Chemical recycling has the potential to reduce the environmental impacts from waste plastics, mitigate climate change, and contribute to circular economy. This study compares the environmental and economic performance of two such technologies, fast pyrolysis and gasification, with conventional disposal methods for treating polypropylene (PP) waste. High-fidelity process simulations for each technology are conducted to obtain the necessary mass, energy, and economic data for subsequent analyses. Through an extensive life cycle assessment utilizing the IPCC 2013, ReCiPe, and ILCD 2.0 methods, fast pyrolysis and gasification are determined to have lower overall greenhouse gas emissions and better overall environmental performance than the conventional methods of incineration and landfilling. The chemical recycling systems are also found to be considerably profitable with fast pyrolysis and gasification having total NPVs of $149MM and $96MM, respectively. The discount rate, waste PP price, and plant life are the most influential factors for the economic performance of both systems.

Thermochemical technologies provide promising pathways to recover energy and reduce environmental impacts from biomass wastes. Poultry manure or litter additionally provides an opportunity for recovering and recycling nutrients and producing valuable soil amendments. This study compared the life cycle environmental impacts and technoeconomic performance of six thermochemical technologies for treating poultry litter wasteslow pyrolysis, fast pyrolysis, gasification, hydrothermal liquefaction, hydrothermal carbonization, and supercritical water gasificationwith direct land application. Using life cycle assessment (LCA), the technologies were compared through 15 different environmental impact categories (midpoints) using the IMPACT 2002+ method. On converting the midpoints to damage categories (end points), it was found that these technologies outperformed the conventional land application method with respect to human health (92−149% improvement), climate change impact (15−53% improvement), ecosystem quality (124−160% improvement), and resource depletion (−24−530% improvement). The technoeconomic analysis (TEA) identified carbon price (breakeven of $127/1000 kg CO 2 equiv for slow pyrolysis) and high capital costs as influential parameters for large-scale applications of these technologies. The TEA results were most sensitive to carbon price and transportation distance (0.69 and 0.52% changes in revenue per change in input, respectively).

This study examines prominent thermochemical conversion technologies, such as slow pyrolysis, fast pyrolysis, gasification, and hydrothermal liquefaction, for treating poultry litter in New York State (NYS). Nine cases involving combinations of the four technologies and different downstream processing options such as bio-oil upgrading and Fischer–Tropsch conversion are chosen based on the product distribution. High-fidelity process simulations are performed to derive the mass and energy balance. Economic performance for the nine cases varied widely with largely overlapping net present values, ranging from $10MM to $170MM (slow pyrolysis), $89MM to $314.5MM (fast pyrolysis), $28MM to $196MM (hydrothermal liquefaction), and $25MM to $234MM (gasification). Both pyrolysis technologies had 18% to 56% lower greenhouse gas (GHG) emissions than the other technologies. GHG balances showed trade-offs with economic performance. Sensitivity analysis identified carbon credits, products’ market price, and plant capacity as the most influential factors. Building one centralized biorefinery in NYS especially for fast pyrolysis was more economically feasible than building multiple smaller biorefineries (biochar breakeven price of −$128 to −$91/ton vs $74 to $93/ton). The trend for slow pyrolysis was similar but with comparatively little difference (biochar breakeven price of $59 to $96/ton for one biorefinery vs $76 to $91/ton for multiple biorefineries).

With the rapid rise in global population over the past decades, there has been a corresponding surge in demand for resources such as food and energy. As a consequence, the rate of waste generation and resultant pollution levels have risen drastically. Currently, most organic solid wastes are either land applied or sent to landfills, with the remaining fraction incinerated or anaerobically digested. However, with the current emphasis on the reduction of emissions, nutrient recovery, clean energy production and circular economy, it is important to revisit some of the conventional methods of treating these wastes and tap into their largely unrealized potential in terms of environmental and economic benefits. Wastewater sludge, with its high organic content and fairly constant supply, provides a great opportunity to implement some of these strategies using thermochemical conversion technologies, which are considered as one of the alternatives for upcycling such waste streams. This paper summarizes the results of prominent studies for valorizing wastewater sludge through thermochemical conversion technologies while drawing inferences and identifying relationships between different technical and operating parameters involved. This is followed by sections emphasizing the environmental and economic implications of these technologies, and their corresponding products in context of the broader fields of waste-to-energy, nutrient recycling and the progress towards a circular economy.