Removal Of Volatile Fatty Acids Research Articles

Microbial populations associated with fixed- and floating-bed reactors during a two-stage anaerobic process.

Microbial populations associated with methanogenic fixed- or floating-bed bioreactors used for anaerobic digestion of lignocellulosic waste were investigated. Fluorescent in situ hybridization (FISH) was used to characterize microorganisms in samples obtained from different heights in the reactors, which were operated in a semi-continuous manner (feeding and mixing once every 2 days). The FISH results showed that Methanosaeta concilii cells were most numerous at the bottom of both reactors. M. concilii cells were more abundant in the fixed-bed reactor (FXBR), which performed better than the floating-bed reactor (FLBR). Species of the Methanosarcina genera (mainly M. barkeri and M. mazei) were also observed in the FLBR but rarely in the FXBR. Methane production in each of the reactors ranged from 0.29 to 0.33 m3 CH(4)/kg COD(rem) (chemical oxygen demand removed). The removal of volatile fatty acids (VFA; 70-75 h) in the FXBR was more efficient than in the FLBR.

Treatment of odorous volatile fatty acids using a biotrickling filter

In this study, a novel fibrous bioreactor was developed for treating odorous compounds present in contaminated air. The first stage of this work was a preliminary study which aimed at investigating the feasibility of using the fibrous bioreactor for the removal of malodorous volatile fatty acids (VFA) that is a common odorous contaminant generated from anaerobic degradation of organic compounds. The kinetics of microbial growth and VFA degradation in the selected culture, and the performance of the submerged bioreactor at different VFA mass loadings were studied. Above 95% of VFA removal efficiencies were achieved at mass loadings up to 22.4 g/m 3/h. In the second stage, the odour treatment process was scaled up with system design and operational considerations. A trickling biofilter with synthetic fibrous packing medium was employed. The effects of inlet VFA concentration and empty bed retention time (EBRT) on the process performance were investigated. The bioreactor was effective in removing VFA at mass loadings up to 32 g/m 3/h, beyond which VFA started to accumulate in the recirculation liquid, indicating the biofilm was unable to degrade all of the VFA introduced. Although VFA accumulated in the liquid phase, the removal efficiency remained above 99%. This suggested that the biochemical reaction rather than gas–liquid mass transfer was the limiting step of the treatment process. In addition, the biotrickling filter was stable for long-term operation with relatively low and steady pressure drop, no clogging and degeneration of the packing material occurred during the four-month study.

Heterotrophic Bacterial Activities and Treatment Performance of Surface Flow Constructed Wetlands Receiving Woodwaste Leachate

Heterotrophic activities were investigated by measuring 3H-leucine incorporation to bacterial protein and 14C-glucose turnover in surface flow constructed wetlands receiving woodwaste leachate. No significant longitudinal variation was found in heterotrophic activities of bacterioplankton. An open wetland, a vegetated wetland, and a fertilized vegetated wetland were used to examine the effects of vegetation and ammonium nitrate amendment. There was not a significant difference in treatment performance among the three wetlands, except for a significant pH increase and more efficient volatile fatty acids removal in the fertilized wetland. The fertilized wetland had the highest leucine incorporation rate and shortest glucose turnover time accompanied by the lowest glucose mineralization percentage, followed by the open wetland, then the vegetated wetland. Planktonic and sedimentary bacteria contributed to the majority of the total heterotrophic activities; epiphytic bacteria played a minor role. Heterotrophic activities were influenced by the availability of nutrient, electron acceptor, and organic substrate.

Evolution of clog formation with time in columns permeated with synthetic landfill leachate

Laboratory column tests conducted to gain insight regarding the biological and chemical clogging mechanisms in a porous medium are presented. To seed the porous medium with landfill bacteria, a mixture of Keele Valley Landfill and synthetic leachate permeated through the column under anaerobic conditions for the first 9 days of operation. After this, 100% synthetic leachate was used. The synthetic leachate approximated Keele Valley Landfill leachate in chemical composition but contained negligible suspended solids and bacteria compared with real leachate. The removal of volatile fatty acids (VFAs), primarily acetate, in leachate as it passed through the medium was highly correlated with the precipitation of calcium carbonate (CaCO 3(s)) from solution. The columns experienced a decrease in drainable porosity from an initial value of about 0.38 to less than 0.1 after steady state chemical oxygen demand (COD) removal, resulting in a five-order magnitude decrease in hydraulic conductivity. The decrease in drainable porosity prior to steady state COD removal was primarily due to the growth of a biofilm on the medium surface. After steady state COD removal, calcium precipitation was at least equally responsible for the decrease in drainable porosity as biofilm growth. Clog composition analyses showed that CaCO 3(s) was the dominant clog constituent and that 99% of the carbonate in the clog material was bound to calcium.

Effectiveness of short-term aeration in treating swine finishing manure to reduce odour generation potential

Abstract The work presented here is to elucidate removals of organic matter, nitrogen and odour generation potential in swine manure treated by short-term aeration. The experiment was composed of a 4 × 3 factorial design, with solids levels ranging from 0.5 to 4.0% and aeration lengths from 0.5 to 4.0 days at an airflow rate of 1.2 L s−1 m−3. Manure samplings were conducted on days 5, 10, and 20 during the storage. Solids (TS: total solids; TVS: total volatile solids), 5-day biochemical oxygen demand (BOD5), total Kjeldahl nitrogen (TKN), and volatile fatty acids (VFAs) for manure samples were measured to characterize the effectiveness of aeration. According to this study, solids (TS and TVS), BOD5, TKN and VFAs were reduced in varying degrees with respect to the aeration length and storage time. Removal ratios of VFAs from 46.6 to 78.5, 49.4 to 86.9, and 48.8 to 95.6% were achieved under the aeration length of 0.5, 2.0, and 4.0 days, respectively. The variation of odour generation potential in the manure treated by short-term aeration can be linearly evaluated by the concentrations of solids, BOD5, and/or TKN, but the feasibility could be impaired for manure with high solids content. Meanwhile, foaming was found troublesome during the process of short-term aeration. Four-day aeration is recommended to treat manure with a total solids level of less than 2.0% for odour control because over 70% of VFAs removal efficiencies can be achieved.

Removal of volatile fatty acids with immobilized Rhodococcus sp. B261

The removal of aqueous volatile fatty acids (VFA) in wastewater and spoiled waste-foods by immobilized Rhodococcus sp. B261 was investigated. The n-valeric acid (0.5%) was completely removed within 25 h under the following conditions; solution pH, 8.0; air flow rate, 0.2 l/min; superficial velocity, 0.96 h −1; temperature, 37 °C. Under the optimized conditions, the acetic (8525 ppm), propionic (7310 ppm) and n-butyric (4360 ppm) except n-valeric (2572 ppm) acids from the wastewater were completely removed by immobilized Rhodococcus sp. B261 in 24 h. The acetic (7810 ppm), propionic (8942 ppm) and butyric (5730 ppm) acids from the solution of spoiled waste-foods were effectively removed by immobilized Rhodococcus sp. B261 from 48 h within 60 h but n-valeric acid (3625 ppm) took 72 h.

Removal of volatile fatty acids with immobilized Rhodococcus sp. B261

The removal of aqueous volatile fatty acids (VFA) in wastewater and spoiled waste-foods by immobilized Rhodococcus sp. B261 was investigated. The n-valeric acid (0.5%) was completely removed within 25 h under the following conditions; solution pH, 8.0; air flow rate, 0.2 l/min; superficial velocity, 0.96 h−1; temperature, 37 °C. Under the optimized conditions, the acetic (8525 ppm), propionic (7310 ppm) and n-butyric (4360 ppm) except n-valeric (2572 ppm) acids from the wastewater were completely removed by immobilized Rhodococcus sp. B261 in 24 h. The acetic (7810 ppm), propionic (8942 ppm) and butyric (5730 ppm) acids from the solution of spoiled waste-foods were effectively removed by immobilized Rhodococcus sp. B261 from 48 h within 60 h but n-valeric acid (3625 ppm) took 72 h.

Effects of bioreactor temperature and time on odor‐related parameters in aerated swine manure slurries

Previous studies have linked odor generation from swine manure to some characteristics of the liquid manure such oxidation‐reduction potential (ORP), five‐day biochemical oxygen demand (BOD5), volatile fatty acids (VFAs), and predominant microbial population. This study investigated the effect of bioreactor temperature and time on the aforementioned parameters during aeration of swine manure. Five reactors (13 1 capacity) loaded with swine manure and maintained at temperatures of 5, 10, 15, 20, and 25oC, were supplied with air for 15 days to maintain aerobic conditions. Large fluctuations in ORP (‐120 to 360 mV) were observed in the first seven days of aeration, which stabilized thereafter regardless of the bioreactor temperature. The percentage removal of VFAs and BOD5 in the manure significantly increased from 0.0% on day one to 87.8% and 65.3%, respectively, on day nine, and remained relatively constant thereafter. The mean percentage of VFAs and BOD5 removed also increased significantly with an increase in the bioreactor temperature. The VFAs and BOD5 removal increased by approximately 25% and 35%, respectively, in going from 5 to 25°C, during the 15 days of aeration. Both VFAs and BOD5 in the manure were significantly correlated with ORP, aerobic bacteria, and anaerobic bacteria. The data suggested that continued aeration for seven days at 20 or 25°C was sufficient for significant reduction of odor precursors (VFAs and BOD5) and in stabilization of swine manure. A linear correlation of 0.97 between VFAs and BOD5 indicated that the two parameters can be used interchangeably as indicators of odor release potential in swine manure.

Investigation of membrane processes for the removal of volatile fatty acids

The accumulation of volatile fatty acids such as acetic acid can cause reactor pH problems and the inhibition of microorganisms utilised in anaerobic digestion processes. A cross-flow membrane process using Teflon and ion-exchange membranes was investigated as a means of separating acetic acid from pure acetic acid solution and rumen fluid. Acetic acid transfer across the Teflon membrane was dependent on the free acid concentration (CH3COOH) in the acid solution. Concurrent transfer of water was minimal due to the hydrophobic nature of the membrane. The strong base anionic exchange membrane facilitated the separation of acetic acid from both pure solutions and rumen fluid with flux again being dependent on the free acid gradient across the membrane. Flux rates were lower than other studies of diffusion dialysis, however, this may be partly attributed to improper preparation of the membrane. The currently achieved rates of transfer using these membranes are very low and are therefore not yet suitable for full-scale use in anaerobic digestion. Additional research is needed to achieve higher trans-membrane transport rates at reasonable costs.

Use of electrodialysis as a vfa recovery process From acidogenic of msw synthetic leachates

An electrodialysis (ED) process was tested for volatile fatty acids (VFA) recovery from a simulated leachate of acidogenesis of municipal solid wastes (MSW). The effect of initial VFA concentration in leachate, applied voltage and flow rate on VFA removal efficiency were evaluated. Four different leachate compositions were examined at three different applied voltages and at three different flow rates. Higher removal levels were obtained at low VFA initial concentration, high voltages levels and high flow rates. ED process was showed higher removal efficiency with shorts chain acids, but VFA final concentration was directly related with initial concentration of each acid. After VFA recovery tests of chemical reaction with ethanol were carried out for ethyl esters production as gas oil additives. Results of these tests showed a transformation efficiency of 26%.

Treatment of winery wastewater by an anaerobic sequencing batch reactor

Treatment of winery wastewater was investigated using an anaerobic sequencing batch reactor (ASBR). Biogas production rate was monitored and permitted the automation of the bioreactor by a simple control system. The reactor was operated at an organic loading rate (ORL) around 8.6 gCOD/L.d with soluble chemical oxygen demand (COD) removal efficiency greater than 98%, hydraulic retention time (HRT) of 2.2 d and a specific organic loading rate (SOLR) of 0.96 gCOD/gVSS.d. The kinetics of COD and VFA removal were investigated for winery wastewater and for simple compounds such as ethanol, which is a major component of winery effluent, and acetate, which is the main volatile fatty acid (VFA) produced. The comparison of the profiles obtained with the 3 substrates shows that, overall, the acidification of the organic matter and the methanisation of the VFA follow zero order reactions, in the operating conditions of our study. The effect on the gas production rate resulted in two level periods separated by a sharp break when the acidification stage was finished and only the breaking down of the VFA continued.

Production and transformation of volatile fatty acids from sludge subjected to hydrothermal treatment

The production of useful organic matter from sludge expands the potential for utilizing the product as a resource. This paper is focused on the accumulation and removal of volatile fatty acids (VFAs) produced from primary, secondary and a mixture of both sludges using hydrothermal treatment with and without the use of oxidants. The results confirmed that the maximum accumulation of VFAs was achieved at moderate hydrothermal treatment temperatures below 200 degrees C, and was dependent on the composition of sludge and the amount of oxidant used for treatment. The maximum accumulation reached 0.26-0.36 mg VFAs as COD per mg VS from the three sludge types. Acetic acid dominated the VFAs and was followed by propionic acid, with the other VFAs accounting for less than 5% of the total VFAs. As hydrothermal treatment progressed in terms of COD removal, the contribution of acetic acid to the total VFAs increased while the contributions of the other VFAs decreased. The VFAs constituted a major component of the accumulated dissolved organic matter, which reached a maximum of 0.5-0.7 mg soluble COD per mg VS from the three sludge types.

ENHANCING DAIRY LAGOON PERFORMANCE WITH HIGH–RATE ANAEROBIC DIGESTERS

In a twostage study, the possibility of using highrate anaerobic digesters to enhance the performance of dairylagoons was explored. Four anaerobic sequencing batch reactors (ASBR) and four downflow anaerobic filters (DFAF) weretested, with two of each type operated at 25
C, and the other two at 35
C. The first stage of the experiment explored usingthe highrate digesters on liquid effluent from a screwpress treating dairy manure slurry. The firststage experimentdemonstrated that settling processes, rather than biodegradation, accounted for most of the organic matter reduction in bothreactor types, when operated at a 0.5d hydraulic retention time. Specifically, settling accounted for an average of 100% ofthe chemical oxygen demand (COD) removal in the ASBR reactors, and for an average of 72% of the COD removal in theDFAF reactors. These results prompted the second stage of the experiment, which explored the possibility of using the reactorsto remove volatile fatty acids (VFAs) from dairy lagoon supernatant. Diluted manure slurry was spiked with acetic acid (HAc)to simulate the supernatant of an overloaded lagoon. At VFA loading rates of 1.0 and 3.0 kg HAc m 3 d 1 , both reactor typesachieved moderate VFA removal. However, at a loading rate of 6.0 kg HAc m 3 d 1 , the ASBR reactors were ineffective,whereas the DFAF reactors, at both 25
C and 35
C, removed more than 80% of the influent HAc. At a loading rate of 12 kgHAc m 3 d 1 , the DFAFs achieved removal rates of 75%; removal rates dropped to 50% at the maximum loading tested, 24 kgHAc m 3 d 1 . Based on these experiments, it appears that the DFAF reactors are suited to the task of rapidly removingaccumulated VFA from lagoon supernatant.

Continuous detoxification, transformation, and degradation of nitrophenols in upflow anaerobic sludge blanket (UASB) reactors

The anaerobic transformation and degradation of nitrophenols by granular sludge was investigated in upflow anaerobic sludge blanket (UASB) reactors continuously fed with a volatile fatty acid (VFA) mixture as the primary substrate. During the start-up, subtoxic concentrations of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2, 4-dinitrophenol (2, 4-DNP) were utilized. 4-NP and 2, 4-DNP were readily converted to the corresponding aromatic amine; whereas 2-NP was converted to nonaromatic products via intermediate formation of 2-aminophenol (2-AP). These conversions led to a dramatic detoxification of the mononitrophenols because the reactors treated the nitrophenolics at the concentrations which were over 25 times higher than those that caused severe inhibition. VFA removal efficiencies greater than 99% were achieved in both reactors at loading rates greater than 11.4 g COD per liter of reactor volume per day even at volumetric loading of mononitrophenols up to 910 mg/L . d.The sludges obtained from each of the reactors at the end of the continuous experiments were assayed for their specific nitrophenol reducing activity in the presence of different primary substrates. Reduction rates of 45 and 26 mg/g volatile suspended solids per day were observed for 2-NP and 4-NP, respectively, when utilizing the VFA mixture as primary substrate. Hydrogen, an interspecies-reduced compound, and substrates that provide interspecies-reducing equivalents-such as butyrate, propionate, and ethanol stimulated nitrophenol reduction, whereas acetate and methanol did not. Anaerobic batch biodegradability tests with the 2-NP-adapted sludge revealed that its corresponding aromatic amine, 2-AP, was degraded to methane at a specific rate of 14.5 mg/g VSS . d. Acetate was observed to be the major intermediate during 2-AP degradation in the presence of a specific methanogenic inhibitor 2-bromoethanesulfonate. The results of this study indicate that UASB reactors can be applied to rapidly detoxify and, under certain circumstances, degrade nitroaromatic compounds. (c) 1996 John Wiley & Sons, Inc.

Design and performance of a fibrous bed bioreactor for odor treatment.

Biological processes have become popular for odor treatment. In this study, a novel fibrous bed bioreactor was applied for treatment of odorous gas. The column reactor was packed with spirally wound fibrous sheet material on which a consortium of microorganisms selected from activated sludge was immobilized. The first stage of this work comprised a preliminary study that aimed at investigating the feasibility of the fibrous bed bioreactor for treatment of odorous volatile fatty acids (VFAs). In this stage, the performance of a fibrous bed bioreactor at increasing mass loadings ranging from 9.7 to 104.2 g/(m3.h) was studied. VFA removal efficiencies above 90% were achieved at mass loadings up to 50.3 g/(m3.h). At a mass loading of 104.2 g/(m3.h), removal efficiency was found to be 87.7%. In the second stage of the work, the process was scaled up with design and operational considerations, namely, packing medium, process condition, and configuration selections. A trickling biofilter with synthetic fibrous packing medium was selected. It was operated under countercurrent flow of gas and liquid streams. The effects of inlet concentration and empty bed retention time on bioreactor performance were studied. The bioreactor was effective in treating odorous VFAs at mass loadings up to 32 g/(m3.h), at which VFAs started to accumulate in the recirculation liquid, indicating that the biofilm was unable to degrade all the VFAs introduced. Although VFAs accumulated in the liquid phase, the removal efficiency remained above 99%, implying that the biochemical reaction rate, rather than gas-to-liquid mass transfer rate, was the limiting factor of this process. The bioreactor was stable for long-term operation; no clogging and degeneration of the packing medium was observed during the 4-mo operation.

Production of useful organic matter from sludge using hydrothermal treatment

The need for readily biodegradable organic matter to support denitrification and enhanced biological phosphorus removal (EBPR) can be satisfied using external or internal carbon sources. This paper examines the production and removal of volatile fatty acids (VFAs), mainly acetic acid, and other hydrolyzed products from sludge using hydrothermal treatment at subcritical (<374°C) and supercritical (>374°C) temperatures. Subcritical water oxidation (SubCWO) achieved effective hydrolysis (>95% as COD) of the sludge organic solids but incomplete oxidation (<95% as COD) of the organic component of sludge. SubCWO also produced COD-rich liquors, which contained as much as 30% wt/wt hydrolyzed COD, including 10% wt/wt acetate. The contribution of acetate to COD in the liquor increased as treatment progressed, accounting for as much as 80% of the soluble COD when the oxidation efficiency exceeded 80%. While SubCWO resulted in partial COD removal, complete oxidation (>99% as COD) of the organic component of sludge, including oxidation of hydrolysis products, was achieved using supercritical water oxidation (SCWO). Accordingly, hydrothermal treatment using SubCWO and SCWO can provide a useful sludge management option, combining sludge mass and volume reduction with the production of useful organic matter to support biological nutrient removal.

Removal of volatile acids from synthetic landfill leachate by anaerobic biofilms on drainage aggregates: a laboratory study

Populations of anaerobic bacteria derived from gassing landfills were established on various solid media in laboratory-scale models of landfill drains. Solutions of salts and volatile fatty acids (VFAs), simulating landfill leachates, were circulated through the models for periods of 400 to 800 days and the removal of VFAs and the formation of gas were measured. The ability of the colonized aggregate to remove VFAs from the leachates increased to a maximum over periods of time ranging from 50 to 150 days after the initial colonization phase. The highest rates of VFA removal [3500 mg l–1 (bed vol.) day–1 at a leachate flow rate of 2.59 l d–1 with 16 500 mg l–1 total VFAs] were found at the tops of the columns, but the lower sections were also colonized by bacteria capable of removing VFAs. The initial adaptation of the bacterial population to propionic acid degradation was slower than the adaptation to acetate and butyrate degradation. Increasing the propionate concentration in the leachate from 2500 to 7500 mg l–1 caused a 50% reduction in the rate of removal of VFAs by a bacterial population adapted to a mixture of acetate, propionate and butyrate. The bacterial population eventually adapted to the higher concentrations of propionate. Changing from saturated to unsaturated flow conditions in the drainage models reduced the specific rate of removal of VFAs by 50%.

Removal of volatile acids from synthetic landfill leachate by anaerobic biofilms on drainage aggregates: a laboratory study

Populations of anaerobic bacteria derived from gassing landfills were established on various solid media in laboratory-scale models of landfill drains. Solutions of salts and volatile fatty acids (VFAs), simulating landfill leachates, were circulated through the models for periods of 400 to 800 days and the removal of VFAs and the formation of gas were measured. The ability of the colonized aggregate to remove VFAs from the leachates increased to a maximum over periods of time ranging from 50 to 150 days after the initial colonization phase. The highest rates of VFA removal [3500 mg 1-1 (bed vol.) day -1 at a leachate flow rate of 2.59 1 d-1 with 16 500 mg 1-1 total VFAs] were found at the tops of the columns, but the lower sections were also colonized by bacteria capable of removing VFAs. The initial adaptation of the bacterial population to propionic acid degradation was slower than the adaptation to acetate and butyrate degradation. Increasing the propionate concentration in the leachate from 2500 to 7500 mg 1 -1 caused a 50% reduction in the rate of removal of VFAs by a bacterial population adapted to a mixture of acetate, propionate and butyrate. The bacterial population eventually adapted to the higher concentrations of propionate. Changing from saturated to unsaturated flow conditions in the drainage models reduced the specific rate of removal of VFAs by 50%.

Psychrophilic anaerobic treatment of low strength wastewaters

Psychrophilic (2 to 20°C) anaerobic treatment of low strength synthetic and malting wastewater was investigated using a single and two module expanded granular sludge bed (EGSB) reactor system. The chemical oxygen demand (COD) removal efficiencies found in the experiments exceeded 90 % in the single module reactor at an organic loading rate up to 12 g COD dm−3 day−1 and a HRT of 1.6 h at 10-12°C ambient temperature using influent concentrations ranging from 500 to 800 mg COD dm−3. When a two module EGSB system was used at the temperature range 10-15°C, soluble COD removal and volatile fatty acids removal of 67-78% and 90-96% were achieved, respectively, and an OLR between 2.8-12.3 kg COD m−3 day−1 and a HRT of 3.5 h. The second module serves mainly as a scavenger of non-degraded volatile fatty acids (VFA) from the first module. The optimal temperatures for substrate conversion of reactor sludge, after it has been exposed to long term psychrophilic conditions, were similar to those of the original mesophilic inoculum. The specific activities of the sludge in the reactor increased in time by a factor 3, indicating enrichment of methanogens and acetogens even at low temperatures. By adapting the process design to the expected prevailing conditions inside the reactor, the loading potentials and overall stability of the anaerobic high-rate process may be distinctly improved under psychrophilic conditions. The results obtained clearly reveal the big potentials of anaerobic wastewater treatment under low ambient (10-12°C) temperature conditions for low strength wastewaters, very likely including domestic sewage.

Performance of fibrous bed bioreactor for treating odorous gas. Scientific note.

A fibrous bed bioreactor was used for treatment of odorous volatile fatty acid (VFA). The effect of gaseous VFA (acetic, propionic, and butyric acids) mass loading on the bioreactor performance was investigated. The VFA degrading microbial culture was selected from activated sludge by the three VFAs using a shake-flask culture. The selected microorganisms were then immobilized in a biofilter using cotton fabric as packing material. In the biofiltration experiment, the inlet gas flow rates ranged from 1 to 4 L/min, the total VFA concentrations ranged from 0.10 to 0.43 g/m3, and the resulting total mass loadings of VFA studied ranged from 9.7 to 104.3 g/m3/h. At total mass loading of 104.3 g/m3/h, the VFA removal efficiency was 87.7%. Higher removal efficiencies (>90%) were achieved at mass loadings below 50.3 g/m3/h.