Anaerobic digestion of post hydrothermal liquefaction wastewater of spent coffee grounds

Author(s)

Maria Eduarda Simões Dias

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2020-02-18

Examining board members

Giovana Tommaso; Marcia Helena Rissato Zamariolli Damianovic; Kelly Johana Dussan Medina

• Advisor: Giovana Tommaso

Abstract

This project aimed the structuring of an energy balance of the process that includes the production of bio-oil by hydrothermal liquefaction of the spent coffee grounds and biogas recovery from the study of anaerobic biodegradability of the effluent resulting from this emerging physicochemical process. The system proposed the waste recovery by using it in the biofuels production to meet growing energy demand and dissociate the focus from the use of fossil fuels. The hydrothermal liquefaction process was conducted by means of an association between the high moisture solid fraction, spent coffee grounds, residue of the soluble coffee production process, and water in a 1:20 ratio, at a temperature of 275 °C and time of 10 minutes. After the hydrothermal liquefaction reaction, a characterization stage of the effluent was conducted. After the characterization, anaerobic biodegradability of the effluent and adaptation of anaerobic sludge was carried out. After characterization, the study proceeded to the anaerobic effluent assays. The sludge previously exposed to the effluent was applied in variant initial COD assays aimed at the determination of biogas production, in order to obtain kinetic parameters of the anaerobic digestion of the effluent as substrate. The assays were carried out in 1000 ml flasks operated in batch and subjected to N2 atmosphere at 37 °C. Calculating the kinetic constants, the intermediate digestion compounds were determined. Once determined the volatile acids, a mathematical modeling was performed according to the Anaerobic Digestion Model No 01 (ADM1). The model proposed by Wu et al. (1988) presented the highest correlation coefficient (R²) when adjusted to experimental data of effluent degradation kinetics. For this adjustment, the n index was 4.61 ± 0.93, which indicates intense inhibition by substrate excess at concentrations above 5304 ± 235 mg L-1. The modified ADM1 modeling of the data indicated inhibition of hydrogenotrophic and acetoclastic methanogenesis due to the toxicity of the effluent. (AU)

• FAPESP's process: 18/16268-6 - Anaerobic digestion of post hydrothermal liquefaction wastewater of spent coffee grounds
• Grantee: Maria Eduarda Simoes Dias
• Support Opportunities: Scholarships in Brazil - Master