Anaerobic Granules Research Articles

Long-term impact of dissolved O2 on the activity of anaerobic granules

The impact of influent dissolved O(2) on the characteristics of anaerobic granular sludge was investigated at various dissolved O(2) concentrations (0.5-8.1 ppm) in 1- and 5-L laboratory-scale upflow anaerobic sludge bed (UASB)-like anaerobic/aerobic coupled reactors with a synthetic wastewater (carbon sources containing 75% sucrose and 25% acetate). The rate of dissolved O(2) supplied to the coupled reactor was as high as 0.40 g O(2)/L(rx).d, and the anaerobic/aerobic coupled reactors maintained excellent methanogenic performances at a COD loading rate of 3 g COD/L(rx).d even after the reactors had been operated with dissolved O(2) for 3 months. The activities of granular sludge on various substrates (glucose, propionate, and hydrogen) were not impaired, and acetate activity was even improved over a short term. However, after 3 months of operation, slight declines on the acetoclastic activities of granules were observed in the coupled reactor receiving the recirculated fluid containing 8.1 ppm dissolved O(2).Methane yield in the anaerobic control reactor and anaerobic/aerobic coupled reactors revealed that a significant aerobic elimination (up to 30%) of substrate occurred in the coupled reactors, as expected. The presence of dissolved O(2) in the recirculated fluid resulted in the development of fluffy biolayers on the granule surface, which imposed a negative impact on the settleability of granular sludge and caused a slightly higher sludge washout. This research shows that the anaerobic/aerobic coupled reactor can be successfully operated under O(2)-limited conditions and is an ideal engineered ecosystem integrating oxic and anaerobic niches. (c) 1996 John Wiley & Sons, Inc.

Differentiation of methanosaeta concilii and methanosarcina barkeri in anaerobic mesophilic granular sludge by fluorescent In situ hybridization and confocal scanning laser microscopy

Oligonucleotide probes, designed from genes coding for 16S rRNA, were developed to differentiate Methanosaeta concilii, Methanosarcina barkeri, and mesophilic methanogens. All M. concilii oligonucleotide probes (designated MS1, MS2, and MS5) hybridized specifically with the target DNA, but MS5 was the most specific M. concilii oligonucleotide probe. Methanosarcina barkeri oligonucleotide probes (designated MB1, MB3, and MB4) hybridized with different Methanosarcina species. The MB4 probe specifically detected Methanosarcina barkeri, and the MB3 probe detected the presence of all mesophilic Methanosarcina species. These new oligonucleotide probes facilitated the identification, localization, and quantification of the specific relative abundance of M. concilii and Methanosarcina barkeri, which play important roles in methanogenesis. The combined use of fluorescent in situ hybridization with confocal scanning laser microscopy demonstrated that anaerobic granule topography depends on granule origin and feeding. Protein-fed granules showed no layered structure with a random distribution of M. concilii. In contrast, a layered structure developed in methanol-enriched granules, where M. barkeri growth was induced in an outer layer. This outer layer was followed by a layer composed of M. concilii, with an inner core of M. concilii and other bacteria.

Chlorophenol sorption to anaerobic granules under dynamic conditions

This study examined the nonideal sorption phenomena and the effect of mixing conditions on sorption of five chlorophenols (CPs) onto anaerobic granules (AG) under dynamic conditions in continuous bioreactors. Under dynamic bioreactor conditions, anaerobic sorption of CPs which follow sorption linearity and sorption–desorption singularity, can be described by a dynamic model incorporating linear sorption. Nonequilibrium sorption caused by diffusion limitations in anaerobic reactors was found to be negligible, which is a result of the strong hydrodynamic dispersion that prevails in anaerobic reactors and the high porosity of AG. However, minor nonideal sorption phenomena were observed for 3,4-dichlorophenol and pentachlorophenol, both of which showed sorption–desorption isotherm hysteresis.

Influence of synthetic and natural polymers on the anaerobic granulation process

The influence of synthetic Percol 763 and natural chitosan polymers on the granulation rate of suspended anaerobic sludge was studied in laboratory-scale upflow anaerobic sludge bed (UASB)-like reactors. The results showed that supplementation of the reactors with polymers, either natural or synthetic, enhanced the granulation in comparison to control reactors (without the addition of polymers). A greater granulation was, however, obtained with chitosan compared to that with Percol 763. Chitosan yielded a granulation rate as high as 56 m/d compared to 35 m/d Percol 763. The superior granulation performance of chitosan was probably related to its polysaccharidic structure, hence acting similarly to the extracellular polymeric substances (EPS) in aggregating anaerobic sludge. The granules specific activities were enhanced in the reactors supplemented with both polymers compared to those in control reactors. Overall, the results showed that polymers play a more critical role than microbial trophic groups in enhancing anaerobic granulation in UASB-like reactors.

Anaerobic degradation kinetics of acetic acid in the presence of 2,4-dichlorophenol (2,4-DCP)

Anaerobic degradation kinetics of acetic acid (HAc) in the presence of 2,4-DCP were investigated, using 2,4-DCP acclimated anaerobic granules. The effect of HAc on 2,4-DCP dechlorination was minimal. On the basis of model discrimination, the degradation kinetics of HAc were found to follow uncompetitive inhibition with 2,4-DCP as an inhibitor.

Precipitates in anaerobic granules treating sulphate-bearing wastewater

Three types of biogranules treating wastewater containing various sulphate concentrations were examined using scanning and transmission electron microscopies. The two biogranules treating wastewater containing sulphate up to 2000 mg·l −1 showed high degrees of activities. However, activities of the third biogranules, which contained 102 mg-S·(g-VSS) −1 after treating wastewater containing sulphate up to 7500 mg·l −1 for over 286 days, dropped drastically. Microscopic examinations showed that precipitates accumulated in the biogranules treating sulphate-bearing wastewater; the degrees of precipitation increased with sulphate concentration in wastewater and the duration of treatment. Excessive precipitation was found throughout the entire biogranule cross-section of the third biogranules. Analyses by X-ray spectrometry further showed that the precipitates were mainly composed of sulphur, plus copper, iron and nickel presumably in the form of metal sulphides. These observations suggest that the inhibition of bioactivities of anaerobic granules was likely resulted from the accumulated sulphureous precipitates on the bacterial surface. This point was overlooked by previous investigators who tended to attribute the inhibition to the toxic effects of either sulphate, sulphide or un-dissociated H 2S.

Effect of Physiochemical Conditions on Anaerobic Sorption of Chlorophenols

Sorption tests based on factorial design were conducted to screen out important physicochemical factors affecting the sorption of chlorophenols to anaerobic granules. The factors considered were pH, temperature, ionic strength, and type of chlorophenol. Two level factorial design was applied and 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) were used as model chemicals in the tests. The results show that, other than the type of chlorophenol, pH is the most significant factor affecting anaerobic sorption of chlorophenols. The effect of temperature on sorption is negligible within the temperature limits in the sorption tests. Ionic strength has a minor effect on PCP sorption but not on 2,4-DCP.

Influence of synthetic and natural polymers on the anaerobic granulation process

The influence of synthetic Percol 763 and natural chitosan polymers on the granulation rate of suspended anaerobic sludge was studied in laboratory-scale upflow anaerobic sludge bed (UASB)-like reactors. The results showed that supplementation of the reactors with polymers, either natural or synthetic, enhanced the granulation in comparison to control reactors (without the addition of polymers). A greater granulation was, however, obtained with chitosan compared to that with Percol 763. Chitosan yielded a granulation rate as high as 56 m/d compared to 35 m/d with Percol 763. The superior granulation performance of chitosan was probably related to its polysaccharidic structure, hence acting similarly to the extracellular polymeric substances (EPS) in aggregating anaerobic sludge. The granules specific activities were enhanced in the reactors supplemented with both polymers compared to those in control reactors. Overall, the results showed that polymers play a more critical role than microbial trophic groups in enhancing anaerobic granulation in UASB-like reactors.

Heavy metal uptake during anaerobic digestion of combined electroplating and brewery wastewaters

Batch and continuous culture laboratory-scale experiments were conducted to quantify the effect of combining chrome and nickel electroplating effluent (EE) and brewery effluent as substrate for established anaerobic digester granules. EE at a 1:12 ratio in brewery effluent was inhibitory to anaerobic digestion but acclimation at a 1:24 ratio occurred during continuous culture experiments. At least 90% of the chromium and nickel was absorbed by the granules with nickel attaching to granule perimeters while chromium penetrated into deeper recesses. © Rapid Science Ltd. 1998

Anaerobic degradation kinetics of acetic acid in the presence of 2,4-dichlorophenol (2,4-dcp)

Anaerobic degradation kinetics of acetic acid (HAc) in the presence of 2,4-DCP were investigated, using 2,4DCP acclimated anaerobic granules. The effect of HAc on 2,4-DCP dechlorination was minimal. On the basis of model discrimination, the degradation kinetics of HAc were found to follow uncompetitive inhibition with 2,4-DCP as an inhibitor.

Influence of metabolic activity on biosorption of halogenated aromatics by anaerobic granules

Equilibrium sorption isotherms and sorption kinetics of 2,4‐dichlorophenol (2,4‐DCP) and 2,3,6‐trichlorophenol (2,3,6‐TCP) on live metabolically dormant, live metabolically active, and chemically inactivated anaerobic granules were investigated using batch serum bottle tests. Two metabolic inhibitors, sodium azide (NaN3) and bromoethane‐sulfonic acid (BESA), were used. Sodium azide was used to specifically inactivate the metabolic activity of the three microbial consortia (hy‐drolytic, acidogenic, and methanogenic bacteria), and BESA was used to specifically inactivate the metabolic activity of the methanogenic bacteria. The sorption of 2,4‐DCP and 2,3,6‐TCP by anaerobic granules was a rapid process, reaching equilibrium in approximately five hours. Experimental results show insignificant difference in the biosorption of live metabolically dormant bacteria (control 1) that make up the whole anaerobic microbial consortia, metabolically dormant hydrolytic and acidogenic bacteria with chemically inactivated methanogens (BESA‐D), metabolically active hydrolytic and acidogenic bacteria with chemically inactivated methanogens (BESA‐A), chemically inactivated hydrolytic, acidogenic, and methanogenic bacteria (NaN3‐I) and live metabolically active anaerobic granule consortia (control 2). Biosorption isotherms for 2,4‐DCP and 2,3,6‐TCP using live metabolically dormant, chemically inhibited (BESA‐A, BESA‐D, NaN3‐I) and live metabolically active biomass fit very well the linear and Freundlich equations, respectively. No large difference in the ? and 1/n constants for the different sludge conditions was observed. Experimental findings indicate that anaerobic biosorption for all three anaerobic microbial groups in the consortia is largely a physical‐chemical process that is relatively unaffected by microbial metabolic activity.

Inhibition of methanogenic activity of starch-degrading granules by aromatic pollutants

The effects of nine common aromatic pollutants from chemical industry on the bioactivity of anaerobic granules were examined. The granules were obtained from an upflow anaerobic sludge blanket (UASB) reactor treating wastewater containing colloidal starch. The specific methanogenic activities (SMA) of granules were measured at 37°C in serum vials using 3000 mg/l of colloidal starch as substrate, plus individual pollutants at various concentrations. The toxicity was expressed by the IR50 and IC50 values, i.e. the toxicant/biomass ratio and concentration at which levels the granules exhibited only 50% of their original bioactivities. Results showed that in general the granules exhibited mild resistance to toxicity of aromatic pollutants, probably due to the granules' layered microstructure. The toxicities, which were dependent on the nature of chemical functional group, of the aromatic pollutants were in the following descending order: cresols > phenol > hydroxyphenols/phthalate > benzoate. There was only marginal difference between the toxicity of the steric isomers. For the seven phenolic pollutants, the more hydrophobic the functional group the higher the toxicity. The granules' resistance to toxicity suggested the plausibility of anaerobic treatment of wastewater from the chemical industry.

Dynamic Model for UASB Reactor Including Reactor Hydraulics, Reaction, and Diffusion

A dynamic model has been developed to describe upflow anaerobic sludge blanket (UASB) reactors from several aspects including reactor hydraulics, biological reaction kinetics, and mass transfer within anaerobic granules. A flow model of a nonideal continuously stirred tank reactor (CSTR) followed by a dispersion plug flow reactor (PFR) was used to simulate the reactor hydraulics as observed from a LiCl tracer study. The dynamic model based on this flow model was then evaluated by a set of acetate impulse data and verified with a data set from a two-step acetate feed increase experiment from a bench-scale UASB reactor. The model describes UASB reactor performance well. Simulation results indicate significant effects of reactor nonideal flow, diffusional resistance, as well as degradation kinetics on overall substrate utilization rate. Sensitivity analyses on model parameters Ks, km, KL, D, R, and nonideal flow factors revealed granule size has a strong impact on the reactor performance. The effect of KL is not significant. Reactor mixing was improved by an increase in biogas production.

Influence of the starting microbial nucleus type on the anaerobic granulation dynamics

The influence of four different granulation precursors, syntroph-enriched methanogenic consortia, Methanosaeta-enriched, Methanosarcina-enriched nuclei and acidogenic flocs, on the time course of complex granule development and the lag time for start-up was investigated in four upflow anaerobic sludge-bed and filter reactors. Although the operational conditions allowed the maintenance of the same specific growth rate of biomass in the four reactors, granulation proceeded rapidly with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei. However, granulation was significantly retarded when acidogenic flocs were used as precursors. The granule mean Sauter diameter increased rapidly in the reactor inoculated with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei and reached, at the end of the experiment, 3.1, 2.7 and 2.4 mm compared to 1.1 mm in that inoculated with acidogenic flocs. This corresponded to a rate of granule size increase of 31, 21, 18 μm/day in syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei, respectively, compared to 7 μm/day in acidogenic flocs. Biomass specific activities (i.e. acidogenic, syntrophic and methanogenic activities) increased stepwise in all reactors with time, especially in those inoculated with syntroph/methanogenic consortia and Methanosaeta nuclei. From these results it appears that syntrophs and Methanosaeta spp. play an important role in the anaerobic granulation process.

Anaerobic degradation kinetics of 2,4-dichlorophenol (2,4-DCP) with linear sorption

Degradation of 2,4-DCP by acclimated anaerobic granules enriched at two specific loading rates was examined experimentally in batch mode. The data from process curves were analyzed by nonlinear regression to estimate parameters in the Haldane inhibition equation and one of its modified forms to obtain quantitative information on degradation kinetics. Linear sorption kinetics of 2,4-DCP were employed in data treatment to discriminate between the effects of sorption and biodegradation. It was observed that the modified inhibition equation described experimental data better than the Haldane inhibition equation since the later failed to predict the trend in experimental data. Parameter values estimated with the modified inhibition equation for two types of anaerobic granule, were 0.14 and 0.17 mg/gVSS.h for maximum degradation rate, k; 2.07 and 2.06 mg/L for saturation coefficient, Ks and 65.1 and 67.5 mg/L for inhibition coefficients, respectively. On the basis of 2,4-DCP toxicity effects on the two anaerobic granule types, it was found that the liquid phase concentration determined toxicity and degradation of the chemical.

Composition and role of extracellular polymers in methanogenic granules

Methanobacterium formicicum and Methanosarcina mazeii are two prevalent species isolated from an anaerobic granular consortium grown on a fatty acid mixture. The extracellular polysaccharides (EPS) were extracted from Methanobacterium formicicum and Methanosarcina mazeii and from the methanogenic granules to examine their role in granular development. The EPS made up approximately 20 to 14% of the extracellular polymer extracted from the granules, Methanobacterium formicicum, and Methanosarcina mazeii. The EPS produced by Methanobacterium formicicum was composed mainly of rhamnose, mannose, galactose, glucose, and amino sugars, while that produced by Methanosarcina mazeii contained ribose, galactose, glucose, and glucosamine. The same sugars were also present in the EPS produced by the granules. These results indicate that the two methanogens, especially Methanobacterium formicicum, contributed significantly to the production of the extracellular polymer of the anaerobic granules. Growth temperature, substrates (formate and H(inf2)-CO(inf2)), and the key nutrients (nitrogen and phosphate concentrations) affected polymer production by Methanobacterium formicicum.

Anaerobic degradation kinetics of 2,4-dichlorophenol (2,4-DCP) with linear sorption

Degradation of 2,4-DCP by acclimated anaerobic granules enriched at two specific loading rates was examined experimentally in batch mode. The data from process curves were analyzed by nonlinear regression to estimate parameters in the Haldane inhibition equation and one of its modified forms to obtain quantitative information on degradation kinetics. Linear sorption kinetics of 2,4-DCP were employed in data treatment to discriminate between the effects of sorption and biodegradation. It was observed that the modified inhibition equation described experimental data better than the Haldane inhibition equation since the later failed to predict the trend in experimental data. Parameter values estimated with the modified inhibition equation for two types of anaerobic granule, were 0.14 and 0.17 mg/gVSS.h for maximum degradation rate, k; 2.07 and 2.06 mg/L for saturation coefficient, Ks, and 65.1 and 67.5 mg/L for inhibition coefficients, respectively. On the basis of 2,4-DCP toxicity effects on the two anaerobic granule types, it was found that the liquid phase concentration determined toxicity and degradation of the chemical.

Inhibition of methanogenic activity of starch-degrading granules by aromatic pollutants

The effects of nine common aromatic pollutants from chemical industry on the bioactivity of anaerobic granules were examined. The granules were obtained from an uptlow anaerobic sludge blanket (UASB) reactor treating wastewater containing colloidal starch. The specific methanogenic activities (SMA) of granules were measured at 37°C in serum vials using 3000 mg/l of colloidal starch as substrate, plus individual pollutants at various concentrations. The toxicity was expressed by the IR50 and IC50 values, i.e. the toxicant/biomass ratio and concentration at which levels the granules exhibited only 50% of their original bioactivities. Results showed that in general the granules exhibited mild resistance to toxicity of aromatic pollutants, probably due to the granules' layered microstructure. The toxicities, which were dependent on the nature of chemical functional group, of the aromatic pollutants were in the following descending order: cresols>phenol>hydroxyphenols/phthalate>benzoate. There was only marginal difference between the toxicity of the steric isomers. For the seven phenolic pollutants, the more hydrophobic the functional group the higher the toxicity. The granules' resistance to toxicity suggested the plausibility of anaerobic treatment of wastewater from the chemical industry.

Biosorption of 2,4-dichlorophenol by live and chemically inactivated anaerobic granules

Equilibrium sorption isotherms and sorption kinetics of 2,4-dichlorophenol (2,4-DCP) on live and chemically inactivated anaerobic granules were investigated using batch serum bottle tests. A general metabolic inhibitor, sodium azide, was used to inactivate the biological activity of the anaerobic biomass. Experimental results showed that the difference in the biosorption of live and chemically inactivated anaerobic granules were not significant, suggesting that anaerobic biosorption is mainly a physical-chemical process and that metabolically mediated diffusion in the process is negligible.

N-Propanol production during ethanol degradation using anaerobic granules

n-Propanol formation and consumption during ethanol oxidation by anaerobic brewery granules was investigated. The granules were taken from an UASB reactor fed with a synthetic brewery waste water. Ethanol degradation assays and an isotopic assay using 13C-labeled ethanol and bicarbonate were performed. Intermediate products propionate, n-propanol, acetate, hydrogen, formate and carbon monoxide were observed. Results have shown a consistent and reproducible trend of ethanol being converted to, primarily intermediates propionate and acetate with some accumulation of n-propanol. Hydrogen and carbon monoxide concentration accumulated to 1120 and 50 ppm in the gas phase, respectively. Methane and carbon dioxide were the terminal products. Bicarbonate was not a significant contributor of carbon for n-propanol production based on 13C assay results. From reaction energetics analysis and ethanol degradation assays, reactions of hydroformylation of ethanol with carbon monoxide and hydrogen, ethanol condensation, propionate reduction, and, ethanol oxidation coupled with propionate reduction are potentially responsible for the formation of propanol during anaerobic ethanol oxidation. Carbon monoxide is likely an additional carbon to ethanol during the formation of n-propanol. Hydrogen appeared to play a strong role as a driving force governing reactions involving propionate.