Valorization of agricultural and food waste digestates is crucial for sustainable waste management to reduce environmental impacts and improve the economics of commercial farms. Hydrothermal liquefaction (HTL) of anaerobic digestates...

No abstract

No abstract

No abstract

No abstract

This paper presents the system analysis and the techno-economic assessment of selected solar hydrogen production paths based on thermochemical cycles. The analyzed solar technology is Concentrated Solar Power (CSP). Solar energy is used in order to run a two-step thermochemical cycle based on two different red-ox materials, namely nickel-ferrite and cerium dioxide (ceria). Firstly, a flexible mathematical model has been implemented to design and to operate the system. The tool is able to perform annual yield calculations based on hourly meteorological data. Secondly, a sensitivity analysis over key-design and operational techno-economic parameters has been carried out. The main outcomes are presented and critically discussed. The technical comparison of nickel-ferrite and ceria cycles showed that the integration of a large number of reactors can be optimized by considering a suitable time displacement among the activation of the single reactors working in parallel. In addition the comparison demonstrated that ceria achieves higher efficiency than nickel-ferrite (13.4% instead 6.4%), mainly because of the different kinetics. This difference leads to a lower LCOH for ceria (13.06 €/kg and 6.68 €/kg in the base case and in the best case scenario, respectively).

No abstract

Struvite (MgNH 4 PO 4 •6H 2 O), a mineral containing bioavailable phosphorus and nitrogen, is a solid slow-release fertilizer that can be produced from the aqueous-phase coproduct of hydrothermal liquefaction (HTL-AP). However, if the struvite crystallization process is carried out at nonoptimal conditions, then the P in the HTL-AP can crystallize with Ca, forming an undesirable hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) solid byproduct that also acts as an adsorbent for potentially phytotoxic organics. To maximize struvite yield and purity, a deeper understanding of struvite and hydroxyapatite crystallization as well as organics adsorption onto hydroxyapatite is critical. In this study, crystallization experiments varying temperature, time, pH, and Mg/Ca ratio were carried out. The experimental results informed a supersaturation-based reversible crystallization model for struvite and hydroxyapatite while the adsorption of organics was satisfactorily described by the classical Ritchie's and Langmuir equations. The Arrhenius and van 't Hoff equations were applied to describe the thermodynamics and kinetics of these processes. Struvite yield and purity are maximized at 25 °C, pH 8, and Mg/Ca ratio of 4, with a P-recovery rate of >90%. A less alkaline pH and higher Mg/Ca ratios maximize the reactivity among NH 4 + , HPO 4 2− , and Mg 2+ , which increases struvite selectivity over hydroxyapatite and reduces organic physisorption onto hydroxyapatite by suppressing organics deprotonation. Lower temperatures reduce struvite endothermic dissolution and organics endothermic adsorption and favor hydroxyapatite exothermic dissolution. The thermodynamics and kinetics data and models from this study are useful in designing a more sustainable and economically feasible HTL-AP valorization route.