Biomethane production by thermophilic co-digestion of sugarcane vinasse and whey in an AnSBBR: Effects of composition, organic load, feed strategy and temperature.

This work investigated the application of a thermophilic (55 °C) anaerobic reactor with immobilized biomass, mechanically stirred and operated in sequential batch and fed batch (AnSBBR) for environmental compliance and methane production by co-digesting cheese whey (W) and sugarcane vinasse (V). The assays were performed in four steps. In the first step the composition of 75%W:25%V (on a COD basis) was determined to be the most adequate for the anaerobic process. In the second step the applied volumetric organic load (AVOL) was increased and in the third step the feed strategy was modified achieving best results at AVOL of 25 gCOD.m-3.d-1, in which the removed organic matter efficiency was 72%, the molar productivity was 278 molCH4.m-3.d-1 and methane yield was 15.3 mmolCH4.gCOD-1. In the fourth step the temperature was modified to 50 °C and 45 °C, achieving worse results. From the kinetic model adjusted to experimental data it was identified that the acetoclastic route was predominant in methane generation. The estimated energy recovered by co-digesting cheese whey and sugarcane vinasse using industrial information was 2.2 × 104 MW h per month, equivalent (in Brazil) to the electricity consumption of about 135 × 103 inhabitants or monthly savings of US$ 1,653,000 replacing the diesel oil consumed in the industry.

Optimization performance of an AnSBBR applied to biohydrogen production treating whey.

The present study investigated the influence of the influent concentration of substrate, feeding time and temperature on the production of biohydrogen from cheese whey in an AnSBBR with liquid phase recirculation. The highest hydrogen yield (0.80 molH2.molLactose(-1)) and productivity (660 mLH2 L(-1) d(-1)) were achieved for influent concentrations of 5400 mgDQO L(-1). No significant difference was noted in the biological hydrogen production for the feeding time conditions analyzed. The lowest temperature tested (15 °C) promoted the highest hydrogen yield and productivity (1.12 molH2 molLactose(-1) and 1080 mLH2 L(-1) d(-1)), and for the highest temperature (45 °C), hydrogen production did not occur. The indicator values for the hydrogen production obtained with this configuration were higher than those obtained in other studies using traditional configurations such as UASBr and CSTR. A phylogenetic analysis showed that the majority of the analyzed clones were similar to Clostridium. In addition, clones phylogenetically similar to the Lactobacilaceae family, notably Lactobacillus rhamnosus, and clones with similar sequences to Acetobacter indonesiensis were observed in small proportion in the reactor.

Co-digestion of Whey with Glycerin in an AnSBBR for Biomethane Production.

This study aimed to evaluate the co-digestion of cheese whey and glycerin in an anaerobic sequencing batch biofilm reactor (AnSBBR) with recirculation of the liquid phase applied to biomethane production. The applied volumetric organic load (AVOL) in all conditions was 7.5 kgCOD m(-3) day(-1). The feeding time was equal to half of the cycle time. The best condition for co-digestion was the wastewater with 75 % of cheese whey and 25 % of glycerin (chemical oxygen demand (COD) basis); it achieved a productivity of 101.8 molCH4 m(-3) day(-1) and a yield of 13.3 molCH4 kgCOD(-1) with 89 % of COD removal. This represents an increase of productivity of almost 9 and 30 % when compared to the anaerobic digestion of cheese whey and glycerin alone, respectively. The co-digestion proposed is a promising solution for both pollutants with the advantage of high energy production. A first-order kinetic model was fitted efficiently to the process.

Anaerobic Biological Treatment of Vinasse for Environmental Compliance and Methane Production.

The energy crisis resulted in increasing awareness that alternative sources of energy should be considered. During this time, Brazil implemented ethanol production from sugarcane as biofuel. However, during this process, large amounts of residues are generated, such as vinasse. This residue can be treated anaerobically to generate methane as a source of bioenergy with the use of sequencing batch reactors operated with immobilized biomass (AnSBBR). In this work, tests were conducted in an AnSBBR laboratory-scale reactor, and the main results regarding the kinetic model fitting and performance of substrate consumption (83 %), methane content in the biogas (77 %), applied organic load (5.54 g COD L(-1) day(-1)), methane productivity (973 N-mL CH4 L(-1) day(-1)), and yield (9.47 mol CH4 kg COD(-1)) show that AnSBBR is a promising technological alternative. After tests conducted in a laboratory-scale reactor, an industrial reactor was scaled and was also operated in a sequencing batch with immobilized biomass (AnSBBR) for the anaerobic treatment of vinasse with the goal of generating methane and environmental suitability to further disposal in soil. The calculations were performed based on data from a sugar and alcohol plant located in São Paulo, Brazil. This study proposes to the operation of the industrial scale reactor was the association of four AnSBBR (each one with a volume of 15849 m(3)) operating in parallel (with a feeding and discharge time of 4 h and a reaction time of 8 h), with the goal of adapting the treatment system from a discontinuous operation to a continuous operation. In this industrial scenario, the methane production was estimated at 1.65 × 10(6) mol CH4 day(-1), and the energy was approximately 17 MW, increasing the possible energy recovery contained in sugarcane from 93 to 96 %.

Influence of Organic Load on Biohydrogen Production in an AnSBBR Treating Glucose-Based Wastewater.

An anaerobic sequencing batch reactor with immobilized biomass (AnSBBR) was applied to the production of biohydrogen treating a glucose-based wastewater. The influence of the applied volumetric organic load was studied by varying the concentration of influent at 3600 and 5250 mg chemical oxygen demand (COD) L(-1) and cycle lengths of 4, 3, and 2 h resulting in volumetric organic loads of 10.5 to 31.1 g COD L(-1). The results revealed system stability in the production of biohydrogen and substrate consumption. The best performance was an organic removal (COD) of 24 % and carbohydrate removal (glucose) of 99 %. Volumetric and specific molar productivity were 60.9 mol H2 m(-3) day(-1) and 5.8 mol H2 kg SVT(-1) day(-1) (biogas containing 40 % H2 and no CH4) at 20.0 g COD L(-1) day(-1) (5250 mg COD L(-1) and 3 h). The yield between produced hydrogen and removed organic matter in terms of carbohydrates was 0.94 mol H2 Mol GLU(-1) (biogas containing 52 % H2 and no CH4) at 10.5 g COD L(-1) day(-1) (3600 mg COD L(-1) and 4 h), corresponding to 23 and 47 % of the theoretical values of the acetic and butyric acid metabolic routes, respectively. Metabolites present at significant amounts were ethanol, acetic acid, and butyric acid. The conditions with higher influent concentration and intermediate cycle length, and the condition with lower influent concentration and longer cycle showed the best results in terms of productivity and yield, respectively. This indicates that the best productivity tends to occur at higher organic loads, as this parameter involves the biogas production, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter also involves substrate consumption.

The effect of organic load and feed strategy on biohydrogen production in an AnSBBR treating glycerin-based wastewater.

An anaerobic sequencing batch biofilm reactor (AnSBBR) with recirculation of the liquid phase (at 30 °C with 3.5 L of working volume and treating 1.5 L per cycle) treating pure glycerin-based wastewater was applied to biohydrogen production. The applied volumetric organic load (AVOL) ranged from 7.7 to 17.1 kgCOD m(-3) d(-1), combining different influent concentrations (3000, 4000 and 5000 mgCOD L(-1)) and cycle lengths (4 and 3 h). The feed strategy used was to maintain the feeding time equal to half of the cycle time. The increase in the influent concentration and the decrease in cycle length improved the molar yield and molar productivity of hydrogen. The highest productivity (100.8 molH2 m(-3) d(-1)) and highest yield of hydrogen per load removed (20.0 molH2 kgCOD(-1)) were reached when the reactor operated with an AVOL of 17.1 kgCOD m(-3) d(-1), with 68% of H2 and only 3% of CH4 in its biogas. It was also found that pretreatment of the sludge/inoculum does not influence the productivity/yield of the process and the use of crude industrial glycerin-based wastewater in relation to the pure glycerol-based wastewater substantially decreased the production and composition of the hydrogen produced.

Biohydrogen production in an AnSBBR treating glycerin-based wastewater: effects of organic loading, influent concentration, and cycle time.

This study evaluated the influence of the applied volumetric organic load on biohydrogen production in an anaerobic sequencing batch biofilm reactor (AnSBBR) with 3.5 L of liquid medium and treating 1.5 L of glycerin-based wastewater per cycle at 30 °C. Six applied volumetric organic loads (AVOLCT) were generated from the combination of cycle periods (3 and 4 h) and influent concentrations (3000, 4000, and 5000 mg chemical oxygen demand (COD) L(-1)), with values ranging from 7565 to 16,216 mg COD L(-1) day(-1). No clear relationship was found between the applied volumetric organic load and the hydrogen production. However, the highest hydrogen molar production (MPr 67.5 mol H2 m(-3) day(-1)) was reached when the reactor was operated with a cycle period of 4 h and an influent concentration of 5000 mg COD L(-1) (AVOLCT 12,911 mg COD L(-1) day(-1)). This condition also reached the highest molar yield per applied load based on the organic matter (MYALC,m 21.1 mol H2 kg COD(-1)). In addition, the pretreatment of the sludge/inoculum was found to not influence the productivity/yield of the process, and the use of crude glycerol as a sole source of carbon exhibited a clear disadvantage for hydrogen production compared to pure glycerol. The AnSBBR used for the hydrogen production experiments operated with pure glycerol as a sole carbon source exhibited important practical potential.

Effect of organic loading rate and fill time on the biohydrogen production in a mechanically stirred AnSBBR treating synthetic sucrose-based wastewater.

This study investigated the feasibility to produce biohydrogen of a mechanically stirred anaerobic sequencing batch biofilm reactor (AnSBBR) treating sucrose-based synthetic wastewater. The bioreactor performance (30 °C) was evaluated as to the combined effect of fill time (2, 1.5, and 1 h), cycle length (4, 3, and 2 h), influent concentration (3,500 and 5,250 mg chemical oxygen demand (COD) L(-1)) and applied volumetric organic load (AVOLCT from 9.0 to 27.0 g COD L(-1) d(-1)). AVOLs were varied according to influent concentration and cycle length (t C). The results showed that increasing AVOLCT resulted in a decrease in sucrose removal from 99 to 86 % and in improvement of molar yield per removed load (MYRLS.n) from 1.02 mol H2 mol carbohydrate(-1) at AVOLCT of 9.0 g COD L(-1) d(-1) to maximum value of 1.48 mol H2 mol carbohydrate(-1), at AVOLCT of 18.0 g COD L(-1) d(-1), with subsequent decrease. Increasing AVOLCT improved the daily molar productivity of hydrogen (MPr) from 15.28 to 49.22 mol H2 m(-3) d(-1). The highest daily specific molar productivity of hydrogen (SMPr) obtained was 8.71 mol H2 kg TVS(-1) d(-1) at an AVOLCT of 18.0 g COD L(-1) d(-1). Decreasing t C from 4 to 3 h decreased sucrose removal, increased MPr, and improved SMPr. Increasing influent concentration decreased sucrose removal only at t C of 2 h, improved MYRLS,n and MPr at all t C, and also improved SMPr at t C of 4 and 3 h. Feeding strategy had a significant effect on biohydrogen production; increasing fill time improved sucrose removal, MPr, SMPr, and MYRLS,n for all investigated AVOLCT. At all operational conditions, the main intermediate metabolic was acetic acid followed by ethanol, butyric, and propionic acids. Increasing fill time resulted in a decrease in ethanol concentration.

Biomethane production in an AnSBBR treating wastewater from biohydrogen process.

An anaerobic sequencing batch reactor containing immobilized biomass (AnSBBR) was used to produce biomethane by treating the effluent from another AnSBBR used to produce biohydrogen from glucose- (AR-EPHG) and sucrose-based (AR-EPHS) wastewater. In addition, biomethane was also produced from sucrose-based synthetic wastewater (AR-S) in a single AnSBBR to compare the performance of biomethane production in two steps (acidogenic and methanogenic) in relation to a one-step operation. The system was operated at 30 °C and at a fixed stirring rate of 300 rpm. For AR-EPHS treatment, concentrations were 1,000, 2,000, 3,000, and 4,000 mg chemical oxygen demand (COD) L(-1) and cycle lengths were 6 and 8 h. The applied volumetric organic loads were 2.15, 4.74, 5.44, and 8.22 g COD L(-1) day(-1). For AR-EPHG treatment, concentration of 4,000 mg COD L(-1) and 4-h cycle length (7.21 g COD L(-1) day(-1)) were used. For AR-S treatment, concentration was 4,000 mg COD L(-1) day(-1) and cycle lengths were 8 (7.04 g COD L(-1) day(-1)) and 12 h (4.76 g COD L(-1) day(-1)). The condition of 8.22 g COD L(-1) day(-1) (AR-EPHS) showed the best performance with respect to the following parameters: applied volumetric organic load of 7.56 g COD L(-1) day(-1), yield between produced methane and removed organic material of 0.016 mol CH4 g COD(-1), CH4 content in the produced biogas of 85 %, and molar methane productivity of 127.9 mol CH4 m(-3) day(-1). In addition, a kinetic study of the process confirmed the trend that, depending on the biodegradability characteristics of the wastewaters used, the two-step treatment (acidogenic for biohydrogen production and methanogenic for biomethane production) has potential advantages over the single-step process.

Effects of organic loading, influent concentration, and feed time on biohydrogen production in a mechanically stirred AnSBBR treating sucrose-based wastewater.

An anaerobic sequencing batch biofilm reactor (AnSBBR-total volume 7.5 L; liquid volume 3.6 L; treated volume per cycle 1.5 L) treated sucrose-based wastewater to produce biohydrogen (at 30 °C). Different applied volumetric organic loads (AVOL of 9.0, 12.0, 13.5, 18.0, and 27.0 kg COD m(-3) day(-1)), which were varied according to the influent concentration (3,600 and 5,400 mg COD L(-1)) and cycle length (4, 3, and 2 h), have been used to assess the following parameters: productivity and yield of biohydrogen per applied and removed load, reactor stability, and efficiency. The removed organic matter (COD) remained stable and close to 18 % and carbohydrates (sucrose) uptake rate remained between 83 and 97 % during operation. The decrease in removal performance of the reactor with increasing AVOL, by increasing the influent concentration (at constant cycle length) and decreasing the cycle lengths (at constant influent concentrations), resulted in lower conversion efficiencies. Under all conditions, when organic load increased there was a predominance of acetic, propionic, and butyric acid as well as ethanol. The highest concentration of biohydrogen in the biogas (24-25 %) was achieved at conditions with AVOL of 12.0 and 13.5 kg COD m(-3) day(-1), the highest daily production rate (0.139 mol H2 day(-1)) was achieved at AVOL of 18.0 kg COD m(-3) day(-1), and the highest production yields per removed and applied load were 2.83 and 3.04 mol H2 kg SUC(-1), respectively, at AVOL of 13.5 kg COD m(-3) day(-1). The results indicated that the best productivity tends to occur at higher organic loads, as this parameter involves the "biochemical generation" of biogas, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter involves "biochemical consumption" of the substrate.

Effects of solid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass.

This work reports on experiments for an anaerobic sequencing batch reactor containing immobilized biomass which aimed at verifying the effects of solid-phase mass transfer on the reactor's overall performance. Four experiments were carried out at 30 degrees C with cubic polyurethane foam particles previously inoculated with anaerobic biomass. Different solid-phase mass transfer conditions were reached in each experiment by varying the size of the bioparticle from 0.5 to 3.0 cm. The reactor was fed with a low-strength synthetic wastewater containing protein, carbohydrates and lipid and the effects of mass transfer were evaluated through dynamic substrate concentration profiles during 8-hour batch cycles. A modified first-order kinetic model provided a good representation of the behavior of the dynamic concentration profiles. The solid-phase mass transfer was found to slightly affect the concentration of effluent organic matter expressed as chemical oxygen demand (COD). The concentration of residual effluent substrate increased as the size of the bioparticle was increased. The cycle time was not affected as the size of the bioparticle was increased from 0.5 to 2.0 cm. However, it was found that the cycle time in a reactor with 3.0-cm cubic particles should be higher than that required in systems with smaller particles. The apparent first-order kinetic parameter was estimated as 0.59+/-0.01 h(-1) for experiments with bioparticle sizes ranging from 0.5 to 2.0 cm, while a value of 0.48 h(-1) was obtained in the experiment with 3.0-cm bioparticles.

Effects of feeding strategies on the performance of an anaerobic discontinuous reactor containing immobilized biomass with circulation system for liquid-phase mixing.

Data on the influence of feeding strategy on the performance of a fed-batch anaerobic sequencing reactor containing biomass immobilized on polyurethane foam and subjected to liquid phase circulation are presented and discussed. Six-hour cycles, temperature of 30 degrees C and circulation flow rate of 6 L/h were used. During each cycle 890 mL of synthetic domestic wastewater, with organic matter concentration of 500 mgCOD/L were fed to the reactor. The feeding strategies were implemented using fill times of 6 min (batch mode), 60, 120, 240 (fed-batch/batch mode) and 360 min (fed-batch mode). The system attained high efficiency and stability for all the operating conditions, and the substrate removal efficiency based on filtered samples presented a slight decrease from 85% to 81% when fill time was increased from 6 min to 360 min. A model considering a first-order kinetic equation was fitted to the experimental data. The apparent kinetic parameters for both batch and fed-batch phases were estimated, thus permitting evaluation of the influence of the feeding strategy on the reactor performance. The current system may be considered flexible in terms of the operating conditions it is subjected to.

Stirred anaerobic sequencing batch reactor containing immobilized biomass: a behavior study when submitted to different fill times.

The effect of the filling stage on the behavior of a mechanically stirred anaerobic sequencing batch reactor containing biomass immobilized on 1 cm polyurethane foam cubes was investigated. The reactor was made of acrylic with a capacity of 6.3 L, treating per cycle 2.5 L synthetic low-strength wastewater with a concentration of 500 mgCOD/L, at 30+/-1 degrees C. Eight-hour cycles (tC) and agitation of 500 rpm were utilized. At the beginning of each cycle 60% of the wastewater volume was treated, sufficient to completely cover the bed. The remaining volume was added at different fill times (tF) of 10, 120, 240, 260 and 480 min. The results obtained showed that ratios of tF/tC < or = 0.5 enabled organic matter removal higher than 75% and 70% for filtered and non-filtered samples, respectively. Ratios of tF/tC > 0.5, despite operation stability, resulted in loss of efficiency and formation of viscous material, similar to extra-cellular polymeric substances.

Operating feasibility of anaerobic whey treatment in a stirred sequencing batch reactor containing immobilized biomass.

The scope of this work was to evaluate the operating feasibility of anaerobic whey treatment in a stirred sequencing batch reactor (ASBR) containing biomass immobilized on inert support. Assays were performed using 8-hour cycles and agitation rate of 200 rpm at 30 +/- 1 degrees C, for treating cheese whey containing 500 to 4,000 mgCOD/L, which corresponded to a volumetric organic load (VOL) of 0.81 to 5.7 gCOD/L x d. Stability and high organic matter removal of about 96% were achieved at effluent concentration below 160 mgCOD/L for non filtered samples. Operating stability of the reactor was shown to be strongly dependent on the alkalinity supplementing strategy during the assay, especially during the startup period, where NaHCO3 supplementation was approximately 20-30% of the chemical oxygen demand (mgNaHCO3/mgCOD). After startup, alkalinity supplementation could be reduced down to 10% maintaining efficiency and stability. Moreover, proper homogenization of the system through mechanical agitation was also shown to be indispensable, especially with increasing organic load.

Influence of agitation rate on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass.

The present work reports on the influence of the mechanical agitation rates on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass on polyurethane foam, as inert support, treating synthetic domestic wastewater. The reactor was operated at 30 degrees C and an 8-hour cycle was used to treat approximately 0.5 L of the synthetic substrate with a COD concentration of nearly 500 mg/L. The studied agitation rates ranged from no agitation to 750 rpm. The system attained non-filtered substrate removal efficiency greater than 83% when agitation was employed. A very short start-up period and good solid retention could be observed. The use of agitation increased the efficiency of the reactor and enabled reduction of the total cycle time. An empirical equation and a first-order kinetic model are proposed to analyze the influence of agitation rates on the reactor's performance.

Anaerobic sequencing batch reactors for wastewater treatment: a developing technology.

This paper describes and discusses the main problems related to anaerobic batch and fed-batch processes for wastewater treatment. A critical analysis of the literature evaluated the industrial application viability and proposed alternatives to improve operation and control of this system. Two approaches were presented in order to make this anaerobic discontinuous process feasible for industrial application: (1) optimization of the operating procedures in reactors containing self-immobilized sludge as granules, and (2) design of bioreactors with inert support media for biomass immobilization.