Valorization of Biomass Residues by Biosorption of Microelements in a Closed-Loop Cycle

The concept of the research data presented assumes the valorization of goldenrod residues from supercritical CO2 extraction following the circular economy principles. The biomass was enriched with microelements (Cr, Zn, Cu) by biosorption from single and multielemental solutions in batch and packed bed reactors. Modeling of biosorption equilibrium supported by instrumental analysis (SEM and FTIR) of material properties was employed to explain the metal ions binding mechanism. The preferential biosorption of Cr(III) over the divalent ions, allows the possibility of valorization of goldenrod residue in a garden-scale biosorption tank acting as a fixed-bed reactor working in an open circulation run and fed with microelements diluted in rainwater. The use of fertigation solution in optimal doses of micronutrients did not show any phytotoxic effect. Using the post-sorptive solution as a source of micronutrients for plants showed significant effects on growth parameters (increased chlorophyll content by 54%) compared to groups fertilized with commercial formulation (13% higher sprout mass). Additionally, fertigation with the post-sorption solution leads to the biofortification of cucumber sprouts. The recycling process results in two products: enriched biomass as a potential feed additive (with Cr(III), Cu(II), and Zn(II)) and a post-sorption solution (with Zn(II) and Cu(II) only) used in the fertigation of plants. Graphical Abstract

Dynamics and Complexity of Dark Fermentation Microbial Communities Producing Hydrogen From Sugar Beet Molasses in Continuously Operating Packed Bed Reactors

This study describes the dynamics and complexity of microbial communities producing hydrogen-rich fermentation gas from sugar-beet molasses in five packed-bed reactors (PBRs). The bioreactors constitute a part of a system producing hydrogen from the by-products of the sugar-beet industry that has been operating continuously in one of the Polish sugar factories. PBRs with different working volumes, packing materials, construction and inocula were tested. This study focused on analysis (based on 16S rRNA profiling and shotgun metagenomics sequencing) of the microbial communities selected in the PBRs under the conditions of high (>100 cm3/g COD of molasses) and low (<50 cm3/g COD of molasses) efficiencies of hydrogen production. The stability and efficiency of the hydrogen production are determined by the composition of dark fermentation microbial communities. The most striking difference between the tested samples is the ratio of hydrogen producers to lactic acid bacteria. The highest efficiency of hydrogen production (130–160 cm3/g COD of molasses) was achieved at the ratios of HPB to LAB ≈ 4:2.5 or 2.5:1 as determined by 16S rRNA sequencing or shotgun metagenomics sequencing, respectively. The most abundant Clostridium species were C. pasteurianum and C. tyrobutyricum. A multiple predominance of LAB over HPB (3:1–4:1) or clostridia over LAB (5:1–60:1) results in decreased hydrogen production. Inhibition of hydrogen production was illustrated by overproduction of short chain fatty acids and ethanol. Furthermore, concentration of ethanol might be a relevant marker or factor promoting a metabolic shift in the DF bioreactors processing carbohydrates from hydrogen-yielding toward lactic acid fermentation or solventogenic pathways. The novelty of this study is identifying a community balance between hydrogen producers and lactic acid bacteria for stable hydrogen producing systems. The balance stems from long-term selection of hydrogen-producing microbial community, operating conditions such as bioreactor construction, packing material, hydraulic retention time and substrate concentration. This finding is confirmed by additional analysis of the proportions between HPB and LAB in dark fermentation bioreactors from other studies. The results contribute to the advance of knowledge in the area of relationships and nutritional interactions especially the cross-feeding of lactate between bacteria in dark fermentation microbial communities.