Long-Term Continuous Extraction of Medium-Chain Carboxylates by Pertraction With Submerged Hollow-Fiber Membranes

A preliminary study on the feasibility of industrialization for n-caproic acid recovery from food wastewater: From lab to pilot

Food wastewater is associated with greenhouse gas emission and has a significant water footprint. Here, the platform chemical n-caproate was recovered from liquor brewing wastewater at maximum and mean concentrations of 26.4 g/L and 17.0 ± 4.3 g/L, respectively, after 377 d operation. Laboratory-scale lactate-driven chain elongation (CE) process was implemented first. Taxonomic composition and metagenomic data analyses revealed that Caproiciproducens (e.g., Ruminococcaceae bacterium CPB6) and bacteria affiliated with Lachnospiraceae transformed lactate to n-caproate by reverse β-oxidation and/or fatty acid biosynthesis. The lactate-driven CE process was then scaled up from 2.5 L to 500 L and achieved a n-caproate production of 14.5 ± 0.6 g/L within 96 h. n-Caproic acid was extracted at a concentration and purity of 815.9 ± 8.3 g/L and 88.6 ± 8.9 %, respectively. The present study demonstrated a commercially viable strategy for resource recovery and carbon fixation from food waste streams.

Degradation of Cellulose and Hemicellulose by Ruminal Microorganisms

As major structural components of plant cell walls, cellulose and hemicellulose are degraded and fermented by anaerobic microbes in the rumen to produce volatile fatty acids, the main nutrient source for the host. Cellulose degradation is carried out primarily by specialist bacteria, with additional contributions from protists and fungi, via a variety of mechanisms. Hemicelluloses are hydrolyzed by cellulolytic bacteria and by generalist, non-cellulolytic microbes, largely via extracellular enzymes. Cellulose hydrolysis follows first-order kinetics and its rate is limited by available substrate surface area. Nevertheless, its rate is at least an order of magnitude more rapid than in anaerobic digesters, due to near-obligatory adherence of microbial cells to the cellulose surface, and a lack of downstream inhibitory effects; in the host animal, fiber degradation rate is also enhanced by the unique process of rumination. Cellulolytic and hemicellulolytic microbes exhibit intense competition and amensalism, but they also display mutualistic interactions with microbes at other trophic levels. Collectively, the fiber-degrading community of the rumen displays functional redundancy, partial niche overlap, and convergence of catabolic pathways that all contribute to stability of the ruminal fermentation. The superior hydrolytic and fermentative capabilities of ruminal fiber degraders make them promising candidates for several fermentation technologies.

Recovery Techniques Enabling Circular Chemistry from Wastewater

In an era where it becomes less and less accepted to just send waste to landfills and release wastewater into the environment without treatment, numerous initiatives are pursued to facilitate chemical production from waste. This includes microbial conversions of waste in digesters, and with this type of approach, a variety of chemicals can be produced. Typical for digestion systems is that the products are present only in (very) dilute amounts. For such productions to be technically and economically interesting to pursue, it is of key importance that effective product recovery strategies are being developed. In this review, we focus on the recovery of biologically produced carboxylic acids, including volatile fatty acids (VFAs), medium-chain carboxylic acids (MCCAs), long-chain dicarboxylic acids (LCDAs) being directly produced by microorganisms, and indirectly produced unsaturated short-chain acids (USCA), as well as polymers. Key recovery techniques for carboxylic acids in solution include liquid-liquid extraction, adsorption, and membrane separations. The route toward USCA is discussed, including their production by thermal treatment of intracellular polyhydroxyalkanoates (PHA) polymers and the downstream separations. Polymers included in this review are extracellular polymeric substances (EPS). Strategies for fractionation of the different fractions of EPS are discussed, aiming at the valorization of both polysaccharides and proteins. It is concluded that several separation strategies have the potential to further develop the wastewater valorization chains.