Biomethane technology for grid injection

This is a poster that describes the state-of-the art and perspectives for biomethane as technology for grid injectio

Electricity-assisted production of caproic acid from grass

Background: Medium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse beta-oxidation of lactic acid, generated from low value lignocellulosic biomass. In situ extraction of caproic acid can be achieved by membrane electrolysis coupled to the fermentation process, allowing recovery by phase separation. Results: Grass was fermented to lactic acid in a leach-bed-type reactor, which was then further converted to caproic acid in a secondary fermenter. The lactic acid concentration was 9.36 +/- 0.95 g L-1 over a 33-day semi-continuous operation, and converted to caproic acid at pH 5.5-6.2, with a concentration of 4.09 +/- 0.54 g L-1 during stable production. The caproic acid product stream was extracted in its anionic form, concentrated and converted to caproic acid by membrane electrolysis, resulting in a >70 wt% purity solution. In a parallel test exploring the upper limits of production rate through cell retention, we achieved the highest reported caproic acid production rate to date from a lignocellulosic biomass (grass, via a coupled process), at 0.99 +/- 0.02 g(-)L(-1) h(-1). The fermenting microbiome (mainly consisting of Clostridium IV and Lactobacillus) was capable of producing a maximum caproic acid concentration of 10.92 +/- 0.62 g L-1 at pH 5.5, at the border of maximum solubility of protonated caproic acid. Conclusions: Grass can be utilized as a substrate to produce caproic acid. The biological intermediary steps were enhanced by separating the steps to focus on the lactic acid intermediary. Notably, the pipeline was almost completely powered through electrical inputs, and thus could potentially be driven from sustainable energy without need for chemical input

MaB-flocs for a more sustainable wastewater treatment

Conventional wastewater treatment with activated sludge has a large carbon footprint, high aeration rates are combined with CO2 emission from bacteria. By using micro-algal bacterial flocs (MaB-flocs), CO2 could be captured within the biomass and oxygen could be produced in situ. In order to maximize this photosynthetic aeration and CO2 mitigation, we investigated whether inorganic carbon could alter the algae/bacteria ratio while keeping a good removal performance and settleability of the MaB-flocs. Therefore, three illuminated sequencing batch reactors with MaB-flocs were fed with synthetic wastewater enriched with 84.2, 42.1 and 0 mg L-1 C-KHCO3 supplemented with 0, 42.1, 84.2 mg L-1 C-sucrose, respectively, representing the inorganic carbon source compared to an organic carbon source. Bicarbonate significantly increased the chlorophyll a concentration of the MaB-flocs, but only poor settling flocs could be obtained causing a high turbidity of the effluent. Moreover, significant lower nitrogen removal efficiencies were measured feeding bicarbonate compared to sucrose and the pH increased (9.5). Sucrose benefited a good reactor performance and showed a good settleability of MaB-flocs. Despite the lower chlorophyll a concentration of the biomass and the lower in situ oxygen concentration, average soluble COD removal efficiencies of 95 % were achieved with sucrose. Furthermore sucrose was successful in containing the optimal pH at 7. This study shows the importance of the carbon source for a good reactor performance. As a consequence, the inorganic/organic carbon ratio of the wastewater should be taken into account when algal bacterial reactors are used for wastewater treatment

Acetate accumulation enhances mixed culture fermentation of biomass to lactic acid

Lactic acid is a high-in-demand chemical, which can be produced through fermentation of lignocellulosic feedstock. However, fermentation of complex substrate produces a mixture of products at efficiencies too low to justify a production process. We hypothesized that the background acetic acid concentration plays a critical role in lactic acid yield; therefore, its retention via selective extraction of lactic acid or its addition would improve overall lactic acid production and eliminate net production of acetic acid. To test this hypothesis, we added 10 g/L of acetate to fermentation broth to investigate its effect on products composition and concentration and bacterial community evolution using several substrate-inoculum combinations. With rumen fluid inoculum, lactate concentrations increased by 80 +/- A 12 % (cornstarch, p 69 % lactic acid bacteria (LAB), predominantly Lactobacillaceae. Higher acetate concentration promoted a more diverse LAB population, especially on non-inoculated bottles. In subsequent tests, acetate was added in a semi-continuous percolation system with grass as substrate. These tests confirmed our findings producing lactate at concentrations 26 +/- A 5 % (p < 0.05) higher than the control reactor over 20 days operation. Overall, our work shows that recirculating acetate has the potential to boost lactic acid production from waste biomass to levels more attractive for application