Undissociated Volatile Fatty Acids Research Articles

Oil-rich filamentous algae cultivation in anaerobic digestate effluent: Inhibition effect of undissociated fatty acids

Microalgae cultivation using organic carbon waste has been proved as a promising way to enhance filamentous algal biomass bio-protection. However, the carbon source in anaerobic digestate (AD; the effluent of biogas plants) contains various organic carbon source and other components, with a complex metabolic process in algae. The utilization of organic carbon including volatile fatty acids (VFAs) and glycerin by Tribonema minus were investigated. The results showed that the utilization of VFAs as the carbon source by T. minus with the addition of 0.3% CO2 decreased pH value below 6.0 and accumulated the undissociated VFAs (UVFAs) (UVFAs contents: 99.29 ± 8.34 mg L−1, 176.52 ± 4.05 mg L−1, 115.02 ± 5.86 mg L−1, and 127.52 ± 7.24 mg L−1 for acetic acid, propanoic acid, butyric acid, and valeric acid, respectively after 1st day cultivation), which inhibited T. minus growth. However, this inhibition effect was not observed when using glycerin as a carbon source (Biomass: 2.95 g L−1). To study the inhibition mechanism of UVFAs on the algae, the growth and metabolism of algae using acetic acid and butyric acid as carbon source was studied under different pH (4.5, 5.5, 6.5). The study found that the UVFAs content at pH 4.5–5.5 was higher than that at pH 6.5 with the same carbon concentrations. UVFAs inhibited the biomass accumulation of T. minus and decreased photosynthetic and enzymatic activities. This study concluded that T. minus can be cultivated with a mixotrophic mode using AD that contains VFAs with controlled pH value around neutral.

In situ biogas upgrading and enhancement of anaerobic digestion of cheese whey by addition of scrap or powder zero-valent iron (ZVI)

Cheese whey is an easily biodegradable substrate with high organic matter that can be anaerobically digested to biogas; however, the process is often inhibited by excess acidification due to the presence of undissociated volatile fatty acids and requires considerable concentration of alkaline buffer. The current study investigates a new approach for biogas upgrading, and increase of total CH4 in conjunction with buffering acidification by using zero-valent iron (powder and scrap metals at concentrations 25, 50, and 100 g/L) in anaerobic granular sludge and cheese whey under mesophilic batch conditions. During the first 2 cycles (total 34 days), a high performance was found in anaerobic bottles with 25 g/L powder zero valent iron (PZVI) and 50 g/L scrap zero valent iron (SZVI) since they had a higher total CH4 production compared to anaerobic bottles free of ZVI, as well as 97% CH4 composition in produced biogas compared to 74% CH4 for anaerobic bottles free of ZVI. Under these conditions, no additional NaOH was added to anaerobic bottles with 25 g/L PZVI and 50 g/L SZVI to increase the pH and at the end of 2nd cycle the concentration of VFAs was substantially lower compared to the anaerobic bottles free of ZVI. However, no positive effects of ZVI in terms of alkaline buffer were found at the 3rd and 4th cycle probably due to ZVI inactivation outer surface layer. Based on the experimental findings (anaerobic bottles: (a) 25 g/L PZVI, (b) 50 g/L SZVI and (c) free of ZVI) an economic comparison for anaerobic digestion of cheese whey by large scale was contacted and pointed out that the best scenario was the anaerobic digestion by addition of 50 g/L SZVI, followed by anaerobic digestion free of ZVI and last was the anaerobic digestion by addition of 25 g/L PZVI. This study highlights a new proof of concept for in-situ biogas upgrading and alleviation of acidification by addition of 50 g/L SZVI or 25 g/L PZVI during anaerobic digestion of cheese whey.

Direct and Indirect Effects of Increased CO2 Partial Pressure on the Bioenergetics of Syntrophic Propionate and Butyrate Conversion.

Simultaneous digestion and in situ biogas upgrading in high-pressure bioreactors will result in elevated CO2 partial pressure (pCO2). With the concomitant increase in dissolved CO2, microbial conversion processes may be affected beyond the impact of increased acidity. Elevated pCO2 was reported to affect the kinetics and thermodynamics of biochemical conversions because CO2 is an intermediate and end-product of the digestion process and modifies the carbonate equilibrium. Our results showed that increasing pCO2 from 0.3 to 8 bar in lab-scale batch reactors decreased the maximum substrate utilization rate (rsmax) for both syntrophic propionate and butyrate oxidation. These kinetic limitations are linked to an increased overall Gibbs free energy change (ΔGOverall) and a potential biochemical energy redistribution among syntrophic partners, which showed interdependence with hydrogen partial pressure (pH2). The bioenergetics analysis identified a moderate, direct impact of elevated pCO2 on propionate oxidation and a pH-mediated effect on butyrate oxidation. These constraints, combined with physiological limitations on growth exerted by increased acidity and inhibition due to higher concentrations of undissociated volatile fatty acids, help to explain the observed phenomena. Overall, this investigation sheds light on the role of elevated pCO2 in delicate biochemical syntrophic conversions by connecting kinetic, bioenergetic, and physiological effects.

Mitigating inhibition of undissociated volatile fatty acids (VFAs) for enhanced sludge-rice bran composting with ferric nitrate amendment

This study investigated the effect of ferric nitrate on mitigating the inhibition of volatile fatty acids (VFAs) during the initial phase of sewage sludge composting amended with rice bran. During the 34-day lab-scale composting, the supplementation of ferric nitrate enhanced the degradation of VFAs by up to 3 times as compared to the control. The organic matters loss (OML) rate in the treatment reactor was almost doubled with supplementation of ferric nitrate as compared to the control reactor during the initial phase. Eventually the treatment reactor achieved a 39.0% OML by the end of composting, which was 22% higher than the control. Ferric nitration addition mitigated the inhibition of VFAs by stimulating denitrification which consumed protons and VFAs. Ferric nitrate addition also decreased the electrical conductivity by 23% in the final compost product, reducing the possibility of phytotoxicity issue upon soil application. In summary, the results demonstrated that ferric nitrate addition could be an effective strategy for enhanced sludge composting.

Augmentation of bacterial homeostasis by regulating in situ buffer capacity: Significance of total dissolved salts over acidogenic metabolism

During anaerobic fermentation, consequent accumulation of acidic fermented products leads to the failure of pH homeostasis. The present study aimed to comprehend the changes in buffering capacity with addition of sodium salts of hydroxide, bicarbonate and phosphate. The results showed notable augmentation in buffer capacity and cumulative hydrogen production (CHP) compared to control. The influential factor is the amount of undissociated volatile fatty acids released that affected the cell metabolism and consequently biohydrogen generation. It is inferred that among the tested salts, sodium bicarbonate has substantial buffering capacity (β, 0.035± mol) ensuing maximum CHP (468± mL). Besides, bioelectrochemical analysis revealed variations in redox currents that aligned with biohydrogen production. The study provides valuable information on the role of inorganic dissolved salts that would be required to regulate H2 generation and acidogenesis in the aspects of acid–gas phase system.

Impact of undissociated volatile fatty acids on acidogenesis in a two-phase anaerobic system

This study investigated the degradation and production of volatile fatty acids (VFAs) in the acidogenic phase reactor of a two-phase anaerobic system. 20mmol/L bromoethanesulfonic acid (BESA) was used to inhibit acidogenic methanogens (which were present in the acidogenic phase reactor) from degrading VFAs. The impact of undissociated volatile fatty acids (unVFAs) on “net” VFAs production in the acidogenic phase reactor was then evaluated, with the exclusion of concurrent VFAs degradation. “Net” VFAs production from glucose degradation was partially inhibited at high unVFAs concentrations, with 59%, 37% and 60% reduction in production rates at 2190mg chemical oxygen demand (COD)/L undissociated acetic acid (unHAc), 2130mg COD/L undissociated propionic acid (unHPr) and 2280mg COD/L undissociated n-butyric acid (unHBu), respectively. The profile of VFAs produced further indicated that while an unVFA can primarily affect its own formation, there were also unVFAs that affected the formation of other VFAs.

Acid‐stressed control of market waste anaerobic digestion using pH adjustment

This work highlights the influence of pH on the acid stress control of market waste in a single‐stage batch reactor for two different pH‐controlled regimes (neutral pH and stepwise increasing pH). The stress from the acid was defined using two primary parameters, the total volatile fatty acid (TVFA) and undissociated acid (UA) concentrations, and the ratio of the two parameters (TVFA/UA). The results indicated that stepwise increases in the pH value of the system are much better than maintaining a neutral pH throughout the entire process because the first option sustains an appropriate value for the TVFA, that is, <20 g of acetic acid (HAc) per liter, which allows its gas to reach a methane concentration of 60%. Conversely, the second regime only reached a maximum methane concentration of 9%, which yielded TVFA values between 30 g HAc/L and 40 g HAc/L. These TVFA concentrations inhibit the system. The stepwise control of the pH thus helps to handle market waste in a single stage digester and avoids acid stress between dissociated and undissociated volatile fatty acids (VFAs). © 2014 American Institute of Chemical Engineers Environ Prog, 34: 132–138, 2015

Effects of an abrupt increase of starch-rich concentrates in the diet of dairy cows on concentrations of volatile fatty acids in the rumen and large intestine and on myoelectric activity of the spiral colon.

To describe the effects of an abrupt increase of concentrates in the diet of dairy cows on myoelectric activity of the spiral colon and on fermentation patterns in the rumen and large intestine. 6 healthy lactating Simmental x Red-Holstein cows. The diet of 6 cows implanted with bipolar electrodes in the spiral colon was changed from hay only to a ration of 50% hay:50% starch-rich concentrates during a period of 60 hours. Myoelectric activity of the spiral colon, concentrations of absolute and undissociated volatile fatty acids (VFA), and pH of ruminal and large intestinal contents were monitored before, during, and after the dietary change. Significant changes in patterns of myoelectric activity of the spiral colon were restricted to phases III and IV of the bovine migrating myoelectric complex and to propagation velocity. Significant alterations were not observed in pH or VFA concentrations in ruminal fluid, but pH decreased and VFA concentrations increased significantly in fecal specimens after the change of diet. Although rumen fluid is of limited value for measurement of certain indicators of fermentation, fecal samples can be used for measurement of pH and VFA concentrations, which serve as indicators of fermentation patterns in the large intestine. Increased concentrations of VFA and low pH in large intestinal digesta have a minimal influence on myoelectric activity of the spiral colon. Increased luminal VFA concentrations are unlikely to play an important role in the etiopathogenesis of motility disorders of the large intestine in cattle.

Microbial carbon mineralisation in an acid surface peat: effects of environmental factors in laboratory incubations

The regulation of terminal carbon mineralisation in an acid surface peat dominated by Sphagnum majus, from a boreal mire was studied in laboratory incubations. A factorial design at two levels were used, with the factors and settings in two different experiments as follows: temperature (7°C, 17°C; 15°C, 25°C), pH (4.3, 6.2; 4.3, 6.8), substrate (none, starch, glucose; none, glucose). Using 13C NMR spectroscopy we found that both aerobic and anaerobic degradation of 13C- U-glucose were restricted by the low native pH (4.3) compared with experimentally increased pH (6.8) in the S. majus peat. The factors included in the statistical models of the rates of CH 4 production for experiment I and II explained 98% and 74% of the variation, and the predictive ability of these models was 95% and 63%, respectively. The statistical models for the rate of CO 2 production for series I and II explained 78% and 81% of the variation, and the predictive ability was 64% and 60%, respectively. In both experiments an increase in temperature from either 7 to 17°C or from 15 or 25°C increased the rates of CH 4 production with approximately 60 nmol g −1 dw h −1. This temperature effect was approximately 3-fold larger than the effect of adding 10 mM glucose in experiment I, but equal to the addition of glucose in experiment II. Addition of starch, in amounts equal to 10 mM glucose-C, increased the rates of CH 4 production with 12 nmol g −1 dw h −1, suggesting that the anaerobic degradation of polymers per se is not restricted in the surface peat studied. The rates of CH 4 production decreased with approximately 20 nmol g −1 dw h −1, when the pH increased from 4.3 to 6.2 or 6.8, probably due to the accumulation of toxic, undissociated volatile fatty acids. Increased temperature had a weaker effect on the rates of CO 2 production than on CH 4 production from the surface peat. Carbon dioxide production rates from the S. majus surface peat were higher under aerobic than under anaerobic conditions, with the average aerobic: anaerobic quotient being 4.3 (S.D.=3.1).

Colonization control of lactose-fermenting Salmonella typhimurium in young broiler chickens by use of dietary lactose

SUMMARY Inclusion of lactose in the diets of chickens has been determined to reduce cecal colonization with Salmonella typhimurium. We hypothesized, therefore, that dietary lactose may be a practical means for reducing the prevalence of Salmonella contamination of chicken products. Because some strains of Salmonella are atypical and ferment lactose, we investigated the effects of dietary lactose on cecal colonization with lactose-fermenting S typhimurium. Broiler chicks were inoculated intracloacally with Lac+ S typhimurium selected for resistance to novobiocin and rifampicin. The chicks also were inoculated orally with certain anaerobes that do not effectively inhibit colonization by S typhimurium, but do appear essential for lactose mediated inhibition of cecal colonization. Control chicks were not given dietary lactose, and chicks in the experimental group were fed a diet containing 7% lactose. Enumeration of Lac+ S typhimurium in cecal contents revealed dietary lactose to be effective at controlling this organism. Control was correlated with changes in cecal pH and increases in undissociated volatile fatty acids, especially propionic acid.

Biological Control of Salmonella typhimurium in Young Chickens

The effect of dietary lactose and anaerobic cultures of cecal microflora of mature chickens on the colonization of young broiler chickens by Salmonella typhimurium was evaluated. Newly hatched chicks were given either no treatment (controls), anaerobic cecal cultures, lactose (2.5%) in the drinking water, or both anaerobic cultures and lactose. Chicks were challenged per os at 3 days of age with either 10(6) or 10(8) S. typhimurium resistant to nalidixic acid and novobiocin. On day 10, the cecal contents of the chicks were examined for S. typhimurium, pH, short-chained volatile fatty acids (VFAs), undissociated VFAs, and lactic acid. Chicks given either lactose alone or cecal anaerobes alone had significantly (P less than 0.05) fewer S. typhimurium recovered from their ceca than the controls. Chicks given the combination of dietary lactose and cecal anaerobes had significantly fewer S. typhimurium recovered from their ceca than the chicks given dietary lactose or cecal anaerobes alone. Chicks given lactose had significant (P less than 0.05) increases in the lactic acid concentration of their cecal contents. Increased lactic acid concentrations were directly correlated to decreased cecal pH values and caused a reduction in the total concentration of VFAs but a significant (P less than 0.05) increase in the undissociated form of some VFAs.

Intracloacal Salmonella typhimurium Infection of Broiler Chickens: Reduction of Colonization with Anaerobic Organisms and Dietary Lactose

The combined effect of treatments with dietary lactose plus anaerobic organisms on cecal colonization of broiler chicks by Salmonella typhimurium was evaluated. Chickens treated with a combination of anaerobic organisms and 7% dietary lactose were resistant to cecal colonization by S. typhimurium. The number of recoverable S. typhimurium cells per gram of cecal contents taken on days 10 and 15 after infection was significantly reduced. Treatment with anaerobes without the addition of lactose did not effectively control cecal colonization. Intracloacal inoculations with bacterial concentrations that varied by 10,000-fold resulted in roughly similar levels of colonization. The treatments resulted in reduced cecal pH and elevated levels of undissociated volatile fatty acids. Statistically significant correlations (P less than 0.01) were observed between the S. typhimurium concentrations in cecal material and the concentrations of undissociated fatty acids (r = -0.79, and between the bacterial counts and pH (r = 0.72).

Ruminal lactic acidosis: forestomach epithelial receptor activation by undissociated volatile fatty acids and rumen fluids collected during loss of reticuloruminal motility

Forty-three reticuloruminal epithelial receptors, with excitatory receptive fields within the reticulum, were isolated in 19 anaesthetised sheep. The responsiveness of these receptors to acetic, propionic, butyric and DL-lactic acids were assessed as well as their ability to be activated by rumen fluids obtained from sheep with induced ruminal lactic acidosis. Eighteen (41.9 per cent) receptors were excited by all three volatile fatty acids (VFAs) and 17 (39.5 per cent) responded to two VFAs. Butyric acid was the most potent volatile fatty acid eliciting responses in 41 (95.3 per cent) receptors. Acetic acid activated 33 (76.7 per cent) receptors and propionic acid excited 22 (53.5 per cent) receptors. DL-lactic acid only activated 13 (30.2 per cent) receptors, six of which required concentrations of 200 mM to be activated. Rumen fluids obtained when forestomach motility was impaired, activated 37 (81.1 per cent) of the 43 receptors, whereas rumen fluids obtained when forestomach motility was normal did not activate any receptors. Despite the high levels of lactic acid in rumen fluids which activated epithelial receptors, this acid was not responsible for receptor excitation.

Characteristics of the pH‐influenced adaptation of methanogenic sludge to ammonium toxicity

AbstractIncreasing ammonium‐nitrogen concentrations caused failure of methanogenesis at 1900‐2000 mg dm−3. After an adaptation period characterised by an almost nil methane production, methanogenesis appeared to be possible at even higher concentrations. A kinetic analysis of methane production during the adaptation process indicated that the adaptation was the result of a metabolic change in the methanogenic bacteria already present, rather than of growth of new bacteria. A high pH value causing toxic concentrations of un‐ionised ammonia during the adaptation period appeared to result in a decreased maximum specific methanogenic activity of the adapted sludge. A low pH value during the adaptation period resulted in a retarded degradation of propionic acid, probably due to inhibition of the hydrogen consuming methanogenic bacteria by undissociated volatile fatty acids, but this did not result in a decreased maximum specific methanogenic activity in the adapted sludge. The maximum specific methanogenic activity at an ammonium‐nitrogen concentration of 2315 mg dm−3 after adaptation as a percentage of that at 1000 mg dm−3 before adaptation was 31, 65 and 61% for a pH during the adaptation period of 7.6, 7.25 and 7.0 respectively. Except for the sludge which was maintained at pH 7.6 during the adaptation period, after adaptation the maximum specific methanogenic activity at an ammonium‐nitrogen concentration of 2315 mg dm−3 was higher than the maximum specific methanogenic activity at an ammonium nitrogen concentration of 1900 mg dm−3 before adaptation.

FORESTOMACH EPITHELIAL RECEPTOR ACTIVATION BY GRAIN OVERLOAD RUMEN FLUIDS

Rumen fluids, obtained during the loss of forestomach motility in sheep experiencing ruminal lactic-acidosis, activated reticulo-ruminal epithelial receptors when applied to the receptive fields of these receptors. Rumen fluids which contained the highest levels of undissociated volatile fatty acids (VFAs) were the most effective. Since the levels of undissociated VFAs in effective rumen fluids were, in some cases, lower than the determined VFA thresholds of the receptors, receptor activation in these instances may have been facilitated by the levels of free lactic acid within these samples. Key words: Grain overload, epithelial receptors, ruminal stasis