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Anaerobic digestion foaming is a common operation problem in biogas plants with negative impacts on the biogas plants economy and environment. A survey of 16 Danish full-scale biogas plants on foaming problems revealed that most of them had experienced foaming in their processes up to three times per year. Foaming incidents often lasted from one day to three weeks, causing 20-50% biogas production loss. One foaming case at Lemvig biogas plant has been investigated and the results indicated that the combination of feedstock composition and mixing pattern of the reactor was the main cause of foaming in this case. Moreover, no difference in bacterial communities between the foaming and non-foaming reactors was observed, showing that filamentous bacteria were not the main reason for foaming in this case. [ABSTRACT FROM AUTHOR]

This study investigates the co-digestion of hydrothermally pretreated empty fruit bunches (EFB) at 190 °C for 5 min (HTP190-EFB) with decanter cake (DC) to improve biogas production in high solid anaerobic digestion (HSAD). The HTP190-EFB exhibited a 67.98 % reduction in total solids, along with the production of 0.89 g/L of sugar, 2.39 g/L of VFA, and 0.56 g/L of furfural in the liquid fraction. Co-digestion of HTP190-EFB with DC at mixing ratios of 5, 10, and 15 %w/v demonstrated improved methane yields and process stability compared to mono-digestion of HTP190-EFB. The highest methane yield of 372.69 mL CH 4 /g-VS was achieved in the co-digestion with 5 %w/v DC, representing a 15 % increase compared to digestion of HTP190-EFB (324.30 mL CH 4 /g-VS) alone. Synergistic effects were quantified, with the highest synergistic methane yield of 77.65 mL CH 4 /g-VS observed in the co-digestion with 5 %w/v DC. Microbial community analysis revealed that co-digestion of hydrothermally pretreated EFB with decanter cake promoted the growth of Clostridium sp., Lactobacillus sp., Fibrobacter sp., Methanoculleus sp., and Methanosarcina sp., contributing to enhanced biogas production compared to mono-digestion of pretreated EFB. Energy balance analysis revealed that co-digestion of HTP190-EFB with DC resulted in a total net energy of 599.95 kW, 52 % higher than mono-digestion of HTP190-EFB (394.62 kW). Economic analysis showed a shorter return on investment for the co-digestion system (0.86 years) compared to the mono-digestion of HTP190-EFB (1.02 years) and raw EFB (2.69 years). The co-digestion of HTP190-EFB with 5 %w/v DC offers a promising approach to optimize methane yield, process stability, and economic feasibility, supporting the palm oil industry for producing renewable energy and sustainable waste management., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

A novel thermotolerant caproic acid-producing bacterial strain, Clostridium M1NH, was successfully isolated from sewage sludge. Ethanol and acetic acid at a molar ratio of 4:1 proved to be the optimal substrates, yielding a maximum caproic acid production of 3.5 g/L. Clostridium M1NH exhibited remarkable tolerance to high concentrations of ethanol (up to 5% v/v), acetic acid (up to 5% w/v), and caproic acid (up to 2% w/v). The strain also demonstrated a wide pH tolerance range (pH 5.5-7.5) and an elevated temperature optimum between 35 and 40 °C. Phylogenetic analysis based on 16S rRNA gene sequences revealed that Clostridium M1NH shares a 98% similarity with Clostridium luticellarii DSM 29923  T . The robustness of strain M1NH and its efficient caproic acid production from low-cost substrates highlight its potential for sustainable bio-based chemical production. The maximum caproic acid yield achieved by Clostridium M1NH was 1.6-fold higher than that reported for C. kluyveri under similar fermentation conditions. This study opens new avenues for valorizing waste streams and advancing a circular economy model in the chemical industry., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

This research performed cellulase production by Aspergillus fumigatus A4112 and evaluated its potential use in palm oil mill effluent (POME) hydrolysis to recover oil simultaneously with the generation of fermentable sugar useful for biofuel production under non-sterilized conditions. Empty fruit bunch (EFB) without pretreatment was used as carbon source. The combination of nitrogen sources facilitated CMCase production. The maximum activity (3.27 U/mL) was obtained by 1.0 g/L peptone and 1.5 g/L (NH 4 ) 2 SO 4 and 20 g/L EFB at 40 °C for 7 days. High level of FPase activity (39.51 U/mL) was also obtained. Interestingly, the enzyme retained its cellulase activities more than 60% at ambient temperature over 15 days. In enzymatic hydrolysis, Triton X-100 was an effective surfactant to increase total oil recovery in the floating form. High yield of reducing sugar (50.13 g/L) and 21% (v/v) of floating oil was recoverable at 65 °C for 48 h. Methane content of the raw POME increased from 41.49 to 64.94% by using de-oiled POME hydrolysate which was higher than using the POME hydrolysate (59.82%). The results demonstrate the feasibility of the constructed process for oil recovery coupled with a subsequent step for methane yield enhancement in biogas production process that benefits the palm oil industry.

This study aimed to convert CO 2 in biogas into acetic acid using immobilized Clostridium thailandense cells on various support materials, including activated carbon, expanded clay, and coir. Immobilized cells and free cells were evaluated for their CO 2 conversion ability into acetic acid using H 2 as an electron donor at an H 2 to CO 2 in biogas ratio of 2:1 (v/v), 30 °C, 150 rpm. Results showed that immobilized cells on activated carbon increased CH 4 content to 96.9% (v/v), and acetic acid production to 15.65 mmol/L within 96 h. These values outperformed free cells. The activated carbon-immobilized cells could be reused two times without losing efficacy in the purification of biogas and acetic acid production. This work indicates that using the immobilized cells offers a sustainable approach to biogas upgrading, reducing the environmental footprint of biogas production by increasing its energy content and purity., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

This study aimed at investigating the biohydrogen and biomethane potential of co-digestion from palm oil mill effluent (POME) and concentrated latex wastewater (CLW) in a two-stage anaerobic digestion (AD) process under thermophilic (55 ± 3 °C) and at an ambient temperature (30 ± 3 °C) conditions, respectively. The batch experiments of POME:CLW mixing ratios of 100:0, 70:30, 50:50, 30:70, and 0:100 was investigated with the initial loadings at 10 g-VS/L. The highest hydrogen yield of 115.57 mLH 2 /g-VS was obtained from the POME: CLW mixing ratio of 100:0 with 29.0 of C/N ratio. While, the highest subsequent methane production yield of 558.01 mLCH 4 /g-VS was achieved from hydrogen effluent from POME:CLW mixing ratio of 70:30 0 with 21.8 of C/N ratio. This mixing ratio revealed the highest synergisms of about 9.21% and received maximum total energy of 19.70 kJ/g-VS. Additionally, continuous hydrogen and methane production were subsequently performed in a series of continuous stirred tank reactor (CSTR) and up-flow anaerobic sludge blanket reactor (UASB) to treat the co-substate. The results indicated that the highest hydrogen yield of POME:CLW mixing ratio at 70:30 of 95.45 mL-H 2 /g-VS was generated at 7-day HRT, while methane production was obtained from HRT 15 days with a yield of 204.52 mL-CH 4 /g-VS. Thus, the study indicated that biogas production yield of CLW could be enhanced by co-digesting with POME. In addition, the two-stage AD model under anaerobic digestion model no. 1 (ADM-1) framework was established, 9.10% and 2.43% of error fitting of hydrogen and methane gas between model simulation data and experimental data were found. Hence, this research work presents a novel approach for optimization and feasibility for co-digestion of POME with CLW to generate mixed gaseous biofuel potentially., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Despite the significant removal of chemical oxygen demand (COD) by anaerobic digestion, anaerobically-treated palm oil mill effluent (POME) still contains tannins and other phenolic compounds, resulting in residual COD and a brownish color. In this study, we investigated the removal of tannins from anaerobically treated POME using protein-tannin complexation in conjunction with electrocoagulation. The amino acid composition of the protein, aqueous pH, and protein: tannin ratios were found to be important parameters affecting the tannin removal efficiency. Pig blood protein was superior to casein protein in removing tannins, possibly because it had aspartic acid as the major amino acid component. At an optimal condition with a pig blood protein: tannin ratio of 0.33 (w/w), a current density of 30 mA/cm 2 , pH 5, and an electrolysis time of 10 min, the removals of tannins, COD, and color were 93%, 96%, and 97%, respectively., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides, Ruminiclostridium, Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38-56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29-42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production., (© 2023. The Author(s).)

High-strength waste activated sludge (WAS) and greasy sludge (GS) were largely generated from canned tuna processing. This study reports the performance of the two-stage anaerobic process for co-digesting WAS and GS. Various WAS:GS mixing ratios of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:00 (volatile solids (VS) basis) were investigated in batch acidogenic stage at ambient (30 °C ± 3 °C), 55 °C, and 60 °C temperatures. Subsequently, the effluents from the first stage were used to produce methane in the second methanogenic stage at an ambient temperature. The highest methane yield of 609 mL CH 4 /g-VS added was achieved using acidogenic effluents generated from a WAS:GS mixing ratio of 40:60 at an ambient temperature. The first-order kinetic constants (k) for the first (k 1 ) and second (k 2 ) stages were subsequently estimated to be 0.457 d -1 and 0.139 d -1 , respectively. The obtained k constants were further used to predict the hydraulic retention time (HRT) for the two continuously stirred tank reactors (CSTR) in series. Consequently, the calculated 4-day HRT and 20-day HRT for 50-L CSTR 1 and 250-L CSTR 2 , respectively, were used to operate the continuous two-stage process at an ambient temperature by feeding with a 40:60-WAS:GS mixing ratio. A satisfactory methane yield of 470-mL CH 4 /g-VS along with 75% chemical oxygen demand (COD) removal was generated. Furthermore, the predicted methane yield of 450-mL CH 4 /g-VS obtained from the simple kinetic CSTR model resembled the experimental yield with 96% accuracy. The obtained experimental results demonstrate that WAS and GS co-digestion could be successfully accomplished using a practical two-stage anaerobic process operated at an ambient temperature., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Waste-activated sludge (WAS) and greasy sludge (GS) discharged from the canned tuna industry are considerably characterized as harsh organic wastes to be individually treated by using traditional anaerobic digestion. This study was attempted to anaerobically co-digest WAS and GS in continuous pilot scale two-stage process, comprising the first 50 L continuous stir tank reactor (CSTR 1 ) and the second 250 L continuous stir tank reactor (CSTR 2 ). The two-stage co-digesting operation of dewatered WAS:GS ratio of 0.4:1 (g-VS) at ambient temperature with the organic loading rate (OLR) of 12.6 ± 0.75 g-VS/L·d and 2.26 ± 0.13 g-VS/L·d, corresponding to 3-day and 17-day hydraulic retention time (HRT) for the first and second stage, respectively generated highest methane production rate of 957 ± 86 mL-CH 4 /L·d, corresponding to methane yield of 423.4 ± 36 mL-CH 4 /g-VS. Organic removal efficiency obtained was around 67.5% on COD basis. The microbial diversity was depended on the process's activity. Bacteria were mostly detected in the CSTR 1 , dominating with the phylum Firmicutes and Proteobacteria, whereas genus Methanosaeta archaea were found dominantly in the CSTR 2 . The economic analysis of process shows payback period (PBP), internal rate of return (IRR), and net present value (NPV) of 3 years, 30%, and 250,177 USD, respectively. This study demonstrated the potential approach to applying the two-stage anaerobic co-digestion process to stabilize both WAS and GS along with generating valuable bioenergy carriers., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Some species of the genus Clostridium are efficient acetate producers and have been deemed useful for upgrading industrial biogas. An acetogenic, strictly anaerobic, Gram-stain-positive, subterminal endospore-forming bacterium designated strain PL3 T was isolated from peatland soil enrichments with H 2 and CO 2 . Cells of strain PL3 T were 0.8-1.0×4.0-10.0 µm in size and rod-shaped. Growth of strain PL3 T occurred at pH 6.0-7.5 (optimum, pH 7.0), at 20-40 °C (optimum, 30 °C) and with 0-1.5 % (w/v) NaCl (optimum, 0.5%). Biochemical analyses revealed that strain PL3 T metabolized lactose, maltose, raffinose, rhamnose, lactic acid, sorbitol, arabinose and glycerol. Acetic acid was the predominant metabolite under anaerobic respiration with H 2 /CO 2 . The major cellular fatty acids were C 16 : 0 , C 16 : 1 cis 9 and C 17 : 0 cyc. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, aminolipid and aminophospholipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PL3 T belongs to the genus Clostridium with the highest sequence similarity to Clostridium aciditolerans DSM 17425 T (98.6 %) followed by Clostridium nitrophenolicum (97.8 %). The genomic DNA G+C content of strain PL3 T was 31.1 mol%.The genomic in silico DNA-DNA hybridization value between strain PL3 T and C. aciditolerans DSM 17425 T was 25.1 %, with an average nucleotide identity of 80.2 %. Based on phenotypic, chemotaxonomic and phylogenetic differences, strain PL3 T was suggested to represent a novel species of the genus Clostridium , for which the name Clostridium thailandense sp. nov. is proposed. The type strain is PL3 T (=DSM 111812 T =TISTR 2984 T ).

Background: Full-scale biogas production from palm oil mill effluent (POME) was inhibited by low pH and highly volatile fatty acid (VFA) accumulation. Three strategies were investigated for recovering the anaerobic digestion (AD) imbalance on biogas production, namely the dilution method (tap water vs. biogas effluent), pH adjustment method (NaOH, NaHCO 3 , Ca(OH) 2 , oil palm ash), and bioaugmentation (active methane-producing sludge) method. The highly economical and feasible method was selected and validated in a full-scale application., Results: The inhibited sludge from a full-scale biogas reactor could be recovered within 30-36 days by employing various strategies. Dilution of the inhibited sludge with biogas effluent at a ratio of 8:2, pH adjustment with 0.14% w/v NaOH, and 8.0% w/v oil palm ash were considered to be more economically feasible than other strategies tested (dilution with tap water, or pH adjustment with 0.50% w/v Ca(OH) 2 , or 1.25% NaHCO 3 and bioaugmentation) with a recovery time of 30-36 days. The recovered biogas reactor exhibited a 35-83% higher methane yield than self-recovery, with a significantly increased hydrolysis constant (k H ) and specific methanogenic activity (SMA). The population of Clostridium sp., Bacillus sp., and Methanosarcina sp. increased in the recovered sludge. The imbalanced full-scale hybrid cover lagoon reactor was recovered within 15 days by dilution with biogas effluent at a ratio of 8:2 and a better result than the lab-scale test (36 days)., Conclusion: Dilution of the inhibited sludge with biogas effluent could recover the imbalance of the full-scale POME-biogas reactor with economically feasible and high biogas production performance., Competing Interests: The authors declare there are no competing interests., (©2021 Wongfaed et al.)

Empty fruit bunches (EFB) have low biodegradability and restrict their commercial utilization in biogas plants. Integration of straw mushroom (Volvariella volvacea) cultivation as a function of bio-pretreatment on EFB to improve biodegradability and methane production by solid-state anaerobic digestion (SS-AD) was investigated. The mushroom yield was 47.3 kg·tonne -1 EFB with remaining weight in spent mushroom-EFB (S-mEFB) of 82%. The cellulose, hemicellulose, and lignin of EFB were degraded by 3.3%, 21.3%, and 17.6%, respectively, with an increased surface area of S-mEFB. The biodegradability of S-mEFB (62.7%) was 2 times higher than raw EFB (33.5%) with the highest methane yield and production of 281 mL CH 4 ·g -1 VS and 50.6 m 3 ·tonne -1 S-mEFB, respectively. The co-digestion of S-mEFB with 5% v/w POME had highest methane yield of 405 mL CH 4 ·g -1 VS with biodegradability of 90.8%. Integrating straw mushroom cultivation with SS-AD is a promising strategy for achieving an environmentally friendly and economically feasible process., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Anaerobic digestion (AD) is a suitable process for treating high moisture MSW with biogas and biofertilizer production. However, the low stability of AD performance and low methane production results from high moisture MSW due to the fast acidify of carbohydrate fermentation. The effects of organic loading and incineration fly ash addition as a pH adjustment on methane production from high moisture MSW in the single-stage AD and two-stage AD processes were investigated., Results: Suitable initial organic loading of the single-stage AD process was 17 gVS L -1 at incineration fly ash (IFA) addition of 0.5% with methane yield of 287 mL CH 4 g -1 VS. Suitable initial organic loading of the two-stage AD process was 43 gVS L -1 at IFA addition of 1% with hydrogen and methane yield of 47.4 ml H 2 g -1 VS and 363 mL CH 4 g -1 VS, respectively. The highest hydrogen and methane production of 8.7 m 3 H 2 ton -1 of high moisture MSW and 66.6 m 3 CH 4 ton -1 of high moisture MSW was achieved at organic loading of 43 gVS L -1 at IFA addition of 1% by two-stage AD process. Biogas production by the two-stage AD process enabled 18.5% higher energy recovery than single-stage AD. The 1% addition of IFA into high moisture MSW was useful for controlling pH of the two-stage AD process with enhanced biogas production between 87-92% when compared to without IFA addition. Electricity production and energy recovery from MSW using the coupled incineration with biogas production by two-stage AD process were 9,874 MJ ton -1 MSW and 89%, respectively., Conclusions: The two-stage AD process with IFA addition for pH adjustment could improve biogas production from high moisture MSW, as well as reduce lag phase and enhance biodegradability efficiency. The coupled incineration process with biogas production using the two-stage AD process was suitable for the management of MSW with low area requirement, low greenhouse gas emissions, and high energy recovery., Competing Interests: The authors declare there are no competing interests, (©2020 Markphan et al.)

Acceleration of the anaerobic digestion (AD) process is crucial to achieving energy-efficient recycling of organic wastes. Hydrochar is produced by hydrothermal liquefaction of biomass, yet its application in the AD process is rarely reported. The present study showed that sewage sludge-derived hydrochar (SH) enhanced the methane production rate of glucose by 37%. SH increased the methane production rate from acetate but did not affect acidification and the methane production rate from H 2 /CO 2 . SH enhanced hydrogenotrophic methanogenesis, which could be due to direct interspecies electron transfer (DIET) by converting H + , e - , and CO 2 to methane. Trichococcus and Methanosaeta were dominant in the AD process with SH. Label-free proteomic analysis showed Methanosaeta was involved in DIET as reflected by the up-regulation of proteins involved in hydrogenotrophic methanogenesis. Hydrochars derived from corn straw (CH), Enteromorpha algae (EH), and poplar wood (PH), as well as activated carbon (AC), were also tested in the AD process. SH, CH, and EH obviously increased the methane production rates, which were 39%, 15%, and 20% higher than the control experiment, respectively. It was neither electrical conductivity nor the total redox property of hydrochars and AC but the abundances of surface oxygen-containing functional groups that correlated to the methane production rates.

Background: The co-fermentation of syngas (mainly CO, H 2 and CO 2 ) and different concentrations of carbohydrate/protein synthetic wastewater to produce volatile fatty acids (VFAs) was conducted in the present study., Results: It was found that co-fermentation of syngas with carbohydrate-rich synthetic wastewater could enhance the conversion efficiency of syngas and the most efficient conversion of syngas was obtained by co-fermentation of syngas with 5 g/L glucose, which resulted in 25% and 43% increased conversion efficiencies of CO and H 2 , compared to syngas alone. The protein-rich synthetic wastewater as co-substrate, however, had inhibition on syngas conversion due to the presence of high concentration of NH 4 + -N (> 900 mg/L) produced from protein degradation. qPCR analysis found higher concentration of acetogens, which could use CO and H 2 , was present in syngas and glucose co-fermentation system, compared to glucose solo-fermentation or syngas solo-fermentation. In addition, the known acetogen Clostridium formicoaceticum , which could utilize both carbohydrate and CO/H 2 was enriched in syngas solo-fermentation and syngas with glucose co-fermentation. In addition, butyrate was detected in syngas and glucose co-fermentation system, compared to glucose solo-fermentation. The detected n -butyrate could be converted from acetate and lactate/ethanol which produced from glucose in syngas and glucose co-fermentation system supported by label-free quantitative proteomic analysis., Conclusions: These results demonstrated that the co-fermentation with syngas and carbohydrate-rich wastewater could be a promising technology to increase the conversion of syngas to VFAs. In addition, the syngas and glucose co-fermentation system could change the degradation pathway of glucose in co-fermentation and produce fatty acids with longer carbon chain supported by microbial community and label-free quantitative proteomic analysis. The above results are innovative and lead to achieve effective conversion of syngas into VFAs/longer chain fatty acids, which would for sure have a great interest for the scientific and engineering community. Furthermore, the present study also used the combination of high-throughput sequencing of 16S rRNA genes, qPCR analysis and label-free quantitative proteomic analysis to provide deep insights of the co-fermentation process from the taxonomic and proteomic aspects, which should be applied for future studies relating with anaerobic fermentation., Competing Interests: Competing interestsThe authors declare that they have no competing interests., (© The Author(s) 2020.)

Biogas production of palm oil mill effluent (POME) and empty fruit bunches (EFB) was performed by coupled liquid (L-AD) and solid-state (SS-AD) anaerobic digestion processes. POME was fed to L-AD digester, while mixed of effluent from L-AD and EFB was fed to SS-AD digester. The maximum overall methane production of 60.9 m 3 -CH 4 ·ton -1 waste was obtained at an optimal hydraulic retention time of 30 days and an organic loading rate of 1.66 gVS·L -1 -reactor·d -1 for L-AD and 6.03 gVS·L -1 -reactor·d -1 for SS-AD with L-AD effluent recycling rate of 16.7 mL·L -1 -reactor·d -1 . The bacterial community in the L-AD reactor was different from the SS-AD reactor, while the archaeal community was similar in both reactors. Synergistaceae, Caldicoprobacteraceae and Lachnospiraceae were increased in the SS-AD reactor. Coupling L-AD and SS-AD is able to increase energy production by 29% and 71% compared to the L-AD and SS-AD alone, respectively, with no outsource SS-AD inoculum required., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The critical challenge of hydrothermal liquefaction (HTL) for bio-oil production from biomass is the production of large amounts of aqueous products (HTL-AP) with high organic contents. The present study investigated the anaerobic digestion (AD) performances of HTL-AP under both thermophilic and mesophilic conditions, and molecular and metabolic analysis were conducted to provide insights into the different performances. The results showed that thermophilic AD had lower COD removal efficiency compared to mesophilic AD (45.0% vs. 61.6%). Liquid chromatography coupled with organic carbon detection and organic nitrogen (LC-OCD-OND) analysis showed that both high molecular weight (HMW) and low molecular weight (LMW) compounds were degraded to some extent and more LMW acids (LMWA) and recalcitrant aromatic compounds were degraded in the mesophilic reactor, which was the main reason of higher COD removal efficiency. Phenyl compounds (e.g. phenol and 2 methoxyphenol), furans and pyrazines were the recalcitrant chemicals detected through GC-MS analysis. Fourier transform ion cyclone resonance mass spectrometry (FT-ICR-MS) analysis demonstrated the complexity of HTL-AP and the proportions of phenolic or condensed aromatic compounds increased especially in the thermophilic effluents. Metabolites analysis showed that the reasons contributing to the differences of mesophilic and thermophilic AD were not only related to the degradation of organic compounds (e.g. benzoate degradation via CoA ligation) in HTL-AP but also related to the microbial autogenesis (e.g. fatty acid biosynthesis) as well as the environmental information processing. In addition, the enrichment of Mesotoga, responsible for the high degradation efficiency of LMWA, and Pelolinea, involved in the degradation of phenyl compounds, were found in mesophilic reactor, which was consistent with higher removal of corresponding organics., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hydrothermal liquefaction of sewage sludge to produce bio-oil and hydro-char unavoidably results in the production of high-strength organic wastewater (HTLWW). However, anaerobic digestion (AD) of HTLWW generally has low conversion efficiency due to the presence of complex and refractory organics. The present study showed that granular activated carbon (GAC) promoted the AD of HTLWW in continuous experiments, resulting in the higher methane yield (259 mL/g COD) compared to control experiment (202 mL/g COD). It was found that GAC increased the activities of both aceticlastic and hydrogenotrophic methanogens. The molecular transformation of organics in HTLWW was further analyzed. It was shown GAC promoted the degradation of soluble microbial by-products, fulvic- and humic-like substances as revealed by 3-dimensional fluorescence excitation-emission matrix (3D-EEM) analysis. Gas chromatography mass spectrometry (GC-MS) analysis showed that GAC resulted in the higher degradation of N-heterocyclic compounds, acids and aromatic compounds and less production of new organic species. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis also showed that GAC promoted the degradation of nitrogenous organics. In addition, it was shown that GAC improved the removal of less oxidized, higher nitrogen content, and higher double bond equivalent (DBE) organic compounds. Microbial analysis showed that GAC not only increased the microbial concentration, but also enriched more syntrophic bacteria (e.g., Syntrophorhabdus and Synergistes), which were capable of degrading a wide range of different organics including nitrogenous and aromatic organics. Furthermore, profound effects on the methanogens and the enrichment of Methanothrix instead of Methanosarcina were observed. Overall, the present study revealed the molecular transformation and microbial mechanism in the AD of HTLWW with the presence of GAC., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Thermotolerant cellulolytic consortium for improvement biogas production from oil palm empty fruit bunches (EFB) by prehydrolysis and bioaugmentation strategies was investigated via solid-state anaerobic digestion (SS-AD). The prehydrolysis EFB with Clostridiaceae and Lachnospiraceae rich consortium have maximum methane yield of 252 and 349 ml CH 4 g -1 VS with total EFB degradation efficiency of 62% and 86%, respectively. Clostridiaceae and Lachnospiraceae rich consortium augmentation in biogas reactor have maximum methane yield of 217 and 85.2 ml CH 4 g -1 VS with degradation efficiency of 42% and 16%, respectively. The best improvement of biogas production was achieved by prehydrolysis EFB with Lachnospiraceae rich consortium with maximum methane production of 113 m 3 CH 4 tonne -1 EFB. While, Clostridiaceae rich consortium was suitable for augmentation in biogas reactor with maximum methane production of 70.6 m 3 CH 4 tonne -1 EFB. Application of thermotolerant cellulolytic consortium into the SS-AD systems could enhance biogas production of 3-11 times., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Thermoanaerobacterium sp. strain PSU-2 was isolated from thermophilic hydrogen producing reactor and subjected to draft genome sequencing on 454 pyrosequencing and annotated on RAST. The draft genome sequence of strain PSU-2 contains 2,552,497 bases with an estimated G + C content of 35.2%, 2555 CDS, 8 rRNAs and 57 tRNAs. The strain had a number of genes responsible for carbohydrates metabolic, amino acids and derivatives, and protein metabolism of 17.7%, 14.39% and 9.81%, respectively. Strain PSU-2 also had gene responsible for hydrogen biosynthesis as well as the genes related to Ni-Fe hydrogenase. Comparative genomic analysis indicates strain PSU-2 shares about 94% genome sequence similarity with Thermoanaerobacterium xylanolyticum LX-11. The nucleotide sequence of this draft genome was deposited into DDBJ/ENA/GenBank under the accession MSQD00000000.

Background and Objective: Toxic nitrogen compounds are one cause decreasing of shrimp production and water pollution. Indigenous Halomonas spp., isolated from Pacific white shrimp farm are benefitted for saline ammonium waste water treatment. This study aimed to isolate the heterotrophic-halophilic Halomonas spp. and investigate their ammonium removal efficiency., Materials and Methods: Halomonas spp., were isolated by culturing of samples collected from shrimp farm into modified Pep-Beef-AOM medium. Ammonium converting ability was tested and monitored by nitrite reagent. Ammonium removal efficiency was measured by the standard colorimetric method. Identification and classification of Halomonas spp., were studied by morphological, physiological and biochemical characteristics as well as molecular information., Results: There were 5 strains of heterotrophic-halophilic nitrifying bacteria including SKNB2, SKNB4, SKNB17, SKNB20 and SKNB22 were isolated. The identification result based on 16S rRNA sequence analysis indicated that all 5 strains were Halomonas spp., with sequence similarity values of 91-99 %. Ammonium removal efficiency of all strains showed a range of 23-71%. The production of nitrite was low detected of 0.01-0.15 mg-N L-1, while the amount of nitrate was almost undetectable., Conclusion: This might suggest that the indigenous Halomonas spp., as nitrifying bacteria involved biological nitrification process for decreasing and transforming of ammonia. Due to being heterotrophic, halophilic and ammonium removing bacteria, these Halomonas spp., could be developed for use in treatment of saline ammonium waste water.

This study investigated the improvement of biogas production from solid-state anaerobic digestion (SS-AD) of oil palm biomass by optimizing of total solids (TS) contents, feedstock to inoculum (F:I) ratios and carbon to nitrogen (C:N) ratios. Highest methane yield from EFB, OPF and OPT of 358, 280 and 324m(3)CH4ton(-1)VS, respectively, was achieved at TS content of 16%, C:N ratio of 30:1 and F:I ratio of 2:1. The main contribution to methane from biomass was the degradation of cellulose and hemicellulose. The highest methane production of 72m(3)CH4ton(-1) biomass was achieved from EFB. Bacteria community structure in SS-AD process of oil palm biomass was dominated by Ruminococcus sp. and Clostridium sp., while archaea community was dominated by Methanoculleus sp. Oil palm biomass has great potential for methane production via SS-AD., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Anaerobic digestion by two-stage process, containing hydrogen-producing (acidogenic) first stage and methanogenic second stage, has been proposed to degrade substrates which are difficult to be treated by single stage anaerobic digestion process. This research was aimed to evaluate the bio-hydrogen and the bio-methane potentials (BHP and BMP) of skim latex serum (SLS) by using sequential batch hydrogen and methane cultivations at thermophilic conditions (55°C) and with initial SLS concentrations of 37.5-75.0% (v/v). The maximal 1.57 L H2/L SLS for BHP and 12.2L CH4/L SLS for BMP were both achieved with 60% (v/v) SLS. The dominant hydrogen-producing bacteria in the H2 batch reactor were Thermoanaerobacterium sp. and Clostrdium sp. Meanwhile, the CH4 batch reactor was dominated by the methanogens Methanosarcina mazei and Methanothermobacter defluvii. The results demonstrate that SLS can be degraded by conversion to form hydrogen and methane, waste treatment and bioenergy production are thus combined., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The newly isolated extreme thermophilic ethanologen Thermoanaerobacter pentosaceus was immobilized in different support materials in order to improve its ethanol production ability. In batch fermentation, a maximum ethanol yield of 1.36 mol mol(-1) consumed sugars was obtained by T. pentosaceus immobilized on rapeseed straw. Additionally, immobilized T. pentosaceus' ethanol production was improved by 11% in comparison to free cells. In continuous mode, it was shown that hydraulic retention time (HRT) affected ethanol yield, and a dramatic shift from ethanol to acetate and lactate production occurred at an HRT of 6 h. The maximum ethanol yield and concentration, 1.50 mol mol(-1) consumed sugars and 12.4 g l(-1), were obtained with an HRT of 12 h. The latter represented an improvement of 60% in relation to previously obtained results. This indicates that immobilization of T. pentosaceus is an effective strategy to improve its ethanol production ability., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Anaerobic digestion of palm oil mill effluent (POME) and deoiled POME was investigated both in batch assays and continuous reactor experiments using up-flow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors. The methane potential determined from batch assays of POME and deoiled POME was 503 and 610 mL-CH(4)/gVS-added, respectively. For the treatment of POME in continuously fed reactors, both in UASB and EGSB reactors more than 90% COD removal could be obtained, at HRT of 5 days, corresponding to OLR of 5.8 gVS/(L-reactor.d). Similar methane yields of 436-438 mL-CH(4)/gVS-added were obtained for UASB and EGSB respectively. However, for treatment of deoiled POME, both UASB and EGSB reactors could operate at lower OLR of 2.6 gVS/(L-reactor.d), with the methane yield of 600 and 555 mL-CH(4)/gVS-added for UASB and EGSB, respectively. The higher methane yield achieved from the deoiled POME was attributed to lower portion of biofibers which are more recalcitrant compared the rest of organic matter in POME. The UASB reactor was found to be more stable than EGSB reactor under the same OLR, as could be seen from lower VFA concentration, especially propionic acid, compared to the EGSB reactor., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The two-stage process for extreme thermophilic hydrogen and thermophilic methane production from wheat straw hydrolysate was investigated in up-flow anaerobic sludge bed (UASB) reactors. Specific hydrogen and methane yields of 89 ml-H(2)/g-VS (190 ml-H(2)/g-sugars) and 307 ml-CH(4)/g-VS, respectively were achieved simultaneously with the overall VS removal efficiency of 81% by operating with total hydraulic retention time (HRT) of 4 days . The energy conversion efficiency was dramatically increased from only 7.5% in the hydrogen stage to 87.5% of the potential energy from hydrolysate, corresponding to total energy of 13.4 kJ/g-VS. Dominant hydrogen-producing bacteria in the H(2)-UASB reactor were Thermoanaerobacter wiegelii, Caldanaerobacter subteraneus, and Caloramator fervidus. Meanwhile, the CH(4)-UASB reactor was dominated with methanogens of Methanosarcina mazei and Methanothermobacter defluvii. The results from this study suggest the two stage anaerobic process can be effectively used for energy recovery and for stabilization of hydrolysate at anaerobic conditions., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Hydrolysate was tested as substrate for hydrogen production by extreme thermophilic mixed culture (70 degrees C) in both batch and continuously fed reactors. Hydrogen was produced at hydrolysate concentrations up to 25% (v/v), while no hydrogen was produced at hydrolysate concentration of 30% (v/v), indicating that hydrolysate at high concentrations was inhibiting the hydrogen fermentation process. In addition, the lag phase for hydrogen production was strongly influenced by the hydrolysate concentration, and was prolonged from approximately 11 h at the hydrolysate concentrations below 20% (v/v) to 38 h at the hydrolysate concentration of 25% (v/v). The maximum hydrogen yield as determined in batch assays was 318.4 +/- 5.2 mL-H(2)/g-sugars (14.2 +/- 0.2 mmol-H(2)/g-sugars) at the hydrolysate concentration of 5% (v/v). Continuously fed, and the continuously stirred tank reactor (CSTR), operating at 3 day hydraulic retention time (HRT) and fed with 20% (v/v) hydrolysate could successfully produce hydrogen. The hydrogen yield and production rate were 178.0 +/- 10.1 mL-H(2)/g-sugars (7.9 +/- 0.4 mmol H(2)/g-sugars) and 184.0 +/- 10.7 mL-H(2)/day L(reactor) (8.2 +/- 0.5 mmol-H(2)/day L(reactor)), respectively, corresponding to 12% of the chemical oxygen demand (COD) from sugars. Additionally, it was found that toxic compounds, furfural and hydroxymethylfurfural (HMF), contained in the hydrolysate were effectively degraded in the CSTR, and their concentrations were reduced from 50 and 28 mg/L, respectively, to undetectable concentrations in the effluent. Phylogenetic analysis of the mixed culture revealed that members involved hydrogen producers in both batch and CSTR reactors were phylogenetically related to the Caldanaerobacter subteraneus, Thermoanaerobacter subteraneus, and Thermoanaerobacterium thermosaccharolyticum., ((c) 2009 Wiley Periodicals, Inc.)

Five methods for preparation of hydrogen-producing seeds (base, acid, 2-bromoethanesulfonic acid (BESA), load-shock and heat shock treatments) as well as an untreated anaerobic digested sludge were compared for their hydrogen production performance and responsible microbial community structures under thermophilic condition (60 degrees C). The results showed that the load-shock treatment method was the best for enriching thermophilic hydrogen-producing seeds from mixed anaerobic cultures as it completely repressed methanogenic activity and gave the a maximum hydrogen production yield of 1.96 mol H(2) mol(-1) hexose with an hydrogen production rate of 11.2 mmol H(2) l(-1)h(-1). Load-shock and heat-shock treatments resulted in a dominance of Thermoanaerobacterium thermosaccharolyticum with acetic acid and butyric acid type of fermentation while base- and acid-treated seeds were dominated by Clostridium sp. and BESA-treated seeds were dominated by Bacillus sp. The comparative experimental results from hydrogen production performance and microbial community analysis showed that the load-shock treatment method was better than the other four methods for enriching thermophilic hydrogen-producing seeds from anaerobic digested sludge. Load-shock treated sludge was implemented in palm oil mill effluent (POME) fermentation and was found to give maximum hydrogen production rates of 13.34 mmol H(2) l(-1)h(-1) and resulted in a dominance of Thermoanaerobacterium spp. Load-shock treatment is an easy and practical method for enriching thermophilic hydrogen-producing bacteria from anaerobic digested sludge.