Highest Biogas Production Research Articles

Effect of bacterial lipase on anaerobic co-digestion of slaughterhouse wastewater and grease in batch condition and continuous fixed-bed reactor

BackgroundThis study aimed to investigate the effects of bacterial lipase on biogas production of anaerobic co-digestion of slaughterhouse wastewater (SHWW) and hydrolyzed grease (HG). A neutrophilic Staphylococcus xylosus strain exhibiting lipolytic activity was used to perform microbial hydrolysis pretreatment of poultry slaughterhouse lipid rich waste.ResultsOptimum proportion of hydrolyzed grease was evaluated by determining biochemical methane potential. A high biogas production was observed in batch containing a mixture of slaughterhouse composed of 75% SHWW and 25% hydrolyzed grease leading to a biogas yield of 0.6 L/g COD introduced.Fixed bed reactor (FBR) results confirmed that the proportion of 25% of hydrolyzed grease gives the optimum condition for the digester performance. Biogas production was significantly high until an organic loading rate (OLR) of 2 g COD/L. d.ConclusionThis study indicates that the use of biological pre-treatment and FBR for the co-digestion of SHWW and hydrolyzed grease is feasible and effective.

Process performance and modelling of anaerobic digestion using source-sorted organic household waste

Three distinctive start-up strategies of biogas reactors fed with source-sorted organic fraction of municipal solid waste were investigated to reveal the most reliable procedure for rapid process stabilization. Moreover, the experimental results were compared with mathematical modeling outputs. The initial inoculations to start-up the reactors were 10, 50 and 100% of the final working volume. While a constant feeding rate of 7.8gVS/d was considered for the control reactor, the organic loading rate for fed-batch reactors with 10 and 50% inoculation was progressively increased during a period of 60 and 13days, respectively. The results clearly demonstrated that an exponentially feeding strategy, considering 50% inoculation relative to final volume, can significantly decrease the alternatively prolonged period to reach steady conditions, as observed by high biogas and methane production rates. The combination of both experimental and modelling/simulation succeeded in optimizing the start-up process for anaerobic digestion of biopulp under mesophilic conditions.

Modeling and optimization of biogas production from cow manure and maize straw using an adaptive neuro-fuzzy inference system

This study was focused on the prediction and optimization of biogas production from cow manure with maize straw under various total solid content (TS), Carbon to Nitrogen (C/N) ratio and stirring intensity. This research used full-scale (1200 L) batch reactor under mesophilic condition. An adaptive neuro-fuzzy interference system (ANFIS) was utilized to predict and optimize biogas production from anaerobic digestion. C/N ratio, TS and stirring intensity of substrates, each of them in three levels, were considered as input variables and biogas production was regarded as the output variable of the model. The coefficient of determination (R2) between observed and predicted biogas production values was 0.99 which showed good match and accuracy of the model. Highest biogas production was achieved from C/N ratio 26.76, TS 9% and moderate stirring. Biogas production increased about 8% with optimal conditions suggested by the ANFIS model.

Potential of biogas production from mixed leaf and food waste in anaerobic reactors

Anaerobic digestion of mixed leaf (MLW) and food wastes (FW) was used to explore the potential use of MLW as an accelerator for FW digestion in two parts for biogas production and as a waste management option in a university community. The effects of the single substrate of FW, co-digestion, ratio of MLW and FW (3:2 and 2:3) and ratio of waste feed to inoculum: F/I (0.1 and 0.4), and feeding frequency (every other day and every 2 days) were evaluated in two neutralized anaerobic reactors. The results showed that different mixture ratios with the same F/I ratio were the major factor on biogas (39.87 m3/kg VSadded) and CH4 yield (25.99 m3/kg VSadded), including %COD removal (84.50%). Co-digestion had the same effect as F/I on biogas production. Only FW provided the lowest biogas and CH4 yield. The use of a MLW:FW 2:3, F/I 0.4 mixture with every 2 days feeding provided higher biogas production and %COD removal than with every other day feeding. Two neutralized anaerobic reactors were suitable for digestion with a high F/I, and a wider interval feeding. This finding affirms the possibility of biogas production using MLW as the co-substrate with FW, as opposed to using FW alone.

The influence of biomass agitation on biogas and methane production using the high-solids thermophilic anaerobic digestion

Abstract In this study, we tested the high-solids thermophilic anaerobic digestion of separated cattle slurry solids inoculated by liquid digestate collected from the 1st stage of the wet process operated in an agricultural mesophilic biogas plant. The process without batch agitation (stirring) was carried out in a barrel bioreactor located in the incubator, whereas the process with batch agitation was carried out in a rotating drum bioreactor (rotation speed: 0.1 min−1). In both cases, the biomass batch was non-liquid and the content of total solids was 18.8 wt%. The processes were conducted discontinuously without any addition for 21 days. The total solids content of both batches decreased to about 15 wt%, with only slight liquefaction. The bulk density increased from 500 to 750 kg m−3. The highest biogas production was achieved consistently on the 7th day. During the 21-day period, the unagitated batch produced 0.120 mN 3 of biogas, and the agitated batch produced 32.5% extra. The average CH4 content in biogas from the unstirred batch amounted to 47.7 vol.%, and biogas from the stirred batch reached 46.2 vol.%. The cumulative methane production rates from the unagitated and agitated batches were 0.095 and 0.121 mN 3 kgVS −1, respectively. Thus, the agitation resulted in 28.5% higher methane yield.

Comparison of the mesophilic and thermophilic anaerobic digestion of spent cow bedding in leach-bed reactors

Anaerobic digestion of spent cow bedding in batch leach-bed reactors (LBRs) was compared in mesophilic and thermophilic conditions for the first time. Results show that the use of thermophilic conditions enhanced only the degradation kinetics of easily-degradable matter during the first days of the digestion, whereas similar methane yields (80% of the Biomethane Potential) were reached after 42days at both temperatures. Therefore, the anaerobic digestion in LBRs of spent cow bedding, a substrate rich in slowly-degradable compounds, was not improved in term of methane production considering the overall digestion time. Moreover, the high initial biogas production rate in thermophilic reactors was found to significantly reduce the energetic performance of the cogeneration unit at industrial scale, leading to a 5.9% decrease in the annual electricity production when compared to a mesophilic one.

Leachate flush strategies for managing volatile fatty acids accumulation in leach-bed reactors

In anaerobic leach-bed reactors (LBRs) co-digesting an easily- and a slowly-degradable substrate, the importance of the leachate flush both on extracting volatile fatty acids (VFAs) at the beginning of newly-started batches and on their consumption in mature reactors was tested. Regarding VFA extraction three leachate flush-rate conditions were studied: 0.5, 1 and 2Lkg−1TSd−1. Results showed that increasing the leachate flush-rate during the acidification phase is essential to increase degradation kinetics. After this initial phase, leachate injection is less important and the flush-rate could be reduced. The injection in mature reactors of leachate with an acetic acid concentration of 5 or 10gL−1 showed that for an optimized VFA consumption in LBRs, VFAs should be provided straight after the methane production peak in order to profit from a higher methanogenic activity, and every 6–7h to maintain a high biogas production rate.

The effect of enzymatic pretreatment and c/n ratio to biogas production from rice husk waste during solid state anaerobic digestion (SS-AD)

Rice husk is one of agricultural waste generated from the mill is potential to be converted to biogas. Otherwise, biogas production facing problem due to the high lignin content. This research is objected to study the effect of enzymatic pretreatment and C/N ratio to biogas production from rice husk by solid state anaerobic digestion (SS-AD). The laboratory scale-anaerobic digestions was used in this work. It is operated in batch system and with room temperature. Total solid (TS) was set 21%. Enzymatic pretreatment was conducted using lignase enzyme. Carbon to Nitrogen (C/N) ratio was varied from 20, 25, 30, and 35. The C/N ratio is varied by adding some quantity of technical urea to the substrate. Biogas formed was measured using water displacement method in every two days. The result showed that enzymatic pretreatment could increase biogas production from 30 to 55 %. The highest biogas production was obtained at C/N ratio 35. Specific biogas production on C/N ratio of 20, 25, 30, and 35 were respectively 12.0, 12.6, 13.5 and 18.2 ml/gr TS. The volumetric loading resulted by SS-AD was higher than liquid anaerobic digestion (L-AD). The further research need to conduct for optimization the enzyme concentration and C/N ratio.

Performance Evaluation of a Large-Scale Swine Manure Mesophilic Biogas Plant in China

Abstract. With the rapid growth of large-scale and intensive swine farms have come many ecological and environmental problems associated with the substantially increased and concentrated animal waste production. In this article, a swine manure and flushed slurry to renewable energy management system is present and discussed. This system was installed in a commercial feeder-to-finish swine farm with 18,000 head of swine in Beijing, China, and included two mesophilic upflow solids reactors (USRI and USRII, 500 m3 and 700 m3) and one psychrophilic plug-flow reactor (PFR, 1000 m3). In this study, USRII was monitored throughout a whole year to evaluate the performance of this swine waste to energy system. The biogas plant used mixed solid swine manure and flushed slurry as substrate with a relatively low organic loading rate (OLR) of 0.7 to 1.8 kg volatile solids (VS) m-3 d-1. The hydraulic retention time (HRT) varied from 15 to 22 days depending on the season. Less added water contributed to the longer HRT and more concentrated influent in winter. In winter, the specific methane production (SMP) of the digester was 0.43 m3 CH4 kg-1 VSadded, which was slightly lower than the value reported in Europe (0.45 m3 CH4 kg-1 VSadded) but about 48.3% higher than that in Asia (0.29 m3 CH4 kg-1 VSadded). This indicated that the performance of this USR in winter was stable, with a higher biogas production, and up to 90% of the VS was removed as well. However, the low OLR limited the volumetric methane production rate to only 0.21 to 0.57 m3 m-3 d-1. Keywords: Flushed slurry, Large-scale biogas plant, Monitoring, Performance, Swine manure.

Impact of anaerobic dynamic membrane bioreactor configuration on treatment and filterability performance

Submerged and external anaerobic dynamic membrane bioreactors (AnDMBRs) have been compared in terms of removal efficiency, filtration characteristics and microbial community structure. High COD removal efficiencies were obtained with both submerged and external AnDMBRs. To obtain an effective dynamic membrane (DM) layer enabling high quality permeate, longer time was required in the external AnDMBR configuration compared to the submerged one. A difference in microbial community structure was identified using pyrosequencing analyses between the submerged and external AnDMBRs. The number of archaeal types decreased in the bulk sludge of the external AnDMBR. External sludge recirculation might have had a negative effect on the archaeal community in the bulk sludge of the external AnDMBR. However, the sludge recirculation in the external AnDMBR configuration led to a filtration at lower total filtration resistance and TMP in comparison to the submerged one at the same gas sparging rate. Results showed that the submerged AnDMBR system can provide a shorter start-up period, slightly better permeate quality in terms of COD concentration, and higher biogas production in comparison to the external one in gas-lift mode.

Anaerobic co-digestion of Tunisian green macroalgae Ulva rigida with sugar industry wastewater for biogas and methane production enhancement

Ulva rigida is a green macroalgae, abundantly available in the Mediterranean which offers a promising source for the production of valuable biomaterials, including methane. In this study, anaerobic digestion assays in a batch mode was performed to investigate the effects of various inocula as a mixture of fresh algae, bacteria, fungi and sediment collected from the coast of Sfax, on biogas production from Ulva rigida. The results revealed that the best inoculum to produce biogas and feed an anaerobic reactor is obtained through mixing decomposed macroalgae with anaerobic sludge and water, yielding into 408mL of biogas. The process was then investigated in a sequencing batch reactor (SBR) which led to an overall biogas production of 375mL with 40% of methane. Further co-digestion studies were performed in an anaerobic up-flow bioreactor using sugar wastewater as a co-substrate. A high biogas production yield of 114mL g−1 VSadded was obtained with 75% of methane. The co-digestion proposed in this work allowed the recovery of natural methane, providing a promising alternative to conventional anaerobic microbial fermentation using Tunisian green macroalgae. Finally, in order to identify the microbial diversity present in the reactor during anaerobic digestion of Ulva rigida, the prokaryotic diversity was investigated in this bioreactor by the denaturing gradient gel electrophoresis (DGGE) method targeting the 16S rRNA gene.

Alkali pretreatment at ambient temperature: A promising method to enhance biomethanation of rice straw

Anaerobic digestion is the most cost effective technology for sustainable biogas production from rice straw. Rice straw was subjected to ambient pretreatment with alkali and subsequently digested anaerobically. A dimensional equation was developed to predict the efficacy of alkali treatment in terms of soluble COD. Biomethanation process parameters like temperature, initial pH, particle size, substrate/inoculum ratio, trace element supplementation, C/N ratio and hydraulic retention time were optimized. The highest biogas production under optimized conditions was 514L/kg VS/day (∼59% CH4) from milled rice straw (1mm) pretreated with sodium hydroxide (1% w/v) at ambient temperature for 180min. The digester was operated at 15days HRT at 37°C and neutral pH. C/N ratio was optimized at 25 using urea. Higher biogas yield from rice straw treated with lower concentration of NaOH at ambient temperature may make this process more economical than the previous reports.

Sulfidogenesis process to strengthen re-granulation for biodegradation of methanolic wastewater and microorganisms evolution in an UASB reactor

A lab-scale methanolic wastewater-fed (3000 mg COD L−1) UASB reactor was operated for 235 days to evaluate the influence of the sulfidogenesis process on metabolic routes, the re-granulation of dispersed granules and long-term process performance. Various sulfidogenesis scenarios were created by stepwise decreasing the influent COD/SO42− ratio from 20 to 0.5 at a fixed organic loading rate (OLR) of 12 g COD L−1 d−1. It was shown that the conversion of methanol to methane was stable at a wide COD/SO42− range of ≥2, attaining high biogas production rate of 3.78 ± 0.32 L L−1 d−1 with efficient concurrent removal of the total COD (96.5 ± 4.4%) and sulfate (56.3 ± 13.0%). The methane content in biogas remained relatively stable at 81.5 ± 1.6% for all COD/SO42− ratios tested. The particle size of the granules was shown to clearly increase as the COD/SO42− ratios decreased. A slight linear decline was noted in the number of electrons utilized by methane producing archaea (MPA) (from 98.5 ± 0.5% to 80.0 ± 2.4%), whereas consumption by sulfate reducing bacteria (SRB) increased (from 1.5 ± 0.5% to 20.0 ± 2.4%) with the decreasing COD/SO42− ratio. According to the results of activity tests and microbial community analysis, the conversion of methanol to methane at a low COD/SO42− ratio, except from Methanomethylovorans sp., depends not only on low levels of acetoclastic and hydrogenotrophic methanogens, but also on incomplete oxidizer SRB species (e.g. Desulfovibrio sp.) that utilize H2-CO2 with acetate to mineralize the methanol. This serves to diversify the metabolic pathway of methanol. Further analysis through scanning electron microscopy (SEM) revealed that a lower COD/SO42− ratio favored the sulfidogenesis process and diversified the microbial community inside the reactor. The benefical sulfidogenesis process subsequently invoked the formation of a sufficient, rigid [-Fe-EPS-]n network (EPS: extracellular polymeric substances), binding and immobilizing the sludge, and resulting in the re-granulation of the dispersed granules.

Anaerobic digestion of grass: the effect of temperature applied during the storage of substrate on the methane production

ABSTRACTWithin this research, biogas production, representation of methane in biogas and volatile solids (VSs) removal efficiency were compared using batch tests performed with the samples of intensively and extensively planted grasses originating from public areas. Before the batch tests, the samples were stored at different temperatures achievable on biogas plants applying trigeneration strategy (−18°C, +3°C, +18°C and +35°C). Specific methane production from intensively planted grasses was relatively high (0.33–0.41 m3/kg VS) compared to extensively planted grasses (0.20–0.33 m3/kg VS). VSs removal efficiency reached 59.8–68.8% for intensively planted grasses and 34.6–56.5% for extensively planted grasses. Freezing the intensively planted grasses at −18°C proved to be an effective thermal pretreatment leading to high biogas production (0.61 m3/kg total solid (TS)), high representation of methane (64.0%) in biogas and good VSs removal efficiency (68.8%). The results of this research suggest that public areas or sport parks seem to be available, cheap and at the same time very effective feedstock for biogas production.

Enhanced biogas production from rice straw by selective micronutrients under solid state anaerobic digestion

Biomethanation of rice straw (RS) was studied in a batch mode at high total solid content (TSC) of 25% in outdoor pilot scale digesters. Performance was monitored for over six months by supplementing Nickel and Cobalt 15 and 10mgkg−1 RS to each of mesophilic and thermophilic digesters for 35 and 21days retention time (RT), respectively. The average biogas production from mesophilic and thermophilic digesters were found varying 310 and 396Lkg−1TS, respectively. The corresponding figures for the control digesters were 225 and 270Lkg−1TS. Around 37 and 46% higher biogas production was recorded by supplementing the micronutrients in mesophilic and thermophilic digesters, respectively. Methane content in biogas was 57–59%. Matured compost had nitrogen, phosphorus and potassium contents of 1.0–1.2, 1.3–2.2, and 1.2–2.1%, respectively. The results demonstrated that the present process is faster, requires less than 85% water and produces green energy in addition to manure in less time compared to conventional process.

Using slaughterhouse waste in a biochemical-based biorefinery – results from pilot scale tests

ABSTRACTA novel biorefinery concept was piloted using protein-rich slaughterhouse waste, chicken manure and straw as feedstocks. The basic idea was to provide a proof of concept for the production of platform chemicals and biofuels from organic waste materials at non-septic conditions. The desired biochemical routes were 2,3-butanediol and acetone–butanol fermentation. The results showed that hydrolysis resulted only in low amounts of easily degradable carbohydrates. However, amino acids released from the protein-rich slaughterhouse waste were utilized and fermented by the bacteria in the process. Product formation was directed towards acidogenic compounds rather than solventogenic products due to increasing pH-value affected by ammonia release during amino acid fermentation. Hence, the process was not effective for 2,3-butanediol production, whereas butyrate, propionate, γ-aminobutyrate and valerate were predominantly produced. This offered fast means for converting tedious protein-rich waste mixtures into utilizable chemical goods. Furthermore, the residual liquid from the bioreactor showed significantly higher biogas production potential than the corresponding substrates. The combination of the biorefinery approach to produce chemicals and biofuels with anaerobic digestion of the residues to recover energy in form of methane and nutrients that can be utilized for animal feed production could be a feasible concept for organic waste utilization.

An enhanced anaerobic membrane bioreactor treating bamboo industry wastewater by bamboo charcoal addition: Performance and microbial community analysis

In this study, two anaerobic membrane bioreactors (AnMBRs) were operated for 150days to treat bamboo industry wastewater (BIWW), and one of them was enhanced with bamboo charcoal (B-AnMBR). During the steady period, average chemical oxygen demand (COD) removal efficiencies of 94.5±2.9% and 89.1±3.1% were achieved in B-AnMBR and AnMBR, respectively. The addition of bamboo charcoal (BC) increased the amount of biomass and improved the performance of the systems. A higher biogas production and methane yield were also observed in B-AnMBR. Regarding the issue of membrane fouling, BC lowered the soluble microbial product (SMP) content by approximately 62.73mg/L and decreased the membrane resistance, thereby mitigating membrane fouling. Analysis of the microbial communities demonstrated that BC increased the microbial diversity and promoted the activity of Methanosaeta, Methanospirillum, and Methanobacterium, which are dominant in methane production.

New insights into the key microbial phylotypes of anaerobic sludge digesters under different operational conditions

Analyses on bacterial, archaeal communities at family level and methane-production metabolism were conducted in thirteen full-scale and pilot-scale anaerobic sludge digesters. These digesters were operated at different conditions regarding solids concentration, sludge retention time, organic loading rate and feedstock composition, seeking to optimize digester capacity. Correlations between process parameters and identified microbial phylotypes were evaluated based on relative abundance of these phylotypes determined by Quantitative PCR and 16S rDNA amplicon sequencing. Results showed that, Total Solids concentration (TS), among the evaluated operational parameters, demonstrated the most positive correlation with chemical parameters (including NH3 and VFAs) and significant impact on the abundance of key microbial phylotypes regardless of other factors. Digesters were grouped into ‘Higher-TS’ with higher stress (TS > 44 g/L, NH3 > 90 mg/L, VFAs > 300 mg/L) and ‘Lower-TS’ under easier status (TS ≤ 44 g/L, NH3 < 120 mg/L, VFAs < 525 mg/L) in this study. We identified the key microbial phylotypes, i.e. the most abundant and discriminating populations, in ‘Higher-TS’ digesters with high biogas production rate, which were the class Clostridia, the family Methanosarcinaceae and the order Methanobacteriales. Thermoanaerobacteraceae and Syntrophomonadaceae were identified as key families of Clostridia. Methane was produced both from acetoclastic and hydrogenotrophic methanogenesis. By contrast, in ‘Higher-TS’ digesters with low biogas production rate, the classes Alpha-, Beta- and Gamma-proteobacteria were detected in higher percentages, of which Rhodobacteraceae, Comamonadaceae and Xanthomonadaceae were the most abundant families respectively, and Methanomicrobiales was the prevailing methanogen order. Consistently, hydrogenotrophic pathway was predominant for methanogenesis, indicating existence of syntrophic acetate oxidation in such ‘high-stress’, low biogas production rate digesters. These microbial phylotypes were therefore considered to be associated to ‘Higher-TS’ operation. In ‘Lower-TS’ digesters, the abundance of the class Delta-proteobacteria, the families Anaerolineaceae, Rikenellaceae, Candidatus Cloacamonas and Methanosaetaceae was obviously higher compared with those in ‘Higher-TS’ digesters, which were thus considered to be marker phylotypes of easy status. The influence of TS and NH3 on the microbiome should be considered when a ‘TS-increasing’ strategy is applied to increase digester capacity.

Anaerobic digestion of heat treated sludge liquor by pilot scale mesophilic EGSB reactor

Biogas recovery from heat treated sludge liquor was tested by a 4 m3 mesophilic expanded granular sludge bed (EGSB) reactor within 206 days. Before pilot experiment, the heat pretreatment effects on hydrolysis and biogas production potential on three sludges from different wastewater plants were evaluated using bench test. One of these sludges was used in the subsequent pilot heat treatment and EGSB reactor. The biogas conversion potential of this sludge filtrate was 79%. Seeded with granular sludge, the EGSB reactor could be quickly activated and adapted to the new filtrate substrate. The EGSB influent COD was 20.0-35.0 g/L, and the effluent COD was lower than 10.0 g/L. The COD removal rate was 60%-70% at an organic loading rate (OLR) of 10.0 kg COD/(m3•d). The fresh supernatant with low pH resulted in the high biogas production in EGSB. The effluent with high nitrogen and phosphor should be considered for further treatment. Keywords: anaerobic digestion, sludge, biogas, heat treatment, EGSB reactor, pilot scale DOI: 10.3965/j.ijabe.20160903.2371 Citation: Zhao J, Qiao W, Wang W, Gao F, Xiao Z. Anaerobic digestion of heat treated sludge liquor by pilot scale mesophilic EGSB reactor. Int J Agric & Biol Eng, 2016; 9(3): 146－153.

Effects of pretreatments on thickened waste activated sludge and rice straw co-digestion: Experimental and modeling study

In order to maximize the biogas production from thickened waste activated sludge (TWAS), co-digestion of TWAS and rice straw (RS) was studied and the application of thermal/thermo-alkaline and NaOH/H2O2 to TWAS and RS, respectively, was evaluated. The batch experiments were conducted at three different TWAS/RS (volume basis) ratios of 1:3, 1:1 and 3:1, respectively. Furthermore, the modified Gompertz model was introduced to predict the biogas yield and evaluate the kinetic parameters. The highest biogas production (409.2 L/kg VSadded) was achieved from co-digestion of TWASthermo-alkaline and RSNaOH at mixing ratio of 1:1, which is greater by 42.2% and 5.9% than that of digesting TWASthermo-alkaline, and RSNaOH alone, respectively. The highest VS removal rate was obtained from the co-digestion of TWASthermo-alkaline and RSNaOH at mixing ratio of 1:3, which is greater by 55.8% and 14.0% than those of mono-digestion. The modified Gompertz model (R2: 0.993–0.998 and 0.993–0.999 for mono- and co-digestions, respectively) showed a good fit to the experimental results and the estimated parameters indicating that the pretreatments and co-digestion of substrates markedly improved the biogas production rate.