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.