جستجوی مقالات مرتبط با کلیدواژه « biogas » در نشریات گروه « مکانیزاسیون کشاورزی »

The yield of methane production in the anaerobic digestion processes of municipal organic solid waste alone is low. Adding animal waste or other additives to municipal solid waste as feed for anaerobic digestion system not only increases the relative composition of methane, but also increases the rate of biogas production (Rivas-García, 2020). Carbon and nitrogen are essential elements for the growth and reproduction of aerobic microorganisms. The balanced ratio for C/N in the process is between 20-30. Simultaneous digestion is used to balance the C/N ratio (Yousefi & Bahri. 2021). This process has many advantages, including the synergistic effect of microorganisms, increasing the stability of the process, increasing the efficiency of biogas, increasing the recycling of nutrients and reducing odor.

This research was carried out with the aim of increasing the rate of biogas production, reducing the feed retention time in the digester and increasing the amount of biogas production, by investigating the effect of co-digestion of urban solid organic waste with cow excrement using anaerobic digestion method. For this purpose, 52 samples of mixed urban waste (during the year 1400, once a week and one sample each time) were prepared from the waste transfer station of Qazvin city, and in order to investigate the effect of animal manure on the studied variables, from a cattle farm located in 50 kg of fresh manure was collected in the region. After preparing the samples, a laboratory bioreactor was used to perform the experiments. The biogas production process was carried out in two stages. In the first stage, urban waste materials were used, and in the second stage, a combination of urban waste materials and animal manure was used.

The ratio of carbon to nitrogen (C/N) in the primary feed and residual materials was obtained in the first and second stages. In this way, this ratio was estimated as 19.39 and 27.64 for the primary feed and the remaining materials in the first stage and 18.60 and 28.23 respectively for the second stage.
In this study, the amount of ash decreased during the process, which indicated the participation of this substance in improving the activity of microorganisms. In both stages of the experiments, the organic matter of the primary feed decreased during the digestion process, which indicates the decomposition of these materials during the process. Also, the conversion percentage of dry material from primary feed to secondary material in stage 1 and 2 was 8.2% and 10.5%, respectively, which shows that in the second stage, in which the combination of animal manure was used, the percentage of conversion The dry matter is more and the process has progressed towards the production of biogas.
The changes in the pressure of biogas inside the tank in the experiment related to stage 1 reached its maximum value (0.19 bar/kg) within 23 days after the start of the process, and then stabilized at 0.14 bar/kg of solid material in the last seven days. Is. Since the criterion for the completion of the digestion process was pressure stabilization in seven consecutive days, therefore, after 38 days, the first stage process was completed and the biogas and residual (secondary) materials were discharged. The maximum biogas pressure in the second stage test was 0.28 bar/kg of solid material, which was achieved on the 15th day, and finally, after 26 days, the pressure reached 0.16 and stabilized at this pressure for seven days. Therefore, the digestion process in the second stage lasted for 32 days. Therefore, it can be seen that by using animal manure in the primary feed and keeping other variables constant, the retention time has decreased by 6 days compared to the first stage.
The maximum amount of biogas produced in stage 1 was equal to 6.27 liters/kg of solid matter and in stage 2 it was equal to 10.3 liters/kg of solid matter. As can be seen, by using animal manure in combination with urban organic waste, the volume of biogas production has increased under the same conditions. Taking into account the cumulative amount of biogas production, it was found that in stage 1 and 2, 140.89 and 230 liters/kg of solid biogas were produced during the digestion period, respectively. Therefore, the efficiency of biogas production has increased by 38%. Although the total amount of biogas produced in both stages of the experiments compared to the theoretical values obtained in this study (at the rate of 370 liters/kg of solid matter) and also reported by other researchers (Salehoun, et.al, 2020 and Kozminesky , 1995) has been less.

According to the results of this study, it was found that in the second stage compared to the first stage, the role of the two elements carbon and nitrogen in the biogas production process became more effective and one should expect more biogas production in the process, because the increase in the conversion of organic matter and nitrogen is The more effective decomposition of these materials by microorganisms has been achieved by adding animal manure to the primary feed.
According to the results obtained from this study, it can be concluded that in the process of biogas production, the combination of animal manure with urban organic waste, in addition to reducing the retention time, can help to increase the efficiency of biogas production, which in this study A 38% increase in biogas production was observed in the case of using a combination of animal manure with urban organic waste compared to using only urban organic waste. Although the role of other variables such as temperature, type and amount of stirring, type of initial preparation of materials in terms of size, humidity, pH, addition of yeast and bacteria, degree of impurity and toxicity of materials, ratio of carbon to nitrogen, type and size of reactor and other examined the variables.

Anaerobic digestion, in addition to producing biogas, can minimize the environmental problems of animal manure and produce high-quality fertilizer. Finding suitable places for the construction of anaerobic digestion reactors is essential for the sustainable development of these types of power plants. Locating the biogas production site is a complex process with different and sometimes contradictory criteria including environmental, economic and technical criteria from which the location-related factors play the main role. The integration of geographic information systems (GIS) with multi-criteria decision making (MCDM) provides a powerful tool that can be useful in locating biogas power plants.

In this study, spatial and non-spatial data were integrated with geographic information system in order to determine the optimal places for installing anaerobic digesters of livestock and poultry waste in the southeast of Khuzestan province. Data related to the type and number of livestock and poultry were collected separately from the Ministry of Agriculture. The location of livestock farms and chicken farms was determined using the GPS system. Livestock and poultry raised in the traditional way in the villages were not taking into account due to the problems of collecting manure and lack of economic justification. In order to determine the evaluation criteria and score them, similar studies, rules and guidelines, as well as the Delphi technique were used. 14 sub-criteria were evaluated in three main environmental, social-safety and topographical groups. Land suitability layers for the construction of anaerobic digestion reactors were prepared from the perspective of all sub-criteria in the GIS environment. In order to simplify calculations and easier weighting of criteria and sub-criteria to obtain the final result, some layers of criteria were combined. In this way, 14 layers were combined and overlapped until 7 layers of final criteria were formed. Since the spatial potential layer of biogas production is the main criterion and has the main effect on the suitability of land for the construction of a power plant, and on the other hand, it has no essential relationship with other criteria, it was valued separately. Roads and residential areas were also valued separately due to the greater importance of lower transport costs, accessibility, reducing transport time and losses, as well as environmental, health and safety impacts. The overall layer of surface water was obtained by multiplying the four layers of land suitability considering the sea, river, wetland and flood prone areas. Sensitive areas including forest, agriculture and protected areas were also considered in an exclusive layer. The other two layers were the combination layer of slope, height and fault, and the combination of railway lines and high voltage power lines. These layers were weighted using pairwise comparisons and hierarchical analysis method. The final layer of land suitability for the construction of anaerobic digesters and power plant was created by overlapping all the criteria layers based on the obtained weight.

The findings showed that anaerobic digestion of livestock and poultry wastes in the region has a potential to produce 7.25 million m3/year of biogas. Cow and chicken excrement have the largest share with 51.32 and 29.34 percent, respectively. The restriction layer showed that 73.28% of the area is unusable due to one or more restrictions. The results also showed that "regional biogas production potential" and "access to roads and energy consumption centers" are respectively the most effective factors in determining the appropriate location for the power plant. Finally, using spatial analysis in ArcGIS environment, the studied area was classified into five suitability levels: "unsuitable", "weak", "moderate", "suitable" and "very suitable". Based on this, 73.28% of the studied area was completely unsuitable and only 1.68% of the studied area was very suitable for the construction of a power plant.  But in almost all the studied areas, there was enough land with suitable or very suitable conditions to build a biogas plant.

In the studied area, lands with suitable conditions for the construction of a power plant from animal waste using anaerobic digestion technology were identified. There is a suitable distribution of "suitable" or "very suitable" levels in the study area for the construction of a biogas power plant. The findings of this study can be a guide for those in charge to make a decision for the construction of a power plant.

This paper aims to examine a combined heating, power, and hydrogen system production using biogas energy. Biogas steam and dry reforming method are designed based on equilibrium data with the EES program. The results show that biogas has two principal roles for combustion and reforming processes simultaneously. The heating energy produced from biogas causes the reforming of biogas and improves the system efficiency by 74%. The maximum exergy efficiency and hydrogen production are obtained at 58.34% and 0.11-0.83 kg/s, respectively. The results also show that the combustion chamber has the highest exergy destruction by about 51% when the amount of electric power plant is considered between 5 to 40 MW. A parametric study for optimizing hydrogen production analyzes the key parameters. The optimal scenarios are when CO2/CH4=0.50-0.66, H2O/CH4=2-3.6, and the reforming temperature is 965-1036K. The conversion of methane and carbon dioxide shows the environmental effect of decreasing greenhouse gases. At 965K or higher, methane and carbon dioxide conversion rates reach 97% and 86%, respectively. This paper aims to develop a novel methodology for identifying thermodynamic cycle conditions and reforming processes only by use of biogas as the source of energy.

Biogas is a natural and cost-effective source of energy that leaves significant impacts on the environment and industries, widely produced and utilized in many countries. This gas is generated through the anaerobic digestion of organic materials, including animal manure, food waste, and sewage. Microorganisms play a crucial role in the biogas production process by feeding on biomass. The digestion carried out by these microorganisms produces methane, constituting approximately 50-70% of biogas, which is flammable and used for cooking, cooling and heating, electricity generation, methanol and steam production, waste management, and mechanical power. Given these benefits, biogas production holds special significance, and extensive research has been conducted globally in this field, yielding valuable results. In the present study, we aim to investigate and evaluate the influence of lentil skin as a biomass on the quantity and constituents of produced biogas.

This research was conducted in the Biosystems Mechanics Workshop of the Faculty of Agriculture, Ilam University. The objective of this study was to investigate the effect of lentil skin on biogas production and analyze its constituent components. The workflow typically comprised four stages. In the first stage, fresh lentil skins were broken down into smaller pieces and stored in a suitable environment to be used as digester feedstock for the experiment. Shredding organic waste aids in the digestion process. The second stage involved providing optimal conditions for microbes, which require warmth. Accordingly, the temperature was maintained at an average of 28-30 degrees Celsius during the experiment.
The third stage involved the actual digestion process, where anaerobic digestion took place in large tanks, resulting in real biogas production. For this purpose, materials were combined in predetermined proportions (1:1) and loaded into the digesters. In each stage, 5 kilograms of lentil skin were combined with 5 kilograms of water and added to the digester. The experiment was conducted in three repetitions, employing fixed digesters, digesters with agitation every three days, and digesters with daily agitation as influencing factors. The quantity of biogas production and its components were examined over a 30-day period. Gas sampling occurred every 10 days, while pH and gas pressure were measured every 72 hours. In the final stage, the gas underwent purification by removing impurities and carbon dioxide. The amount of gases produced from lentil skin was measured using a chromatograph with a TCD detector. This instrument employs chromatography-based separation. It's worth noting that 9 gas capsules specifically designed for automobiles were used to construct the digesters. The construction stages of the digesters included cleaning, coloring, and installing connections. Moreover, to create uniform temperature and concentration conditions inside the tank, inlet and outlet connections were carefully designed and installed. A safety valve was also installed to ensure the safety of the digesters.

The obtained results, including loading conditions, pH levels, and internal pressure within the digester during the experiment, and the quantity and components of biogas, were examined across all samples. Statistical methods, including Analysis of Variance (ANOVA) and Duncan's mean comparison test, were employed for data analysis. The results indicated that digester agitation directly influences the pH levels, with the highest pH observed in digesters with daily agitation, displaying the most significant fluctuations. Furthermore, digester agitation has a direct impact on the biogas production levels, enhancing structural effects within the digester. However, frequent agitation repetition has a negligible effect on the amount of biogas produced. The average methane production rates in this process were 34.06% mol for digesters with daily agitation, 23.09% mol for digesters with agitation every three days, and 17.32% mol for fixed digesters.

  Currently, a significant portion of the world's energy demand is met through fossil fuels, the combustion of which releases carbon dioxide and various pollutants, including sulfur and nitrogen oxides, which are highly harmful. Consequently, in recent years, there has been a growing inclination towards utilizing various renewable energy sources. One crucial energy source that also provides a solution for waste reduction is biogas. Given the increasing importance of sustainable energy development and the need for waste management, anaerobic digestion technology and biogas production have rapidly grown. Therefore, the findings of this research underscore the importance of exploring innovative methods and utilizing diverse biological resources in managing and optimizing the biogas production process.

The need to develop alternative energy sources especially renewable energy has become increasingly apparent with the incident of fuel shortages and escalating energy prices in recent years. With the advent of renewable energy, various studies have been conducted to investigate the potential of biogas production from agricultural waste. Considering the importance of retention time and methane production potential for designing industrial digesters, many studies on potential analysis and modeling of the digestion process of different products have been carried out by various researchers. These studies are valuable for the design and implementation of anaerobic digesters. Apple is one of the most popular fruits in many parts of the world and is widely cultivated in many temperate regions of the world. Considering the large volume of apple waste in Iran, this study was designed based on potential evaluation and modeling of biogas production from apple pulp.

In order to measure the potential of biogas production from apple pomace, a number of lab-scale digesters with a capacity of 600 ml and a working capacity of 400-500 ml were made. pH and C/N ratio were modified by adding NaOH and urea solution, respectively. Three different temperature treatments including psychrophilic (ambient temperature), mesophilic (37ºC), and thermophilic (47ºC) were applied to the substrate. Used pomace samples were collected from the output of an apple juice factory in southern Isfahan province, Iran. Anaerobic Biodegradability (ABD) was obtained by dividing the experimental methane production potential (BMP) obtained from the experimental results on the theoretical methane production potential. Three most common kinetic models of Gompertz, Logistic, and Richards were used to predict and stimulate the cumulative methane production of treatments.

Under ambient temperature, the digestive process took a longer time, and the time of maximum dilly biogas production was considerably more than the other two treatments. Statistically, production time and peak time of this treatment was higher than the other two treatments at 1% significance level. Maximum daily biogas production in the ambient treatment was observed on day 37th with a volume of 6.99 g-VS-1 ml, while maximum daily biogas production in the treatments of 37 °C and 47 °C were observed on days 22th (20.16 ml g-VS-1) and 20th (25.57 ml g-VS-1), respectively. In all three treatments, daily biogas production increased sharply in the first incubation days and after that reduced and then production increased again. In mesophilic and thermophilic treatments, the production of biogas modestly stopped after 35 days, but under the ambient temperature, the process of production continued after 55 days. The methane concentration of biogas in the psychrophilic treatment was significantly lower than the other two treatments at 1% level. Two treatments of 37°C and 45°C have a significant difference in methane yield at 1% level. Nevertheless, the production of biogas in two treatments was not statistically different. In all three treatments, the lowest pH was recorded after 7 days of production and the highest pH was recorded on days 34-40. All three kinetic equations were able to simulate the methane production process with high precision, although the results of the Logistic model provided higher accuracy. In the treatment 47 °C, the efficiency of the studied equations was higher than other treatments and models were able to predict the production process with higher accuracy. Results of the experiment show the high biochemical methane production potential of apple pomace (473.17 ml g-VS-1), which under laboratory condition of this study up to 63.9% of this potential (302.70 ml g-VS-1) was obtained. 

This study results are valuable for the design and implementation of industrial digesters. The results indicate the apple pomace has a high potential for the production of methane and its biodegradability is high. Apart from pH that is acidic, other apple pulp factors are appropriate for the activity of methanogenic bacteria. In terms of nutrients, apple pomace is also a good environment for the growth of anaerobic bacteria.

Anaerobic digestion in order to produce biogas is a proven method for producing renewable energy from municipal solid waste. In this research, organic fractions of municipal solid waste compounds were determined in Karaj metropolitan area. The organic waste components were monitored in five categories of fruits, fat and protein, starches, vegetables, and cellulose wastes in the winter and summer seasons. Then, a sample representing the average amount of waste components was synthesized and biomethane yield, digestibility indicators and kinetic modeling parameters of biogas production were investigated in batch tests at mesophilic temperature at two concentrations of 8 and 15 TS%. The most part in the organic fraction was fruit and vegetable waste with a total of 62.9% and 70.6% in winter and summer, respectively. The biomethane yield and methane content at 8% and 15% TS had significant difference with 385.2 and 289.2 L/kg VS and of 66.8 and 58.8%, respectively, but there was no significant difference for VS removal with 87.99% and 84.72%. As a result, for source separated MSW, anaerobic digestion at the lower TSs has better results than dry. Continuous anaerobic digestion at 30 day hydraulic retention time is more effective for specific biomethane production and high volumetric biogas production under stable conditions.

Introduction:

 The limitation of fossil fuels and environmental pollution by using them have encouraged researchers toward renewable fuels.  The most important renewable fuels are bioethanol, biodiesel and biogas. Biogas is a gas that is produced from biodegradable fermentation, agricultural products and wastes, animal waste and urban waste by anaerobic digestion.  One of the products that has a significant amount of waste is sugar cane. This plant is widely cultivated in Khuzestan Province and annually produces a lot of waste which is currently not useful. One of the most important wastes is bagasse. Bagasse is the solid residues after crushing sugar cane and extracting it. Bagasse is composed of cellulose (45%), humiculus (27%), lignin (21%), extract (5%) and a small amount of inorganic salts (2%). A lot of bagasse is produced in sugar cane production process (about 240 kg with a moisture content of 50% per ton of sugar cane). Every year, a lot of bagasse is wasted. One of the most useful ways is to convert it into biogas and provide the percentage of the required thermal and electrical energy of the plant. Therefore, in this study, the effect of temperature and percentage of cow manure as an additive on biogas production from bagasse sugar cane was investigated.

Materials and Methods:

 The used bagasse in this research was provided from Farabi industry and Cultivation, located 48 km from Ahwaz, and a cow manure was provided from a livestock farm in Hamidieh, Ahwaz. In order to increasing the production efficiency of biogas, sugar cane bagasse was milled. Batch reactors of 4 liters was used to produce biogas from sugar cane bagasse.  To control and maintain the working temperature, the reactors were placed in a water bath and the temperature of the bath was kept constant by using the thermal element and the thermostat. Cow manure was used to provide source of microorganisms. Cow manure with 5, 10, 15 and 20% weight percentages (B5, B10, B15 and B20) was blended with bagasse (numeric index of B indicates the percentage of cow manure in the blends). Sodium bicarbonate was used to control the pH of the reactors. Stirring was carried out manually in order to homogenize the materials and prevent the formation of hard layer at the top of the reactors. The amount of produced biogas was daily measured by water displacement method. Another measured parameter was the total Solid Index (TS), which represents the percentage of organic and inorganic matter for materials of the reactors. The experiments were carried out by using eight reactors for 30 days and the results were analyzed by completely randomized factorial design.

Results and Discussion:

 The results of variance analysis of biogas production in terms of bagasse to cow manure ratio and temperature changes showed that they had a significant effect at 1% level on biogas production. Considering the interaction effects of temperature and bagasse to cow manure ratios have a significant effect on the produced biogas at a 1% level. The results showed that with increasing in the percentage of cow manure in the materials, the amount of biogas production increased at both temperatures, so that by increasing the ratio of cow manure in the blends from 5 to 20% at 35 and 45 ° C, the produced biogas increased by 27.78% and 81.83%, respectively. By increasing the percentage of cow manure in the blends, the number of microorganisms in the digestion increased, and as a result of their activity, the amount of produced biogas increased. It was also observed that with increasing the temperature of digestion from 35 ° C to 45 ° C, the biogas production for B5, B10, B15 and B20 blends increased by 19.82%, 22.5%, 15.85% and 80.8%, respectively. The highest amount of cumulative production of biogas was obtained 0.3 m3.kg.VS-1 for 45 ° C and 20% cow manure to bagasse ratio.

Conclusion:

 In this research, the effect of cow manure in blend of sugar cane bagasse and temperature on produced biogas was investigated. The experiments were carried out at two temperatures of 35 and 45 ° C, and four blends with different weight percentages from cow manure to bagasse (5, 10, 15 and 20 percent). The results showed that with increasing the percentage of cow manure in blends, the amount of biogas production increased. Also, with increasing temperatures from 35 ° C to 45 ° C, the production of biogas in all blends increased.

Anaerobic digestion has progressed rapidly since the late 1960s. With the progress of the anaerobic fermentation process in the world, anaerobic reactors have been developed to digest different types of organic wastes in each country. So various types of reactors have been built, and that they have been in different shapes, dimensions, and operating conditions. One of these reactors is the static granular bed reactor (SGBR). SGBR with its granular bed digests a substrate in less hydraulic retention time (HRT). SGBR is a downstream reactor that consists of active anaerobic granules. The biomass contacts the granular surfaces and does not require the use of mixers, gas, solid, and a separator. The reactor startup is very short since there is no need for some operations, such as extra time to grow microorganisms in the granule. One of the most important residues in the alcohol production plant from molasses is vinesse which has become a major problem in this industry. The conversion of vinasse to biogas and using it to supply the energy of the industry is one of the basic ways to solve this problem. Several studies have been conducted in this field by using various reactors, but there is no research about SGBR. In this study, an SGBR producing biogas from vinasse has been designed and constructed. Also, the performance of the reactor was investigated at three HRTs (2, 3, and 4 days) and the thermophile temperature of 55 °C. The best diameter to height ratio (reactor volume) in the SGBR is 1:7. Accordingly, the shape of the reactor is a pipe. Based on the volume of the reactor and the maximum pressure inside it, a 4-inch polyethylene tube with a height of 1 meter was selected to carry out the testes. According to the thermophile temperature (55 °C) and the accuracy of the element (0.9 °C), the maximum temperature of the reactor is 329 K. Therefore, the minimum power for obtaining this temperature is 405.316 watts. The water displacement method was used to measure the amount of biogas. An iron sponge was used for removing hydrogen sulfide gas from biogas. Sodium hydroxide solution was used to remove carbon dioxide from biogas. The reactors were loaded daily with organic matter (86002, 28667, and 21500 mgCOD/L.d) for different HRTs (2, 3, and 4 days). For three HRTs, the amount of methane production was high during the first day which is due to the thermal shock caused by the microorganisms in the granule. Methane production in HRT of 2 days had fewer variations than HRT of 3 and 4 days, and after 13 days, it reached a nearly constant value of 4600 ml/day. For HRT of 3 days, the daily rate of methane production reached a constant value of 4800 ml/day after 12 days and for HRT of 4 days, it reached 4,900 ml/day after 10 days. For HRTs of 2 and 3 days, the rate of methane production per unit of volatile solids had less variation and remained constant approximately after 7 days. The average methane production per unit of volatile solids at HRT of 4 is days higher than the other HRTs. The average methane production for HRTs of 2, 3, and 4 was 379, 380, and 433 CH4 (L)/VS (kg), respectively. The maximum value of methane production was 582 m3/kgCOD, which was obtained at HRT of 2 days. In this study, 31 liters of methane were produced per one liter of vinasse at HRT of 4 days, which was more than other studies. In this study, the required heat power and pressure inside the SGBR laboratory have been calculated. The minimum required heat is 261 watts. Also, this reactor should be able to bear at least 4.34 bar for biogas production. The average amount of methane production per unit of volatile solids was 379, 380, and 433 CH4 (L)/VS (kg) at HRTs of 2, 3, and 4 days, respectively. The maximum amount of produced methane was 582 m3/kgCOD, which was achieved at HRT of 2 days, and the maximum percentage of COD reduction was 39%, which was achieved at HRT of 4 days. In general, the results indicated that SGBR produced higher biogas from vinasse than other reactors, but it is not suitable for reducing pollutions.

The manure management cycle from collection to application in dairy farming was evaluated from environmental and economic aspects for different scenarios including biogas production. For this purpose, manure characteristic is determined regarding the real feed ration composition. Environmental impacts and economic profitability of each scenario was calculated using standards and COMFAR program, respectively. The results showed although biogas production is costly but it is profitable with initial investment of 125 billion Rials (2,777,778 €) and a payback period of about 3 to 4 years. The internal rate of return was calculated as 24% considering a discount rate of 20%. The internal rate of return shows that although this investment is risky, the amount of income is acceptable. Scenario 4 including digestate processing using a mechanical separator followed by composting has the maximum avoided methane emission (-261 kg CO2eq m-3). Emissions mitigation was calculated to be 36% and 17% in scenario 2 and 4, respectively. Solid/liquid separation and sand separation have less impact on emission reduction withy different economic advantages. Regarding the results of this study, a large amount of greenhouse gases and emissions to water and soil has mitigated thank to biogas production

IntroductionAnaerobic digestion (AD) is a process of breaking down organic matter, such as manure, in the absence of oxygen by concerted action of various groups of anaerobic bacteria. The AD process generates biogas, an important renewable energy source that is composed mostly of methane (CH4), and carbon dioxide (CO2) which can be used as an energy source. Biogas originates from biogenic material and is therefore a type of biofuel. Enhancement of biogas production from cattle dung or animal wastes by co-digesting with crop residues like sugarcane stalk, maize stalks, rice straw, cotton stalks, wheat straw, water hyacinth, onion waste and oil palm fronds as well as with liquid waste effluent such as palm oil mill effluent. Nevertheless, the search for cost effective and environmentally friendly methods of enhancing biogas generation (i.e. biogas yield) still needs to be further investigated. Many workers have studied the reaction kinetics of biogas production and developed kinetic models for the anaerobic digestion process. Objective of this study is to investigate the effect of biological additive using of organic loading rate (OLR) in biogas production from cow dung. In addition, cumulative biogas production was simulated using logistic growth model, and modified Gompertz models, respectively.
Materials and MethodsThe study was performed in 2015-2016 at the agricultural research center of Ardabil Province, Moghan (39.39 °N, 48.88° E). Fresh cow manure used for this research was collected from the research farm of the Institute for Animal Breeding and Animal Husbandry, Moghan. It was kept in 30 l containers at ambient temperature until fed to the reactors. In this study, experiments were conducted to investigate the biogas production from anaerobic digestion of cow manure (CM) with effect of organic loading rate (OLR) at mesophilic temperature (35°C±2) in a long time experiment with completely stirred tank reactor (CSTR) under semi continuously feeding. The complete-mix, pilot-scale digester with working volume of 180 l operated at different organic feeding rates of 2 and 3 kg VS. (m-3.d-1). the biogas produced was measured daily by water displacement method and its composition was measured by gas chromatograph. Total solids (TS), volatile solids (VS), pH and etc. were determined according to the APHA Standard Methods. The biogas production kinetics for the description and evaluation of methanogens was carried out by fitting the experimental data of biogas production to various kinetic equations. In addition, Specific cumulative biogas production was simulated using logistic kinetic model exponential Rise to Maximum and modified Gompertz kinetic model.
Results and DiscussionThe experimental protocol was defined to examine the effect of the change in the organic loading rate on the efficiency of biogas production and to report on its steady-state performance. The biogas produced had methane composition of 58- 62% and biogas production efficiency 0.204 and 0.242 m3 biogas (kg VS input) for 2 and 3 kg VS.(m-3.d-1), respectively. The reactor showed stable performance with VS reduction of around 64 and 53% during loading rate of 2 and 3 kg VS.(m-3.d-1), respectively. Other studies showed similar results. Modified Gompertz and logistic plot equation was employed to model the biogas production at different organic feeding rates. The equation gave a good approximation of the biogas yield potential (P) and correlation coefficient (R2) over 0.99.
ConclusionsThe performance of anaerobic digestion of cow dung for biogas production using a completely stirred tank reactor was successfully examined with two different organic loading rate (OLR) under semi continuously feeding regime in mesophilic temperature range at (35°C±2). The methane content of 58- 62% and actual biogas yield of 0.204 and 0.242 m3 biogas.(kg VS input-1) were observed for 2 and 3 kg VS. (m-3.d-1), respectively. The modeling results suggested Modified Gompertz plot and Logistic growth plot both had higher correlation for simulating cumulative biogas production. Therefore, arising from the increasing environmental concern and prevailing wastes management crises, optimizing biogas production by 2 kg VS. (m-3.d-1) represents a viable and sustainable energy option.

In recent years the growing trend of energy consumption has created energy crisis in the world. In our country the use of renewable energy can have a special place due to the growing need for energy and diminishing fossil fuel resources, protect the environment, reduce air pollution, restrictions on electricity and the fuel supply for remote villages. Due to the significant amount of the annual production of biomass sources in Iran the importance of using these resources for biogas production is more specific. The production of biogas using anaerobic digestion technology and its application in CHP plants in Iran can supply part of the required energy and achieve sustainable development. In this study has been done economic calculations for biogas plant as a case study for combined heat and power production. The results show that during the project life (20 years),the Internal Rate of Return (IRR) is 19%, the net present value (NPV) is equal to 180,587,908 and the ratio of benefits to costs is equal to 1/032. Financial evaluation of energy production in this system shows it is economical to run.

Seventy million tons of agricultural crops are produced from 18 million hectares of agricultural lands in Iran every year. Since 80% of the crops (wt. basis) ends up as residues, therefore, about 50 million tons of crop residues are generated annually the majority of which is burnt on field leading to vast emissions of greenhouse gases (GHG) due to the incomplete combustion process. These residues could potentially be transformed into heat energy directly by adopting a burning process or indirectly by first transforming them into secondary fuel as hydrogen, bio-methane, methanol or ethanol.
The present study was conducted using, wheat and rapeseed straws dried at ambient temperature co-digested with fresh cow dung while the total solid content and detention time were kept constant. To conduct the Anaerobic Digestion (AD) experiments, cylinder reactors (13 L) were constructed and placed in a water bath equipped with a heater and sensor to maintain the temperature at 35±2 oC. The biogas produced in the digester was investigated by measuring the displacement of the water in a measuring tube connected to the reactor. Gas samples were obtained from the sampling port and were analyzed gas chromatograph. The temperature for detector, injector and oven were 170, 110 and 50 oC respectively. Before the test, the first CH4 and CO2 net gases, peaks corresponding percentage was determined with respect to the retention time of the area. Then sample was compared with standard gas and samples gas percentage was determined. The residues were mechanically pretreated using a mill in order to increase the availability of the biomass to enzymes. After the pre-treatment, the material ( A decrease in the process pH was observed in the first few days of the digestion and this is due to high volatile fatty acid (VFA) formation. These results were compatible with sanaee moghadam et al. (2013). The results obtained showed that, the highest rate of VS reduction belonged to rapeseed residues at 52.22%.The lowest rate of VS reduction attributed to wheat residues at 36.79%. The rapeseed residues with 311.45 Lit.kg-1 VS had the highest accumulated methane followed by wheat straw with 167.69.28 L.Kg-1 VS in probability level of 5%. The average percentages of methane production for rapeseed straw and wheat straw during the 140 days experiment under mesophilic condition were 66% and 55%, respectively. Production of methane had delay and started after 46th day. Much reason may be possible. Inoculums used in this study were only fresh cattle dung. The mixture of fresh cattle dung and effluent of anaerobic digester or fresh rumen fluid may be decrease retention time and increase biogas production. According results of Budiyono the rumen fluid inoculated to biodigester significantly affected the biogas production. Rumen fluid inoculums caused biogas production rate and efficiency increase more than two times in compare to manure substrate without rumen fluid inoculums (Budyono et al., 2010). The other reason was pretreatment. This study applied just mechanical pretreatment. According to Cecilia studies, different pretreatment combined with mechanical pretreatment decrease retention time and increase biogas production efficiency (Cecilia et al, 2013). However, Zhang et al. claimed that it is hard to say which method is the best because each has its own strong point and weak point. Yet, until now, none of the pretreatment technologies has found a real breakthrough.
According to this study, rapeseed residues had the highest level of methane production in comparison with wheat residues. The rapeseed residues combine with cattle dung had suitable potential to methane production. The 140 days, Biomaethane Potential (BMP) of rapeseed residues combine with cattle manure had 311. 45 Lit/kg vs. add. Moreover, it had high percentage of VS content reduction (52.22%). The high retention time was observed (140 day). One reason was lack of suitable inoculums and pretreatment. Furthermore, the lingo-cellulose nature of the crop residues, lower will be the biodegrade ability. Furthermore, the anaerobic co-digestion of rapeseed straw with cattle manure is feasible for production of methane.

Nowadays, one of the main applications and management challenges for various activities is the study of the energy efficiency. In this study, effects of temperature and stirrer on energy indices and biogas production from animal manure were determined. The biogas was generated by using an anaerobic digestion with volume of 925 (lit) in industrial scale of manure in different temperature and stirrer conditions. Experiments were performed in 8 treatment groups containing (20 to 25°C), (26 to 30° C), (31 to 35° C) and (36 to 40° C) temperature, with and without stirrer, through a completely random factorial design test. Maximum amount of biogas produced with temperature (36 to 40° C), when the apparatus reaches certain stability with stirrer and also least amount of biogas which it related to temperature (20 to 25° C) without stirrer, was 61 and 8.7 (lit/ kg) fresh manure, respectively. The amount of energy ratio for the treatment which has maximum biogas produced was equal to 0.8. Maximum amount of energy ratio (with temperature (31 to 35° C) and stirrer), and least amount of energy ratio (with temperature (20 to 25° C) without stirrer) was 1.13 and 0.58, respectively.

Agricultural residues have high potential to produce biogas، but they contain lignocellulosic materials which are not easily degradable، so the pretreatment is required. Chemical pretreatment increases the rate of degradation and efficiency of biogas production. This study has been investigated the effect of 4% -urea، 5%-ammonia and 8%-sodium hydroxide on degradation of rice straw and production of biogas combined with sheep manure with three Carbon to Nitrogen ratios (15، 20 and 29) in anaerobic digester at temperature of 40±2 °C. The process was performed in a factorial design with two factors in three replications. Results showed that the cumulative production of biogas and the maximum percent of Methane are 594 (ml/VSadd) (that is 133. 33% more than the control) and 71% that they achieved by 8%-NaOH-pretreated straw combined with manure in Carbon to Nitrogen ratio of 29. The results show the positive effect of chemical pretreatment of rice straw on efficiency of biogas production combined with sheep manure.