On the behavior of the periodic anaerobic baffled reactor (PABR) during the transition from carbohydrate to protein-based feedings

The influence of the organic substrate composition in the feed of an innovative reactor, the periodic anaerobic baffled reactor (PABR) is examined. A laboratory-scale PABR fed on a synthetic medium composed of mixtures of glucose (a carbohydrate) and gelatin (a protein) in various ratios performed well. The PABR seemed to be minimally affected during the gradual substitution of glucose by gelatin. In fact, the reactor performance remained at an optimal level (approximately 98%), while operated under an organic loading rate of 3.125 gCOD/l/d.     

Performance of a periodic anaerobic baffled reactor fed on Chinese traditional medicine industrial wastewater

A four-compartment periodic anaerobic baffled reactor (PABR) was run in a 'clockwise sequential' switching manner continuously fed on chinese traditional medicine industrial wastewater under an alkalinity concentration between 1000 and 1500 mg CaCO(3)/L of the feed with average organic load rate (OLR) at about 1, 2, 4 and 6 kg COD/(m(3)d) for 12, 24, 24 and 6d, respectively. Hydraulic residence time was 2d, while switching period was 4d. As the average OLR increased to 6 kg COD/(m(3)d), the time of the sharp fall in pH, chemical oxygen demand (COD) removal, gas production and methane percentage of the biogas of all the compartments and the time of rapid volatile fatty acids accumulation in effluent coincided, hence the PABR became sour. Denaturing gradient gel electrophoresis (DGGE) community fingerprints and their cluster analysis revealed that community structures of each compartment tended to be more closely related if the PABR was not overloaded.     

Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 2. Model prediction

A model was developed for the anaerobic digestion of a glucose-based medium in an innovative high-rate reactor, the periodic anaerobic baffled reactor (PABR). The model considers each PABR compartment as two variable volume interacting sections, of constant total volume, one with high solids and one with low solids concentration, with the gas and liquid flows influencing the material flows between the two sections. For the simulation of glucose degradation, the biomass was divided into acidogenic, acetogenic and methanogenic groups of microorganisms. The kinetic part of the model accounted for possible inhibition of acidogenesis, acetogenesis and methanogenesis by volatile fatty acids. The model succeeded in predicting the reactor performance upon step increases in the organic loading rate.     

Effect of feeding strategy on the stability of anaerobic sequencing batch reactor responses to organic loading conditions

The goal of this study was to examine the effect of feeding strategy on the capability for treatment and the stability of an anaerobic sequencing batch reactor (ASBR) under increasing organic loading. The lab-scale ASBR systems were operated at 35 degrees C using synthetic organic wastewater under both batch and fed-batch operational modes with different feed to cycle time (F:C) ratios. Experimental studies were conducted over a wide range of volumetric organic loading rates (VOLRs) (1.524 g COD/l/d) by varying the hydraulic retention time (HRT) (1.25, 2.5, and 5d) and the feed wastewater's COD (3750-30,000 mg/l). With an F:C ratio greater than or equal to 0.42, the fed-batch mode operation showed higher system efficiency in COD removal, volumetric methane production rate (VMPR), and specific methane production rate (SMPR) as compared to those in the batch mode with identical VOLR and HRT. In the fed-batch mode, the COD removals reached 86-95% with VOLR up to 12 g COD/l/d. The maximums for VMPR of 3.17 l CH4/l/d and for SMPR of 1.63 g CH4-COD/g VSS/d were achieved with a VOLR of 12 g COD/l/d at HRTs of 2.5 and 1.25 d, respectively. The fed-batch operation presented a lower concentration of volatile fatty acids (VFAs) than those in the batch operation. A lower concentration of VFAs confirmed the stability and efficiency of the fed-batch mode operation. The specific methanogenic activity (SMA) analysis showed that the VFA-degrading activity of the biomass in the fed-batch mode was higher for acetate and butyrate, and lower for propionate. Determined biomass yield and bacterial decay coefficients in the fed-batch operational mode were 0.05 g VSS/g COD rem and 0.001 d(-1), respectively.     

Ecological clarification of cheese whey prior to anaerobic digestion in upflow anaerobic filter

Anaerobic digestion of cheese whey wastewaters (CW) was investigated in a system consisting of an ecological pretreatment followed by upflow anaerobic filter (UAF). The pretreatment was conducted to solve the inhibition problems during anaerobic treatment of CW caused by the amounts of fats, proteins and carbohydrates and to avoid the major problems of clogging in the reactor. The optimized ecological pretreatment of diluted CW induce removal yields of 50% of chemical oxygen demand (COD) and 60% of total suspended solids (TSS) after acidification by Lactobacillus paracasei at 32 degrees C during 20 h and neutralization with lime. The pretreated CW was used to feed UAF (35 degrees C). The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the pretreated CW anaerobic degradation were examined. The average total COD removals achieved was 80-90%. The performance of the reactor was depressed by increasing the COD concentration to 20 g/l (OLR = 4 gCOD/ld) and the COD removal efficiency was reduced to 72%. Significant methane yield (280 l/kg COD removal) was obtained at an HRT of 2 days.     

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.     

Biodegradation of high phenol containing synthetic wastewater by an aerobic fixed bed reactor

The continuous aerobic degradation of phenol, mixed with readily degradable synthetic wastewater was studied over a period of 400 days at 25+/-5 degrees C temperature in a fixed bed biofilm reactor using 'Liapor' clay beads as packing material. The phenol concentration added to the reactor ranged from 0.19 to 5.17g/l and was achieved by a gradual increase of phenol in wastewater, thus adapting the microbial flora to high contaminant concentrations. A maximal removal rate of 2.92g phenol/(ld) at a hydraulic retention time (HRT) of 0.95 days and a total organic loading rate (OLR) of 15.3g COD/(ld) with a phenol concentration of 4.9g/l was observed. However, this was not a stable rate at such high phenol loading. At the end of reactor operation on day 405, the phenol removal rate was 2.3g/(ld) at a influent phenol concentration of 4.9g/l. There were no phenol intermediates present in the reactor, as evident from corresponding COD, phenol removal and the absence of fatty acids. Omission of organic nitrogen compounds or of urea in influent feed was not favourable for optimal phenol removal. The phenol degradation profile that was studied in shake flasks indicated that the presence of a acetate which represent as an intermediate of phenol degradation retarded the phenol degradation. The highest phenol degradation rate observed in batch assays was 3.54g/(ld).     

Performance evaluation of a mesophilic anaerobic fluidized-bed reactor treating wastewater derived from the production of proteins from extracted sunflower flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale, mesophilic (35 degrees C) fluidized-bed reactor with saponite as bacterial support. Chemical oxygen demand (COD) removal efficiencies in the range of 98.3-80.0% were achieved in the reactor at organic loading rates (OLR) of between 0.6 and 9.3 g COD/I d, hydraulic retention times (HRT) of between 20.0 and 1.1 d and average feed COD concentration of 10.6 g/l. Eighty percent of feed COD could be removed up to OLR of 9.3 g COD/l d. The yield coefficient of methane production was 0.33 l of methane (at STP) per gram of COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favorable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. The experimental data indicated that a total alkalinity in the range of 2,000-2,460 mg/l as CaCO3 was sufficient to prevent the pH from dropping to below 7.0 for OLR of up to 9.3 g COD/l d. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3-0.4) for OLR and HRT up to 9.3 g COD/l d and 1.1 d, respectively. For a HRT of 0.87 d (OLR of 12.1 g COD/l d) the start of acidification was observed in the reactor.     

Performance of inverse anaerobic fluidized bed reactor for treating high strength organic wastewater during start-up phase

The aim of this work is to report on the physical characteristics of carrier material (perlite), biomass growth on the carrier material and the biogas production during an apparent steady state period in an inverse anaerobic fluidized bed reactor (IAFBR) for treating high strength organic wastewater. Before starting up the reactor, physical properties of the carrier material were determined. One millimeter diameter perlite particle is found to have a wet specific density of 295 kg/m(3) with specific surface area of 7.010 m(2)/g. This material has provided a good surface for biomass attachment and development. The biofilm concentration (in terms of attached volatile solids (AVS)) attached to carrier material was found to be 0.66 g(AVS)/g(solid). Most particles have been covered with a thin biofilm of uniform thickness. Once the inverse anaerobic fluidized bed system reached the steady state, the organic load was increased step wise by reducing hydraulic retention time (HRT) from 2 days to 0.16 day, while maintaining the constant feed of chemical oxygen demand (COD) concentration. This system has achieved 84% COD removal and reached the biogas production of 13.22 l/l/d at an organic loading rate (OLR) of 35 kgCOD/m(3)/d.     

Effect of high nitrate concentration on PHB storage in sequencing batch reactor under anoxic conditions

The study investigated effect of high influent nitrate concentration on poly-beta-hydroxybutyrate, (PHB), storage in a sequencing batch reactor, (SBR), under anoxic conditions. Acetate was fed as pulse during anoxic phase, sustained with external nitrate feeding. SBR operation involved three runs at steady state with COD/N ratios of 3.84, 2.93 and 1.54 gCOD/gN, where external nitrate concentrations gradually increased from 50 mg N/l to 114 mg N/l and 226 mg N/l, in 1st, 2nd and 3rd runs, respectively. In 1st run, acetate was fully converted into PHB with the storage yield value of 0.57-0.59 gCOD/gCOD, calculated both in terms of PHB formation and NO(X) utilization, confirming storage was the sole substrate utilization mechanism. In the following runs, PHB formation was reduced and the storage yield based on PHB dropped down to 0.40 and 0.33 gCOD/gCOD with increasing influent nitrate concentrations, indicating that higher portions of acetate were diverted to simultaneous direct growth. The observations suggested that nitrite accumulation detected at low COD/N ratios was responsible for inhibition of PHB storage.     

Interpreting the effect of increasing COD loading rates on the performance of a pre-anoxic MBBR system: implications on the attached and suspended biomass dynamics and nitrification–denitrification activity

A pre-anoxic MBBR system was subjected to increasing organic loading rates up to 18 gCOD/(m² day). At 3 gCOD/(m² day), most of the incoming organic matter was removed via denitrification. However, at higher loads, anoxic COD removal became limited by the nitrite/nitrate supply from the aerobic reactor, which assumed an important role in this conversion. Despite the application of low dissolved oxygen (DO) levels (<2 mg/L) in this tank, nitrification was observed to be nearly complete until 8 gCOD/(m² day). As the organic input was increased, the maximum specific nitrifying activity gradually declined. Activity tests suggested that an oxygen-limited environment was established in the biofilm. At lower loads [3–8 gCOD/(m² day)], the nitrification product obtained was affected by the DO concentration, whereas from 16 to 21 gCOD/(m² day), nitrite/nitrate profiles were likely associated with microbial stratification in the biofilm. The results also indicated that the role of the suspended biomass in the overall nitrification and denitrification can be very significant in high loaded MBBRs and should not be neglected, even at low HRTs.     

实验室模拟高负荷SPAC厌氧反应器运行

采用模拟废水, 对新型高负荷螺旋式自循环(Spiral automatic circulation, SPAC)厌氧反应器的运行性能进行了实验室模拟研究。结果表明: 在30oC, 水力停留时间(HRT)为12 h, 进水COD浓度从8000 mg/L升至20 000 mg/L的条件下, 反应器的COD去除率为91.1%~95.7%, 平均去除率为93.6％。在进水浓度为20 000 mg/L, HRT由5.95 h缩短至1.57 h的工况下, COD去除率从96.0%降低至78.7%, 反应器达到最高容积负荷率306 g COD/(L·d), 最大容积COD去除率240 g/(L·d), 最高容积产气率131 L/(L·d)。该反应器对基质浓度的连续提升具有良好的适应能力。进水COD浓度由8000 mg/L提升至20 000 mg/L时, 出水COD浓度一直处在较低水平(平均为852?mg/L), 容积COD去除率和容积产气率分别提高162%和119%。该反应器对HRT的连续缩短也有良好的适应能力。HRT由5.95 h缩短至1.57 h时,反应器容积COD去除率和容积产气率分别升高191%和195%。     

Co-degradation of resorcinol and catechol in an UASB reactor

Co-degradation of resorcinol and catechol was studied in a catechol acclimated up flow anaerobic sludge blanket (UASB) reactor. Synthetic binary aqueous solution having a total concentration of 1000 mg/L with the resorcinol/catechol (R/C) ratio of 1/19, 1/9, 3/17, 1/4, 1/3, 3/7, 2/3 and then 1/3 was fed at various time intervals to the UASB reactor with a fixed organic loading rate of 5.7 kg COD/m(3) d and hydraulic retention time of 8h. The reactor was operated over a period of 145 days after its acclimation with catechol bearing synthetic wastewater at a constant feed rate of 1.2 L/h. When the resorcinol concentration was increased to have a R/C ratio of 1/4, the COD removal efficiency and the biogas production increased to the maximum levels. Pseudo steady state condition for COD removal was achieved at each of the stepped-up loading condition. An increase in the R/C ratio above 1/4 in the binary feed solution led to a decrease in the COD removal efficiency and the biogas production rate.     

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.     

Use of fixed film and CSTR reactor for anaerobic treatment of stillage of wood hydrolysate

Summary The application of fixed film and CSTR reactor-systems for the treatment of stillage from wood hydrolysates was studied in laboratory units at 35° and 55°C. Organic loads of 10.7 (10) gCOD/l/d with COD-reduction of 86.6 (84.4)% and a biogas production rate of 400 (380) ml/ gCOD with 63 (62) % methane were feasible using fixed film systems, whereas organic loads with CSTR reactor-systems were only 2.4 gCOD/l/day.     

Influence of media-packing ratio on performance of anaerobic hybrid reactors

In this study, the influence of media-packing ratio on the performances of anaerobic hybrid reactors (AHRs) at low, medium and high organic loading rates was evaluated by conducting COD profile, granulation and tracer studies. Four laboratory upflow anaerobic hybrid reactors, each with a total unpacked volume of 7.85 l, with varying packing depths, were operated at organic loading rates from 1 to 24 g COD/l d. The media-packing ratios were 75%, 60%, 40% and 20% of the total reactor height in the AHRs. Three types of soluble COD profiles along the reactor height were observed when the organic loading rate was gradually increased. When operated at 1 and 2 g COD/l d the COD profiles along the reactor height from bottom to top showed a plug-flow regime. From 4 to 12 g COD/l d the COD profiles were distorted in the reactors with 20%, 40% and 60% packing, while at 16 g COD/l d and above the COD profile indicated homogeneity in each reactor, suggesting a perfectly-mixed regime. The distorted COD profiles were considered to be caused by the non-ideal flow pattern prevalent in the reactors. The dead-space volume and the bypass flowrate due to short-circuiting were determined using the Cholette and Cloutier model. A `distortion index' (DI), which was calculated from the ratio of the average COD value of the sludge bed over the average COD value of the reactor, was used to describe distortion of the COD profile. The distortion index correlated well with the short-circuiting fraction.     

Differential bacterial growth kinetic and nitrification of fisheries wastewaters containing high ammonium and organic matter concentration by using pure oxygen

Nitrification with pure O of fisheries wastewaters high in N-NH4+ (0.2-1g/l) and in organic matter (1-2gCOD/l) gave specific growth rates for the bacteria degrading organic matter of 0.24h and for nitrifying bacteria of 0.15h. Average organic matter abatement was 75% whereas N-NH (0.7g/l as initial concentration) oxidation to nitrite and nitrate was 20%.     

Organic and nitrogen removal in a two-stage rotating biological contactor treating municipal wastewater

A laboratory scale rotating biological contactor (RBC) predenitrification system incorporating anoxic and aerobic units was evaluated for the treatment of settled high-strength municipal wastewater. The system was operated under four recycle ratios (1, 2, 3 and 4) and loading rates of 38-182 gCOD/m(2)d and 0.22-14 gOxid-N/m(2)d on the anoxic unit and 3.4-18 gCOD/m(2)d and 0.24-1.8 gNH(4)-N/m(2)d on the aerobic. The average removal efficiency in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD(5)), total suspended solids (TSS) and total nitrogen (Total-N) was 82%, 86%, 63% and 54%; settling of the RBC effluent increased COD and TSS removal to 94% and 97%. An increase in hydraulic loading resulting from higher recirculation, had limited negative effect on organic removal but improved nitrogen removal, and in terms of Total-N removal efficiency increased up to a ratio of 3 and then decreased.     

Anaerobic treatment of a chemical synthesis-based pharmaceutical wastewater in a hybrid upflow anaerobic sludge blanket reactor

In this study, performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor, treating a chemical synthesis-based pharmaceutical wastewater, was evaluated under different operating conditions. This study consisted of two experimental stages: first, acclimation to the pharmaceutical wastewater and second, determination of maximum loading capacity of the hybrid UASB reactor. Initially, the carbon source in the reactor feed came entirely from glucose, applied at an organic loading rate (OLR) 1 kg COD/m(3) d. The OLR was gradually step increased to 3 kg COD/m(3) d at which point the feed to the hybrid UASB reactor was progressively modified by introducing the pharmaceutical wastewater in blends with glucose, so that the wastewater contributed approximately 10%, 30%, 70%, and ultimately, 100% of the carbon (COD) to be treated. At the acclimation OLR of 3 kg COD/m(3) d the hydraulic retention time (HRT) was 2 days. During this period of feed modification, the COD removal efficiencies of the anaerobic reactor were 99%, 96%, 91% and 85%, and specific methanogenic activities (SMA) were measured as 240, 230, 205 and 231 ml CH(4)/g TVS d, respectively. Following the acclimation period, the hybrid UASB reactor was fed with 100% (w/v) pharmaceutical wastewater up to an OLR of 9 kg COD/m(3) d in order to determine the maximum loading capacity achievable before reactor failure. At this OLR, the COD removal efficiency was 28%, and the SMA was measured as 170 ml CH(4)/g TVS d. The hybrid UASB reactor was found to be far more effective at an OLR of 8 kg COD/m(3) d with a COD removal efficiency of 72%. At this point, SMA value was 200 ml CH(4)/g TVS d. It was concluded that the hybrid UASB reactor could be a suitable alternative for the treatment of chemical synthesis-based pharmaceutical wastewater.     

Evaluation of straw as a biofilm carrier in the methanogenic stage of two-stage anaerobic digestion of crop residues

Straw was evaluated as a biofilm carrier in the methanogenic stage of the two-stage anaerobic digestion of crop residues. Three reactor configurations were studied, a straw-packed-bed reactor, a glass packed-bed reactor and a reactor containing suspended plastic carriers. The reactor with the packed straw bed showed the best results. It had the highest methane production, 5.4 11(-1) d(-1), and the chemical oxygen demand (COD) removal ranged from 73-50% at organic loading rates from 2.4-25 g COD l(-1) d(-1). The degradation pattern of volatile fatty acids showed that the degradation of propionate and longer-chain fatty acids was limiting at higher organic loading rates. A stable effluent pH showed that the packed-bed reactors had good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in the two-stage process. The conclusion is that straw would work very well in the intended application. A further benefit is that straw is a common agricultural waste product and requires only limited resources concerning handling and cost.