Abstract Anaerobic Digestion Research Articles

Theoretical and Numerical Modeling of Turbulent Flow Problems in an Anaerobic Digester of Household Waste in Morocco

Anaerobic digestion can play a strategic role in the development of waste management systems, since it is capable of treating almost all the biodegradable fractions and generally the majority of agricultural residues, animal waste, and household waste, waste from urban and industrial centers. Methanisation is a complex biochemical process carried out in the absence of oxygen and involving different microbial communities in the degradation and conversion of polymers of organic matter into reduced end products, including high-energy biogas. We present a mathematical modeling of the turbulent flow of fluids based on the model of K-epsilon. Thus, the numerical methods that we have chosen to solve the equations of our problem are based on the finite volume method and the Gauss-Seidel method. Our study is very important, since gathered between several physical, chemical and biological domains to determine the different factors that influence the biological degradation. This study allows us to know the advantage of the mechanical agitation on the time of stays of the waste and the increase of yield of digesters and subsequently the production of biogas.

Holistic Scrubber for the Purification of Biogas from Community and Household Digesters

Anaerobic digestion has a dual role in waste management by producing biogas and mitigating the GHG emission from waste disposal sites. Failure in optimization of the various factors affecting anaerobic digestion will result in increased impurities affecting the quality and efficiency of the biogas generated. In the current scenario, a holistic scrubber will help in removing most impurities and increasing efficiency of biogas utilization. In the present study, a scrubber for biogas purification was fabricated and it consists of two separate units for the removal of H2S and CO2. It was evident that the charcoal was more efficient in removal of H2S than metallic scrap in all the bed sizes and the maximum removal rate for charcoal was observed at 100cm bed size with H2S concentration of 50 ppm at the outlet of scrubber, whereas it was 300 ppm for metallic scrap. Outcomes of biogas purification using different molar solutions of NaOH, KOH and Ca(OH)2 were studied . Results of Variation in molarities from 0.5M to 2.5M using three caustic solutions, resulted in CO2 removal at 34% to 5% for NaOH, 35% to 7% for KOH and 39% to 17% for Ca(OH)2. High caustic nature and absorption capacity of solutions made it appropriate to absorb carbon dioxide from biogas and keeping its impurities low.

Screening The Effect of Cu, Mn, and Mg on Ethanol Formation in Degradation Process of Palm Oil Mill Effluent (POME) under Anaerobic Condition Using Two-Level Factorial Design Method

Anaerobic digestion can be used for the treatment of POME to reduce organic content and generate some substances, such as volatile acids, ethanol, and various gasses. During anaerobic fermentation process, microorganism requires the presence of trace elements for growth to improve their performance. This research will be carried out as a study of the presence of trace elements, such as metals (Cu2+, Mn2+, and Mg2+) that has significant effects on ethanol formation. Circulating Bed Reactor was used and operated in a batch system for 48 hours. Metal ions were screened and analyzed by using two-level factorial design method whether there is any correlation effect between the addition of Cu2+, Mn2+, and Mg2+ and ethanol formation. Several parameters which consists of Total Volatile Acids (TVA), dissolved Chemical Oxygen Demand (CODs), Volatile Suspended Solid (VSS), pH, Dissolved Oxygen (DO), and ethanol were measured every sampling. Mn metal is proven statistically affect both TVA and ethanol formation while Mg metal only affect TVA formation. Cu2+ and Mg2+ metals combination affect ethanol formation with largest detected ethanol concentration is 7,483.07 mg/L. The result from this study had identified the metal ions which has significant effect as a foundation for optimization ethanol formation.

Parametric Evaluation of Bio-Digestion Process-A Review

Anaerobic digestion is the biodegradation of the organic waste with the aid of bacteria which performs it work in the absence of oxygen. The main objective of anaerobic digestion is the degradation and destruction of organic substances, with consequent reduction of the pathogens. & odorous emissions. Anaerobic digestion process consists of four major steps: hydrolysis, acidogenesis, acetogenesis an methanogenesis vegetable wastes are a fine substrate with possibility to produce methane and are available. In abundance This work reviews the various parameters affecting the biodigestion process. A careful consideration when selecting the working method parameter such, organic loading rate (OLR), C/N ratio, Gas production rate inoculums to substrate ration (ISR) temperature & pressure hydraulic retention time, Electricity generation calculations are given. Improvement in C/N ratio, higher bio-degradability, effective volatile solids (VS) elimination, eco-friendly sludge production has been regarded as advantage of co-digestion process.

The Impact of Ultradisperse Humic Sapropel Suspensions in Ethyl Alcohol Production

Anaerobic bio digestion of fruit peel wastes is one of the potential for biogas production which subsequently reduces environmental pollution. In order to test the biogas potential of avocado fruit peel wastes co-digested with either cow dung or poultry manure, the raw materials were collected from juice vending house, dairy farm, and poultry farm, respectively. A finely grinded avocado fruit peel wastes was prepared for the different setups. The experiments include 100% avocado fruit peel wastes (T1), 100% poultry manure (T2), 100% cow dung (T3), 50% T1+50% T2 (T4), 50% T1+50% T3 (T5), 75% T1+25% T2 (T6) and 75% T1+25% T3 (T7). The total weight of the raw material was 100 g either solely or in mixture with the animal manure. 15 ml of rumen fluid collected from slaughterhouse was added into each treatment as inoculums. The total volume of the biodigesters was made 1800 ml by adding distilled water; and the setups were completely sealed in plastic bottles. The gas produced was estimated by water displacement method. Feedstocks containing both 100% poultry manure (T2) and 50% poultry manure (T4) attained maximum biogas production within 3-4 days of incubation. The highest in cumulative biogas was produced from the two treatments at 20thday. The optimum temperature, salt and pH for biogas production from the fruit wastes co-digested with animal manure were 25°C, 0.5% and 7 respectively. Under this environmental condition, the highest biogas (453.5 ± 0.5 mL) was produced by T6 that was significantly higher than the othertreatments. In general, the feed stock containing poultry manure co-digested with avocado fruit waste was fast and high in biogas generation. Therefore, co-digestion of avocado fruit peel waste with animal manure is a good strategy to produce bioenergy and minimize urban solid wastes discharge although it demands controlling some physical parameters.

Experimental and Modelling Approach of Biogas Production by Anaerobic Digestion of Agricultural Resources

Anaerobic digestion processes of agricultural resources, as single substrates (wheat bran and barley) or as combination of substrates (75 % corn&25% corn cob � named MIX1 and 40 % corn & 40 % wheat&20 % sunflower husks � named MIX2), were performed, at a mesophilic temperature in a batch reactor, at pilot scale. The results proved that the higher quantity of biogas yield was achieved for barley, followed by MIX1, and finally MIX2. The same order was obtained when the total methane production was evaluated. The performances of digesters were mathematically evaluated by using the modified Gompertz equation. The kinetic parameters, such as the methane production potential (MP), the maximum methane production rate (Rm) and the extent of lag phase (l) were calculated, for each experimental case. The values of the performance indicators confirmed that all the models fitted well with the experimental data.

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.

Anaerobic co-digestion of food waste for energy production - a review

Anaerobic digestion is a recognised methodology for stabilising any kind of wastewater as well as degradation of organic matter. A useful end-product of anaerobic digestion process is bio-gas. Bio-gas is fuel gas, which is a mixture consisting of methane having concentration of about 65% and carbon dioxide having concentration of about 35%. In order to increase the yield of anaerobic digestion one of the options is carrying co-digestion with several substrates. When co-substrate is used along with anaerobic decomposition process it results in positive synergism between digestions medium improves yield of biogas. Solid waste management currently focuses only on disposal options instead of harnessing or recovering energy. Therefore, by moving energy-rich food waste from landfill sites to anaerobic treatment, it can help the society to manage solid waste in a sustainable manner and also generate renewable energy. Anaerobic co-digestion as a treatment option for solid waste is discussed here. Attention is laid towards anaerobic digestion using various substrates like municipal solid waste, domestic sludge, industrial sludge, animal waste, crop residues, weeds, etc.

English

Anaerobic digestion of poultry litter was studied with reutilization of its effluent in the process by pumping into reactor feeding, contributing to the moisture content and making part of the feeding organic load: 0.5 and 1.0 kg VS/m3/day, at evaluations 1 and 2, respectively. The hydraulic residence time lasted 10 days for both evaluations and the useful volume of reactor was 35 m3, with a semi-continuous reactor feeding, under field conditions. The stability of anaerobic digestion was verified through Shewhart control chart. Average efficiency of biogas production was 0.0119 m3/(kg VSadded) at evaluation 1 and 0.0429 m3/(kg VSadded) at evaluation 2. In the second evaluation, the study revealed that biogas produced more energy as methane than spent with electric energy in reactor feeding. According to Lower Process Capability Index (Cpl), measure developed for convenience engineering to quantify the performance of a process, the anaerobic digestion in the second evaluation was capable in its energy operations. Key words: Biogas, Lower Process Capability Index, operational energy viability index, Shewhart control chart, statistical process control.

System Performance and Microbial Communities of Anaerobic Digestion Systems Fed Dairy Manure

Abstract Anaerobic digestion (AD) is the most feasible technology to harness the energy of dairy manure as biogas. However, long retention time (21 days or longer) is needed because of recalcitrance of dairy manure fiber. In this study, we evaluated a thermophilic one-stage AD (T-1stg-AD), a thermophilic-mesophilic two-stage AD (referred to as temperature-phased AD, TPAD), and a mesophilic two-stage AD (M-2stg-AD) system, all at a 15-day retention time, for performance in digesting dairy manure and for variations of microbial populations. The T-1stg-AD system achieved the best performance, followed by the TPAD and the M-2stg-AD systems. For the TPAD system, its first-stage thermophilic digester outperformed its second-stage mesophilic digester, whereas the two digesters of the M-2stg-AD system had similar performance. Each digester harbored distinctive microbial populations, several of which were significantly correlated with system performance. Microbiomes of the two digesters of the TPAD system differed...

Evaluating biochemical methane production from brewer's spent yeast.

Anaerobic digestion treatment of brewer's spent yeast (SY) is a viable option for bioenergy capture. The biochemical methane potential (BMP) assay was performed with three different samples (SY1, SY2, and SY3) and SY1 dilutions (75, 50, and 25% on a v/v basis). Gompertz-equation parameters denoted slow degradability of SY1 with methane production rates of 14.59-4.63mL/day and lag phases of 10.72-19.7days. Performance and kinetic parameters were obtained with the Gompertz equation and the first-order hydrolysis model with SY2 and SY3 diluted 25% and SY1 50%. A SY2 25% gave a 17% of TCOD conversion to methane as well as shorter lag phase (<1day). Average estimated hydrolysis constant for SY was 0.0141 (±0.003) day(-1), and SY2 25% was more appropriate for faster methane production. Methane capture and biogas composition were dependent upon the SY source, and co-digestion (or dilution) can be advantageous.

Biomethanation potential of marine macroalgal Ulva biomass in sequencing batch mode: Changes in process performance and microbial community structure over five cycles

Anaerobic digestion (AD) of Ulva biomass, a promising next-generation feedstock for energy production, was investigated in sequencing batch mode. Over five cycles of operation, the methane yield decreased more than twofold (from 0.15 to 0.07 L/g CODfed), while the organic treatment efficiency (i.e., chemical oxygen demand (COD) removal) remained fairly constant (53.7–61.1%). Such changes in reactor performance were related with structural variations in the microbial community, particularly the bacterial community, with repeated cycles. Methanosaeta- and Methanolinea-related populations were most likely the main aceticlastic and hydrogenotrophic methanogens, respectively, in the reactor. The emergence and prevalence of sulfate-reducing bacteria (SRBs), primarily a Solitalea-related population, most likely resulted in increased consumption of organic substrates for sulfate reduction, rather than methane production, in later cycles. Our observations suggest that the metabolic properties of the reactor changed with the transition of the bacterial community structure over cycles, and the metabolic shift had a negative effect on methanogenesis. The sequencing batch operation strategy applied in this study was not suitable for maximizing methane production from Ulva biomass, although the treatment efficiency was fairly stable. Robust control of SRB activity is necessary for more stable and efficient biomethanation of Ulva biomass in sequencing batch mode.

Effect of Microwave Pretreatment on BMP of Decanter Cake from Palm Oil Mill Factory

Anaerobic digestion is an effective method for treating decanter cake in the biogas production. Decanter cake usage is limited by its slow fiber degradation for anaerobic digestion process. The aim of this study is to study the possibility of using microwave pretreatment to enhance decanter cake digestibility. The power and heating time are the parameters that influence the biogas production and methane yield. The Biochemical Methane Potential (BMP) tests are used in this study to find the optimization setting of a microwave pretreatment for decanter cake solubilization and anaerobic digestibility. The results show that the microwave pretreatment provides a better performance in terms of COD solubilization and anaerobic digestibility. The increasing power and heating time can improve the biogas production and methane yield for microwave pretreated decanter cake under anaerobic digestion process. Finally, the optimum power and heating time used in the microwave pretreatment, found in this study, is 160 watts and 8 min for methane yield under the anaerobic digestion process. The highest methane yield is 309.9 mL CH4/g COD removed. The microwave pretreated decanter cake at 160 watts of power and 8 min of heating time can improve the methane yield with an improvement of 24.6% in comparison with the non-microwave pretreated decanter cake. It can be concluded that the microwave pretreatment of decanter cake from palm oil mill factory could be the rapid and environmental method for biogas production enhancement.

Effect of control of pH in anaerobic digestion of organic fraction of municipal solid waste

Anaerobic digestion often encounters the problem of higher population of the acid-forming bacteria relative to the slower growing methanogenic bacteria which inhibits the methanogenic process leading to problems such as low gas yield and process instability. In this study, anaerobic digestion of organic fraction of municipal solid waste has been carried out in two identical model laboratory-scale single stage anaerobic digesters simultaneously; one without the control of pH and other with the control of pH, with same substrate keeping all other conditions identical. Results indicated that the hydraulic retention time of AD reaction could be reduced by at least seven days and the overall efficiency of gas production of the digester could be increased by more than 21.95% (at 50 days time) by the control of pH in the digester.

An Approach on Environmental Sanitation Situation and Toilets Septic Tank Design in Urban Nigeria: A Case Study of Calabar South

Anaerobic digestion of sewage concentrates represents a very suitable means of generating bioenergy while reducing a huge amount of waste to disposal. Effective biogas production from sewage sludge can be achieved by optimizing operational conditions. In this study, the research was designed to compare the biogas production efficiency from sewage sludge recovered from coagulation and absorption process with sludge recovered from bioflocculation, centrifuged and chemical coagulation (Al2(SO4)3+CMC) processes through biomethane potential experiment (BMP). From the results obtained, the maximum methane production rate of 56.85 mLCH4/gCOD was achieved from concentrates collected during coagulation and absorption treatment process without solid retention time (SRT), concentrates collected during 0.5 d SRT had maximum methane production rate of 110.88 mLCH4/gCOD, methane production rate of 154.28 mLCH4/gCOD was achieved from 2 d SRT concentrate. The Al2(SO4)3+CMC treated concentrate had methane yield of 143 mLCH4/gCOD while bioflocculation concentrate had methane yield of 139 mL/gCOD and centrifuged concentrate had the yield of 124 mL/gCOD within the period of 22 to 29 days. The overall result showed that concentrates recovered from coagulation, adsorption and Al2(SO4)3+CMC processes produced the highest methane with better efficiency and recorded the most stable performance throughout the period of the experiment and this encouraged the future use in anaerobic digestion for large scale methane production.

Persistence of Methanosaeta populations in anaerobic digestion during process instability

Anaerobic digestion is a sustainable technology for the treatment of organic waste and production of biogas. Acetoclastic methanogenesis accounts for the majority of methane production in anaerobic digestion. Therefore, sustaining robust acetoclastic methanogens is important for stable process performance. Due to faster growth kinetics at high acetate concentrations, it has been considered that Methanosarcina would be more prevalent than Methanosaeta in unstable anaerobic digestion processes which frequently experience high acetate levels. Methanogen population dynamics were monitored in multiple continuous anaerobic digesters for 500days. Results from quantitative polymerase chain reaction analysis show that Methanosaeta dominated over Methanosarcina in anaerobic digestion at high acetate levels up to 44mM, suggesting the potential of Methanosaeta as a robust and efficient acetoclastic candidate for resilient anaerobic methane conversion. Further efforts are needed to identify mechanisms contributing to the unexpected competitiveness of these methanogens at high acetate levels observed in this study.

Two-Stage Anaerobic Digestion Process Combining Pre-digestion with Methanization

Anaerobic digestion of a mixture of manure and sewage sludge by combination of the biological predigestion at 73°C with methanization at 55°C was studied with regard to the biogas process efficiency,energy balance and sanitation effect. Performance of the two-stage digestion was compared with theconventional, one-stage moderate thermophilic digestion at 55°C and mesophilic digestion at 37°C,respectively. The best performance was achieved by the two-stage treatment both in terms of VolatileSolids (VS) removal and biogas yield. Up to 60% of VS was removed and a specific methane yield of 300ml CH4 gVS-1 was achieved. Sanitation effect was measured as inactivation of the indicators of bacterialpathogens - the faecal enterococci and spores of Clostridium perfringens. Elimination of faecal enterococcito non-detectable level occurred only during treatments at 73°C and 55°C. Numbers of Clostridiumperfringens spores were reduced solely by the combined 73°C/55°C treatment.

Investigation of Bacterial and Methanogen Community Composition and Diversity in full-scale Anaerobic Manure Digesters

Anaerobic digestion of biopolymers into methane is accomplished by complex microbial communities that remain poorly characterized. Their composition tends to vary, likely as a result of many factors such as substrate composition, operating parameters, and microbial succession. In order to gain further insight, we performed a comparative analysis of microbial community composition amongst four mesophilic full scale anaerobic digesters, using a combined total of 133,789 high quality, non-chimeric bacterial and methanogen sequence reads from PCR-generated amplicons of the 16S rRNA gene. In three digesters that used manure as their main substrate, methanogen populations were composed predominantly of a common Methanosarcina-related Operational Taxonomic Unit (OTU). The composition of bacterial populations in these digesters was more diverse, with the most highly represented OTUs consisting of different combinations of Bacteroidetes-Chloroflexi or Bacteroidetes-Firmicutes-unclassified bacteria. In contrast, the dominant methanogen OTU in the remaining digester, whose substrate consisted of manure and offfarm lipid waste, was related to species of the genus Methanoculleus, and two bacterial OTUs (Chloroflexi and unclassified) together represented 83.7% of bacterial sequence reads. Our results suggest that while methanogen composition in anaerobic dairy manure digesters appeared to be limited to two main profiles, there was very limited convergence in bacterial phylogenetic composition. Since the major bacterial OTUs identified corresponded to uncultured species belonging to uncharacterized genera, future investigations will be required to determine their biochemical roles and assess the level of functional redundancy among them.

Beating treatment to enhance digestibility of fresh grass

Anaerobic digestion (AD) is one of the most popular biomass conversion technologies. AD can be further divided into four stages: pre–treatment, digestion, gas upgrading and digestate. The main goal of pre–treatment is to improve degradability of the material in order to enhance gas production and anaerobic digester performance. Beating treatment as a new mechanical treatment technique has been applied in this work. Laboratory scale mesophilic AD was operated to determine the methane yield from fresh grass and the potential efficiency increase in methane production. Fresh grass as main substrate has been treated in three deferent levels of beating treatment (5–min, 15–min treatment, and 40–min treatment). Many experiments have been carried out according to these levels of treatment and the amount of biogas was measured for each treatment. The average amount of biogas produced before and after beating treatment was compared. Composition analyses of different chemical compounds in biogas have been measured. Significant improvements were achieved in the degradability during the AD and in the biogas production from the pre–treated fresh grass.

Numerical Optimization of Biogas Production through a 3-Steps Model of Anaerobic Digestion: Sensitivity of Biokinetic Constants Values

Anaerobic digestion (AD) of organic substrates can produce biogas, which consists mainly of methane and carbon dioxide. The objective of this study is to perform, for a given wastewater, useful numerical simulations following model number 1 by integrating an optimization sequence to show biokinetic constants effects on the biogas production rate. Therefore, we obtain via an accurate and simple simulation with less time of calculations a reliable estimation of biokinetic values. Indeed, we evaluate the effect of certain biokinetic constants on the response of 3-steps AD model to select the most significant ones. Thus, the constants in question were varied in specific ranges by setting the others. We conclude that main parameters were saturation constant for acidogenic bacteria (KS1), the solublization rate per unit of acidogenic biomass (ᵝ) and the yield coefficient for the yield of volatile acids from soluble organics (Yb) they have an important effect on the biogas production rate Q max and period to reaches its plateau value.