Kaikki aineistot
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Two heat–treated inocula, fresh and digested activated sludge from the same municipal wastewater treatment plant, were compared for their H2 production via dark fermentation at mesophilic (37 °C), thermophilic (55 °C) and hyperthermophilic (70 °C) conditions using xylose as the substrate. At both 37 and 55 °C, the fresh activated sludge yielded more H2 than the digested sludge, whereas at 70 °C, neither of the inocula produced H2 effectively. A maximum yield of 1.85 mol H2 per mol of xylose consumed was obtained at 55 °C. H2 production was linked to acetate and butyrate production, and there was a linear correlation (R2 = 0.96) between the butyrate and H2 yield for the fresh activated sludge inoculum at 55 °C. Approximately 2.4 mol H2 per mol of butyrate produced were obtained against a theoretical maximum of 2.0, suggesting that H2 was produced via the acetate pathway prior to switching to the butyrate pathway due to the increased H2 partial pressure. Clostridia sp. were the prevalent species at both 37 and 55 °C, irrespectively of the inoculum type. Although the two inocula originated from the same plant, different thermophilic microorganisms were detected at 55 °C. Thermoanaerobacter sp., detected only in the fresh activated sludge cultures, may have contributed to the high H2 yield obtained with such an inoculum.
The removal of volatile fatty acids was examined through adsorption on anion exchange resins in batch systems. During the initial screening step, granular activated carbon and 11 anion exchange resins were tested and the resins Amberlite IRA-67 and Dowex optipore L-493 were chosen for further investigation. The adsorption kinetics and diffusion mechanism and adsorption isotherms of the two resins for VFA were evaluated. Based on the selective adsorption capacity of the resins, a sequential batch process was tested to achieve separation of acetic acid from the VFA mixture and selective recoveries > 85% acetic acid and ~ 75% propionic acid was achieved.
Microbial electrochemical technologies (MET), also known as bioelectrochemical systems (BES), use microorganisms as biocatalysts to recover valuable resources like bioelectricity, hydrogen, nutrients, metals, and industrial chemicals from wastes and wastewaters. MET are therefore expected to play a key role in waste management and reduction of the carbon footprint in the near future. However, considerable fundamental and technological challenges still need to be addressed before using MET in practice. Rapid start-up, as well as an efficient and stable performance, are the pre-requisites to achieve commercialization of MET. Although considerable advancements have been made in this field in the past two decades, no general conclusion has been drawn about how to start-up BES in the most efficient manner. This review aims to survey and critically analyze start-up strategies proposed in the literature to favor a fast and efficient establishment of electrochemically active microorganisms onto bioanodes or biocathodes and promote their activity over a long period of operation. Various aspects of BES start-up, including inoculum selection, elimination of competitive microorganisms, and selection of operational parameters for enrichment of electroactive biofilms are covered. In summary, inoculation with already enriched culture, imposing of an anode potential or using polarity reversal at the cathode are the potential methods for ensuring fast and efficient BES start-up. Electrode configuration and hydrodynamic conditions are also major aspects to be considered for biofilm formation and development.
Removal of H2S from gas streams using NO3--containing synthetic wastewater was investigated in an anoxic biotrickling filter (BTF) at feed N/S ratios of 1.2-1.7 mol mol-1 with an initial nominal empty bed residence time of 3.5 min and a hydraulic retention time of 115 min. During 108 days of operation under autotrophic conditions, the BTF showed a maximum elimination capacity (EC) of 19.2 g S m-3 h-1 and H2S removal efficiency (RE) above 99%. Excess biofilm growth reduced the HRT from 115 to 19 min and decreased the desulfurization efficiency of the BTF. When the BTF was operated under mixotrophic conditions by adding organic carbon (43.2 g acetate m-3 h-1) to the synthetic wastewater, the H2S EC decreased from 16.4 to 13.1 g S m-3 h-1, while the NO3- EC increased from 9.9 to 11.1 g NO3--N m-3 h-1, respectively. Thiobacillus sp. (98-100% similarity) was the only sulfur-oxidizing nitrate-reducing bacterium detected in the BTF biofilm, while the increased abundance of heterotrophic denitrifiers, i.e. Brevundimonas sp. and Rhodocyclales, increased the consumed N/S ratio during BTF operation. Residence time distribution tests showed that biomass accumulation during BTF operation reduced gas and liquid retention times by 17.1% and 83.5%, respectively.
This study evaluates the use of non-pretreated thermo-mechanical pulping (TMP) wastewater as a potential substrate for hydrogen production by dark fermentation. Batch incubations were conducted in a temperature gradient incubator at temperatures ranging from 37 to 80 °C, using an inoculum from a thermophilic, xylose-fed, hydrogen-producing fluidised bed reactor. The aim was to assess the short-term response of the microbial communities to the different temperatures with respect to both hydrogen yield and composition of the active microbial community. High throughput sequencing (MiSeq) of the reversely transcribed 16S rRNA showed that Thermoanaerobacterium sp. dominated the active microbial community at 70 °C, resulting in the highest hydrogen yield of 3.6 (±0.1) mmol H2 g−1 CODtot supplied. Lower hydrogen yields were obtained at the temperature range from 37 to 65 °C, likely due to consumption of the produced hydrogen by homoacetogenesis. No hydrogen production was detected at temperatures above 70 °C. Thermomechanical pulping wastewaters are released at high temperatures (50–80 °C), and thus dark fermentation at 70 °C could be sustained using the heat produced by the pulp and paper plant itself without any requirement for external heating.
An anoxic sulfur-oxidizing moving bed biofilm reactor (MBBR) treating sulfur and nitrate-contaminated synthetic wastewater was monitored for 306 days under feed nitrogen-to-sulfur (N/S) molar ratios of 0.5, 0.3 and 0.1. Thiosulfate (S2O32−) removal efficiencies (RE) exceeding 98% were observed at a N/S ratio of 0.5 and a S2O32− loading rate of 0.9 g S2O32−–S L−1 d−1, whereas a RE of 82.3 (±2.6)% and 37.7 (±3.4)% were observed at N/S ratios of 0.3 and 0.1, respectively. Complete nitrate (NO3−) removal was obtained at all tested N/S ratios. A comparison of the kinetic parameters of the MBBR biomass under the same stoichiometric conditions (N/S ratio of 0.5) revealed a 1.3-fold increase of the maximum specific rate of S2O32− oxidation (rmax) and a 30-fold increase of the affinity constant for S2O32− (Ks) compared to those observed after long-term NO3− limitation (N/S ratio of 0.1). The MBBR showed optimal resilience to NO3− limitation as the S2O32− RE recovered from 37.3% to 94.1% within two days after increasing the N/S ratio from 0.1 to 0.5. Based on PCR-DGGE analysis, sulfur-oxidizing nitrate-reducing bacteria, i.e. Thiobacillus sp. and Sulfuritalea sp., dominated in the MBBR biofilm during the entire study.
The application of an anoxic biotrickling filter (BTF) for H2S removal from contaminated gas streams is a promising technology for simultaneous H2S and NO3− removal. Three transient–state conditions, i.e. different liquid flow rates, wet–dry bed operations and H2S shock loads, were applied to a laboratory–scale anoxic BTF. In addition, bioaugmentation of the BTF with a H2S removing–strain, Paracoccus MAL 1HM19, to enhance the biomass stability was investigated. Liquid flow rates (120, 60 and 30 L d−1) affected the pH and NO3− removal efficiency (RE) in the liquid phase. Wet–dry bed operations at 2–2 h and 24–24 h reduced the H2S elimination capacity (EC) by 60–80%, while the operations at 1–1 h and 12–12 h had a lower effect on the BTF performance. When the BTF was subjected to H2S shock loads by instantly increasing the gas flow rate (from 60 to 200 L h−1) and H2S inlet concentration (from 112 (± 15) to 947 (± 151) ppmv), the BTF still showed a good H2S RE (>93%, EC of 37.8 g S m–3 h–1). Bioaugmentation with Paracoccus MAL 1HM19 enhanced the oxidation of the accumulated S0 to sulfate in the anoxic BTF.
The utilization of foul condensate (FC) collected from a Kraft pulp mill for the anaerobic production of volatile fatty acids (VFA) was tested in upflow anaerobic sludge blanket (UASB) reactors operated at 22, 37 and 55°C at a hydraulic retention time (HRT) of ∼75 h. The FC consisted mainly of 11370, 500 and 592 mg/L methanol, ethanol and acetone, respectively. 42–46% of the organic carbon (methanol, ethanol and acetone) was utilized in the UASB reactors operated at an organic loading of ∼8.6 gCOD/L.d and 52–70% of the utilized organic carbon was converted into VFA. Along with acetate, also propionate, isobutyrate, butyrate, isovalerate and valerate were produced from the FC. Prior to acetogenesis of FC, enrichment of the acetogenic biomass was carried out in the UASB reactors for 113 d by applying operational parameters that inhibit methanogenesis and induce acetogenesis. Activity tests after 158 d of reactor operation showed that the biomass from the 55°C UASB reactor exhibited the highest activity after the FC feed compared to the biomass from the reactors at 22 and 37°C. Activity tests at 37°C to compare FC utilization for CH4 versus VFA production showed that an organic carbon utilization >98% for CH4 production occurred in batch bottles, whereas the VFA production batch bottles showed 51% organic carbon utilization. Furthermore, higher concentrations of C3–C5 VFA were produced when FC was the substrate compared to synthetic methanol rich wastewater.
Anoxic thiosulfate (S2O3 2−) oxidation using autotrophic denitrification by a mixed culture of nitrate reducing, sulfur oxidizing bacteria (NR-SOB) was studied in a fluidized bed reactor (FBR). The long-term performance of the FBR was evaluated for 306 days at three nitrogen-to-sulfur (N/S) molar ratios (0.5, 0.3 and 0.1) and a hydraulic retention time (HRT) of 5 h. S2O3 2− removal efficiencies >99% were obtained at a N/S ratio of 0.5 and a S2O3 2− and nitrate (NO3 −) loading rate of 820 (±84) mg S-S2O3 2− L−1 d−1 and 173 (±10) mg N-NO3 − L−1 d−1, respectively. The S2O3 2− removal efficiency decreased to 76% and 26% at N/S ratios of 0.3 and 0.1, respectively, and recovered to 80% within 3 days after increasing the N/S ratio from 0.1 back to 0.5. The highest observed half-saturation (Ks) and inhibition (KI) constants of the biofilm-grown NR-SOB obtained from batch cultivations were 172 and 800 mg S-S2O3 2− L−1, respectively. Thiobacilus denitrificans was the dominant microorganism in the FBR. Artificial neural network modeling successfully predicted S2O3 2− and NO3 − removal efficiencies and SO4 2− production in the FBR. Additionally, results from the sensitivity analysis showed that the effluent pH was the most influential parameter affecting the S2O3 2− removal efficiency.
A mesophilic (37 °C) and a thermophilic (55 °C) two-chamber microbial fuel cell (MFC) were studied and compared for their power production from xylose and the microbial communities involved. The anode-Attached, membrane-Attached, and planktonic microbial communities, and their respective active subpopulations, were determined by next generation sequencing (Illumina MiSeq), based on the presence and expression of the 16S rRNA gene. Geobacteraceae accounted for 65% of the anode-Attached active microbial community in the mesophilic MFC, and were associated to electricity generation likely through direct electron transfer, resulting in the highest power production of 1.1 W m-3. A lower maximum power was generated in the thermophilic MFC (0.2 W m-3), likely due to limited acetate oxidation and the competition for electrons by hydrogen oxidizing bacteria and hydrogenotrophic methanogenic archaea. Aerobic microorganisms, detected among the membrane-Attached active community in both the mesophilic and thermophilic MFC, likely acted as a barrier for oxygen flowing from the cathodic chamber through the membrane, favoring the strictly anaerobic exoelectrogenic microorganisms, but competing with them for xylose and its degradation products. This study provides novel information on the active microbial communities populating the anodic chamber of mesophilic and thermophilic xylose-fed MFCs, which may help in developing strategies to favor exoelectrogenic microorganisms at the expenses of competing microorganisms.
The inoculum source plays a crucial role in the anaerobic treatment of wastewaters. Lipids are present in various wastewaters and have a high methanogenic potential, but their hydrolysis results in the production of long chain fatty acids (LCFAs) that are inhibitory to anaerobic microorganisms. Screening of inoculum for the anaerobic treatment of LCFA-containing wastewaters has been performed at mesophilic and thermophilic conditions. However, an evaluation of inocula for producing methane from LCFA-containing wastewater has not yet been conducted at low temperatures and needs to be undertaken. In this study, three inocula (one granular sludge and two municipal digester sludges) were assessed for methane production from LCFA-containing synthetic dairy wastewater (SDW) at low temperatures (10 and 20°C). A methane yield (based on mL-CH4/g-CODadded) of 86-65% with acetate and 45-20% with SDW was achieved within 10 days using unacclimated granular sludge, whereas the municipal digester sludges produced methane only at 20°C but not at 10°C even after 200 days of incubation. The acetotrophic activity in the inoculum was found to be crucial for methane production from LCFA at low temperatures, highlighting the role of Methanosaeta (acetoclastic archaea) at low temperatures. The presence of bacterial taxa from the family Syntrophaceae (Syntrophus and uncultured taxa) in the inoculum was found to be important for methane production from SDW at 10°C. This study suggests the evaluation of acetotrophic activity and the initial microbial community characteristics by high-throughput amplicon sequencing for selecting the inoculum for producing methane at low temperatures (up to 10°C) from lipid-containing wastewaters.
Dark fermentative biohydrogen production in a thermophilic, xylose-fed (50 mM) fluidised bed reactor (FBR) was evaluated in the temperature range 55-70 °C with 5-degree increments and compared with a mesophilic FBR operated constantly at 37 °C. A significantly higher (p = 0.05) H2 yield was obtained in the thermophilic FBR, which stabilised at about 1.2 mol H2 mol-1 xylose (36% of the theoretical maximum) at 55 and 70 °C, and at 0.8 mol H2 mol-1 xylose at 60 and 65 °C, compared to the mesophilic FBR (0.5 mol H2 mol-1 xylose). High-throughput sequencing of the reverse-transcribed 16S rRNA, done for the first time on biohydrogen producing reactors, indicated that Thermoanaerobacterium was the prevalent active microorganism in the thermophilic FBR, regardless of the operating temperature. The active microbial community in the mesophilic FBR was mainly composed of Clostridium and Ruminiclostridium at 37 °C. Thermophilic dark fermentation was shown to be suitable for treatment of high temperature, xylose-containing wastewaters, as it resulted in a higher energy output compared to the mesophilic counterpart.
The microbial communities developed from a mixed-species culture in up-flow and flow-through configurations of thermophilic (55 °C) microbial fuel cells (MFCs), and their power production from acetate, were investigated. The up-flow MFC was operated for 202 days, obtaining an average power density of 0.13 W/m3, and Tepidiphilus was the dominant transcriptionally-active microorganisms. The planktonic community developed in the up-flow MFC was used to inoculate a flow-through MFC resulting in the proliferation of Ureibacillus, whose relative abundance increased from 1 to 61% after 45 days. Despite the differences between the up-flow and flow-through MFCs, including the anode electrode, hydrodynamic conditions, and the predominant microorganism, similar (p = 0.05) volumetric power (0.11–0.13 W/m3), coulombic efficiency (16–18%) and acetate consumption rates (55–69 mg/L/d) were obtained from both. This suggests that though MFC design can shape the active component of the thermophilic microbial community, the consortia are resilient and can maintain similar performance in different MFC configurations.
The influence of different inoculum pretreatments (pH and temperature shocks) on mesophilic (37 °C) and thermophilic (55 °C) dark fermentative H2 production from xylose (50 mM) and, for the first time, on the composition of the active microbial community was evaluated. At 37 °C, an acidic shock (pH 3, 24 h) resulted in the highest yield of 0.8 mol H2 mol−1 xylose. The H2 and butyrate yield correlated with the relative abundance of Clostridiaceae in the mesophilic active microbial community, whereas Lactobacillaceae were the most abundant non-hydrogenic competitors according to RNA-based analysis. At 55 °C, Clostridium and Thermoanaerobacterium were linked to H2 production, but only an alkaline shock (pH 10, 24 h) repressed lactate production, resulting in the highest yield of 1.2 mol H2 mol−1 xylose. This study showed that pretreatments differentially affect the structure and productivity of the active mesophilic and thermophilic microbial community developed from an inoculum.
Distinct microbial assemblages evolve in anaerobic digestion (AD) reactors to drive sequential conversions of organics to methane. The spatio-temporal development of three such assemblages (granules, biofilms, planktonic) derived from the same inoculum was studied in replicated bioreactors treating long-chain fatty acids (LCFA)-rich wastewater at 20 °C at hydraulic retention times (HRTs) of 12–72 h. We found granular, biofilm and planktonic assemblages differentiated by diversity, structure, and assembly mechanisms; demonstrating a spatial compartmentalisation of the microbiomes from the initial community reservoir. Our analysis linked abundant Methanosaeta and Syntrophaceae-affiliated taxa (Syntrophus and uncultured) to their putative, active roles in syntrophic LCFA bioconversion. LCFA loading rates (stearate, palmitate), and HRT, were significant drivers shaping microbial community dynamics and assembly. This study of the archaea and syntrophic bacteria actively valorising LCFAs at short HRTs and 20 °C will help uncover the microbiology underpinning anaerobic bioconversions of fats, oil and grease.
The aim of this study was to determine an optimal anode material for electricity production and COD removal from xylose containing synthetic wastewater in an up-flow microbial fuel cell (MFC), and assess its suitability for treatment of thermomechanical pulping (TMP) wastewater with an enrichment culture at 37 °C. The anode materials tested included carbon-based electrodes (graphite plate, carbon cloth and zeolite coated carbon cloth), metal-based electrodes (tin coated copper) and a metal-carbon assembly (granular activated carbon in stainless steel cage). During continuous operation with xylose, COD removal was 77–86% of which 25–28% was recovered as electricity. The highest power density of 333 (±15) mW/m 2 was obtained with the carbon cloth electrode. However, based on an overall analysis including electrode performance, surface area and scalability, the granular activated carbon in stainless steel cage (GAC in SS cage) was chosen to be used as electrode for bioelectrochemical treatment of TMP wastewater. The TMP fed MFC was operated in continuous mode with 1.8 days hydraulic retention time, resulting in 47 (±13%) COD removal of which 1.5% was recovered as electricity with the average power production of 10–15 mW/m 2 . During operation with TMP wastewater, membrane fouling increased the polarization resistance causing a 50% decrease in power production within 30 days. This study shows that MFC pretreatment removes half of the TMP wastewater COD load, reducing the energy required for aerobic treatment.