Propionic Acid Degradation Research Articles

Effect of ammonia on anaerobic digestion: Focusing on energy flow and electron transfer

Ammonia inhibition often occurs during anaerobic digestion (AD) of N-rich organic waste. To decipher how ammonia affects microbial electron transfer activity and energy generation pathways, this study implemented mesophilic reactors subjected to incremental increase in ammonia concentrations from 600 to 5000 mg NH4+-N/L through urea regulation. The first comprehensive analyses of AD performance, mass and energy flow, thermodynamics, microbial communities, and metabolic activities were conducted in the digesters. The results showed that accumulation of volatile fatty acids, a reduction in methane production, and a mere 18.5% of the energy flow being directed towards biogas generation occurred under 4000 mg NH4+-N/L. Furthermore, we demonstrated that the changes in the Gibbs free energy were effective in evaluating the feasibility of propionic and butyric acid degradation under ammonia stress, but not for acetate. The alteration in microbial community composition indicated that the growth of acetogens surpassed that of methanogens under ammonia stress. Metagenomic analysis revealed a significant decrease in the abundance of genes associated with electron transfer and ATP generation, resulting in reduced efficiency in methanogenesis. Based on these findings, the supplementation of electrons via electro-fermentation into the AD system emerged as a potential approach to mitigate ammonia inhibition and enhance overall process efficiency.

Tuning the visible-light-driven photocatalytic properties of multi-decorated TiO2 by noble metals towards both propionic acid and NOx degradation

Multiple noble metals-modified micrometric TiO2-based photocatalysts were prepared by a cheap and sustainable approach based on the use of metal-enriched wastewaters (Ag, Au, Pt) and used for the photodegradation of propionic acid (PA) and NOx under LED. Properly tuning the metal decoration step, the material's photoactivity was optimized. 0.1%Pt @Ag/TiO2 led to 60% PA removal, whereas the strong PA adsorption on the 0.1%Au @Ag/TiO2 surface caused a partial deactivation. In contrast, 0.1%Au @Ag/TiO2 showed the highest photoactivity in the NOx decomposition (90%) due to the high tolerance of Au to HNO3 produced on the catalyst surface.

Semi-wet methanogen cathode composed of oak white charcoal for developing sustainable microbial fuel cells

The present study aimed to evaluate a semi-wet biocathode composed of oak white charcoal and agarose gel as an alternative to the standard carbon felt biocathodes used in microbial fuel cells (MFCs). The MFC containing the oak white charcoal cathode (Oak-MFC) recorded a higher current value than that of the MFC containing a carbon felt cathode (CF-MFC). The Oak-MFC produced approximately 4.0-fold more electrons in the external circuit and 1.7-fold more methane (CH4) than the CF-MFC. A real-time PCR targeting mcrA showed that the number of methanogens adhering to the oak white charcoal cathode was approximately 15-fold that adhering to the carbon felt cathode. These results suggest that the methanogens attached to the cathode of both MFCs received electrons and CH4 was produced from carbon dioxide (CO2). Furthermore, Oak-MFC performed better than CF-MFC, thereby suggesting that oak white charcoal bound by agarose gel can be used as an alternative methanogen cathode. The propionic acid degradation rate of Oak-MFC was faster than that of CF-MFC suggesting that the cathodic reaction may affect the anodic reaction. The use of oak-derived electrode as a methanogen cathode also could contribute to sustainable forest management and promote regular thinning of oak trees. Further, its use will enable carbon fixation and efficient energy conversion from CO2 to CH4, thus contributing to sustainable energy use.

One-Step Synthesis of CuxOy/TiO2 Photocatalysts by Laser Pyrolysis for Selective Ethylene Production from Propionic Acid Degradation.

In an effort to produce alkenes in an energy-saving way, this study presents for the first time a photocatalytic process that allows for the obtention of ethylene with high selectivity from propionic acid (PA) degradation. To this end, TiO2 nanoparticles (NPs) modified with copper oxides (CuxOy/TiO2) were synthetised via laser pyrolysis. The atmosphere of synthesis (He or Ar) strongly affects the morphology of photocatalysts and therefore their selectivity towards hydrocarbons (C2H4, C2H6, C4H10) and H2 products. Specifically, CuxOy/TiO2 elaborated under He environment presents highly dispersed copper species and favours the production of C2H6 and H2. On the contrary, CuxOy/TiO2 synthetised under Ar involves copper oxides organised into distinct NPs of ~2 nm diameter and promotes C2H4 as the major hydrocarbon product, with selectivity, i.e., C2H4/CO2 as high as 85% versus 1% obtained with pure TiO2.

Propionic acid degradation in anaerobic digestion and recovery strategies for full-scale biogas plants

This work investigated the degradation of propionic acid (PA) and its influence on anaerobic digestion (AD) at laboratory scale and in full scale. First, an increase in PA concentration was induced by adding PA at the laboratory scale and at full scale. Second, an internal increase was provoked in a full-scale plant by straining feeding. It was found that high PA concentrations correlated with a deterioration of the other process indicators, such as the ratio of volatile organic acids to total inorganic carbon (VOA/TIC) and pH. However, a sudden PA addition to a mismatched process affected process stability more than the addition to a matched process. Further, it was found that the addition of slurry and quasi-continuous feeding stabilized the biogas process in the full-scale plant. The knowledge gained will help to improve AD simulation models and provide plant operators with solutions in case of process disturbances.

Effect of nano-magnetite on the propionic acid degradation in anaerobic digestion system with acclimated sludge

In this study, a batch of acid-tolerant inoculation sludge was domesticated as inoculum, and different concentrations of nano-magnetite were added to the propionic acid (PA) anaerobic digestion system to explore its effect on the PA degradation. It was found the PA degradation rates of nano-magnetite groups were 10.96–74.62% higher than the control group without magnetite in the 6th day, especially with the dosage of 100 mg/L. Microbial community analysis showed some potential DIET participants of Chloroflexi, Proteobacteria and Bacteroidetes had the highest abundance, while metabolite analysis showed that nano-magnetite promoted the transformation of malic acid to oxaloacetic acid and the PA disproportionation to butyric acid. It indicated that nano-magnetite could effectively promote the early degradation of PA in the sludge acclimation system by accelerating DIET or PA disproportionation, so as to prevent the PA accumulation, which could provide reference for the acid accumulation regulation of anaerobic digestion system.

Synthetic Effect of EDTA and Ni2+ on Methane Production and Microbial Communities in Anaerobic Digestion Process of Kitchen Wastes

Batch tests were carried out to study the effect of simultaneous addition of ethylenediaminetetraacetic acid and Ni2+ (EDTA-Ni) on anaerobic digestion (AD) performances of kitchen wastes (KWs). The results indicated that the cumulative biogas yield and methane content were enhanced to 563.82 mL/gVS and 63.7% by adding EDTA-Ni, respectively, which were almost 1.15 and 1.07-fold of that in the R2 with Ni2+ addition alone. At the same time, an obvious decrease of propionic acid was observed after EDTA-Ni addition. The speciation analysis of Ni showed that the percentages of water-soluble and exchangeable Ni were increased to 38.8% and 36.3% due to EDTA-Ni addition, respectively. Also, the high-throughput sequencing analysis revealed that the EDTA-Ni promoted the growth and metabolism of Methanosarcina and Methanobacterium, which might be the major reason for propionic acid degradation and methane production.

The contribution of selected organic substrates to the anaerobic cometabolism of sulfamethazine

Biodegradation of organic micropollutants is likely to occur due to cometabolism by particular microbial groups. In an effort to identify the stages of anaerobic digestion potentially involved in the biodegradation of the veterinary antimicrobial sulfamethazine (SMZ), the influence of selected carbon sources (sucrose, glucose, fructose, ethanol, meat extract, cellulose, soluble starch, soy oil, acetic acid, propionic acid and butyric acid) on SMZ removal by anaerobic sludge was evaluated in short-term batch experiments. Adsorption to the granular sludge constituted a significant removal mechanism, accounting for 39% of SMZ removal in control experiments. The presence of glucose, fructose, sucrose and meat extract exerted an inducing effect on SMZ degradation, resulting in removal efficiencies of 54, 53, 58 and 61%, respectively, indicating the occurrence of cometabolism. Time courses of sucrose and meat extract degradation revealed markedly distinct organic acid profiles but resulted in similar SMZ removals. Temporal profiles of acetic and propionic acid degradation were not associated with SMZ removal, as changes in SMZ concentration were observed even after the organic acids had been completely removed. The experimental results suggest that SMZ cometabolism is not associated to sucrose hydrolysis, acetoclastic methanogenesis and acetogenesis from propionic acid.

Ammonia Inhibition of Anaerobic Volatile Fatty Acid Degrading Microbial Communities.

Ammonia inhibition is an important reason for reactor failures and economic losses in anaerobic digestion. Its impact on acetic acid degradation is well-studied, while its effect on propionic and butyric acid degradation has received little attention and is consequently not considered in the Anaerobic Digestion Model No. 1 (ADM1). To compare ammonia inhibition of the degradation of these three volatile fatty acids (VFAs), we fed a mixture of them as sole carbon source to three continuous stirred tank reactors (CSTRs) and increased ammonium bicarbonate concentrations in the influent from 52 to 277 mM. The use of this synthetic substrate allowed for the determination of degradation efficiencies for the individual acids. While butyric acid degradation was hardly affected by the increase of ammonia concentration, propionic acid degradation turned out to be even more inhibited than acetic acid degradation with degradation efficiencies dropping to 31 and 65% for propionic and acetic acid, respectively. The inhibited reactors acclimatized and approximated pre-disturbance degradation efficiencies toward the end of the experiment, which was accompanied by strong microbial community shifts, as observed by amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism (T-RFLP) of mcrA genes. The acetoclastic methanogen Methanosaeta was completely replaced by Methanosarcina. The propionic acid degrading genus Syntrophobacter was replaced by yet unknown propionic acid degraders. The butyric acid degrading genus Syntrophomonas and hydrogenotrophic Methanomicrobiaceae were hardly affected. We hypothesized that the ammonia sensitivity of the initially dominating taxa Methanosaeta and Syntrophobacter led to a stronger inhibition of the acetic and propionic acid degradation compared to butyric acid degradation and hydrogenotrophic methanogenesis, which were facilitated by the ammonia tolerant taxa Syntrophomonas and Methanomicrobiaceae. We implemented this hypothesis into a multi-taxa extension of ADM1, which was able to simulate the dynamics of both microbial community composition and VFA concentration in the experiment. It is thus plausible that the effect of ammonia on VFA degradation strongly depends on the ammonia sensitivity of the dominating taxa, for syntrophic propionate degraders as much as for acetoclastic methanogens.

Understanding the photocatalytic degradation by P25 TiO2 of acetic acid and propionic acid in the pursuit of alkane production

Towards the application of harvesting valuable hydrocarbon products from wastewater and associated fermentation processes, the traditional P25 Degussa TiO2-assisted decarboxylation of simple carboxylic acid substrates - in this case acetic and propionic acids – was re-examined for its alkane production capacity. Avoiding doping or the introduction of other elements into the commercially available TiO2 lattice, we modified other parameters of the reaction not yet explored. Under nitrogen, highly concentrated (50%) and pure (100%) solutions of both acetic acid and propionic acid demonstrated good selectivity for the decarboxylation over any other side reaction or complete mineralization, nearing or exacting a 1:1 hydrocarbon/CO2 ratio in each case. This behaviour proves that the direct reaction of h+ with the acid in either case is the key parameter to favour this selectivity. In the case of acetic acid, methane’s yield was increased significantly by the periodic aeration of the catalyst when exhausted under nitrogen. The modification of solution pH to more physiological and fermentation-compatible levels (pH of 6.0) lead to improve the selectivity and the ethane’ yield in 50% propionic acid degradation and also resulted in virtually no unidentified carbon products. The Photo-Kolbe coupling and dehydration products, meanwhile, were favoured in the less concentrated solutions, suggesting that more dilute solutions may be more promising for deriving longer length hydrocarbons from substrates of smaller size. Mechanistically, these results also implicate that OH° radicals are at the origin of product generation by way of Photo-Kolbe coupling and dehydration. Finally, acetic acid and propionic acid were degraded simultaneously, in which the latter was degraded preferentially or at least initially before the former, along with the appearance of propane as a result of cross-coupling.

Investigation of the impact of trace elements on anaerobic volatile fatty acid degradation using a fractional factorial experimental design

The requirement of trace elements (TE) in anaerobic digestion process is widely documented. However, little is understood regarding the specific requirement of elements and their critical concentrations under different operating conditions such as substrate characterisation and temperature.In this study, a flask batch trial using fractional factorial design is conducted to investigate volatile fatty acids (VFA) anaerobic degradation rate under the influence of the individual and combined effect of six TEs (Co, Ni, Mo, Se, Fe and W). The experiment inoculated with food waste digestate, spiked with sodium acetate and sodium propionate both to 10 g/l. This is followed by the addition of a selection of the six elements in accordance with a 26−2 fractional factorial principle. The experiment is conducted in duplicate and the degradation of VFA is regularly monitored.Factorial effect analysis on the experimental results reveals that within these experimental conditions, Se has a key role in promoting the degradation rates of both acetic and propionic acids; Mo and Co are found to have a modest effect on increasing propionic acid degradation rate. It is also revealed that Ni shows some inhibitory effects on VFA degradation, possibly due to its toxicity. Additionally, regression coefficients for the main and second order effects are calculated to establish regression models for VFA degradation.

Comment on “Thermodynamically enhancing propionic acid degradation by using sulfate as an external electron acceptor in a thermophilic anaerobic membrane reactor” by Qiao, W., Takayanagi, K., Li, Q., Shofie, M., Gao, F., Dong, R., Li, Y-Y. Water Res. (2016)

Comment on “Thermodynamically enhancing propionic acid degradation by using sulfate as an external electron acceptor in a thermophilic anaerobic membrane reactor” by Qiao, W., Takayanagi, K., Li, Q., Shofie, M., Gao, F., Dong, R., Li, Y-Y. Water Res. (2016)

The performance efficiency of bioaugmentation to prevent anaerobic digestion failure from ammonia and propionate inhibition

This study aims to investigate the effect of bioaugmentation with enriched methanogenic propionate degrading microbial consortia on propionate fermentation under ammonia stress from total ammonia nitrogen concentration (TAN) of 3.0gNL−1. Results demonstrated that bioaugmentation could prevent unstable digestion against further deterioration. After 45days of 1dosage (0.3g dry cell weight L−1d−1, DCW L−1d−1) of bioaugmentation, the average volumetric methane production (VMP), methane recovery rate and propionic acid (HPr) degradation rate was enhanced by 70mLL−1d−1, 21% and 51%, respectively. In contrast, the non-bioaugmentation reactor almost failed. Routine addition of a double dosage (0.6g DCW L−1d−1) of bioaugmentation culture was able to effectively recover the failing digester. The results of FISH suggested that the populations of Methanosaetaceae increased significantly, which could be a main contributor for the positive effect on methane production.

Thermodynamically enhancing propionic acid degradation by using sulfate as an external electron acceptor in a thermophilic anaerobic membrane reactor

In this study, sulfate was employed as an external electron acceptor for enhancing the degradation of propionate in a thermophilic anaerobic membrane reactor (AnMBR). The organic loading rate (OLR) was increased gradually from the initial 3.9 kg-COD/m3d to the inhibiting OLR of 14.6 kg-COD/m3d. Feeding was stopped for 98 days but the process did not recover until 500 mg/L of sulfate was added into the AnMBR. After that, the enhanced propionate degradation was achieved up to an OLR of 15 kg-COD/m3d with a reduced sulfate addition of 300 mg/L. However, the thermodynamic calculation indicated that the syntrophic propionic acid degradation, coupled with methanogenesis, was unfavorable with a △G of +3 kJ/mol under the enhanced conditions. Conversely, the utilization of propionic acid by sulfate reduction bacterial (SRB) would be more favourable by having a much lower △G of −180 kJ/mol. The hydrogen conversion was presumed to go through the methanogenesis pathway according to the thermodynamic results. The mechanism of the propionic and hydrogen metabolism was supported as well by comparing the microbial communities with and without sulfate addition. As a result, the role of the sulfate enhancing propionic degradation can be concluded by combining the process performance, thermodynamic, and microbiology results.

Process simulation and modeling: Anaerobic digestion of complex organic matter

This work is focused on evaluating kinetic models of complex organic matters hydrolysis and volatile fatty acids degradation in anaerobic digestion process, simulated using SuperPro design software. Kinetic model evaluation was also carried for simulated integrated system of liquid anaerobic digestion (LAD) of dairy manure and solid state anaerobic digestion (SS-AD) of corn stover. Already developed hydrolysis and volatile fatty acid (VFA) degradation kinetic constants were used to simulate anaerobic digestion processes of dairy manure and corn stover separately and in the integrated process as well. Hydrolysis of complex soluble organic matters such as protein, carbohydrate and fat was modelled using first-order kinetics. Monod model was tested for the VFAs such as acetic, propionic and butyric acid degradation and biogas production. Comparative study has been done between the experimental data published already and results obtained from SuperPro simulated processes. The simulated results were well comparable with the experimental results.

Evaluating the potential impact of proton carriers on syntrophic propionate oxidation.

Anaerobic propionic acid degradation relies on interspecies electron transfer (IET) between propionate oxidisers and electron acceptor microorganisms, via either molecular hydrogen, formate or direct transfers. We evaluated the possibility of stimulating direct IET, hence enhancing propionate oxidation, by increasing availability of proton carriers to decrease solution resistance and reduce pH gradients. Phosphate was used as a proton carrying anion, and chloride as control ion together with potassium as counter ion. Propionic acid consumption in anaerobic granules was assessed in a square factorial design with ratios (1:0, 2:1, 1:1, 1:2 and 0:1) of total phosphate (TP) to Cl−, at 1X, 10X, and 30X native conductivity (1.5 mS.cm−1). Maximum specific uptake rate, half saturation, and time delay were estimated using model-based analysis. Community profiles were analysed by fluorescent in situ hybridisation and 16S rRNA gene pyrosequencing. The strongest performance was at balanced (1:1) ratios at 10X conductivity where presumptive propionate oxidisers namely Syntrophobacter and Candidatus Cloacamonas were more abundant. There was a shift from Methanobacteriales at high phosphate, to Methanosaeta at low TP:Cl ratios and low conductivity. A lack of response to TP, and low percentage of presumptive electroactive organisms suggested that DIET was not favoured under the current experimental conditions.

Kinetic characterization of thermophilic and mesophilic anaerobic digestion for coffee grounds and waste activated sludge

This study was conducted to characterize the kinetics of an anaerobic process (hydrolysis, acetogenesis, acidogenesis and methanogenesis) under thermophilic (55°C) and mesophilic (35°C) conditions with coffee grounds and waste activated sludge (WAS) as the substrates. Special focus was given to the kinetics of propionic acid degradation to elucidate the accumulation of VFAs. Under the thermophilic condition, the methane production rate of all substrates (WAS, ground coffee and raw coffee) was about 1.5times higher than that under the mesophilic condition. However, the effects on methane production of each substrate under the thermophilic condition differed: WAS increased by 35.8–48.2%, raw coffee decreased by 76.3–64.5% and ground coffee decreased by 74.0–57.9%. Based on the maximum reaction rate (Rmax) of each anaerobic stage obtained from the modified Gompertz model, acetogenesis was found to be the rate-limiting step for coffee grounds and WAS. This can be explained by the kinetics of propionate degradation under thermophilic condition in which a long lag-phase (more than 18days) was observed, although the propionate concentration was only 500mg/L. Under the mesophilic condition, acidogenesis and hydrolysis were found to be the rate-limiting step for coffee grounds and WAS, respectively. Even though reducing the particle size accelerated the methane production rate of coffee grounds, but did not change the rate-limiting step: acetogenesis in thermophilic and acidogenesis in mesophilic.

Dynamics of propionic acid degradation in a two-phase anaerobic system

This paper reports on propionic acid (HPr) degradation in a laboratory scale two-phase anaerobic system, where HPr was accumulated in the acidogenic reactor and degraded in the methanogenic reactor. Batch tests using biomass from the two-phase anaerobic system showed HPr degradation was rarely detectable in the acidogenic reactor when HPr concentration ranged from 639 to 4531mgHPrL−1 and at pH 4.50 to 6.50. Biomass from the methanogenic reactor could, however, successfully degrade HPr at its initial concentration of up to 4585mgHPrL−1 at pH 6.40–7.30. ATP results showed that differences in the degradation ability of HPr by the acidogenic and methanogenic biomass may be related with their respective different biomass activities. Results from pyrosequencing showed that the predominant propionic acid oxidizing bacteria (POB) in the methanogenic reactor were Smithella (2.68%) and Syntrophobacter (0.35%); while poor degradation of HPr in the acidogenic reactor may be associated with the low abundance of POB (0.02% Desulfacinum and 0.08% Desulfobulbus). This might have been induced by the long-term unfavorable environment for POB growth in the acidogenic reactor.

Characterization of the sulfate reduction process in the anaerobic digestion of a very high strength and sulfate rich vinasse

Abstract This article characterizes the sulfate reduction process in the anaerobic digestion of a very high strength and sulfate rich vinasse, where chemical oxygen demand (COD) and sulfate (SO 4 2− ) pulses were applied at different SO 4 2− /COD ratios to obtain dynamical responses. The results showed an increase in H 2 S gas of up to 33%, when influent COD (inf_COD) and influent SO 4 2− (inf_SO 4 2− ) increased at a SO 4 2− /COD ratio of 0.05. A decrease of inf_COD together with an increase of inf_SO 4 2− caused propionic acid degradation (up to 90%), suggesting strong contribution of propionate degrading sulfate reducing bacteria at SO 4 2− /COD ratios ⩽0.10, in contrast to literature results. The inf_COD and inf_SO 4 2− fluctuations at a SO 4 2− /COD ratio of 0.10 caused inhibition by H 2 S aq, [H 2 S] free and propionic acid to sulfate reducing bacteria (SRBs), methanogens or both. At a SO 4 2− /COD ratio of 0.20 this inhibition became severe for methanogens and SRBs, leading to reactor failure. Mass balance calculations showed COD and sulfur recoveries from 90% to 98% in most cases. Increments of inf_COD within a constant SO 4 2− /COD ratio (0.05 or 0.10) accumulated as effluent COD rather than as COD_CH 4gas , showing deterioration of the anaerobic digestion, while the sulfur was displaced to the gas phase at a SO 4 2− /COD ratio of 0.05 or to the liquid phase at SO 4 2− /COD ratios ⩾0.10. Based on the closed mass balances results, the data presented here are considered reliable for calibrating mathematical models, when sulfate reduction in the anaerobic digestion of a very high strength and sulfate rich vinasse is of primary interest.

Anaerobic digestion of swine manure under natural zeolite addition: VFA evolution, cation variation, and related microbial diversity

Batch experiments were carried out on anaerobic digestion of swine manure under 10 % of total solids and 60 g/L of zeolite addition at 35 °C. Four distinctive volatile fatty acid (VFAs) evolution stages were observed during the anaerobic process, i.e., VFA accumulation, acetic acid (HAc) and butyric acid (HBu) utilization, propionic acid (HPr) and valeric acid (HVa) degradation, and VFA depletion. Large decreases in HAc/HBu and HPr/HVa occurred respectively at the first and second biogas peaks. Biogas yield increased by 20 % after zeolite addition, about 356 mL/g VSadded with accelerated soluble chemical oxygen demand degradation and VFA (especially HPr and HBu) consumption in addition to a shortened lag phase between the two biogas peaks. Compared with Ca(2+) and Mg(2+) (100-300 mg/L) released from zeolite, simultaneous K(+) and NH4 (+) (580-600 mg/L) adsorptions onto zeolite particles contributed more to the enhanced biogasification, resulting in alleviated inhibition effects of ammonium on acidogenesis and methanogenesis, respectively. All the identified anaerobes could be grouped into Bacteroidetes and Firmicutes, and zeolite addition had no significant influence on the microbial biodiversity in this study.