Taxonomic and functional characterization of the microbial community involved in obtaining biogas and other compounds of biotechnological interest from citrus peel waste

Author(s)

Franciele Pereira Camargo

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2021-03-11

Examining board members

Maria Bernadete Amancio Varesche Silva; Tânia Forster Carneiro; Fabiana Fantinatti Garboggini; Silvana de Queiroz Silva; Marcelo Zaiat

• Advisor: Maria Bernadete Amancio Varesche Silva; Iolanda Cristina Silveira Duarte

Abstract

Energy recovery from lignocellulosic biomass, such as citrus peel waste (CPW), has been studied as an alternative to its reuse. This research aimed at evaluating the use of CPW as substrate to obtain H2 and other by-products in batch reactors, as well as characterizing the microbial community involved in this process. It was possible to obtain an autochthonous consortium through the self-fermentation of CPW, in addition to isolating a strain similar to Enterococcus casseliflavus (99%), as well as obtaining its growth kinetic parameters in glucose, namely specific growth (μ = 0.35 h), generation time (Tg = 1.98 h-1), maximum H2 concentration potential (P = 9.1 mmol H2.L-1), maximum H2 production rate (Rm = 1.99 mmol H2.h-1) and starting time of H2 production (λ = 4.08 h). The effect of hydrothermolysis (180 °C; 15 minutes) and alkaline delignification (NaOH 5 mol.L-1; 1% H2O2; 24 hours) pretreatments in CPW were evaluated, where it was observed that the H2 obtainment was higher in reactors containing fresh CPW (13.31 mmol H2.L-1) when compared to hydrothermolysis (P = 8.19 mmol H2.L-1) and alkaline delignification (P = 7.27 mmol H2.L-1). By means of applying the Plackett & Burman statistical method, the variables pH (5.5,7.0 and 8.5), temperature (30, 37 and 44 °C), inoculum (1, 2 and 3 gSTV.L-1) and CPW (5,10 and 15 g.L-1) concentrations, headspace volume (40, 50 and 60%) and components of the culture medium were evaluated, namely yeast extract (0, 0.5 and 1 g.L-1), CaCO3, NaCl and peptone (0, 2.5 and 5 g.L-1) concentrations, with pH, inoculum and CPW concentrationthe most significant variables. The optimal condition established by the Rotational Central Composite Design was 4 gSTV.L-1 of inoculum (sludge of sugarcane vinasse anaerobic treatment), 29.8 g.L-1 of CPW and pH 8.98, with maximum production of 48.47 mmol H2.L-1. After the shotgun sequencing, it was possible to confirm, from differential gene expression, that the cellulose degradation acetogenic pathways were overexpressed in the optimized reactor, with Clostridium and Paraclostridium the most abundant genera. (AU)

• FAPESP's process: 17/01722-0 - Biogas obtainment and other compounds of biotechnological interest from citrus/orange processing residues
• Grantee: Franciele Pereira Camargo
• Support Opportunities: Scholarships in Brazil - Doctorate