Two-phase Anaerobic Digestion Process Research Articles

Optimization of Operating Parameters for Two-Phase Anaerobic Digestion Treating Slaughterhouse Wastewater for Biogas Production: Focus on Hydrolytic–Acidogenic Phase

In a two-phase anaerobic digestion process, enhanced biogas production and organic pollutant removal depend on the stability and performance of the hydrolytic–acidogenic and methanogenic phases. Additionally, the hydrolytic–acidogenic phase is a rate-limiting step, which calls for the further optimization of operating parameters. The objective of this study was to optimize the operating parameters of the hydrolytic–acidogenic reactor (HR) in the two-phase anaerobic digestion treating slaughterhouse wastewater. The experiment was carried using bench-scale sequential bioreactors. The hydrolytic–acidogenic reactor operating parameters were optimized for six different hydraulic retention times (HRTs) (6–1 day) and organic loading rates (OLRs) (894.41 ± 32.56–5366.43 ± 83.80 mg COD/L*day). The degree of hydrolysis and acidification were mainly influenced by lower HRT (higher OLR), and the highest values of hydrolysis and acidification were 63.92% and 53.26% at an HRT of 3 days, respectively. The findings indicated that, at steady state, the concentrations of soluble chemical oxygen demand (SCOD) and total volatile fatty acids (TVFAs) decrease as HRT decreases and OLR increases from HRTs of 3 to 1 day and 894.41–1788.81 mg COD/L*day, respectively, and increase as the HRT decreases from 6 to 4 days. The concentration of NH4+-N ranges from 278.67 to 369.46 mg/L, which is not in the range that disturbs the performance and stability of the hydrolytic acidogenic reactor. It was concluded that an HRT of 3 days and an ORL of 1788.81 mg COD/L*day were selected as optimal operating conditions for the high performance and stability of the two-phase anaerobic digestion of slaughterhouse wastewater in the hydrolytic–acidogenic reactor at a mesophilic temperature. The findings of this study can be applicable for other agro-process industry wastewater types with similar characteristics and biowaste for value addition and sustainable biowaste management and safe discharge.

바이오가스화를 위한 음폐수 내 유분의 영향

The grease contained in the food wastewater is not easily decomposed at a short residence time and may cause scum by combining with the solids in the food wastewater. Therefore, it is necessary to effectively remove the grease in order to efficiently treat the food wastewater and solve the operational problems in the anaerobic digester. The purpose of this research was to compare the grease effects for biogas production before and after grease removals in food wastewater using by two-phase anaerobic digestion process. After removing the grease in the food wastewater, the anaerobic digester could be operated stably, and the biogas production was also high. Biosorp and ferric chloride had an excellent effect on removing hydrogen sulfide (H₂S) in the digester. Considering economic feasibility and convenience, ferric chloride is judged to be more suitable for hydrogen sulfide removal than Biosorp.

Enhanced methane yield through sludge two-phase anaerobic digestion process with the addition of calcium hypochlorite

This study investigated the effects of calcium hypochlorite (Ca(ClO)2) on biomethane generation from sludge two-phase anaerobic digestion system. In first (acidogenic) phase, volatile fatty acids (VFAs) were largely generated when pretreated by Ca(ClO)2, while the methane yield was severely inhibited. In second (methanogenic) phase, the methane yield was observably enhanced by Ca(ClO)2. Further calculation showed that the total methane yield from the two phases was firstly promoted from 156.0 ± 4.5 to 269.9 ± 5.2 mL when Ca(ClO)2 dosage enhanced from 0 to 1.6 g/L, which then reduced to 235.4 ± 5.5 mL when Ca(ClO)2 content reached 2.0 g/L. Mechanism analysis showed that the suppression of Ca(ClO)2 on coenzyme F420 activity was relieved in methanogenic phase, and the abundances of functional microbes in methanogenic phase were enriched when added with Ca(ClO)2. The Ca(ClO)2-based method well realized the balance between efficacy and economy, possessing outstanding potential for large-scale applications.

Innovations in anaerobic digestion: a model-based study

BackgroundIncreasing the efficiency of the biogas production process is possible by modifying the technological installations of the biogas plant. In this study, specific solutions based on a mathematical model that lead to favorable results were proposed. Three configurations were considered: classical anaerobic digestion (AD) and its two modifications, two-phase AD (TPAD) and autogenerative high-pressure digestion (AHPD). The model has been validated based on measurements from a biogas plant located in Poland. Afterward, the TPAD and AHPD concepts were numerically tested for the same volume and feeding conditions.ResultsThe TPAD system increased the overall biogas production from 9.06 to 9.59%, depending on the feedstock composition, while the content of methane was slightly lower in the whole production chain. On the other hand, the AHPD provided the best purity of the produced fuel, in which a methane content value of 82.13% was reached. At the same time, the overpressure leads to a decrease of around 7.5% in the volumetric production efficiency. The study indicated that the dilution of maize silage with pig manure, instead of water, can have significant benefits in the selected configurations. The content of pig slurry strengthens the impact of the selected process modifications—in the first case, by increasing the production efficiency, and in the second, by improving the methane content in the biogas.ConclusionsThe proposed mathematical model of the AD process proved to be a valuable tool for the description and design of biogas plant. The analysis shows that the overall impact of the presented process modifications is mutually opposite. The feedstock composition has a moderate and unsteady impact on the production profile, in the tested modifications. The dilution with pig manure, instead of water, leads to a slightly better efficiency in the classical configuration. For the TPAD process, the trend is very similar, but the AHPD biogas plant indicates a reverse tendency. Overall, the recommendation from this article is to use the AHPD concept if the composition of the biogas is the most important. In the case in which the performance is the most important factor, it is favorable to use the TPAD configuration.

Effect of substrate concentrations on methane and hydrogen biogas production by anaerobic digestion of a cassava starch-based polymer

This study aims to evaluate the two-phase anaerobic digestion process of a cassava starch-based polymer, determining the ideal organic load to obtain the best results in terms of removal of solids and production of methane and hydrogen. Two reactors were used: one with an agitation and mixing system for the acidogenic phase, and the other was a tubular reactor for the methanogenic phase, both with ascending flow and semi-continuous feeding, with the effluent from the acidogenic reactor conducted from the methanogenic reactor. The loads were defined as concentrations of 8, 10, 12, and 14 g L−1 (on a wet basis), having HRT of 5 days for the acidogenic reactor and 20 days for the methanogenic. The analysis of the results showed that the concentration of 10 g L−1 had the best results for hydrogen and methane production in acidogenic and methanogenic phases, presenting 19.9 mL gVS-1 and 249.1 mL gVS−1, respectively. This treatment also showed the highest levels of gases in the biogas (43.2 % hydrogen in the acidogenic phase, and 76.6 % methane in the methanogenic phase). In addition, it showed the highest volatile solid removal means, reaching 84.0 % in the methanogenic phase. Thus, the anaerobic biodigestion process in two phases for the degradation of the polymer based on cassava starch presents technical feasibility, with high methane and hydrogen production; and concentrations above 10 g L−1, under the test conditions, cause destabilization in the reactors by the great formation of volatile acids and consequent reduction in the stability of microbiological cultures.

Comparative assessment on two full-scale food waste treatment plants with different anaerobic digestion processes

Single-phase anaerobic digestion (SPAD) and two-phase anaerobic digestion (TPAD) are compared based on two full-scale food waste treatment plants using a hybrid life cycle assessment (LCA) method combining process LCA and economic input output LCA. Plant S uses a SPAD process with thermal pretreatment and waste oil recovery, while Plant T adopts a TPAD process without pretreatment. Biogas yield, electricity consumption, and waste oil recovery are the three vital factors determining environmental benefits, and digested wastewater treatment is another key factor influencing economic performance. Plant S has 8.2% higher biogas yield than Plant T, but it also consumes steam and 1.7 times electricity on its pretreatment unit. Plant S can also recover waste oil for biodiesel production, reduce methane emission from landfill sites, and offset the negative effect of high energy consumption. As a consequence, Plant S has a carbon emission of −158.15 kg CO2-eq/t, a cumulative energy demand (CED) of −1868 MJ/t, and an energy efficiency of 64.6%; while the three values are −127.0 kg CO2-eq/t, 1713 MJ/t, and 59.2% for Plant T. Plant T achieves 66% higher reduction of acidic gases than Plant S due to the substitution effect of grid electricity, and it also gets 10% higher revenue with less cost. In the hypothetical optimal scenarios, Plant T should be upgraded by combining thermal pretreatment to enhance biogas yield and waste oil recovery, and the two plants should recycle digested effluent through land use other than traditional wastewater treatment. Thus, their carbon emissions and CEDs could decline to −326 CO2-eq/t and −2514 MJ/t for Plant and −243 kg CO2-eq/t and −1973 MJ/t for Plant S.

A Study for Production of Biogas from Two-phase Anaerobic Digestion Process and Hydrogen from Reforming Reaction of Biogas

A Study for Production of Biogas from Two-phase Anaerobic Digestion Process and Hydrogen from Reforming Reaction of Biogas

Transient performance during start-up of a two-phase anaerobic digestion process demonstration unit treating carbohydrate-rich waste with biochar addition

The paper reports an experimental investigation into the transient performance during the start-up of a pilot-scale two-phase anaerobic digestion (TPAD) process demonstration unit (PDU) treating food waste with biochar addition. Hydrogen (H2) was produced in the first phase (R1) and methane (CH4) was produced in the second phase (R2). A fed-batch operation strategy was applied to the start-up of both phases, followed by semi-continuous operation. Production rates and yields of H2 and CH4 and volatile fatty acids (VFA) were measured while the pH and temperature were monitored throughout the process. Fed-batch operation allowed microbe enrichment and gradual VFA production in both phases, which was observed to be efficient in starting up the TPAD PDU. Under semi-continuous operation, R1 produced biogas with composition up to 49% of H2 and at a yield of 46 L H2.kg −1 VS. CH4 composition and yield reached up to 59% and 301 L CH4.kg−1 VS in the R2.

Co-production of biohydrogen and biomethane from food waste and paper waste via recirculated two-phase anaerobic digestion process: Bioenergy yields and metabolic distribution

To achieve the co-production of H2 and CH4, co-digestion of food waste (FW) and paper waste (PW) was performed on the recirculated two-phase anaerobic digestion (R-TPAD). The PW content in the feedstock increased from 0% to 20%, 40% and 50% (in total solids) with FW as the rest. The results showed that bioH2 and bioCH4 were simultaneously and stably produced in the long-term operation. With the increasing PW content, the removal efficiency of volatile solids decreased slightly from 84.9% to 78.4%; the bioH2 yields increased from 50 to 79 NL-H2/kg-VSfed while the bioCH4 yields decreased from 426 to 329 NL-CH4/kg-VSfed. With the fixed amount of FW, adding PW could significantly increase the total bioenergy yields. The relative abundance showed that the key H2-producing bacteria, Caproiciproducens and Thermoanaerobacterium, increased after PW addition. The microbial distribution suggests that the H2-producers were recirculated to the first stage after proliferating in the second stage.

Effects of free nitrous acid and nitrite on two-phase anaerobic digestion of waste activated sludge: A preliminary study

Nitrite, a product of the nitritation of sewage or digestion liquid, has been used to pretreat waste activated sludge (WAS) before anaerobic digestion. In this study, the effects of free nitrous acid (FNA) and nitrite on two-phase anaerobic sludge bioconversion were investigated. The experimental results indicated that both nitrite and FNA promoted sludge organic solubilization. Notably, nitrite promoted volatile fatty acids (VFAs) accumulation while FNA inhibited VFA accumulation in the first phase (acidogenic phase). In the second phase (methanogenic phase), neither nitrite nor FNA improved the net cumulative methane production from WAS. Although net cumulative methane production was not enhanced by the addition of nitrite or FNA, the volatile solids (VS) degradation rate was improved with nitrite addition in the two-phase anaerobic digestion process, indicating that nitrite is more favorable than FNA for the two-phase anaerobic digestion of WAS. It is expected that these findings can offer useful insights into future design of anaerobic digestion system with the treatment by the nitrite from digestion liquid.

Effect of Biochar Addition and Temperature on Hydrogen Production From the First Phase of Two-Phase Anaerobic Digestion of Carbohydrates Food Waste

This paper reports an experimental study of the effect of biochar addition and temperature on hydrogen production in the first phase of the two-phase anaerobic digestion (TPAD) of carbohydrates food waste. Anaerobic digestion (AD) experiments using white bread representing carbohydrate food wastes were conducted in bench scale 100 ml reactors. The cultures with biochar addition were placed in the reactors and incubated at different temperatures (18, 35, and 52 °C) over a period of 8 days. The biochar addition ratio was varied from 0 to 18.6 g l−1. The daily volumetric hydrogen production was measured, and the cumulative yield (YH) and daily production rate (RH) of hydrogen were calculated. Both biochar addition and temperature affected hydrogen production significantly. YH and maximum RH increased as the biochar addition ratio increased from 0 to 10 g l−1 then decreased as the biochar addition ratio further increased up to 18.6 g l−1. At different temperatures, YH varied significantly, increasing from 846 ± 18 ml l−1 at 18 °C to 1475 ± 53 ml l−1 at 35 °C and dropped to 1149 ± 26 ml l−1 at 52 °C. The maximum RH also peaked at 35 °C, reaching 858 ± 57.1 ml l−1 day−1. The effect of biochar addition was more profound under mesophilic conditions. The results of this study confirmed the beneficial effect of biochar addition in hydrogen production of carbohydrate food waste in the TPAD process.

Microbial Structure of an Enhanced Two-phase High-solid Anaerobic Digestion System Treating Sludge

High-solid anaerobic digestion (HSAD) of sludge has several advantages like smaller reactor, lower energy consumption and less digestate. However, the understanding about the mechanism especially the microbial mechanism is still limited. In this study, microbial communities of a pilot-scale sludge HSAD system at steady state were investigated with 16S rRNA clone library technology. The system employed an enhanced two-phase anaerobic digestion process, i. e. 'hyperthermophilic acidogenesis (70℃, 3 d)-thermophilic methanogenesis (55℃, 12.5 d)' to treat waste activated sludge with a solid content of about 9%. The volatile solid (VS) removal rate was 35.7% and methane yield (CH4/VSremoved) was 0.648 m3·kg-1. The bacterial compositions of the two phases were significantly different:there were plenty of proteolytic bacteria in hyperthermophilic acidogenesis phase; and the bacteria degrading polysaccharides like cellulose and the bacteria utilizing long-chain fatty acids were found in thermophilic methanogenesis phase; some bacteria degrading simple saccharides existed in both phases. In both phases, the dominant archaea were Methanothermobacter. Especially, 100% of the retrieved archaea in the thermophilic methanogenesis phase belonged to genus Methanothermobacter. This indicated that hydrogenotrophic methanogenesis was the predominant methanogenesis pathway in this system since methane was only detected in the methanogenesis phase.

A fast linear predictive adaptive model of packed bed coupled with UASB reactor treating onion waste to produce biofuel.

BackgroundAgro-industrial wastes are an energy source for different industries. However, its application has not reached small industries. Previous and current research activities performed on the acidogenic phase of two-phase anaerobic digestion processes deal particularly with process optimization of the acid-phase reactors operating with a wide variety of substrates, both soluble and complex in nature. Mathematical models for anaerobic digestion have been developed to understand and improve the efficient operation of the process. At present, lineal models with the advantages of requiring less data, predicting future behavior and updating when a new set of data becomes available have been developed. The aim of this research was to contribute to the reduction of organic solid waste, generate biogas and develop a simple but accurate mathematical model to predict the behavior of the UASB reactor.ResultsThe system was maintained separate for 14 days during which hydrolytic and acetogenic bacteria broke down onion waste, produced and accumulated volatile fatty acids. On this day, two reactors were coupled and the system continued for 16 days more. The biogas and methane yields and volatile solid reduction were 0.6 ± 0.05 m3 (kg VSremoved)−1, 0.43 ± 0.06 m3 (kg VSremoved)−1 and 83.5 ± 9.8 %, respectively. The model application showed a good prediction of all process parameters defined; maximum error between experimental and predicted value was 1.84 % for alkalinity profile.ConclusionsA linear predictive adaptive model for anaerobic digestion of onion waste in a two-stage process was determined under batch-fed condition. Organic load rate (OLR) was maintained constant for the entire operation, modifying effluent hydrolysis reactor feed to UASB reactor. This condition avoids intoxication of UASB reactor and also limits external buffer addition.

Two-phase anaerobic co-digestion of dairy manure with swine manure

In order to solve the problems associated with high fiber content, and the ensuing lower biogas volume yield in anaerobic digestion of dairy manure, a study of the co-digestion of separated liquids from dairy manure combined with swine manure using a two-phase anaerobic digestion process was conducted. The influence of level of total solids (TS) and hydraulic retention time (HRT) of the mixed liquor on the specific methane production were studied. Three TS levels 8%, 10% and 12% were investigated. Analysis of the results show that a maximum specific methane yield of 132.99 L/kg volatile solids (VS), can be obtained with a TS of 9%, an inoculation rate of 30%, the duration of hydrolytic acidification phase of 5 d, and an HRT of the methanogenic phase of 10 d. These findings could provide directions for improving the biogas production by performing the co-digestion of dairy manure with swine manure. Keywords: co-digestion, two-phase anaerobic digestion, dairy manure, swine manure, biogas DOI: 10.3965/j.ijabe.20160902.1637 Citation: Guan Z J, Sun X L, Bi L P, Li W Z, Zhang Y, Wang Z G. Two-phase anaerobic co-digestion of dairy manure with swine manure. Int J Agric & Biol Eng, 2016; 9(2): 146－152.

Influence of two-phase anaerobic digestion on fate of selected antibiotic resistance genes and class I integrons in municipal wastewater sludge

The response of representative antibiotic resistance genes (ARGs) to lab-scale two-phase (acidogenic/methanogenic phase) anaerobic digestion processes under thermophilic and mesophilic conditions was explored. The associated microbial communities and bacterial pathogens were characterized by 16S rRNA gene sequencing. A two-phase thermophilic digestion reduced the presence of tetA, tetG, tetX, sul1, ermB, dfrA1, dfrA12 and intI1 exhibiting 0.1–0.72 log unit removal; in contrast, tetO, tetW, sul3, ermF and blaTEM even increased relative to the feed, and sul2 showed no significant decrease. The acidogenic phase of thermophilic digestion was primarily responsible for reducing the quantity of these genes, while the subsequent methanogenic phase caused a rebound in their quantity. In contrast, a two-phase mesophilic digestion process did not result in reducing the quantity of all ARGs and intI1 except for ermB and blaTEM. ARGs patterns were correlated with Proteobacteria and Actinobacteria during the two-phase anaerobic digestion.

Improving anaerobic digestion of a cellulosic waste via routine bioaugmentation with cellulolytic microorganisms

This study investigated routine bioaugmentation in the acid-phase of a two-phase anaerobic digestion (AD) process treating a largely cellulosic waste material generated from sweet corn processing. A proprietary cellulolytic bioculture was used for bioaugmentation with the aim of increasing substrate hydrolysis to improve overall methanogenic efficiency. In a sequencing batch experiment routine bioaugmentation achieved significantly greater soluble chemical oxygen demand (sCOD) generation (+25%) and methane production (+15%) compared to one-time bioaugmentation. In a continuous bench-scale system, routine bioaugmentation increased acid-phase sCOD by 29–68% and acetic acid concentrations by 31–34%. This benefit to hydrolysis and acetogenesis subsequently led to sustained increase in methane production (+56%) compared to non-bioaugmentation. A cursory economic analysis indicated that routine bioaugmentation could improve the economics of corn waste AD by $27–$34/dry tonne of waste. Overall, routine bioaugmentation showed significant promise for improving AD of corn waste by achieving sustained increases in substrate hydrolysis and methane production.

Automatic process control for stable bio-hythane production in two-phase thermophilic anaerobic digestion of food waste

The paper reports the results of a long term (310 days) pilot-scale trial where food waste as sole substrate was treated in a two-phase thermophilic anaerobic digestion process. This was optimized for concurrent hydrogen and methane production. First phase's optimization for hydrogen production was obtained recirculating the effluent coming from the methanogenic phase and without the addition of external chemicals. A drawback of such approach is the recirculation of ammonia into the first phase reactor for hydrogen production with possibility of consequent inhibition.Therefore this study was focused on the development of a control protocol based on ammonia concentration. The first part of this paper illustrates how the use of a variable recirculation flow makes possible to control the whole process, preventing the ammonia inhibition in the system. In order to lay down the groundwork for an automatic control of the process, in the second part of the study a preliminary statistical study is presented. In the latter are developed models to predict ammonia levels in system using the measure of Electrical Conductivity, Volatile Fatty Acids and Alkalinity.During steady state conditions, managed by a variable recirculation flow, the system produced a mixture of gas that met the standards for the biohythane mix with an average composition range of 7% H2, 58% CH4 and 35% CO2. The overall average specific gas production (SGP) reached 0.69 m3Biogas/kgTVS and gas production rate (GPR) of 2.78 m3/m3rd.

Performance assessment of two-stage anaerobic digestion of kitchen wastes

This study is aimed at investigating the performance of the two-phase anaerobic digestion of kitchen wastes in a lab-scale setup. The semi-continuous experiment showed that the two-phase anaerobic digestion of kitchen wastes had a bioconversion rate of 83%, biogas yield of 338 mL·(g chemical oxygen demand (COD))−1 and total solid conversion of 63% when the entire two-phase anaerobic digestion process was subjected to an organic loading rate (OLR) of 10.7 g·(L d)−1. In the hydrolysis–acidogenesis process, the efficiency of solubilization decreased from 72.6% to 41.1%, and the acidogenesis efficiency decreased from 31.8% to 17.8% with an increase in the COD loading rate. On the other hand, the performance of the subsequent methanogenic process was not susceptible to the increase in the feeding COD loading rate in the hydrolysis–acidogenesis stage. Lactic acid was one of the main fermentation products, accounting for over 40% of the total soluble COD in the fermentation liquid. The batch experiments indicated that the lactic acid was the earliest predominant fermentation product, and distributions of fermentation products were pH dependent. Results showed that increasing the feeding OLR of kitchen wastes made the two-stage anaerobic digestion process more effective. Moreover, there was a potential improvement in the performance of anaerobic digestion of kitchen wastes with a corresponding improvement in the hydrolysis process.

Optimisation of the two-phase dry-thermophilic anaerobic digestion process of sulphate-containing municipal solid waste: Population dynamics

Microbial population dynamics and anaerobic digestion (AD) process to eight different hydraulic retention times (HRTs) (from 25d to 3.5d) in two-phase dry-thermophilic AD from sulphate-containing solid waste were investigated. Maximum values of gas production (1.9 ± 0.2 l H2/l/d; 5.4 ± 0.3 l CH4/l/d and 82 ± 9 ml H2S/l/d) and microbial activities were obtained at 4.5d HRT; where basically comprised hydrolysis step in the first phase (HRT=1.5d) and acidogenic step finished in the second phase as well as acetogenic-methanogenic steps (HRT=3d). In the first phase, hydrolytic-acidogenic bacteria (HABs) was the main group (44-77%) and Archaea, acetogens and sulphate-reducing bacteria (SRBs) contents were not significant; in the second phase (except to 2d HRT), microbial population was able to adapt to change in substrate and HRTs to ensure the proper functioning of the system and both acetogens and Archaea were dominated over SRBs. Decreasing HRT resulted in an increase in microbial activities.

Comparison of One-Phase and Two-Phase Anaerobic Digestion of Swine Manure

The possible exploitation of two-phase anaerobic digestion for swine manure was investigated in this study. One-phase and two-phase anaerobic digestion process were investigated in continuous stirred-tank reactor with hydraulic retention times 15 days (hydrolysis and acidification for 3 days and methanogenic12 days in two-phase). When the organic loading rates were equal to or less than 4 g VS/L day, the biogas yield and volumetric production of two processes were no significant difference. However, in the case of organic loading rates being equal to or higher than 5.0 g VS/L day, two-phase biogas yield and volumetric biogas production averaged 0.294 L CH4/g VS added and 2.218 L/L day, compared with one-phase averaged 0.255L CH4/g VS added and 2.168 L/L day, respectively. Significant advantages in saving cost of biogas project were indicated by the comparison of biogas production and COD degradation in the one-phase and two-phase processes.