrant COD after treatment may require further attention before it can be adequately discharged. The insights gained from this study are poised to interest engineers and treatment plant operators in search of efficient strategies for SS‐HTLWW management and the broader application of HTL.

The hydrothermal liquefaction (HTL) process offers an energetic advantage over pyrolysis because it does not require prior drying of the biomass feedstock. However, there are significant challenges in simultaneously estimating both the yields and characteristics of products from the HTL of biomass with theoretical support. This study developed a unique element-based kinetic model to predict the yields, higher heating values, and fuel characteristics of solid residue and heavy bio-oil, based on the temperature, residence time, solid loading, and elemental composition (C, H, N, and O) of corn stover. Furthermore, the model predicted the weights of dissolved carbon and nitrogen in the aqueous phase. HTL experiments were conducted using corn stover at temperatures ranging from 250 to 350 °C for residence times between 5 and 60 min. The resulting solid and liquid products were analyzed for the elemental composition and ash content. The experimental data and MATLAB program were used to predict the products. The fuel characteristics derived from predicted elemental weight data of solid residues followed the trend line of the observed data on the van Krevelen diagram. In those of heavy bio-oil, the H/C atomic ratio of the average predicted data matched the one calculated from the observed data. Additionally, power function relationships between the amounts of corn stover and obtained product fractions were identified under identical temperature and residence time conditions by varying solid loading, providing insights into the partial nonlinear behavior of the reaction system.

High-salinity crude glycerol generated from biodiesel production poses significant challenges to microbial valorization due to inhibitory ingredients that severely limit microbial growth. This study identified and mitigated inhibitory substances contained in high-salinity glycerol sludge to enable its conversion to polyhydroxyalkanoates (PHAs) by the extreme halophilic archaeon Haloferax mediterranei. The long-chain fatty acids (LCFAs) were consistently identified as the primary inhibitors by liquid chromatography–mass spectrometry, Fourier transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Acid precipitation at pH 2 efficiently removed these LCFAs, substantially reducing the required feedstock dilution from 23 to 3 times, improving PHA titer by 40%. Furthermore, this dilution reduction also increased the feedstock salinity utilization, achieving a 46% reduction in external salt supplementation for H. mediterranei growth. In contrast, overliming and arrested anaerobic digestion were confirmed to be ineffective in inhibitor removal. This study provides deep insights into inhibitor chemistry and presents acid precipitation as an effective pretreatment strategy for waste valorization of high-salinity crude glycerol.