Methanogenesis Phase Research Articles

Bioaugmentation with targeted recombinant functional consortia to improve lignocellulosic biowaste co-anaerobic digestion performance

Hydrolysis rate limitation and acid-methanogenesis phase imbalance are critical challenges in the anaerobic digestion (AD) of lignocellulosic substrates, hindering substrate utilization and methane conversion. Bioaugmentation is widely employed to promote biochemical and metabolic reactions at all stages of AD to enhance methanogenic efficiency. However, synergistic reinforcement for simultaneous enhancement of the hydrolysis and methanogenesis phases requires further elucidation. This study investigated the effect of lignocellulolytic mutualistic methanogenic culture (LMMC) obtained by targeted domestication on the AD system. The results showed that the bioaugmented reactor enhanced the methane production by 21.03%-239.12% and the peak daily methanogenesis by 6.54%-127.85%. Introducing LMMC was directly related to improving methanogenic performance and significantly affected the AD key indicator, which facilitated the timely consumption of volatile fatty acid (VFA) for utilization. Microbial analysis results showed that the enriched hydrolytic acidifying bacteria, anaerobic fungi, and acetoclastic methanogens formed a microbial synergistic reinforcement alliance, which jointly stimulated methane production, alleviated the potential risk of instability, and promoted the stable operation of the AD system. Collectively, the role of synergistic reinforcement in the microbial consortium was highlighted to improve the stability and efficiency of AD process of lignocellulosic biomass.

Improving the Anaerobic Digestion Process of Wine Lees by the Addition of Microparticles

Wine lee generation, a by-product of the wine industry, implies economic challenges for producers in terms of management due to its high organic load and low pH value. Biological treatment based on controlled anaerobic digestion may emerge as a viable management alternative given its promising potential for biogas production thanks to the organic content of the substrate. However, the complex properties of wine lees may lead to microbial activity inhibition and process kinetics failure. Various solutions have already been explored, including co-digestion with other substrates, or the application of different pretreatments, to mitigate the effects of the accumulation of phenolic compounds, volatile fatty acids, antioxidants, or the acidic pH value of the medium. In this study, laboratory-scale batch reactors were established, adding iron- (magnetite) or carbon (graphite)-based microparticles to assess their impact on the kinetics of the process. The results demonstrate a significant improvement of 35% in the potential production of biomethane after four days of operation with graphite particles and 42% after five days using magnetite particles. Methane production rates, as determined by the Gompertz model, were 45.38 and 46.54 mL CH4∙gVS−1∙d−1 for the application of graphite and magnetite microparticles to the medium, respectively, compared to the value of 33.46 mL CH4∙gVS−1∙d−1 for the control trial, confirming kinetic process improvements of 36% and 39%, respectively. Evidences of the acceleration of the methanogenesis phase were detected along the essays; however, the strong inhibition mediated by the carboxylate accumulation was not avoided in any of the tested conditions.

Bioenergy production from pretreated rice straw in Nigeria: An analysis of novel three-stage anaerobic digestion for hydrogen and methane co-generation

The response to Nigeria's energy inadequacies and waste management issues is projected in this research to be achieved with hydrogen and methane co-produced from pretreated (PT) rice straw (RS) in a three-stage digestion process. This study also demonstrated a novel pretreatment (PTM) agent to improve biological energy recovery from RS. The objectives were accomplished using acidogenic and methanogenic procedures in batch, semi-continuous and continuous systems after pretreating RS with chemical/potash extract (PE) followed by a biological agent. At the same time, the energy assessments were done using data from the laboratory study and the literature. The research findings indicated that at the acidogenesis stage, specific hydrogen yield was insignificant when chemical agents and PE were employed alone. However, the daily H2 production increased when the PT RS residues were enzymatically hydrolysed with NaOH-PT (114 NmL H2 g−1 TS d−1) and PE-PT (103 NmL H2 g−1 TS d−1) RS substrates having the highest values at steady states and raw RS producing the least (30 NmL H2 g−1 TS d−1). In the methanogenesis phase, chemical/ PE PTM followed by enzymatic hydrolysis of RS improved the daily specific methane production by 18%, 31.7% and 41.5% for HCl, PE and NaOH-PT RS residues. The methane production efficiency was 80% for NaOH, 75% for PE, and 68% for HCl RS PT samples, while the raw RS was 48%. The total output energy expressed in electricity and thermal production using combined cooling, heat, and power (CCHP) showed that NaOH and PE-PT RS digesters gave the highest electricity (892.43 and 852.00 KWhelect. tonne-1 TS) and thermal (1194.10 and 1140 KWhtherm. tonne-1 TS) yield respectively. Similarly, the cooling fluid in KWhcool produced per tonne of TS RS was 835.57, 798.00 and 741.66 for NaOH, PE and HCl PT RS samples. Finally, whereas the Firmicutes, especially the Clostridium, Ruminococcus and Thermoanaerobacterium, were the dominant microbial community in acidogenic digestates, the Euryarchaeota typified by Methanobacterium, Methanosarcina and Methanosaeta were the principal phyla for most methanogenic reactors.

Impacts of organic loading rate and hydraulic retention time on organics degradation, interspecies interactions and functional traits in thermophilic anaerobic co-digestion of food waste and sewage sludge

This study provided novel insights into the effects of organic loading rate (OLR) and hydraulic retention time (HRT) on thermophilic anaerobic co-digestion of food waste and sewage sludge. The obtained maximum methane (CH4) yield of 328 ± 4 mL CH4/g CODfed at HRT of 15 days (OLR = 5.8 g VS/L/d) was partly attributable to the enhanced acidogenesis, acetogenesis, and methanogenesis phases. The increased key enzyme activities, particularly acetate kinase (improved by 5.2-fold), providing substantial methanogenic substrates for efficient CH4 production. The functional syntrophs that were related to syntrophic decarboxylation, novel acetate oxidation & reductive acetyl-CoA, and β-oxidation pathways could drive trophic interactions with methanogens. This markedly stimulated hydrogenotrophic Methanoculleus thermophilus metabolism and concomitantly enriched mixotrophic Methanosarcina thermophila. The distinctive cross-feeding interspecies interactions significantly affected the assembly and dynamics of thermophilic consortia. These findings shed light on the physicochemical and microbial mechanisms of HRT- and OLR-dependent enhancement of methanogenesis.

Optimization of operating parameters for biogas production using two-phase bench-scale anaerobic digestion of slaughterhouse wastewater: Focus on methanogenic step.

The objective of the present study was an optimization of operating parameters and the performance of the methanogenesis reactor in phased anaerobic digestion (AD) of slaughterhouse wastewater at 37.5°C. Accordingly, the feedstock of the methanogenic reactor was effluent from the hydrolytic-acidogenic reactor operating at HRT of 3-days and OLR of 1789 mg/L. The methanogenesis phase was also investigated at different hydraulic retention time (HRT) values ranging from 12 to 3days at 3-day intervals, and organic loading rates (OLR) of 149, 199, 298, and 596mg of COD/L. The methanogenesis reactor effluent concentrations of TN, TP, PO4-3, SO4-2, and S2-2 were ranging between 424-464, 83-117, 63-86, 130-197, and 0.98-1.02mg/L, respectively. The removal efficiencies of TN and TP were vary from 10-17% to 17-21%, respectively. The average biogas production was 125 ± 16, 150 ± 10, 185 ± 4, and 154 ± 17mL at HRT of 12, 9, 6, and 3days, respectively. Methane quality (%) and yield (mg/L of COD) were 55-67% and 0.02-0.03, respectively. Furthermore, the average stability indicator parameter values of (total volatile fatty acid (TVFA) = 520 ± 19mg/L, total alkalinity (TotA) = 1424 ± 10mg/L, TVFA:TotA. Ratio = 0.36, salinity = 1172mg/L, pH = 6.92) and performance indicator parameters removal efficiency (RE) for (chemical oxygen demand (COD) = 81%, volatile solid (VS) RE = 95%, biogas production = 185 ± 4mL, methane yield = 0.03 per mg COD consumed) were achieved at HRT of 6days and OLR of 298mg of COD/L. Low removal efficiencies of TP and TN at all HRT/OLR were observed for the methanogenic reactor signifying further treatment system.

Acetoclastic methanogenesis pathway stability despite the high microbial taxonomic variability in the transition from acidogenesis to methanogenesis during food waste anaerobic digestion

Anaerobic digestion (AD) is a microbial-mediated biogeochemical process that includes hydrolysis, acidogenesis, acetogenesis and methanogenesis. AD instability usually occurs in the transition from the acidogenesis phase (AP) to the methanogenesis phase (MP) due to over acidification. However, the underlying microbial mechanism of this transition has not been well characterized. In the present study, the transition of bacterial and methanogenic community composition, methanogenesis functional gene expression and metabolic pathways from AP to MP during food waste (FW) AD were investigated in a bioreactor using metagenomics and reverse transcription PCR technology. AP and MP were identified by changes in methane production, gas accumulation, pH and volatile fatty acids (VFAs). Concomitant with the changes in these physiochemical parameters, the bacterial and methanogenic community composition showed succession patterns. The bacterial composition transformed from acidogenic bacteria (Propionispira and Bacteroides) to hydrolytic bacteria (Smithella, Syntrophus and Syntrophorhabdus), and the methanogen composition transformed from the domination of acetoclastic methanogens (Methanosaeta) to the codomination of hydrogenotrophic methanogens (Methanoculleus, Methanolinea and Methanobacterium) and acetoclastic methanogens (Methanosaeta). The expression level of the methanogenesis functional gene mcrA significantly (p < 0.05) increased in response to the increasing methane production. In contrast, acetoclastic methanogenesis as the main methanogenesis metabolic pathway remained stable. These results showed that FWAD key physiochemical parameters drive the variation in microbial community composition and functional genes expression but not the methanogenesis metabolic pathway. The finding suggests that FWAD process may be better predicted by methanogenic functional characteristics than by microbial community composition.

Specific degradation of phenolic compounds from palm oil mill effluent using ozonation and its impact on methane fermentation

In this study, the inhibition to anaerobic digestion of phenolic compounds present in palm oil mill effluent (POME) was quantified in batch and continuous operations to assess their effects on methane fermentation. Caffeic acid (CAF), at its concentration in POME, was found to be the most effective inhibitor of the microbial community in hydrolysis, acidogenesis, and methanogenesis phases. To mitigate the toxicity of anaerobic digestion (AD), the pretreatment of POME with various ozone dosages (0.1 to 0.4 gO3/Lwastewater) was performed to determine the effectiveness of specific phenolic compounds destruction. The ozone pretreatment was able to significantly degrade these phenolic molecules and alter their profile in POME over the wide ranges of ozone dosage. Ozone dosage of 0.2 gO3/Lwastewater was optimal to cause the individual concentration to drop below the strong inhibitory levels. When POME was ozonized, the overall total phenolic compounds in the effluent were reduced by 75 % from 613 to 155 mg/L. The overall volumetric biogas yields correspondingly increased by 67 % from 0.3 to 0.5 L/Lreactor.d with the improved specific methane yield from 6.3 ± 0.2 to 9.3 ± 0.1 LCH4/m3. The results demonstrated that the inhibitory effects of phenolic compounds could significantly be detoxified by pretreatment with ozone to enhance anaerobic digestion performance.

Leachate characteristics: Potential indicators for monitoring various phases of municipal solid waste decomposition in a bioreactor landfill

Leachate is a contaminated liquid generated during the bio-chemical decomposition processes of municipal solid waste (MSW) that occurred at semi-solid or solid-state in a bioreactor landfill (BLF). Conceptually, leachate from a BLF is analogous to the urine generated in the ‘human body’, on which the medical practitioners rely to diagnose and remediate ailments. In line with this practice, to monitor the complex MSW decomposition processes, prolonged investigations were performed to establish the temporal variation of different chemical parameters (such as pH, electrical conductivity, chemical oxygen demand, organic- and inorganic carbon, nitrate- and ammonium-nitrogen, sugars and volatile fatty acids) of the leachate collected from different cells (age≈ 6–48 months) of a fully functional BLF in Mumbai, India. Furthermore, to understand the effect of the climate, MSW composition and landfill operating conditions on the rate of the decomposition process, chemical parameters of the leachate obtained from a landfill located in the central part of Poland were compared with the BLF. The study reveals that the chemical parameters, except for the pH, evince a rapid reduction with time and attain a constant value, which indicates the ‘stabilized MSW’. Also, native microorganisms that are an integral part of MSW consume volatile fatty acids within a year in the BLF, which facilitate the rapid transformation of the decomposition process from acidogenesis and acetogenesis to the methanogenesis phase. It is worth iterating here that based on the long-term field study, a convenient and efficient methodology, which is currently missing from the literature, has been established to understand the kinetics of different phases of anaerobic decomposition. This study would be very helpful to the landfill operators, who are interested in accelerating MSW decomposition by augmenting leachate properties.

Mathematical Study of a Two-Stage Anaerobic Model When the Hydrolysis Is the Limiting Step

A two-step model of the anaerobic digestion process is mathematically and numerically studied. The focus of the paper is put on the hydrolysis and methanogenesis phases when applied to the digestion of waste with a high content of solid matter: existence and stability properties of the equilibrium points are investigated. The hydrolysis step is considered a limiting step in this process using the Contois growth function for the bacteria responsible for the first degradation step. The methanogenesis step being inhibited by the product of the first reaction (which is also the substrate for the second one), and the Haldane growth rate is used for the second reaction step. The operating diagrams with respect to the dilution rate and the input substrate concentrations are established and discussed.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45–10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68–95% of the total organics), particularly the fraction of 1–5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

Optimization of Hydrolysis-Acidogenesis Phase of Swine Manure for Biogas Production Using Two-Stage Anaerobic Fermentation

The traditional pig manure wastewater treatment in Taiwan has been low in methane production efficiency due to unstable influent concentration, wastewater volume, and quality. Two-stage anaerobic systems, in contrast, have the advantage of buffering the organic loading rate in the first stage (hydrolysis-acidogenesis phase), allowing a more constant feeding rate to the second stage (methanogenesis phase). Response surface methodology was applied to optimize the operational period (0.5–2.0 d) and initial operational pH (4–10) for hydrolysis and acidogenesis of the swine manure (total solid 5.3%) at 35 °C in batch operation mode. A methanogenesis verification experiment with the optimal condition of operational period 1.5 d and pH 6.5 using batch operation resulted in peak volatile acid production 7 g COD/L, methane production rate (MPR) 0.3 L-CH4/L-d, and methane yield (MY) 92 mL-CH4/g-CODre (chemical oxygen demand removed). Moreover, a two-stage system including a hydrolysis-acidogenesis reactor with the optimal operating condition and a methanogenesis reactor provided an average MPR 163 mL/L-d and MY 38 mL/g volatile solids, which values are 60% higher than those of a single-stage system; both systems have similar dominant methane-producing species of Firmicutes and Bacteroidetes with each having around 30%–40%. The advantages of a two-stage anaerobic fermentation system in treating swine manure for biogas production are obvious.

Long-term operation of the pilot scale two-stage anaerobic digestion of municipal biowaste in Ho Chi Minh City

A pilot-scale two-stage anaerobic digestion system, which includes a feed tank (0.4 m3), a hydrolysis reactor (1.2 m3) followed by a methane fermenter (4.0 m3) was set up and run at the municipal solid waste landfill located in Ho Chi Minh City (HCMC), Vietnam. The feed that was separated from urban organic solid waste was collected at households and restaurants in District 1, HCMC. This study aimed to investigate the resource recovery performance of the pilot two-stage anaerobic digestion system, in terms of carbon recovery via biogas production and nutrient recovery from digestate. The average organic loading rate (OLR) of the system was step increased from 1.6 kg volatile solids (VS)·m−3·d−1, 2.5 kg VS·m−3·d−1 and 3.8 kg VS·m−3·d−1 during 400 days of operation. During the long-term operation at three OLRs, pH values and alkalinity were stable at both hydrolysis and methanogenesis stages without any addition of alkalinity for the methanogenesis phase. High buildup of propanoic acid and total volatile fatty acid concentrations in the fermenter did not drop pH values and inhibit the methanogenic process at high OLRs (2.5–3.8 kg VS m−3·d−1). The obtained total chemical oxygen demand (tCOD) removal performance was 83–87% at the OLRs ranging from 2.5 kg VS·m−3·d−1 and 3.8 kg VS·m−3·d−1, respectively. The highest biogas yield of 263 ± 64 L·kg−1 tCOD removed obtained at OLR of 2.5 kg VS·m−3·d−1. It is expected that a full scale 2S-AD plant with capacity of 5200 tons day−1 of biowaste collected currently from municipal solid waste in HCMC may create daily electricity of 552 MWh, thermal energy of 630 MWh, and recovery of 16.1 tons of NH4+-N, 11.4 tons of organic-N, and 2.1 tons of TP as both organic liquid and solid fertilizers.

Insights into Anaerobic Co-Digestion of Lignocellulosic Biomass (Sugar Beet By-Products) and Animal Manure in Long-Term Semi-Continuous Assays

Biogas production through anaerobic digestion has proven to be one of the most important pillars of the transition into the circular economy concept, a sustainable approach for biorefinery. This work aims to extend and improve knowledge in the anaerobic co-digestion of complementary substrates, given insights into wastes biodegradability and the influence of manure composition on the anaerobic process stability. Anaerobic co-digestion of sugar beet by-products with two kinds of animal manure (pig and cow) was investigated in semi-continuous assays, analyzing both common and non-classical parameters. Co-digestion with manure clearly mitigated the inhibitory effect of volatile fatty acids at high organic loading rates, leading to increases in methane production by 70% and 31% in comparison with individual digestion of sugar beet by-products, for co-digestion with pig and cow manure, respectively. Non-classical parameters could give more insight into the coupling/uncoupling of the anaerobic digestion phases and the involved microorganisms. Indirect parameters indicated that the process failure at the critical organic loading rates was mainly due to methanogenesis inhibition in the co-digestion with pig manure, while in co-digestion with cow manure or in individual digestion of sugar beet by-products, both hydrolysis–acidogenesis and methanogenesis phases were affected. Biomethanation degree refers to the maximum methane potential of organic wastes. Sugar beet by-products required a long digestion-time to reach high biodegradability. However, short digestion-times for co-digestion assays led to a high biomethanation degree.

Novel thermodynamic early warning method for anaerobic digestion failure of energy crops

To investigate whether thermodynamic calculations of anaerobic digestion processes can be applied to the early warning for unstable anaerobic digestion, a group of semi-continuous digesters fed with an energy crop (Hybrid Pennisetum) were operated via a step-wise increase in the organic load rates until overload occurred. Traditional early warning indicators, such as biogas production and content, pH, alkalinity, and volatile fatty acids as well as the methane/carbon dioxide (CH4/CO2) and volatile fatty acid/alkalinity ratios, were regularly monitored during the process. The Gibbs free energy changes (ΔG) of the methanogenesis phases of valerate, butyrate, and propionate were calculated based on Nernst and Van’t Hoff equations. The results demonstrate that ΔG of the three syntrophic methanogenesis phases can be used as an early warning indicator for unstable anaerobic digestion, indicating anaerobic digestion failure (ceased biogas production) up to 21 days in advance, that is, 1–8 days earlier than some other indicators.

Two Phase Anaerobic Digestion System of Municipal Solid Waste by Utilizing Microaeration and Granular Activated Carbon

In an anaerobic digestion (AD) process, the hydrolysis phase is often limited when substrates with high concentrations of solids are used. We hypothesized that applying micro-aeration in the hydrolysis phase and the application of granular activated carbon (GAC) in the methanogenesis phase could make the AD process more efficient. A packed bed reactor (PBR) coupled with an up-flow anaerobic sludge blanket (UASB) was conducted, and its effects on methane generation were evaluated. The micro-aeration rate applied in PBR was 254 L-air/kg-Total solids (TS)-d was compared with a control reactor. Micro-aeration showed that it reduced the hydrolysis time and increased the organic matter solubilization as chemical oxygen demand (COD) increasing 200%, with a volatile fatty acids (VFAs) increment higher than 300%, compared to the control reactor (without aeration). Our findings revealed that the implementations of microaeration and GAC in the two-phase AD system could enhance methane production by reducing hydrolysis time, increasing solid waste solubilization.

Effect of combined mechanical–ultrasonic pretreatment on mesophilic anaerobic digestion of household organic waste fraction in Morocco

Methanization is a technology that involves complex biological reactions and it is the subject of several scientific studies. The paper aims to evaluate the effect of the combined mechanical and ultrasonic pretreatment (CMUP) on the anaerobic digestion (AD) of the household organic waste fraction in Morocco (HOWF), using a continuous stirred tank reactor (CSTR) at mesophilic conditions.This article presents and compares a results obtained by operating two experiments in lab scale reactors with mechanical pretreatment (MP) and with CMUP. The experiment with MP was considered in this study as a control. During the handling period, the effect of CMUP on the AD of HOWF was studied. The process was evaluated in terms of methane production and biodegradability. The stability was maintained within correct parameters throughout the process for each experiment, while the methane yield and biodegradability of the control and CMUP experiments were 382 (mL CH4 g−1VS) (0°C, 1 atm), 72%, and 493 (mL CH4 g−1VS) (0°C, 1 atm), 86 % respectively. This shows clearly that the CMUP enhance the methane production and increase the biodegradability, suggesting that this combination pretreatment improve the hydrolysis and methanogenesis phases of the process.A kinetic study on anaerobic digestion results using the first order model was also used. The mathematical model shows a good fit with the experimental data.

Microbial community dynamics and process performance of a full‐scale two‐stage anaerobic digester under the replacement from energy crop to poultry manure

AbstractBACKGROUNDThis study assessed the composition and dynamics of the bacterial and archaeal communities in a full‐scale two‐stage anaerobic digester over five months. The plant was fed on a variable mixture of feedstock, in which the energy crops were replaced with poultry manure/litter (from 1.6% to 7.5%) to reduce the operational costs.RESULTSThe elevated concentration of ammonia in the digester did not hamper biogas production and its concentration of methane. The low level of acetate, butyrate and propionate in the methanogenesis phase indicated a strong activity of acetotrophic methanogens. PCR‐DGGE and sequencing have demonstrated that the stability of the volatile fatty acid distribution concurred with low level of population shifts as shown by the moving windows analysis. Nevertheless, PCoA analyses revealed that the variation in the digester alimentation and the carbon:nitrogen (C:N) ratio had a key role in assembly the bacterial and archaeal communities. The high ammonia level favoured the growth of Caldicoprobacteraceae and Syntrophomonadaceae, whereas dominant archaea detected belonged to the family of Methanosarcinaceae.CONCLUSIONCheap and readily available N‐rich feedstock could be used safely to decrease the costs of the anaerobic digestion process. © 2019 Society of Chemical Industry

Application of the IWA Anaerobic Digestion Model (ADM1) for the Valorization of Maize Residues in Morocco

The modeling of the natural biological process of anaerobic digestion (AD) or methanization is a metabolic process of fermenting the organic waste in a biogas reactor without oxygen. The Anaerobic Digestion Model No. 1 (ADM1) discovered by international water association (IWA) is the model used for the simulation study conducted in order to demonstrate and evaluate the applicability of ADM1 to lignocellulosic biomass (LB) such as maize waste (MW) in Morocco which is the subject of this research. In this paper, the technique of anaerobic digestion has been used as a way to recover the solid waste, which is the MW into biogas, by the process of fermentation of the complex polymers into monomers and oligomers. The use of ADM1 has been based on the integrity of this model that takes into account many variables and many settings, such as the physico-chemical processes, which are very important systems in the modeling of anaerobic digestion, as well as the biochemical process that includes biochemical equations which compose the core of any model that include biological reactions. This study has been done by using the anaerobic digestion model 1 (ADM1) under mesophilic temperature (35C), knowing that the mathematical and numerical modeling of this study is the main objective. This work has been done with the intention of modeling and simulating the production of methane from the degradation of organic waste, under different ranges of pH, in order to see what effects may be applied to the acidogenesis and methanogenesis phases, taking in consideration the effect of the inhibition phenomena. The results indicate a significant decrease in glucose along with the increase of methane.

An experimental study on the influence of zeolite on changes of pH and alkalinity in anaerobic treatment of compost leachate

AbstractWith the increase of urbanization, municipal solid waste has also increased. Therefore, the need for solid waste management is also increasing compared with earlier decades. Composting is a good option for the recycling of solid waste; however, it produces leachate, which requires proper treatment systems to prevent environmental degradation. Due to high chemical oxygen demand (COD) concentrations in compost leachate, anaerobic treatment is the best option for handling the effluent, and an anaerobic baffled reactor (ABR) is one such anaerobic reactor that can be used for its treatment. Because of high ammonia and heavy metal concentrations, as well as the possibility of sludge washout in ABRs, it is important to use proper media, such as zeolite, which can reduce inhibition effects and sludge washout from the reactor. Anaerobic treatment, especially during the methanogenesis phase, is sensitive, and pH and alkalinity are parameters that influence the treatment. Therefore, adjusting these parameters within a normal range is very important to the proper functioning of anaerobic systems. In this study, a pilot‐scale ABR was used, and the last 4 of the 8 ABR compartments were filled with zeolite. The bioreactor was operated at hydraulic retention times (HRT) of 3, 4, and 5 days, with zeolite filling ratios of 10%, 20%, and 30%, and influent COD concentrations of 10,000, 20,000, and 30,000 milligrams per liter (mg/L). In this study, pH value was 6.43 ± 0.1, 6.96 ± 0.3, and 6.96 ± 0.25 at filling ratios of 10%, 20%, and 30%, respectively. According to the results, in all filling ratios, no significant changes were observed in the pH value when the organic loading rate increased and its amount was within a constant range. Influent alkalinity was equal to 2015 ± 510, 2884 ± 505, and 4154 ± 233 milligrams of calcium carbonate per liter (mg CaCO3/L) at influent COD concentrations of 10,000, 20,000, and 30,000 mg/L, respectively, and in effluent, they were 2536 ± 336, 3379 ± 639, and 4377 ± 325 mg CaCO3/L, respectively. The amount of alkalinity in the effluent increased compared with the alkalinity in the influent. The results show that the amount of alkalinity in the influent and effluent was similar, and the alkalinity enhancement was lower when the filling ratio was increased from 10% to 20%, and 20% to 30%. Comparisons of the results from zeolite with and without biofilm showed that, in cases of zeolite with biofilm, the amounts of silica and oxygen decreased and the amount of carbon increased, and it showed the formation of biofilm on the surface of zeolite. In addition, the absence of sodium in the zeolite with the biofilm indicated that sodium was exchanged with ammonium ions. According to the results, zeolite can be used in anaerobic reactors as a medium, and it also reduces fluctuations in pH and alkalinity at different organic loading rates, providing a normal range for anaerobic treatment.

Performance evaluation of methanogenic digester using kitchen waste for validation of optimized hydrolysis conditions for reduction in ammonia accumulation

Ammonia accumulation above the inhibitory level is the major cause of failure of anaerobic digesters (AD) treating kitchen waste (KW). In the present investigation a biphasic system (hydrolysis and methanogenesis) was evaluated for validation of previously optimized hydrolysis conditions [pH 7.2–7.5, Aeration 0.19–0.22 vvm (volume of air per unit volume of media per minute), Temperature 44 - 48 °C] for reduction in ammonia accumulation in the methanogenic digester. The pre hydrolyzed KW was fed to methanogenic reactor with the organic loading 1.16 gVS/L - 2.97 gVS/L. Specific biogas and methane yield were 0.589 L biogas/gVSfeed and 0.321 L methane/gVSfeed under mesophilic condition, and 0.633 L biogas/gVSfeed and 0.329 L methane/gVSfeed under thermophilic condition, respectively. The ammonia concentration in the methanogenic phase remained below 250 ppm and 550 ppm under mesophilic and thermophilic conditions, respectively, validate the optimized conditions for hydrolysis of KW for reduction in ammonia accumulation in methanogenesis phase. The Microbial diversity analysis of methanogenic phase was carried out to monitor the shifting of microbial population under mesophilic and thermophilic conditions. Results on these aspects have also been presented and discussed in this paper.