Two-stage Anaerobic System Research Articles

A Cost Analysis of Two-Stage Thermophilic-Mesophilic Anaerobic Wastewater Treatment Systems

Anaerobic bacteria have displayed great potential as a wastewater treatment method because of their efficiency, high methane yield, and low input requirements. In the past, studies have investigated various aspects of these systems, including their chemical oxygen demand (COD) removal efficiency, methane yield, and retention times. However, they have mostly focused on single stage high rate anaerobic (HRAA) reactors such as the upflow anaerobic sludge blanket (UASB) reactor. In this paper, we aim to synthesize the results of these studies to investigate the advantages of building upon the UASB via a two-stage thermophilic-mesophilic (T-M) reactor system with an anaerobic filter (AF) as the acidification tank. The key constraint for adopting two-stage anaerobic systems is primarily related to construction and O&M costs. Therefore, we propose adjusting pH levels and influent flow rates to enhance energy generation and cost-efficiency. This approach aims to encourage greater utilization of two-stage anaerobic systems for wastewater treatment by lowering costs and increasing profits.

Effect of temperature on biohydrogen and biomethane production using a biochemical potential test with different mixtures of sewage sludge, vinasse and poultry manure

A two-stage anaerobic co-digestion system has been proposed, comprising a first acidogenic stage at different temperatures, where biohydrogen is obtained; and a second mesophilic methanogenic stage where biomethane is obtained. The objective of this research was to evaluate the biochemical hydrogen potentials (BHP) at different temperature ranges, and their effect on the biochemical methane potentials subsequently carried out with the effluents from the BHP, in batch trials. Also, to evaluate the effect of adding a third co-substrate (poultry manure) to the mixture of sewage sludge and wine vinasse.For the BHP tests, temperatures of 35°, 55° and 70 °C were tested in mixtures of sewage sludge:vinasse (50:50) and sewage sludge:vinasse:poultry manure (49.5:49.5:1). It was found that the addition of poultry manure and a thermophilic temperature of 55 °C was ideal for biohydrogen generation with the highest recorded yield of 27.1mLH2/gVS.In the BMP trials consisting of effluent from the BHP and programmed at 35 °C, it was found that the effluent from the hyperthermophilic BHP trials (70 °C) generated more biogas and had a higher methane yield (117.36 mLCH4/gVS), and that this yield was higher for the sewage sludge and vinasse mixture alone. This proportion also had the highest percentage of VS removal (45.74%). The Modified Gompertz model was the best fit to the experimental data, with R2 > 0.983 in all cases.The search for the most suitable temperature ranges for the production of H2 and CH4 is necessary in order to be able to efficiently realise this technology on a larger scale.

Application of a Two-Stage Anaerobic System from Guava Processing Waste to Bioenergy

Application of a Two-Stage Anaerobic System from Guava Processing Waste to Bioenergy

Is anaerobic co-digestion the missing link to integrate sugarcane biorefinery?

This study evaluated the potential of energy generation from anaerobic co-digestion (AcD) of vinasse and hemicelluloses hydrolysate within the context of an integrated 1G-2G sugarcane biorefinery as a mean to ensure its technical, economic and environmental feasibility. Environmental impact indexes for 2G ethanol and biogas production process, such as carbon footprint, which varied from 12.3 to 50.02 g CO2/MJ and reduction of greenhouse gas (GHG) emissions (from 42.7 to 85.9%), were obtained in all scenarios. Economic indicators showed the unviability of 1G-2G sugarcane mill integration adopting AcD of wastes, considering technologies for 2G ethanol production in view of their high capital and operational costs (pretreatment). However, by fixing the experimental methane yield at 0.245 Nm3 kg COD−1r which has been obtained for two-stage anaerobic systems and by considering the use of 50% of bagasse surplus for biogas production, it was possible to achieve internal rate of return (IRR), return on investment (ROI) and payback period of 21.8%, 59.50% and 10.55 years respectively. Moreover, when experimental methane yield is increased in 10% in such scenario, it was possible to achieve internal rate of return (IRR), return on investment (ROI) and payback period of 26%,89.05% and 5.36 years, respectively.

Archaeal and Bacterial Content in a Two-Stage Anaerobic System for Efficient Energy Production from Agricultural Wastes.

Anaerobic digestion (AD) is a microbially-driven process enabling energy production. Microorganisms are the core of anaerobic digesters and play an important role in the succession of hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes. The diversity of participating microbial communities can provide new information on digester performance for biomass valorization and biofuel production. In this study anaerobic systems were used, operating under mesophilic conditions that realized biodegradation processes of waste wheat straw pretreated with NaOH—a renewable source for hydrogen and methane production. These processes could be managed and optimized for hydrogen and methane separately but combining them in a two-stage system can lead to higher yields and a positive energy balance. The aim of the study was to depict a process of biohydrogen production from lignocellulosic waste followed by a second one leading to the production of biomethane. Archaeal and bacterial consortia in a two-stage system operating with wheat straw were identified for the first time and the role of the most important representatives was elucidated. The mixed cultures were identified by the molecular-biological methods of metagenomics. The results showed that biohydrogen generation is most probably due to the presence of Proteiniphilum saccharofermentans, which was 28.2% to 45.4% of the microbial community in the first and the second bioreactor, respectively. Archaeal representatives belonging to Methanobacterium formicicum (0.71% of the community), Methanosarcina spelaei (0.03%), Methanothrix soehngenii (0.012%), and Methanobacterium beijingense (0.01%) were proven in the methane-generating reactor. The correlation between substrate degradation and biogas accumulation was calculated, together with the profile of fatty acids as intermediates produced during the processes. The hydrogen concentration in the biogas reached 14.43%, and the Methane concentration was 69%. Calculations of the energy yield during the two-stage process showed 1195.89 kWh·t−1 compared to a 361.62 kWh·t−1 cumulative yield of energy carrier for a one-stage process.

Effect of Sodium on Methanogens in a Two-Stage Anaerobic System

This study evaluated the effects of sodium on anaerobic biomass from the second-stage reactor of a two-stage anaerobic digester. The results indicated that methanogens showed a relatively high sodium tolerance of 2.4 g Na+ L−1. Microbial community analysis showed that viable Methanomicrobiales was the most abundant population by a combined propidium monoazide cross-linking quantitative polymerase chain reaction technique. There was a population shift towards higher abundance of Thermotoga (0.02%), Clostridium (2.50%) and Methanoculleus (13.80%). Biomass activity in relation to increased sodium concentrations was investigated with the adenosine triphosphate test coupled with extracellular polymeric substances measurement. The results showed biomass activity decreased from 33 to 16 µg g−1 volatile suspended solids as sodium concentrations increased from 1.3 to 9.1 g Na+ L−1. Higher EPS production, particularly a greater predominance of carbohydrates, was stimulated by higher sodium concentrations. This study provides insights into the superiority of sodium tolerance of two-stage anaerobic digester in compared with a single-stage anaerobic system.

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.

Techno-economic analysis of two-stage anaerobic system for biohydrogen and biomethane production from palm oil mill effluent

The proliferation of biobased-renewable fuel industries was driven by the depletion of the finite fossil fuel reserves and the rising consciousness on sustainable and environmental consequences. Hence, the present study aims to establish baseline economics for a two-stage anaerobic system by performing a comprehensive analysis using a set of assumptions for what can plausibly be achieved within a twenty-year timeframe. The techno-economic analysis was carried out to elucidate the viability of the proposed anaerobic system that produces biohydrogen (BioH2), and biomethane (BioCH4) from locally generated palm oil mill effluent (POME). Process modelling and economic analysis were performed using a modelling software SuperPro Designer. The plant conditions were temperature at 50 °C for both stages, and HRT of 1 and 10 days for BioH2 and BioCH4, respectively. The economic profitability assessment demonstrated the feasibility of the project with the dynamic payback period (DPP), return on investment (ROI), internal rate of return (IRR), and net present value (NPV) of 8.01 years, 19.87%, 21.48% and USD 4624,705, respectively. Furthermore, the economics of this system was most sensitive to POME quality and product selling prices. The results revealed that a two-stage anaerobic system might both expand the production of renewable energy and enable improved productivity and revenue of palm oil mills to move forward cleaner production industry.

Comparison of bio-hydrogen and bio-methane production performance in continuous two-phase anaerobic fermentation system between co-digestion and digestate recirculation

The effect of co-digestion of food waste (FW) and cow dung (CD) with different ratios, and digestate recirculation with different recirculation ratios (RR) on the substrate degradation and energy production in continuous two-stage anaerobic fermentation system was investigated. Results from experiments indicated that co-digestion and digestate recirculation could promote the hydrogen production rate (HPR) and the methane production rate (MPR). Maximum HPR and MPR of 3.3 and 3.1 L/L/d were achieved for two-stage fermentation with recirculation system at RR of 0.4. Meanwhile, both co-digestion and digestate recirculation technology could reduce the amount of alkali addition to maintain pH in the hydrogen-reactor. Compared to digestate recirculation, co-digestion of FW and CD promote much more energy production, 654.9 and 4854.8 kJ/kgVSr were obtained from the co-digestion of FW and CD with the ratio of 2:1 in the hydrogen reactor and the methane reactor.

Comparison of single-stage and two-stage anaerobic co-digestion of food waste and activated sludge for hydrogen and methane production

In this study, the co-digestion of food waste and activated sludge was evaluated in a two-stage anaerobic system and compared to the traditional single-stage process. The two-stage system was composed by two reactors connected in series able to perform the fermentative and the methanogenic phases separated. Experiments were carried out in semi-continuous mode under mesophilic conditions (37 °C). The two-stage technology achieved an overall improvement of the anaerobic performances. Results highlighted an increase in biogas production and volatile solids degradation of 26% and 9%, respectively. Considering the whole two-stage system, i.e. the sum of the biogas productions of the first and the second digester, these percentages increased up to 35.0%. Concerning gas quality, the two-stage system achieved a hydrogen rich biogas in the first fermentative reactor and an improvement of methane content in the second methanogenic digester. The average methane content shifted from 61.2% to 70.1%. The highest methane production of the two-stage process was due to improved substrate hydrolysis, with increased amounts of volatile fatty acids made readily available in the second stage.

Feasibility of bio-hythane production by co-digesting skim latex serum (SLS) with palm oil mill effluent (POME) through two-phase anaerobic process

Hydrogenogenic batch fermentation without nutrients addition was investigated at different SLS: POME mixing ratios of 100:0, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45,50:50, and 0:100 (Volatile Solid, VS basis) at initial organic concentrations of 21 and 7 g-VS/L. Satisfactory hydrogen yield of 84.5 ± 0.7 mL H2/g-VSadded was achieved from 7 g-VS/L batch having SLS: POME-VS mixing ratio of 55:45. Adding NaHCO3 3 g/L or 0.43 g-NaHCO3/g-VS) in the two-stage anaerobic system at 7 g-VS/L could provide sufficient buffering capacity. Hydrogenogenic effluent from 7 g-VS/L batch at SLS: POME mixing ratio of 55:45 (VS basis) could further generate rather high methane yield of 311.2 ± 8.0 mL- CH4/g-VSadded in themethanogenic stage.According to the experimental results, bio-hythane approximately 55.5 × 106 m3/year with 21% (V/V) of hydrogen, equivalent to51.0 × 106 l-gasoline could be produced potentially from 3.88 × 106 m3 of mixed SLS and POME through the two-stage anaerobic co-digestion.

Determination and Variation of Core Bacterial Community in a Two-Stage Full-Scale Anaerobic Reactor Treating High-Strength Pharmaceutical Wastewater.

Knowledge on the functional characteristics and temporal variation of anaerobic bacterial populations is important for better understanding of the microbial process of two-stage anaerobic reactors. However, owing to the high diversity of anaerobic bacteria, close attention should be prioritized to the frequently abundant bacteria that were defined as core bacteria and putatively functionally important. In this study, using MiSeq sequencing technology, the core bacterial community of 98 operational taxonomic units (OTUs) was determined in a two-stage upflow blanket filter reactor treating pharmaceutical wastewater. The core bacterial community accounted for 61.66% of the total sequences and accurately predicted the sample location in the principal coordinates analysis scatter plot as the total bacterial OTUs did. The core bacterial community in the first-stage (FS) and second-stage (SS) reactors were generally distinct, in that the FS core bacterial community was indicated to be more related to a higher-level fermentation process, and the SS core bacterial community contained more microbes in syntrophic cooperation with methanogens. Moreover, the different responses of the FS and SS core bacterial communities to the temperature shock and influent disturbance caused by solid contamination were fully investigated. Co-occurring analysis at the Order level implied that Bacteroidales, Selenomonadales, Anaerolineales, Syneristales, and Thermotogales might play key roles in anaerobic digestion due to their high abundance and tight correlation with other microbes. These findings advance our knowledge about the core bacterial community and its temporal variability for future comparative research and improvement of the two-stage anaerobic system operation.

Effects of target pH-value on organic acids and methane production in two-stage anaerobic digestion of vegetable waste

Vegetable waste is one of the major organic residues available for sustainable bioenergy production. The aim of this work is to study the influence of pH-value on process stability, hydrolysis, degradation degree and methane production in two-stage anaerobic system. A mixture of vegetable wastes with carrot mousse, carrots, celery, cabbage and potatoes was treated in two-stage system at target pH-values 5.5 and 6 in acidification reactor (AR). At pH 6, high concentrations of organic acids were recorded whereas high amount of hydrolysate was produced at pH 5.5. The chemical oxygen demand (COD) concentration in the hydrolysate produced in AR was 21.85% higher at pH 6 compared to pH 5.5, whereas the overall specific methane yield was slightly higher at pH 5.5 (354.35±31.95 and 326.79±41.42Lkg−1 oDMadded, respectively). It could be shown, that the described two-stage system is well suited for manure-free digestion of vegetable waste.

Effect of volumetric organic loading rate (OLR) on H2 and CH4 production by two-stage anaerobic co-digestion of food waste and brown water

Two-stage anaerobic digestion system consisting of two continuously stirred tank reactors (CSTRs) operating at mesophillic conditions (37°C) were studied. The aim of this study is to determine optimum Hydraulic Retention Time (HRT) of the two-stage anaerobic digester system for hydrogen and methane production. This paper also discusses the effect of OLR with change in HRT on the system. Four different HRTs of 48, 24, 12, 8h were monitored for acidogenic reactor, which provided OLR of 17.7, 34.8, 70.8, 106gVS/L·d respectively. Two HRTs of 15days and 20days were studied with OLR of 1.24 and 1.76gVS/L·d respectively in methanogenic reactor. Hydrogen production at higher OLR and shorter HRT seemed favorable 106gVS/L·d (8h) in acidogenic reactor system. In methanogenic reactor system HRT of 20day with OLR of 1.24gVS/L·d was found optimum in terms of methane production and organic removal. The result of this study illustrated the optimum HRT of 8h and 20days in acidogenic stage and methanogenic stage for maximum hydrogen and methane production.

Acetic acid effects on methanogens in the second stage of a two-stage anaerobic system.

This study reports on biomass tolerance towards high concentrations of acetic acid (HAc) within the system. Biomass from the second stage of a two-stage anaerobic sludge digestion system was used for this study. Microbial community analysis by 454 pyrosequencing highlighted hydrogenotrophic Methanomicrobiales was the predominant archaeal population in the second stage (>99% of the total archaeal community). Second stage biomass degraded HAc up to 4200 mg HAc L(-1) without observable lag phase. However, at HAc-shock loading of 7400 mg HAc L(-1), it showed a one day lag phase associated with decreased biomass activity. After stepwise HAc-acclimation over 27 d, the biomass degraded HAc of up to 8200 mg HAc L(-1) without observable lag phase. The dominance of Methanomicrobiales had remained unchanged in proportion - while the total archaeal population increased during acclimation. This study showed stepwise acclimation could be an approach to accommodate HAc accumulation and hence higher concentrations resulting from an enhanced first stage.

Substrate Removal Kinetics of Domestic Wastewater Treatment in a Two-Stage Anaerobic System

An investigation was done on the process kinetics of a two-stage (modified septic tank plus anaerobic filter) anaerobic bioreactor while treating actual domestic wastewater. The individual values of second-order substrate removal rate constant (k) for septic tank and anaerobic filter were observed as 0.36 and 0.26 per day, respectively. It was 0.49 for the combined system. The maximum removal rate constant (Umax) and saturation value constant (KS) were 737 and 934 mg/L/d, respectively, for anaerobic filter when the modified Stover-Kincannon model was applied to this part of system. Both the second-order and the modified Stover-Kincannon models exhibited high correlation coefficents (R2 = 98-99%).

Performance enhancement of leaf vegetable waste in two-stage anaerobic systems under high organic loading rate: Role of recirculation and hydraulic retention time

Abstract Continuous laboratory-scale experiments were conducted on two-stage anaerobic systems treating vegetable waste (VW) to improve CH 4 production. The acidogenic reactors were employed with a serial methanogenic reactor configuration with volume distribution ratios of 3 L/4 L and 3 L/7 L (acidogenic reactor/methanogenic reactor), as well as recirculation rates (RRs) of 0.8 and 1.6. Results showed that recirculation improved the performance of VW anaerobic digestion under an organic loading rate (OLR) of 2.6 g VS/L/d. The OLR increased from 2.6 g VS/L/d to 3.0 g VS/L/d to compare the stability of the processes and to study the behavior response of serial systems. System control without recirculation was susceptible to overloading and volatile fatty acids (VFAs) utilization was inhibited in the methanogenic reactor, which was implemented as a fixed-bed biofilm reactor with active carbon fiber textiles. These findings indicated overall process failure. The ratio of total volatile fatty acid (TVFA) and alkalinity gives a good indication of the process stability of anaerobic digestion. The TVFA/alkalinity ratio of the methanogenic reactor in the 3 L/4 L configuration, with RR of 1.6, increased to approximately 0.5, which indicates potential imminent failure of the methanogenic process. However, the methanogenic reactorin the 3 L/7 L configuration helped in utilizing the VFA produced by the overloading in the acidogenic reactor, which improved the CH 4 production and conversion efficiency of the system.

Pretreatment of vinegar residue and anaerobic sludge for enhanced hydrogen and methane production in the two-stage anaerobic system

To enhance the conversion of vinegar residue to bio-energy gas, pretreatment of vinegar residue and anaerobic sludge were investigated in a two-stage anaerobic system. SEM and XRD were applied to observe the variation of cellulosic materials in vinegar residue. Alkaline and acid pretreatments were applied. The alkaline pretreatment of anaerobic sludge was an effective approach for hydrogenogen enrichment. Compared with oxalic acid, hydrochloric acid released more organic substrates. Analysis of SEM and XRD illustrated that the amorphous cellulosic structure of vinegar residue was significantly disintegrated by acid. The higher hydrogen yield, the shorter lag phase and digestion time indicated that the performance of anaerobic digestion was enhanced by pretreatment of vinegar residue and anaerobic sludge. The fracture of cellulosic materials and the higher concentration of reducing sugar explained the higher efficiency of the two-stage anaerobic digestion.

Comparing the hydrolysis and biogas production performance of alkali and acid pretreatments of rice straw using two-stage anaerobic fermentation

To enhance rice straw degradation and improve biogas production in a two-stage anaerobic system, rice straw was treated with either dilute alkali or acid. Firstly, the effects of NaOH or HCl concentration, temperature and time on glucose conversion, degradation of cellulose and hemi-cellulose were investigated. It was found that glucose conversion rate and the organic matter content were greater with alkali rather than acid pretreatment. Suitable conditions for hydrolysis using NaOH pretreatment were 2% (w/w), 60 h and 60 °C. With these conditions the glucose conversion rate was 55.5%. Secondly, the hydrolysate was used as substrate for batch anaerobic fermentation tests at different organic loadings. The maximum methane yield of hydrolysate from NaOH pretreatment was 193.2 ml g−1 [COD]. For the HCl pretreatment, the maximum methane production rate was 287.0 ml g−1 [COD] which was 43.89% higher than with NaOH. Although the NaOH solution was more efficient in improving rice straw hydrolysis, the hydrolysate from the HCl pretreatment had greater methane production at a similar organic loading.

Reductive Decolourisation of Sulphonated Mono and Diazo Dyes in One- and Two-Stage Anaerobic Systems

This work assessed the application of one- and two-stage mesophilic anaerobic systems to colour removal of sulphonated mono and diazo dyes with ethanol as electron donor. The dyes Congo Red (CR), Reactive Black 5 (RB5) and Reactive Red 2 (RR2) were selected as model compounds and tested separately in seven different periods. The one-stage system (R(1)) consisted of a single up-flow anaerobic sludge blanket (UASB) reactor, whereas the two-stage system (R(2)) consisted of an acidogenic UASB reactor (R(A)), a settler and a methanogenic UASB reactor (R(M)). For CR and RB5, no remarkable difference was observed between the colour removal performance of both anaerobic systems R(1) and R(2). The experiments with RR2 revealed that R(2) was more efficient on colour removal than R(1), showing efficiencies almost 2-fold (period VI) and 2.5-fold (period VII) higher than those found by R(1). Additionally, R(2) showed a higher stability, giving a good prospect for application to textile wastewaters. Finally, the acidogenic reactor (R(A)) had an important role in the overall decolourisation achieved by R(2) during the experiments with CR and RB5 (>78 %), whereas for RR2, a more recalcitrant dye, R(A) was responsible for up to 38 % of the total colour removal.