Browsing by Author "Tester, Jefferson W."

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    Enhancing energy recovery of wastewater treatment plants through hydrothermal liquefaction
    (2023) Cabrera, Daniela V.; Barria, David A.; Camu, Esteban; Celis, Crispin; Tester, Jefferson W.; Labatut, Rodrigo A.
    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 but recovers only a fraction of the chemical energy stored therein and produces large amounts of un-stabilized sludge. Hydrothermal liquefaction (HTL) coupled with AD can enhance the treatment and energy recovery of SS. Standalone AD was compared against (1) an HTL-AD configuration, with SS as HTL input, and the generated aqueous product (AP) as AD input; and (2), an AD-HTL-AD configuration, with SS as AD input, the digestate as HTL input, and the generated AP as AD input. Both configurations decreased the SS' COD from 27.5 to 0.6 g L-1, while the overall energy recovered was increased up to 2.2-fold relative to conventional SS treatment using only AD. Under the HTL-AD configuration, biocrude yields were higher (i.e., 26.4 vs. 15.8) and the AP generated was more biodegradable (0.78 vs. 0.65), than those obtained under the AD-HTL-AD configuration. Monte Carlo uncertainty analyses confirmed that overall energy recoveries would follow the order AD-HTL-AD > HTL-AD > AD; with energy recoveries (95% confidence) between, 63.5-94.7%, 54.6-91.2%, and 33.2-71.1%, respectively. This study shows that, by implementing HTL as a standalone SS treatment, WWTPs can recover more energy than using AD alone. Furthermore, WWTPs with existing AD would recover additional energy through HTL of the generated digestate, significantly reducing the environmental impacts and costs of conventional solids management.
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    Grease trap waste valorization through hydrothermal liquefaction and anaerobic digestion: a circular approach to dairy wastewater treatment
    (2024) Cabrera, Daniela V.; Adema-Yusta, Ingrid; Santibanez, Maria J.; Celis, Crispin; Tester, Jefferson W.; Labatut, Rodrigo A.
    Grease traps are commonly used in the dairy industry to separate fats from their generated wastewater. Due to its properties, grease trap waste (GTW) is predominantly incinerated or landfilled despite its high energy content. In this study, hydrothermal liquefaction (HTL) was used to convert dairy industry GTW into biocrude while the generated HTL-wastewater (AP) was subjected to anaerobic digestion (AD) to recover biomethane. To maximize organic carbon to biocrude conversion, and to minimize the use of freshwater, a fraction of the AP was recirculated in subsequent HTL reactions. AP recirculation increased biocrude yields (73 vs. 78 wt%) but decreased both the higher heating value (HHV) (38 vs. 37 MJ kg-1) and the fraction (72 vs. 64%) of lighter hydrocarbons. Continuous AD using an EGSB reactor proved to be an effective method to further reduce the COD of the AP from 6.5 g L-1 to 0.7 g L-1 and enhance the overall energy recovery of the GTW from 81% (HTL only) to 83.1% (HTL-AD). Integrating HTL with AD and recycling a fraction of the AP in the HTL process allows for efficient wastewater treatment and a recovery of up to 84.8% of the energy contained in the GTW.