The amount of organic waste is rapidly increasing, and so do the environmental impacts and costs associated with its management. Hydrothermal liquefaction (HTL) is a promising technology that can convert...

Sewage sludge (SS) management constitutes both a challenge and an opportunity for the sustainability of wastewater treatment plants (WWTPs). Standalone anaerobic digestion (AD) stabilizes the biodegradable organics contained in SS...

Industrial wastewaters rich in organic carbon have potential for value generation, but conventional, low-rate, anaerobic–aerobic wastewater treatment (WWT) processes often incur significant capital expenses and energy consumption. In this study, we leveraged experimental data for biorefinery-derived wastewaters to characterize the implications of transitioning from a conventional, low-rate process to a high-rate, multistage anaerobic process. We designed and simulated these WWT processes across seven first- and second-generation (1G/2G) biorefineries and evaluated the implications for biorefinery sustainability through techno-economic analysis (TEA) and life cycle assessment (LCA). Compared to the conventional design, the new process can substantially reduce capital costs and electricity usage. These improvements were particularly evident for 2G biorefineries, translating to 5%–13% lower minimum product selling prices (MPSPs) and 7%–135% lower 100-year global warming potentials (GWPs; the 135% reduction is due to the transition of one biorefinery from net emission [0.87 kg of CO2e·gal–1] to net sequestration [−0.31 kg of CO2e·gal–1]). Biorefineries could further reduce the MPSP through the renewable identification number (RIN) credits by upgrading and selling the biogas as renewable natural gas, but at the expense of increasing GWP. When normalized, the COD management cost ranged from $–56 to $465 per tonne of COD, indicating that wastewater could be a net source of revenue for some biorefineries.

We evaluated natural clay minerals representing all classes of phyllosilicates as in situ catalysts for hydrothermal liquefaction (HTL) of anaerobically digested cattle manure at 350 °C for 1 h, i.e., kaolinite, montmorillonite, talc, vermiculite, phlogopite, meixnerite, attapulgite, and alumina. The relative compositions of strong Bronsted (SBrA), strong Lewis (SLA), and weak Lewis acidic (WLA) sites and the strong (SBS) and weak (WBS) basic sites of clay minerals significantly affected the formation of HTL products (i.e., biocrude oil, hydrochar, and aqueous-and gas-phase coproducts) and the distribution and speciation of elements. The general mechanistic roles of these active sites are as follows: (1) SBrA catalyzed the biocrude-forming reactions and inhibited the hydrochar-repolymerizing reactions; (2) SLA promoted the production of hydrochar precursors; (3) WLA enhanced the hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of biocrude by utilizing the hydrogen generation catalyzed by WBS; and (4) SBS increased the production of organic acids solubilizing nutrients into the aqueous-phase coproduct (HTL-AP). Montmorillonite was the most suitable for the HTL catalyst due to the optimal composition of these active sites, leading to achieving maximal biocrude energy recovery (i.e., 82%) with low heteroatoms content (i.e., 15% O, 0.24% N, and 0.08% S), minimal hydrochar yield (i.e., 10%), and maximal nutrient yield in HTL-AP, i.e., 71% P, 54% Mg, 29% NH 3 -N, and 14% Ca. In addition, the crystalline structure of montmorillonite remained intact after the HTL process. This study informs comprehensive catalytic roles of different surface-active sites of clay minerals useful for future development of clay-based catalysts for more sustainable overall HTL systems.