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...

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Improper management of dairy wastewater (acid whey) leads to water basin eutrophication and greenhouse gas emissions. We evaluated hydrothermal liquefaction as a means to sustainably manage and valorize acid whey wastes by converting them into biocrude oil and recovering nutrients in aqueous-phase byproducts. In a set of well-defined experiments, we studied the effects of reaction temperatures (280−360 °C), reaction times (7.5−37.5 min), feedstock pH values (2.5−8.5), and feedstock salt contents (0−2 wt %) on the energy recovered and the yields of products and elements. Response surface analysis showed that an alkaline feedstock pH (8.5) and a short reaction time (7.5 min) combined with a specific optimal reaction temperature for certain salt content in the feedstock were required to maximize biocrude energy recovery and nutrient recovery for a range of feedstock compositions. In general, 280−290 °C was optimal for salt contents ≤1.675 wt % and 360 °C for salt contents 1.675−2 wt %. Carbon and nitrogen were mostly distributed between biocrude and aqueous-phase products, added with distribution to the gas phase at higher temperatures. Partitioning of inorganics, for example, calcium and phosphorus, into aqueous-phase and solid hydrochar products depended on reaction conditions. This study provides new information for controlling target product composition as well as specifying desirable operating conditions for practical systems.

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Uncontrolled emission of carbon and nutrients due to mismanagement of dairy waste leads to global warming, eutrophication of water bodies, aerosol pollution, and acidification of ecosystems. We studied hydrothermal liquefaction (HTL) to sustainably recover resources by converting the dairy wastes into carbon-dense biocrude oil and a nutrient-rich aqueous-phase coproduct. We evaluated acid whey as an alternative source of acid catalyst, replacing acetic acid, for the HTL of anaerobically digested cattle manure (manure digestate). Using well-designed HTL experiments, we investigated the effects of several factors on the product formation and the fate of elements as well as the underlying chemistry. The investigated factors included reaction temperature (280−360 °C), reaction time (10−50 min), mixing ratio of acid whey to manure digestate (AW/MD of 0−2), and the amount of additional acetic acid required, that is, specified based on the final feedstock pH between 3.5 and 5.5. The experimental results suggested the following optimal conditions for enhanced biocrude oil formation and maximal nutrient yield in the aqueous-phase coproduct: AW/MD of 1.21, feedstock mixture pH of 4.5, and reaction temperature and time of 354 °C and 21 min, respectively. Under such conditions, the biocrude oil yield was enhanced to 40−50% (equivalent to 60−80% energy recovery) via cyclic acetalization, hydroxymethylation, isomerization, Piancatelli rearrangement, oxidation, and condensation with heteroatom removal via several deoxygenation and denitrogenation mechanisms. Moreover, these conditions provided adequate acidification to solubilize Mg-carbonate and Ca-phosphate minerals and catalyzed the deamination of N-heterocyclics and other nitrogenous compounds, producing a higher recoverable yield of Mg, NH 3 -N, P, and K nutrients in the aqueous-phase coproduct, that is, 60−70, 30−40, ∼40, and >95%, respectively. This study demonstrated the potential of using HTL for coprocessing manure digestate and acid whey to measurably valorize biomass waste as a key component of achieving a circular bioeconomy for the dairy industry.

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.

Abstract. Palm Fatty Acid Distillate (PFAD) is a byproduct of CPO production. PFAD conversion into monoglyceride would give significant economic added value to it. With free fatty acid as the major component which composes the PFAD, then the esterification process was the right choice. Utilization of strong acidic cation resin as a catalyst is interesting. The catalyst could be easily separated physically. Natural esterification reaction would run reversibly so that the reflux system would be created to remove water. Reflux system used xylene as the solvent. To find the optimum condition for reaction parameters, reaction temperature, mole ratio of PFAD-glycerol, and catalyst loading were varied. Two heterogeneous reaction mechanisms, Langmuir-Hinshelwood and Eley-Rideal model, were tried to fit with the experimental data which resulted in the first model fitted the experimental data better than the second model. The reaction mechanism would involve the side reaction of diglyceride and triglyceride formation.