Dark fermentation effectiveness as a key step for waste biomass refineries: influence of organic matter macromolecular composition and bioavailability

Abstract

SUMMARYIn next generation bio-based refineries, hydrolysis and primary (or extractive) fermentations by undefined microbial cultures (UMC) are precursors of secondary bio-transformations, in which H 2 , CO 2 and mixed carboxylates are used as substrate for achieving added-value target products (e.g. bio-based chemicals, bio-plastics and pigments). Dark fermentation (DF) is the most simple UMC-driven hydrolysis and primary fermentations to extract gaseous and soluble mixtures of compounds from raw biomass. Which solid fractions (types of macro-molecules) of mixed raw organic matter (OM) are efficiently hydrolyzed + fermented during DF is an aspect that was rarely considered in depth.Here, a first attempt was made to propose a new approach for understanding the effects of DF on different fractions of biomass. A set of seven different biomasses underwent optimized DF tests and, for simplicity, only the gaseous main product, i.e. bio-hydrogen potential (BHP) production, was used as parameter to assess DF efficacy. BHP was studied in relation with OM characteristics: on one side, chemical composition (macro-molecular fractions) and, on the other side, bioavailability to UMC attack (using two different biological assays). BHP was found significantly correlated (Pearson's test for p < 0.05, n = 7) only to acid detergent lignin (negatively), soluble sugars and sugars + starch (positively). Bioavailability was negatively correlated with fibrous fractions and to fat-like fractions, but correlations with BHP were poorer (p > 0.05, n = 7). A statistical model (partial least square regression) was proposed for predicting BHP from OM characteristics, with interesting predictability. In the next future, the proposed approach should be widened to better understand the DF effectiveness not only referred to its gaseous products, but especially focusing on the wide range of soluble products (carboxylates), thought as substrates for secondary biorefinery.

Nitrogen‐doping activated biomass carbon from tea seed shell for CO 2 capture and supercapacitor

“…1 Much attention has been paid on conversion of biomass into bio-oil, bio-char, and fuel gases by thermal-chemical methods. 2,3 Activated carbon is carbonaceous material containing developed internal pore structure with high specific surface area. 4 It is an ideal carbon material that has great application in many fields.…”

A Comprehensive Understanding of Electro-Fermentation

“…Electro-fermentation (EF) is a fairly new field that can manipulate microbe metabolism by utilizing solid-state electrodes as electron mediators wherein the anodic terminal is used as an electron acceptor and the cathodic terminal as an electron donor ( Figure 2) [10]. All the electrochemical redox reactions can be catalyzed by incorporating a microbial environment with electrochemistry, which the EF approach is known for [27]. The relationship between electrochemical and biochemical reactions together helps in inhibiting the thermochemical limitations of conventional AF.…”

“…Other applications in lactic acid fermentation using secondary and waste products could use hyperthermophilic strains. Even in the presence of waste effluents, the purity of the culture can be maintained due to the presence of the extreme temperature conditions (80 to 90 • C) [27]. Thermotoga neapolitana, a Gram-negative bacterium, supports dark fermentation, which is an efficient way to produce lactic acid; this bacterium grows most efficiently over about 80 • C. The hence produced lactic acid, along with the other substrates, can be used as feed for cultures.…”

“…Thermotoga neapolitana, a Gram-negative bacterium, supports dark fermentation, which is an efficient way to produce lactic acid; this bacterium grows most efficiently over about 80 • C. The hence produced lactic acid, along with the other substrates, can be used as feed for cultures. In the latest experiment, it had been observed that the bacterium T. neapolitana when used with acetic acid and carbon dioxide, enhanced lactic acid production [27]. Capnophilic lactic fermentation is a patented process observed to be a potential advantage where microbial synthesis can be combined with carbon dioxide.…”

Bioelectrochemical synthesis of caproate through chain elongation as a complementary technology to anaerobic digestion

“…Anaerobic digestion is a multifarious process that occurs in a solid‐liquid phase, in which the degradation of solid substrates takes place in the same bioreactor as methanogenic and fermentation processes. This indicates the versatility of the process regarding types of substrates . The BES is still not mature enough to function as a stand‐alone technology for caproate production from wastewater.…”