Post-hydrothermal Wastewater Research Articles

Anaerobic digestion model number 1 applied to the modeling of anaerobic digestion of residues generated in soluble coffee processing

The Anaerobic Digestion Model No. 1 (ADM1) was applied in this study to simulate the anaerobic digestion (AD) of wastewaters from soluble coffee processing in sequential batch reactors. As these substrates present considerable levels of phenolic compounds, modifications were made to the basic structure of the ADM1. Additionally, the Luong inhibition model replaced the Monod model to describe the consumption of soluble organic matter. On the other hand, the removal of phenolic compounds was carried out using the Haldane model, appropriate when the inhibition by excess substrate is present, taking into account in this case the quantification of phenols and benzoic acid as total phenols. The new ADM1-based model was calibrated with experimental data from the AD of post hydrothermal wastewater (PHWW) of spent coffee grounds (SCG) and validated with experimental data of the AD of effluents produced during the soluble coffee processing. The simulation results demonstrated that the new model moderately described the removal of phenolic compounds ( > 90 %), methane production (2.243 kgCODm−3 in calibration and 6.16 kgCODm−3 in validation), and the production and consumption of organic acids over time. However, in future research new metabolic pathways may be included in the model to improve its quality even more.

From sweet sorghum to supercapacitor and biogas: A new utilization strategy for an energy crop

To seek a possible path to being carbon neutral by using an energy crop, a comprehensive model integrating energy storage and energy supply was developed utilizing sorghum juice as raw material. We prepared a microporous activated carbon with an ultra-high surface area of 3278 m2 g−1 by integrating hydrothermal carbonization, high temperature pyrolysis, and KOH activation. The resulting supercapacitor electrode exhibited a high specific capacitance (314.0 F g−1), exceptional cycling stability (99.3% after 10,000 cycles), and a considerable energy density (8.6 Wh kg−1). Additionally, ∼570 kg ha−1 methane can be produced from the post-hydrothermal waste water through anaerobic digestion, which can compensate for the energy consumed in preparing carbon and allow for a cleaner process. This work offers a novel concept for integrating energy storage, carbon sequestration, and energy supply from energy crops.

Anaerobic digestion of hydrothermal liquefaction wastewater from spent coffee grounds

Spent coffee grounds (SCG) are high water content lignocellulosic residues generated in large amounts by the instant coffee production industry. Recent interest in the use of SCG as biomass for biocrude oil production via hydrothermal liquefaction (HTL) pointed to the generation of an aqueous effluent rich in organic matter of high aromaticity, denominated post hydrothermal wastewater (PHWW). The anaerobic digestion of PHWW was investigated as a treatment option and was evaluated for its energy recovery potential through methane production. Sequencing batch reactors were subjected to increasing initial chemical oxygen demand (COD) levels from 1000 mg COD L−1 to 8000 mg COD L−1, to allow for gradual biomass adaptation to the substrate recalcitrance and toxicity. The highest COD removal rate was observed for an initial COD level of 4000 mg COD L−1. Under this condition, the average methane yield was 187 ± 13 mLCH4 g−1 CODadded, with average COD and total phenols removal efficiencies of 60 ± 1% and 48 ± 4%, respectively. A kinetic evaluation revealed that the methane yield decreased sharply for initial phenolic compounds concentrations above 900 mg GAE L−1. Methane production represented a 22.8% increase in the energy recovered from SCG.