Lab-scale Upflow Anaerobic Sludge Research Articles

Simultaneous granulation, biomass retainment and carbon tetrachloride (CT) removal in an upflow anaerobic sludge blanket (UASB) reactor

The granulation process was examined during carbon tetrachloride (CT) biodegradation in a laboratory scale upflow anaerobic sludge blanket (UASB) reactor operated at 35 °C for 220 days. Anaerobic, unacclimated sludge and glucose were used as seed and primary substrate, respectively. CT degrading granules developed after 48 days of start-up. They grew at an accelerated pace for 6.5 months and had a maximum diameter of 2.2 mm following the pre-granulation and maturation period. Maximum specific methanogenic activity (SMA) was 1.63 g chemical oxygen demand (COD) per g total suspended solid (TSS) per day while, maximum specific organic loading rate to achieve 96% of COD removal efficiency was determined to be 12.5 g COD per l per day. About 95% CT removal efficiencies were achieved when the reactor was operating at loading rates as high as 17.5 mg CT per l per day after 220 days of continuous operation. The methane content in the total biogas collected was between 50 and 68% depending to shock organic loadings. About 96% of the total COD removed, was converted to methane, 0.024 g of TSS was yielded for each gram of COD removed at the end of 230 days of operation period. Kinetic coefficients of k (maximum specific substrate utilization rate), K s (half velocity coefficient), were determined to be 2.4×10 −3 mg CT per mg TSS per day and 1.37 mg CT per l, respectively, for CT biotransformation during granulation. Methanothrix ( Methanosaeta) sp., Methanosarecina mazei, Methanobacterium sp., Methanobrevibacter sp., Syntrophobacter sp., Methanolobus vulcani and Acetobacter woodii were identified in UASB.

Application of redox mediators to accelerate the transformation of reactive azo dyes in anaerobic bioreactors.

Azo dyes are nonspecifically reduced under anaerobic conditions but the slow rates at which reactive azo dyes are converted presents a serious problem for the application of anaerobic technology as a first stage in the complete biodegradation of these compounds. As quinones have been found to catalyze reductive transfers by acting as redox mediators, the application of anthraquinone-2,6-disulfonic acid (AQDS) during continuous anaerobic treatment of the reactive azo dye, Reactive Red 2 (RR2), was evaluated. A mixture of volatile fatty acids was used as the electron-donating primary substrate. Batch experiments demonstrated that AQDS could increase the first-order rate constant of RR2 reductive cleavage by one order of magnitude. In the continuous experiment, treatment of RR2 containing synthetic wastewater in a lab-scale upflow anaerobic sludge blanket (UASB) reactor yielded low dye removal efficiencies (<30%). Consequently, severe toxicity problems occurred, eventually resulting in almost complete inhibition of the methanogenic activity. Addition of catalytic concentrations of AQDS (19 microM) to the reactor influent caused an immediate increase in the dye removal efficiency and recovery of biological activity. Ultimately, RR2 removal efficiency stabilized at 88%, and higher AQDS loads resulted in higher RR2 removal efficiencies (up to 98% at 155 microM AQDS). Examination of the RR2 decolorizing properties of dye-adapted reactor sludge and of nonadapted reactor seed sludge revealed that RR2 decolorization was principally a biologically driven transfer of reducing equivalents from endogenous and added substrates to the dye. Hydrogen, added in bulk, was clearly the preferred electron donor. Bacteria that couple dye decolorization to hydrogen oxidation were naturally present in seed sludge. However, enrichment was required for the utilization of electrons from volatile fatty acids for dye reduction. The stimulatory effect of AQDS on RR2 decolorization by AQDS-unadapted sludge was mainly due to assisting the electron transfer from endogenous substrates in the sludge to the dye. The stimulatory effect of AQDS on RR2 decolorization by sludge from the AQDS-exposed reactor was, in addition, strongly associated with the transfer of electrons from hydrogen and acetate to the dye, probably due to enrichment of specialized AQDS-reducing bacteria.

Reductive biodegradation of 1,2-dichloroethane by methanogenic granular sludge in lab-scale UASB reactors

Dechlorination of 1,2-dichloroethane (1,2-DCA) dosed to a model wastewater in lab-scale upflow anaerobic sludge blanket (UASB) reactors was examined. Anaerobic granular sludge was used as a biocatalyst. Ethanol served as the main methanogenic substrate. For 3 months, two types of UASB reactors were studied, the first type consisting of a sludge blanket and the second type containing an additional layer of activated carbon. When subjected to 1,2-DCA at an average volumetric loading rate of 87.6 mg l −1 day −1, the latter type obtained an average removal efficiency of 82%. Increasing the volumetric loading rate of ethanol from 5 to 15 g COD l −1 day −1 resulted in higher 1,2-DCA conversion rates. No chlorinated intermediates or residues were found. 1,2-DCA was converted mainly to ethene (65–80%) and ethane (<1%). Both autoclaved sludge and cell extracts were not able to degrade 1,2-DCA, which indicates the need for metabolic activity. The reactor effluents were less toxic relative to the influent when analyzed by Nitrox tests, indicating that such UASB treatments can protect a subsequent aerobic nitrifying system. The 1,2-DCA removal rates achieved, and the safe nature of the endproducts, warrant the combination of granular sludge and UASB technology for practical decontamination of waters containing such types of organochlorines.

Thermophilic anaerobic digestion of methanol in UASB reactor

A 5.1 L laboratory scale upflow anaerobic sludge bed (UASB) reactor was operated at 55 degrees C over 130 days in order to investigate the feasibility of treating methanol-containing wastewater under thermophilic conditions, focussing on start-up and process stability. Batch assays were conducted to elucidate the most probable pathway for methanol conversion. The results demonstrated a good performance, with a chemical oxygen demand (COD) removal averaging 82% throughout the experiment. No significant VFA accumulation was detected in the effluent, even with bicarbonate concentration exceeding 20 mM. Acetate was the main component of the VFA at relatively low organic loading rates (OLR). At high OLR, the main components were propionate and butyrate. Reactor performance was hardly affected when the system was exposed to non-optimal conditions, i.e., temperature drop, overloading and no feeding. Good thermophilic granular sludge was retained in the reactor. Washout of biomass was not severe during the experiment. From the pathway analysis it could be concluded that indirect pathways play an important role in the methanol degradation by the cultivated consortia.

Enhanced decolourisation of acid orange 7 in a continuous UASB reactor with quinones as redox mediators

The reductive biotransformation of acid orange 7 (AO7) was explored in a lab-scale upflow anaerobic sludge blanket (UASB) reactor at low hydraulic residence times (HRT). A colour removal of 85% was achieved when the reactor was operated at a HRT of 6 hours, but decreased up to 70% when the HRT was lowered to 2 hours. Addition of the quinone model compound, anthraquinone 2,6-disulfonate (AQDS), as redox mediator, allowed for a considerably higher decolourising efficiency (> 90% at all the HRT evaluated). The results indicate that the use of catalytic concentrations of AQDS (AQDS/AO7 molar ratio about 0.01) can accelerate decolourising processes achieving satisfying extent of decolourisation.

Rapid granulation and sludge retention for tetrachloroethylene removal in an upflow anaerobic sludge blanket reactor

A laboratory scale upflow anaerobic sludge blanket (UASB) reactor was operated at 35 °C for over 200 days to investigate the granulation mechanism during tetrachloroethylene (TCE) biodegradation. Anaerobic, unacclimated sludge and glucose were used as seed and primary substrate, respectively. TCE-degrading granules developed after 1.5 months of start-up. They grew at an accelerated pace for 7 months. The TCE-degrading granules had a maximum diameter of 2.5 mm and specific methanogenic activity of 1.32 g chemical oxygen demand (COD) g−1 total suspended solid (TSS) day−1. 94% COD and 90% TCE removal efficiencies were achieved when the reactor was operating at loading rates as high as 160 mg TCE l−1 day−1 and 14 g COD l−1 day−1, after 230 days of continuous operation.

Quantification of Methanosaeta Species in Anaerobic Bioreactors Using Genus- and Species-Specific Hybridization Probes.

A BSTRACTTo evaluate the role of Methanosaeta spp. in a variety of anaerobic environments, small-subunit rRNA targeted oligonucleotide hybridization probes were developed and experimentally characterized. The probes were designed to be genus specific for Methanosaeta and species specific for Methanosaeta concilii and Methanosaeta thermophila. The temperature of dissociation was determined for each probe. Probe specificities were determined using a diverse collection of Archaea and through an evaluation of probe nesting using samples from a variety of anaerobic bioreactors. Cell fixation and hybridization conditions for fluorescence in situ hybridizations were also evaluated. Although permeability of methanogens was variable, M. concilii cells could be permeabilized using a range of paraformaldehyde and ethanol based fixation conditions. Using the newly designed probes together with previously designed probes for methanogens, it was determined that Methanosaeta spp. were the dominant aceticlastic methanogens in a variety of anaerobic bioreactors when acetate concentrations were low. Their levels were higher in bioreactors with granular sludge than in those with flocculent sludge. In lab-scale upflow anaerobic sludge blanket reactors, the levels of M. concilii rRNA were as high as 30% of the total rRNA.

Anaerobic treatment of hemp thermomechanical pulping wastewater

Biological treatment is an indispensable instrument for water management of non-wood pulp mills, either as internal measure or end of pipe. In this paper, anaerobic treatment of wastewaters derived from the thermomechanical pulping (TMP) of hemp ( Cannabis sativa L.) is described. Hemp stem wood and hemp bark TMP wastewaters were treated in laboratory scale upflow anaerobic sludge blanket (UASB) reactors. For both types of wastewater, maximal COD removal of 72% were obtained at loading rates of 13–16 g COD·l −1 d −1, providing 59–63% recovery of the influent COD as methane. The reactors continued to provide excellent COD removal efficiencies of 63–66% up to a loading rate of 27 g COD·l −1 d −1, being the highest loading rate tested. Batch toxicity assays revealed the absence of methanogenic inhibition by hemp TMP wastewaters, coinciding with the high acetoclastic activity of the reactor sludge of approximately 1 g COD·g VSS −1 d −1. Due to the relatively low molecular weight of hemp TMP lignin, its removal (measured as UV 280) during anaerobic treatment was remarkably high and averaged 45 and 31% for the hemp stem wood and the hemp bark TMP UASB reactors, respectively. Gel permeation chromatography revealed that the lignin removed corresponded to the lowest molecular weight derivatives. Subsequent batch aerobic post-treatment led to a considerable increase of color levels and polymerization of the residual lignin to molecular weights in excess of 34 kD.

Common anaerobic treatability of pharmaceutical and yeast industry wastewater

The purpose of this study is to demonstrate the feasibility of anaerobic treatment of pharmaceutical and baker's yeast industry effluents in a joint treatment system. Anaerobic treatability studies have been performed in a lab-scale upflow anaerobic sludge blanket reactor (UASBR). The experimental study has been carried out for 333 days. The influent COD's during the experimental study were about 10,000 mg/l. Pharmaceutical wastewater has a 5% of inhibition on the COD removals at the dilution rate of 1/100 or more in the joint anaerobic treatment with baker's yeast industry effluents. Maximum inhibition of 10% on the average was observed when the system was characterized with acclimation periods. The study has shown that, following the solvent extraction with pre-aeration process, a common anaerobic treatment can be applied to baker's yeast industry wastewater and to pharmaceutical industry effluents.

Effects of high calcium concentrations on the development of methanogenic sludge in upflow anaerobic sludge bed (UASB) reactors

The feasibility of anaerobic treatment of wastewaters with a high calcium content (600–1200 mgCa 2+.l −1) was studied. The influence of the amount of precipitation and the influence of differences in biomass yield were investigated on the development of anaerobic sludge. The experiments were performed in lab scale Upflow Anaerobic Sludge Blanket (UASB) reactors, inoculated with crushed granular sludge. Four reactors were operated during 180 days at a constant organic loading rate of 14 gCOD.l −1.d −1, treating completely and partly acidified wastewater with different calcium concentrations in the influent. Treatment of completely acidified wastewater with a calcium concentration of 1200 mgCa 2+.l −1 resulted in an unstable COD removal efficiency (60–90%). Furthermore, cementation of the sludge bed occurred after 180 days of operation, leading to operational problems. With completely acidified wastewater and a lower calcium concentration in the influent (600 mgCa 2+.l −1), less calcium precipitated and COD removal efficiency always exceeded 98%. The cultivated sludge had a high ash content, 80–90%, and methanogenic activity remained more or less constant at 0.7 gCOD.gVSS −1.d −1. However, scaling of reactor compartments occurred under the latter condition. The presence of a fraction of non-acidified substrate, i.e. glucose, decreased the risk of cementation, resulted in better granulation of the methanogenic sludge and seemed to prevent scaling of reactor compartments. Considerable amounts of phosphate were shown to be removed from the influent, most probably by coprecipitation, and incorporated in the anaerobic sludge. The results indicate that anaerobic treatment of high calcium wastewaters in UASB reactors is more feasible for partly than for completely acidified substrates.

High upflow velocity and organic loading rate improve granulation in upflow anaerobic sludge blanket reactors

Five laboratory scale upflow anaerobic sludge blanket (UASB) reactors were seeded with nongranular sewage sludge. Granulation was obtained after 15–35 days when between 0.5 and 2.0m/h upflow liquid velocity was applied, with an organic loading rate (OLR) of 8g COD/l.d (COD is the chemical oxygen demand). Granules had different physical characteristics and specific activity (g CODREMOVED/g volatile suspended solids) depending on the upflow liquid velocity applied. Granules were obtained in short startup periods (5 and 14 days) when a pilot-scale (180l) UASB reactor with a height of 4.7m was used to study hydraulic effects on the granulation process.

Common anaerobic treatability of pharmaceutical and yeast industry wastewater

The purpose of this study is to demonstrate the feasibility of anaerobic treatment of pharmaceutical and baker's yeast industry effluents in a joint treatment system. Anaerobic treatability studies have been performed in a lab-scale upflow anaerobic sludge blanket reactor (UASBR). The experimental study has been carried out for 333 days. The influent COD's during the experimental study were about 10,000 mg/1. Pharmaceutical wastewater has a 5% of inhibition on the COD removals at the dilution rate of 1/100 or more in the joint anaerobic treatment with baker's yeast industry effluents. Maximum inhibition of 10% on the average was observed when the system was characterized with acclimation periods. The study has shown that, following the solvent extraction with pre-aeration process, a common anaerobic treatment can be applied to baker's yeast industry wastewater and to pharmaceutical industry effluents.

Anaerobic Biogranulation as Microbial Response to Substrate Adequacy

Microbial granulation was examined in four lab-scale upflow anaerobic sludge blanket (UASB) reactors under varied microbial load indices (MLIs). The dimensionless MLI is defined as the ratio of the sludge loading rate to the specific methanogenic activity, and represents the relative substrate sufficiency subjected to by the sludge. A synthetic feed consisting of glucose, peptone, and meat extract was used as substrate and anaerobic digested sludge as seed. The four reactors were designed with the same diameters yet different heights, aiming at achieving a different biological selection pressure (solely MLI) yet a similar physical selection pressure in the reactors. Granulation under the high MLIs of 0.8 and 0.6 developed well within three and four months of operation, respectively, whereas that under the low MLIs of 0.3 and 0.2 did not even after six months. The granulation process was characterized by three phases of acclimation, granulation, and maturation. The MLI provides a quantitative approach toward stepwise sludge loading rate increases during start-up, with the appropriate values of 0.6–0.8 for fast and well-proceeded granulation.

Tracer Studies in a Laboratory and Pilot Scale UASB Reactor

Residence time distribution studies on laboratory and pilot scale upflow anaerobic sludge blanket reactors (UASB) were carried out in order to measure and evaluate the influence, on the reactor's hydraulic performance, of the biogas collection device position (gas-liquid-solid separator), of the presence of granular sludge and of the arrangement of the influent distribution system within the reactor. The main purpose of the pilot scale experiment was to assess the influence of the biogas collection device on the reactor hydraulic performance accurately. The results show that if the biogas collector system is located in a lower position (nearer to the sludge bed), the dead volume fraction decreases and a better performance of the settler could be obtained. In addition, it can be appreciated that the mixed flow pattern has more dead volume fraction than a plug flow hydraulic pattern.

Anaerobic treatment of olive mill effluents

The anaerobic treatability of olive mill effluent was investigated using a laboratory scale upflow anaerobic sludge blanket reactor (UASBR) operated for about six months. The effects of various operating conditions including pH, feed strength and hydraulic retention time on the performance of the anaerobic treatment process were determined. In the first part of this study, the reactor was operated with feed COD concentrations from 5000 to 19,000 mg/l and a retention time of 1 day, giving organic loading rates from 5 to 18 kg COD/m3d. Soluble COD removal was around 75% under these conditions. In the second part of the study, feed CODs were varied from 15,000 to 22,600 mg/l while retention times ranged from 0.83 to 2 days; soluble COD removal was around 70%. A methane conversion rate of 0.35 m3 per kg COD removed was achieved during the study. The average volatile solids (VS) concentration in the reactor had increased from 12.75 g l−1 to 60 g l−1 by the end of the study. Sludge volume index (SVI) determinations performed to evaluate the settling characteristics of the anaerobic sludge in the reactor indicated excellent settleability with SVI values of generally less than 20 ml g−1. Sludge granules ranging from 3 to 8 mm in diameter were produced in the reactor. The second order substrate removal kinetics was applied by assuming that hydraulic conditions in the UASBR are approximately completely mixed and the model fitted well to the steady state operating results.

Anaerobic treatment of olive mill effluents

The anaerobic treatability of olive mill effluent was investigated using a laboratory scale upflow anaerobic sludge blanket reactor (UASBR) operated for about six months. The effects of various operating conditions including pH, feed strength and hydraulic retention time on the performance of the anaerobic treatment process were determined. In the first part of this study, the reactor was operated with feed COD concentrations from 5000 to 19,000 mg/l and a retention time of 1 day, giving organic loading rates from 5 to 18 kg COD/m 3 d. Soluble COD removal was around 75% under these conditions. In the second part of the study, feed CODs were varied from 15,000 to 22,600 mg/l while retention times ranged from 0.83 to 2 days; soluble COD removal was around 70%. A methane conversion rate of 0.35 m 3 per kg COD removed was achieved during the study. The average volatile solids (VS) concentration in the reactor had increased from 12.75 g l −1 to 60 g l −1 by the end of the study. Sludge volume index (SVI) determinations performed to evaluate the settling characteristics of the anaerobic sludge in the reactor indicated excellent settleability with SVI values of generally less than 20 ml g −1 . Sludge granules ranging from 3 to 8 mm in diameter were produced in the reactor. The second order substrate removal kinetics was applied by assuming that hydraulic conditions in the UASBR are approximately completely mixed and the model fitted well to the steady state operating results.

A Simplified Analysis of Reaction and Mass Transfer in UASB and EGSB Reactors

The paper is focused on the study of the hydrodynamics, reaction kinetics and mass transfer in lab-scale Upflow Anaerobic Sludge Blanket (UASB) and Expanded Granular Sludge Bed (EGSB) reactors treating wastewaters with low volatile fatty acids concentrations. The fluid pattern in the UASB approached a plug-flow reactor because of the low turbulence provided by the upflow velocity and gas production. The EGSB behaved as a continuous-stirred tank reactor due to the effects of the high recirculation rate. Liquid film mass transfer resistance seemed negligible in the EGSB but important in the UASB reactor. This should be the consequence of the different hydrodynamic conditions in the two reactors. The rate of acetate degradation was best fitted by an apparent half-order kinetics in both reactors. Internal mass transfer limitations, associated to an intrinsic zero-order kinetics, was detected in the degradation of low acetate concentrations by the granular biomass.

Detection and localization of syntrophic propionate-oxidizing bacteria in granular sludge by in situ hybridization using 16S rRNA-based oligonucleotide probes.

In situ hybridization with fluorescent oligonucleotides was used to detect and localize microorganisms in the granules of two lab-scale upflow anaerobic sludge blanket reactors that had been fed for several months with either sucrose or a mixture of volatile fatty acids. Sections of the granules were hybridized with 16S rRNA-targeted oligonucleotide probes for Bacteria, Archaea, specific phylogenetic groups of methanogens, and two syntrophic propionate-oxidizing strains, MPOB and KOPROP1. Cells of the syntrophic strain KOPROP1 were not detected in either type of sludge granules. Hybridizations of the sucrose-fed granules showed an outer layer of mainly bacterial microcolonies with different morphologies. More inwards of these granules, a layer of different methanogenic microcolonies mixed with large colonies of the syntrophic strain MPOB could be detected. The MPOB colonies were intertwined with hydrogen- or formate-consuming methanogens, indicating their syntrophic growth. The granules fed with volatile fatty acids showed an outer layer of mainly bacteria and then a thick layer of Methanosaeta-like methanogens mixed with a few bacteria and a layer of methanogens mixed with syntrophic MPOB microcolonies. The centers of both sludge types consisted of large cavities and methanogenic microcolonies. These results indicate a juxtapositioning of syntrophic bacteria and methanogens and provide additional evidence for a layered microbial architecture of anaerobic granular sludge.

Start-up criteria for a Upflow Anaerobic Sludge Blanket (UASB) reactor

A laboratory scale Upflow Anaerobic Sludge Blanket (UASB) reactor study was done with spentwash (distillery effluent) as substrate. The start-up studies revealed that the recirculation of biogas, produced during the initial stages, under low organic loading rates helps in mixing as well as partial supplementation of carbon dioxide for excess hydrogen in the reactor. The gas composition before and after recirculation, the volatile acids profile and the solids variation along the reactor height before and after recirculation were studied. The process efficiency and methane content increases substantially after recirculation of biogas and the microscopic examination of the sludge during the experiment indicates that the granules mainly composed of long multicellular filaments of rod shaped organisms, presumably methanothrix soehngenii.

Granular sludge growth under different reactor liquid surface tensions in lab-scale upflow anaerobic sludge blanket reactors treating wastewater from sugar-beet processing

The formation of anaerobic granular sludge on wastewater from sugar-beet processing was examined in upflow anaerobic sludge blanket reactors. Two strategies were investigated: addition of high-energy substrate, i.e. sugars, and varying the reactor liquid surface tension. When there were insufficient amounts of sugars i.e. less than 7% of the chemical O2 demand of the influent, no granulation was observed; moreover lowering the reactor liquid surface tension below 48 mN/m was found to increase biomass wash-out. On the other hand, when there were sufficient sugars, granular sludge growth occurred; moreover operating the reactor at a low reactor liquid surface tension reduced biomass wash-out and increased granular yield.