Biogas Methane Research Articles

Characteristics of CO2 adsorption and desorption on activated carbon in comparison with zeolite 13X and carbon molecular sieve and applications in biogas upgrading using vacuum pressure swing adsorption

AbstractBACKGROUNDBiogas upgrading is the process that increases the fraction of methane (CH4) in biogas, making the biogas suitable for use as vehicle fuel or as fuel with high and stable heating values for combustion engines. The advantages and disadvantages of activated carbon (AC) in CO2/CH4 adsorptive separation should be well understood before application for biogas upgrading. In the first part of this study, characteristics of CO2 adsorption and desorption on AC were investigated using Aspen Adsorption. In the second part, vacuum pressure swing adsorption (VPSA) was modeled, and the performances of the VPSA process using zeolite 13X, carbon molecular sieve (CMS) and AC were compared.RESULTSThe simulations showed that the advantages of AC for CO2 adsorption include relatively high dynamic adsorption capacity and high mass transfer coefficient of CO2 (KLDF,CO2) in AC and consequently relatively high CO2 desorption rates. However, due to the relatively high mass transfer coefficient of CH4 (KLDF,CH4) in AC, the molecular sieving characteristics for CO2 that were estimated from the ratio between KLDF,CO2 and KLDF,CH4 of AC were not significantly higher than that of zeolite 13X and significantly lower than that of CMS (9.85, 8.41 and 20.92 for AC, zeolite 13X and CMS, respectively).CONCLUSIONSThe modeling results predicted that the VPSA process using zeolite, CMS and AC adsorbents gives a biomethane product of around 98%, 97% and 93% CH4, respectively. © 2023 Society of Chemical Industry (SCI).

Effect of Fe Addition on Anaerobic Digestion Process in Treating Vinasse: Experimental and Kinetic Studies

Vinasse is a continuously resulting waste by a bioethanol industry with a high chemical oxygen demand (COD) concentration and a large volume. Anaerobic digestion (AD) is the best method to treat vinasse because it converts COD to biogas, so the biogas can support the Indonesia's primary energy need. The goal of this study was to study the effect of Fe concentration on the AD process in treating the vinasse. The Fe concentration was varied to 0.06, 0.29, 0.64, 0.99 g/L. The results showed that increasing the Fe concentration from 0.06 to 0.29 g/L intensified the biogas yield by 360% (from 10.8 to 49.6 mL/g COD). However, further increasing the Fe concentration to 0.99 g/L decreased the biogas yield by 37.8% (from 10.8 to 6.7 mL/g COD). The Fe significantly affected the methane formation stage, but not the acid formation stage. A mechanistic model was built and successfully applied to predict the AD process. Based on the simulation results, Fe concentration of 0.29 g/L resulted in the highest values of YVFA/X2 (yield of volatile fatty acids (VFAs) consumption per biomass of X2 ), μm,2 (specific growth rate for X2 ), fCH4 (composition of methane in biogas) and the lowest values of Ks,VFA (affinity coefficient in VFAs consumption), kd2 (death rate constant for X2 ), kVFA (consumption rate of VFAs for maintenance). The addition of Fe until 0.29 g/L was recommended to increase the quantity and quality (methane content reached 53.4%) of biogas production.

Challenges in part load operation of biogas-based power-to-gas processes (part I)

Direct methanation of biogas enables the storage of electrical energy in carbon-neutral (bio-)methane and subsequent injection into the national gas distribution grid. The intermittent availability of renewable electricity, as well as the varying nature of biogas production by e.g. anaerobic digestion, necessitate enhanced operational flexibility of such a Power-to-Gas process and intermediate buffer storage. This work provides experimental data of dynamic part load operation of a TRL 5 methanation plant with gas upgrading to grid-ready biomethane. Full recycling of unreacted H2 could be achieved by a commercial biogas upgrading membrane (Evonik SEPURAN® Green). Using real biogas, a sequence of load levels down to 45% of the full load capacity were tested. Stable operation of the plant could be demonstrated and grid injection limitations could be fulfilled after equilibration of the system. Additionally, an idealised PtG process chain was simulated with the focus on a sensitivity analysis of the H2 storage capacity on the methanation operation hours. It was shown that increasing the hydrogen storage capacity decreases the number of start-up and shut down procedures of the methanation plant. It could be shown that by using an equally sized electrolyser and methanation unit, allowing part load operation of the methanation only during the emptying of the H2 tank leads to longer activity phases of the methanation unit, while allowing part load operation of the methanation reactor during filling of the H2 storage tank had a negative effect.

Operation of a circular economy, energy, environmental system at a wastewater treatment plant

Decarbonising economies and improving environment can be enhanced through circular economy, energy, and environmental systems integrating electricity, water, and gas utilities. Hydrogen production can facilitate intermittent renewable electricity through reduced curtailment of electricity in periods of over production. Positioning an electrolyser at a wastewater treatment plant with existing sludge digesters offers significant advantages over stand-alone facilities. This paper proposes co-locating electrolysis and biological methanation technologies at a wastewater treatment plant. Electrolysis can produce oxygen for use in pure or enhanced oxygen aeration, offering a 40% reduction in emissions and power demand at the treatment facility. The hydrogen may be used in a novel biological methanation system, upgrading carbon dioxide (CO 2 ) in biogas from sludge digestion, yielding a 54% increase in biomethane production. A 10MW electrolyser operating at 80% capacity would be capable of supplying the oxygen demand for a 426,400 population equivalent wastewater treatment plant, producing 8,500 tDS/a of sludge. Digesting the sludge could generate 1,409,000 m 3 CH 4 /a and 776,000 m 3 CO 2 /a. Upgrading the CO 2 to methane would consume 22.2% of the electrolyser generated hydrogen and capture 1.534 ktCO 2 e/a. Hydrogen and methane are viable advanced transport fuels that can be utilised in decarbonising heavy transport. In the proposed circular economy, energy, and environment system, sufficient fuel would be generated annually for 94 compressed biomethane gas (CBG) heavy goods vehicles (HGV) and 296 compressed hydrogen gas fuel cell (CHG) HGVs. Replacement of the equivalent number of diesel HGVs would offset approximately 16.1 ktCO 2 e/a. • Curtailed electricity from a 144 MW offshore wind farm can supply a 10MW electrolyser • A 10 MW electrolyser can supply O 2 to a 426,400 person wastewater treatment facility • Only 22% of the H 2 is required for methanation of biogas from sludge digestion • Pure O 2 aeration can result in a 40% reduction in emissions at the treatment facility • Excess H 2 and biomethane could together fuel 390 heavy goods vehicles

Comparative life cycle assessment of power-to-methane pathways: Process simulation of biological and catalytic biogas methanation

Power-to-Methane (P2M) pathways are proposed as an innovative solution to utilize surplus renewable electricity for long-term and long-distance storage. This electricity can produce hydrogen using electrolysis and, with the input of CO2 from biogas, be further used for the production of synthetic methane. The methanation reaction can be done with a biocatalyst or nickel catalyst, each with a different pathway of pre- and post-treatment steps. To date, only a limited number of studies have analysed the environmental impact of P2M pathways using life cycle assessment, and no study has directly compared the biological and catalytic P2M pathways. The goal of this research is to close this knowledge gap by quantifying the environmental impact of synthetic methane production and identifying differences between both pathways. Mass and heat balances of both pathways were simulated with AspenPlus and used as basis for a thorough life cycle inventory of the material and energy demand. The global warming potential per MWh synthetic CH4 is similar for the biological and catalytic pathways, but the impact is differently distributed between the processes. The catalytic pathway requires more sulfur removal, compression power and cooling demand. In the biological pathway, the bioreactor has a large impact due to its electricity and nutrient demand, whereas the catalytic reactor's impact is almost negligible.

A FCM-clustered neuro-fuzzy model for estimating the methane fraction of biogas in an industrial-scale bio-digester

Real-time and offline monitoring, control and optimization of significant variables of bio-digester plants is crucial for optimal yield and maximum recovery of bioenergy at an industrial scale. Methane is an energy carrier and a critical component in the total biogas generated in a digestion process, thus necessitating more attention on the fraction of methane in the biogas yield. However, most previous studies in literature had focused on the volumetric yield of methane with little or no attention given to the fractional composition of methane in the total biogas produced. The deficiency of the classical technique in controlling the process parameters for optimal yield has motivated the need for machine learning-based techniques for modelling the methane fraction of biogas in a large-scale plant. In this study, a fuzzy c-mean (FCM)-clustered adaptive neuro-fuzzy inference system (ANFIS) was developed to model the methane fraction of biogas in an industrial-scale plant. The FCM clustering technique was preferred owing to its computational speed boost capability. The model was simulated using the control parameters of the algorithms while the optimal model was selected after testing their performance using relevant statistical metrics. The best model was obtained with ANFIS-FCM model with 8 clusters giving Root Mean Square Error (RMSE), Mean Absolute Deviation (MAD), Average Absolute Percentage Relative Error (AAPRE), Relative Mean Bias Error (rMBE) and correlation coefficient (R2) values of 3.156, 2.236, 3.015, 0.306, 0.978 respectively at the training phase and 4.936, 3.245, 3.456. 0.306, 0.956 respectively at the testing phase. The statistical metrics values obtained implied that FCM-ANFIS is a satisfactory model to predict methane fraction successfully.

CO2 Methanation of Biogas over Ni-Mg-Al: The Effects of Ni Content, Reduction Temperature, and Biogas Composition

Biogas is mainly composed of CH4 and CO2, so it is used as an alternative energy to CH4 with high energy density by separating and removing CO2 from biogas. In addition, it can be utilized by producing synthesis gas (CO and H2) through thermal decomposition of biogas or by synthesizing CH4 by methanation of CO2. The technique of CO2 methanation is a method that can improve the CH4 concentration without CO2 separation. This study aims to produce more efficient methane through CO2 methanation of biogas over Ni-Mg-Al catalyst. So, the effect of Ni contents in catalyst, catalyst reduction temperature, CO2 concentration in biogas, and the initial concentration of CH4 on CO2 conversion rate and CH4 selectivity was investigated. In addition, the effect of increasing CO2 concentration, H2/CO2 ratio, and GHSV (gas space velocity per hour) on H2 conversion, CH4 productivity, and product was investigated. In particular, the durability and stability of CO2 methanation was tested over 60 wt% Ni-Mg-Al catalyst at 350 °C and 30,000/h for 130 h. From the long-term test results, the catalyst shows stability by maintaining a constant CO2 conversion rate of 72% and a CH4 selectivity of 95%.

Anaerobic digestion of algal–bacterial biomass of an Algal Turf Scrubber system

This study investigated the anaerobic digestion of an algal–bacterial biofilm grown in artificial wastewater in an Algal Turf Scrubber (ATS). The ATS system was located in a greenhouse (50°54′19ʺN, 6°24′55ʺE, Germany) and was exposed to seasonal conditions during the experiment period. The methane (CH4) potential of untreated algal–bacterial biofilm (UAB) and thermally pretreated biofilm (PAB) using different microbial inocula was determined by anaerobic batch fermentation. Methane productivity of UAB differed significantly between microbial inocula of digested wastepaper, a mixture of manure and maize silage, anaerobic sewage sludge, and percolated green waste. UAB using sewage sludge as inoculum showed the highest methane productivity. The share of methane in biogas was dependent on inoculum. Using PAB, a strong positive impact on methane productivity was identified for the digested wastepaper (116.4%) and a mixture of manure and maize silage (107.4%) inocula. By contrast, the methane yield was significantly reduced for the digested anaerobic sewage sludge (50.6%) and percolated green waste (43.5%) inocula. To further evaluate the potential of algal–bacterial biofilm for biogas production in wastewater treatment and biogas plants in a circular bioeconomy, scale-up calculations were conducted. It was found that a 0.116 km2 ATS would be required in an average municipal wastewater treatment plant which can be viewed as problematic in terms of space consumption. However, a substantial amount of energy surplus (4.7–12.5 MWh a−1) can be gained through the addition of algal–bacterial biomass to the anaerobic digester of a municipal wastewater treatment plant. Wastewater treatment and subsequent energy production through algae show dominancy over conventional technologies.Graphical abstract

Innovative Technological Approach for the Cyclic Nutrients Adsorption by Post-Digestion Sewage Sludge-Based Ash Co-Formed with Some Nanostructural Additives under a Circular Economy Framework.

This paper presents a new, innovative technological approach, in line with Circular Economy principles, to the effective management of sludge generated during municipal wastewater treatment processes and subsequently used for biogas production. This approach allows for optimal, functional, and controlled cascade-type biotechnological thermal conversion of carbon compounds present in sewage sludge, later in solid digestate residues (after biogas production), and finally in the ash structure (after incineration, purposefully dosed nanostructural additives make the production of a useful solid product possible, especially for cyclic adsorption and slow release of nutrients (N, P, K) in the soil). The idea is generally targeted at achieving an innovative conversion cycle under a Circular Economy framework. In particular, it is based on an energy carrier (methane biogas) and direct energy production. The functionalized combustion by-products can be advantageous in agriculture. The use of ashes with nanostructural additives (halloysite, kaolinite) from combustion of sewage sludge after the anaerobic fermentation as an adsorbent of selected nutrients important in agriculture (Na+, K+, NO3−, SO42−, PO43−, Cl−) was verified at laboratory scale. The tests were carried out both for pure ash and for the ash derived from combustion with the purposeful addition of kaolinite or halloysite. The equilibrium conditions for nitrate, potassium, sodium, phosphate(V), sulphate(VI), and chloride ions from aqueous solutions with the use of the three adsorbent structures were determined. The obtained innovative results were interpreted theoretically with adsorption isotherm models (Langmuir, Freundlich, Temkin, Jovanović). The most spectacular and clearly favorable results related to the influence of nanostructural additives in the process of sludge combustion, and formation of sorption surfaces under high temperature conditions were identified in the case of sorption-based separation of phosphate(V) ions (an increase from 1.13% to 61.24% with the addition of kaolinite, and even up to 76.19% with addition of halloysite).

Status and future trends of hollow fiber biogas separation membrane fabrication and modification techniques.

With the increasing global demand for energy, renewable and sustainable biogas has attracted considerable attention. However, the presence of various gases such as methane, carbon dioxide (CO2), nitrogen, and hydrogen sulfide in biogas, and the potential emission of acid gases, which may adversely influence the environment, limits the efficient application of biogas in many fields. Consequently, researchers have focused on the upgrade and purification of biogas to eliminate impurities and obtain high-quality and high-purity biomethane with an increased combustion efficiency. In this context, the removal of CO2 gas, which is the most abundant contaminant in biogas, is of significance. Compared to conventional biogas purification processes such as water scrubbing, chemical absorption, pressure swing adsorption, and cryogenic separation, advanced membrane separation technologies are simpler to implement, easier to scale, and incur lower costs. Notably, hollow fiber membranes enhance the gas separation efficiency and decrease costs because their large specific surface area provides a greater range of gas transport. Several reviews have described biogas upgrading technologies and gas separation membranes composed of different materials. In this review, five commonly used commercial biogas upgrading technologies, as well as biological microalgae-based techniques are compared, the advantages and limitations of polymeric and mixed matrix hollow fiber membranes are highlighted, and methods to fabricate and modify hollow fiber membranes are described. This will provide more ideas and methods for future low-cost, large-scale industrial biogas upgrading using membrane technology.

Systematic generation of a once-through staged reactor design for direct methanation of biogas

With 40 mol% CO2, the energy content of biogas is too low to be used as motor fuel. Motor-grade compressed bio-methane can be produced by direct methanation of biogas with the use of hydrogen. A direct methanation process is considered here as the pre-processing step of separating the biogas is avoided. A systematic staging method is applied to design the process to upgrade biogas to motor-grade bio-methane by maximizing the production of methane with the use of the least possible reaction volume and subject to a quality specification. Here, a once-through process is the target so as to avoid the post-processing separation of the product and recycling. The most promising design is a three-stage configuration with water condensation after each stage. Shell and tube reactors are considered to be less expensive than micro-channel reactors. All three stages are placed in a single shell with boiling water on the shell side. The proposed design is verified by rigorous simulation. The method makes process intensification of chemical reaction systems possible, which is here demonstrated for direct methanation of biogas.

Enhancing methane production of co-digested food waste with granular activated carbon coated with nano zero-valent iron in an anaerobic digester

Anaerobic digestion (AD) possesses dual benefits of waste treatment and energy generation. The use of conductive additives in AD matrix has potential to improve process yield. Hence, the study aimed to investigate a thermophilic AD (TAD) inserted by granular activated carbon coated with nano zero-valent iron (GAC/nZVI) in the matrix and was operated for mono-digestion and co-digestion of cow manure with food wastes (rice and bread) to check the bioprocess improvement. The results were compared with the control TAD without conductive additives. Biogas production increased by 11 folds upon using GAC/nZVI addition compared to the control TAD. Moreover, the addition of GAC/nZVI increased the methane in biogas by 20.7 folds compared to control one. With GAC/nZVI, the maximum COD removal of 78.29% and 85.21% were noticed for co-digestion and mono digestion, respectively. Such improvement of TAD performance was due to easy bacterial communication and electron exchange through the conductive particles.

Enhancing anaerobic digestion of food waste with granular activated carbon immobilized with riboflavin

Previous studies have shown that anaerobic digestion of food waste can be enhanced by addition of conductive materials that stimulate direct interspecies electron transfer (DIET) between bacteria and methanogens. However, at extremely high organic loading rates (OLRs), volatile fatty acids (VFAs) still tend to accumulate even in the presence of conductive materials because of an imbalance between the formation of fermentation products and the rate of methanogenesis. In this study, granular activated carbon (GAC) immobilized with riboflavin (GAC-riboflavin) was added to an anaerobic digester treating food waste. The GAC-riboflavin reactor operated stably at OLRs as high as 11.5 kgCOD/ (m3·d) and kept VFA concentrations below 69.4 mM, COD removal efficiencies, methane production rates, and biogas methane concentrations were much higher in the GAC-riboflavin reactor than the GAC- and non-amended reactors. Transcripts associated with genes that code for proteins involved in DIET based metabolism were somewhat more highly expressed by Methanothrix in the GAC-riboflavin reactor. However, it is unlikely that riboflavin acted as an electron shuttle to stimulate DIET. Rather, it seemed to provide nutrients that enhanced the growth of microorganisms involved in the anaerobic digestion process, including those that are capable of DIET.

Enhancement of Anaerobic Digestion with Nanomaterials: A Mini Review

In recent years, the number of articles reporting the addition of nanomaterials to enhance the process of anaerobic digestion has exponentially increased. The benefits of this addition can be observed from different aspects: an increase in biogas production, enrichment of methane in biogas, elimination of foaming problems, a more stable and robust operation, absence of inhibition problems, etc. In the literature, one of the current focuses of research on this topic is the mechanism responsible for this enhancement. In this sense, several hypotheses have been formulated, with the effect on the redox potential caused by nanoparticles probably being the most accepted, although supplementation with trace materials coming from nanomaterials and the changes in microbial populations have been also highlighted. The types of nanomaterials tested for the improvement of anaerobic digestion is today very diverse, although metallic and, especially, iron-based nanoparticles, are the most frequently used. In this paper, the abovementioned aspects are systematically reviewed. Another challenge that is treated is the lack of works reported in the continuous mode of operation, which hampers the commercial use of nanoparticles in full-scale anaerobic digesters.

System performance and functional analysis for the methanogenic bioreactor of a two-phase anaerobic digestion system: The effect of influent sulfate

In this study, a lab-scale bioreactor was built to investigate the influence of sulfate on the overall performance, microbial community, and metabolic pathways in the methanogenic bioreactor of a two-phase anaerobic digestion system. The results demonstrated that by gradually cultivating the sludge of the methanogenic bioreactor, a chemical oxygen demand (COD) degradation efficiency of over 65% was achieved for sulfate contents from 10,000 mg/L to 30,000 mg/L. The sulfate reduction performance could only be maintained at a high level for influent COD/sulfate ratios no less than 1.88. In addition, the methane production rate (MPR) decreased from 0.92 L/L/d to 0.28 L/L/d, and the proportion of methane in biogas dropped from 51% to 33% when the influent sulfate exceeded 30,000 mg/L. High-throughput sequencing coupled with PICRUSt2 revealed that the dissimilatory sulfate process could be enhanced by sulfate within 30,000 mg/L. While an amount of greater than 5000 mg/L sulfate remarkably inhibited the assimilatory sulfate reduction process, and this inhibition was induced by the down-regulation of the cysNC, cysC, cysI and cysJ genes. For the methanogenic process, sulfate contents within 30,000 mg/L had no obvious impact on all of the acetoclastic, hydrogenotrophic, and methylotrophic methanogenesis processes, but serious suppression was observed for sulfate amounts greater than 30,000 mg/L. This inhibition primarily originated from the decrease in mcrA, mcrB, and mcrG genes that regulate the conversion of methylcoenzyme M to methane, the last step of all three methanogenesis pathways.

Effect of Fe and La on the Performance of NiMgAl HT-Derived Catalysts in the Methanation of CO2 and Biogas

Bulk Ni-based catalysts derived from hydrotalcite-type (HT) compounds show enhanced stability in the hydrogenation of CO2 into CH4, in comparison to their supported counterparts. The composition of the parent hydrotalcite determines the Ni loading and particle size, as well as the basicity of the catalysts. In this work, a comparison between the effect of Fe and La on the performance of NiMgAl HT compounds (Ni/Mg/Al = 25/50/25 atomic ratio) calcined at 600 °C is investigated. After a reduction pretreatment at 750 °C, both promoters enhance the activity in the low-temperature range; however, the La-containing catalyst reaches a better CH4 productivity rate at high oven temperature (i.e., 200 L gNi–1 h–1 at 325 °C). Although the formation of the NiFe alloy improves the activity, lanthanum keeps smaller Ni0 particles and provides a higher basicity to the mixed oxide than Fe. The activity of the NiMgLaAl catalyst can be further tailored by increasing the Ni loading from 25.6 wt % (Ni25Mg50La5Al20) to 44.6 wt % (Ni50Mg25La5Al20). Lastly, the feasibility of HT-derived catalysts in the direct methanation of clean biogas is proved.

Influence of low operating temperature on biomass yield during anaerobic treatment of chocolate confectionery wastewater in a pilot-scale UASB reactor

It has been found that biomass yield (Yobs) increases as operating temperature decreases in batch reactors fed with synthetic substrate; nevertheless, there is a gap in literature about this phenomenon in pilot-scale reactors treating real industrial wastewaters, such as from the chocolate confectionery industry. Therefore, the effect of low operating temperature on the Yobs during the anaerobic treatment of chocolate confectionery wastewater (CCWW) was studied. In this research, the CCWW was treated in a 244-L pilot-scale upflow anaerobic sludge blanket reactor, which was operated for 275 days at short hydraulic retention time (6 h), medium total applied organic loading rates (OLRTappl) (6.7–11.6 kg-total chemical oxygen demand (CODT/m3/d)), and low operating temperature (14–20 °C). The COD removal efficiency ranged from 70 to 90 % and the methane production rate varied between 230 and 393 L-CH4/d at standard temperature and pressure (84 % of methane in biogas). The results showed that Yobs was higher at 14 °C [0.20 g-volatile suspended solids/g-removed COD (g-VSS/g-CODrem)] than at 20 °C (0.15 g-VSS/g-COD). Also, high Yobs values lead to a larger anaerobic biomass washout in the reactor effluent. The anaerobic biomass washout was also influenced by the presence of sodium in CCWW, the high OLRTappl and the low operating temperature, which made difficult the solids-liquid separation.

Assessment of Sustainable Biogas Production from Co-Digestion of Jatropha De-Oiled Cake and Cattle Dung Using Floating Drum Type Digester under Psychrophilic and Mesophilic Conditions

Biodiesel is an emerging alternative fuel that is generally made from edible and non-edible oilseed crops. Jatropha curcus has a high potential for producing biodiesel, which yields 25–35% oil along with 75–65% solid byproduct, generally called a de-oiled cake. The present manuscript deals with the co-digestion of Jatropha de-oiled cake along with cattle dung (1:1 ratio) for biogas production in a floating-type biogas digester. The experimental study was carried out in a modified KVIC biogas plant of 6 cubic meter capacity for 60 days’ retention time under psychrophilic and mesophilic temperature conditions. During all the experiments, the total solid content of the slurry was maintained fixed at 10–12% by mixing 10 kg Jatropha de-oiled cake and 10 kg cattle dung with 80 kg water. The experimental results showed that the average specific biogas production of Jatropha de-oiled cake and cattle dung slurry was observed to be 0.216 m3/kg TS, 0.252 m3/kg VS and 0.287 m3/kg TS, 0.335 m3/kg VS, respectively, under the aforementioned conditions. Moreover, the biogas methane concentration was observed to be 62.33% to 69.16% under mesophilic temperature conditions compared to the psychrophilic temperature conditions, 65.21% to 69.15%, respectively. Furthermore, the average total volatile solids mass removal efficiency of feeding material in the abovementioned process was 7% higher under mesophilic temperature conditions than psychrophilic temperature conditions. Additionally, the results indicated that a total 588.8 kg of input volatile solids produced a total of 7306.56 MJ/m3 and 5177.88 MJ/m3 energy in 60 days under psychrophilic and mesophilic temperature conditions. On the basis of the results, it is concluded that Jatropha de-oiled cake may be a superior solution for improving biogas quality and composition as well as a value-added product, i.e., organic manure.

Dark fermentative biohydrogen production from confectionery wastewater in continuous-flow reactors

The production of biohydrogen from industrial wastewater through the dark fermentation (DF) process has attracted increased interest in recent years. To implement a DF process on a large scale, a thorough knowledge of laboratory scale process control is required. The operating parameters and design features of the reactors have a great influence on the efficiency of the process. In this work, the possibility of continuous production of biohydrogen from confectionery wastewater was evaluated. The DF process was carried out at 37 ± 1 °C in two different reactors: an upflow anaerobic filter (AF) and a fluidized bed reactor (AFB). Polyurethane foam (PU) was used to immobilize the biomass. The DF process was studied at four hydraulic retention times (HRT) (1.5, 2.5, 7.5 and 15 days) and the corresponding organic loading rates (OLR) (9.21, 6.12, 2.04 and 1.02 g CODinit/(L day)). The highest hydrogen yield (HY) (44.73 ml/g CODinit) and hydrogen production rate (HPR) (92.5 ml/(L day)) was observed in AFB at HRT of 7.5 days and 2.5 days, respectively. The highest concentration of hydrogen in biogas was 34% in AF and 36% in AFB at HRT of 7.5 days. In contrast to AF, the COD removal efficiency in AFB increased with increasing HRT. The pH of the effluent was low (3.95–4.38). However, due to the use of PU for biomass immobilization, it is possible that there were local zones in the reactor that were optimal for the functioning of not only acidogens, but also methanogens. This was evidenced by a rather high content of methane in biogas (2.5% in AF and 9.6% in AFB at HRT of 15 days). These results provide valuable data for optimizing the continuous DF of wastewater from confectionery and other food industries to produce biohydrogen or biohythane.

Experimental and simulation analysis of biogas production from beverage wastewater sludge for electricity generation

This study assessed the biogas and methane production potential of wastewater sludge generated from the beverage industry. The optimization of the biogas production potential of a single fed-batch anaerobic digester was operated at different temperatures (25, 35, and 45 ℃), pH (5.5, 6.5, 7.5, 8.5, and 9.5), and organic feeding ratio (1:3, 1:4, 1:5, and 1:6) with a hydraulic retention time of 30 days. The methane and biogas productivity of beverage wastewater sludge in terms of volatile solid (VS) and volume was determined. The maximum production of biogas (15.4 m3/g VS, 9.3 m3) and methane content (6.3 m3/g VS, 3.8 m3) were obtained in terms of VS and volume at 8.5, 35 ℃, 1:3 of optimal pH, temperature, and organic loading ratio, respectively. Furthermore, the maximum methane content (7.4 m3/g VS, 4.4 m3) and biogas production potential (17.9 m3/g VS, 10.8 m3) were achieved per day at room temperature. The total biogas and methane at 35 ℃ (30 days) are 44.3 and 10.8 m3/g VS, respectively, while at 25 ℃ (48 days) increased to 67.3 and 16.1 m3/g VS, respectively. Furthermore, the electricity-generating potential of biogas produced at room temperature (22.1 kWh at 24 days) and optimum temperature (18.9 kWh) at 40 days was estimated. The model simulated optimal HRT (25 days) in terms of biogas and methane production at optimum temperature was in good agreement with the experimental results. Thus, we can conclude that the beverage industrial wastewater sludge has a huge potential for biogas production and electrification.