Mesophilic Upflow Anaerobic Sludge Blanket Research Articles

Microbiological insights into anaerobic phenol degradation mechanisms and bulking phenomenon in a mesophilic upflow anaerobic sludge blanket reactor in long-term operation

In this study, a long-term operation of 2,747 days was conducted to evaluate the performance of the upflow anaerobic sludge blanket (UASB) reactor and investigated the degradation mechanisms of high-organic loading phenol wastewater. During the reactor operation, the maximum chemical oxygen demand (COD) removal rate of 6.1 ± 0.6 kg/m3/day under 1,680 mg/L phenol concentration was achieved in the mesophilic UASB reactor. After a significant change in the operating temperature from 24.0 ± 4.1 °C to 35.9 ± 0.6 °C, frequent observations of floating and washout of the bloated granular sludge (novel types of the bulking phenomenon) were made in the UASB reactor, suggesting that the change in operating temperature could be a trigger for the bulking phenomenon. Through the metagenomic analysis, phenol degradation mechanisms were predicted that phenol was converted to 4-hydroxybenzoate via two possible routes by Syntrophorhabdaceae and Pelotomaculaceae bacteria. Furthermore, the degradation of 4-hydroxybenzoate to benzoyl-CoA was carried out by members of Syntrophorhabdaceae and Smithellaceae. In the bulking sludge, a predominant presence of Nanobdellota, belonging to DPANN archaea, was detected. The metagenome-assembled genome of the Nanobdellota lacks many biosynthetic pathways and has several genes for the symbiotic lifestyle such as trimeric autotransporter adhesin-related protein. Furthermore, the Nanobdellota have significant correlations with several methanogenic archaea that are predominantly present in the UASB reactor. Considering the results of this study, the predominant Nanobdellota may negatively affect the growth of the methanogens through the parasitic lifestyle and change the balance of microbial interactions in the granular sludge ecosystem.

From start-up to maximum loading: An approach for methane production in upflow anaerobic sludge blanket reactor fed with the liquid fraction of fruit and vegetable waste

This investigation provides a reproducible approach for determining the limits of an upflow anaerobic sludge blanket (UASB) reactor designed for the methanization of the liquid fraction of fruit and vegetable waste (FVWL). Two identical mesophilic UASB reactors were operated for 240 days with a three-day fixed hydraulic retention time and an organic load rate (OLR) increased from 1.8 to 10 gCOD L−1 d−1. Because of the previous estimation of flocculent-inoculum methanogenic activity, it was possible to design a safe OLR for the quick start-up of both UASB reactors. The operational variables obtained from the operation of the UASB reactors did not show statistical differences, ensuring the experiment's reproducibility. As a result, the reactors achieved methane yield close to 0.250 LCH4 gCOD−1 up to the OLR of 7.7 gCOD L−1 d−1. Furthermore, the maximum volumetric methane production rate of 2.0 LCH4 L−1 d−1 was discovered for the OLR ranges between 7.7 and 10 gCOD L−1 d−1. The possible overload at OLR of 10 gCOD L−1 d−1 resulted in a significant reduction of methane production in both UASB reactors. Based on the methanogenic activity of the UASB reactors sludge, a maximum loading capacity of approximately 8 gCOD L−1 d−1 was estimated.

High-rate cotreatment of purified terephthalate and dimethyl terephthalate manufacturing wastewater by a mesophilic upflow anaerobic sludge blanket reactor and the microbial ecology relevant to aromatic compound degradation

Polyethylene terephthalate (PET) is produced worldwide, mainly as material for plastic drink bottles. PET is produced by polymerization of purified terephthalate (PTA) or dimethyl terephthalate (DMT) with ethylene glycol. During the synthetic manufacturing processes of PTA and DMT, high organic loading wastewater is produced, which is typically treated separately by anaerobic wastewater treatment technologies. Given the high demand for PET, manufacturing plants are expanding globally, which will result in an increase in the amounts of PTA and DMT wastewater in need of treatment. In terms of effective treatment, the cotreatment of PTA and DMT wastewater has several advantages, including lower area and energy requirements. In this study, we examined the performance of an upflow anaerobic sludge blanket (UASB) reactor in cotreating PTA and DMT wastewater with high organic loading, evaluating its removal characteristics after 518 days of continuous operation. In addition, we performed a microbiome analysis of the UASB granular sludge to uncover the microbial interactions and metabolic functions within the reactor. By continuous operation, we achieved an organic removal rate of 6.6 kg m−3 day−1. In addition, we confirmed that aromatic compounds in the complex wastewater from the PTA and DMT manufacturing processes are biodegradable in the following order: benzoate > orthophthalate > terephthalate > isophthalate > p-toluic acid. 16S rRNA gene-based network analysis shows that anaerobic Woesearchaeales belonging to phylum Nanoarchaeota has a positive correlation with Methanoregula, Candidatus Methanofastidiosum, and Methanosarcina, suggesting a symbiotic relationship with methanogens in granular sludge. Shotgun metagenomic analysis revealed that terephthalate, isophthalate/orthophthalate, and benzoate were degraded by different members of Pelotomaculaceae and Syntrophorhabdaceae. According to the genomic information, we propose two new possible routes for orthophthalate degradation by the Syntrophorhabdaceae organism.

Performance evaluation of three mesophilic upflow anaerobic sludge blanket bioreactors treating olive mill wastewater: Flocculent and granular inocula tests, organic loading rate effect and anaerobic consortia structure

This work evaluates the performance of two upflow anaerobic sludge blanket (UASB) bioreactors and a hybrid-UASB bioreactor treating olive mill wastewater (OMW) under mesophilic conditions. The UASB bioreactor, which was inoculated with flocculent sludge (UASB-F), achieved greater operation efficiency and higher methane production rate (1.13 L CH4/LR.d) than the other bioreactors seeded with granular sludge. The hybrid-UΑSB and the second UASB bioreactor, which were inoculated with granular sludge, exhibited low performance due to the loss of granulation. It appears that OMW phenolics have negative impact on granular sludge structure and performance efficiency. Acidogenesis was mainly carried out by Clostridiales and Sporolactobacillus spp. in all bioreactors examined. Molecular data also showed that the hydrogenotroph Methanobacterium beijingense was the main methanogen in the bioreactors inoculated with granular sludge, while the UASB-F bioreactor was exclusively dominated by a novel archaeal methanogenic linkage, distantly related to the rare methanol-reducing archaeon Methanosphaera stadtmanae.

Calcium phosphate granules formation: Key to high rate of mesophilic UASB treatment of toilet wastewater

Toilet wastewater, a rich source of organic matter and nutrients, can be treated anaerobically to recover energy and resources at mesophilic conditions (35 °C) using an upflow anaerobic sludge blanket (UASB) digester. However, low organic loading rates (OLR) have often been reported, which may be attributed to the flocs biomass applied in previous studies. In the present study, CaP granules were developed in the UASB reactor during the reactor operation of 250 days, which accounted for 89.2% of the UASB sludge, and had high VSS (25.9 ± 0.3 g/L) and high methanogenesis rates (0.34 ± 0.04 g CH4-COD/(gVSS·d)). An OLR of 16.0 g/(L·d) and a hydraulic retention time (HRT) of 0.25 days, were achieved, with a total chemical oxygen demand (COD) removal rate of 75.6 ± 6.0%, and a methane production rate of 8.4 ± 0.9 g CH4-COD/(L·d). The efficiency of the hydrolysis of organic substrates ranged from 32.6 ± 2.8% to 43.4 ± 1.4%. Microbial community analysis revealed that syntrophic bacteria Syntrophus, together with diverse H2-utilizing methanogens, proliferated; and eventually resulted in a hydrogenotrophic dominant pathway in the UASB reactor. The performance, mechanism of CaP granule formation, and the application of the process were discussed in detail. The present paper provided insight of high rate biomethane production from anaerobic toilet wastewater treatment.

Inoculum origin and waste solid content influence the biochemical methane potential of olive mill wastewater under mesophilic and thermophilic conditions

The biological valorization of olive mill wastewater (OMW) is often problematic due to the characteristically high organic load and phenolic compound content of this waste stream. The present study aimed at determining the optimal conditions (i.e. temperature, solid content) for the anaerobic digestion of OMW, striving for the maximum methane yield. Therefore, inocula originating from a wastewater treatment plant and two lab-scale bioreactors treating OMW (mesophilic Up-flow Anaerobic Sludge Blanket (UASB) reactor and thermophilic Up-flow Packed Bed Reactor (UPBR)), were tested in terms of OMW degradation potential and methane yield under mesophilic and thermophilic conditions, through Biochemical Methane Potential (BMP) assays. The methane yields were in all cases higher for the raw OMW (325–472 mL CH4/g VSadded) compared to the centrifuged OMW (219–391 mL CH4/g VSadded). Moreover, the greatest biodegradability extent (94.0–98.5%) was achieved by the mesophilic sludge originating from the UASB reactor. The maximum specific methane production rate (121 mL CH4/g VSSadded∙d) was reached by the inoculum obtained from the mesophilic UASB reactor using centrifuged OMW. These results indicate that the mesophilic temperatures are optimal for the anaerobic digestion (AD) of OMW in terms of methane productivity and biodegradation potential, while no solid removal is necessary.

Biological treatment of electronic industry wastewater containing TMAH, MEA and sulfate in an UASB reactor

This study investigated the feasibility of the methanogenic treatment of electronic industry wastewater containing tetramethylammonium hydroxide (TMAH), monoethanolamine (MEA) and sulfate in a lab-scale mesophilic up-flow anaerobic sludge blanket reactor. Feeding a mixture of electronic industry wastewater and co-substrate organics to the reactor for smooth acclimatization of sludge gave complete degradation of each organics within five days. When the reactor was fed only electronic industry wastewater, total COD removal, TMAH removal and MEA removal were achieved over 80, 99 and 99%, respectively, at an organic loading rate of 11.5 kg-COD m−3 day−1. 173 mg-S L−1 of influent sulfate was almost reduced simultaneously with the COD removal. In order to evaluate performance stability, the TMAH shock load event was performed under the conditions of 11,000 mg-COD L−1 for 24 h. Inflow of high TMAH concentration inhibited TMAH degradation and sulfate reduction for more than one month, however, not MEA. The batch feeding experiment and specific activity measurement revealed degradation pathways of each organics. TMAH was degraded via methanogenic pathway without sulfate reduction, MEA was degraded via methanogenic pathway with sulfate reduction. The results indicated that methanogenic treatment was applicable to electronic industry wastewater by appropriate reactor handling.

Continuous biological removal of selenate in the presence of cadmium and zinc in UASB reactors at psychrophilic and mesophilic conditions

This study investigated the continuous biological removal of selenate [Se(VI)] in the presence of cadmium [Cd(II)] and zinc [Zn(II)] by anaerobic granular sludge in two upflow anaerobic sludge blanket (UASB) reactors operating under psychrophilic (17.5 ± 0.4 ℃) and mesophilic (30 ± 0.5 ℃) conditions for 42 and 74 days, respectively. Se(VI) and total selenium (Se) removal efficiencies reached, respectively, 99.6% and 95.0% in the UASB reactor operating at psychrophilic conditions. Cd(II) and Zn(II) removal efficiencies by the mesophilic UASB reactor reached, respectively, 99.2% and 96.2%. In the presence of Cd and/or Zn in the influent, both Se(VI) and total Se had a higher removal efficiency than when solely feeding Se(VI), both at 17.5 ℃ and 30 ℃. The lactate removal rates of the UASB reactors amounted to 1.0–1.2 mM/h. The mass balance showed 64.8%–79.5% of the supplied Se was entrapped in the biomass at the end of the experiment. The polysaccharides and protein concentrations of the extracellular polymeric substances (EPS) increased ∼3 to 5 times upon heavy metal exposure. A dramatic change in the microbial community occurred in the UASB reactors during long term operation. This study showed that UASB reactors have desirable Se(VI), Cd(II) and Zn(II) removal efficiencies both at 17.5 and 30 ℃.

Turf soil enhances treatment efficiency and performance of phenolic wastewater in an up-flow anaerobic sludge blanket reactor

Phenols are industrially generated intermediate chemicals found in wastewaters that are considered a class of environmental priority pollutants. Up-flow anaerobic sludge blanket (UASB) reactors are used for phenolic wastewater treatment and exhibit high volume loading capability, favorable granule settling, and tolerance to impact loads. Use of support materials can promote biological productivity and accelerate start-up period of UASB. In the present study, turf soil was used as a support material in a mesophilic UASB reactor for the removal of phenols in wastewater. During sludge acclimatization (45–96 days), COD and phenols in the treatments were both reduced by 97%, whereas these contents in the controls were decreased by 81% and 75%, respectively. The phenol load threshold for the turf soil UASB reactor was greater (1200 mg/L, the equivalent of COD 3000 mg/L) in comparison with the control UASB reactor (900 mg/L, the equivalent of COD 2250 mg/L) and the turf soil UASB reactor was also more resistant to shock loading. Improved sludge settling, shear resistance, and higher biological activity occurred with the turf soil UASB reactor due to the formation of large granular sludge (0.6 mm or larger) in higher relative percentages. Granular sludge size was further enhanced by the colonization of filamentous bacteria on the irregular surface of the turf soil.

Feedforward neural network model estimating pollutant removal process within mesophilic upflow anaerobic sludge blanket bioreactor treating industrial starch processing wastewater

In this a, three-layered feedforward-backpropagation artificial neural network (BPANN) model was developed and employed to evaluate COD removal an upflow anaerobic sludge blanket (UASB) reactor treating industrial starch processing wastewater. At the end of UASB operation, microbial community characterization revealed satisfactory composition of microbes whereas morphology depicted rod-shaped archaea. pH, COD, NH4+, VFA, OLR and biogas yield were selected by principal component analysis and used as input variables. Whilst tangent sigmoid function (tansig) and linear function (purelin) were assigned as activation functions at the hidden-layer and output-layer, respectively, optimum BPANN architecture was achieved with Levenberg-Marquardt algorithm (trainlm) after eleven training algorithms had been tested. Based on performance indicators such the mean squared errors, fractional variance, index of agreement and coefficient of determination (R2), the BPANN model demonstrated significant performance with R2 reaching 87%. The study revealed that, control and optimization of an anaerobic digestion process with BPANN model was feasible.

Start Up of a UASB Treating Malted Ingredient Manufacturing Wastewater

With a greater push to achieve waste management and renewable energy targets technologies such as anaerobic digestion (AD) have increased in popularity. One such technology option is the Upflow Anaerobic Sludge Blanket (UASB) reactor, these have been shown to be a particularly robust option for high strength organic wastewaters, such as those generated by the malted ingredient manufacturing industry. Despite their effectiveness they are reported to have lengthy and complex start ups due to the range of physiochemical and biological interactions influencing sludge blanket stability. This process can be sped up by seeding the plant from sludge from similar plants, however this is not always possible. This paper aims to investigate the start up of a full-scale mesophilic UASB treating malted ingredient wastewater that was initially seeded with a granular sludge treating dairy wastewater. Operational performance during the first 75 days of start up was comparable to that of a fully established plant with a COD removal efficiency in excess of 81.89% and a biogas methane concentration greater than 57.24%. During this period the plant remained operationally robust with the Organic Loading Rates (OLR) exuding the greatest influence on plant performance. Similar to operations during stable conditions key operational parameters such as HRT times, temperatures and pH did not exert a strong influence on the plant.

Modelling Biogas Fermentation from Anaerobic Digestion: Potato Starch Processing Wastewater Treated Within an Up flow Anaerobic Sludge Blanket

Herein, a modeling approach to predict biogas yield within a mesophilic (35 ± 1°C) upflow anaerobic sludge blanket (UASB) reactor treating potato starch processing wastewater (PSPW) for pollutant removal was conducted. HRTs and seven anaerobic process-related parameters viz; chemical oxygen demand (COD), ammonium (), alkalinity, total Kjeldahl Nitrogen, total phosphorus, volatile fatty acids (VFAs) and pH with average concentration of 4028.91, 110.09, 4944.67, 510.47, 45.20, 534.44 mg/L and 7.09, respectively, were used as input variables (x) to develop stochastic models for predicting biogas yield from the anaerobic digestion of PSPW. Based on the prediction accuracy of the models, it was established that, prediction of biogas yield from the UASB with the combination of COD, NH4+ and HRT, or COD, NH4+, HRT and VFAs as input variables proved more efficient as opposed to HRT, alkalinity, total Kjeldahl Nitrogen, total phosphorus and pH. Highest coefficient of determination (R2) observed was 97.29%, suggesting the efficiency of the models in making predictions. The developed models efficiencies concluded that the models could be employed to control the dynamic anaerobic process within UASBs since prediction of biogas obtained in the UASB agreed with the experimental result.

Lentimicrobium saccharophilum gen. nov., sp. nov., a strictly anaerobic bacterium representing a new family in the phylum Bacteroidetes, and proposal of Lentimicrobiaceae fam. nov.

A novel, strictly anaerobic, short rod-shaped bacterium, designated strain TBC1T, was isolated from methanogenic granular sludge in a full-scale mesophilic upflow anaerobic sludge blanket reactor treating high-strength starch-based organic wastewater. Cells of this strain were 2-4 µm long and 0.4-0.6 µm wide. They were non-motile and Gram-stain-negative. The optimum growth temperature was 30-37 °C, with a range of 20-40 °C. The optimum pH for growth was around pH 7.0, while growth occurred in a range of pH 6.5-9.0. Strain TBC1T grew chemo-organotrophically on a narrow range of carbohydrates under anaerobic conditions. Yeast extract was required for its growth. The major fermentative end products from glucose, supplemented with yeast extract, were acetate, malate, propionate, formate and hydrogen. Doubling time under optimal growth conditions was estimated to be 1 day. The DNA G+C content of strain TBC1T was 49.2 mol% as determined by HPLC. Major cellular fatty acids were C16 : 0, C18 : 0, C16 : 1ω9c and C18 : 1ω9c. Based on its 16S rRNA gene sequence, strain TBC1T was shown to represent a distinct lineage at the family level in the phylum Bacteroidetes. Among previously described species of this phylum, Mucilaginibacter boryungensis BDR-9T (Sphingobacteriaceae) displayed the highest sequence similarity (85.9 %) with strain TBC1T. Phylogenomic analyses using 38-83 single copy marker genes also supported the novelty of strain TBC1T at the family level. Based on its characteristics, strain TBC1T (=JCM 30898T=DSM 100618T) is considered to be the type strain of a novel species of a new genus, Lentimicrobium saccharophilum gen. nov., sp. nov. A new family, Lentimicrobiaceae fam. nov., is also proposed encompassing the strain and related environmental 16S rRNA gene clone sequences.

Effect of temperature on selenium removal from wastewater by UASB reactors

The effect of temperature on selenium (Se) removal by upflow anaerobic sludge blanket (UASB) reactors treating selenate and nitrate containing wastewater was investigated by comparing the performance of a thermophilic (55 °C) versus a mesophilic (30 °C) UASB reactor. When only selenate (50 μM) was fed to the UASB reactors (pH 7.3; hydraulic retention time 8 h) with excess electron donor (lactate at 1.38 mM corresponding to an organic loading rate of 0.5 g COD L−1 d−1), the thermophilic UASB reactor achieved a higher total Se removal efficiency (94.4 ± 2.4%) than the mesophilic UASB reactor (82.0 ± 3.8%). When 5000 μM nitrate was further added to the influent, total Se removal was again better under thermophilic (70.1 ± 6.6%) when compared to mesophilic (43.6 ± 8.8%) conditions. The higher total effluent Se concentration in the mesophilic UASB reactor was due to the higher concentrations of biogenic elemental Se nanoparticles (BioSeNPs). The shape of the BioSeNPs observed in both UASB reactors was different: nanospheres and nanorods, respectively, in the mesophilic and thermophilic UASB reactors. Microbial community analysis showed the presence of selenate respirers as well as denitrifying microorganisms.

Isolation and characterization of Flexilinea flocculi gen. nov., sp. nov., a filamentous, anaerobic bacterium belonging to the class Anaerolineae in the phylum Chloroflexi.

A novel obligately anaerobic bacterium, designated strain TC1T, was isolated from methanogenic granular sludge in a full-scale mesophilic upflow anaerobic sludge blanket reactor treating high-strength starch-based wastewater. Cells had a multicellular filamentous morphology, stained Gram-negative and were non-motile. The filaments were flexible, generally >100 μm long and 0.3-0.4 μm wide. Growth of the isolate was observed at 25-43 °C (optimum 37 °C) and pH 6.0-8.5 (optimum pH 7.0). Strain TC1T grew chemo-organotrophically on a range of carbohydrates under anaerobic conditions. Yeast extract was required for growth. The major fermentative end products of glucose, supplemented with yeast extract, were acetate, lactate, succinate, propionate, formate and hydrogen. Co-cultivation with the hydrogenotrophic methanogen Methanospirillum hungatei DSM 864T enhanced growth of the isolate. The DNA G+C content was determined experimentally to be 42.1 mol%. The major cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0 and iso-C17 : 0 3-OH. Based on 16S rRNA gene sequence analysis, strain TC1T belonged to the class Anaerolineae in the phylum Chloroflexi, in which Ornatilinea apprima P3M-1T was its closest phylogenetic relative (88.3 % nucleotide identity). Phylogenomic analyses using 38 and 83 single-copy marker genes also supported the novelty of strain TC1T at least at the genus level. Based on phylogenetic, genomic and phenotypic characteristics, we propose that strain TC1T represents a novel species of a new genus, for which we suggest the name Flexilinea flocculi gen. nov., sp. nov. The type strain of Flexilinea flocculi is strain TC1T ( = JCM 30897T = CGMCC 1.5202T).

High organic loading treatment for industrial molasses wastewater and microbial community shifts corresponding to system development

Molasses wastewater contains high levels of organic compounds, cations, and anions, causing operational problems for anaerobic biological treatment. To establish a high organic loading treatment system for industrial molasses wastewater, this study designed a combined system comprising an acidification tank, a thermophilic multi-stage (MS)-upflow anaerobic sludge blanket (UASB) reactor, mesophilic UASB reactor, and down-flow hanging sponge reactor. The average total chemical oxygen demand (COD) and biochemical oxygen demand removal rates were 85%±3% and 95%±2%, respectively, at an organic loading rate of 42kgCODcrm−3d−1 in the MS-UASB reactor. By installation of the acidification tank, the MS-UASB reactor achieved low H2-partial pressure. The abundance of syntrophs such as fatty acid-degrading bacteria increased in the MS-UASB and 2nd-UASB reactors. Thus, the acidification tank contributed to maintaining a favorable environment for syntrophic associations. This study provides new information regarding microbial community composition in a molasses wastewater treatment system.

Evaluation of performance in a combined UASB and aerobic contact oxidation process treating acrylic wastewater

The lab-scale and full-scale performance of a combined mesophilic up-flow anaerobic sludge blanket (UASB) and aerobic contact oxidation (ACO) process for treating acrylic wastewater was studied. During lab-scale experiment, the overwhelmed volumetric load for UASB was above 6 kg chemical oxygen demand (COD) ·(m−3·d−1) since COD removal efficiency dropped dramatically from 73% at 6 kg COD·(m−3·d−1) to 61% at 7 kg COD·(m−3·d−1) and 53% at 8 kg COD·(m−3·d−1). Further results showed that an up-flow fluid velocity of 0.5 m h−1 for UASB obtained a highest COD removal efficiency of 75%, and the optimum COD volumetric load for the corresponding ACO was 1.00 kg COD·(m−3·d−1). Based on the configuration of the lab-scale experiment, a full-scale application with an acrylic wastewater treatment capacity of 8 m3 h−1 was constructed and operated at a volumetric load of 5.5 kg COD·(m−3·d−1), an up-flow fluid velocity of 0.5 m h−1 for UASB and a volumetric load of 0.9 kg COD·(m−3·d−1) for ACO; and the final effluent COD was around 740 mg L−1. The results suggest that a combined UASB–ACO process is promising for treating acrylic wastewater.

Bacteroides luti sp. nov., an anaerobic, cellulolytic and xylanolytic bacterium isolated from methanogenic sludge

A mesophilic, anaerobic, cellulolytic and xylanolytic strain, UasXn-3T, was isolated from anaerobic granular sludge in a mesophilic upflow anaerobic sludge blanket reactor, which was used to treat municipal sewage. The cells were Gram-stain-negative, non-motile, and non-spore-forming rods. The optimal temperature for growth was 37-40 °C and the optimal pH for growth was pH 6.5-7.0. Strain UasXn-3T could grow on several polysaccharides and sugars, including cellulose, cellobiose, xylan, xylose, glucose, fructose, arabinose, mannose, raffinose, trehalose and starch. The DNA G+C content was 44.4 mol%. On the basis of comparative 16S rRNA gene sequence analysis, strain UasXn-3T was identified as a member of the genus Bacteroides and most closely related to Bacteroides oleiciplenus, B. intestinalis, B. cellulosilyticus and B. graminisolvens (sequence similarities of 91.3-91.6%). Since the genetic and phenotypic properties suggest that strain UasXn-3T represents a novel species, we propose the name Bacteroides luti sp. nov. The type strain is UasXn-3T (=JCM 19020T=DSM 26991T).

Development of Ann-Based Models to Predict Biogas and Methane Productions in Anaerobic Treatment of Molasses Wastewater

Two three-layer artificial neural network (ANN) models were respectively developed to predict biogas and methane production rates in a pilot-scale mesophilic up-flow anaerobic sludge blanket (UASB) reactor treating molasses wastewater. Eight process-related variables such as volumetric organic loading rate (OLR), influent and effluent pH, operating temperature, influent and effluent alkalinity, effluent chemical oxygen demand (COD), and volatile fatty acid (VFA) concentrations were selected for the implementation of an artificial intelligence-based approach. A tangent sigmoid transfer function (tansig) at the hidden layer and a linear transfer function (purelin) at the output layer were conducted for the proposed ANN models. Several benchmark comparisons were conducted to obtain an optimal algorithm for training the network. After backpropagation training combined with principal component analysis (PCA), the scaled conjugate gradient algorithm (trainscg) was found as the best of the 11 training algorithms. The number of neurons in the hidden layer was optimized as nine and 12 with the minimum mean squared errors (MSE) of 0.06238 and 0.06488, respectively, for the estimation of biogas and methane production rates. ANN-predicted results were also compared to the outputs of two non-linear regression models by means of several statistical indicators, such as determination coefficient (R2), unsystematic root mean-square error (RMSEU), index of agreement (IA), and fractional variance (FV). Computational results clearly demonstrated that, compared to the conventional multiple regression-based methodology, the proposed ANN-based models produced smaller deviations and exhibited superior predictive accuracy with satisfactory determination coefficients of about 0.935 and 0.924, respectively, for the forecasts of biogas and methane production rates.

Bioaugmentation with an acetate-oxidising consortium as a tool to tackle ammonia inhibition of anaerobic digestion

Ammonia is the major inhibitor of anaerobic digestion (AD) process in biogas plants. In the current study, the bioaugmentation of the ammonia tolerant SAO co-culture (i.e. Clostridium ultunense spp. nov. in association with Methanoculleus spp. strain MAB1) in a mesophilic up-flow anaerobic sludge blanket (UASB) reactor subjected to high ammonia loads was tested. The co-cultivation in fed-batch reactors of a fast-growing hydrogenotrophic methanogen (i.e. Methanoculleus bourgensis MS2(T)) with the SAO co-culture was also investigated. Results demonstrated that bioaugmentation of SAO co-culture in a UASB reactor was not possible most likely due to the slow maximum growth rate (μmax=0.007 h(-1)) of the culture caused by the methanogenic partner. The addition of M. bourgensis to SAO led to 42% higher growth rate (μmax=0.01 h(-1)) in fed-batch reactors. This indicates that methanogens were the slowest partners of the SAO co-culture and therefore were the limiting factor during bioaugmentation in the UASB reactor.