Granulation of biomass in thermophilic upflow anaerobic sludge blanket reactors treating acidified wastewaters

The development of granular sludge in thermophilic (55 degrees C) upflow anaerobic sludge blanket reactors was investigated. Acetate and a mixture of acetate and butyrate were used as substrates, serving as models for acidified waste-waters. Granular sludge with either Methanothrix or Methanosarcina as the predominant acetate utilizing methanogen was cultivated by allowing the loading rate to increase whenever the acetate concentration in the effluent dropped below 200 and 700 mg COD/L, respectively. The highest methane generation rates, up to 162 kg CH(4)-COD/m(3) day, or 2.53 mole CH(4)/L day, were achieved at hydraulic retention times down to 21 min, with granules consisting of Methanothrix. The formation of Methanothrix granules did not depend on the type of seed material, nor on the addition of inert support particles. The growth of granules proceeded rapidly with adapted seed material, even when the reactors were inoculated with low concentrations. With mesophilic seed materials growth of granules took much longer. Thermophilic Methanothrix granules strongly resemble mesophilic granules of the "filamentous" type. Some factors governing the thermophilic granulation process are discussed.     

Granulation in thermophilic upflow anaerobic sludge blanket (UASB) reactors

The state of the art for thermophilic UASB reactors is discussed focusing on the start-up of UASB reactors, the influence of the waste water composition and temperature on the development and maintenance of thermophilic granules, and the microbial composition and structure of thermophilic granules.     

Performance of staged and non-staged up-flow anaerobic sludge bed (USSB and UASB) reactors treating low strength complex wastewater

The use of anaerobic processes to treat low-strength wastewater has been increasing in recent years due to their favourable performance-costs balance. For optimal results, it is necessary to identify reactor configurations that are best suited for this kind of application. This paper reports on the comparative study carried out with two high-rate anaerobic reactor systems with the objective of evaluating their performances when used for the treatment of low-strength, complex wastewater. One of the systems is the commonly used up-flow anaerobic sludge blanket (UASB) reactor. The other is the up-flow staged sludge bed (USSB) system in which the reactor was divided longitudinally into 3, 5 and 7 compartments by the use of baffles. The reactors (9 l) were fed with a synthetic, soluble and colloidal waste (chemical oxygen demand (COD) < 1000 mg/l) and operated at 28°C and 24 h hydraulic retention time. Intermediate flow hydraulics, between plug-flow and completely-mixed, in the UASB and 7 stages USSB reactors allowed efficient degradation of substrates with minimum effluent concentrations. Low number of compartments in the USSB reactors increased the levels of short-circuiting thus reducing substrate removal efficiencies. All reactors showed high COD removal efficiencies (93–98%) and thus can be regarded as suitable for the treatment of low strength, complex wastewater. Staged anaerobic reactors can be a good alternative for this kind of application provided they are fitted with a large enough (≥7) number of compartments to fully take advantage of their strengths. Scale factors seem to have influenced importantly on the comparison between one and multi staged sludge-bed reactors and, therefore, observations made here could change at larger reactor volumes.     

Granulation of digested sewage sludge in mesophilic UASB reactors treating distillery waste waters from sugar cane molasses

Five 4.02-1 UASB (Upflow Anaerobic Sludge Blanket) reactors were continuously operated at 30°C under different hydrodynamic regimes for more than 120 days. The effect of the upflow liquid velocity (ULV) over the range of 0.25 to 2.0 m/h on the biological characteristics of the granules formed by treating vinasses (waste water of alcohol distilleries) from sugar cane molasses was investigated constantly maintaining the volumetric loading rate (VLR) (8 g COD/l · d). Granular sludge was found at all the ULV tested. The size, shape, etc., of the granules indicated that the ULV had a considerable effect on the sludge cultivated in this type of system, thereby acting as a selection process for the biomass. The best results in relation to the time of appearance, size, shape, consistence, stability, composition, and the accumulation were observed in the ULV range between 0.25 and 0.5 m/h. Microscopic studies of the granules using optical and epifluorescence microscopes and the scanning electron micrograph (SEM) showed a heterogeneous biomass and revealed the cell characteristics.     

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.     

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.     

Biotransformation of nitrophenols in upflow anaerobic sludge blanket reactors

Four identical bench-scale upflow anaerobic sludge blanket (UASB) reactors, R1, R2, R3 and R4, were used to assess nitrophenols degradation at four different hydraulic retention times (HRT). Reactor R1 was used as control, whereas R2, R3, and R4 were fed with 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), respectively. The concentration of each nitrophenol was gradually varied from 2 to 30 mg/l during acclimation. After acclimation reactors were operated under steady-state conditions at four different HRTs – 30, 24, 18, and 12 h, to study its effect on the removal of nitrophenols. Overall removal of 2-NP and 4-NP was always more than 99% but 2,4-DNP removal decreased from 96% to 89.7% as HRT was lowered from 30 to 12 h. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophenol (2-A,4-NP) were found to be the major intermediates during the degradation of 2-NP, 4-NP and 2,4-DNP, respectively. Out of the total input of nitrophenolic concentration (30 mg/l), on molar basis, about 41.2–48.4% of 2-NP, 59.4–68% of 4-NP, 30–26.6% of 2,4-DNP was recovered in the form of their respective amino derivatives at 30–12 h HRT. COD removal was 98–89%, 97–56%, 97–52%, and 94–46% at 30–12 h HRT for R1, R2, R3 and R4, respectively. Average cell growth was observed to be 0.15 g volatile suspended solid (VSS) per g COD consumed. Methanogenic inhibition was observed at lower HRTs (18 and 12 h), however denitrification was always more than 99% with non-detectable level of nitrite. The granules developed inside the reactors were black in color and their average size varied between 1.9 and 2.1 mm.     

Granulation and immobilisation of methanogenic and sulfate-reducing bacteria in high-rate anaerobic reactors

The formation of anaerobic granular sludge on a sulfate-containing waste-water was studied in up-flow anaerobic sludge blanket reactors. Three systems were examined: a sulfidogenic system, a methanogenic system and a mixed sulfidogenic/methanogenic system. No significant granulation was observed in the sulfidogenic system. For the methanogenic and the mixed methanogenic/sulfidogenic system granulation proceeded well, and no significant difference in the granule diameter could be detected. In the three systems studied, different types of sludge developed. A (mainly) methanogenic granular sludge was developed in the methanogenic system, a (more) sulfate-reducing granular sludge was developed in the mixed methanogenic/sulfidogenic system, and a flocculant sulfate-reducing sludge was developed in the sulfidogenic system. Correspondence to: A Visser     

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.     

Nitrate removal in a packed bed reactor using volatile fatty acids from anaerobic acidogenesis of food wastes

A packed bed reactor (PBR) was fed with nitrate containing synthetic wastewater or effluent from a sequencing batch reactor used for nitrification. The C source introduced into the PBR consisted of volatile fatty acids (VFAs) produced from anaerobic acidogenesis of food wastes. When nitrate loading rates ranged from 0.50 to 1.01 kg N/m³·d, the PBR exhibited 100∼98.8% NO₃ ⁻-N removal efficiencies and nitrite concentrations in the effluent ranged from 0 to 0.6 NO₂ ⁻-N mg/L. When the PBR was further investigated to determine nitrate removal activity along the bed height using a nitrate loading rate less than 1.01 kg N/m³·d, 100% nitrate removal efficiency was observed. Approximately 83.2% nitrate removal efficiency was observed in the lower 50% of the packed-bed height. When reactor performance at a C/N ratio of 4 and a C/N ratio of 5 was compared, the PBR showed better removal efficiency (96.5%) of nitrate and less nitrite concentration in the effluent at the C/N ratio of 5. VFAs were found to be a good alternative to methanol as a carbon source for denitrification of a municipal wastewater containing 40 mg-N/L.     

Modeling the liquid flow in up-flow anaerobic sludge blanket reactors

By means of stimulus-response experiments an Li(+) tracer, models for the fluid flow in a 30-m(3) UASB reactor, used for the anaerobic treatment of wastewater, were tested. From the model with the best fit it could be derived that both the sludge bed and the sludge blanket can be described as perfectly mixed tank reactors with short-circuiting flows; the settler volume acts like a plug-flow region.Apart from the volumes of the different flow regions, two parameters are necessary and sufficient to describe the fluid flow in a well functioning UASB reactor, i.e., the short-circuiting flow over the sludge bed and the short-circuiting flow over the sludge blanket. The volumes could be measured accurately.The short-circuiting flow over the sludge bed is a linear function of the sludge bed height. When the optimal height of the sludge bed is defined as the height for which the short-circuiting flows are as small as possible, a bed-height of 3.5-4 m is sufficient (for superficial gas velocities between 1 and 1.5 m/h). This is in contradiction to the results of other authors. The short-circuiting flows over the sludge bed and the sludge blanket were also influenced by the superficial gas velocity.     

Influence of total solid and inoculum contents on performance of anaerobic reactors treating food waste

The aim of this paper was to analyze the biomethanization process of food waste (FW) from a university campus restaurant in six reactors with three different total solid percentages (20%, 25% and 30% TS) and two different inoculum percentages (20-30% of mesophilic sludge). The experimental procedure was programmed to select the initial performance parameters (total solid and inoculum contents) in a lab-reactor with V: 1100mL and, later, to validate the optimal parameters in a lab-scale batch reactor with V: 5000mL. The best performance for food waste biodegradation and methane generation was the reactor with 20% of total solid and 30% of inoculum: give rise to an acclimation stage with acidogenic/acetogenic activity between 20 and 60 days and methane yield of 0.49L CH4/g VS. Also, lab-scale batch reactor (V: 5000mL) exhibit the classical waste decomposition pattern and the process was completed with high values of methane yield (0.22L CH4/g VS). Finally, a protocol was proposed to enhance the start-up phase for dry thermophilic anaerobic digestion of food waste.     

Brewery wastewater treatment using anaerobic inverse fluidized bed reactors

Two anaerobic inverse fluidized bed reactors were utilized to evaluate organic matter removal from brewery wastewater, applying different OLR and testing two support materials. Hydrodynamic tests varying liquid flow and solid concentration were developed on the supports in order to establish operational conditions. A batch colonization stage was applied using 25% active volume of extendosphere and triturated polyethylene as support materials. The reactors were subsequently operated continuously with stepwise increments in organic loading rate until limiting conditions was reached. For the supports studied, IFBR technology was suitable for organic matter removal present in brewery wastewater with COD removal efficiencies greater than 90%. The reactor with triturated polyethylene support showed an excellent COD removal with OLR values up to 10 g COD/Ld, whereas the reactor with extendosphere support had an excellent hydrodynamic and biologic behavior working with OLR values up to 70 g COD/Ld.     

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.     

Anaerobic methanethiol degradation in upflow anaerobic sludge bed reactors at high salinity (> or =0.5 M Na(+))

The feasibility of anaerobic methanethiol (MT) degradation at elevated sodium concentrations was investigated in a mesophilic (30 degrees C) lab-scale upflow anaerobic sludge bed (UASB) reactor, inoculated with estuarine sediment originating from the Wadden Sea (The Netherlands). MT was almost completely degraded (>95%) to sulfide, methane and carbon dioxide at volumetric loading rates up to 37 mmol MT x L(-1) x day(-1), 0.5 M sodium (NaCl or NaHCO(3)) and between pH 7.3 and 8.4. Batch experiments revealed that inhibition of MT degradation started at sodium (both NaCl and NaHCO(3)) concentrations exceeding 0.8 M. Sulfide inhibited MT degradation already around 3 mM (pH 8.3).     

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