Influence of Inhibitory Compounds on Biofuel Production from Oxalate-Rich Rhubarb Leaf Hydrolysates Using Thermoanaerobacter thermohydrosulfuricus Strain AK91

Abstract

The present investigation is on bioethanol and biohydrogen production from oxalate-rich rhubarb leaves which are an underutilized residue of rhubarb cultivation. Rhubarb leaves can be the feedstock for bioethanol and biohydrogen production using thermophilic, anaerobic bacteria. The fermentation of second-generation biomass to biofuels by Thermoanaerobacter has already been reported as well as their high ethanol and hydrogen yields although rhubarb biomass has not been examined for this purpose. Thermoanaerobacter thermohydrosulfuricus strain AK91 was characterized (temperature and pH optima, substrate utilization spectrum) which demonstrates that the strain can utilize most carbohydrates found in lignocellulosic biomass. Additionally, the influence of specific culture conditions, namely the partial pressure of hydrogen and initial glucose concentration, were investigated in batch culture and reveals that the strain is inhibited. Additionally, batch experiments containing common inhibitory compounds, namely carboxylic acids and aldehydes, some of which are present in high concentrations in rhubarb. Strain AK91 is not affected by alkanoic carboxylic acids and oxalate up to at least 100 mM although the strain was inhibited by 40 mM of malate. Interestingly, strain AK91 demonstrated the ability to reduce alkanoic carboxylic acids to their primary alcohols; more detailed studies with propionate as a model compound demonstrated that AK91’s growth is not severally impacted by high propionate loadings although 1-propanol titers did not exceed 8.5 mM. Additionally, ethanol and hydrogen production from grass and rhubarb leaf hydrolysates was investigated in batch culture for which AK91 produced 7.0 and 6.3 mM g−1, respectively.

Biogas Production from Organic Wastes: Integrating Concepts of Circular Economy

“…The first one derived from the fermentation of sugars, needing a great energy demand for separating the alcohol from the broth, and the second not being exempt from debate due to the origin of vegetable oils. The use of lignocellulosic biomass for producing ethanol (second-generation ethanol) is an alternative for increasing the availability of materials dedicated to biofuel production, but it also implies the application of pre-treatments, increasing the demand for energy and the formation of undesirable compounds that inhibit the fermentation [140]. Biogas is easily separated from the biological reactor because it forms a differentiated gas phase.…”

Data Science and Plant Metabolomics

“…Gene expression analysis can also be used to study the regulation of metabolic pathways and identify the genes responsible for the production of specific metabolites [ 128 , 129 ]. Some plants contain cyanide or other poisons [ 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 ]. Machine learning-based classification algorithms can be used to classify cells of different plant species based on their metabolic profiles and predict the potential production of harmful metabolites, such as allelochemicals and cyanide.…”