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BACKGROUND The high rate production of n‐caproic acid (C6) through chain elongation can be achieved with the use of pertraction systems for the continuous and selective extraction of C6. However, although the biological conversion processes are enhanced at a neutral pH, high extraction efficiency depends on acidic conditions. Understanding of these divergent pH effects is fundamental for a reliable operation and scale‐up of these C6‐producing systems. RESULTS: A bench‐scale anaerobic filter (12.8 L) fed with fermented sugarcane at organic loading rates of ≈7.2 g of chemical oxygen demand (COD) L−1 day−1 achieved C6 production rates of 2.1 and 3.8 gCOD L−1 day−1, without and with in‐line extraction, respectively. Compared to previous studies, a high average extraction rate of 24.7 gCOD m−2 day−1 was observed due to a high reactor volume‐to‐membrane‐area ratio. The novel model described here with biological and pertraction processes for continuously operated systems indicates that an optimal operative pH can simultaneously maximize C6 production and extraction. The hydraulic retention time was another key parameter for balancing inhibition by undissociated C6 and losses due to nonextracted C6. CONCLUSIONS: Sugarcane biorefineries can produce C6, which has a market value that is >10‐fold higher than ethanol. Simulations of chain elongation processes require the implementation of hydrogenotrophic methanogens to allow for a comprehensive description of ethanol consumption together with the C6 formation, in‐line C6 extraction processes, and formation of gaseous by‐products. Although these simulations were possible using parameter sets from the literature, further studies are needed for parameter identification, especially under inhibition at low pH. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary: Pure (single) cultures of microorganisms and mixed microbial communities (microbiomes) have been important for centuries in providing renewable energy, clean water and food products to human society and will continue to play a crucial role to pursue the Sustainable Development Goals. To use microorganisms effectively, microbial engineered processes require adequate control. Microbial communities are shaped by manageable deterministic processes, but also by stochastic processes, which can promote unforeseeable variations and adaptations. Here, we highlight the impact of stochasticity in single culture and microbiome engineering. First, we discuss the concepts and mechanisms of stochasticity in relation to microbial ecology of single cultures and microbiomes. Second, we discuss the consequences of stochasticity in relation to process performance and human health, which are reflected in key disadvantages and important opportunities. Third, we propose a suitable decision tool to deal with stochasticity in which monitoring of stochasticity and setting the boundaries of stochasticity by regulators are central aspects. Stochasticity may give rise to some risks, such as the presence of pathogens in microbiomes. We argue here that by taking the necessary precautions and through clever monitoring and interpretation, these risks can be mitigated. [ABSTRACT FROM AUTHOR]

Despite its long history of technological development, much charcoal production still relies on polluting and inefficient technologies utilizing traditional kiln designs. In addition to the need for improved charcoal production systems, the growing interest globally in pyrolysis of biomass to generate biochar as a soil fertility improver and for climate change mitigation may drive an increasing demand for such technologies. Accordingly, there is a clear need in developing countries for access to safe, affordable, and efficient open-source designs and technology that can be fabricated locally. The design described here includes computational fluid dynamics modeling which demonstrated that the design exhibits a stable flow and combustion pattern. A hazard and operability (HAZOP) study, mass and energy modeling, and costing of all components and fabrication were also conducted for a prototype kiln that will accept up to 250 kg biomass h-1. Fabrication and installation costs were estimated using actual commercial quotations based on detailed engineering drawings and design, and were found to be $580 000 for a 250 kg h-1 unit. We therefore find that this pyrolysis system promises to be economical on a small scale. It can utilize waste lignocellulosic materials for feedstock, thus alleviating demand pressure on woodlands to provide feedstocks. It was, therefore, concluded that the pyrolysis unit described here promises to provide an affordable and efficient open-source design that can be fabricated locally in developing countries without licensing restrictions or royalties. © 2017 The Authors Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

ABSTRACT Syngas fermentation is an anaerobic bioprocess that could become industrially relevant as a biorefinery platform for sustainable production of fuels and chemicals. An important prerequisite for commercialization is adequate performance of the biocatalyst (i.e., sufficiently high production rate, titer, selectivity, yield, and stability of the fermentation). Here, we compared the performance of three potential candidate Clostridium strains in syngas-to-ethanol conversion: Clostridium ljungdahlii PETC, C. ljungdahlii ERI-2, and Clostridium autoethanogenum JA1-1. Experiments were conducted in a two-stage, continuously fed syngas-fermentation system that had been optimized for stable ethanol production. The two C. ljungdahlii strains performed similar to each other but different from C. autoethanogenum. When the pH value was lowered from 5.5 to 4.5 to induce solventogenesis, the cell-specific carbon monoxide and hydrogen consumption (similar rate for all strains at pH 5.5), severely decreased in JA1-1, but hardly in PETC and ERI-2. Ethanol production in strains PETC and ERI-2 remained relatively stable while the rate of acetate production decreased, resulting in a high ethanol/acetate ratio, but lower overall productivities. With JA1-1, lowering the pH severely lowered rates of both ethanol and acetate production; and as a consequence, no pronounced shift to solventogenesis was observed. The highest overall ethanol production rate of 0.301 g · L−1 · h−1 was achieved with PETC at pH 4.5 with a corresponding 19 g/L (1.9% w/v) ethanol concentration and a 5.5:1 ethanol/acetate molar ratio. A comparison of the genes relevant for ethanol metabolism revealed differences between C. ljungdahlii and C. autoethanogenum that, however, did not conclusively explain the different phenotypes. Biotechnol. Bioeng. 2016;113: 531-539. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Obtaining a reliable estimation of the methane potential of organic waste streams in anaerobic digestion, for which a biochemical methane potential ( BMP) test is often used, is of high importance. Standardization of this BMP test is required to ensure inter-laboratory repeatability and accuracy of the BMP results. Therefore, guidelines were set out; yet, these do not provide sufficient information concerning origin of and the microbial community in the test inoculum. Here, the specific contribution of the methanogenic community on the BMP test results was evaluated. The biomethane potential of four different substrates (molasses, bio-refinery waste, liquid manure and high-rate activated sludge) was determined by means of four different inocula from full-scale anaerobic digestion plants. A significant effect of the selected inoculum on the BMP result was observed for two out of four substrates. This inoculum effect could be attributed to the abundance of methanogens and a potential inhibiting effect in the inoculum itself, demonstrating the importance of inoculum selection for BMP testing. We recommend the application of granular sludge as an inoculum, because of its higher methanogenic abundance and activity, and protection from bulk solutions, compared with other inocula. [ABSTRACT FROM AUTHOR]

ABSTRACT Many bioelectrochemical systems (BESs) harness the ability of electrode-active microbes to catalyze reactions between electrodes and chemicals, often to perform useful functions such as wastewater treatment, fuel production, and biosensing. A microbial fuel cell (MFC) is one type of BES, which generates electric power through microbial respiration with an anode as the electron acceptor, and typically with oxygen reduction at the cathode to provide the terminal electron acceptor. Oxygen intrusion into MFCs is typically viewed as detrimental because it competes with anodes for electrons and lowers the coulombic efficiency. However, recent evidence suggests that it does not necessarily lead to lower performances-particularly for the model organism Shewanella oneidensis MR-1. Because flavin-mediated electron transfer is important for Shewanella species, which can produce this electron shuttle endogenuously, we investigated the role of flavins in the performance of pure-culture BESs with S. oneidensis MR-1 with and without oxygen. We found that oxygen increases current production more than twofold under continuously fed conditions, but only modestly increases current production under batch-fed conditions. We hypothesized that oxygen is more beneficial under continuously fed conditions because it allows S. oneidensis to grow and produce flavins at a faster rate, and thus lowers flavin washout. Our conclusions were supported by experiments with a flavin-secretion deficient mutant of S. oneidensis. Biotechnol. Biotechnol. Bioeng. 2014;111: 692-699. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT Bacteroides thetaiotaomicron is a prominent member of the human distal gut microbiota that specializes in breaking down diet and host-derived polysaccharides. While polysaccharide utilization has been well studied in B. thetaiotaomicron, other aspects of its behavior are less well characterized, including the factors that allow it to maintain itself in the gut. Biofilm formation may be a mechanism for bacterial retention in the gut. Therefore, we used custom GeneChips to compare the transcriptomes of biofilm and planktonic B. thetaiotaomicron during growth in mono-colonized chemostats. We identified 1,154 genes with a fold-change greater than 2, with confidence greater than or equal to 95%. Among the prominent changes observed in biofilm populations were: (i) greater expression of genes in polysaccharide utilization loci that are involved in foraging of O-glycans normally found in the gut mucosa; and (ii) regulated expression of capsular polysaccharide biosynthesis loci. Hierarchical clustering of the data with different datasets, which were obtained during growth under a range of conditions in minimal media and in intestinal tracts of gnotobiotic mice, revealed that within this group of differentially expressed genes, biofilm communities were more similar to the in vivo samples than to planktonic cells and exhibited features of substrate limitation. The current study also validates the use of chemostats as an in vitro 'gnotobiotic' model to study gene expression of attached populations of this bacterium. This is important to gut microbiota research, because bacterial attachment and the consequences of disruptions in attachment are difficult to study in vivo. Biotechnol. Bioeng. 2014;111: 165-173. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Short-chain carboxylic acids generated by various mixed- or pure-culture fermentation processes have been considered valuable precursors for production of bioalcohols. While conversion of carboxylic acids into alcohols is routinely performed with catalytic hydrogenation or with strong chemical reducing agents, here, a biological conversion route was explored. The potential of carboxydotrophic bacteria, such as Clostridium ljungdahlii and Clostridium ragsdalei, as biocatalysts for conversion of short-chain carboxylic acids into alcohols, using syngas as a source of electrons and energy is demonstrated. Acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, and n-caproic acid were converted into their corresponding alcohols. Furthermore, biomass yields and fermentation stoichiometry from the experimental data were modeled to determine how much metabolic energy C. ljungdahlii generated during syngas fermentation. An ATP yield of 0.4-0.5 mol of ATP per mol CO consumed was calculated in the presence of hydrogen. The ratio of protons pumped across the cell membrane versus electrons transferred from ferredoxin to NAD+ via the Rnf complex is suggested to be 1.0. Based on these results, we provide suggestions how n-butyric acid to n-butanol conversion via syngas fermentation can be further improved. Biotechnol. Bioeng. 2013; 110: 1066-1077. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We report a laminar flow-based microfluidic bioelectrochemical system (BES) that was fabricated by using polydimethyl siloxane (PDMS) channels and gold electrodes. The microfluidic BES was operated as a potentiostatically controlled two-electrode system. A pure culture of Geobacter sulfurreducens strain PCA, which is a model electrode-respiring bacterium, was grown in the channel and respired with the electrode under strict anaerobic conditions. We took advantage of the short hydraulic retention time (≈2 min) and response times (<21 min) to rapidly test the effect of certain chemical stimuli, such as O2 and anthraquinone disulfide (AQDS), on electric current production by G. sulfurreducens. The results showed that: i) short-term (2 min) exposure to O2-saturated solution did not cause any irreversible toxicity to G. sulfurreducens, and ii) AQDS can be used as a redox mediator by G. sulfurreducens for shuttling electrons between the microbe and the electrode. We, therefore, demonstrate that the microfluidic BES is a promising research tool for gaining insight into microbial electrochemical activity. In our two-dimensional microfluidic-based research tool, a well-defined electrochemical environment can be maintained with the help of laminar flow without a membrane to separate two electrodes. [ABSTRACT FROM AUTHOR]

n-Butanol was produced continuously in a two-stage fermentor system with integrated product removal from a co-feed of n-butyric acid and glucose. Glucose was always required as a source of ATP and electrons for the conversion of n-butyrate to n-butanol and for biomass growth; for the latter it also served as a carbon source. The first stage generated metabolically active planktonic cells of Clostridium saccharoperbutylacetonicum strain N1-4 that were continuously fed into the second (production) stage; the volumetric ratio of the two fermentors was 1:10. n-Butanol was removed continuously from the second stage via gas stripping. Implementing a two-stage process was observed to dramatically dampen metabolic oscillations (i.e., periodical changes of solventogenic activity). Culture degeneration (i.e., an irreversible loss of solventogenic activity) was avoided by periodical heat shocking and re-inoculating stage 1 and by maintaining the concentration of undissociated n-butyric acid in stage 2 at 3.4 mM with a pH-auxostat. The system was successfully operated for 42 days during which 93% of the fed n-butyrate was converted to n-butanol at a production rate of 0.39 g/(L × h). The molar yields Y n-butanol/ n-butyrate and Y n-butanol/glucose were 2.0, and 0.718, respectively. For the same run, the molar ratio of n-butyrate to glucose consumed was 0.358. The molar yield of carbon in n-butanol produced from carbon in n-butyrate and glucose consumed (Y n-butanol/carbon) was 0.386. These data illustrate that conversion of n-butyrate into n-butanol by solventogenic Clostridium species is feasible and that this can be performed in a continuous system operating for longer than a month. However, our data also demonstrate that a relatively large amount of glucose is required to supply electrons and ATP for this conversion and for cell growth in a continuous culture. Biotechnol. Bioeng. 2012; 109:913-921. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We investigated bacterial and archaeal community structures and population dynamics in two anaerobic bioreactors processing a carbohydrate- and sulfate-rich synthetic wastewater. A five-compartment anaerobic migrating blanket reactor (AMBR) was designed to promote biomass and substrate staging, which partially separates the processes of methanogenesis and sulfidogenesis in the middle and outer compartment(s) respectively. The second reactor was a conventional, single-compartment upflow anaerobic sludge blanket (UASB) reactor. Both reactors, which were seeded with the same inoculum, performed well when the influent chemical oxygen demand (COD)/SO42– mass ratio was 24.4. The AMBR performed worse than the UASB reactor when the influent COD/SO42– mass ratio was decreased to 5.0 by raising the sulfate load. Terminal restriction fragment length polymorphism analyses of bacterial 16S rRNA genes showed that the increase in sulfate load had a greater impact on bacterial diversity and community structure for the five AMBR compartments than for the UASB reactor. Moreover, bacterial community profiles across AMBR compartments became more similar through time, indicating a converging, rather than a staged community. While similar populations were abundant in both reactors at the beginning of the experiment, fermenting bacteria (clostridia, streptococci), and sulfate-reducing bacteria became more abundant in the AMBR, after shifting to a higher sulfate load, while a novel Thermotogales-like population eventually became predominant in the UASB reactor. A similar shift in the community structure of the hydrogenotrophic methanogens in the AMBR occurred: representatives of the Methanobacteriaceae out-competed the Methanospirillaceae after increasing the sulfate load in the AMBR, while the archaeal community structure was maintained in the UASB. [ABSTRACT FROM AUTHOR]

The article discusses studies regarding molecular methods in environmental engineering, and also mentions information on steps involved in biological waste treatment like activated sludge, nitrogen removal and phosphorus removal.

It has generally been accepted that the formation of granules in anaerobic wastewater treatment systems requires a hydraulic upflow pattern. To evaluate this hypothesis, we operated an anaerobic migrating blanket reactor (AMBR) without a hydraulic upflow pattern, using a synthetic wastewater containing acetate, propionate, butyrate and sucrose. We provided conditions amenable to the formation of granules by operating the system with a moderate hydraulic selection pressure, which in this system was not the result of a hydraulic upflow pattern, but was provided by migration of biomass and intermittent mechanical mixing. Granules were first noticed after 2 months of operation, and it took another 2 months for a mature granular blanket to develop. Besides granules, ≈ 1-cm-long Methanosaeta fibres developed and, after 6 months of operation, 30% of biomass consisted of these fibres. Quantitative membrane hybridization showed that almost all the total 16S rRNA extracted from fibres consisted of 16S rRNA from Methanosaeta concilii. This finding indicates that it was possible to develop pockets consisting almost entirely of an organism with a very limited substrate utilization spectrum (only acetate) in a system that was fed a synthetic wastewater containing acetate, propionate, butyrate and sucrose and that is known for its ability to develop biomass with a complex microbial community structure. [ABSTRACT FROM AUTHOR]

Distributed, wasted, or stranded feedstocks, when converted and upgraded into fuels, could replace about 6% of the U.S. demand for liquid fuels, which is about 25% of the net import of petroleum by the United States. We review the current state of modular approaches for conversion of these feedstocks, including the technology and economics associated with processing carbon‐containing waste and stranded, carbon‐containing gas. The wide geographic distribution of the feedstocks will require technology that can be scaled down effectively and that can be manufactured, installed, operated and monitored in ways that gain economies of mass production rather than economies of throughput scaling. This article is categorized under:Energy Research & Innovation > Science and MaterialsBioenergy > Systems and InfrastructureEnergy Research & Innovation > Systems and Infrastructure Notional, modular system for converting landfill gas to energy products. [ABSTRACT FROM AUTHOR]

The cover image, by Dominic Woolf et al., is based on the In the Field An open-source biomass pyrolysis reactor, DOI: . [ABSTRACT FROM AUTHOR]