Feasibility of expanded granular sludge bed reactors for the anaerobic treatment of low-strength soluble wastewaters

The application of the expanded granular sludge bed (EGSB) reactor for the anaerobic treatment of low-strength soluble wastewaters using ethanol as a model substrate was investigated in laboratory-scale reactors at 30oC. Chemical oxygen demand (COD) removal efficiency was above 80% at organic loading rates up to12 g COD/L . d with influent concentrations as low as 100 to 200 mg COD/L. These results demonstrate the suitability of the EGBS reactor for the anaerobic treatment of low-strength wastewaters. The high treatment performance can be attributed to the intense mixing regime obtained by high hydraulic and organic loads. Good mixing of the bulk liquid phase for the substrate-biomass contact and adequate expansion of the substrate-biomass contact and adequate expansion of the sludge bed for the degassing were obtained when the liquid upflow velocity (V(up)) was greater than 2.5 m/h. Under such conditions, an extremely low apparent K(s) value for acetoclastic methanogenesis of 9.8 mg COD/L was observed. The presence of dissolved oxygen in the wastewater had no detrimental effect on the treatment performance. Sludge piston flotation from pockets of biogas accumulating under the sludge bed occurred at V(up) lower than 2.5 m/h due to poor bed expansion. This problem is expected only in small diameter laboratory-scale reactors. A. more important restriction of the EGSB reactor was the sludge washout occurring at V(up) higher than 5.5 m/h and which was intensified at organic loads higher than 7 g COD/L. d due to buoyancy forces from the gas production. To achieve an equilibrium between the mixing intensity and the sludge hold-up, the operation should be limited to an organic loading rate of 7 g COD/L d. and to a liquid up-flow velocity between 2.5 and 5.5 m/h (c) 1994 John Wiley & Sons, Inc.     

Biogas production from potato-juice, a by-product from potato-starch processing, in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors

In this study, the utilization of potato-juice, the organic by-product from potato-starch processing, for biogas production was investigated in batch assay and in high rate anaerobic reactors. The maximum methane potential of the potato-juice determined by batch assay was 470 mL-CH₄/gVS-added. Anaerobic digestion of potato-juice in an EGSB reactor could obtain a methane yield of 380 mL-CH₄/gVS-added at the organic loading rate of 3.2 gCOD/(L-reactor.d). In a UASB reactor, higher organic loading rate of 5.1 gCOD/(L-reactor.d) could be tolerated, however, it resulted in a lower methane yield of 240 mL-CH₄/gVS-added. The treatment of reactor effluent was also investigated. By acidification with sulfuric acid to pH lower than 5, almost 100% of the ammonia content in the effluent could be retained during the successive up-concentration process step. The reactor effluent could be up-concentrated by evaporation to minimize its volume, and later be utilized as fertilizer.     

Extracellular polymers in granular sludge from different upflow anaerobic sludge blanket (UASB) reactors

Thermal extraction was used to quantify extracellular polymers (ECP) in granules from anaerobic upflow reactors. The optimal time for extraction was determined as the time needed before the intracellular material gives a significant contribution to the extracted extracellular material due to cell lysis. ECP contents of 41 to 92 mg · g^–1 volatile suspended solids of granules were found depending on the type of granular sludge examined. The content of polysaccharides, protein and lipids in the extracted ECP was quantified. Furthermore, the different methyl esters of the lipids were determined and quantified. Lower amounts of polysaccharides and proteins were found in the extracellular material from granules grown on methanogenic and acetogenic substrates compared to granules grown on more complex substrates. In contrast, the lipid content was lower on complex substrates. Changing the feed of an upflow anaerobic sludge blanket reactor from a sugar-containing waste-water to a synthetic waste-water containing acetate, propionate and butyrate resulted in a decrease in both the protein and polysaccharide content and an increase in the lipid content of the extracellular material. Furthermore, the amount of protein and polysaccharides in the ECP found under mesophilic conditions was significantly higher than under thermophilic conditions, while the lipid content was lower.     

Molecular characterization of mesophilic and thermophilic sulfate reducing microbial communities in expanded granular sludge bed (EGSB) reactors

The microbial communities established in mesophilic and thermophilic expanded granular sludge bed reactors operated with sulfate as the electron acceptor were analyzed using 16S rRNA targeted molecular methods, including denaturing gradient gel electrophoresis, cloning, and phylogenetic analysis. Bacterial and archaeal communities were examined over 450 days of operation treating ethanol (thermophilic reactor) or ethanol and later a simulated semiconductor manufacturing wastewater containing citrate, isopropanol, and polyethylene glycol 300 (mesophilic reactor), with and without the addition of copper(II). Analysis, of PCR-amplified 16S rRNA gene fragments using denaturing gradient gel electrophoresis revealed a defined shift in microbial diversity in both reactors following a change in substrate composition (mesophilic reactor) and in temperature of operation from 30°C to 55°C (thermophilic reactor). The addition of copper(II) to the influent of both reactors did not noticeably affect the composition of the bacterial or archaeal communities, which is in agreement with the very low soluble copper concentrations (3–310 μg l⁻¹) present in the reactor contents as a consequence of extensive precipitation of copper with biogenic sulfides. Furthermore, clone library analysis confirmed the phylogenetic diversity of sulfate-reducing consortia in mesophilic and thermophilic sulfidogenic reactors operated with simple substrates.     

High-rate denitrifying sulfide removal process in expanded granular sludge bed reactor

An expanded granular sludge bed (EGSB) reactor was adopted to incubate bio-granules that could simultaneously convert 4.8 kg-S m^?3 d^?1 of sulfide in 97% efficiency; 2.6 kg-N m^?3 d^?1 of nitrate in 92% efficiency; and 2.7 kg-C m^?3 d^?1 acetate in 95% efficiency. Mass balance calculation of sulfur, nitrogen, and carbon over the EGSB reactor confirmed the performance results. This noted reactor performance is much higher than those reported in literature. Stoichiometric relation suggests that the nitrate was reduced to nitrite via autotrophic denitrification pathway, then the formed nitrite was converted via heterotrophic denitrification pathway to N₂.     

Cluster structure of anaerobic aggregates of an expanded granular sludge bed reactor

The metabolic properties and ultrastructure of mesophilic aggregates from a full-scale expanded granular sludge bed reactor treating brewery wastewater are described. The aggregates had a very high methanogenic activity on acetate (17.19 mmol of CH(4)/g of volatile suspended solids [VSS].day or 1.1 g of CH(4) chemical oxygen demand/g of VSS.day). Fluorescent in situ hybridization using 16S rRNA probes of crushed granules showed that 70 and 30% of the cells belonged to the archaebacterial and eubacterial domains, respectively. The spherical aggregates were black but contained numerous whitish spots on their surfaces. Cross-sectioning these aggregates revealed that the white spots appeared to be white clusters embedded in a black matrix. The white clusters were found to develop simultaneously with the increase in diameter. Energy-dispersed X-ray analysis and back-scattered electron microscopy showed that the whitish clusters contained mainly organic matter and no inorganic calcium precipitates. The white clusters had a higher density than the black matrix, as evidenced by the denser cell arrangement observed by high-magnification electron microscopy and the significantly higher effective diffusion coefficient determined by nuclear magnetic resonance imaging. High-magnification electron microscopy indicated a segregation of acetate-utilizing methanogens (Methanosaeta spp.) in the white clusters from syntrophic species and hydrogenotrophic methanogens (Methanobacterium-like and Methanospirillum-like organisms) in the black matrix. A number of physical and microbial ecology reasons for the observed structure are proposed, including the advantage of segregation for high-rate degradation of syntrophic substrates.     

Effects of free long-chain fatty acids on thermophilic anaerobic digestion

Summary Low concentrations of the long-chain fatty acids oleate and stearate inhibited all steps of the anaerobic thermophilic biogas process during digestion of cattle manure. The lag phase increased when the concentrations of oleate and stearate were 0.2 g/l and 0.5 g/l, respectively, and no growth was found at concentrations of 0.5 g/l for oleate and 1.0 g/l for stearate. The toxic effect of these acids was permanent as growth did not occur when inhibited cultures were diluted to a non-inhibitory concentration. No adaptation to the fatty acids toxicity was observed by pre-exposing the cultures to non-inhibitory concentrations and the inhibitory response was the same as for cultures not pre-exposed to the fatty acids. Oleate was less inhibitory when added as a neutral oil in the form of the glycerol ester. This indicates that it is the free fatty acid that influences the bacterial activity. Correspondence to: B. K. Ahring     

The settling characteristics and mean settling velocity of granular sludge in upflow anaerobic sludge blanket (UASB)-like reactors

Mean settling velocity of granular sludge in full-scale UASB (upflow anaerobic sludge blanket) and EGSB (expanded granular sludge bed) reactors was evaluated by settling column tests, and a settling velocity model based on the experimental results and available literature data was developed. It is concluded that the settling velocity should be calculated by the Allen formula, because the settling process of the granules is in the category of intermediate flow regime rather than in the laminar flow one. The comparison between calculated and measured values of the settling velocity shows an excellent agreement, with an average relative error of 4.04%. A simple but reliable mathematical method to determine the settling velocity is therefore proposed.     

Mechanism of inhibition caused by long-chain fatty acids in anaerobic digestion process

The inhibitory effect of long-chain fatty acids on the anaerobic digestion process was examined in batch experiments using synthetic substrates. The addition of long-chain fatty acids caused the appearance of the appearance of the lag period in the methane production from acetate and in the degradation of both long-chain fatty acids and n-butyrate. Methane production from hydrogen proceeded without lag period although its rate was lowered. Fermentation of glucose was not inhibited. Neutral fat in the whole milk was easily hydrolyzed to long-chain fatty acids, which brought about the inhibition. The addition of calcium chloride reduced the inhibitory effect of long-chain fatty but it did not do so after the culture had been exposed to long-chain fatty acids for more than several hours. The addition of calcium carbonate could not reduce the inhibition because of its insolubility.     

Anaerobic treatment of raw domestic sewage at ambient temperatures using a granular bed UASB reactor

Results obtained in a 120 liter 2 m high UASB-reactor with raw domestic sewage and using a granular sugar beet waste cultivated seed sludge, reveal the feasibility of this type of anaerobic treatment for domestic sewage. Under dry weather conditions 65-85% COD reduction can be achieved at temperatures in the range of 8-20 degrees C and at hydraulic loads as high as 2 m(3) . m(-3) . day(-1). In the case of heavy rainfall the COD-reduction drops to 50-70% and occasionally, viz.at very low influent COD, even below 50%. The net methane production amounts to 7.1-7.3 m(3) . PE(-1) . year(-1), and the excess sludge production ranges form 5.0-8.6 kg TS . PE(-1) . year(-1). Regarding the results obtained anaerobic treatment of raw sewage not only looks an attractive proposition for tropic areas but also for moderate climatic areas.     

Granular sludge formation in upflow anaerobic sludge blanket (UASB) reactors

The state of the art for upflow anaerobic sludge blanket (UASB) reactors is discussed, focusing on the microbiology of immobilized anaerobic bacteria and the mechanism of granule formation. The development of granular sludge is the key factor for successful operation of the UASB reactors. Criteria for determining if granular sludge has developed in a UASB reactor is given based on the densities and diameters of the granular sludge. The shape and composition of granular sludge can vary significantly. Granules typically have a spherical form with a diameter from 0.14 to 5 mm. The inorganic mineral content varies from 10 to 90% of the dry weight of the granules, depending on the wastewater composition etc. The main components of the ash are calcium, potassium, and iron. The extracellular polymers in the granular sludge are important for the structure and maintenance of granules, while the inorganic composition seems to be of less importance. The extracellular polymer content varies between 0.6 and 20% of the volatile suspended solids and consists mainly of protein and polysaccharides. Both Methanosaeta spp. (formerly Methanothrix) and Methanosarcina spp. have been identified as important aceticlastic methanogens for the initial granulation and development of granular sludge. Immunological methods have been used to identify other methanogens in the granules. The results have showed that, besides the aceticlastic methanogens Methanosaeta spp. and Methanosarcina spp., hydrogen and formate utilizing bacteria are also present, e.g., Methanobacterium formicicum, Methanobacterium thermoautotrophicum, and Methanobrevibacter spp. Microcolonies of syntrophic bacteria are often observed in the granules, and the significant electron transfer in these microcolonies occurs through interspecies hydrogen transfer. The internal organization of the various groups of bacteria in the granules depends on the wastewater composition and the dominating metabolic pathways in the granules. Internal organization is observed in granules where such an arrangement is beneficial for an optimal degradation of the wastewater. A four-step model is given for the initial development of granular sludge. (c) 1996 John Wiley & Sons, Inc.     

Long-term competition between sulfate reducing and methanogenic bacteria in UASB reactors treating volatile fatty acids

The competition between acetate utilizing methane-producing bacteria (MB) and sulfate-reducing bacteria (SRB) was studied in mesophilic (30 degrees C) upflow anaerobic sludge bed (UASB) reactors (upward velocity 1 m h-1; pH 8) treating volatile fatty acids and sulfate. The UASB reactors treated a VFA mixture (with an acetate:propionate:butyrate ratio of 5:3:2 on COD basis) or acetate as the sole substrate at different COD:sulfate ratios. The outcome of the competition was evaluated in terms of conversion rates and specific methanogenic and sulfidogenic activities. The COD:sulfate ratio was a key factor in the partitioning of acetate utilization between MB and SRB. In excess of sulfate (COD:sulfate ratio lower than 0.67), SRB became predominant over MB after prolonged reactor operation: 250 and 400 days were required to increase the amount of acetate used by SRB from 50 to 90% in the reactor treating, respectively, the VFA mixture or acetate as the sole substrate. The competition for acetate was further studied by dynamic simulations using a mathematical model based on the Monod kinetic parameters of acetate utilizing SRB and MB. The simulations confirmed the long term nature of the competition between these acetotrophs. A high reactor pH (+/-8), a short solid retention time (<150 days), and the presence of a substantial SRB population in the inoculum may considerably reduce the time required for acetate-utilising SRB to outcompete MB.     

Anaerobic biodegradation of linear alkylbenzene sulfonate (LAS) in upflow anaerobic sludge blanket (UASB) reactors

The anaerobic biodegradation of Linear Alkylbenzene Sulfonate (LAS) was studied in Upflow Anaerobic Sludge Blanket Reactors (UASB). One reactor was fed with easily degradable substrates and commercial LAS solution during a period of 3 months (Reactor 1), meanwhile a second reactor was fed with a commercial LAS solution without co-substrate (Reactor 2) during 4 months. Both reactors were operated with an organic loading rate of 4–5 mg-LAS/l*day and a hydraulic retention time of one day.The LAS biodegradation was determined by full mass balance. LAS was analysed by HPLC in the liquid phase (influent and effluent streams of the reactors) as well as in the solid phase (granular sludge used as biomass). The results indicate a high level of removal (primary biodegradation: 64–85%). Biodegradation was higher in the absence of external co-substrates than in the presence of additional sources of carbon. This indicates that the surfactant can be partially used as carbon and energy source by anaerobic bacteria. Under the operating conditions used, inhibition of the methanogenic activity or any other negative effects on the biomass due to the presence of LAS were not observed. The methanogenic activity remained high and stable throughout the experiment.     

COD removal from expanded granular sludge bed effluent using a moving bed biofilm reactor and their microbial community analysis

The bioreactor performance of a moving bed biofilm reactor (MBBR) as post-treatment of expanded granular sludge bed (EGSB) effluent was investigated. Moreover, the microbial communities of the two bioreactors during different operation periods were studied. The MBBR was efficient for COD removal with the mean efficiency of 82.4%, and produced an effluent with high and stable quality against shock loading resulting from the low temperature applied to EGSB. The study indicates that the microbial community in the reactors could adapt to perturbations such as influent wastewater characteristics and operation temperature, which is beneficial to maintain efficient and stable COD removal in the combined EGSB-MBBR system. Archaeal 16S rRNA gene sequence analysis indicated the presence of Methanomethylovorans, Methanolinea, Methanoregula boonei, Methanosarcina barkeri, and Methanospirillum hungatei in the EGSB. Bacterial 16S rRNA gene sequence analysis indicated the presence of Runella limosa, Dokdonella, Sphaerotilus, Hydrogenophaga, and Pseudomonas in the MBBR. The EGSB-MBBR system established here could be used as an efficient option for organic matter removal, which holds a great potential in practical applications for nutrients (N and P) removal.     

Filamentous granular sludge bulking in a laboratory scale UASB reactor

Filamentous bulking was observed in a lab scale upflow anaerobic sludge blanket (UASB) reactor. Granules failed to settle normally and disintegrated. The characteristics of the granules in structure and microbial composition during the granulation process were investigated by means of scanning electron microscopy (SEM) and denaturing gradient gel electrophoresis (DGGE) technique. Granules with high porosity instead of compact ones were developed in the reactor and Methanosaeta concilii and Methanobacterium formicicum were identified as the predominant methanogens present in granules. The excess growth of the filamentous bacteria could be the contributing factor causing floatation and disintegration.     

Different types of sludge granules in UASB reactors treating acidified wastewaters

The influence of a high energy substrate, i.e. sucrose, on the granular sludge yield and the development of different types of granular sludge was investigated by using Upflow Anaerobic Sludge Bed (UASB) reactors fed with synthetic wastewater. The feed COD was a mixture of volatile fatty acids (VFA) i.e., 20, 40, and 40% of the COD as C₂-, C₃-, and C₄-VFA, respectively. Furthermore, experiments were carried out in which 10 and 30% of the VFA COD was substituted with sucrose. The following distinctly different types of granules were observed in each testrun: in the reactor fed with solely VFA, black (B) and white (W) granules developed; in the reactor fed with a mixture of 90% VFA and 10% sucrose, three types of granules i.e., B, W, and grey (G) granules could be seen; in the reactor fed with 70% VFA and 30% sucrose, only W and G granules were found. The granular sludge yield increased proportional to the amount of sucrose COD. At steady-state performance of the reactors, specific acidogenic (SAA) and methanogenic (SMA) activity tests on these granules revealed that B granules had the highest SMA with low SAA. The W granules had very high SMA with low SAA. G granules gave the highest SAA with a considerable SMA. Measurement of coenzyme F₄₂₀ revealed that B granules consist mainly of acetoclastic methanogens. The fore-mentioned tests were supplemented with analyses of the wash-out cells present in the reactor effluent and the results suggested that acidogens, if present, prevail at the granule surface. The B granules were particularly rich in Ca, Mn, and Zn minerals. The size distribution analysis showed that the granule diameter increased in the following order: B相似文献