Mesophilic Reactor Research Articles

Whole genome sequence of Clostridium bornimense strain M2/40 isolated from a lab-scale mesophilic two-phase biogas reactor digesting maize silage and wheat straw

The bacterium Clostridium bornimense M2/40 is a mesophilic, anaerobic bacterium isolated from a two-phase biogas reactor continuously fed with maize silage and 5% wheat straw. Grown on glucose, it produced H2, CO2, formiate, lactate and propionate as the main fermentation products, of which some compounds serve as substrates for methanogenic Archaea to form methane. Here, the whole genome sequence of the bacterium consisting of two circular replicons is reported. This genome information provides the basis for further studies addressing metabolic features of the isolate and its role in anaerobic biomass degradation.

Bioreactor Performance in the Anaerobic Digestion of Cattle Manure: A Review

A literature review has been undertaken to investigate the potential of anaerobic digestion for material recovery and energy production from cattle manure. These wastes constitute 8–20% total solid, with a volatile solid content of 70–85%. The biodegradable fractions include about 11% hemicellulose, 26–53% cellulose, and 11% lignin. Anaerobic digestion of cattle manure was studied under various operating conditions using different types of bioreactors and it allows the conversion of 50–75% of organic matter to methane with an organic loading rate of 1–6 g VS/L day. Continuous two-stage configuration involving a first-stage thermophilic reactor and mesophilic second reactor emerges to be superior and the most effective technologies for anaerobic digestion of cattle manure. It was demonstrated that 41% of volatile solids were converted to methane at an organic loading rate of 5.82 g VS/L day. The methane yield was found to be 620 L/kg VS added.

Performance comparison between mesophilic and thermophilic anaerobic reactors for treatment of palm oil mill effluent

The anaerobic digestion of palm oil mill effluent (POME) was carried out under mesophilic (37°C) and thermophilic (55°C) conditions without long-time POME storage in order to compare the performance of each condition in the field of Sumatra Island, Indonesia. The anaerobic treatment system was composed of anaerobic hybrid reactor and anaerobic baffled filter. Raw POME was pretreated by screw decanter to reduce suspended solids and residual oil. The total COD removal rate of 90–95% was achieved in both conditions at the OLR of 15kg[COD]/m3/d. The COD removal in thermophilic conditions was slightly better, however the biogas production was much higher than that in the mesophilic one at high OLR. The organic contents in pretreated POME were highly biodegradable in mesophilic under the lower OLRs. The biogas production was 13.5–20.0l/d at the 15kg[COD]/m3/d OLR, and the average content of carbon dioxide was 5–35% in both conditions.

Novel Microbial Populations in Ambient and Mesophilic Biogas-Producing and Phenol-Degrading Consortia Unraveled by High-Throughput Sequencing

Methanogenesis from wastewater-borne organics and organic solid wastes (e.g., food residues) can be severely suppressed by the presence of toxic phenols. In this work, ambient (20 °C) and mesophilic (37 °C) methane-producing and phenol-degrading consortia were enriched and characterized using high-throughput sequencing (HTS). 454 Pyrosequencing indicated novel W22 (25.0 % of bacterial sequences) in the WWE1 and Sulfurovum-resembled species (32.0 %) in the family Campylobacterales were the most abundant in mesophilic and ambient reactors, respectively, which challenges previous knowledge that Syntrophorhabdus was the most predominant. Previous findings may underestimate bacterial diversity and low-abundance bacteria, but overestimate abundance of Syntrophorhabdus. Illumina HTS revealed that archaeal populations were doubled in ambient reactor and tripled in mesophilic reactor, respectively, compared to the ∼4.9 % (of the bacteria and archaea sequences) in the seed sludge. Moreover, unlike the dominance of Methanosarcina in seed sludge, acetotrophic Methanosaeta predominated both (71.4-76.5 % of archaeal sequences) ambient and mesophilic enrichments. Noteworthy, this study, for the first time, discovered the co-occurrence of green sulfur bacteria Chlorobia, sulfur-reducing Desulfovibrio, and Sulfurovum-resembling species under ambient condition, which could presumably establish mutualistic relationships to compete with syntrophic bacteria and methanogens, leading to the deterioration of methanogenic activity. Taken together, this HTS-based study unravels the high microbial diversity and complicated bacterial interactions within the biogas-producing and phenol-degrading bioreactors, and the identification of novel bacterial species and dominant methanogens involved in the phenol degradation provides novel insights into the operation of full-scale bioreactors for maximizing biogas generation.

Trace element supplementation in the biogas production from wheat stillage – Optimization of metal dosing

A trace element dosing strategy for the anaerobic digestion of wheat stillage was developed in this study. Mesophilic CSTR reactors were operated with the sulfuric substrate wheat stillage in some cases under trace element deficiency. After supplementing trace elements during the start-up, one of the elements of Fe, Ni, Co, Mo, and W were depleted in one digester while still augmenting the other elements to determine minimum requirements for each element. The depletion of Fe and Ni resulted in a rapid accumulation of volatile fatty acids while Co and W seem to have a long-term effect. Based on the results it was possible to reduce the dosing of trace elements, which is positive with reference to economic and environmental aspects.

Key factors affecting on bio-hydrogen production from co-digestion of organic fraction of municipal solid waste and kitchen wastewater

The effects of sludge residence time (SRT) and dilution ratio (DR) on the continuous H2 production (HP) from co-digestion of organic fraction of municipal solid waste (OFMSW) and kitchen wastewater (KWW) via mesophilic anaerobic baffled reactor (ABR) was investigated. Increasing DR from 1:2 to 1:3 significantly (P<0.1) increased the H2 yield (HY) from 116.5±76 to 142.5±54mlH2/gCODremovedd, respectively. However, at a DR of 1:4, the HY was dropped to 114.5±65mlH2/gCODremovedd. Likewise, HY increased from 83±37 to 95±24mlH2/gCODremovedd, when SRT increased from 3.6 to 4.0d. Further increase in HY of 148±42mlH2/gCODremovedd, was occurred at a SRT of 5.6d. Moreover, hydrogen fermentation facilitated carbohydrate, lipids, protein and volatile solids removal efficiencies of 87±5.8%, 74.3±9.12%, 76.4±11.3% and 84.8±4.1%, respectively.

Effect of moisture of municipal biowaste on start-up and efficiency of mesophilic and thermophilic dry anaerobic digestion

Methane production from biowaste with 20–30% dry matter (DM) by box-type dry anaerobic digestion and contributing bacteria were determined for incubation at 20, 37 and 55°C. The same digestion efficiency as for wet anaerobic digestion of biowaste was obtained for dry anaerobic digestion with 20% DM content at 20, 37 and 55°C and with 25% DM content at 37 and 55°C. No or only little methane was produced in dry anaerobic reactors with 30% DM at 20, 37 or 55°C.Population densities in the 20–30% DM-containing biowaste reactors were similar although in mesophilic and thermophilic biowaste reactors with 30% DM content significantly less but phylogenetically more diverse archaea existed. Biogas production in the 20% and 25% DM assays was catalyzed by Methanosarcinales and Methanomicrobiales. In all assays Pelotomaculum and Syntrophobacter species were dominant propionate degraders.

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).

Comparison of operating strategies for increased biogas production from thin stillage

The effect of increasing organic loading rate (OLR) and simultaneously decreasing hydraulic retention time (HRT) during anaerobic digestion of sulphur- and nitrogen-rich thin stillage was investigated during operation of continuously stirred tank laboratory reactors at two different temperatures. The operating strategies and substrate were set in order to mimic an existing full-scale commercial biogas plant in Sweden. The reactors were operated for 554–570 days with a substrate mixture of thin stillage and milled grain, resulting in high ammonium concentrations (>4.5gL−1). Initially, one reactor was operated at 38°C, as in the full-scale plant, while in the experimental reactor the temperature was raised to 44°C. Both reactors were then subjected to increasing OLR (from 3.2 to 6.0gVSL−1d−1) and simultaneously decreasing HRT (from 45 to 24 days) to evaluate the effects of these operational strategies on process stability, hydrogen sulphide levels and microbial composition. The results showed that operation at 44°C was the most successful strategy, resulting in up to 22% higher methane yield compared with the mesophilic reactor, despite higher free ammonia concentration. Furthermore, kinetic studies revealed higher biogas production rate at 44°C compared with 38°C, while the level of hydrogen sulphide was not affected. Quantitative PCR analysis of the microbiological population showed that methanogenic archaea and syntrophic acetate-oxidising bacteria had responded to the new process temperature while sulphate-reducing bacteria were only marginally affected by the temperature-change.

A comparative study on thermomechanical pulping pressate treatment using thermophilic and mesophilic sequencing batch reactors

A comparative study on the treatment of thermomechanical pulping (TMP) pressate was conducted under thermophilic (55°C) and mesophilic (30°C) temperatures to explore in-mill biological treatment, with the intention to operate under heat-efficient conditions. The experimental study involved sequencing batch reactors (SBRs) operated over 114 days. Receiving a total influent chemical oxygen demand (COD) of 3700–4100 mg L−1, the COD removal efficiencies of 80–90% and 75–85% were achieved for the mesophilic and thermophilic SBRs, respectively, at a hydraulic retention time (HRT) of 12 and 24 h. Excellent sludge settleability (sludge volume index<100 mL g−1 mixed liquor suspended solids) was obtained at both thermophilic and mesophilic SBRs. A higher level of effluent suspended solids was observed under thermophilic conditions. The results support the feasibility of applying thermophilic biological treatment of TMP pressate. The treated effluent has the potential for subsequent reuse as process water after polishing, thus addressing the long-standing desire to develop water system closure for the pulp and paper mill operation.

Mesophilic and thermophilic anaerobic laboratory-scale digestion of Nannochloropsis microalga residues

This paper studies methane production using a marine microalga, Nannochloropsis sp. residue from biodiesel production. Residue cake from Nannochloropsis, oils wet-extracted, had a methane potential of 482LCH4kg(-1) volatile solids (VS) in batch assays. However, when dry-extracted, the methane potential of residue cake was only 194LCH4kg(-1) VS. In semi-continuous reactor trials with dry-extracted residue cake, a thermophilic reactor produced 48% higher methane yield (220LCH4kg(-1)VS) than a mesophilic reactor (149LCH4kg(-1)VS). The thermophilic reactor was apparently inhibited due to ammonia with organic loading rate (OLR) of 2kgVSm(-3)d(-1) (hydraulic retention time (HRT) 46d), whereas the mesophilic reactor performed with OLR of 3kgVSm(-3)d(-1) (HRT 30d). Algal salt content did not inhibit digestion. Additional methane (18-33% of primary digester yield) was produced during 100d post-digestion.

Feasibility of Biogas Production from Napier Grass

The current study focused on the feasibility of biogas production from Napier grass. Napier grass, a tropical plant, can grow up in drought and dry conditions. Napier grass contains 30.9% total carbohydrates, 27% protein, lipid 14.8%, total ash 18.2%, fiber 9.1% (dry weight). Its organic compositions are an ideal feedstock for biogas production. The fresh grass was harvested after 5 week plantation, grounded in 0.5 to 1 mm diameter size before fermentation in mesophilic batch reactors, with varying solid concentrations of 5 - 15%. The optimum condition for the biogas production was found at 5% solid concentration. Methane content, yield and production rate were 53%, 122.4 mL CH4/g TVS remove, 4.8 mL/hr at the optimum condition. Economic analysis of biogas obtained from the experiment with liquid petroleum gas (LPG) with benefit/cost ratio (B/C ratio) greater than 1 suggested that the Napier grass is considered as a potential energy crop.

Anaerobic digestion of autoclaved and untreated food waste

Anaerobic digestion of autoclaved (160°C, 6.2bar) and untreated source segregated food waste (FW) was compared over 473days in semi-continuously fed mesophilic reactors with trace elements supplementation, at organic loading rates (OLRs) of 2, 3, 4 and 6kg volatile solids(VS)/m3d. Methane yields at all OLR were 5–10% higher for untreated FW (maximum 0.483±0.013m3 CH4/kgVS at 3kgVS/m3d) than autoclaved FW (maximum 0.439±0.020m3 CH4/kgVS at 4kgVS/m3d). The residual methane potential of both digestates at all OLRs was less than 0.110m3 CH4/kgVS, indicating efficient methanation in all cases. Use of acclimated inoculum allowed very rapid increases in OLR. Reactors fed on autoclaved FW showed lower ammonium and hydrogen sulphide concentrations, probably due to reduced protein hydrolysis as a result of formation of Maillard compounds. In the current study this reduced biodegradability appears to outweigh any benefit due to thermal hydrolysis of ligno-cellulosic components.

A comparison of microbial characteristics between the thermophilic and mesophilic anaerobic digesters exposed to elevated food waste loadings

Thermophilic and mesophilic anaerobic digestion reactors (TR and MR) using food waste as substrate were compared with emphasis on microbial responses to increasing organic loading rate (OLR). At OLR ranging from 1.0 to 2.5 g VS L(-1) d(-1), MR exhibited more stable performance compared to TR in terms of methane yield. Amplicons pyrosequencing results revealed the distinct microbial dynamics in the two reactors. Primarily, MR had greater richness and evenness of bacteria species. With OLR elevated, larger shifts of bacterial phylogeny were observed in MR; Methanosaeta dominated in archaeal community in MR while Methanothermobacter and Methanoculleus were favored in TR. The high functional redundancy in bacterial community integrated with acetoclastic methanogenesis in MR resulted in its better performance; whereas delicate interactions between hydrogen-producer and hydrogenotrophic methanogens in TR were much more prone to disruption. These results are conductive to understanding the microbial mechanisms of low methane yield during food waste anaerobic digestion.

Drivers of microbial community composition in mesophilic and thermophilic temperature-phased anaerobic digestion pre-treatment reactors

Temperature-phased anaerobic digestion (TPAD) is an emerging technology that facilitates improved performance and pathogen destruction in anaerobic sewage sludge digestion by optimising conditions for 1) hydrolytic and acidogenic organisms in a first-stage/pre-treatment reactor and then 2) methogenic populations in a second stage reactor. Pre-treatment reactors are typically operated at 55–65 °C and as such select for thermophilic bacterial communities. However, details of key microbial populations in hydrolytic communities and links to functionality are very limited. In this study, experimental thermophilic pre-treatment (TP) and control mesophilic pre-treatment (MP) reactors were operated as first-stages of TPAD systems treating activated sludge for 340 days. The TP system was operated sequentially at 50, 60 and 65 °C, while the MP rector was held at 35 °C for the entire period. The composition of microbial communities associated with the MP and TP pre-treatment reactors was characterised weekly using terminal-restriction fragment length polymorphism (T-RFLP) supported by clone library sequencing of 16S rRNA gene amplicons. The outcomes of this approach were confirmed using 454 pyrosequencing of gene amplicons and fluorescence in-situ hybridisation (FISH). TP associated bacterial communities were dominated by populations affiliated to the Firmicutes, Thermotogae, Proteobacteria and Chloroflexi. In particular there was a progression from Thermotogae to Lutispora and Coprothermobacter and diversity decreased as temperature and hydrolysis performance increased. While change in the composition of TP associated bacterial communities was attributable to temperature, that of MP associated bacterial communities was related to the composition of the incoming feed. This study determined processes driving the dynamics of key microbial populations that are correlated with an enhanced hydrolytic functionality of the TPAD system.

Determination of biogas generation potential as a renewable energy source from supermarket wastes

Fruit, vegetable, flower waste (FVFW), dairy products waste (DPW), meat waste (MW) and sugar waste (SW) obtained from a supermarket chain were anaerobically digested, in order to recover methane as a source of renewable energy. Batch mesophilic anaerobic reactors were run at total solids (TS) ratios of 5%, 8% and 10%. The highest methane yield of 0.44LCH4/gVSadded was obtained from anaerobic digestion of wastes (FVFW+DPW+MW+SW) at 10% TS, with 66.4% of methane (CH4) composition in biogas. Anaerobic digestion of mixed wastes at 5% and 8% TS provided slightly lower methane yields of 0.41 and 0.40LCH4/gVSadded, respectively. When the wastes were digested alone without co-substrate addition, the highest methane yield of 0.40LCH4/gVSadded was obtained from FVFW at 5% TS. Generally, although the volatile solids (VS) conversion percentages seemed low during the experiments, higher methane yields could be obtained from anaerobic digestion of supermarket wastes. A suitable carbon/nitrogen (C/N) ratio, proper adjustment of the buffering capacity and the addition of essential trace nutrients (such as Ni) could improve VS conversion and biogas production yields significantly.

Influence of hydrodynamic shear on performance and microbial community structure of a hybrid anaerobic reactor

AbstractBACKGROUNDHydrodynamic shear plays a major role in the formation, maintenance, structure, and metabolism of self‐immobilized microbial communities in reactors. The study attempts to correlate the performance and microbial community structure of granular sludge in a mesophilic hybrid anaerobic reactor under different upflow velocities to fluidize the bed. The reactor was started with an initial upflow velocity of 4 m h‐1, which was increased gradually till system deterioration to observe its effect on granule size, reactor performance, and microbial community structure. Monte Carlo method was used to quantify hydrodynamic shear range at different upflow velocities using a modified Ergun equation for the respective ranges of granule size.RESULTSUp to 6 m h‐1 performance was positively affected, but beyond this upflow velocity, the system started showing reduced performance and completely deteriorated at 10 m h‐1. Significant reduction in the abundance and diversity of both Archaea and Bacteria was observed. Among all methanogenic groups, Methanosaetaceae was most severely affected due to breakage and wash out of granules.CONCLUSIONIt can be concluded that hydrodynamic shear can be employed as a sensitive control parameter to improve reactor performance, and a specified range should be determined experimentally to avoid negative influences associated with this. © 2013 Society of Chemical Industry

An innovative sewage sludge reduction by using a combined mesophilic anaerobic and thermophilic aerobic process with thermal-alkaline treatment and sludge recirculation

Lab-scale High Efficiency Digestion (HED) systems containing a Mesophilic Anaerobic Reactor (MAR), Thermophilic Aerobic Reactor (TAR), liquid/solid separation unit, and thermal-alkaline treatment were developed to evaluate the efficiencies of sludge reduction and methane production. The HED process was divided into three phases to examine the influence of sludge pretreatment and pretreated sludge recirculation using TCOD and VSS reduction, COD solubilization, and methane production. The VSS removal with a solid/liquid separation unit, sludge recirculation, and thermal-alkaline treatment drastically increased up to 95% compared to the feed concentration. In addition, the results of COD solubilization and VSS/TSS showed that the solubilization of cells and organic matters by the thermal-alkaline treatment was highly increased, which was also consistent with the SEM images. In particular, the methane production rate increased 24-fold when the feed sludge and recirculated sludge were pretreated together. Collectively, the HED experiments performed with sludge recirculation and thermal-alkaline treatment demonstrated that the HED systems can be successfully employed for highly efficient sewage sludge reduction and methane gas production.

Pilot-scale experiment on thermally hydrolyzed sludge liquor anaerobic digestion using a mesophilic expanded granular sludge bed reactor

A pilot process of thermal hydrolysis combined with an expanded granular sludge bed reactor (EGSB) was carried out to evaluate pretreated sludge liquor into biogas conversion, process stability, and energy input/output balance. Approximately 25% of suspended solids of sludge were liquefied into aqueous phase during thermal hydrolysis pretreatment, which resulted in chemical oxygen demand (COD) concentration of 20.0 to 35.0 g/L. A mesophilic EGSB reactor was operated for 206 days treating pretreated liquor. Under an organic loading rate of 11.0 kg COD/(m(3)·d) and hydraulic retention time of 60 h, COD conversion efficiency was maintained at 63%. The energy from biogas provided 80% of that demand for heating pretreatment. Dewatered sludge after thermal hydrolysis could be incinerated with municipal solid waste in an industrial-scale incinerator. Total energy production from combined biogas anaerobic digestion and sludge incineration, treating 1.0 kg raw sludge with moisture content of 82%, was 2419 kJ. The energy demand of thermal hydrolysis pretreatment was 340 kJ.

Effect of thermal pre-treatment on inoculum sludge to enhance bio-hydrogen production from alkali hydrolysed rice straw in a mesophilic anaerobic baffled reactor

The effect of thermal pre-treatment on inoculum sludge for continuous H2 production from alkali hydrolysed rice straw using anaerobic baffled reactor (ABR) was investigated. Two reactors, ABR1 and ABR2, were inoculated with untreated and thermally pre-treated sludge, respectively. Both reactors were operated in parallel at a constant hydraulic retention time of 20 h and organic loading rate ranged from 0.5 to 2.16 g COD/L d. The results obtained indicated that ABR2 achieved a better hydrogen conversion rate and hydrogen yield as compared with ABR1. The hydrogen conversion rates were 30% and 24%, while the hydrogen yields were 1.19 and 0.97 mol H2/mol glucose for ABR2 and ABR1, respectively. Similar trend was observed for chemical oxygen demand (COD) and carbohydrate removal, where ABR2 provided a removal efficiency of 53±2.3% for COD and 46±2% for carbohydrate. The microbial community analysis using 16S rRNA phylogeny revealed the presence of different species of bacteria, namely Clostridium, Prevotella, Paludibacter, Ensifer, and Petrimonas within the reactors. Volatile fatty acids generated from ABR1 and ABR2 were mainly in the form of acetate and butyrate and a relatively low fraction of propionate was detected in ABR1. Based on these results, thermal pre-treatment of inoculum sludge is preferable for hydrogen production from hydrolysed rice straw.