Highest Biogas Production Research Articles

Efficient organic carbon utilization for combined nutrient removal and biogas production in hybrid biofilm activated sludge system

Moving bed biofilm technology is a successful and promising biological treatment process considered for cost-effective management of wastewaters. In this study, a hybrid moving bed biofilm pilot plant was operated and obtained results were compared with simulation results of two biological processes: a conventional Biological Nutrient Removal (BNR) system and a novel hybrid activated sludge configuration implemented with Moving Bed Biofilm Reactor (MBBR) and a reactive primary clarifier (RPC). An efficient organic carbon entrapment (87%) was obtained in reactive primary clarifier where the major component (95%) of the total Chemical Oxygen Demand (COD) was determined as slowly hydrolysable (XS1), according to respirometric tests. Pilot plant and simulation studies exhibited that an improved nitrogen and phosphorus removal performance, as well as higher biogas production (47%) were obtained by organic carbon redirection in proposed hybrid configurations, securing a 40% less reactor volume. Investigation of the economic aspects indicated that hybrid system has a lower operating cost (i.e., 23% less air requirement, 40% less mixing energy requirement), does not require internal recirculation pumps, and produces more energy through anaerobic digestion compared to conventional BNR. Therefore, proposed novel hybrid configuration is more efficient for the treatment of municipal wastewater in terms of Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) within the energy self-sufficient treatment plant approach and sustainable treatment plant operation.

Comparing the effect of mesophilic and thermophilic anaerobic co-digestion for sustainable biogas production: An experimental and recurrent neural network model study

Anaerobic digestion is a promising technology for treating bio wastes from energetic and environmental point of views. Co-digestion of wastes and process temperature are essential parameters that affect biogas production. In this study, comparing the effect of mesophilic and thermophilic anaerobic co-digestion of waste activated sludge and wheat straw at different mixing ratios is applied for sustainable biogas production based on energetic, environmental, and economic perspectives. Moreover, modeling and optimizing the process by using a time-series model and a partially connected recurrent neural network (RNN) based a slime mold algorithm (SMA) is established to calculate the optimal structure of the RNN model and the optimal values of its parameters such as the optimal number of neurons in the hidden layers, number of feedback connections, activation functions, and connection weights. The results show that the co-digestion of sludge and straw improves the carbon to nitrogen (C/N) ratio and enhances biogas production. The highest biogas production is recorded at C/N ratio of 33.15 and is approximately 30% higher in thermophilic digesters compared to mesophilic ones. Moreover, thermophilic digesters show higher chemical oxygen demand (COD) (75.38%) and total volatile solids (TVS) (72.37%) elimination than mesophilic digesters. The thermophilic digester increases the produced energy by 25.67% and decreases the production cost by 20.43% compared to the mesophilic digester in case using evacuated tube solar collectors. Furthermore, the RNN model could effectively predict biogas production, and the SMA could determine the optimal structure of the RNN model.

Influence of Molasses Residue on Treatment of Cow Manure in an Anaerobic Filter with Perforated Weed Membrane and a Conventional Reactor: Variations of Organic Loading and a Machine Learning Application.

This study highlighted the influence of molasses residue (MR) on the anaerobic treatment of cow manure (CM) at various organic loading and mixing ratios of these two substrates. Further investigation was conducted on a model-fitting comparison between a kinetic study and an artificial neural network (ANN) using biomethane potential (BMP) test data. A continuous stirred tank reactor (CSTR) and an anaerobic filter with a perforated membrane (AF) were fed with similar substrate at the organic loading rates of (OLR) 1 to OLR 7 g/L/day. Following the inhibition signs at OLR 7 (50:50 mixing ratio), 30:70 and 70:30 ratios were applied. Both the CSTR and the AF with the co-digestion substrate (CM + MR) successfully enhanced the performance, where the CSTR resulted in higher biogas production (29 L/d), SMP (1.24 LCH4/gVSadded), and VS removal (>80%) at the optimum OLR 5 g/L/day. Likewise, the AF showed an increment of 69% for biogas production at OLR 4 g/L/day. The modified Gompertz (MG), logistic (LG), and first order (FO) were the applied kinetic models. Meanwhile, two sets of ANN models were developed, using feedforward back propagation. The FO model provided the best fit with Root Mean Square Error (RMSE) (57.204) and correlation coefficient (R2) 0.94035. Moreover, implementing the ANN algorithms resulted in 0.164 and 0.97164 for RMSE and R2, respectively. This reveals that the ANN model exhibited higher predictive accuracy, and was proven as a more robust system to control the performance and to function as a precursor in commercial applications as compared to the kinetic models. The highest projection electrical energy produced from the on-farm scale (OFS) for the AF and the CSTR was 101 kWh and 425 kWh, respectively. This investigation indicates the high potential of MR as the most suitable co-substrate in CM treatment for the enhancement of energy production and the betterment of waste management in a large-scale application.

Thermal Disintegration of Sewage Sludge as a Method of Improving the Biogas Potential

Operating and research experiments indicate that the potential benefits of thermal treatment of sewage sludge before methane fermentation include increasing the biodegradability of substrates, reducing the amount and improving the dewaterability of the fermentate and its hygienization, reducing the emission of odours during stabilization, higher production of biogas, and improving the energy balance of the process. The process of disintegration (liquefaction) can be carried out, for example, through the use of mechanical homogenization, microwaves and ultrasonic waves, chemical agents, thermal methods, and biological processes. The article reviews the literature data on thermal hydrolysis research, from the first source information to the present. The thermal hydrolysis achieved enhanced hydrolysis, biogas potential, and faster sludge degradation during anaerobic digestion without compromising the quality of the end products.

Co-digestion of food waste with cow dung by anaerobic digestion for biogas production.

Food waste is categorized under household waste which were produce in large amount every day and it can be a good potential to generate biogas production via anaerobic digestion. In this research, the characteristics of co-digestion process are measured to determine the biogas production between food waste and cow dung. The food waste is co-digest with two different type of cow dung are collected depends on their food consuming (grass:bran); 100% grass and 95% grass : 5% bran. The digester is maintained at 35°C of temperature for mesophilic condition. pH values and C/N ratio are noted until 35 days. The biogas production is analysed by using biogas analyzer. The highest biogas production in this study is 67.2% which are co-digest between food waste and cow dung (100%) compared cow dung (95%) is 53.9% on day 26. This shows that the cow dung (100%) produces more biogas than cow dung (95%). Anaerobic digestion process will best suits for biogas production and for the best utilization of food waste.

Effect of Pretreatment and C/N Ratio in Anaerobic Digestion on Biogas Production from Coffee Grounds and Rice Husk Mixtures

Indonesia has great potential in producing large quantities of renewable energy sources, such as biomass. Biogas is a renewable energy source produced from biomass. It is can be developed in agricultural countries producing rice and coffee, where a large amount of waste is produced in the form of rice husks and coffee grounds. This study examined the effect of physiochemical pretreatment and the C/N ratio on biogas production using coffee grounds and rice husk mixtures. Physical pretreatment was conducted by grinding the mixture up to 50 mesh size, followed by chemical pretreatment by soaking the mixture in 3% KOH; moreover, the variation in the C/N ratio was set at 25 and 30. Anaerobic bacteria were acquired from rumen fluid. The ratio of the coffee ground material, rice husks, and rumen fluid was 1:1:1. This research was conducted in duplicate under batch conditions at ambient temperature (25–35 oC) with a digester volume of 1.5 L. Biogas productivity was measured every 2 d for 60 d. The experimental results indicated that biogas production with a C/N ratio of 30 was 13.3–66.5% higher than that with a C/N ratio of 25. The inclusion of physical pretreatment at a C/N ratio of 30 increased biogas production by up to 31.3%. Moreover, the inclusion of a chemical pretreatment at a C/N ratio of 30 resulted in 30.3% higher biogas production. The kinetics model of biogas production showed that a C/N ratio of 30 with physical and alkaline pretreatment can produce maximum biogas yields of 6,619 mL and 6,570 mL, respectively. Overall, both pretreatments sequentially increased the biogas production significantly.

Influence of pH and the Insulation of Reactor on The Biogas Production of Livestock Waste by Batch Anaerobic Reactor

This study presents the improved biogas production by determining the optimum pH and insulation reactor from cow, sheep, and poultry manure (which are the most available in our location). The experiment was carried out in 2000 mL digester put in the water bath at 37 ˚C. The mixing ratio of animal manure and water used was 1:1 in 12 days of Hydraulic Retention Time (HRT). Produced gas was measured by the volumetric water replacement method. The optimum pH will be chosen in the experimental test with different pH ranges in the first phase. Three set-ups were prepared with different pHs (6.5, 7, 7.5).The results showed that the pH had significant effects on biogas yield, where pH7 had the highest biogas production and pH 6.5 is the lowest. The second phase, investigated the effect of the insulation of the reactor on the biogas yield. The biogas was produced from an insulated reactor higher than the photoreactor because of the growth of algae which produces oxygen in the photoreactor. Therefore, it is given that the study which gave a maximum yield of biogas from the batch digestion process might be met the future energy demand.

Torrefaction at low temperature as a promising pretreatment of lignocellulosic biomass in anaerobic digestion

The lignocellulosic structure of agricultural biomass, which makes it resistant to microbial attack, is the main obstacle in its anaerobic digestion. However, not all biomasses behave the same in the face of anaerobic digestion. Instead, depending on their composition in terms of lignin, cellulose and hemicellulose content, the anaerobic digestion process may be more or less favoured, although a pretreatment stage is usually necessary. This paper presents the results of a laboratory scale batch experiment to study the effect of thermal pretreatment (torrefaction) on the anaerobic digestion of two biomass materials: barley straw and vine shoot. For this, thermal pretreatment temperatures of 100, 130, 180 and 210 °C, with a residence time of 24 h, were studied for both biomasses and the results were compared with the material without pretreatment. Significant differences in biogas production were observed for both biomasses depending on the pretreatment temperature. The highest biogas yields of 458 and 213 mL/gVS for straw and vine shoot, respectively, were observed from biomass pretreated at 100 °C. Barley straw pretreated at 100 °C showed 275% higher methane yield compared to untreated straw. In the case of the vine shoot, the increase was 210%. Furthermore, FTIR-ATR analysis and thermogravimetric analysis coupled with a pseudocomponent kinetic model revealed changes in the lignocellulosic composition of both biomasses while SEM analysis revealed also structural changes. The modified Gompertz model fitted the production data well and predicted shorter lag time and higher biogas production at pretreatment temperatures from 100 to 180 °C compared with the untreated materials. From there, a reduction in methanogenic activity is observed when the pretreatment temperature increases. In general, the change in the lignocellulosic structure and the decrease in the hemicellulose content could be considered as the main reasons to improve the biogas production.

Importance of Feedstock in a Small-Scale Agricultural Biogas Plant

Although no legal sustainability criteria have been formulated for electricity and heat production from biogas, the sustainability and profitability of large-scale biogas plants which use mainly energy crops is now questioned. Small (farm-size) biogas plants characterized by CHP electrical output in the range between 15 kWel and 99 kWel, operating on agricultural wastes and by-products, seem more suitable; however, the variety of feedstock may be crucial in the proper design and operation of such family biogas plants. This paper aims to present the problems that occurred in small agricultural biogas plants fed with sheep manure (SM), horse manure (HM), and grass-clover silage (GCS). This paper also focuses on analyzing the energy balance and carbon dioxide (CO2) emissions related to four technological solutions (Scenarios 1–4) based on various feedstocks, grinding and feeding systems, and wet/dry fermentation. The biogas plant was originally based on dry fermentation with an organic loading rate ~10.4 kgVS·m−3·d−1, a hydraulic retention time of 16 days, and temperature of 45 °C in the fermentation chamber. The material was shredded and mixed in a mixing device, then the mixture of manures and silage was introduced to the horizontal fermentation chamber through a system of screw feeders. The biogas and the digestate were collected in a reinforced concrete tank. The biogas was sent to the CHP unit of an installed electrical power of 37 kWel, used to produce electricity and recover the heat generated in this process. Scenario 1 is based on the design assumptions used for the biogas plant construction and start-up phase. Scenario 2 includes a new feeding and grinding system, in Scenario 3 the feedstock is limited to SM and HM and wet fermentation is introduced. In Scenario 4, a dry fermentation of SM, HM, and maize silage (MS) is assumed. Avoided CO2 emissions through electricity and heat production from biogas were the highest in the case of Scenarios 1 and 4 (262,764 kg CO2·y−1 and 240,992 kg CO2·y−1) due to high biogas production, and were the lowest in Scenario 3 (7,481,977 kg CO2·y−1) because of the low specific methane yield (SMY) of SM and HM. Nevertheless, in all scenarios, except Scenario 3, CO2 emissions from feedstock preparation and biogas plant operation are much lower than that which can be avoided by replacing the fossil fuel energy for the electricity and heat produced from biogas. Our observations show that a small agricultural biogas plant can be an effective energy source, and can contribute to reducing CO2 emissions only if the appropriate technological assumptions are adopted, and the entire installation is designed correctly.

Optimization and microbial diversity of anaerobic co-digestion of swine manure with waste kitchen oil at high organic loading rates

Anaerobic co-digestion of swine manure (SM) and waste kitchen oil (WKO) was conducted to evaluate the effect of high organic loading rates (OLRs) on biogas production efficiency and microbial changes. Combinations of different loading rates of SM and WKO, with total OLRs from 2 to 8 g VS (volatile solid)/L/d, were evaluated in a laboratory-scale study. While feeding more than 4 g VSSM/L/d did not result in higher biogas production in both mono- and co-digestion scenarios, the addition of WKO increased the total OLR up to 6 g VS/L/d without significant reduction of system productivity. Biogas yields of M2O1 (2 g VSSM/L/d + 1 g VSWKO/L/d) and M4O2 were 910 ± 35 and 849 ± 85 mL/g VSfed which were 25.2 % and 16.9 % higher than the mono-digestion of M2, respectively. A significant increase of bacterial alpha-diversity (Shannon index) was observed in M2O1, at 233.0 ± 3.6 compared with 218.7 ± 5.1 of M2 (p < 0.05). Less bacterial alpha-diversity and accumulation of volatile fatty acids were observed in M4O1 and M4O2, suggesting their potential instability. When digesters were fed with M2, the introduction of 1.4 g VSWKO/L/d or more did not increase biogas yield and could cause system imbalance. The study suggests the limit of WKO could be increased when higher OLRs of SM were applied but should not be more than 4 g VSSM/L/d, and ratio between SM and WKO should be considered to avoid failure. Some of the system disturbances took up to three months to show.

Foaming Tendency in Anaerobic Digestion of Wastewater Inoculated with Anaerobic Sludge and Cow Manure: Effect of Protein Concentration

Foaming has impacted the digestion process causing severe process failures. The basis of foaming is often unclear due to multiple foaming compounds in a single system. This study aims to elucidate the effect of protein concentration on foaming in anaerobic sludge and cow manure (CM) digesters inoculated with synthetic wastewater as a substrate. Gelatine was used to alter the protein concentration in the digesters. The foaming tendency, biogas production, protein, and chemical oxygen demand (COD) removal were measured to comprehend the findings. The results show that the foaming tendency increased with protein concentration in anaerobic sludge digesters. It also had the highest biogas production. There was no evident process inhibition observed in the anaerobic sludge digester, even at higher protein and COD concentrations. For CM digester, the foaming tendency and biogas production increased to 9 g/L; however, the biogas production decreased with increased substrate protein concentration, indicating process inhibition. The results indicate that the biogas production, foaming tendency, COD and protein removal increased steadily for both digesters. However, the trend decreased for CM digester at increased protein concentrations. This study also concluded that protein creates foaming when inoculated with anaerobic sludge and CM even at low substrate protein concentration.

Evaluation of electro-oxidation and Fenton pretreatments on industrial fruit waste and municipal sewage sludge to enhance biogas production by anaerobic co-digestion

This study presents the effect of electro-oxidation and Fenton pre-treatment on anaerobic co-digestion (AnCoD) of fruit-juice industrial waste (FJW) and municipal sewage sludge (MSS). Biogas production increased from 767 mL to 857 mL and 918 mL after EO and Fenton pretreatment, respectively. The methane amount increased by 28% and 39% for EO and Fenton processes. The removal efficiencies of soluble COD, carbohydrate, and protein for the conditions with the highest biogas production as a result of the pretreatment process were 48%, 65%, 61% for the Fenton pre-treatment, and 37%, 52%, and 39% for the EO pre-treatment, respectively. Cumulative biogas production efficiency for all pre-treated mixtures was estimated with kinetic models. In addition, an evaluation has been made regarding cost, economic gain, and energy consumption of the pre-treatment processes.

Investigating the Enhancement in Biogas Production by Hydrothermal Carbonization of Organic Solid Waste and Digestate in an Inter-Stage Treatment Configuration

In recent years, sewage sludge (SS) and bio-waste management have attracted increasing environmental attention. In this study, hydrothermal carbonization (HTC) technology is investigated in the framework of a co-treatment of sewage sludge digestate (SSD) and an organic fraction of municipal solid waste (OW). The proposed configuration integrates HTC with anaerobic digestion (AD) in an inter-stage configuration (AD1 + HTC + AD2). The effects of different percentages of OW added to SSD in the HTC treatment are evaluated in terms of characteristics and methane yield of the produced HTC liquor (HTCL) and HTC slurry (i.e., the mixture hydrochar-HTCL), as well as dewaterability of the HTC slurry. Results show that, with the increase in the percentage of OW in the OW-SSD mixture fed to the HTC process, production of biogas and biomethane of both HTC slurry and HTCL increases. The highest biogas production is achieved when a mixture consisting of half SSD and half OW is used, reaching 160 ± 10 and 240 ± 15 mL biogas g−1 CODadded, respectively, for HTCL and HTC slurry. Furthermore, sludge dewaterability is significantly improved by the combined AD1-HTC-AD2 process. Finally, an energy assessment allows estimating that the co-treatment of OW with SSD in HTC can cover up to 100% of the energy consumption of the system.

Evaluation of the biogas potential of mucilage formed in the Marmara Sea

The mucilage, which emerged as a result of increasing global warming and the deterioration of marine ecosystem balances, has taken the Marmara Sea under its influence. Mucilage appears in some periods and there is not much information about its bioenergy production potential. In this study, the biogas and biohydrogen production potential was determined when mucilage collected from the coasts is used as a substrate. Different S/X ratios were evaluated for biogas production. The highest biogas production was observed as 682 ml/g VS at the S/X ratio of 2. Dark fermentation was carried out using mixed Clostridium sp. to produce biohydrogen. As a result of fermentation, a maximum biohydrogen yield of 117 ml H 2 /g VS hydrogen was obtained. In terms of both biogas and hydrogen results, the bioenergy potentials of the mucilage sample taken from the surface were determined to be higher than the bottom sediment. • The highest biogas production was observed at the S/X ratio of 2. • A maximum biohydrogen yield of 117 ml H 2 /g VS was obtained. • The methane content was ranged between 25 and 30% for both samples. • The bioenergy potential of the white mucilage was higher.

Investigation of anaerobic degradability and biogas production of the starch and industrial sewage mixtures

Today, with the increase in industrialization, the disposal of organic sludge formed after industrial activities has started to pose a serious problem. For this reason, biogas production from such organic wastes under anaerobic conditions is very valuable in terms of both sustainable environmental policy and renewable energy recovery. In this study, the effects of mono-digestion and co-digestion of starch sludge (SS), industrial sewage sludge (IS), and wastewater (CIWW) from the cardboard manufacturing industry on the biogas production potential and the changes in parameters such as dissolved COD, carbohydrates and pH were presented. In addition, a pH-controlled study was carried out with the sample with the lowest final pH level (100% SS) after anaerobic fermentation. The mixtures were prepared to contain 100%SS, 100%IS, 100%CIWW, 75%SS-25IS, 66%SS-33IS, 50%SS-50%IS, 33%SS-66IS, and 25%SS-75%IS on a dry weight basis. The amount of biogas produced by 100%SS (257 mL) was almost 5 times greater than 100%IS (56 mL). The utilization of the CIWW together with SS and IS increased the biogas production potential approximately 10 times and 2 times, respectively. The highest biogas production was achieved with the anaerobic co-digestion (ACoD) of 25%SS and 75%IS as 332 mL. Under these conditions, biogas production increased by 29% and 493%, respectively, compared to mono-digestion of the substrates. As the SS ratio in the mixture increased, the pH value decreased due to VFA accumulation in the medium. In addition, there was a decrease of approximately 11% in biogas production. The soluble COD concentration of all mixtures increased after anaerobic fermentation except 100%IS. On the contrary, carbohydrate removal was observed in all reactors except 50%SS-50%IS mixture.

Anaerobic co-digestion of cheese whey and septage: Effect of substrate and inoculum on biogas production

Cheese whey is an industrial waste generated from the cheese processing unit of the dairy industry and requires treatment before its disposal. The present study investigated the possibilities of improving the digestibility from anaerobic digestion of lipid rich dairy by-product, cheese whey using septage as the co-substrate with different inoculum. Biochemical methane potential assays were conducted under mesophilic temperature conditions and results were validated using Modified Gompertz Model. Two sets of BMP tests were done; to assess the individual and combined digestion abilities of septage in anaerobic co-digestion of whey and to assess the ability of 3 inoculum sources (cattle manure, sewage sludge, and acclimatized anaerobic sludge) in the co-digestion process. The results indicated that septage is an excellent co-substrate that has better adaptability with cheese whey and the optimum mix ratio was found as 40:60 (SCW: SSP). BMP tests were also conducted with inoculum at S/I ratio of 1 and statistical analysis was performed to study the synergistic effect of both co-digestion and inoculum. The tests revealed that the cattle manure resulted in the highest biogas production (342.22mL/gVS) at 60% whey fraction. Modified Gompertz model fitted the experimental data well and identified an increase in lag phase times when whey fraction is increased. Comparatively higher lag phase times ranging from 1.98 to 4.35 days were obtained for sewage sludge inoculated samples. The maximum methane production (Pmax) was obtained at 60% whey fraction (369.63 ± 4.05mL/gVS) at a very short lag time of 0.76 ± 0.17days for cattle manure inoculated mixture.

Alkaline pre-treatment (NAOH) as a strategy to increase the performance and feasibility of the anaerobic digestion of cattle slurry

ABSTRACT Dairy cattle manure with bedding (CB), including manure, urine, water, and shavings, is lignocellulosic biomass and needs to be pre-treated in anaerobic reactors to enhance biomass digestibility. This study analyzed the technical and economic feasibility of physical treatment (milling) and alkaline treatment of CB for biogas production. Pre-treatment included drying, milling, and alkaline hydrolysis at room temperature for 24 h. Maximum biogas production was determined using the biochemical methane potential (BMP) test. Physicochemical analyses were performed to characterise CB before and after pre-treatment and the BMP test. The characteristics of the lignocellulosic material were examined by scanning electron microscopy. The economic feasibility (return on investment) of each treatment (USD per ton of CB) was determined. Treatment with 3% NaOH achieved the highest biogas production (771 mL per kg of volatile solids) and was 104.5% higher than that of milling and 124.7% higher than that of chemical pre-treatment with 4% NaOH. The analysis of economic feasibility showed that the payback period of treatment with 3% NaOH was 1.4 years for scenario 1 (continuous stirred tank reactor - CSTR) and 3 years for scenario 2 (covered lagoon digester). These results demonstrate the feasibility of producing biogas as a renewable energy source via the anaerobic digestion of CB.

Comparison Effect on Biogas Production from Vegetable and Fruit Waste with Rumen Digesta Through Co-Digestion Process

Biogas is the best renewable energy as it can be produced from any biomass for example any plant or living organism. The purpose of this research was to produce biomethane from co-digestion of vegetable and fruit waste with rumen digesta through anaerobic digestion process. In this research, two trials of experiment were conducted. Each trial has three different sample with different mixing ratios. Raw materials used in the experiment was rumen digesta of goat and cow, potato, capsicum, cucumbers, onions, radish, cauliflower, carrot, leafy vegetables, apple, banana, and papaya. In each sample, 1200 gram of raw materials were used. Hydraulic retention time was 30 days. Data was collected by water displacement method. The experiment found that the gas production started from 2nd or 3rd days and stops in 28th or 29th day. Highest production of biogas was 35, 33, 30, 40, 50 and 35 mL/day on the 17th, 14th, 17th, 11th, 12th and 7th day at the mixing ratios of 1:1:2, 1:2:1, 1:1.5:1.5, 1:0.5:0.5, 1:2:2 and 1.5:1.5:1 (Rumen Digesta: Vegetable Waste: Fruit Waste) respectively. The study suggests making digester for the recycling of waste to produce biogas, a renewable and environment friendly energy.

Progress in the Production of Biogas from Maize Silage after Acid-Heat Pretreatment

One of the most effective technologies involving the use of lignocellulosic biomass is the production of biofuels, including methane-rich biogas. In order to increase the amount of gas produced, it is necessary to optimize the fermentation process, for example, by substrate pretreatment. The present study aimed to analyze the coupled effects of microwave radiation and the following acids: phosphoric(V) acid (H3PO4), hydrochloric acid (HCl), and sulfuric(VI) acid (H2SO4), on the destruction of a lignocellulosic complex of maize silage biomass and its susceptibility to anaerobic degradation in the methane fermentation process. The study compared the effects of plant biomass (maize silage) disintegration using microwave and conventional heating; the criterion differentiating experimental variants was the dose of acid used, i.e., 10% H3PO4, 10% HCl, and 10% H2SO4 in doses of 0.02, 0.05, 0.10, 0.20, and 0.40 g/gTS. Microwave heating caused a higher biogas production in the case of all acids tested (HCl, H2SO4, H3PO4). The highest biogas volume, exceeding 1800 L/kgVS, was produced in the variant with HCl used at a dose of 0.4 g/gTS.

Enhancing Efficiency of Anaerobic Digestion by Optimization of Mixing Regimes Using Helical Ribbon Impeller

The appropriate mixing system and approach to effective management can provide favorable conditions for the highly sensitive microbial community, which can ensure process stability and efficiency in an anaerobic digester. In this study, the effect of mixing intensity on biogas production in a lab-scale anaerobic digester has been investigated experimentally and via modeling. Considering high mixing efficiency and unique feature of producing axial flow, helical ribbon (HR) impeller is used for mixing the slurry in this experiment under various conditions. Three parallel digesters were analyzed under identical operating conditions for comparative study and high accuracy. Effects of different mixing speeds (10, 30, and 67 rpm for 5 min h−1) on biogas production rate were determined in 5-L lab-scale digesters. The results demonstrated 15–18% higher biogas production at higher mixing speed (67 rpm) as compared to 10 rpm and 30 rpm and the results proved statistically significant (p &lt; 0.05). Biogas production at 10, 30, and 67 rpm were 45.6, 48.6, and 52.5 L, respectively. Higher VFA concentrations (7.67 g L−1) were recorded at lower mixing intensity but there was no significant difference in pH and ammonia at different speeds whereas the better mixing efficiency at higher speeds was also the main reason for increase in biogas production. Furthermore, model simulation calculations revealed the reduction of dead zones and better homogeneous mixing at higher mixing speeds. Reduction of dead zones from 18% at 10 rpm to 2% at 67 rpm was observed, which can be the major factor in significant difference in biogas production rates at various mixing intensities. Optimization of digester and impeller geometry should be a prime focus to scale-up digesters and to optimize mixing in full-scale digesters.