Acetate Degradation at 70 degrees C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70 degrees C

Anaerobic acetate degradation at 70 degrees C and at 55 degrees C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70 degrees C and less than 15 days was needed at 55 degrees C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55 degrees C up to 90% of the COD was removed. Batch assays showed that sludges from two 70 degrees C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70 degrees C. Both 70 degrees C sludges, as well as the 55 degrees C sludge, produced methane at temperatures of 37 to 73 degrees C. The 55 degrees C sludge exhibited shorter lag phases than the 70 degrees C sludges and higher specific methane production rates between 37 and 65 degrees C.     

Comparison of laboratory-scale thermophilic biofilm and activated sludge processes integrated with a mesophilic activated sludge process

A combined thermophilic-mesophilic wastewater treatment was studied using a laboratory-scale thermophilic activated sludge process (ASP) followed by mesophilic ASP or a thermophilic suspended carrier biofilm process (SCBP) followed by mesophilic ASP, both systems treating diluted molasses (dilution factor 1:500 corresponding GF/A-filtered COD (COD(filt)) of 1900+/-190 mgl(-1)). With hydraulic retention times (HRTs) of 12-18 h the thermophilic ASP and thermophilic SCBP removed 60+/-13% and 62+/-7% of COD(filt), respectively, with HRT of 8 h the removals were 48+/-1% and 69+/-4%. The sludge volume index (SVI) was notably lower in the thermophilic SCBP (measured from suspended sludge) than in the thermophilic ASP. Under the lowest HRT the mesophilic ASP gave better performance (as SVI, COD(filt), and COD(tot) removals) after the thermophilic SCBP than after the thermophilic ASP. Measured sludge yields were low (less than 0.1 kg suspended solids (SS) kg COD(filt removed)(-1)) in all processes. Both thermophilic treatments removed 80-85% of soluble COD (COD(sol)) whereas suspended COD (COD(susp)) and colloidal COD (COD(col)) were increased. Both mesophilic post-treatments removed all COD(col) and most of the COD(susp) from the thermophilic effluents. In conclusion, combined thermophilic-mesophilic treatment appeared to be easily operable and produced high effluent quality.     

Effect of effluent recycling and shock loading on the biodegradation of complex phenolic mixture in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up flow anaerobic sludge blanket (HUASB) reactors (R1, R2, R3 and R4) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. Effluent recirculation was employed at four different effluent to feed recirculation ratios (R/F) of 0.5, 1.0, 1.5 and 2.0 for 100 days to study the effect of recirculation on the performance of the reactors. Phenolics and COD removal was found to improve with increase in effluent recirculation. An effluent to feed recycle ratio of 1.0 resulted in maximum removal of phenolics and COD. Phenolics and COD removal improved from 88% and 92% to 95% each, respectively. The concentration of volatile fatty acids in the effluent was lower than the influent when effluent to feed recirculation was employed. Effect of shock loading on the reactors revealed that phenolics shock load up to 2.5 times increase in the normal input phenolics concentration in the form of continuous shock load for 4days did not affect the reactors performance irreversibly.     

Thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate reduction in methanol and formate-fed UASB reactors

The feasibility of thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate-reducing processes was investigated in three lab-scale upflow anaerobic sludge bed (UASB) reactors fed with either methanol or formate as the sole substrates and inoculated with mesophilic granular sludge previously not exposed to high temperatures. Full methanol and formate degradation at temperatures up to, respectively, 70 and 75 degrees C, were achieved when operating UASB reactors fed with sulfate rich (COD/SO4(2-)=0.5) synthetic wastewater. Methane-producing archaea (MPA) outcompeted sulfate-reducing bacteria (SRB) in the formate-fed UASB reactor at all temperatures tested (65-75 degrees C). In contrast, SRB outcompeted MPA in methanol-fed UASB reactors at temperatures equal to or exceeding 65 degrees C, whereas strong competition between SRB and MPA was observed in these reactors at 55 degrees C. A short-term (5 days) temperature increase from 55 to 65 degrees C was an effective strategy to suppress methanogenesis in methanol-fed sulfidogenic UASB reactors operated at 55 degrees C. Methanol was found to be a suitable electron donor for sulfate-reducing processes at a maximal temperature of 70 degrees C, with sulfide as the sole mineralization product of methanol degradation at that temperature.     

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.     

Thermophilic anaerobic digestion of high strength wastewaters

Investigations on the thermophilic anaerobic treatment of high-strength wastewaters (14-65 kg COD/m(3)) are presented. Vinasse, the wastewater of alcohol distilleries, was used as an example of such wastewaters. Semicontinuously fed digestion experiments at high retention times revealed that the effluent quality of digestion at 55 degrees C is comparable with that at 30 degrees C at similar loading rates. The amount of methane formed per kilogram of vinasse drops almost linearly with increasing vinasse concentrations. This can be attributed to increasing concentrations of inhibitory compounds, resulting in increasing volatile fatty acid (VFA) concentrations in the effluent. The treatment of vinasse was also investigated using upflow anaerobic sludge blanket (UASB) reactors. Thermophilic granular sludge, cultivated on sucrose, was used as seed material. The sludge required a 4-month adaptation period, during which the size of the sludge granules decreased significantly. However, the settling characteristics remained satisfactory. After adaptation, high loading and methane generation rates could be accommodated at satisfactory treatment efficiencies, namely, 86.4 kg COD/m(3) day and 26 m(3) CH(4)(STP)/m(3) day, respectively. As in the semicontinuously fed digesters, the effluent VFA concentrations were virtually independent of the loading rates applied, indicating that the toxicity of the vinasse is more important than the loading rate in determining the efficiency of the conversion of vinasse to methane.     

High-rate treatment of terephthalate in anaerobic hybrid reactors.

The anaerobic degradation of terephthalate as sole substrate was studied in three anaerobic upflow reactors. Initially, the reactors were operated as upflow anaerobic sludge bed (UASB) reactors and seeded with suspended methanogenic biomass obtained from a full-scale down-flow fixed film reactor, treating wastewater generated during production of purified terephthalic acid. The reactors were operated at 30, 37, and 55 degrees C. The terephthalate removal capacities remained low in all three reactors (<4 mmolxL-1xday-1, or 1 g of chemical oxygen demand (COD)xL-1xday-1) due to limitations in biomass retention. Batch experiments with biomass from the UASB reactors revealed that, within the mesophilic temperature range, optimal terephthalate degradation is obtained at 37 degrees C. No thermophilic terephthalate-degrading culture could be obtained in either continuous or batch cultures. To enhance biomass retention, the reactors were modified to anaerobic hybrid reactors by introduction of two types of reticulated polyurethane (PUR) foam particles. The hybrid reactors were operated at 37 degrees C and seeded with a mixture of biomass from the UASB reactors operated at 30 and 37 degrees C. After a lag period of approximately 80 days, the terephthalate conversion capacity of the hybrid reactors increased exponentially at a specific rate of approximately 0.06 day-1, and high removal rates were obtained (40-70 mmolxL-1xday-1, or 10-17 g of CODxL-1xday-1) at hydraulic retention times between 5 and 8 h. These high removal capacities could be attributed to enhanced biomass retention by the development of biofilms on the PUR carrier material as well as the formation of granular biomass. Biomass balances over the hybrid reactors suggested that either bacterial decay or selective wash-out of the terephthalate fermenting biomass played an important role in the capacity limitations of the systems. The presented results suggest that terephthalate can be degraded at high volumetric rates if sufficiently long sludge ages can be maintained, and the reactor pH and temperature are close to their optima.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.     

Acetate Degradation at 70°C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70°C

Anaerobic acetate degradation at 70°C and at 55°C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70°C and less than 15 days was needed at 55°C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55°C up to 90% of the COD was removed. Batch assays showed that sludges from two 70°C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70°C. Both 70°C sludges, as well as the 55°C sludge, produced methane at temperatures of 37 to 73°C. The 55°C sludge exhibited shorter lag phases than the 70°C sludges and higher specific methane production rates between 37 and 65°C.     

Comparative performance and microbial diversity of hyperthermophilic and thermophilic co-digestion of kitchen garbage and excess sludge

The objective of this study was to evaluate the performance characteristics of a hyperthermophilic digester system that consists of an acidogenic reactor operated at hyperthermophilic (70 degrees C) conditions in series with a methane reactor operated at mesophilic (35 degrees C), thermophilic (55 degrees C), and hyperthermophilic (65 degrees C) conditions. Lab-scale reactors were operated continuously, and were fed with co-substrates composed of artificial kitchen garbage (TS 9.8%) and excess sludge (TS 0.5%) at the volumetric ratio of 20:80. In the acidification step, COD solubilization was in the range of 22-46% at 70 degrees C, while it was 21-29% at 55 degrees C. The average protein solubilization was 44% at 70 degrees C. The double bond fatty acid removal ratio at 70 degrees C was much higher than at 55 degrees C. These results suggested that the optimal operation conditions for the acidogenic fermenter were about 3.1 days of HRT and 4 days of SRT at 70 degrees C. Methane conversion efficiency and the VS removal percentage in the methanogenic step following acidification was around 65% and 64% on average at 55 degrees C, respectively. The optimal operational conditions for this system are acidogenesis performed at 70 degrees C and methanogenesis at 55 degrees C. The key microbes determined in the hyperthermophilic acidification step were Anaerobic thermophile IC-BH at 6.4 days of HRT and Thermoanaerobacter thermohydrosulfuricus DSM 567 at 2.4 days of HRT. These results indicated that the hyperthermophilic system provides considerable advantages in treating co-substrates containing high concentrations of proteins, lipids, and nonbiodegradable solid matter.     

Effects of process stability on anaerobic biodegradation of LAS in UASB reactors

Anaerobic biodegradation of linear alkylbenzene sulfonates (LAS) was studied in upflow anaerobic sludge blanket (UASB) reactors operated under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. LAS C12 concentration in the influents was 10 mg.L(-1), and the hydraulic retention time in the reactors was 2 days. Adsorption of LAS C12 was assessed in an autoclaved control reactor and ceased after 115 days. The reactors were operated for a minimum of 267 days; 40-80% removal of LAS C12 was observed. A temperature reduction from 55 degrees C to 32 degrees C for 30 h resulted in process imbalance as indicated by increase of volatile fatty acids (VFA). The imbalance was much more intense in the LAS amended reactor compared with an unamended reactor. At the same time, the process imbalance resulted in discontinued LAS removal. This finding indicates that process stability is a key factor in anaerobic biological removal of LAS. After a recovery period, the removal of LAS resumed, providing evidence of biological anaerobic LAS degradation. The removal remained constant until termination of experiments in the reactor. Biodegradation of LAS in the mesophilic reactor was at the same level as in the thermophilic reactor under stable conditions.     

Thermophilic aerobic wastewater treatment,process performance,biomass characteristics,and effluent quality

Thermophilic aerobic wastewater treatment is reviewed. Thermophilic processes have been studied in laboratory and pilot-scale while full-scale applications are rare. The paper focuses on the microbiology of aerobic thermophiles, performance of the aerobic wastewater treatments, sludge yield, and alternatives to enhance performance of thethermophilic process. Thermophilic processes have been shown to operate under markedly high loading rates (30–180 kg COD m⁻³d⁻¹).Reported sludge production values under thermophilic conditions vary between 0.05 and0.3 kg SS kg COD_removed, which are about the same or lower than generally obtained in mesophilic processes. Compared to analogous mesophilic treatment, thermophilic treatment commonly suffers from poorer effluent quality, measured by lower total COD and filtrated (GF-A) COD removals. However, in the removal of soluble (bacterial membrane filtered) COD both mesophilic and thermophilic treatments have produced similar results. Sludge settle ability in thermophilic processes have been reported to be better or poorer than in analogous mesophilic processes, although cases with better settling properties are rare. Combining thermophilic with mesophilic treatment or ultrafiltration may in some cases markedly improve effluent quality. This revised version was published online in June 2006 with corrections to the Cover Date.     

A comparison of the performance of mesophilic and thermophilic anaerobic filters treating papermill wastewater

Two anaerobic filters, one mesophilic (35 degrees C) and one thermophilic (55 degrees C), were operated with a papermill wastewater at a series of organic loadings. The hydraulic retention time (HRT) ranged from 6 to 24 h with organic loading rates (OLR) 1.07-12.25 g/l per day. At loading rates up to 8.4 g COD/l d, there was no difference in terms of the removal of soluble COD (SCOD) and gas production. At the higher organic loading rate, the SCOD removal performance of thermophilic digester was slightly better compare to mesophilic digester. Similar trend was also observed in terms of the daily methane production. The stability of thermophilic digester was also better than mesophilic digester particularly for the higher organic loadings. Volatile fatty acid accumulation was observed in the effluent of the mesophilic filter at the higher organic loading rates. The Stover-Kincannon model was applied to both digesters and it was found that model was applicable to both digesters for papermill wastewater. K(B) and U(max) constants from the Stover-Kincannon model were also derived.     

Effect of nutrients supplementation on anaerobic sludge development and activity for treating distillery effluent

Startup of laboratory anaerobic reactors and treatment efficiency were investigated by supplementing the distillery effluent feed with macronutrients (Ca, P) and micronutrients (Ni, Fe and Co) under mesophilic conditions. Calcium and phosphate were deterimental to the treatment efficiency and sludge granulation. Traces of salts of iron, nickel and cobalt, individually and in combinations improved the COD removal efficiency and sludge granulation process.     

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.     

Long-term, high-rate anaerobic biological treatment of whey wastewaters at psychrophilic temperatures

Two laboratory-scale anaerobic hybrid reactors, R1 and R2, treated low- (1 kg COD m-3) and high-strength (10 kg COD m-3) whey-based wastewaters, respectively, in a 500-day trial. The chemical oxygen demand (COD) removal efficiencies of R1 averaged 70-80%, at organic loading rates of 0.5-1.3 kg COD m-3 day-1, between 20 and 12 degrees C. The COD removal efficiencies of R2 exceeded 90%, at organic loading rates up to 13.3 kg COD m-3 day-1, between 20 and 14 degrees C. Lowering the operating temperature of R2 to 12 degrees C resulted in a decrease in COD removal efficiency, to between 50% and 60%, and a disintegration of granular sludge. The decline in performance, and granule disintegration, was reversed by decreasing the organic loading rate of R2 to 6.6 kg m-3 day-1. Specific methanogenic activity profiles revealed mesophilic (37 degrees C) temperature optima for biomass in both reactors, even after 500 days of psychrophilic operation, although the development of psychrotolerance in the biomass was noted.     

Anaerobic treatment of poultry mortality in a temperature-phased leachbed-UASB system

Anaerobic digestion has been proposed as an alternative to the conventional disposal methods of burial, incineration, rendering and aerobic composting. A temperature-phased system consisting of one UASB (at 55 degrees C) and three leach-bed reactors (at ambient temperatures) was tested for its efficiencies in treating poultry mortality. The thermophilic UASB was difficult to start-up. It also showed signs of inhibited methanogenesis. Chemical parameters such as long chain fatty acids, volatile fatty acids and ammonia concentrations were all very high for the thermophilic UASB. Lowering its temperature to 35 degrees C enhanced its stability and improved its performances. Lowering the pH of the 55 degrees C UASB also improved its chemical oxygen demand (COD) reduction efficiency as well as its methane production rate. The results were compared to that of another similar system where the UASB reactor was maintained at 35 degrees C instead of at 55 degrees C.     

Effect of chitosan on UASB treating POME during a transition from mesophilic to thermophilic conditions

The effects of chitosan addition on treatment of palm oil mill effluent were investigated using two lab-scale upflow anaerobic sludge bed (UASB) reactors: (1) with chitosan addition at the dosage of 2 mg chitosan per g volatile suspended solids on the first day of the operation (R1), (2) without chitosan addition (the control, R2). The reactors were inoculated with mesophilic anaerobic sludge which was acclimatized to a thermophilic condition with a stepwise temperature increase of 5 °C from 37 to 57 °C. The OLR ranged from 2.23 to 9.47 kg COD m⁻³ day⁻¹. The difference in biogas production rate increased from non-significant to 18% different. The effluent volatile suspended solids of R1 was 65 mg l⁻¹ lower than that of R2 on Day 123. 16S rRNA targeted denaturing gradient gel electrophoresis (DGGE) fingerprints of microbial community indicated that some methanogens in the genus Methanosaeta can be detected in R1 but not in R2.     

Thermophilic anaerobic digestion of sewage sludge: focus on the influence of the start-up. A review

The thermophilic anaerobic digestion (TAD) of sewage sludge has often been found to be less stable than mesophilic treatment. In comparison to mesophilic digesters, thermophilic reactors treating sludge are generally characterized by relatively high concentrations of volatile fatty acids (VFA) in the effluent along with poor effluent quality, indicating a lower level of process stability. However, reviewing the literature related to the procedure for obtaining a thermophilic inoculum, it seems that most of the problems associated with the instability and the accumulation of organic intermediates are the result of the manner in which the thermophilic sludge has been obtained. In this paper, the different options available for obtaining an anaerobic digester operating at thermophilic temperature (55°C) have been reviewed. In this light, rapid heating to the target temperature followed by the development of thermophilic microorganisms, which can be determined by VFA dropping to ≤500?mg acetic acid L^?1 before increasing the organic loading rate (OLR), has been determined the most suitable means of establishing TAD.     

Systematic analysis of biochemical performance and the microbial community of an activated sludge process using ozone-treated sludge for sludge reduction

Two lab-scale bioreactors (reactors 1 and 2) were employed to examine the changes in biological performance and the microbial community of an activated sludge process fed with ozonated sludge for sludge reduction. During the 122 d operation, the microbial activities and community in the two reactors were evaluated. The results indicated that, when compared with the conventional reactor (reactor 1), the reactor that was fed with the ozonated sludge (reactor 2) showed good removal of COD, TN and cell debris, without formation of any excess sludge. In addition, the protease activity and intracellular ATP concentration of reactor 2 were increased when compared to reactor 1, indicating that reactor 2 had a better ability to digest proteins and cell debris. DGGE analysis revealed that the bacterial communities in the two reactors were different, and that the dissimilarity of the bacterial population was nearly 40%. Reactor 2 also contained more protozoa and metazoa, which could graze on the ozone-treated sludge debris directly.