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Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study

  • Zainab B. Mohamed , Mohammed Y. Fattah EMAIL logo , Esraa Q. Shehab and Ali G. Shamkhy
Published/Copyright: October 29, 2024
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Open Engineering
From the journal Open Engineering Volume 14 Issue 1

Abstract

Anaerobic digestion (AD) of feedstocks yields biogas, a potentially useful new energy source. This study looked into the anaerobic co-digestion of cow dung and organic garbage to produce biogas. An anaerobic biodigester, with a volume of 20 L, was used to digest organic waste (OW) and to trace the changes that occur during the AD process. It was equipped with tools that ensure complete control of the conditions affecting anaerobic biological reactions such as temperature, pH function, and mixing speed. Therefore, an anaerobic biodigester was designed to contain such biological transformations and to improve the biogas production process from OW. Based on the present investigation, the AD of OW was improved by integrating the substrate with sewage sludge or cow manure (CM) during the digestion process to provide the basic microorganisms to complete the digestion process. Feeding into the digester was a blend of 100 kg of cow dung (CM) and OW per day, diluted 1:1 with water. A gasbag was used to capture the methane that resulted. Biogas production began on the seventh day after the substrate was fed into the digester. A performance test was carried out on the produced biogas to determine its composition. For OW–CM, the generated biogas’s methane (CH4) concentration was determined to be 60%, but the rates of decline for TS and VS were 57 and 50.6%, respectively. Anaerobic biodegradation of OW–CM experiments was observed at 37°C, a mesophilic temperature. For OW–CM, the pH value was 6.7. After being adjusted to standard circumstances, the cumulative volume of methane produced which had been recorded as 4,914 mL became 3964.5 mL.

Keywords: solid waste biogas; anaerobic co-digestion; municipal solid waste; methane production; biogas

1 Introduction

An exciting new source of energy is biogas, which is created when feedstocks undergo anaerobic digestion (AD). It is mostly composed of CO2 and CH4 (40–60% and 35–55%), with minor amounts of moisture, various pollutants, and hydrogen sulfide (H2S). The four phases of AD are methanogenesis, acetogenesis, acidogenesis, and hydrolysis. Maintaining the ideal conditions for the AD process is essential to increasing biogas generation since the methanogenesis stage, which is carried out by a specific microbial type of archaea, is extremely sensitive to changes in temperature, pH, and carbon-to-nitrogen (C/N) ratio [1]. Insufficient use is being made of the co-digestion of diverse biomaterials with manures and other biowastes in current biogas generation systems.

One potential renewable energy source that might lessen the consequences of global warming by reducing dependency on fossil fuels is municipal solid waste (MSW). Two of the most important concerns that emerging nations need to solve are waste management and energy access [2]. The growing world population has led to a demand for energy that is greater than the available supply. Moreover, it is possible that traditional energy sources like coal, oil, and natural gas are exhausting their reserves and releasing greenhouse gases that worsen climate change [3]. Because of this, research priorities have shifted in many countries to finding and implementing environmentally friendly substitutes for these harmful and limited conventional energy sources, such renewable resources [4]. Biogas is a clean, renewable energy source that may be produced by the AD of waste [5]. It has to do with producing renewable energy, cutting down on pollution in the environment, and the current global emphasis on addressing climate change. An eco-friendly and promising method for digesting the organic portion of MSW is AD. Biogas, which may be used to produce heat or electricity, is another source of energy that is recovered. In terms of producing bioenergy and managing garbage, it is crucial [6,7,8]. Microbes oxidize and reduce biodegradables to their highest oxidized state (carbon dioxide [CO2]) and reduced form methane (CH4) in the absence of oxygen [9,10]. AD employs a range of waste products, including agricultural waste from cultivating crops and rearing animals, wastewater from manufacturing operations, industrial waste, and organic MSW. Recently, the technique of converting animal waste into electricity has gained popularity as a means of reducing uncontrolled emissions of carbon dioxide, methane, and nitrous oxide. Cattle dung is a great substrate for AD because it is packed with nutrients that are essential for the development of anaerobic bacteria. AD is a biological process that produces biogas, which is a combination of methane, carbon dioxide, and traces of other chemicals. To generate biogas, the substrate of the bio-digester through four processes: hydrolysis, acidogenesis, acetogenesis, and methanogenesis [11]. Methane (55–70%) and carbon dioxide (30–45%) are the main anaerobic breakdown products of animal manure, sewage sludge, and agro-industrial bio-waste. Furthermore, trace amounts of siloxane molecules, nitrogen (N2), H2S, and ammonia (NH3) are found [12,13].

The potential for producing biogas from organic MSW produced in an urban context in a tropical climate was assessed by Getahun et al. [14]. Fruit waste, food waste (FW), yard garbage, paper waste, and mixed waste were the five types of waste that were taken into consideration. Using a laboratory-scale batch digester, these fractions were evaluated for their biogas generation efficiency over the course of 8 weeks at a temperature between 15 and 30°C. The amount of biogas produced by fruit waste, food trash, yard waste, paper waste, and mixed waste per kilogram of volatile solids (VS) was reported to be 0.15, 0.17, 0.10, 0.08, and 0.15 m3 during this period. The daily production of biogas and the corresponding caloric value of the feedstocks varied from 1.25  ×  10−3 m3 (17 kW h) for paper trash to 15  ×  10−3 m3 (170 kW h) for mixed waste. The potential for producing methane from mixed organic MSW had a caloric value that was many times greater than the region’s overall energy needs.

With the use of an internal mixer for compounding and a hot press molding machine for film production, biodegradable plastic films were created from blends of PVA, starch, and lignin with glycerol acting as a plasticizer. Ratnawati et al. [15] adjusted the lignin percentage (2–10%), glycerol (25–65%), and mixing temperature (190–230°C) in accordance with the three Box–Behnken design levels. Glycerol was shown to have the most significant impact on the mechanical properties of the film based on the analysis of variance evaluation. Next, three models were created to estimate the tensile strength, tear resistance, and elongation at break. The formulas provided the ideal temperature of 197.6°C, lignin content of 10%, and glycerol content of 45.1% for film preparation. The optimally made biodegradable plastic had an elongation at break of 139.00 ± 8.59%, a tensile strength of 8.46 ± 1.08 MPa, and a tear resistance of 69.50 ± 2.50 N/mm.

The anaerobic assimilation of strong blows has drawn more interest given current ecological issues, particularly those worried about an Earth-wide temperature boost. Hence, it fundamentally expanded the lab-scale research around here. This review article summarizes AD and its benefits and describes the biogas produced from this process and its composition, benefits, and characteristics [16].

The importance of the present study comes from that little research was done on the energy potential of mixing cow dung (CM) with organic waste (OW); further research is needed to deal with the massive volume of OW in the substrate for biogas generation. The fact that biogas is used in Iraqi colleges and organizations is evidence of its global significance. The main aim of the research is to estimate the amount of MSW generated and its components, treat the OW present in it, and use an environmentally friendly approach to biogas production by digesting this waste with substrates [sewage sludge and cow manure (CM)] to improve process conditions. A 20-L biogas digestion (bioreactor) was used for the research project in an effort to transform OW into a sustainable energy source. Given this significance, the research examines how temperature, pH, and substrate mixing affect the inoculum of cow dung (CM) and OW to promote methanogenic digestion which improves the process.

2 Stratified sampling

Samples of municipal trash were gathered for this study from the Civil Engineering Department. To evaluate the amount of waste created rate and physical composition data, sample research was conducted. The rate of solid waste generation was determined using the weight of the rubbish each day. The trash was put in plastic bags to be weighed after it was picked up by staff members each day. The entire process took fifteen working days. The study’s conclusions showed that the daily generation rate is 0.183 kg per person, the largest daily amount of MSW generated is 165 kg, and the lowest daily amount of solid waste generated is 141 kg.

3 Feedstock preparation and characterization

3.1 OW

Seven distinct forms of organic solid waste (OSW) were gathered from the Civil Engineering Department and the cafeteria of Technology University (Iraq). Among them were potatoes, cucumbers, oranges, bread, shawarma, tomatoes, and yard waste. To support the hydrolysis process and increase biogas output when it is time to start gas production, the feedstock was prepared. An electrical blender was used to continuously mix the material for size reduction to improve the surface area to volume ratio. Before being fed into the digester, the substrate underwent physical processing to reduce the size of the raw material particles, which increases bacterial activity and increases the volume of biogas produced [17,18]. Anaerobic codigestion representative samples of feedstock were obtained using quartering and sampling procedures, which were followed by the protocols examined. High thermic content and essential nutrients for living things are present in this waste, which enhances the efficiency of methane generation. OSW is perfect for AD because of its high-water content and low lignin concentration.

3.2 CM

Fresh cow dung, or manure, was collected from a nearby farm in Baghdad, Iraq (33°48′16.8″N, 44°45′77.4″E), which is known to have a high concentration of methanogenic anaerobic bacteria. Consequently, the decision was made to inoculate the anaerobic digester. To test the advantages of anaerobic co-digestion at the biodigester, it is fed OSW.

3.3 Construction of bio-digester

According to Jagani et al. [19], the pilot bio-digester used in this work design is based on the creation of systems employing contemporary technology and simple, dependable application methodologies, as well as the use of materials resistant to AD processes. The pilot bio-digester was built at the University of Technology’s civil engineering department with a capacity of 20 L and dimensions of 400.0 mm high, 250.0 mm in diameter, and a high/diameter ratio of 1.6 for the study. The digester was also composed of stainless steel with a thickness of 5 mm. The idea was to generate biogas as well as conduct research. In the inflow tank, a certain amount of feedstock is blended with water to form a slurry, which is subsequently discharged into the digesting compartment. The digested slurry, or digestate, is poured into the output chamber via a manhole and collected for use as organic fertilizer. A flexible rubber tube transports the biogas from the dome to the point of usage. The outflow chamber of the biodigester serves as the slurry’s compensation tank. Mechanical agitation systems with a long axis and vertical bioreactor entrance, heating systems with an element outside the bioreactor, biogas collection and storage, and control and monitoring systems are all included in the bio-digester. The designed bio-digester and its components are depicted in Figure 1.

Figure 1 An experimental model of a biodigester. (a) Detailed biodigester (1) storage of biogas. Two electric motors, a gearbox, a valve, a feeding inlet, an addition port, a biodigester body, a peephole, a thermocouple, a temperature gauge, a drainage valve, a thermocouple, and a stand are all included. (b) Thermocouple and heater. (c) Temperature control thyristor.
Figure 1

An experimental model of a biodigester. (a) Detailed biodigester (1) storage of biogas. Two electric motors, a gearbox, a valve, a feeding inlet, an addition port, a biodigester body, a peephole, a thermocouple, a temperature gauge, a drainage valve, a thermocouple, and a stand are all included. (b) Thermocouple and heater. (c) Temperature control thyristor.

Jagani et al. [19] recommended the characteristics design of the impeller and control units that were connected to the biodigester as summarized in Tables 1 and 2.

Table 1

Characteristics of design of the impeller [19]

Agitator Turbine
Distance between the impeller and the bottom of the digester, h (cm) 8
Space between turbine impellers, L (cm) 16
Diameter of impeller, d (cm) 12.5
Diameter of impeller, d/diameter of digester, D 0.5
Table 2

Main units used in the bio-digester

No. Part Description
1 Motor Placed at the center of upper cover of digester above gear-box, used for operating the turbine paddles in agitation process
2 Gear box used to control motor work, placed in the center of the upper lid to control the desired mixing speed to achieve substrate homogeneity
3 Heater heater need for maintaining the variation in working temperature placed at the bottom plate, which is critical for microorganism growth
4 pH meter sed for measuring the daily variation in pH values during digestion process. (Model: WTW, Inolab 720, Germany)
5 Glass bottles 1,000 mm in volume fill it with pure water and added the NaOH to it
6 Beakers With 1,000 mm volume fill it with pure water, the cylinder glass placed inside it
7 Cylinder glass 1,000 mm volume fills it by water put in beaker used for measure
8 Biogas storage Used To collect the biogas that has been produced, for gas analysis
9 Rubber tube Used for transmission of gas from outlet port of digester to beaker for measuring the volume of gas
10 Valves used to regulate gas in tubes, both closed and open

3.4 Analytical methods

The materials were assessed using approved protocols. Measurements included moisture content, gas chromatography (GC), total solids (TSs), carbon-to-nitrogen ratio, chemical oxygen demand (COD), and VS. The traditional technique of air oven-drying in a laboratory oven was used to produce the TSs [20]. Similarly, using a muffle furnace and the gravimetric valorization method, VSs were created gravimetrically. The ASTM [21] Standard Test Method for Total Kjeldahl Nitrogen was utilized to carry out an analytical determination of the C/N ratio. Three steps made up the experiment: digestion, distillation, and titration.

GC (HP 5890II Series USA) in conjunction with a thermal conductivity detector was used to examine the samples and estimate the percentage composition of elements.

3.5 Methodology

Laboratory-scale experiments were conducted to evaluate biogas generation in a batch system. Anaerobic co-digestion experiments were conducted in a reactor with a 15 L operating capacity. Different FWs and specific selected MSWs were co-digested in different reactors. On the co-digested feedstock with the highest yield, further factors were looked at. We looked at the impacts of pH, temperature, and substrate mixing. This study typically examined the following parameters: a pH of 4.2, a temperature range of 35–40°C, with an increase of 5°C, and a ratio of 1:1 (OW:CM). This value was increased to 5.1 by adding 42 mL of NaOH solution, which is equivalent to Korres and Nizami [22]. Measurements were also taken of the VSs and moisture content. The amounts of VSs and moisture were also measured in the second run. In the second run, 7.8 kg of cow dung and OW were mixed together, put in a specific plastic barrel that had been diluted with water in a 1:10 ratio (to lower the number of solids), properly mixed, and allowed to ferment for a week before being utilized in the digester. To achieve a 1:1 mixing ratio, the same volume of treated OW from the first run was added after the mixture was poured into the digester through the intake hole. During the fermenting stage, there was one feeding, and then the air-drawing process was finished. Six kilograms of OW from the input port were introduced to the digester 1 week later. To promote the hydrolysis stage, they were completely mixed with inoculum substrates mechanically at 12 rpm for ten hours during the first 5 days. Afterward, intermittent mixing was used for 4 h a day to produce the best methane output. To get a fine and uniform shape, the OW was completely combined in an electrical blender after being diluted 1:1 with water. The biogas was measured using the water displacement technique. For analysis, the biogas was collected in a sample gasbag. During this run, all pH value changes that happened during the digestion process were recorded, along with TS, VS, and MC.

4 Results and discussion

4.1 Characterization of feedstock

The physicochemical parameters of cow dung (CM), OW, and a blend of cow dung and OWs (CW:OW) are shown in Table 3. Cow dung and OW had TS contents of 74.2 and 20.6%, respectively, and VS contents of 71.8 and 88.3%. The results for goat dung (84.7% [23]) and FW (87.1% [24]) were comparable to these VS levels. The VS percentages in the feedstocks indicate a high concentration of organic components that degrade readily, allowing for the formation of biogas [25]. OW was found to have a greater moisture content (79.40%) than cow dung (25.8%). The increased moisture content of OW is critical for maintaining optimal moisture levels during co-digestion [26]. While the pH of cow dung (7.84) was somewhat over neutral, the pH of OW (4.60) was rather acidic. It has been suggested that the ideal pH range for AD is 6.8–7.2 [27,28]. Low pH values of 3.50 and 4.30 were found for FW, respectively. These findings are compatible with the results of Zhang et al. [29] and Shamurad et al. [30].

Table 3

Main characteristics of substrate used

Property OW CM OW–CM
pH 4.6 ± 0.03 7.84 ± 0.05 6.7 ± 0.05
COD (mg/L) 159 98 116
Moisture content (%) 79.4 ± 0.05 25.8 ± 0.05 82
Total solid, TS (%) 20.6 ± 0.05 74.2 ± 0.05 18
Volatile solid, VS (%) 88.3 ± 0.05 71.8 ± 0.05 81.3
C/N 17.4 24.3 21.1

Table 3 shows that the pH rose from 4.60 to 6.7 when FWs were co-digested with a suitable substrate – in this case, cow dung. The proportions of C/N in cow dung and OW. These readings are within the AD range of 9.00–30.00 [31]. Since the C/N ratio is essential to the survival and metabolic processes of bacteria, it must always be at ideal values. As seen in Table 3, both feedstocks are suitable as biogas production substrates, and their co-digestion can improve process parameters and raise biogas yield.

4.2 Effect of temperature on biogas yield

The digester used in this experiment has a heater in the bottom plate that was regulated by a thyristor to keep an approximate average temperature of 37°C with minimal changes. Days with higher substrate temperatures suggested an increase in the activity of hydrolytic bacteria to break down organic matter and create biogas, which explains the temperature variability during the digestion process. As shown in Figure 2, the temperature of the substrate varies according to the phases of digestion and the activity of microbes. The results revealed that the maximum temperature for total gas production was 41°C and that biogas production declined as the temperature dropped from 41 to 39.5°C. The temperature of the digester influences anaerobic bacterial activity and waste decomposition. The rate of degradation and the generation of biogas increases with rising temperatures [32]. Due to the lack of organic materials and the response being oriented to the end, there was a slow drop after day 25.

Figure 2 The fluctuation in temperature that occurs during digesting.
Figure 2

The fluctuation in temperature that occurs during digesting.

4.3 Effect of pH on biogas yield

The pH value was measured and monitored every day as one of the key elements influencing biogas generation to analyze the influence of fluctuations during digestion on the activity of bacteria. Figure 3 depicts the pH value fluctuation. The pH steadily lowered at the start of the experiment because easily digested organic matter was degraded and converted into fatty acids. The pH value quickly decreases, reaching 5.7 on the ninth day. After that, the pH value increased over the course of twenty days to reach 6.9 as a result of methanogenic microorganisms’ activity in response to an increase in biogas generation over the allotted time. Methane-producing methanogenic bacteria prefer a pH of 6.5 or higher [33].

Figure 3 pH variation during the digestion process.
Figure 3

pH variation during the digestion process.

Following that, the pH began to drop until it reached a consistent value of 5.65 at the end of the process. The experiment’s pH varied because of the fatty acid buildup in the solid phase reactor on a regular basis and the subsequent transfer and consumption of volatile fatty acid (VFA) through the production of methane.

4.4 TS and VS

Figures 4 and 5 show the observed reductions in TS and VS of 57 and 50.6%, respectively. The greatest drop happens during the third week when gas generation is at its peak due to the metabolic activities of the bacteria.

Figure 4 Variation in TS during the digestion process.
Figure 4

Variation in TS during the digestion process.

Figure 5 Variation in VS during the digestion process.
Figure 5

Variation in VS during the digestion process.

4.5 C/N ratio

When producing biogas, one of the most crucial factors to take into account is the C/N ratio. When the digester was turned on, the C/N ratio was recorded as 21.1. The ideal range of C/N ratios for biogas generation is 20–30:1, according to Athanasoulia et al. [34]. The biogas produced is reduced when the C/N ratio surpasses the allowed limit because methanogenic bacteria consume nitrogen rapidly to meet their protein needs. AD of multi-component substrates yields higher methane production when the feeding mix and C/N ratio are changed, according to other research [35] (Figure 6).

Figure 6 Value of C/N ratio during the digestion process.
Figure 6

Value of C/N ratio during the digestion process.

4.6 Methane production

Methane was not identified over the first 6 days, as seen in Figure 7. On the seventh day, when the methane’s measured volume reached 55 mL, methane production started. This is due to the creation of VFAs in the early stages of digestion, which causes a reduction in pH. Following that, the volume of gas produced increased noticeably, eventually reaching 367 mL. The biggest amount generated throughout the digestive process on day 21 was 488 mL. Methane production follows an irregular pattern at the end of the digestive process, with a continuous decrease in its amount.

Figure 7 Daily volume of methane production.
Figure 7

Daily volume of methane production.

The amount of methane generated on average per day was 163.8 mL, while the total amount generated over time was 4,914 mL. Figure 8 shows the measured cumulative volume.

Figure 8 Total amount of methane produced over time.
Figure 8

Total amount of methane produced over time.

Under standard circumstances (temperature 273 K and air pressure 1,013), the daily and cumulative methane production was adjusted further using the Deponieverordnung Formula (1). During the digesting process, an average air pressure of 1,009 mbar was employed, and the water vapor pressure was 72 mbar at 40°C. [36]. The water vapor pressure at 40°C was chosen to be 55.3 mmHg, as stated. As shown in Figures 9 and 10, the greatest quantity of methane generated during the digestion process was 393.7 mL, and the total amount produced at the end of the operation was 3964.5 mL. Figures 9 and 10 show the adjustment of the volume and total gas generated.

(1) V 0 = V × ( p air − p water × T ˚ ) / P ˚ × T ,

where V 0 is the adjusted gas volume (mL), V is the measured volume of gas (mL), P air is the air pressure at the measurement time (mbar), P water is the pressure of water vapor at operating temperature (mbar), P° and T° are the normal temperature and normal air pressure, and T is the measurement time’s temperature (°C).

Figure 9 The corrected methane production volume.
Figure 9

The corrected methane production volume.

Figure 10 The cumulative volume of methane produced after correction.
Figure 10

The cumulative volume of methane produced after correction.

4.7 Methane content in produced biogas

Figure 11 depicts the fluctuation in methane concentration during the biogas manufacturing process. Methane level was low in the early stages of digestion; this might be owing to the presence of easily digestible organic elements, such as carbohydrates, and the OW’s rapid acidification [37]. On day 20, the highest methane level was 56%. Following that, the methane fraction gradually decreased till the process was completed.

Figure 11 CH4 and CO2 content percentage during the digestion process.
Figure 11

CH4 and CO2 content percentage during the digestion process.

Table 4 displays the results of the measurements of carbon (C), nitrogen (N), potassium (K), and phosphorous (P) in the current investigation, along with a comparison with some findings from the literature.

Table 4

Percentage biogas composition [40]

Digester C (%) N (%) K (%) P (%)
Run 1 51 3.4 2.8 1.8
Run 2 56 2.6 3.1 2.2
Farmyard manure 25–55 0.4–0.8 0.6–0.8 0.5–0.65
Horse manure NF 0.7 0.6 0.3
Chicken manure NF 1.1 0.5 0.8
Sheep manure NF 0.7 0.9 0.3
Pig manure NF 0.8 0.5 0.7
FW-human waste 20.1 + −0.4 0.7 + −0.03 NF NF

NF = not found.

The availability of easily biodegradable OW in the substrate, a high methanogen concentration, and shorter lag phase growth may also have contributed to the digester’s initial quick methane output.

In AD, the concentration of N, P, and K keeps increasing. This could have something to do with the way bacteria work, which significantly reduces microbial infections [38]. The presence of dissolved phosphorous and nitrogen-fixing organisms in the digester suggests that it can be utilized as a productive biofertilizer to promote crop growth. According to Owamah et al. [39], FW and human waste (CM–OW and SS–OW) biodigested slurry can be co-digested and used as an organic fertilizer. As a result, the problem associated with OW removal can be reduced.

The experimental findings demonstrated that a minimum inoculum volume is to be favored in some situations. A selective pressure against methanogens must be applied in order to further optimize the process [41]. According to Aragaw et al. [42], adding 25% of cattle manure (CM) and 75% of organic kitchen waste produced the greatest methane yield of 14653.5 mL/g VS. On the other hand, the AD process was inhibited when 75% cattle manure was added, and the cumulative methane output was 23% lower than when 25% cattle manure was added.

5 Conclusions and future prospects

The goal of the experimental effort was to maximize MSW biogas production.

The following are the conclusions that can be made from the study’s findings:

  1. The university campus generates around 3,280 kg of waste per day (151.7 kg on a daily average) and the average generation rate per person is 0.183 kg.

  2. The achieved OW methanogenic digestion is seen as a promising strategy that could be used in areas with a lot of OW because it produces a lot of biogases with a high methane quality. This industrial use would help improve eco-friendly practices to deal with climate change because it would cut down on pollution and greenhouse gas emissions, reduce OW, and provide technical solutions for energy needs in especially rural areas.

  3. The results of the research indicate that the anaerobic co-digestion of OW and cattle manure phase produced 393.7 mL of methane during the course of the digestion process’s 31 days.

  4. Laboratory studies showed that the OW–CM had an accumulation volume of 3964.5 mL. This indicates that the significantly higher C/N ratio and higher volatile organic content contributed to the more efficient OW–CM digestion.

  5. Methane content was 60% during the research, while TS and VS reductions were 57 and 50.6%, respectively.

  6. By turning trash into usable energy, AD of MSW not only produces clean energy but also contributes to environmental cleanup. Therefore, the technology should be taken into consideration by municipal authorities as a means of achieving sustainable waste management.

  1. Funding information: Authors state no funding involved.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results, and approved the final version of the manuscript. ZBM and MYF designed the experiments and AGS carried them out. EQS developed themodel code and performed the simulations. AGS prepared the manuscript with contributions from all coauthors.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Data availability statement: Most datasets generated and analyzed in this study are comprised in this submitted manuscript. The other datasets are available on reasonable request from the corresponding author with the attached information.

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Received: 2023-11-27
Revised: 2024-03-12
Accepted: 2024-03-12
Published Online: 2024-10-29

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/eng-2024-0011
Keywords for this article
solid waste biogas; anaerobic co-digestion; municipal solid waste; methane production; biogas
Creative Commons
BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Methodology of automated quality management
  3. Influence of vibratory conveyor design parameters on the trough motion and the self-synchronization of inertial vibrators
  4. Application of finite element method in industrial design, example of an electric motorcycle design project
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  68. Developing ANFIS-FMEA model for assessment and prioritization of potential trouble factors in Iraqi building projects
  69. Numerical and experimental comparison study of piled raft foundation
  70. Effect of asphalt modified with waste engine oil on the durability properties of hot asphalt mixtures with reclaimed asphalt pavement
  71. Hydraulic model for flood inundation in Diyala River Basin using HEC-RAS, PMP, and neural network
  72. Numerical study on discharge capacity of piano key side weir with various ratios of the crest length to the width
  73. The optimal allocation of thyristor-controlled series compensators for enhancement HVAC transmission lines Iraqi super grid by using seeker optimization algorithm
  74. Numerical and experimental study of the impact on aerodynamic characteristics of the NACA0012 airfoil
  75. Effect of nano-TiO2 on physical and rheological properties of asphalt cement
  76. Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt
  77. Performance analysis, evaluation, and improvement of selected unsignalized intersection using SIDRA software – Case study
  78. Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies
  79. Influence of fiber types on the properties of the artificial cold-bonded lightweight aggregates
  80. Experimental investigation of RC beams strengthened with externally bonded BFRP composites
  81. Generalized RKM methods for solving fifth-order quasi-linear fractional partial differential equation
  82. An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala
  83. Role of individual component failure in the performance of a 1-out-of-3 cold standby system: A Markov model approach
  84. Implementation for the cases (5, 4) and (5, 4)/(2, 0)
  85. Center group actions and related concepts
  86. Experimental investigation of the effect of horizontal construction joints on the behavior of deep beams
  87. Deletion of a vertex in even sum domination
  88. Deep learning techniques in concrete powder mix designing
  89. Effect of loading type in concrete deep beam with strut reinforcement
  90. Studying the effect of using CFRP warping on strength of husk rice concrete columns
  91. Parametric analysis of the influence of climatic factors on the formation of traditional buildings in the city of Al Najaf
  92. Suitability location for landfill using a fuzzy-GIS model: A case study in Hillah, Iraq
  93. Hybrid approach for cost estimation of sustainable building projects using artificial neural networks
  94. Assessment of indirect tensile stress and tensile–strength ratio and creep compliance in HMA mixes with micro-silica and PMB
  95. Density functional theory to study stopping power of proton in water, lung, bladder, and intestine
  96. A review of single flow, flow boiling, and coating microchannel studies
  97. Effect of GFRP bar length on the flexural behavior of hybrid concrete beams strengthened with NSM bars
  98. Exploring the impact of parameters on flow boiling heat transfer in microchannels and coated microtubes: A comprehensive review
  99. Crumb rubber modification for enhanced rutting resistance in asphalt mixtures
  100. Special Issue: AESMT-6
  101. Design of a new sorting colors system based on PLC, TIA portal, and factory I/O programs
  102. Forecasting empirical formula for suspended sediment load prediction at upstream of Al-Kufa barrage, Kufa City, Iraq
  103. Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide
  104. Sediment transport modelling upstream of Al Kufa Barrage
  105. Study of energy loss, range, and stopping time for proton in germanium and copper materials
  106. Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant
  107. Enhancing structural behaviour of polypropylene fibre concrete columns longitudinally reinforced with fibreglass bars
  108. Sustainable road paving: Enhancing concrete paver blocks with zeolite-enhanced cement
  109. Evaluation of the operational performance of Karbala waste water treatment plant under variable flow using GPS-X model
  110. Design and simulation of photonic crystal fiber for highly sensitive chemical sensing applications
  111. Optimization and design of a new column sequencing for crude oil distillation at Basrah refinery
  112. Inductive 3D numerical modelling of the tibia bone using MRI to examine von Mises stress and overall deformation
  113. An image encryption method based on modified elliptic curve Diffie-Hellman key exchange protocol and Hill Cipher
  114. Experimental investigation of generating superheated steam using a parabolic dish with a cylindrical cavity receiver: A case study
  115. Effect of surface roughness on the interface behavior of clayey soils
  116. Investigated of the optical properties for SiO2 by using Lorentz model
  117. Measurements of induced vibrations due to steel pipe pile driving in Al-Fao soil: Effect of partial end closure
  118. Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor
  119. Evaluation of clay layer presence on shallow foundation settlement in dry sand under an earthquake
  120. Optimal design of mechanical performances of asphalt mixtures comprising nano-clay additives
  121. Advancing seismic performance: Isolators, TMDs, and multi-level strategies in reinforced concrete buildings
  122. Predicted evaporation in Basrah using artificial neural networks
  123. Energy management system for a small town to enhance quality of life
  124. Numerical study on entropy minimization in pipes with helical airfoil and CuO nanoparticle integration
  125. Equations and methodologies of inlet drainage system discharge coefficients: A review
  126. Thermal buckling analysis for hybrid and composite laminated plate by using new displacement function
  127. Investigation into the mechanical and thermal properties of lightweight mortar using commercial beads or recycled expanded polystyrene
  128. Experimental and theoretical analysis of single-jet column and concrete column using double-jet grouting technique applied at Al-Rashdia site
  129. The impact of incorporating waste materials on the mechanical and physical characteristics of tile adhesive materials
  130. Seismic resilience: Innovations in structural engineering for earthquake-prone areas
  131. Automatic human identification using fingerprint images based on Gabor filter and SIFT features fusion
  132. Performance of GRKM-method for solving classes of ordinary and partial differential equations of sixth-orders
  133. Visible light-boosted photodegradation activity of Ag–AgVO3/Zn0.5Mn0.5Fe2O4 supported heterojunctions for effective degradation of organic contaminates
  134. Production of sustainable concrete with treated cement kiln dust and iron slag waste aggregate
  135. Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review
  136. A comparative analysis of the energy dissipation efficiency of various piano key weir types
  137. Special Issue: Transport 2022 - Part II
  138. Variability in road surface temperature in urban road network – A case study making use of mobile measurements
  139. Special Issue: BCEE5-2023
  140. Evaluation of reclaimed asphalt mixtures rejuvenated with waste engine oil to resist rutting deformation
  141. Assessment of potential resistance to moisture damage and fatigue cracks of asphalt mixture modified with ground granulated blast furnace slag
  142. Investigating seismic response in adjacent structures: A study on the impact of buildings’ orientation and distance considering soil–structure interaction
  143. Improvement of porosity of mortar using polyethylene glycol pre-polymer-impregnated mortar
  144. Three-dimensional analysis of steel beam-column bolted connections
  145. Assessment of agricultural drought in Iraq employing Landsat and MODIS imagery
  146. Performance evaluation of grouted porous asphalt concrete
  147. Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method
  148. Effect of waste tire products on some characteristics of roller-compacted concrete
  149. Studying the lateral displacement of retaining wall supporting sandy soil under dynamic loads
  150. Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)
  151. Behavior of soil reinforced with micropiles
  152. Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers
  153. An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials
  154. Forecasting changes in precipitation and temperatures of a regional watershed in Northern Iraq using LARS-WG model
  155. Experimental investigation of dynamic soil properties for modeling energy-absorbing layers
  156. Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams
  157. An experimental study on the tensile properties of reinforced asphalt pavement
  158. Self-sensing behavior of hot asphalt mixture with steel fiber-based additive
  159. Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers
  160. Optimizing asphalt binder performance with various PET types
  161. Investigation of the hydraulic characteristics and homogeneity of the microstructure of the air voids in the sustainable rigid pavement
  162. Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study
  163. Special Issue: AESMT-7 - Part I
  164. Preparation and investigation of cobalt nanoparticles by laser ablation: Structure, linear, and nonlinear optical properties
  165. Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior
  166. The effect of urban environment on large-scale path loss model’s main parameters for mmWave 5G mobile network in Iraq
  167. Formatting a questionnaire for the quality control of river bank roads
  168. Vibration suppression of smart composite beam using model predictive controller
  169. Machine learning-based compressive strength estimation in nanomaterial-modified lightweight concrete
  170. In-depth analysis of critical factors affecting Iraqi construction projects performance
  171. Behavior of container berth structure under the influence of environmental and operational loads
  172. Energy absorption and impact response of ballistic resistance laminate
  173. Effect of water-absorbent polymer balls in internal curing on punching shear behavior of bubble slabs
  174. Effect of surface roughness on interface shear strength parameters of sandy soils
  175. Evaluating the interaction for embedded H-steel section in normal concrete under monotonic and repeated loads
  176. Estimation of the settlement of pile head using ANN and multivariate linear regression based on the results of load transfer method
  177. Enhancing communication: Deep learning for Arabic sign language translation
  178. A review of recent studies of both heat pipe and evaporative cooling in passive heat recovery
  179. Effect of nano-silica on the mechanical properties of LWC
  180. An experimental study of some mechanical properties and absorption for polymer-modified cement mortar modified with superplasticizer
  181. Digital beamforming enhancement with LSTM-based deep learning for millimeter wave transmission
  182. Developing an efficient planning process for heritage buildings maintenance in Iraq
  183. Design and optimization of two-stage controller for three-phase multi-converter/multi-machine electric vehicle
  184. Evaluation of microstructure and mechanical properties of Al1050/Al2O3/Gr composite processed by forming operation ECAP
  185. Calculations of mass stopping power and range of protons in organic compounds (CH3OH, CH2O, and CO2) at energy range of 0.01–1,000 MeV
  186. Investigation of in vitro behavior of composite coating hydroxyapatite-nano silver on 316L stainless steel substrate by electrophoretic technic for biomedical tools
  187. A review: Enhancing tribological properties of journal bearings composite materials
  188. Improvements in the randomness and security of digital currency using the photon sponge hash function through Maiorana–McFarland S-box replacement
  189. Design a new scheme for image security using a deep learning technique of hierarchical parameters
  190. Special Issue: ICES 2023
  191. Comparative geotechnical analysis for ultimate bearing capacity of precast concrete piles using cone resistance measurements
  192. Visualizing sustainable rainwater harvesting: A case study of Karbala Province
  193. Geogrid reinforcement for improving bearing capacity and stability of square foundations
  194. Evaluation of the effluent concentrations of Karbala wastewater treatment plant using reliability analysis
  195. Adsorbent made with inexpensive, local resources
  196. Effect of drain pipes on seepage and slope stability through a zoned earth dam
  197. Sediment accumulation in an 8 inch sewer pipe for a sample of various particles obtained from the streets of Karbala city, Iraq
  198. Special Issue: IETAS 2024 - Part I
  199. Analyzing the impact of transfer learning on explanation accuracy in deep learning-based ECG recognition systems
  200. Effect of scale factor on the dynamic response of frame foundations
  201. Improving multi-object detection and tracking with deep learning, DeepSORT, and frame cancellation techniques
  202. The impact of using prestressed CFRP bars on the development of flexural strength
  203. Assessment of surface hardness and impact strength of denture base resins reinforced with silver–titanium dioxide and silver–zirconium dioxide nanoparticles: In vitro study
  204. A data augmentation approach to enhance breast cancer detection using generative adversarial and artificial neural networks
  205. Modification of the 5D Lorenz chaotic map with fuzzy numbers for video encryption in cloud computing
  206. Special Issue: 51st KKBN - Part I
  207. Evaluation of static bending caused damage of glass-fiber composite structure using terahertz inspection
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