# Soy-Derived Agroindustrial Byproducts as Sustainable Substrates for Biohydrogen Production via Dark Fermentation

## TL;DR

This study explores using soy-based byproducts to produce biohydrogen through dark fermentation, offering a sustainable energy solution.

## Contribution

A new microbial consortium was developed for efficient biohydrogen production using soybean molasses and soapstock.

## Key findings

- Clostridium butyricum was the dominant species in the microbial consortium.
- Sucrose was the preferred sugar, producing acetic and butyric acids as byproducts.
- Maximum bioH2 production reached 1.6 L per liter of culture medium after 48 hours.

## Abstract

The valorization
of byproducts from biofuel production is crucial
in advancing sustainable energy solutions. Particularly in biodiesel
processes, byproducts such as glycerin, soapstock, and wastewater
with high Chemical Oxygen Demand (COD) and Biological Oxygen Demand
(BOD) contain rich organic content suitable for biological conversion.
Among these, soybean molasses and soapstock stand out as cosubstrates
for dark fermentation to produce biohydrogen. This study aimed to
obtain a new microbial consortium from the sludge of an anaerobic
reactor thermally pretreated at 80 °C for 60 min and its use
in bioH2 production in a culture medium composed of soybean
molasses diluted in a pretreated lysogoma. All experiments were conducted
at bench scale under batch conditions. The physicochemical parameters
(soybean molasses concentration, pH, and temperature) were optimized
using Central Composite Rotatable Design (CCRD) and response surface
analysis. The profiles of bioH2 production, sugar consumption,
and volatile fatty acid production were evaluated through kinetic
analysis under optimal conditions. The kinetic analysis of the points
0, 26, and 54 h was also used to verify the consortium’s behavior
throughout dark-fermentation. Clostridium butyricum was the predominant species in the initial consortium and throughout
fermentation, indicating the success of the inoculum’s thermal
pretreatment method, which resulted in its enrichment with spores
of this microorganism, widely used in dark-fermentation trials. Sucrose
was consumed as the preferred sugar, yielding acetic and butyric acids
as fermentation byproducts. The maximum bioH2 production
was achieved after 48 h of fermentation, resulting in a gas composed
of H2 (57.14%) and CO2 (42.86%), culminating
in a yield of 1.6 L of bioH2/L of culture medium. These
findings underscore the viability of soybean byproducts as sustainable
feedstocks for biological hydrogen production, contributing to circular
bioeconomy strategies and renewable energy development.