The effect of methanogenesis inhibition, inoculum and substrate concentration on hydrogen and carboxylic acids production from cassava wastewater

Abstract

Manipueira is a carbohydrate-rich agro-industrial waste from cassava processing. It is considered well suitable for biotechnological processes, such as hydrogen and carboxylic acids production, due to the high content of easily degradable organic matter. However, the proper methanogenesis inhibition method, inoculum type, and organic loads are factors still limiting the processes. The objective in this work was to evaluate the effects of such factors on byproducts production in anaerobic reactors. Batch experiments were conducted with 2.3-L flasks during two operational phases. In the first phase (P1), inhibition of methanogens in the sludge was evaluated using acetylene (1% v/v of headspace) and heat treatment (120 °C, 1 atm for 30 min). In the second phase (P2), three inoculum types obtained from common anaerobic sludges (bovine rumen and sludges from municipal and textile industrial wastewater treatment plants) were individually assayed. P2 aimed to identify the best inoculum, based on hydrogen production ability, which was tested for three initial concentrations of manipueira in terms of chemical oxygen demand (COD) (10, 20 and 40 g O/L). Results of P1 indicated that either acetylene or heat treatment efficiently inhibited methanogenesis, with no methane production. However, the maximum H production potential by applying heat treatment (~ 563 mL) was more than twice compared with that by acetylene treatment (~ 257 mL); and butyrate was the main carboxylic acid by-product (~ 3 g/L). In P2 experiments after sludge heat treatment, the highest hydrogen yield (1.66 ± 0.07 mol H/mol glucose) and caproic acid production (~ 2 g/L) were observed at 20 g O/L of manipueira COD, when bovine rumen was the inoculum. The primary metabolic degradation products in all P2 experiments were ethanol, acetic, butyric, propionic and caproic acids. The finding of caproic acid detection indicated that the applied conditions in manipueira anaerobic degradation favored carbon chain elongation over methanogenesis.

Medium Chain Carboxylic Acids from Complex Organic Feedstocks by Mixed Culture Fermentation

“…Estimated values were calculated as reported in Appendix A. Data collected from [20,40,70,83,88,90,91,96,101,108,122,126,148,157,161,162,163], the full data for the figure can be consulted in the following database [55].…”

Directional Selection of Microbial Community Reduces Propionate Accumulation in Glycerol and Glucose Anaerobic Bioconversion Under Elevated pCO2

“…However, its accumulation is a symptom of reactor malfunctioning in anaerobic digestion (AD), attributed to dissimilarities between acidogenic, acetogenic, and methanogenic bio-conversion rates ( Hickey and Switzenbaum, 1991 ). The identified causes leading to VFA accumulation are associated with substrate overload ( Amorim et al, 2018 ), possible toxicity due to increasing concentrations of undissociated acids at low pH ( Russell and Diez-Gonzalez, 1998 ), and disparities in the proportionality of acidogenic, syntrophic, and methanogenic microorganisms ( McMahon et al, 2004 ; Li et al, 2016 ; Town and Dumonceaux, 2016 ). When VFA production is targeted under anaerobic conditions, the product spectrum selectivity is influenced by operational parameters such as temperature, substrate type, concentration, pH, solids retention time (SRT) and headspace composition ( Arslan et al, 2016 ; Zhou et al, 2018 ; Wainaina et al, 2019 ).…”

Acidogenic Fermentation of Sugarcane Vinasse and Glucose Using Two Different Anaerobic Digestion Inocula

“…For some metabolites concentration profiles, modified Gompertz equation, typically employed to model accumulated hydrogen content in anaerobic digestion aiming biogas generation (CHEN et al , 2006; AMORIM et al , 2017), was used to describe kinetics of production. …”