Anaerobic Fluidized Bed Reactor Research Articles

Changes in microbial communities during high-rate microbial selenate reduction in an up-flow anaerobic fluidized bed reactor

Biological fluidized bed reactor (FBR) is a promising treatment option for removing selenium oxyanions from wastewater by converting them into elemental selenium. The process can achieve high rates and be efficiently operated at low hydraulic retention times (HRT). However, the effects of HRT on the changes in microbial community in the FBR process have not been previously explored. In this study, dynamic changes of microbial communities both on biofilm carrier and in suspension of a selenate-reducing FBR were explored at various HRTs (0.3–120 h). Based on partial 16S rRNA gene sequencing of the microbial communities, alpha diversity of microbial communities in suspension rather than in the biofilm were impacted by low HRTs (0.3 h–3 h). Members from genera Geobacter, Geoalkalibacter, and Geovibrio were the main selenate-reducing bacteria on carrier throughout the FBR process. Genus Geobacter was dominant in FBR carrier at HRT of 24 h–120 h, whereas Geoalkalibacter and Geovibrio dominated at low HRT of 0.3 h–6 h. Suspended microbial communities detected in the FBR effluent were more sensitive to HRT changes than that in biofilm. “Shock loading” at HRT of 0.3 h had a great impact on microbial community compositions both in the biofilm and effluent. Reactor operation in batch mode and long HRT of 24 h helped recover the community from “shock loading” and improved selenite reduction and ethanol oxidation. Redundancy analysis revealed that HRT, influent pH and selenate loading were key operational parameters impacting both the FBR performance and the composition of microbial communities associated with both the FBR carrier and effluent. Overall, the microbial communities in FBR biofilm flexibly responded to the changes of HRT and showed resilience to the temporary shock loading, enabling efficient selenate removal.

Synergizing sugarcane waste valorization: Optimization of two-stage anaerobic co-digestion for enhanced methane recovery and organic matter removal

Multiple strategies have been used in anaerobic digestion of effluents aiming to enhance the efficiency of the methane (CH4) recovery process, where co-digestion and the two-stage process emerge as prominent methods. In this context, this study aimed at evaluating the co-digestion of sugarcane vinasse and molasse in a two-stage process using anaerobic fluidized bed reactors (AFBR), verifying the effect of increasing the organic loading rate (OLR) (5–22.5 kg COD.m−3.d−1) and temperature in the second stage methanogenic reactor. Regarding the two-stage process, sugarcane vinasse and molasses fermentation demonstrated the maximum energy potential (E.P) of 57.08 kJ.d−1 (7.5 g COD.L−1). Regarding the methanogenic sequential reactors, organic matter removal reached high values (up to 84.5 % in a thermophilic sequential reactor (TSR); up to 84.5 % in a mesophilic sequential reactor (MSR)). The highest CH4 yield (MY) of 306.77 ± 38.84 mL CH4.g−1 COD rem was observed in MSR (9 kg COD.m−3.d−1). Meanwhile, the maximum value of MPR (3.8 ± 0.5 L CH4.L−1.d−1) was observed in TSR (21 kg COD.m−3.d−1). Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be identified, in which the genera Methanobacterium and Methanothermobacter were the most abundant in MSR and TSR, respectively. This study demonstrates that anaerobic digestion of sugarcane vinasse and molasses enhances anaerobic treatment using two-stage AFBRs. It not only produces CH4 but also generates hydrogen and high-value products through an acidogenic reactor. This research marks a significant advancement in managing sugarcane processing by-products, offering promising approaches to maximize biogas production and improve pollutant removal efficiency.

Ideal performance assessment of non-recirculating anaerobic fluidized bed reactors treating low to high strength organic loads with low retention time

This study investigated the ideal performance of non-recirculating Anaerobic Fluidized Bed Reactors (AnFBRs) for treating organic wastewater of varying strengths under low Hydraulic Retention Time (HRT). Four 4.58 L AnFBRs were used to treat synthetic wastewater with an Organic Loading Rate (OLR) ranging from 4.50 to 40.11 gCOD/L-d, and HRT between 1.1 and 4.4 hours. The AnFBRs achieved high removal efficiencies ranging from 83 % to 96 % at steady state, except during the organic shock load, which reduced removal performance to 12 %. Shortened HRT conditions led to a decreasing trend in reactor pH due to an incomplete anaerobic cycle. The modified Stover-Kincannon model estimated the maximum substrate utilization rate of AnFBR's to be 196.08 gCOD/L-d, with a correlation coefficient of 0.98. Under shortended HRT, microbial diversity analysis identified predominant non-filamentous bacterial families, such as Streptococcaceae and Veillonellaceae, which collaborate during biofilm development in anaerobic environments. It was suggested that the porous media provided secure attachment sites for the biomass growth and biofilm formation under shock load and high shear force conditions. While these results offer valuable insights, further studies are needed to confirm these findings and enhance the understanding of the use porous media in non-recirculating AnFBRs.

Unlocking potential: Exploring the methane production potential in anaerobic co-digestion of cassava wastewater and glycerol

This study aimed at evaluating the feasibility of CH4 production in a mesophilic (30 °C) single-stage anaerobic co-digestion of cassava wastewater (CW) and glycerol in an anaerobic fluidized bed reactor (AFBR) with mixing ratio of 50 % / 50 % CW/Gly on a (chemical oxygen demand)COD basis. Thus, the following strategy was used: increasing the organic loading rate (OLR) (1–20 g COD.L−1.d−1) by increasing the substrate concentration (1–20 g COD.L−1) and applying a hydraulic detention time (HRT) of 24 h. The AFBR presented a maximum methane (CH4) content of 88.38±1.94 % and a CH4 yield (MY) of 293.48±18.37 mL of CH4.mL−1CODrem in the OLR of 1 g COD.L−1.d−1 and the maximum methane production rate (MPR) of 62.09±2.75 mL of CH4.L−1.h−1 in the OLR of 20 g COD.L−1.d−1. The conversion of glycerol and carbohydrates remained above 91±0.54 % and 82±2.79 %, respectively, and the COD conversion was above 80±0.65 %. The main metabolites were HAc, HPr, HBu, EtOH and HVa. The most abundant genera identified in the AFBR were Izemoplasmatales and Enterobacteriaceae for the bacteria domain, and Methanosaeta, Methanobacterium for the archaea domain. The single-stage system is robust and can operate with higher OLR without reducing the efficiency of wastewater treatment and CH4 production.

A techno-economic assessment of hydrogen and methane production from the anaerobic treatment of vinasse and glycerol: Single- vs. two-stage process

The best-case scenario for anaerobic digestion (AD) could include co-digestion and two-stage systems, a combination that has not yet been extensively studied. This study aimed at evaluating the effect of increasing the organic loading rate from 5 to 20 kg-COD/m3/d in second-stage thermophilic (55 °C, CH4-RThermo) and mesophilic (25 ± 5 °C, CH4-RMeso) anaerobic fluidized bed reactors (AFBR) fed with sugarcane vinasse and glycerol (1:1 on a COD basis) previously fermented in a thermophilic AFBR. AD was stable with high methane production and COD removal up to 20 kg-COD/m3/d for CH4-RThermo (4.53 L-CH4/L/d; 79 %) and CH4-RMeso (3.85 L-CH4/L/d; 66 %), respectively. At 20 kg-COD/m3/d, CH4-RMeso failed due to acid accumulation (1279 mg/L), which probably inhibited methanogenic activity. Results of two-stage thermophilic + thermophilic (H2-RThermo + CH4-RThermo) were compared with a thermophilic single-stage AFBR. In comparison to the two-stage system, for 10, 15, and 20 kg- COD/m3/d, the single-stage energetic yields were higher at 33, 26 and 22 %, respectively. A techno-economic assessment was conducted. The scale-up and economic analyses revealed that the single-stage would be the most compact system (17,820 vs. 20,560 m3) with the lowest initial investment (USD 45 M vs. USD 52 M), highest net present value (NPV) (USD 58 M vs. USD 47 M), and internal rate of return (IRR) (18 vs. 16 %) compared to the best two-stage system (thermophilic + thermophilic). A Monte Carlo simulation indicated a 12 % risk of financial loss at 20 kg-COD/m3/d for the single-stage system. Furthermore, it showed that variation on the capitalization rate, inflation, and the electricity sales price can significantly affect the NPV. Therefore, in addition to better laboratory performance, the single-stage system is simpler to operate, less costly, and would be more suitable for industrial scale implementation.

Influence of pH on the anaerobic fluidised bed reactor performance for palm oil mill effluent treatment

The effect of pH on the performance of a pilot-scale anaerobic fluidised bed reactor (AnFBR) was studied using palm oil mill effluent (POME) as the substrate. The performance of the 2000-litre reactor at different operating conditions, such as organic loading rates and retention times was studied. This acidic agro-industrial wastewater (pH 4.0–5.0) was neutralised by adding slacked lime. It was observed that, within 12 hr of hydraulic retention time (HRT), the AnFBR removes as high as 85% of the substrate chemical oxygen demand (COD) at a loading rate of 4 kg/m3 day. High pre-treatment cost is needed to neutralise the bulk volume of wastewater that was generated from the palm oil industries. Thus, an attempt was made to study the performance of the AnFBR under pH shock load. The influent pH was increased to 9.2 and then dropped around 5.0 to intensify the effect of the pH shock load. At shock load, the reactor performance for COD removal dropped by about 25% lower than the optimum condition. The maximum and minimum COD removal rates during the short period of continuous shock load were 60% and 56.5%, respectively. The average effluent pH remained steady at around 6.1. From the analysis, it was revealed that the anaerobic fluidised bed had the buffering ability and was capable of treating POME with moderate removal efficiency at an influent pH of 5.0.

Evaluation of the effect of increasing the organic load in the thermophilic co-fermentation of sugarcane industry by-products on hydrogen, ethanol and lactic acid generation

The effects of increased organic loading rate (OLR) on H2 production and soluble metabolites in a thermophilic anaerobic fluidized bed reactor (AFBR-AT) at 55 °C were evaluated by the fermentation of vinasse and molasses from sugarcane (at a ratio of 1:1). The OLR varied between 30 and 135 kg COD.m−3.d−1, while the hydraulic retention time (HRT) was fixed at 4 h, and the initial co-substrate concentration varied between 5 and 22.5 g COD.L−1. The thermophilic acidogenic reactor showed a maximum hydrogen yield (HY) (2.49 mmol H2.g−1CODapp) at an OLR of 30 kg COD.m−3.d−1 and a higher hydrogen production rate (HPR) (2.8 L H2.L−1.d−1) at an OLR of 45 kg COD.m−3.d−1. Increasing the OLR negatively influenced H2 production. The results showed an increase in ethanol (EtOH) concentrations of up to 47.3 times and lactic acid (HLa) concentrations of up to 15.2 times when comparing OLRs of 30 and 135 kg COD.m−3.d−1, indicating changes in metabolic pathways for acid formation at organic loads ≥90 kg COD.m−3.d−1. Thermoanaerobacterium was the bacteria with higher relative abundance and was directly involved in H2 production, while Lactobacillus was mainly involved in HLa production in higher OLR, decreasing H2 production instead. Besides that, higher OLRs were favorable for sulfidogenesis and the development of sulfate-reducing bacteria, such as Desulfobacterota, due to the higher COD/sulfate ratio in OLR 135 kg COD.m−3.d−1. According to the metabolic inference in this condition, the enzyme activity of sulfite reductase and sulfite dehydrogenase may have occurred, consuming H+, thereby reducing H2 production.

Sustainable Technological Advancements for Dairy Waste Water Treatment-A Review

The dairy industry has global importance due to its essential contribution towards human nutrition as well as high economic opportunities. There is a consistent and steep growth in India's dairy sector in the last few decades and now India is one of the major milk-producing countries in the world. Highstrength dairy wastewaters, if discharged without proper treatment, severely pollute the receiving water bodies. In this scenario 'Waste as a resource' concept has been gaining the interest of researchers. The present review delineates different technological advancements for treating dairy wastewater and compares which is the better option in terms of sustainability. In the aerobic process, advanced bioaugmented systems which use bacterial and fungal consortia were found to be effective and sustainable with biological oxygen demand removal of 78.7% and 74.7%. Physio-chemical methods using natural coagulants like Moringa oleifera (MO) and pomegranate peel powder were also found to be effective with 81.8 % nitrogen removal from dairy wastewater treatment. Phytoremediation using water fern (Azolla pinnata R. Br.) was found to be efficient with dissolved solids reduction efficiency of 71.56 %. The fluidized bed anaerobic reactor unit was found to generate a biohydrogen content of 35.72±9.43% when the OLR was 53.25± 7.81 kg. COD m–3d–1. Microbial fuel cells treatment of real dairy wastewater (RDW) using Shewanella algae (MTCC-10608) has generated maximum current density and power density of 141 mA/m2 and 50 mW/m2 respectively. These two technologies are better sustainable options for dairy wastewater treatment since waste to energy aspect is satisfied.

Anaerobic Fluidized Bed Reactor for the Treatment of Tannery Wastewater Using Crushed Tire Scraps as Support Material

Purpose: Due to tannery high pollution potential, is has become necessary to investigate in new treatment technologies that use recycled solid wastes as tires that are abundantly present in the environment. The application of anaerobic biological processes offers several advantages compared to aerobic processes, including lower energy consumption, reduced sludge production, and a smaller footprint, in addition to the potential utilization of methane as a fuel. Methods: A pilot scale anaerobic fluidized bed reactor was implemented, using crushed tire scraps with diameters ranging from 2.00 mm to 2.83 mm as support material. Results and conclusion: The maximum COD removal efficiency achieved in the system was 77.79% in the first stage and 92.9% in the second stage, while methane production reached 2,930.5 mL. The tire scraps demonstrated efficiency as a support material for biofilm development, with microbial biofilm growth observed through optical microscopy, showing morphologies similar to cocci. Research implications: The implications of this study are to verify the possibility of treatment of tannery wastewater along with the possibility of reuse of an environmental pollutant as tire residues. Originality/value: After the literature research, no study has focused in anaerobic fluidized bed reactors using tire scraps as a support media for the treatment of tannery wastewater.

One versus two-stage codigestion of sugarcane vinasse and glycerol: Assessing combinations at mesophilic and (hyper) thermophilic conditions

Sugarcane vinasse exits the distillation process at high temperatures, which may differ from the optimal temperatures for dark fermentation and anaerobic digestion. A 15 °C temperature increase, for example, stops sugarcane vinasse methane generation, making distillery vinasse digestion complicated. Conversely, in other aspects, co-digesting vinasse and glycerol has been proven to stabilize methane production from vinasse because of sulfate dilution. However, glycerol has not been tested to stabilize vinasse digestion under temperature changes. Thus, this study compared the effects of different temperature settings on the co-digestion of 10 g COD L−1 of vinasse and glycerol (50 %:50 % on a COD basis) in anaerobic fluidized bed reactors (AFBR), i.e., an acidogenic and a methanogenic one-stage AFBRs operated at 55, 60, and 65 °C, and two methanogenic AFBRs fed both with acidogenic effluent (one operated at room temperature (25 °C) and the other at 55, 60, and 65 °C). The co-digestion provided steady methane generation at all AFBRs, with methane production rates ranging from 2.27 to 2.93 L CH4 d−1 L−1, whether in one or two stages. A feature of this research was to unravel the black box of the role of sulfate in the digestion of sugarcane vinasse, which was rarely studied. Desulfovibrio was the primary genus degrading 1,3-propanediol into 3-hydroxypropanoate after genome sequencing. Phosphate acetyltransferase (EC: 2.3.1.8, K00625) and acetate kinase (EC: 2.7.2.1, K00925) genes were also found, suggesting propionate was metabolized. In practical aspects, regarding the two-stage systems, the thermophilic-mesophilic (acidogenic-methanogenic) configuration is best for extracting additional value-added products because 1,3-propanediol may be recovered at high yields with steady methane production at reduced energy expenditure in a reactor operated at room temperature. However, the one-stage design is best for methane generation per system volume since it remained stable with rising temperatures, and all systems presented similar methane production rates.

Iron zero valent nanoparticles applied in the biorefinery concept: Functional genes in continuous bioreactor fermenting vinasse

Increased production of biogas and volatile acids was evaluated by the addition of Fe0 Nanoparticles (NP) on Anaerobic Fluidized Bed Reactor (AFBR-NP) with expanded clay as support material (45.1 mg Fe0 g−1 expanded clay), fermenting vinasse, and operated at 37 °C and 3h Hydraulic Retention Time (HRT). Higher H2 percentage in the biogas composition was observed in AFBR-NP (50–65%) when compared to AFBR without NP, AFBR-Control (24–43%). A 1.2-fold higher valeric acid production was also observed as a result of NPs supplementation. Genes related to the first steps of vinasse anaerobic degradation in AFBR-NP (beta-glucosidase, glucokinase and pyruvate-ferredoxin oxidoreductase) and the genes related to volatile acids production (L- and d-lactate dehydrogenase, 3-hydroxybutyryl-CoA dehydrogenase, acetate kinase, pyruvate kinase and fumarate reductase flavoprotein) were observed by metagenome sequencing. A 4.2-fold higher relative abundance of Secundilactobacillus genus in AFBR-NP was evidenced. The genetic and microbial community differences observed with the addition of NP resulted in improved biorefinery products of anaerobic digestion.

Application of nanoparticles to increase biological hydrogen production: the difference in metabolic pathways in batch and continuous reactors

ABSTRACT An alternative to improve the production of biorefinery products, such as biohydrogen (H2) and volatile fatty acids (VFA), is the combination of nanotechnology and biological processes. In order to compare the use of both processes in two different reactor configurations, batch reactors and continuous anaerobic fluidized bed reactors (AFBR) were studied under the same conditions (37°C, pH 6.8, Clostridium butyricum as an inoculum and glucose as a substrate) to evaluate the influence of zero valence iron and nickel nanoparticles (NPs) on H2 and VFA production. There was a shift in the production of acetic and butyric acids to produce mainly valeric acid when NPs were added in batch reactors. Meanwhile, in AFBR the change was from lactic acid to butyric and acetic acids with the addition of NPs. It showed that the effect of NPs on the fermentation process was different when the configuration of batch and continuous reactors was compared. The H2 yield in both reactor configurations increased with the addition of NPs. In batch reactors from 6.6 to 8.0 mmol H2 g−1 of COD and in AFBR from 4.9 to 6.2 mmol of H2 g−1 of COD. Therefore, given the simplicity and low cost of the synthesis of metallic NPs, it is a promising additive to optimize the fermentation process in different reactor configurations.

Microbial community stratification in scale-up Anaerobic Fluidized Bed Reactor applied for 4-Nonylphenol degradation

This is the first report of the microbial community stratification in a scale-up (20 L) Anaerobic Fluidized Bed Reactor (AFBR) during the degradation of the endocrine disruptor 4-Nonylphenol (4-NP). Bed stratification occurred after 100 running days. The bed visually characterized as granules were, actually, thick biofilm covering the entire surface of the sand particle, acting as a protection strategy of microbial populations against 4-NP addition. The community differentiation may have occurred to the Quorum-Sensing (QS) system due to the greater abundance of biofilm-forming genera in the granule. Furthermore, the syntrophic relation between electrogenic bacteria and methanogenic archaea via Direct Interspecies Electron Transfer (DIET) may also explain the bed stratification, due to the higher abundance of Geothrix (8.3 %), Enterococcus (4.8 %), Lactobacillus (3.9 %), Bacillus (2.0 %) and Methanosaeta (15.6 %) in the granular bed. Bed stratification is an extremely complex issue and can influence the AFBR operation, modeling and scaling up.

Biomethane recovery through co-digestion of cheese whey and glycerol in a two-stage anaerobic fluidized bed reactor: Effect of temperature and organic loading rate on methanogenesis

Anaerobic digestion for CH4 recovery in wastewater treatment has been carried out with different strategies to increase process efficiency, among which co-digestion and the two-stage process can be highlighted. In this context, this study aimed at evaluating the co-digestion of cheese whey and glycerol in a two-stage process using fluidized bed reactors, verifying the effect of increasing the organic loading rate (OLR) (2–20 g-COD.L−1.d−1) and temperature (thermophilic and mesophilic) in the second stage methanogenic reactor. The mesophilic methanogenic reactor (R-Meso) (mean temperature of 22 °C) was more tolerant to high OLR and its best performance was at 20 g-COD.L−1.d−1, resulting in methane yield (MY) and methane production (MPR) of 273 mL-CH4.g-COD−1 and 5.8 L-CH4.L−1.d−1 (with 67% of CH4), respectively. Through 16S rRNA gene massive sequencing analysis, a greater diversity of microorganisms was identified in R-Meso than in R-Thermo (second stage methanogenic reactor, 55 °C). Firmicutes was the phyla with higher relative abundance in R-Thermo, while in R-Meso the most abundant ones were Proteobacteria and Bacteroidetes. Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be observed, being the genera Methanothermobacter and Methanobacterium the most abundant in R-Thermo and R-Meso, respectively. The two-stage system composed with a thermophilic acidogenic reactor + R-Meso was more adequate for the co-digestion of cheese whey and glycerol than the single-stage process, promoting increases of up to 47% in the energetic yield (10.3 kJ.kg-COD−1) and 14% in organic matter removal (90.5%).

Relating biomass composition and the distribution of metabolic functions in the co-fermentation of sugarcane vinasse and glycerol

This study aimed to determine the effect of increasing the organic loading rate (OLR) from 60 to 90 and 120 kg COD m−3 d−1 in the co-fermentation of glycerol and sugarcane vinasse (50%: 50% proportion on a COD basis) in a thermophilic anaerobic fluidized bed reactor (55 °C) at the fixed hydraulic retention time of 4 h. The highest values of hydrogen production rate (1851 mL H2 d−1 L−1bed) and yield (0.29 mmol H2 g−1 CODadded) were found at 120 kg COD m−3 d−1 and coincided with butanoate as a major liquid metabolite (2620 mg L−1). The reverse β-oxidation of lactate into butanoate contributed to its synthesis and was linked to synergism between Clostridium (relative abundance of 77.8%) and Lacticaseibacillus (7.2%) in the reactor. The identification of the butyryl-CoA/acetate-CoA transferase gene, which may have catalyzed the conversion of butyryl-CoA into butanoate using acetate as an acceptor, also supported this.

Two problems in one shot: Vinasse and glycerol co-digestion in a thermophilic high-rate reactor to improve process stability even at high sulfate concentrations

Anaerobic co-digestion (AcoD) of sugarcane vinasse and glycerol can be profitable because of the destination of two biofuel wastes produced in large quantities in Brazil (ethanol and biodiesel, respectively) and the complementary properties of these substrates. Thus, the objective of this study was to assess the effect of increasing the organic loading rate (OLR) from 2 to 20 kg COD m−3 d−1 on the AcoD of vinasse and glycerol (50 %:50 % on a COD basis) in a thermophilic (55 °C) anaerobic fluidized bed reactor (AFBR). The highest methane production rate was observed at 20 kg COD m−3 d−1 (8.83 L CH4 d−1 L−1), while the methane yield remained stable at around 265 NmL CH4 g−1 CODrem in all conditions, even when influent vinasse reached 1811 mg SO42− L−1 (10 kg COD m−3 d−1). Sulfate was not detected in the effluent. Bacterial genera related to sulfate removal, such as Desulfovibrio and Desulfomicrobium, were observed by means of shotgun metagenomic sequencing at 10 kg COD m−3 d−1, as well as the acetoclastic archaea Methanosaeta and prevalence of genes encoding enzymes related to acetoclastic methanogenesis. It was concluded that process efficiency and methane production occurred even in higher sulfate concentrations due to glycerol addition.

Iron and nickel nanoparticles role in volatile fatty acids production enhancement: Functional genes and bacterial taxonomy in an anaerobic fluidized bed reactor

This study is the first report that describes Iron (16.7 mg Fe0 g-1) and Nickel (0.04 mg Ni0 g-1) nanoparticles (NPs) immobilization on the support material of an Anaerobic Fluidized Bed Reactor (AFBR-NP) and the assessment of its influence on fermentation pathway when compared with a reactor without NPs (AFBR-Control). AFBRs were operated at initial pH 6.8, 37 °C, 3.0 h Hydraulic Retention Time. Natural fermentation along with bioaugmentation with Clostridium butyricum were used as inoculation strategy. Both reactors were fed with glucose as main substrate (56 ± 6 and 21 ± 2 g COD L-1 d-1 at operational Stages I and II, respectively). 78–98% higher Volatile Fatty Acid (VFA) was observed on AFBR-NP. Metals higher availability specifically favored butyric (1.04 ± 0.37 g L-1) and acetic (1.22 ± 0.33 g L-1) acid production metabolic route on AFBR-NP. Under the same operational conditions, lactic acid was observed as main metabolite on AFBR-Control (1.23 ± 0.25 g L-1). Enzymes related to butyric (butyryl-CoA dehydrogenase, phosphate butyryltransferase, butyrate kinase) and propionic acid (pyruvate-ferredoxin oxidoreductase) metabolic routes were identified on AFBR-NP reactor biofilm. Through these results, it is possible to infer that Fe0 and Ni0 NPs could effectively improve VFA production and the fermentation process.

Thermophilic anaerobic co-digestion of glycerol and cheese whey – Effect of increasing organic loading rate

The organic loading rate (OLR) is one of the variables that directly affects anaerobic digestion. An increase in OLR can improve methane production, but it can also lead to process failures. Therefore, determining the proper OLR for the process is of great importance. This study analyzed the effect of increasing the OLR on cheese whey and glycerol co-digestion in a thermophilic anaerobic fluidized bed reactor (AFBR) by varying both the influent concentration and the hydraulic retention time (HRT). The increase in OLR from 5 to 20 gCOD.L−1.d−1 was initially performed by increasing the influent concentration from 5 to 7.5, 10, 15, and 20 gCOD.L−1, at HRT of 24 h. Organic matter removal (87.7%), methane yield (MY) (253.0 mL CH4.gCOD−1rem), and methane production rate (MPR) (3.2 L CH4. L−1.d−1) showed the best performance at 10 gCOD.L−1.d−1. Conversely, raising the OLR to 20 gCOD.L−1 enhanced the buildup of volatile fatty acids, resulting in a 38.5% decrease in MY. Based on these findings, the HRT was reduced from 24 h to 20 h and 16 h at influent concentration of 10 gCOD.L−1 resulting in OLR of 10, 12, and 15 gCOD.L−1.d−1, respectively. The HRT at 20 h (12 gCOD.L−1.d−1) provided the highest MY values (around 292.5 mL CH4.gCOD−1rem), while the maximum MPR was observed at 16 h (5.1 L CH4. L−1.d−1). The main metabolites observed in all conditions were acetic acid (31.1–66.8%) and propionic acid (10.9–61.5%). The OLR also affected the microbial community, with Proteobacteria accounting for 53.1% of the relative abundance at 5 gCOD.L−1.d−1 while Firmicutes accounted for 76.6% at 10 gCOD.L−1.d−1. At 10 gCOD.L−1.d−1, with maximum MY, the bacteria observed with the highest relative abundance were an unidentified genus of Lentimicrobiaceae (8.9%), “Blvii28 wastewater sludge group” (2.9%), and Tolumonas (1.4%). The archaea identified with the highest relative abundance at both OLRs (5 and 10 gCOD.L−1.d−1) was hydrogenotrophic Methanobacterium (27.3% and 2.6%, respectively).

Performance and kinetics of a fluidized bed anaerobic reactor treating distillery effluent

Abstract The kinetic analysis of an anaerobic fluidized bed bioreactor treating distillery effluent was carried out. Natural zeolite was used as biomass carrier at various organic loading rates and hydraulic retention times (HRT). The degradation followed first order kinetics and fitted Michaelis–Menten kinetic model for substrate utilization. The kinetic analysis showed that 9% of the TOC was nonbiodegradable which corresponds to about 14% COD. The non-biodegradable component was responsible for the dark-brown color of the distillery effluent and therefore there was a need for employing a post-treatment technology for their removal. Biomass yield was found to be 0.4658 g/g while endogenic microorganisms decay coefficient was 0.0293, which suggested that there was a need to install a sludge handling unit prior to post-treatment. The maximum micro-organisms’ growth rate was found to be 0.136 d−1 while the specific growth rate of the micro-organisms reduced with an increase in HRT at constant feed concentration. The specific substrate utilization rate was found to increase linearly with an increase in the ration of food to micro-organisms and the mean cell residence time was found to be at least 2.5 times the HRT due to application of zeolite as microbial support in the reactor.

Producing hydrogen from the fermentation of cheese whey and glycerol as cosubstrates in an anaerobic fluidized bed reactor

This study aimed to evaluate the effect of the organic loading rate (OLR) (60, 90, and 120 g Chemical Oxygen Demand (COD). L −1 . d −1 ) on hydrogen production from cheese whey and glycerol fermentation as cosubstrates (50% cheese whey and 50% glycerol on a COD basis) in a thermophilic fluidized bed reactor (55 °C). The increase in the OLR to 90 gCOD.L −1 . d −1 favored the hydrogen production rate (HPR) (3.9 L H 2 . L −1 . d −1 ) and hydrogen yield (HY) (1.7 mmol H 2 . gCOD −1 app ) concomitant with the production of butyric and acetic acids. Employing 16S rRNA gene sequencing, the highest hydrogen production was related to the detection of Thermoanaerobacterium (34.9%), Pseudomonas (14.5%), and Clostridium (4.7%). Conversely, at 120 gCOD.L −1 . d −1 , HPR and HY decreased to 2.5 L H 2 . L −1 . d −1 and 0.8 mmol H 2 . gCOD −1 app , respectively, due to lactic acid production that was related to the genera Thermoanaerobacterium (50.91%) and Tumebacillus (23.56%). Cofermentation favored hydrogen production at higher OLRs than cheese whey single fermentation. • The organic loading rate was evaluated in a thermophilic fluidized bed reactor. • Cofermentation of cheese whey and glycerol was suitable for bio-H 2 production. • A higher H 2 yield of 1.7 mmol. gCOD −1 app was observed at 90 gCOD.L −1 . d −1 . • The highest H2 yield was concomitant with butyric acid (41.1% molar) production. • Thermoanaerobacterium was the main genus involved in H 2 production.