High OLR Research Articles

Performance comparison between mesophilic and thermophilic anaerobic reactors for treatment of palm oil mill effluent

The anaerobic digestion of palm oil mill effluent (POME) was carried out under mesophilic (37°C) and thermophilic (55°C) conditions without long-time POME storage in order to compare the performance of each condition in the field of Sumatra Island, Indonesia. The anaerobic treatment system was composed of anaerobic hybrid reactor and anaerobic baffled filter. Raw POME was pretreated by screw decanter to reduce suspended solids and residual oil. The total COD removal rate of 90–95% was achieved in both conditions at the OLR of 15kg[COD]/m3/d. The COD removal in thermophilic conditions was slightly better, however the biogas production was much higher than that in the mesophilic one at high OLR. The organic contents in pretreated POME were highly biodegradable in mesophilic under the lower OLRs. The biogas production was 13.5–20.0l/d at the 15kg[COD]/m3/d OLR, and the average content of carbon dioxide was 5–35% in both conditions.

Optimization of thermophilic anaerobic-aerobic treatment system for Palm Oil Mill Effluent (POME)

Optimization of an integrated anaerobic-aerobic bioreactor (IAAB) treatment system for the reduction of organic matter (Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) concentrations) in Palm Oil Mill Effluent (POME) to legal standards with high methane yield was performed for the first time under thermophilic condition (50°C–55°C) by using response surface methodology (RSM). The experiments were conducted based on a central composite rotatable design (CCRD) with three independent operating variables, organic loading rates in anaerobic compartment (OLRan) and mixed liquor volatile suspended solids (MLVSS) concentration in anaerobic (MLVSSan) and aerobic compartments (MLVSSa). The optimum conditions for the POME treatment were determined as OLRan of 15.6 g COD·L−1·d−1, MLVSSan of 43100 mg·L−1, and MLVSSa of 18600 mg·L−1, where high aerobic COD, BOD and TSS removal efficiencies of 96.3%, 97.9%, and 98.5% were achieved with treated BOD of 56 mg·L−1 and TSS of 28 mg·L−1 meeting the discharge standard. This optimization study successfully achieved a reduction of 42% in the BOD concentrations of the final treated effluent at a 48% higher OLRan as compared to the previous works. Besides, thermophilic IAAB system scores better feasibility and higher effectiveness as compared to the optimized mesophilic system. This is due to its higher ability to handle high OLR with higher overall treatment efficiencies (more than 99.6%), methane yield (0.31 L CH4·g−1 CODremoved) and purity of methane (67.5%). Hence, these advantages ascertain the applicability of thermophilic IAAB in the POME treatment or even in other high-strength wastewaters treatment.

Long-term stability of thermophilic co-digestion submerged anaerobic membrane reactor encountering high organic loading rate, persistent propionate and detectable hydrogen in biogas

The performance of thermophilic anaerobic co-digestion of coffee grounds and sludge using membrane reactor was investigated for 148 days, out of a total research duration of 263 days. The OLR was increased from 2.2 to 33.7 kg-COD/m(3)d and HRT was shortened from 70 to 7 days. A significant irreversible drop in pH confirmed the overload of reactor. Under a moderately high OLR of 23.6 kg-COD/m(3)d, and with HRT and influent total solids of 10 days and 150 g/L, respectively, the COD removal efficiency was 44.5%. Hydrogen in biogas was around 100-200 ppm, which resulted in the persistent propionate of 1.0-3.2g/L. The VFA consumed approximately 60% of the total alkalinity. NH4HCO3 was supplemented to maintain alkalinity. The stability of system relied on pH management under steady state. The 16SrDNA results showed that hydrogen-utilizing methanogens dominates the archaeal community. The propionate-oxidizing bacteria in bacterial community was insufficient.

Effect of Operation Conditions on Performance of Treating Actual Domestic Wastewater Bioreactor at Ambient Temperature

To determine the operation parameters of the expanded granular sludge bed (EGSB) reactor treating actual domestic wastewater at ambient temperature of 15-26°C, the effects of influent flow, HRT, recycle ratio,Vup and temperature on the performance of the EGSB reactor were investigated in this paper. The results indicated that when treating actual domestic wastewater, the EGSB reactor could support high influent flow and low HRT. For 9L.h-1, 11L.h-1, 15L.h-1, 24L.h-1 influent flow, with the optimal recycle ratios of 1.6-2.5, 1.2-1.6, 0.4-0.8, 0.0, the COD removal efficiencies could attain to 86-90%, 88-89%, 83%, 83%, respectively. For lower influent flow, higher Vup could slightly increase COD removal, but accordingly higher recycle ratio need to supply. Meanwhile, for higher influent flow, higher Vup will damage the granular characteristic and thus cause the decreasing of COD removal, and thus for the EGSB reactor treating actual domestic wastewater, 2.7-3.0m.h-1 optimal Vup should be employed. The EGSB reactor could work well at ambient temperature of 15°C-26°C. The optimal influent flow and Vup were 15-24L.h-1 and 3.0m.h-1. High average OLR of 18.6kgCOD.m-3.d-1 and high average COD removal efficiencies of above 81.4% could achieve, and only very low recycle ratio of 0.0 to 0.4 need employ.

Maximum organic loading rate for the single-stage wet anaerobic digestion of food waste

Anaerobic digestion of food waste was conducted at high OLR from 3.7 to 12.9kg-VSm−3day−1 for 225days. Periods without organic loading were arranged between the each loading period. Stable operation at an OLR of 9.2kg-VS (15.0kg-COD) m−3day−1 was achieved with a high VS reduction (91.8%) and high methane yield (455mLg-VS-1). The cell density increased in the periods without organic loading, and reached to 10.9×1010cellsmL−1 on day 187, which was around 15 times higher than that of the seed sludge. There was a significant correlation between OLR and saturated TSS in the sludge (y=17.3e0.1679×, r2=0.996, P<0.05). A theoretical maximum OLR of 10.5kg-VS (17.0kg-COD) m−3day−1 was obtained for mesophilic single-stage wet anaerobic digestion that is able to maintain a stable operation with high methane yield and VS reduction.

Canteen based composite food waste as potential anodic fuel for bioelectricity generation in single chambered microbial fuel cell (MFC): Bio-electrochemical evaluation under increasing substrate loading condition

Canteen based composite food waste, which is rich in organic constituents was evaluated as anodic fuel (substrate) in single chambered microbial fuel cell (MFC; mediator less; non-catalyzed graphite electrodes; open-air cathode) to harness electrical energy via anaerobic treatment. The performance of MFC was evaluated with anaerobic consortia as anodic biocatalyst under various increasing organic loading rates (OLR1, 1.01 kg COD/m 3-day; OLR2, 1.74 kg COD/m 3-day; OLR3, 2.61 kg COD/m 3-day). The experimental results illustrated the feasibility of bioelectricity generation from food waste along with treatment but depend on the applied organic load. The maximum power output was observed at OLR2 (295 mV; 390 mA/m 2), followed by OLR3 (250 mV; 311 mA/m 2) and OLR1 (188 mV; 211 mA/m 2). The variation in substrate degradation has also showed a relation with organic load applied (OLR1, 44.28% (0.47 kg COD/m 3-day); OLR2, 64.83% (1.13 kg COD/m 3-day); OLR3, 46.28% (1.39 kg COD/m 3-day)). The increase in loading from OLR1 to OLR2, the catalytic ability of biocatalyst increased from 7.5 mA (24 h) to 11.22 mA (24 h) along with the increase in power generation from 39.38 mW/m 2 to 107.89 mW/m 2. At the higher OLR (OLR3), the bioelectrocatalytic current decreased to 5.3 mA (24 h) along with decrement in power to 78.92 mW/m 2. The optimum organic load (OLR2) showed maximal catalytic activity and power output. Fuel cell behavior with respect to polarization, anode potential and bio-electrochemical behavior supported the higher performance of MFC at OLR2. Specific power yield was also observed to be higher at OLR2 (0.320 W/kg COD R) indicating the combined process efficiency. Volatile fatty acids generation and pH profiles also correlated well with the observed results.

Use of down-flow hanging sponge (DHS) reactor as a promising post-treatment system for municipal wastewater

The aim of the present study was the treatment of municipal wastewater to be used for irrigation using a technology that is robust and simple to operate with minimum energy consumption. In order to achieve these objectives, two treatment schemes have been investigated. The first scheme consisted of a hybrid up-flow anaerobic sludge blanket (HUASB) reactor followed by a down-flow hanging sponge (DHS) reactor. The second one consisted of a primary sedimentation tank (PST) followed by a DHS reactor. Both systems were fed continuously with raw municipal wastewater. The study lasted for more than 140 days, the results of which revealed that the efficiency of both systems was comparable with regard to carbonaceous and nitrogenous compounds removal. The average removal values of COD total, COD soluble, BOD 5total, TSS and TN in the first scheme were 90 ± 4, 78 ± 8, 95 ± 2, 96 ± 5 and 72 ± 8%, respectively. However, the residual geometric mean of faecal coliform counts in the final effluent of the first treatment scheme was only 2.7 × 10 2 MPN/100 ml compared to 6.5 × 10 3 MPN/100 ml in the second treatment scheme. In general, available data proved that the DHS reactor can cope with higher organic loads. The performance of DHS reactor was quite good for carbonaceous organic matter and nitrogen removal even at high OLR of 4.8 kg COD/m 3 d.

Biomethanization of orange peel waste

Recent research has demonstrated that orange peel waste is a potentially valuable resource that can be developed into high value products such as methane. Following a pre-treatment to extract D-limonene, the anaerobic digestion of orange peel waste was evaluated at laboratory and pilot scale under mesophilic and thermophilic conditions. D-limonene removals of 70% were reached with pre-treatment. The results showed the convenience of thermophilic conditions for treating this waste as the methane production rate and biodegradability were higher than at mesophilic temperature. At pilot scale, a thermophilic continuously stirred-tank reactor working in semi-continuous mode was employed. The OLR was found to be in the range of 1.20-3.67 kg COD/m(3) d; the most appropriate range for working under stable conditions at SRT of 25 d. The methane yield coefficient was found to be 0.27-0.29 L(STP)CH(4)/g added COD and the biodegradability 84-90% under these conditions. However, acidification occurred at the highest OLR.

Evaluation of a hybrid upflow anaerobic sludge-filter bed reactor: effect of the proportion of packing medium on performance

The aim of this study was to determine the effects of the volume occupied by the filter bed zone on the behavior of an anaerobic hybrid UASFB reactor. This configuration contains a sludge bed in the lower part of the reactor and a filter bed in the upper part. Three such reactors, each with a working volume of 9.8-L, were studied; these differed in proportion of packing medium occupying 50, 35 and 20% of the working volume of the reactors, respectively. All the reactors were fed with wine distillery vinasse and were operated for a period of 232 days at 33+/-1 degrees C with increasing OLRs. No significant differences were observed between the reactors for the range of OLRs studied. Indeed, relatively high OLRs could be reached for all the three reactors with an average OLR of about 18 g COD/L d towards the end of the experiment, while maintaining a constant HRT of 26 h. COD(t) and COD(s) removal efficiencies were always more than 80 and 86%, respectively, even for the highest OLR. High quantities of VS were accumulated in the reactors with an average value of 438+/-17 g per reactor. Most of the biomass was in the sludge bed zone suggesting that this part was playing a major role in COD removal. The internal packing medium on the top of the reactor had a key role in retaining the small flocculated particles inside the reactor, while minimizing the escape of solids in the effluent. This study suggests that low packing volume ratios can be used in the design of UASFB reactors, which allows a reduction in the costs of packing medium required as the supports are expensive.

Carbon‐nitrogen‐phosphorus removal and biofilm growth characteristics in an integrated wastewater treatment system involving a rotating biological contactor

AbstractA new rotating biological contactor‐packed media technology (RBC‐PMT) is locally innovated using light polyethylene Amazon screen material as disc media. A single‐stage co‐current fed of this type, which is connected with a series of equalization tanks as an integrated wastewater treatment system (IWWTS), showed good carbon‐nitrogen‐phosphorus (C‐N‐P) removal and unveiled biofilm growth characteristics noteworthy for treating pollutants in wastewater.The equalization tanks approached facultative anaerobic conditions while the RBC‐PMT exhibited a completely aerated system, both with a slightly alkaline pH, whose temperatures are ranging from 21 to 24 °C, and both performed as biological nutrient removal systems. The combined nutrient removal efficiency at high organic loading rate (HOLR) and low organic loading rate (LOLR) showed fair chemical oxygen demand (COD) removal at 65.68 and 67.89%, respectively. Nitrate‐nitrogen removal demonstrated good removal at 79.17% at HOLR and 83.43% at LOLR. There was excellent phosphate‐phosphorus removal determined at 91.64 and 94.35% at high and low OLRs, respectively. This indicates that increasing the organic loading rate decreases the C‐N‐P removal in the IWWTS.Biofilm growth was characterized by the selection and survival of microorganisms present under aerobic environmental conditions in the RBC‐PMT system and their respective metabolism in removing C‐N‐P substrates. Yeasts, coliform bacteria particularly E. coli, Cyanobacteria, and benthic diatoms were dominant microorganisms found upon oil‐immersion microscopy. Protozoans and algae including Chlorococcum, Chlorella, Diatoma, Tribonema, Oscillatoria, Euglena, and other motile rotifiers were also dominantly found in the biofilm samples. Biofilm growth is observed and its average thickness was measured to be 7.71 µm at HOLR and 2.81 µm at LOLR. Thicker biofilm at HOLR has caused the reduced rate of diffusion of the microorganisms and their metabolic products as manifested by the low C‐N‐P removal during HOLR. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Extraction of antioxidants from olive mill wastewater and electro-coagulation of exhausted fraction to reduce its toxicity on anaerobic digestion

Liquid–liquid extraction was used in order to recover phenolic compounds from centrifuged olive mill wastewater (OMW), a polluting by-product of olive oil production process, and to reduce their toxicity for a subsequent aerobic or anaerobic digestion. Phenolic compounds were identified in untreated and treated OMW by gas chromatography coupled to mass spectrometry (GC–MS). The experimental results of ethyl acetate extraction showed that the monomers recovery efficiency was over 90%. This pre-treatment resulted in the removal of the major LMM phenolic compounds and a small part of HMM polyphenols. The aerobic treatment of the exhausted OMW fraction removed 78.7% of the soluble COD. In the case of anaerobic digestion at OLR ranged from 1 to 3.5 g COD l −1 day −1, methanisation process exhibited high methane yield as 0.3 l CH 4 produced per g COD introduced and high COD removal (80%). However, a disruption of the process was observed when the OLR was increased to 4.5 g COD l −1 day −1. A pre-treatment by electro-coagulation resulted in decreasing the toxicity and enhancing the performance of methanisation operated at higher OLR from 4 to 7.5 g COD l −1 day −1.

Integration of Ozonation and an Anaerobic Sequencing Batch Reactor (AnSBR) for the Treatment of Cherry Stillage

Cherry stillage is a high strength organic wastewater arising from the manufacture of alcoholic products by distillation of fermented cherries. It is made up of biorefractory polyphenols in addition to readily biodegradable organic matter. An anaerobic sequencing batch reactor (AnSBR) was used to treat cherry stillage at influent COD ranging from 5 to 50 g/L. Different cycle times were selected to test biomass organic loading rates (OLR(B)), from 0.3 to 1.2 g COD/g VSS.d. COD and TOC efficiency removals higher than 80% were achieved at influent COD up to 28.5 g/L but minimum OLR(B) tested. However, as a result of the temporary inhibition of acetogens and methanogens, volatile fatty acids (VFA) noticeably accumulated and methane production came to a transient standstill when operating at influent COD higher than 10 g/L. At these conditions, the AnSBR showed signs of instability and could not operate efficiently at OLR(B) higher than 0.3 g COD/g VSS.d. A feasible explanation for this inhibition is the presence of toxic polyphenols in cherry stillage. Thus, an ozonation step prior to the AnSBR was observed to be useful, since more than 75% of polyphenols could be removed by ozone. The integrated process was shown to be a suitable treatment technology as the following advantages compared to the single AnSBR treatment were observed: greater polyphenols and color removals, higher COD and TOC removal rates thus enabling the process to effectively operate at higher OLR, higher degree of biomethanation, and good stability with less risk of acidification.

A membrane assisted hybrid bioreactor for the post treatment of an anaerobic effluent from a fish canning factory

An innovative membrane assisted hybrid bioreactor was used to treat a mixture of two streams produced in a fish canning factory: a highly loaded stream that had previously been treated in an anaerobic contact reactor, and a second stream with a relatively low COD and N concentration. Experiments were carried out during two experimental stages: an aerobic stage, which is focused in the study on the aerobic oxidation of ammonia and COD and a nitrification-denitrification stage in which the study was mainly focused on the removal of nitrogen. Results of the aerobic period pointed out that it was feasible to achieve ammonia and COD removals of around 99% at OLR of 6.5 kg COD/m3 x d and NLR of 1.8 kg N-NH4+/m3 x d. Specific nitrifying activities of up to 0.78 g N-NH4+/g protein x d and 0.25 g N-NH4+/g VSS x d, were recorded for the attached and suspended biomass, respectively. Around 50-60% of the nitrifying capacity of the reactor was a result of the nitrifying capacity of the biofilm. During the nitrification-denitrification stage 76% of nitrogen removal was attained at an NLR of 0.8 kg N-NH4+/m3 x d. The biofilm nitrifying activity was not affected by the operating conditions of the system, as a result of the preferential consumption of COD by suspended biomass in the reactor. Thus, the combination of a hybrid system, with both suspended and attached biomass, and an ultrafiltration membrane module might be an alternative for treating wastewaters in compact biological systems. The intrinsic characteristics of the system made it feasible to operate at high OLR without problems related with the settling properties of the sludge or the drop in the nitrogen conversion. There were no solids in the effluent as a result of the use of the membrane filtration module.

Reactor Configuration-Part I Comparative Process Stability and Efficiency of Mesophilic Anaerobic Digestion

The comparative process stability and efficiency of mesophilic anaerobic digestion (35 °C) has been evaluated for four different reactor configurations, which are: daily batch-fed single-stage continuously stirred tank reactor (CSTR) (MB), continuously fed single-stage CSTR (MC), daily batch-fed two-phase CSTR (MTP), and daily batch-fed non-mixed single-stage reactor (MNMR). The results are discussed for 2 periods, 1) start-up until steady state (HRT = 20 days, Days 0 - 200) and 2) OLR increase from 4 % solids at steady state to reactor failure by increasing solids concentration in the feed and decreasing the HRT (Days 201 -). During the start-up period, the MB showed the lowest stability with a pH drop whenever the solids concentration in the feed was increased. Conversely the MNMR reached steady state with 4 % feed solids in the shortest time with a relatively stable pH and low VFA. The superior performance of the MNMR confirms the importance of microbial consortia proximity especially for the removal of propionate. A cocktail of nutrients (Ca, Ni, Fe, and Co) was added daily into the reactors which showed high VFA except the MNMR which did not exhibit the elevated VFA. The results indicated that adding nutrients stimulated gas production and facilitated removal of almost all VFA except propionate confirming the importance of inorganic nutrients bioavailability. During the long-term operation with OLR increase until reactor failure (pH below 5.5), the results show that the MC reached the highest OLR while the MNMR failed first. Compared with the daily batch fed reactors, the constant pH of the MC seems to be the reason why the MC reached the highest OLR. Considering the best performance of the MNMR during the start-up period, the failure of the MNMR first is hypothesized to be due to the lack of trace nutrients at high OLR. Overall, two-phase digestion showed no benefit over single stage and all reactors demonstrated comparable VS removal percentage. Additional experiments in which the reactor configuration was changed from CSTR to non-mixed reactor showed significant benefit with respect to gas production and lowered propionate threshold concentration. This once again manifests the importance of microbial consortia proximity with respect to the degradation of propionate.

Reactor Configuration-Part II Comparative Process Stability and Efficiency of Thermophilic Anaerobic Digestion

Comparative process stability and efficiency of thermophilic anaerobic digestion (55 °C) has been evaluated for four different reactor configurations, which are: daily batch-fed single-stage continuously stirred tank reactor (CSTR) (TB), continuously-fed single-stage CSTR (TC), daily batch-fed two-phase CSTR (TTP), and daily batch-fed non-mixed single-stage reactor (TNMR). The results are discussed for 2 periods, 1) start-up until steady state (Days 0 - 200) and 2) OLR increase from 4 % solids at steady state to reactor failure by increasing solids concentration in feed and decreasing the HRT (Days 201 -). During the start-up period, the TB showed the worst stability with a pH drop whenever the solids concentration in the feed was increased. Conversely the TNMR reached steady state with 4 % feed solids in the shortest time with relatively stable pH and very low VFA. The superior performance of the TNMR confirms the importance of microbial consortia proximity especially for the removal of propionate. The cocktail of inorganic nutrients (Ca, Ni, Fe, and Co) was added daily into all reactors showing high VFA. In the case of the TNMR, complete removal of propionate occurred after supplementation of nutrients. The results indicated that adding nutrients stimulated gas production and facilitated removal of almost all VFA confirming the importance of inorganic nutrients bioavailability. During the long-term operation with OLR increases until reactor failure (pH below 5.5), the results show that TB failed at the lowest OLR while the TC and the TNMR reached the highest OLR. Compared with the daily batch fed reactors, the constant pH of the MC seems to be the reason why the MC reached the highest OLR. The superior performance of the TNMR during both the start-up and the long-term period confirms the importance of microbial consortia proximity. Two-phase digestion showed little benefit over single stage during the start-up period and no benefit was observed during the long-term period. Additional experiments in which the reactor configuration was changed from CSTR to non-mixed reactor showed significant benefit with respect to gas production and VFA threshold concentration. This once again manifests the importance of microbial consortia proximity.

Relations between carbon removal rates, biofilm size and density of a novel anaerobic reactor: the inverse turbulent bed

An anaerobic inverse turbulent bed, in which the biogas only ensures fluidisation of floating carrier particles, was investigated for carbon removal kinetics and for biofilm growth and detachment. The range of operation of the reactor was kept within 5 and 30 kgCOD· m−3· d−1, with Hydraulic Retention Times between 0.28 and 1 day. The carbon removal efficiency remained between 70 and 85%. Biofilm size were rather low (between 5 and 30 μm) while biofilm density reached very high values (over 80 kgVS· m−3). The biofilm size and density varied with increasing carbon removal rates with opposite trends; as biofilm size increases, its density decreases. On the one hand, biomass activity within the reactor was kept at a high level, (between 0.23 and 0.75 kgTOC· kgVS· d−1, i.e. between 0.6 and 1.85 kgCOD·kgVS · d−1).This result indicates that high turbulence and shear may favour growth of thin, dense and active biofilms. It is thus an interesting tool for biomass control. On the other hand, volatile solid detachment increases quasi linearly with carbon removal rate and the total amount of solid in the reactor levels off at high OLR. This means that detachment could be a limit of the process at higher organic loading rates.

The 1997–98 El Niño Evolution Relative to Previous El Niño Events

The evolution of the 1997–98 El Niño is described using NCEP SST and OLR data, NCEP–NCAR reanalysis sea level pressure (SLP) fields, and The Florida State University surface wind data. From November 1996 to January 1997, the eastern Pacific is characterized by equatorial cold SST and high SLP anomalies, while the western Pacific is marked by off-equatorial warm SST anomalies and off-equatorial anomalous cyclones. Corresponding to this distribution are high OLR anomalies in the equatorial central Pacific and low OLR anomalies in the off-equatorial far western Pacific. The off-equatorial anomalous cyclones in the western Pacific are associated with a switch in the equatorial wind anomalies over the western Pacific from easterly to westerly. These equatorial westerly anomalies then appear to initiate early SST warmings around the date line in January/February 1997 and around the far eastern Pacific in March 1997. Subsequently, both the westerly wind and warm SST anomalies, along with the low OLR anomalies, grow and progress eastward. The eastward propagating warm SST anomalies merge with the slower westward spreading warm SST anomalies from the far eastern Pacific to form large-scale warming in the equatorial eastern and central Pacific. The anomaly patterns in the eastern and central Pacific continue to develop, reaching their peak values around December 1997. In the western Pacific, the off-equatorial SST anomalies reverse sign from warm to cold. Correspondingly, the off-equatorial SLP anomalies in the western Pacific also switch sign from low to high. These off-equatorial high SLP anomalies initiate equatorial easterly wind anomalies over the far western Pacific. Like the equatorial westerly wind anomalies that initiate the early warming, the equatorial easterly wind anomalies over the far western Pacific appear to have a cooling effect in the east and hence help facilitate the 1997–98 El Niño decay. This paper also compares the 1997–98 El Niño with previous warm events and discusses different ENSO mechanisms relevant to the 1997–98 El Niño.

Methanogenic activity and performance of UASB, DSFF and USFF reactors

This paper presents correlation of methanogenic activity with performance of bench scale models of UASB, DSFF and USFF reactors at varying OLRs while maintaining EBHRT in the range of 0.80-1.10 d. At lower OLR, performance of the reactors appears to be similar. However, at higher OLR, the performance of DSFF and USFF reactors is fairly steady whereas UASB reactor shows poor performance in terms of methane production. This is in conformity with methanogenic activity test results. The results of AMA and TMA tests also reveal that at higher OLR, acetoclastic methanogens population decreases considerably in UASB reactor and a large fraction of methane is produced due to the activity of non-acetoclastic methanogens.

Methanogenic activity and performance of UASB, DSFF and USFF reactors

This paper presents correlation of methanogenic activity with performance of bench scale models of UASB, DSFF and USFF reactors at varying OLRs while maintaining EBHRT in the range of 0.80–1.10 d. At lower OLR, performance of the reactors appears to be similar. However, at higher OLR, the performance of DSFF and USFF reactors is fairly steady whereas UASB reactor shows poor performance in terms of methane production. This is in conformity with methanogenic activity test results. The results of AMA and TMA tests also reveal that at higher OLR, acetoclastic methanogens population decreases considerably in UASB reactor and a large fraction of methane is produced due to the activity of non-acetoclastic methanogens.