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This study focused on determining the effect of the inoculum to substrate ratio (ISR) on biogas production efficiency from the anaerobic co-digestion of two substrates: synthetic food waste and common reeds (Phragmites australis) that were ground and pre-treated using sodium hydroxide at a concentration of 2% to increase access to their cellulose. It also studied the role of different mixing ratios of the two substrates in improving the stability of the digestion process and increasing biogas production. A series of batch tests were carried out under mesophilic conditions using three ratios of ISR: 1:4, 1:2, and 1:1, and five substrate mixing ratios (synthetic food waste: pre-treated P. australis): 25:75, 50:50, 75:25, 100:0, and 0:100. The results showed low biogas production at the ISR 1:4 (21.58±0.00–44.46±0.01 mL/g volatile solid (VS) added), and the reactors suffered from acidification at the different substrates mixing ratios, while the biogas production increased at an ISR of 1:2, where the reactors with the substrate mixing ratio of 25:75 presented the highest biogas production (82.17±0.62 mL/g VS added), and the digestion process was stable. However, the reactors with substrate mixing ratios of 50:50, 75:25, and 100:0 suffered from acidification effects at this ISR. In contrast, at ISR of 1:1, the reactors did not expose to acidification inhibition at all the substrates mixing ratios, and the highest biogas production was found at synthetic food waste: pre-treated P. australis mixing ratios of 75:25 and 100:0 (76.15±1.85 and 82.47±1.85 mL/g VS added, respectively). [ABSTRACT FROM AUTHOR]

This study aims to identify the optimal conditions for generating biogas from poultry manure with respect to pH, C/N ratio, and temperature. The study was conducted in lab batch bioreactor having a working volume of 2 l at different conditions with respect to pH, carbon to nitrogen ratio (C/N), and temperature. A full factorial design is designed to analyze the impact of the three parameters and their interactions. Experiments are replicated four times to ensure the reproducibility of data. Results indicate that temperature is the only influencing parameter on biogas production from poultry manure within a pH range of 6–8 and a C/N ratio range of 10/1 to 40/1. Moreover, there is no interaction between the three parameters, and mesophilic conditions are found to be the optimum conditions for biogas production. The maximum biogas yield of 285 ml/g VS is found in mesophilic conditions at 37 °C with a retention time of 20 days. Biogas production kinetics are similar in mesophilic and thermophilic conditions but vary in psychrophilic conditions.

Despite the awareness on the importance of using biogas produced from various biomasses that were previously considered as wastes, the fact remains that its applicability or usage in domestic purposes such as cooking stoves has not really gained attention especially in developing countries. Based on this reason, this research designed a batch system biogas generating facility that will serve the energy needed for cooking meals by a family size of six members, using rumen contents of cattle (Bos indicus) as biomass. The results made known that an anaerobic digester having a capacity of 2.7m³ will perfectly serve for such facility to meet its intended use when fed with 72kg of substrate per batch, while the gas holder volume should be 0.527m³. Necessary appurtenances including water jacket were designed and detailed dimensions, drawings as well as costing of the entire facility were provided to ease fabrication and possibly adjustment in the future if the need arise. [ABSTRACT FROM AUTHOR]

Variation of the digester temperature during the year enables the operation of digesters as seasonal heat storage contributing to a holistic heat management at water resource recovery facilities. Full‐ and lab‐scale process data were conducted to examine the effect of the digester temperature on process stability, sludge liquor quality, and dewaterability. Both full‐ and lab‐scale digesters show a stable anaerobic degradation process with a hydraulic retention time of more than 20 days and organic load rates up to 2.2‐kg COD/(m3·day) at temperatures between 33 and 53°C. The concentrations of soluble COD and ammonium‐nitrogen in the sludge liquor digested at 53°C are 2.6 to 5.8 times and 1.3 times higher, respectively, than in the sludge liquor digested at 37°C. Dewatering tests show an enhancement of the dewaterability but a clear increase in the polymer demand at increased digester temperature. Practitioner Points: Digesters can operate as seasonal heat storage within mesophilic and thermophilic temperaturesStable anaerobic degradation process for HRT above 20 daysMaintenance of process stability as well as quantity and quality of biogasIncrease of soluble COD in sludge liquor at higher temperaturesBetter dewaterability but higher demand for polymers with increasing temperature [ABSTRACT FROM AUTHOR]

In this two-phase study, it was shown that a mixture with equal parts of manure and resulting animal blood was the optimal combination for obtaining biogas and biol. A quadratic growth trend in variable gas pressure over time—as well as its behavior—was confirmed for pHs around the neutral value for the substrate used in both the pilot phase and in the microplant, which had a mechanical implementation and mechatronic system for the control of variables that intervene in the anaerobic digestion process; this allowed for the confirmation of the results found in the first phase of research—without concerns that a lack of control over the process variables would cause—in such a way that it constituted a path for the industrialization of the waste treatment process in slaughterhouses that could be optimized by the use of the optimal combination that produces the greatest cm3 amount of gas. Anaerobic digestion in biodigesters is carried out at different constant temperature values within the mesophilic range, with a hydraulic retention time of 25 days. A direct relationship was found between temperature, biogas production and pH behavior in the buffer(s). The pH remained close to neutral and the gas pressure increased from 15 to 20. The findings indicated that the value for the C/N ratio of the blood of four was compensated for by its buffer system, composed of bicarbonate, hemoglobin, proteins and phosphates. [ABSTRACT FROM AUTHOR]

[Display omitted] • All the feeding conditions were stable for the sufficient support from mineral alkalinity. • VS and COD removal maintained about 80% all along the experiment. • Prokaryotic community decreased in diversity and shifted greatly for PW = 50 %. • PW contents as 40% is TS (13.1% in total weights) was suggested. • Mesophilic co-digestion of PW with FW recovered biomethane as 445 ∼ 350 NL/kg-VS fed. Biomethane recovery from paper waste (PW) was achieved by mesophilic co-digestion with food waste. The feeding material containing 0%, 20%, 40% and 50% of PW in total solids (TS) were investigated in the long-term continuous operation. The results showed that the biogas production, pH, alkalinity and biodegradation of volatile solids (79.8 ± 3.6%) were stable for PW contents no more than 50%. The PW = 50% condition was considered the critical limit for the reasons of pump clogging, sufficient alkalinity (2.0 ± 0.3 g-CaCO 3 /L) and depletion of ammonia. Prokaryotic diversity indices decreased with the increased PW contents. Great shifts were observed in the prokaryotic communities before and after the PW contents reaches 50% as TS (18.4% as total weights). Biomethane recovery yields were deceasing from 445 to 350 NL-CH 4 /kg-fed-volatile-solids. The PW contents as 40% as TS (13.1% as total weights) obtained the optimal performance among all the feeding conditions. [ABSTRACT FROM AUTHOR]

The share of biogas in renewable energy sources is increasing as variety of feedstocks are now used for biogas production among which lignocellulosic biomass is emerging feedstock that can be used after proper pretreatment under best suited temperature. Although lot of pretreatments and temperature combinations have been tested but still there is a gap that can be filled by the current study focused on the effect of the temperature gradient (mesophilic and thermophilic) on biogas production potential of maize straw and rice husk using a modified Gompertz equation. Pretreatment was done by using alkali (NaOH and Ca(OH)2) and acids (HCl and H2SO4) each at 2, 4 and 6%.The pretreatment of crop residue with 6% NaOH degraded lignin contents significantly. The pretreated crop residue was further used for biogas production. A multistage anaerobic bioreactor containing three diagonally inline reactors provided with one water bath connected to reactors for better utilization of energy was used for biogas production. The temperature of water bath was adjusted to that the first reactor achieved 37°C and 55 °C for different experiments. The working temperatures found to be 31-37°C and 46-55°C were achieved to maintain the internal temperature of the reactors within mesophilic and thermophilice temperature ranges, respectively. The 36 days incubation time was equally divided for three reactors. The biogas production rate was297 mL/g-VSadded and 244.07 mL/g-VSadded from maize straw and rice husk under mesophilic conditions, respectively. The results showed an increased biogas yield for both feedstocks under mesophilic conditions as compared to thermophilic conditions. The central reactor showed better production as compared to other two rectors in all experiments. [ABSTRACT FROM AUTHOR]

The present study investigated the feasibility of using pilot-scale anaerobic filter to treat by-product liquid (brown juice, BJ) from grass protein extraction in a green biorefinery, and produce biogas via anaerobic digestion without co-digestion substrate. Prior to feed into the un-heated anaerobic filter reactor, the BJ was warmed up to 55−60 °C in order to maintain the digestion temperature. The influence of retention time and feeding frequencies were tested in order to optimize the overall performance. The study demonstrated that anaerobic filter is feasible for converting BJ to biogas. The specific CH production reached 230 mL gCOD−1 d −1 while up to 80 % of influent COD was removed within a hydraulic retention time of 5.5 days. In addition, higher feeding frequencies enhanced the process stability as it narrowed the temperature variation and decreased the instant impact on buffer capacity. [ABSTRACT FROM AUTHOR]

The demand for uniformly sized and shaped produce that are aesthetically pleasing results in significant food waste throughout the world. Cucumber waste is a major agricultural waste product in a number of countries, especially areas with high pickle production. Opportunity exists for wastewater treatment plants containing anaerobic digesters to utilize cucumber agricultural and industrial waste for biogas production. The biomethane potential of cucumber waste as a substrate for co-digestion with sewage sludge was assessed. The impact of long-term co-digestion of cucumber was then evaluated using mesophilic continuously stirred tank reactors (CSTRs), in both single- and two-stage anaerobic co-digestion with sewage sludge. Ground cucumber waste was added to sewage sludge at 8% of the volume (4.5–4.6% of the organic load) and CSTRs were maintained for five hydraulic retention times (HRTs). One-stage co-digestion of cucumber waste produced comparable gas levels as CSTRs without cucumbers (averaging 219 and 221 m3/kgVS/h, respectively) after two HRTs. The two-stage cucumber co-digestion CSTR averaged 64% higher specific gas than the control and single-stage digester, although the volumetric gas produced was lower (averaging 152 m3/kgVS/h) likely due to gas loss in the first stage resulting in a lower organic load rate. After four HRTs, relative methanogen content showed dramatic differences in levels of hydrogenotrophic methanogens for the two-stage digester, while the one-stage digester containing cucumber waste showed minor differences relative to the control. Cucumber waste co-digestion with sewage sludge is effective although numerous conditions could be utilized to optimize gas production. [ABSTRACT FROM AUTHOR]

This study investigated the production of methane using various substrates. Plantain peels, pig dung, poultry droppings, walnut peels/plantain peels and cow blood/wheat waste were all co-digested, charged in digesters (A-E) and allowed to ferment anaerobically for forty-five (45) days within the mesophilic temperature range of 20.0-39.0°. Digester A contained 3.9 Kg of wheat waste/cow blood and 19.5 Kg of water in the ratio of 1.5 which gave a total gas yield of 22.5 L of biogas; B contained 7.8 Kg of walnut peels/plantain peels and 15.6 Kg of water in the ratio 1:2 which gave a total gas yield of 115.0 L; C contained 8 Kg of plantain peels and 16 Kg of water which yielded 133.0 L of biogas; D contained 8 Kg of pig dung mixed thoroughly with 16 Kg of water which gave a total of 321.0 L; and E contained 8 Kg of poultry droppings mixed with 16 Kg of water which yielded 168.5 L of biogas. From the cumulative comparison of the biogas yields of the samples, pig dung gave the highest yield of 321 L and cow blood/wheat husk produced the lowest yield of 22.5 L. Pig dung (animal waste) gave the highest total viable count (TVC) of 7 × 106 cfu/mL. The sludge contains NPK which is a good biofertilizer. [ABSTRACT FROM AUTHOR]

Biogas plants are a widespread renewable energy technology. However, the use of digestate for agronomic purposes has often been a matter of concern. It is controversial whether biogas plants might harbor some pathogenic clostridial species, which represent a biological risk. Moreover, the inhabitance of Clostridium hard-cheese spoiling species in anaerobic digesters can be problematic for hard-cheese manufacturing industries, due to the issue of cheese blowing defects. This study investigated the effect of mesophilic anaerobic digestion processes on the Clostridium consortia distribution over time. Specifically, three lab-scale CSTRs treating agricultural biomass were characterized by considering both the whole microbial community and the cultivable clostridial spores. It is assessed an overall reduction of the Clostridium genus during the anaerobic digestion process. Moreover, it was evidenced a slight, but steady decrease of the cultivable clostridial spores, mainly represented by two pathogenic species, C. perfringens and C. bifermentans, and one hard-cheese spoiling species, C. butyricum. Thus, it is revealed an overall reduction of the clostridial population abundance after the mesophilic anaerobic digestion treatment of agricultural biomass. [ABSTRACT FROM AUTHOR]

Purpose: Anaerobic digestion is a promising technology for simultaneous treatment of biodegradable organic matter of municipal solid waste (MSW) and production of renewable energy. Mixing modes and temperature have influences on biogas production in anaerobic digesters treating MSW. Therefore, in this study, digester was operated at different modes of mixing and temperatures to obtain design criteria. Methods: The experiments were carried out in a semi-continuous digester. In the first part of the investigation, temperature was set at 25, 28, 31 and 34 °C. During this step, digester content was mixed in an intermittent mode by mechanical mixers. In the second part of the study, mixing condition of the digester was set at various modes: continuous, intermittent (15 min on and 30 min off) and minimal (twice in a batch). Results: Digestion with a temperature in this range resulted in biogas yield of 0.23–0.33 m3 biogas/kg VS, with a methane content of 60.2–71.8% in biogas. The methane content and yield decreased with reduction of digestion temperature. However, this reduction was almost negligible from 34 to 31 °C. In addition, in comparison to intermittent mixing, continuous and minimal mixing modes reduced the biogas production by 40% and 50%, respectively. Therefore, in this digester greatest biogas yield of 0.33 ± 0.02 m3 biogas/kg VS were obtained at 34 °C and intermittent mixing mode. Conclusions: Based on the data obtained from this study, temperature in the range of 31–34 °C and intermittent mixing is suggested as a base for design purposes. [ABSTRACT FROM AUTHOR]

Co-fermentation of glycerol and acetic acid in anaerobic digestion was set up to generate biogas in batch reactors under mesophilic condition, pH 7. The experiments were varied COD ratios of glycerol and acetic acid were varied with the total combined COD of 5,20 0 mg/L. The maximum methane yield was obtained from glycerol/acetic acid ratio of 6:4. The cumulative methane, production rate and lag phase were 240 mL, 14 mL hr−1, and 11 hr. The research indicated acetic acid boosted methane production when it was co-fermented with glycerol. • CH 4 production from waste glycerol and acetic acid co-digestion with initial 52,000 g COD L−1. • Addition of acetic acid to co-digest with waste glycerol greatly promotes CH 4 production. • Glycerol/acetic acid with 1.25:1 mass ratio gave maximum CH 4 yield. [ABSTRACT FROM AUTHOR]

Low-temperature thermo-alkaline pretreatment with alkyl polyglucosides (APGs) was employed for improving the utilization of low-organic-content sludge in anaerobic digestion (AD). An orthogonal experiment (L9 (34)) was designed to estimate the influence of four factors on pretreatment, and the order determined by significance level was: pH > temperature > APG dosage > time. Under the conditions of pH 11, 60 °C, and 60 min, the content of organic matter dissolved from sludge increased as the APG dosage increased to 18 g/L. When fermenting at a dosage above its critical micelle concentration (CMC), however, APG inhibited aerogenesis due to the adverse impact on methanogen activity. Thus, the optimal APG dosage was fixed at 3.0 g/L. After 35 days of mesophilic AD, the biogas volume, the methane volume fraction, and the organics utilization rate reached their respective peaks. The methane volume fraction (45.8%) was lower than normal biogas (at least 53%), so further evaluation is needed. [ABSTRACT FROM AUTHOR]

Objective: Biogas technology is being seriously promoted as an important option to meet the growing energy demand of rural areas in developing countries, particularly Ethiopia ongoing progress, nowadays, cow dung (CD), banana peels (BPs), and mango peels (MPs) promising application for biogas generation. The objective of the present study was to investigate the effectiveness and the performance characteristics of anaerobic digestion of CD mixed with fruit peels for biogas production. Materials and Methods: The study was done with three different digesters containing a mixture of varying levels of three different substrates (CD + BP MPs) labeled as digester A to C. In each digester, the substrates were mixed with the appropriate amount of water in the ratio of 1:10. They were subjected to anaerobic digestion for production of biogas under a 15 days retention period and mesophilic temperature range of 26-35°C. Results: Significant amount (43.5 L) of 60-70% methane composition, flammable biogas was produced from the dry sample mixtures of CD and fruit pills (digester-A) compared to digester-B and digester C starting from the 3rd day of the digestion period. Conclusion: The result of the present study shown that anaerobic digestion from the mixture dry sample of CD, BPs, and MPs can be formed a renewable energy production process and comfortable and easy ways of replace fossil fuel as an environmentally friendly. [ABSTRACT FROM AUTHOR]

Biogas upgrading via carbon dioxide hydrogenation is an emerging technology for electrofuel production. The biomethanation efficiency is strongly dependent on a balanced microbial consortium, whose high-resolution characterization along with their functional potential and interactions are pivotal for process optimization. The present work is the first genome-centric metagenomic study on mesophilic and thermophilic biogas upgrading reactors aiming to define the metabolic profile of more than 200 uncultivated microbes involved in hydrogen assisted methanogenesis. The outcomes from predictive functional analyses were correlated with microbial abundance variations to clarify the effect of process parameters on the community. The operational temperature significantly influenced the microbial richness of the reactors, while the H2 addition distinctively alternated the abundance of the taxa. Two different Methanoculleus species (one mesophilic and one thermophilic) were identified as the main responsible ones for methane metabolism. Finally, it was demonstrated that the addition of H2 exerted a selective pressure on the concerted or syntrophic interactions of specific microbes functionally related to carbon fixation, propionate and butanoate metabolisms. Novel bacteria were identified as candidate syntrophic acetate oxidizers (e.g., Tepidanaerobacter sp. DTU063), while the addition of H2 favored the proliferation of potential homoacetogens (e.g., Clostridia sp. DTU183). Population genomes encoding genes of Wood-Ljungdahl pathway weremainly thermophilic, while propionate degraders were mostly identified at mesophilic conditions. Finally, putative syntrophic interactions were identified between microbes that have either versatile metabolic abilities or are obligate/facultative syntrophs. [ABSTRACT FROM AUTHOR]

The effects of organic loading rate (OLR) and operating temperature on the performance of siphon-driven self-agitated anaerobic reactor (SDSAR) in an on-site food waste (FW) treatment system were investigated. Two reactors were operated in parallel for comparison between mesophilic condition (35 ± 1 °C) and thermophilic condition (55 ± 1 °C). With HRT above 15 d and OLR below 4.8 kg-COD/m 3 /d, relatively high COD removal in the range of 84.5–92.3% was obtained in both reactors. The limits of the loading capacity of the mesophilic SDSAR were observed when OLR was further increased to 7.3 kg-COD/m 3 /d by shortening HRT. Blocking and gas production reduction occurred and COD removal decreased sharply to 75.9% in the mesophilic reactor. In contrast, the thermophilic reactor can be operated at this OLR with satisfactory COD removal and biogas production. Furthermore, at OLR of 14.4 kg-COD/m 3 /d, the COD removal was maintained as high as 87.5% in the thermophilic reactor. The conversion of influent COD to methane was maintained above 80% at all the OLR applied in both reactors. The results of this study indicated that thermophilic SDSAR is preferred for the on-site FW treatment. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to examine the effect of the increase in organic loading rates (OLRs), by reducing the solids retention time (SRT) from 20 d to 5 d, in single-phase mesophilic anaerobic co-digestion of sewage sludge with glycerine (1% v/v). It was experimentally confirmed that anaerobic co-digestion of these biowastes under steady-state conditions can achieve an 85 ± 5% reduction in volatile fatty acids (VFA) at SRTs of between 20 and 9 d, with a methane production yield of around 0.8 l CH 4 /l/d. Decreases in the SRT not only allow the sludge stability and biogas production to be maintained, but also lead to an increase in the waste that could be treated and lower operating costs. Therefore, mesophilic anaerobic co-digestion of sewage sludge and glycerin at a SRT lower than 20 d is possible and preferable due to being more economical and environmentally friendly. [ABSTRACT FROM AUTHOR]

Direct anaerobic digestion of dewatered sludge with total solids (TS) content of 15–20% was tested in a horizontal digester for one and half years. The system kept stable with pH 7–8. The concentration of volatile fatty acids was lower than 800 mg/L, free ammonia nitrogen was lower than 200 mg/L, and total alkalinity kept higher than 6000 mg/L. The performance was influenced by organic load rate (OLR) and organic content in feed sludge. When volatile solids (VS) in TS of feed sludge reached 60–65% at OLR 3.50–3.70 g/(L·d), the process exhibited the best performance with organic removal rate of 32.19 ± 7.73% and methane production of 156.86 ± 13.05 ml/g VS added. Microbial analyses indicated that Methanosarcina became predominant and Methanosaeta almost disappeared. Moreover, hydrogenotrophic and methylotrophic methanogens accounted for 18.13–29.40% and 11.58–29.56% of the total, respectively. These provide a new guideline for small-scale or centralized sludge treatment. [ABSTRACT FROM AUTHOR]

In this study a natural mix of microalgae grown in wastewater of municipal character was co-digested with sewage sludge in mesophilic conditions, in both batch and semi-continuous modes. The semicontinuous experiment was divided into two periods with OLR1 (organic loading rate) of 2.4 kg volatile solids (VS) m-3 d-1 and HRT1 (hydraulic retention time) of 15 days, and OLR2 of 3.5 kg VS m-3 d-1 and HRT2 of 10 days, respectively. Results showed stable conditions during both periods. The methane yield was reduced when adding microalgae (from 200±25 NmL CH4 g VSin-1, to 168±22 NmL CH4 g VSin-1) but VS reduction was also decreased by 51%. This low digestibility was confirmed in the anaerobic batch test. However, adding microalgae improved the dewaterability of the digested sludge. The high heavy metals content in the microalgae resulted in a high heavy metals content in the digestate, making it more difficult to reuse the digestate as fertilizer on arable land. The heavy metals are thought to originate from the flue gas used as a CO2 source during the microalgae cultivation. Therefore the implementation of CO2 mitigation via algal cultivation requires careful consideration regarding the source of the CO2-rich gas. [ABSTRACT FROM AUTHOR]

Fermentation and anaerobic digestion of organic waste and wastewater is broadly studied and applied. Despite widely available results and data for these processes, comparison of the generated results in literature is difficult. Not only due to the used variety of process conditions, but also because of the many different growth media that are used. Composition of growth media can influence biogas production (rates) and lead to process instability during anaerobic digestion. To be able to compare results of the different studies reported, and to ensure nutrient limitation is not influencing observations ascribed to process dynamics and/or reaction kinetics, a standard protocol for creating a defined growth medium for anaerobic digestion and mixed culture fermentation is proposed. This paper explains the role(s) of the different macro- and micronutrients, as well as the choices for a growth medium formulation strategy. In addition, the differences in nutrient requirements between mesophilic and thermophilic systems are discussed as well as the importance of specific trace metals regarding specific conversion routes and the possible supplementary requirement of vitamins. The paper will also give some insight into the bio-availability and toxicity of trace metals. A remarkable finding is that mesophilic and thermophilic enzymes are quite comparable at their optimum temperatures. This has consequences for the trace metal requirements of thermophiles under certain conditions. Under non-limiting conditions, the trace metal requirement of thermophilic systems is about 3 times higher than for mesophilic systems. [ABSTRACT FROM AUTHOR]

This paper reports the results of the temperature profile of the unheated and unstirred continuous fermenting bio-slurry in a fixed-dome Deenbandhu 2000 model. The digester is a brick-built system of bulk size 6 m3. The digester was monitored for eight months, measuring internal bio-slurry temperature. A K-type nickel chromium-nickel temperature sensor with a sensitivity of approximately 41 μV °C and response time of 0.8s in liquids was positioned at the centre of the digester to measure the slurry temperature. The sensor was connected to the data logger and programmed to record temperature readings every second for the entire study period. The study results reported give a clear indication about the reaction of bio-slurry temperature in the digester at a local level, particularly for the eight months' period, which covered all seasons. The calculated values of the daily average temperature reveal that the digester was operating within the range of psychrophilic 10.32 °C and mesophilic 28.80 °C, although it sometimes operated at 35 °C and above during certain hours in summer. This study is useful for anaerobic digestion processes for biogas production. The results obtained can be used as a basis to estimate the amount of heat required to raise the temperature of digesters to reach an optimum temperature of mesophilic digesters. [ABSTRACT FROM AUTHOR]

Production of bio-hydrogen from stale rice was conducted in an aerobic digester. It was applied 3 types of pressure control range to the digester, they are (0-3/3%), (0-2/3%), (0-1/3%) of maximum pressure during the production of bio-hydrogen in mesophilic (35 °C) condition which is equal to (0-10 psi), (0-6 psi), (0-3 psi), and as small as possible pressure in the digester. This research shows that the optimum pressure control range to increase total gas production is (0-2/3%) or (0-6 psi), with total production of 19 liters biogas. [ABSTRACT FROM AUTHOR]

This study examined the influence of altered operating temperature on microbial community composition and how this affects the ability of anaerobic degradation (AD) processes to cope with increasing loading rate. Four digesters fed household and slaughterhouse waste, mimicking two large-scale processes, were operated in sets of two at 37°C or 52°C, followed by a gradual increase or decrease in temperature in one digester in each set. All digesters were then subjected to step-wise increases in organic loading rate (OLR) from 3 to 7g VS/L/day, concurrently with decreased hydraulic retention time (HRT). Temporal microbial changes were monitored by Illumina MiSeq analysis of bacterial and archaeal 16S rRNA gene sequences. The digester transformed from thermophilic to mesophilic conditions failed at 6g VS/L/day, whereas the reference digesters and the mesophilic-to-thermophilic digester remained stable at all OLR investigated. The bacterial community was characterised by relatively diversified structure dominated by Bacteriodetes and Firmicutes in mesophilic conditions. Increasing temperature caused loss of complexity at phyla level and enhanced the relative abundance of Firmicutes and Thermotogae. Temperature adaptation in the thermophilic-to-mesophilic digester resulted in a bacterial community structure reflecting the communities observed in digesters with initial temperature of 37°C. However, certain populations found in the mesophilic digesters did not appear at detectable levels during operation at 37°C in the thermophilic-to-mesophilic digester. Overall, the results showed that anaerobic process stability was highly dependent on the innate resilience of the microbial community. The mesophilic microbiota formed from a thermophilic community had a slightly different structure than its mesophilic counterpart and was considerably less resistant to increased OLR in digesters examined within this study. [ABSTRACT FROM AUTHOR]

Excessive acidification and low methane (CH 4) percentage are technical challenges restricting anaerobic digestion (AD) of kitchen waste, especially under high organic loading rate (OLR) conditions. Although the contribution of Fe0 powder to excessive acidification elimination and CH 4 yield improvement in mesophilic AD (MAD) has been extensively reported, its impact on the thermophilic AD (TAD) process with more frequent excessive acidification problem is rarely studied. Moreover, the difference in microbial interactions and metabolic pathways between MAD and TAD reactors under Fe0 regulation was still unclear. In this study, we compared the performance of Fe0 dosing on excessive acidification elimination and biogas upgrading quality in both MAD and TAD reactors at different OLRs. The results showed that compared with excessive acidification or low CH 4 percentage (less than 70%) in control reactors without Fe0 addition, the CH 4 yield of MAD and TAD reactors with addition of Fe0 at OLR of 35 gVS/L were 470.88 mLCH 4 /gVS and 270.40 mLCH 4 /gVS, with higher CH 4 composition of 81.32%–82.23% and 83.68%–88.48% respectively. Microbial diversity analysis showed a sharp distinction between MAD and TAD reactors with addition of Fe0. Analyses of co-occurrence networks and metabolic pathway presented hydrogenotrophic methanogenic pathway, in addition to acetoclastic methanogenesis, was dominant in MAD reactors as results of enhanced interspecies hydrogen transfer between Methanoculleus and some hydrogen producers, especially under high OLR condition. In contrast, syntrophilic acetate oxidization - hydrogenotrophic methanogenesis, which dominated by Methanothermobacter and Alkaliphilus or Pelotomaculum , was the sole methanogenic pathway in TAD reactors. The results will shed lights on the regulation mechanisms of Fe0 in AD of kitchen waste under mesophilic and thermophilic conditions, offering new insight into development of more efficient waste to energy conversion technologies. [Display omitted] • Fe0 in-situ upgraded CH 4 percentage around 85% in both MAD and TAD reactors. • At OLR of 35 gVS/L, CH 4 yields of MAD and TAD reactors were 470.88 and 270.40 mLCH 4 /gVS. • Fe0 played more important role in determining microbial consortia in MAD than TAD. • Methanoculleus and Methanothermobacter produced CH 4 in MAD and TAD respectively. • IHT was key pathway for eliminating acidification in MAD, but it is SAO-HM in TAD. [ABSTRACT FROM AUTHOR]

Deep separate collection of the organic fraction of municipal solid waste generates streams with relatively low content of inert material and high biodegradability. This material can be conveniently treated to recovery both energy and material by means of simplified technologies like screw-press and extruder: in this study, the liquid fraction generated from pressed biowaste from kerbside and door-to-door collection was anaerobically digested in both mesophilic and thermophilic conditions while for the solid fraction composting is suggested. Continuous operation results obtained both in mesophilic and thermophilic conditions indicated that the anaerobic digestion of pressed biowaste was viable at all operating conditions tested, with the greatest specific gas production of 0.92 m 3 /kgVS fed at an organic loading rate of 4.7 kgVS/m 3 d in thermophilic conditions. Based on calculations the authors found that the expected energy recovery is highly positive. The contents of heavy metals and pathogens of fed substrate and effluent digestates were analyzed, and results showed low levels (below End-of-Waste 2014 criteria limits) for both the parameters thus indicating the good quality of digestate and its possible use for agronomic purposes. Therefore, both energy and material were effectively recovered. [ABSTRACT FROM AUTHOR]

Biogas originates from bacteria in the process of biological breakdown of organic material under anaerobic conditions. A research work was conducted to investigate the production ability of biogas from mesophilic anaerobic digestions of cow dung (CD) using silica gel as catalyst. Two laboratory scale digesters were constructed to digest cow dung, where one set-up was used for digestion of cow dung without catalyst and the other set-up was used for digestion with catalyst. The digesters were made of glass conical flask of 1-liter capacity each. Cow dung was used 390 gm and water was used 310 gm in each experiment. In the slurry, total solid content was maintained 8% (wt.) for all the observations. The digesters were fed on batch basis. The digesters were operated at ambient temperatures of 27–31 °C. The total gas yield was obtained about 27.3 L/kg CD for digestion without catalyst and about 30.5 L/kg of CD for digestion with catalyst. The retention time was about 76 days for both the digestions. The gas yields were compared with the previous work of mesophilic digestions of cow dung without catalyst of operating temperatures 18–28 °C. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) treatment of agricultural and animal waste can be considered as a means of enabling environmental remediation. This research investigated two conditions of anaerobic co-digestion of maize waste and cow dung. This was done by placing a mixture of cow dung and maize waste together in a floating drum digester that was run at two different cow dung/maize ratios of 10:1 and 10:5. Batch conditions were on a bench-scale of AD, 5 L in volume, developed to operate under mesophilic (36 ± 1°C). Results showed that biogas and methane yields from mesophilic digestion at the ratio of 10:1 were lower than yields obtained at ratio tested in the second run (10:5). Biogas yields were 250 and 480 L/kg VS for first and second runs, respectively. In the case of methane, these amounts were presented at 130 and 300 L/kg VS. Furthermore, the average methane content of biogas was calculated as 51 and 62%, in first and second runs respectively. The total biogas production of the reactor increased by 92% when substrates were fed in second condition ratio compared to biogas production during the first condition ratio. In continue the effect of adding maize waste on biogas yield from cow dung was evaluated in batch digesters under mesophilic conditions. The addition of maize waste to cow dung presents a viable method to improve biogas yield, as well as a means to use maize waste. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 597-601, 2014 [ABSTRACT FROM AUTHOR]

Biogas production is a clean renewable energy source that can improve lives in developing countries. However, winter temperatures in some areas are too low to enable enough biogas production in small unheated digesters to meet the energy requirements of households. Low-cost, high yield reactors adapted to the local climate are needed in those situations. A decision-support model was developed to assist in the design of biogas reactors capable of meeting households' year-round energy needs. Monthly biogas production relative to household energy needs was calculated for the scenario of suburban Hanoi, Vietnam. Calculations included pig number, slurry (manure water mixture) dilution, retention time and biogas/solar heating. Although using biogas to heat the digester increased biogas production, it did not lead to an energy surplus, particularly with the 1:9 slurry dilution rate commonly used on pig farms. However, at a 1:3 slurry dilution, the use of solar heating to provide 90% and biogas 10% of the heat required to heat the digester to 35 °C improved the biogas production by 50% compared to psychrophilic production. The energy needs of an average five-person family throughout the year required 17 fattening pigs. This model can establish the best solution for producing sufficient energy throughout the year. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestions with fat, oil, and grease (FOG) were investigated in semi-continuous flow digesters under various operating conditions. The effects of hydraulic retention times (HRTs) of 12 and 24 days, organic loading rates (OLRs) between 1.19 and 8.97 g TVS/Ld, and digestion temperatures of 37°C and 55°C on biogas production were evaluated. It was proposed that, compared to anaerobic digestion with wastewater treatment plant sludge (primary raw sludge), semi-continuous flow anaerobic co-digestion with FOG could effectively enhance biogas and methane production. Thermophilic (55°C) co-digestions exhibited higher biogas production and degradation of organics than mesophilic co-digestions. The best biogas production rate of 17.4±0.86 L/d and methane content 67.9±1.46% was obtained with a thermophilic co-digestion at HRT=24 days and OLR=2.43±0.15 g TVS/Ld. These were 32.8% and 7.10% higher than the respective values from the mesophilic co-digestion under similar operating conditions. [ABSTRACT FROM PUBLISHER]

Seaweed biomass has emerged as an alternative for the production of renewable fuels such as biogas from anaerobic digestion (AD). In relation to the biogas production rate, digester temperature setting is one of the most critical factors for an economically viable digester operation, especially in temperate countries like Ireland, as most annual temperatures are below the mesophilic range. In this study, the effect of digester temperature on biogas and methane production efficiency during the AD of Laminaria digitata was evaluated. 120 ml batch reactors were incubated at 20, 35 and 45 °C for 54 days to determine a temperature profile for the AD process. Reactors incubated at 35 °C produced the highest biogas and methane yields (336 ml biogas/g VS and 184 ml methane/g VS). Thermophilic reactors (45 °C) produced 30 % less biogas and 23.3 % less methane, followed by psychrophilic reactors (20 °C) which produced 41 % less biogas and 39.7 % less methane. A drop in pH in the mesophilic and thermophilic reactors was identified as an inhibitory factor during the first days of digestion. Psychrophilic reactors were better able to withstand the observed changes. Mesophilic temperatures will be used in further studies to examine scaling up of the process. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays, the protection of the environment begins to go beyond the simple notion of citizenship and gestures towards nature, but it is an opportunity to improve the quality of life of every living being, including the production of clean energy and the reduction of greenhouse gas emissions. In this sense, one of the processes that contribute to this new situation, the process of anaerobic digestion, sector which is formerly known, though it has great potential in terms of biogas production, it remains relatively untapped compared to other renewable energy sources due to low yields recorded. The aim of the present study was to determine the influence of particle size on the performance of anaerobic digestion of municipal solid waste, In order to contribute to improving the efficiency of biogas process. In this context, the Laboratory for Energy, Environment and Materials procured an experimental digester with the capacity of 14 liters, equipped with an integrated control. The particle size of 10mm, 20mm, 30mm and 100mm in diameter were evaluated; the laboratory reactor was operated under mesophilic conditions (40° C) and with a retention time of 21 days. The results show a high correlation between particle size and the production of biogas, with optimum production recorded for small particle sizes. [Copyright &y& Elsevier]

Abstract: Anaerobic contact reactor is a high rate anaerobic process consisting of an agitated reactor and a solids settling tank for recycling. It was proved earlier that this type of reactor design offers highly efficient performance in the conversion of organic matter to biogas. In this study, the effect of transient loading on reactor performance in terms of a number of key intermediates and parameters such as, COD removal, pH and alkalinity change, VFAs, effluent MLSS concentration and biogas efficiency over time was examined. For this purpose, a step increase of organic loading rate from 3.35kg COD/m3 day to 15.61kg COD/m3 day was employed. The hydraulic retention time decreased to a value of 8.42h by an increase in the influent flow-rate during the transient loading. It was observed that the mesophilic anaerobic contact reactor (MACR) was quite resistant to large transient shocks. The reactor recovered back to its baseline performance only in 15h after the shock loading was stopped. Hence, it can be concluded that this type of reactor design has a high potential in treating food processing wastewaters with varying flow characteristics. [Copyright &y& Elsevier]

Abstract: Two pilot-scale (1 m3) digesters filled with untreated rice straw and co-digested with raw pig wastewater were operated to obtain design parameters for a farm-scale biogas plant. Both digesters contained 50 kg of dry straw mixed with diluted pig wastewater to create dry digestion conditions (20% TS) and operated for 189 days with leachate recirculation. Digester A was designed for optimum performance (150 L of pig wastewater and mesophilic temperatures) while Digester B was designed to establish minimum inputs (60 L of pig wastewater at ambient temperatures). The pig wastewater provided sufficient buffering capacity to maintain appropriate pH values (between 7.0 and 8.1) and nutrient balances (TOC to TKN ratios of 20 in Digester A and 32 in Digester B). Total biogas production was 22,859 L in Digester A and 1420 L from Digester B, resulting in specific methane yields of 231 and 12 L CH4/kgVS added, respectively. Gas production in Digester A was directly correlated with temperature, but the overall lack of methanogenic activity was caused primarily by the reduced wastewater volume. Two theoretical farm-scale scenarios (considering both untreated and pretreated rice straw) were developed for a 100-ha rice farm. Either scenario can produce 100,000 m3CH4 per year, yielding 328 MWh. Major differences including heat input, space requirements, loading frequency, digester volume, engine size, wastewater quantities, and additives are quantitatively defined. The appropriate choice for a farm-scale operation is the simplest model using untreated rice straw without additives, although six times more heat and twice as much reactor volume is required. [Copyright &y& Elsevier]

Abstract: Dry mesophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) is a widespread technology. However, OFMSW is a very heterogeneous waste and therefore specific studies are needed to optimise the AD process with each type of OFMSW that will be used. The main operational variables to optimise are the solids retention time (SRT) and the organic loading rate (OLR), which are closely related to each other when the concentration of organic matter of OFMSW remains relatively constant. In this work three different experimental conditions (corresponding to the SRT of 30, 20 and 15days) were tested in a semi-continuous stirred tank reactor, operating at mesophilic range (35°C) and high solids concentration (20% TS). The OLR corresponding to the above mentioned SRT were 22.8, 27.3 and 35.9mgDOC/Lreactor/d, respectively. The results obtained in this study indicate that 20days is the optimum SRT for the dry mesophilic anaerobic digestion of the OFMSW used. Thus, in general, all the parameters analysed show better performance for 20-day SRT with regard to 30-day and 15-day SRT. More specifically, it can be pointed out than at SRT of 20days (27.3mgDOC/Lreactor/d), both the highest productivity of methane (0.11LCH4/gwaste-fed) and the highest organic matter removal rate (66.3% DOC removal) were reached. [Copyright &y& Elsevier]

The biomass of industrially grown Phaeodactylum tricornutum was subjected in a novel way to bio-methanation at 33°C, i.e., in an anaerobic membrane bioreactor (AnMBR) at a hydraulic retention time of 2.5 days, at solid retention times of 20 to 10 days and at loading rates in the range of 2.6-5.9 g biomass-COD L day with membrane fluxes ranging from 1 to 0.8 L m h. The total COD recovered as biogas was in the order of 52%. The input suspension was converted to a clear effluent rich in total ammonium nitrogen (546 mg TAN L) and phosphate (141 mg PO-P L) usable as liquid fertilizer. The microbial community richness, dynamics, and organization in the reactor were interpreted using the microbial resource management approach. The AnMBR communities were found to be moderate in species richness and low in dynamics and community organization relative to UASB and conventional CSTR sludges. Quantitative polymerase chain reaction analysis revealed that Methanosaeta sp. was the dominant acetoclastic methanogen species followed by Methanosarcina sp. This work demonstrated that the use of AnMBR for the digestion of algal biomass is possible. The fact that some 50% of the organic matter is not liquefied means that the algal particulates in the digestate constitute a considerable fraction which should be valorized properly, for instance as slow release organic fertilizer. Overall, 1 kg of algae dry matter (DM) could be valorized in the form of biogas (€2.07), N and P in the effluent (€0.02) and N and P in the digestate (€0.04), thus totaling about €2.13 per kilogram algae DM. [ABSTRACT FROM AUTHOR]

Abstract: The effects of microwave (MW) pretreatment, staging and digestion temperature on anaerobic digestion were investigated in a setup of ten reactors. A mesophilic reactor was used as a control. Its performance was compared to single-stage mesophilic and thermophilic reactors treating pretreated and non-pretreated sludge, temperature-phased (TPAD) thermophilic-mesophilic reactors treating pretreated and non-pretreated sludge and thermophilic–thermophilic reactors also treating pretreated and non-pretreated sludge. Four different sludge retention times (SRTs) (20, 15, 10 and 5 d) were tested for all reactors. Two-stage thermo–thermo reactors treating pretreated sludge produced more biogas than all other reactors and removed more volatile solids. Maximum volatile solids (VS) removal was 53.1% at an SRT of 15 d and maximum biogas increase relative to control was 106% at the shortest SRT tested. Both the maximum VS removal and biogas relative increase were measured for a system with thermophilic acidogenic reactor and thermophilic methanogenic reactor. All the two-stage systems treating microwaved sludge produced sludge free of pathogen indicator bacteria, at all tested conditions even at a total system SRT of only 5 d. MW pretreatment and staging reactors allowed the application of very short SRT (5 d) with no significant decrease in performance in terms of VS removal in comparison with the control reactor. MW pretreatment caused the solubilization of organic material in sludge but also allowed more extensive hydrolysis of organic material in downstream reactors. The association of MW pretreatment and thermophilic operation improves dewaterability of digested sludge. [Copyright &y& Elsevier]

Abstract: Anaerobic digestion of whole stillage from a dry-grind corn-based ethanol plant was evaluated by batch and continuous-flow digesters under thermophilic and mesophilic conditions. At whole corn stillage concentrations of 6348 to 50,786mg total chemical oxygen demand (TCOD)/L, at standard temperature (0°C) and pressure (1atm), preliminary biochemical methane potential assays produced 88±8L (49±5L CH4) and 96±19L (65±14L CH4) biogas per L stillage from mesophilic and thermophilic digesters, respectively. Continuous-flow studies for the full-strength stillage (TCOD=254g/L) at organic loadings of 4.25, 6.30 and 9.05g TCOD/Ldays indicated unstable performance for the thermophilic digester. Among the sludge retention times (SRTs) of 60, 45 and 30days tested, the mesophilic digestion was successful only at 60days-SRT which does not represent a practical operation time for a large scale bioethanol plant. Future laboratory studies will focus on different reactor configurations to reduce the SRT needed in the digesters. [ABSTRACT FROM AUTHOR]