Consistent gut bacterial and short-chain fatty acid signatures in hypoabsorptive bariatric surgeries correlate with metabolic benefits in rats.

OBJECTIVE: The study aimed at comparing how changes in the gut microbiota are associated to the beneficial effects of the most clinically efficient hypoabsorptive bariatric procedures, namely Roux-en-Y gastric bypass (RYGB), biliopancreatic diversion with duodenal switch (BPD-DS) and single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S). METHODS: Diet-induced obese (DIO) male Wistar rats were divided into seven groups. In addition to the groups subjected to RYGB, BPD-DS and SADI-S, the following four control groups were included: SHAM-operated rats fed a high-fat diet (SHAM HF), SHAM fed a low-fat diet (SHAM LF), SHAM HF-pair-weighed to BPD-DS (SHAM HF-PW) and sleeve-gastrectomy (SG) rats. Body weight, food intake, glucose tolerance, insulin sensitivity/resistance, and L-cell secretion were assessed. The gut microbiota (16 S ribosomal RNA gene sequencing) as well as the fecal and cæcal contents of short-chain fatty acids (SCFAs) were also analyzed prior to, and after the surgeries. RESULTS: The present study demonstrates the beneficial effect of RYGB, BPD-DS and SADI-S on fat mass gain and glucose metabolism in DIO rats. These benefits were proportional to the effect of the surgeries on food digestibility (BPD-DS > SADI-S > RYGB). Notably, hypoabsorptive surgeries led to consonant microbial signatures characterized by decreased abundance of the Ruminococcaceae (Oscillospira and Ruminococcus), Oscillospiraceae (Oscillibacter) and Christensenellaceae, and increased abundance of the Clostridiaceae (Clostridium), Sutterellaceae (Sutterella) and Enterobacteriaceae. The gut bacteria following hypoabsorptive surgeries were associated with higher fecal levels of propionate, butyrate, isobutyrate and isovalerate. Increases in the fecal SCFAs were in turn positively and strongly correlated with the levels of peptide tyrosine-tyrosine (PYY) and with the beneficial effects of the surgery. CONCLUSION: The present study emphasizes the consistency with which the three major hypoabsorptive bariatric procedures RYGB, BPD-DS and SADI-S create a gut microbial environment capable of producing a SCFA profile favorable to the secretion of PYY and to beneficial metabolic effects.

Synergistic effect of lotus seed resistant starch and short-chain fatty acids on mice fecal microbiota in vitro.

This study aimed to investigate the synergistic effect of lotus seed resistant starch (LRS) and short-chain fatty acids (SCFAs) on mice fecal bacterial flora and the contents of SCFAs in vitro. Following 24 h of fermentation, 16S rRNA analysis revealed several differences in the fecal microbiota community structure among primal bacteria (PB), LRS and different SCFAs combined with LRS groups (SCFAs-LRS). The LRS group increased the relative abundance of Lactobacillus, Allobaculum, Clostridium, Bacteroides and Prevotella. Among the SCFAs-LRS group, AA-LRS increased the relative abundance of Prevotella, and Bacillus. PA-LRS increased abundance of Sphingomonas and the BA-LRS group significantly increased the relative abundance of Rhizobiales, Brucellaceae and Ochrobactrum. Meanwhile, propionic acid and BA productions significantly increased in the BA-LRS group. The SCFAs-LRS group elicited a beneficial effect on the fecal microbiota by increasing production of SCFAs. We highlight the fact that the combination of LRS and SCFA can increase the contents of SCFAs produced by mice fecal microbiota. In short, the combination of LRS and SCFA can influence intestinal flora by promoting the growth of beneficial bacteria and can serve as new prebiotics for promoting health and disease management.

Volatile fatty acid platform - a cornerstone for the circular bioeconomy.

Annually, the EU produces more than 100 million tonnes of urban biowaste, which is largely under-valorized and in some cases even still landfilled without any energy or material recovery. If Europe wants to be ready for the future, it will need to make better use of this large biomass potential within a circular economy approach. The research project funded by the European Commission under the Horizon 2020 programme entitled 'VOLATILE-Biowaste derived volatile fatty acid platform for biopolymers, bioactive compounds and chemical building blocks' aimed to produce volatile fatty acids (VFAs) from biowaste for reprocessing into products, materials or substances to close the material loop. During the project, the partners were able to obtain average volatile fatty acid yields of 627 g COD/kg organic matter (OM) for food waste, 448 g COD/kg OM for separately collected vegetable, garden and fruit waste (VGF) and 384 g COD/kg OM for the organic fraction of municipal solid waste (OF-MSW) at concentrations ranging from 12 to 48 g/L, 6 to 40 g/L and 13 to 26 g/L, respectively. A membrane filtration cascade consisting of micro-, ultra- and nano-filtration followed by reverse osmosis was identified as a feasible way to purify and concentrate the VFA effluent, making them a suitable carbon source for further fermentation processes. Besides technical optimization, socio-economic and legal aspects associated with this platform technology were also studied and show that although this technology is still in development, it is providing an answer to changing societal and market expectations both regarding organic waste treatment and bio-based production strategies. Based on the current technological, economic and market evolutions, it is expected that the VFAP will play an important role in organic waste treatment in the coming years.

Increasing grass hay inclusion level on weaned dairy calf growth, intake, digestibility, and ruminal fermentation.

The objective was to determine effects of increasing grass hay (GH) inclusion level on weaned dairy calf growth, intake, digestibility, and ruminal fermentation. Holstein calves (n = 45) were randomly assigned to 1 of 3 total mixed rations with increasing GH [10, 17.5, or 25% on a dry matter (DM) basis; LGH, MGH, or HGH, respectively]. Calves were weaned at 6 wk of age, housed individually, and studied from 7 to 16 wk of age. Rations, consisting of texturized calf starter (20% crude protein) and coarsely chopped GH, were offered ad libitum as separate components from 7 to 9 wk of age. After 9 wk, feed was offered as a total mixed ration containing the assigned level of GH and fed according to the clean bunk feeding strategy as a means of limiting refusals. Initial 9-wk body weight was 81.6 ± 9 kg (mean ± standard deviation). Intake and growth were measured weekly. Blood samples were collected at 9, 10, 12, 14, and 16 wk of age for analysis of plasma glucose and ß-hydroxybutyrate. Total fecal collection (12 calves; 4 per treatment) was conducted at 11 and 15 wk of age for 4 d consecutively. Rumen samples were collected over the final 24 h of each fecal collection period to evaluate pH and volatile fatty acid profile. Feeds and feces were evaluated for DM, neutral detergent fiber, acid detergent fiber, and starch to estimate total-tract digestibility. Intake and weight gain were analyzed from 7 to 9 wk and 9 to 16 wk, representing pretreatment and treatment periods. No differences were observed between treatments from 7 to 9 wk. However, differences were found from 9 to 16 wk. Final body weight, average daily gain, DM intake, and metabolizable energy intake all decreased with increased GH. However, skeletal frame measurements did not vary between treatments. Plasma ß-hydroxybutyrate tended to decrease with increased GH. No differences were observed in DM or starch digestibility, but neutral detergent fiber and acid detergent fiber digestibility increased with increased GH. Mean rumen pH and total volatile fatty acid did not change with increasing GH inclusion; however, there was an interaction with time indicating that ruminal fermentation patterns throughout the day were different for calves offered MGH and HGH versus those offered LGH. These results indicate that feeding levels of GH >10% reduce growth and intake before 16 wk and alter ruminal fermentation patterns.

Variation Patterns of the Volatiles during Germination of the Foxtail Millet (Setaria Italic): The Relationship between the Volatiles and Fatty Acids in Model Experiments.

Functional and nutritional compounds are increased during foxtail millet germination while bad smell is produced due to the fatty acid oxidation. To eliminate the unpleasant aroma, the origins of the volatiles must be known. A comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry showed forty-nine volatiles containing 8 ketones, 10 aldehydes, 20 alkanes, 4 alcohols, 5 alkenes, and 2 furans were tentatively identified, and they increased during the germination of the foxtail millet. To identify the origin of some volatiles, model experiments by adding 6 fatty acids to the crude enzymes of the foxtail millet was designed, and 17 volatiles could be detected. The saturated fatty acids (palmitic acid and stearic acid) had no contributions to the formation of the volatiles, whereas the unsaturated fatty acid played important roles in the formation of volatiles. Among the unsaturated fatty acids, palmitoleic acid and linoleic acid produced most aldehydes, alcohols, and ketones, while linolenic acid produced the most alkanes and alkenes. This study will be helpful for controlling the smell of germinated seeds from the raw material selection.

B cell-intrinsic epigenetic modulation of antibody responses by dietary fiber-derived short-chain fatty acids.

Short-chain fatty acids (SCFAs) butyrate and propionate are metabolites from dietary fiber's fermentation by gut microbiota that can affect differentiation or functions of T cells, macrophages and dendritic cells. We show here that at low doses these SCFAs directly impact B cell intrinsic functions to moderately enhance class-switch DNA recombination (CSR), while decreasing at higher doses over a broad physiological range, AID and Blimp1 expression, CSR, somatic hypermutation and plasma cell differentiation. In human and mouse B cells, butyrate and propionate decrease B cell Aicda and Prdm1 by upregulating select miRNAs that target Aicda and Prdm1 mRNA-3'UTRs through inhibition of histone deacetylation (HDAC) of those miRNA host genes. By acting as HDAC inhibitors, not as energy substrates or through GPR-engagement signaling in these B cell-intrinsic processes, these SCFAs impair intestinal and systemic T-dependent and T-independent antibody responses. Their epigenetic impact on B cells extends to inhibition of autoantibody production and autoimmunity in mouse lupus models.

Selective Separation of Acetic and Hexanoic Acids across Polymer Inclusion Membrane with Ionic Liquids as Carrier.

This paper first reports on the selective separation of volatile fatty acids (VFAs) (acetic and hexanoic acids) using polymer inclusion membranes (PIMs) containing quaternary ammonium and phosphonium ionic liquids (ILs) as the carrier. The affecting parameters such as IL content, VFA concentration, and the initial pH of the feed solution as well as the type and concentration of the stripping solution were investigated. PIMs performed a much higher selective separation performance toward hexanoic acid. The optimal PIM composed of 60 wt% quaternary ammonium IL with the permeability coefficients for acetic and hexanoic acid of 0.72 and 4.38 µm s-1, respectively, was determined. The purity of hexanoic acid obtained in the stripping solution increased with an increase in the VFA concentration of the feed solution and decreasing HCl concentration of the stripping solution. The use of Na2CO3 as the stripping solution and the involvement of the electrodialysis process could dramatically enhance the transport efficiency of both VFAs, but the separation efficiency decreased sharply. Furthermore, a coordinating mechanism containing hydrogen bonding and ion exchange for VFA transport was demonstrated. The highest purity of hexanoic acid (89.3%) in the stripping solution demonstrated that this PIM technology has good prospects for the separation and recovery of VFAs from aqueous solutions.

Development of an analytical method to detect short-chain fatty acids by SPME-GC-MS in samples coming from an in vitro gastrointestinal model.

Short chain fatty acids (SCFA) are end-products of intestinal bacterial fermentation. The concentrations of fermentation metabolites are closely related to the microbial activity that occurs in various digestive compartments. The fermentation products may vary qualitatively and quantitatively, especially within the colon. The Simulator of the Human Intestinal Microbial Ecosystem (SHIME), an in vitro dynamic and multicompartment model of the human intestinal tract, can be adapted to mimic the piglet gastrointestinal tract. In this context, a quantitative method, based on solid phase microextraction gas chromatography coupled to mass spectrometry (SPME-GC-MS), was developed for the determination of seven short chain fatty acids, i.e. acetic, propionic, butyric, isobutyric, valeric, isovaleric and hexanoic acids, in samples coming from this experimental in vitro gastrointestinal model. The advantage of the SPME-GC-MS technique is that the seven compounds could be determined in a single run, after a simple and rapid sample treatment, without any other extraction than the automatic SPME. The developed method was validated in accordance to the European and US FDA guidelines and showed good specificity/selectivity. In addition, limits of detection and quantification ranged from 8 to 72 mg L-1 and from 16 to 144 mg L-1, respectively. Two internal quality control samples spiked at different concentrations were analyzed to assess the trueness of the developed method, which ranged between 97.7 and 122.4% of the expected value, for the seven compounds analyzed. The method was successfully applied to twenty samples coming from a gastrointestinal model, with different inocula. The developed method might be used as a general method for measuring SCFA in biological samples.

Roseburia intestinalis supernatant ameliorates colitis induced in mice by regulating the immune response.

Inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD), has a complex etiology that may be associated with dysbiosis of the microbiota. Previously, our study revealed significant loss of Roseburia intestinalis from the gut of untreated patients with CD, and that R. intestinalis exerted anti­inflammatory functions in TNBS­induced colitis; however, the function of R. intestinalis supernatant is unknown. Therefore, LPS­induced macrophages, including RAW264.7 macrophages and bone marrow­derived macrophages were treated with R. intestinalis supernatant. The results indicated that R. intestinalis supernatant suppressed expression of interleukin (IL)­6 and signal transducer and activator of transcription 3 (STAT3) by macrophages. Additionally, these findings were further verified in vivo in DSS­ and TNBS­induced mouse models of colitis. It was observed that R. intestinalis supernatant ameliorated IBD colitis by reducing the number of inflammatory macrophages and Th17 cells in the colon, and by downregulating the expression of IL­6 and STAT3. Finally, the non­protein components of R. intestinalis supernatant were examined using gas chromatography­mass spectrometry analysis and identified the presence of short­chain fatty acids. In conclusion, the results of the present study indicated that R. intestinalis supernatant may regulate immune responses and ameliorate colitis.

Volatile Fatty Acid Production from Anaerobic Digestion of Organic Residues.

Short chain volatile fatty acids (VFAs) from acetic acid (C2) to valeric acid (C5) are important starting chemicals for chemical industry. The production of VFAs from rejected resources (organic residues) using self-sustaining technologies has an exciting potential in supporting the US chemical industry to achieve the goal that 20% of chemicals produced in the USA will be bio-based. Acidogenic anaerobic digestion as a robust, well-established, and versatile biological technology can be applied as an alternative approach for the valorization of organic residues (municipal, agricultural, and industrial wastes) by the production of VFAs. In a typical acidogenic anaerobic digestion operation, residue type, pretreatment, reactor operation, and VFA recovery are the key factors that influence VFA production. This chapter discusses these factors and provides an experimental approach of VFA production from organic residues.

Evaluation and Optimization of Sample Handling Methods for Quantification of Short-Chain Fatty Acids in Human Fecal Samples by GC-MS.

The gut microbiota has attracted a great deal of interest in recent years due to its association with many diseases. Short-chain fatty acids (SCFAs), the end products of dietary fiber fermentation by the intestinal microbiota, are among the most frequently discussed gut metabolites. As the sample handling method greatly affects the integrity of data, this study investigated the most important parameters that affect the bias of SCFA comparisons in human fecal studies. An accurate gas chromatography-mass spectrometry (GC-MS) method was first established and validated for quantifying six SCFAs, including acetic, propionic, butyric, isobutyric, isovaleric, and valeric acids. To remove interfering species, we used butanol to extract SCFAs from acidified fecal suspensions. The validated quantification method was then applied to evaluate fecal sample handling protocols. We found that lyophilization of fecal samples can not only minimize bias due to the water content but also provide better stability of SCFAs. Six SCFAs were stable and that their recoveries were higher than 90% after lyophilization. Lyophilization of a large fecal sample is extremely time-consuming, and 1 g of fecal sample is suggested for lyophilization to minimize sampling bias. The interindividual difference was significantly higher than the intra-individual difference when using 1 g of fecal sample to study SCFAs. Finally, an effective protocol from sample collection to GC-MS analysis was proposed. As SCFAs have been shown to play an important role in health maintenance and disease development, the proposed protocol is anticipated to be applicable to clinical studies to delineate the biological functions of each SCFA.

Simultaneous HS-SPME GC-MS determination of short chain fatty acids, trimethylamine and trimethylamine N-oxide for gut microbiota metabolic profile.

Trimethylamine (TMA), trimethylamine-N-oxide (TMAO) and short chain fatty acids (SCFAs), as acetic, propionic, butyric and valeric acids are among the most important products of the gut microbiota (GM) metabolism. The present study is aimed at the determination of TMA, TMAO and SCFAs by a double step headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) analysis, allowing the simultaneous quantitation of both the acidic and basic metabolites in faecal samples. TMAO amount was evaluated after its reduction to TMA by using Fe(II)-EDTA complex as a reagent. Under the fully validated experimental conditions, adequate sensitivity (LOQ 0.011-0.23 µmol g-1), good accuracy (79 - 110%) and precision (CV% < 11%) were achieved for all the target analytes. The presented method is successfully applied to the quantitation of the considered gut metabolites in faecal samples from Italian healthy volunteers.

Fast quantification of short chain fatty acids and ketone bodies by liquid chromatography-tandem mass spectrometry after facile derivatization coupled with liquid-liquid extraction.

Short chain fatty acids (SCFA) and ketone bodies recently emerged as important physiological relevant metabolites because of their association with microbiota, immunology, obesity and other metabolic states. They were commonly analyzed by GC-MS with long run time and laborious sample preparation. In this study we developed a novel LC-MS/MS method using fast derivatization coupled with liquid-liquid extraction to detect SCFA and ketone bodies in plasma and feces. Several different derivatization reagents were evaluated to compare the efficiency, the sensitivity and chromatographic separation of structural isomers. O­benzylhydroxylamine was selected for its superior overall performance in reaction time and isomeric separation that allowed the measurement of each SCFAs and ketone bodies free from interferences. The derivatization procedure is facile and reproducible in aqueous-organic medium, which abolished the evaporation procedure hampering the analysis of volatile short chain acids. Enhancement in sensitivity remarkably improved the detection limit of SCFA and ketone bodies to sub-fmol level. This novel method was applied to quantify these metabolites in fecal and plasma samples from lean and DIO mouse.

Biorefinery of cellulosic primary sludge towards targeted Short Chain Fatty Acids, phosphorus and methane recovery.

Cellulose from used toilet paper is a major untapped resource embedded in municipal wastewater which recovery and valorization to valuable products can be optimized. Cellulosic primary sludge (CPS) can be separated by upstream dynamic sieving and anaerobically digested to recover methane as much as 4.02 m3/capita·year. On the other hand, optimal acidogenic fermenting conditions of CPS allows the production of targeted short-chain fatty acids (SCFAs) as much as 2.92 kg COD/capita·year. Here propionate content can be more than 30% and can optimize the enhanced biological phosphorus removal (EBPR) processes or the higher valuable co-polymer of polyhydroxyalkanoates (PHAs). In this work, first a full set of batch assays were used at three different temperatures (37, 55 and 70 °C) and three different initial pH (8, 9 and 10) to identify the best conditions for optimizing both the total SCFAs and propionate content from CPS fermentation. Then, the optimal conditions were applied in long term to a Sequencing Batch Fermentation Reactor where the highest propionate production (100-120 mg COD/g TVSfed·d) was obtained at 37 °C and adjusting the feeding pH at 8. This was attributed to the higher hydrolysis efficiency of the cellulosic materials (up to 44%), which increased the selective growth of Propionibacterium acidopropionici in the fermentation broth up to 34%. At the same time, around 88% of the phosphorus released during the acidogenic fermentation was recovered as much as 0.15 kg of struvite per capita·year. Finally, the potential market value was preliminary estimated for the recovered materials that can triple over the conventional scenario of biogas recovery in existing municipal wastewater treatment plants.

Derivatization and Gas Chromatography of Fatty Acids from Yeast.

Analysis of fatty acids by gas chromatography (GC) is facilitated by the generation of volatile fatty acid methyl ester (FAME) derivatives. Here we describe the esterification procedure and a typical program for separating FAMEs using a gas chromatograph equipped with a flame ionization detector or a dual stage quadrupole-mass spectrometry detector. GC is a rather simple technique that provides quantitative information on cellular fatty acid content and composition by use of an internal fatty acid standard.

[The volatile fatty acids in children with dysfunction of biliary tract].

The volatile fatty acids are metabolites of bacteria reflecting condition and disbiotic alterations of microflora of gastrointestinal tract. The study was carried out to determine qualitatively volatile fatty acids in saliva of children with dysfunction of biliary tract and healthy ones. The indices of volatile fatty acids were analyzed in 46 children aged 7-17 years and with dysfunction of biliary tract. The comparison group included 34 healthy children aged from 7 to 17 years. The gas-liquid chromatography was applied to qualitatively detect acetic, butyric, isovaleric acids (volatile fatty acids). The automatedgas chromatograph "Crystal deluxe 4000" with capillary column "HP-FFAP" and flame ionizing detector was used. The study established decreasing of anaerobic index, increasing of acetic, propionic acids and sum of volatile fatty acids in saliva of children of main group as opposed to children of comparison group. The possible role of bacterial metabolites and bacteria in pathogenesis of dysfunction of biliary tract in children. The description is made of one of possible mechanisms of increasing of volatile fatty acids in saliva under dysfunction of biliary tract. The integral indices of volatile fatty acids of saliva are the new additional criteria for diagnostic of dysfunction of biliary tract in children.

Sensitive and Simplified Detection of Antibiotic Influence on the Dynamic and Versatile Changes of Fecal Short-Chain Fatty Acids.

Short-chain fatty acids (SCFAs), produced by anaerobic fermentation of mainly indigestible dietary carbohydrates by gut microbiota, have a profound influence on intestinal function and host energy metabolism. Antibiotics may seriously disturb the balance of fecal SCFAs. To evaluate the impacts of antibiotics on fecal SCFAs produced by gut microbiota, a simple, reproducible and accurate gas chromatography (GC) method, which can simultaneously analyze seven SCFAs in fecal samples, was developed and validated. The ranges of detection and quantitation of the SCFAs reached 0.0868 ~ 0.393 and 0.261 ~ 1.18 µg·mL-1 respectively, in an optimized protocol for SCFAs extraction and analysis that used 10 mL 75% ethanol aqueous solution containing 1% HCl, without ultrasonication. The technique exhibited excellent intra-day (relative standard deviation (RSD) ≤ 2.54%) and inter-day (RSD ≤ 4.33%) precisions for all the SCFAs. Later, we administered broad-spectrum antibiotics, cefdinir or azithromycin to rats and analyzed the alterations in fecal SCFAs. The total amount, types and distribution of nearly all fecal SCFAs were significantly altered during the administration and even after withdrawal of the antibiotics in rats. The effects of cefdinir on the SCFAs were more pronounced than those of azithromycin. Our findings suggest SCFAs may serve as sensitive indicators to monitor the influences of antibiotics on SCFAs originated by intestinal bacteria. Our improved SCFAs analysis method is a potential platform for a standard clinical test of the effects of new antibiotics on SCFAs.

Removal of volatile fatty acids and ammonia recovery from unstable anaerobic digesters with a microbial electrolysis cell.

Continuous assays with a microbial electrolysis cell (MEC) fed with digested pig slurry were performed to evaluate its stability and robustness to malfunction periods of an anaerobic digestion (AD) reactor and its feasibility as a strategy to recover ammonia. When performing punctual pulses of volatile fatty acids (VFA) in the anode compartment of the MEC, simulating a malfunction of the AD process, an increase in the current density was produced (up to 14 times, reaching values of 3500mAm(-2)) as a result of the added chemical oxygen demand (COD), especially when acetate was used. Furthermore, ammonium diffusion from the anode to the cathode compartment was enhanced and the removal efficiency achieved up to 60% during daily basis VFA pulses. An AD-MEC combined system has proven to be a robust and stable configuration to obtain a high quality effluent, with a lower organic and ammonium content.

Extraction and Esterification of Low-Titer Short-Chain Volatile Fatty Acids from Anaerobic Fermentation with Ionic Liquids.

Ionic liquids can both act as a solvent and mediate esterification to valorize low-titer volatile fatty acids and generate organic solvents from renewable carbon sources including biowaste and CO2 . In this study, four phosphonium ionic liquids were tested for single-stage extraction of acetic acid from a dilute stream and esterification to ethyl acetate with added ethanol and heat. The esterification proceeded with a maximum conversion of 85.9±1.3 % after 30 min at 75 °C at a 1:1 stoichiometric ratio of reactants. Extraction and esterification can be tailored using mixed-anion ionic liquids; this is demonstrated herein using a common trihexyl(tetradecyl)phosphonium cation and a mixed chloride and bis(trifluoromethylsulfonyl)imide anion ionic liquid. As a further proof-of-concept, ethyl acetate was generated from an ionic liquid-driven esterification of an acetic acid extractant generated using CO2 as the only carbon source by microbial electrosynthesis.

Cascade degradation of organic matters in brewery wastewater using a continuous stirred microbial electrochemical reactor and analysis of microbial communities.

A continuous stirred microbial electrochemical reactor (CSMER), comprising of a complete mixing zone (CMZ) and microbial electrochemical zone (MEZ), was used for brewery wastewater treatment. The system realized 75.4 ± 5.7% of TCOD and 64.9 ± 4.9% of TSS when fed with brewery wastewater concomitantly achieving an average maximum power density of 304 ± 31 m W m(-2). Cascade utilization of organic matters made the CSMER remove a wider range of substrates compared with a continuous stirred tank reactor (CSTR), in which process 79.1 ± 5.6% of soluble protein and 86.6 ± 2.2% of soluble carbohydrates were degraded by anaerobic digestion in the CMZ and short-chain volatile fatty acids were further decomposed and generated current in the MEZ. Co-existence of fermentative bacteria (Clostridium and Bacteroides, 19.7% and 5.0%), acetogenic bacteria (Syntrophobacter, 20.8%), methanogenic archaea (Methanosaeta and Methanobacterium, 40.3% and 38.4%) and exoelectrogens (Geobacter, 12.4%) as well as a clear spatial distribution and syntrophic interaction among them contributed to the cascade degradation process in CSMER. The CSMER shows great promise for practical wastewater treatment application due to high pre-hydrolysis and acidification rate, high energy recovery and low capital cost.