Improve Biogas Production Research Articles

Bioenergy potential of paper waste: Fungal pretreatment and kinetics modelling

Using the fungi Phanerochaete chrysosporium and Aspergillus niger as a biopretreatment agent to improve degradation of lignocellulosic paper with analogous increase in biogas production, anaerobic digestion (AD) was executed. Milled and hydrothermally-treated (HT) or steamed paper were separately inoculated for 360 hr at 28 °C with each fungal species, with an uninoculated treatment as control. AD experiment was conducted in bench-scale batch bioreactors for 48 days at 40°C. The initial characteristics of the feedstock and inoculum were examined in addition to biomethane yield, total and volatile solids degradation, and lignocellulosic content removal. The pretreatment of milled paper with P. chrysosporium resulted in the highest biogas yield of 1035 mL/gVS, followed by A. niger with a yield of 550 mL/gVS. These values represented a significant increase (p < 0.05) of 226 % and 73 % compared to the untreated feedstock, respectively. P. chrysosporium pretreatment achieved the highest total solids removal of 66.85 %, whereas A. niger pretreatment resulted in the maximum volatile solids removal of 64.63 % in HT-paper waste. P. chrysosporium also exhibited the highest lignin removal efficiency, with 84.31 % in milled feedstock and 79.17 % in the steamed state. A. niger showed 77.28 % and 67.09 % lignin removal in the milled and HT paper, respectively. The study demonstrated that pretreatment with P. chrysosporium and A. niger significantly (p<0.05) improved biogas production by facilitating the biodegradation of lignocellulosic components. All measured biomethane data from experiments fitted adequately to the modified Gompertz model with R2 ranging from 0.97 to 0.99.

Solar-integrated biogas reactor for efficient kitchen waste conversion to biogas

This study aimed to improve biogas production by co-digesting kitchen waste and animal manure in a solar-integrated biogas reactor. The panel then heated the substrate mixture to the right temperature for the reactor after turning solar energy into electricity. The experiment was conducted at mesophilic (37°C) and thermophilic (40°C) conditions. After 45 days of co-digestion of animal dung, kitchen trash, cow manure, and grasses, the solar-integrated biogas plant generated 1,445 mL of biogas with 60% CH4, 14% CO, and 21% other gases; in comparison, the conventional biogas digester produced 501 mL, 479 mL, and 525 mL, respectively, with 35-50% Methane, 18% CO, and 22% other gases. The data show that a solar-integrated biogas plant may react faster produce more gas, and have a higher methane concentration using kitchen waste and animal manure. An environmental effect analysis and prediction of biogas plant construction has been accomplished. The proposed biogas plant, supported by a solar-integrated reactor strategy, appears economically viable, projecting a five-year payback period. This research evaluates efficient biogas production techniques, emphasizing their importance in advancing engineering sustainability. It promotes the role of renewable energy, energy efficiency, and environmental sustainability in solving global energy problems and reducing climate change.

Optimizing the microbial community composition in anaerobic digesters to improve biogas yields from food waste

Methods: Food waste collected from local restaurants and households in New York city will be used in this study. The food waste will be characterized to analyze its composition. Batch anaerobic digesters will be inoculated with microbial communities from existing food waste digesters. DNA analysis using 16S rRNA gene sequencing will be done to show the initial microbial consortia. Various perturbations will be applied to the digesters including changes in temperature, pH, feeding rates, mixing intensities to select for microbial populations yielding higher biogas production. Biogas production will be monitored over time. DNA analysis will be repeated after perturbation to analyze changes in the microbial community structure. Results: Preliminary results show Food waste characterized was found to contain 35% proteins, 45% carbohydrates and 20% fats. The initial microbial consortia in the digesters was dominated by bacteria from the genera Clostridium, Bacteroides and Methanothermobacter. Increasing feeding rates led to a 40% increase in biogas yields. Microbial analysis indicated a shift in populations with Clostridium becoming the most abundant genus. Decreasing pH from 7 to 6.5 further enhanced biogas by 25% with Clostridium and Syntrophomonas becoming dominant. Discussion: The study demonstrates that optimizing operational conditions can effectively manipulate the microbial communities in anaerobic digesters processing food waste. By applying selective pressures, populations better suited to degrade the local food waste and produce higher methane yields can be enriched. Further experiments will aim to construct stable, optimized consortia through controlled perturbation for robust and efficient food waste digestion. The approach holds promise for improving biogas production from food waste globally

Improving biogas production with application of trimetallic nanoparticle using response surface methods

The potential of trimetallic nanoparticles (TMNPs) to enhance biogas production through microbe-to-microbe interactions and boost biogas yield is evident. This present study employed the central composite design (CCD) of response surface methods (RSM) to determine the optimal conditions of iron-cobalt-zinc TMNPs influenced anaerobic digestion for higher biogas yield. The impact of initial pH (6.6–7.4), TMNPs concentration (0–30 mg L−1), temperature (25-45 °C), and hydraulic retention time (HRT) (0-4 days) were modelled for improved biogas production. The results indicated that the linear model terms of pH and TMNPs concentration, and quadratic model terms of temperature and HRT, significantly affect the biogas production. Linear model terms of TMNPs, temperature, pH, and HRT have significant interactive effects and the numerical analysis identified the best conditions for the evaluated parameters. Ideal anaerobic process settings generated a maximum cumulative biogas production of 3700 mL−1POME than blank (2000 mL−1), corresponding to an 85 % yield. Optimizing the initial pH, TMNPs concentration, temperature, and HRT can significantly improve biogas yield and could be helpful for developing more efficient AD processes at large volume and commercial biogas plants. Promoting TMNPs as catalysts positively improves an AD process towards sustainable biogas production.

Textile waste pretreatment for anaerobic digestion: a review and technology feasibility study

AbstractThe increasing volume of textile waste in landfills and incineration poses severe environmental challenges. Waste valorisation of textile waste via anaerobic digestion (AD) is preferable, as it offers economic and environmental benefits, but it is hindered by textile complexity, necessitating effective pretreatment technologies to improve biogas production. This study aims to evaluate various pretreatment technologies for biogas production from textile fibres via AD. A weighted‐scoring analysis (WSA) assessed pretreatment methods based on technical, economic, environmental and operational criteria. Hydrothermal pretreatment emerged as the most technically effective method, scoring 140 owing to its substantial methane enhancement. Economically, shredding was the most viable option, scoring 125, as a consequence of low capital and O&amp;M cost. Environmentally, hydrothermal and deep eutectic solvent (DES) pretreatments were top performers with 100 points owing to low environmental impact and positive heat reactions. In a case study conducted in the Auckland region, the potential environmental impact (PEI) obtained from hydrothermal and DES were 169 and 92 per year, respectively, resulting in minimal environmental impact. Operationally, ultrasonic and biological pretreatments scored highest owing to their ease of operation, and minimal health and safety requirements. Overall, hydrothermal pretreatment achieved the highest WSA score of 340, reflecting its balanced performance across all criteria. Hydrothermal pretreatment is the most promising technology for enhancing biogas production from textile waste. Its technical efficiency, economic feasibility and environmental benefits regarding the WSA score make it suitable for upscaling and providing a viable solution for managing textile waste in the AD plant. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).

Determinant factors for optimal anaerobic digestion of agro-industrial sardine residues

ABSTRACT In this study, nutritious and abundant waste generated by sardine canneries was used as the main substrate to assess the effect of fundamental parameters in anaerobic digestion. The temperature range studied, between 37°C and 45°C, allowed for a comparison between the performance of the thermophilic and mesophilic processes. The free water content in the substrate also enabled us to compare fermentation in solid-state fermentation (SSF) with its counterpart, liquid-state fermentation (LSF). The study parameters also included the integration of Aspergillus niger (AN) and molasses. The results revealed significant effects of the AN inoculum and thermophilic conditions in improving biogas production. Optimal biotransformation generated a safe digestate that complies with French standards for use as a biofertilizer. Germination tests demonstrated that it has no inhibitory effect on tomato seeds and has the potential to enhance crop yields better than chemical fertilisers.

Synergistic integration of hydrothermal pretreatment and co-digestion for enhanced biogas production from empty fruit bunches in high solids anaerobic digestion

This study investigates the co-digestion of hydrothermally pretreated empty fruit bunches (EFB) at 190 °C for 5 min (HTP190-EFB) with decanter cake (DC) to improve biogas production in high solid anaerobic digestion (HSAD). The HTP190-EFB exhibited a 67.98 % reduction in total solids, along with the production of 0.89 g/L of sugar, 2.39 g/L of VFA, and 0.56 g/L of furfural in the liquid fraction. Co-digestion of HTP190-EFB with DC at mixing ratios of 5, 10, and 15 %w/v demonstrated improved methane yields and process stability compared to mono-digestion of HTP190-EFB. The highest methane yield of 372.69 mL CH4/g-VS was achieved in the co-digestion with 5 %w/v DC, representing a 15 % increase compared to digestion of HTP190-EFB (324.30 mL CH4/g-VS) alone. Synergistic effects were quantified, with the highest synergistic methane yield of 77.65 mL CH4/g-VS observed in the co-digestion with 5 %w/v DC. Microbial community analysis revealed that co-digestion of hydrothermally pretreated EFB with decanter cake promoted the growth of Clostridium sp., Lactobacillus sp., Fibrobacter sp., Methanoculleus sp., and Methanosarcina sp., contributing to enhanced biogas production compared to mono-digestion of pretreated EFB. Energy balance analysis revealed that co-digestion of HTP190-EFB with DC resulted in a total net energy of 599.95 kW, 52 % higher than mono-digestion of HTP190-EFB (394.62 kW). Economic analysis showed a shorter return on investment for the co-digestion system (0.86 years) compared to the mono-digestion of HTP190-EFB (1.02 years) and raw EFB (2.69 years). The co-digestion of HTP190-EFB with 5 %w/v DC offers a promising approach to optimize methane yield, process stability, and economic feasibility, supporting the palm oil industry for producing renewable energy and sustainable waste management.

Design and Implementation of a Biogas Pilot Plant for Bioaugmentation Strategies in a rural municipality

The transition towards renewable energy sources is imperative for achieving sustainability and mitigating climate change impacts. Among various renewable energies, biogas stands out for its dual role in waste management and energy production. This study introduces the design and implementation of a biogas pilot plant aimed at exploring bioaugmentation strategies to enhance biogas yield and quality. The pilot plant, located at Aras de los Olmos, features two independent 3.4m3 digesters, allowing for parallel comparison between standard anaerobic digestion and digestion with microbial enhancements. The plant is equipped with monitoring and control systems for precise regulation of environmental conditions, such as temperature, and for real-time measurement of biogas composition. Some initial experiments using a mix of agricultural wastes demonstrated the plant's capability to adapt to varied feedstock. Despite suboptimal temperature conditions, preliminary results indicated a high methane content, suggesting significant potential for bioaugmentation to improve biogas production efficiency. The study highlights the importance of controlled environmental conditions and introduces a novel bioaugmented digestion approach using selected microbial consortia. This research contributes to the broader goal of enhancing biogas technology's efficiency and sustainability, offering insights into the practical application of bioaugmentation in biogas production.

Optimization of the Factors Affecting Biogas Production Using the Taguchi Design of Experiment Method

The present study analyzed the effect of temperature, pH, pre-treatment and mixing ratio on the anaerobic digestion process. The parameters during the anaerobic co-digestion of cow manure and food waste were then optimized using the Taguchi experimental design method. ANOVA was carried out to find the significant parameters which influence biogas production. Experimental tests were carried out at laboratory-scale reactors kept at different temperatures (28 °C, 35 °C, and 50 °C). The specific methanogenic performance (SMP) during anaerobic digestion at higher temperatures was characterized with the analysis of acetate, propionate, butyrate, hydrogen, glucose, and formate, and was validated with the literature. The improvement of biogas production with different pre-treatments, i.e., ultrasonic, autoclave, and microwave techniques, was also analyzed. The results showed that the reactor that was maintained at 35 °C showed the highest biogas production, while the reactor that was maintained at a lower temperature (28 °C) produced the lower volume of biogas. As the retention time increases, the amount of biogas production increases. Methanogenic activities of microorganisms were reduced at higher temperature conditions (65 °C). Biogas production increased by 28.1%, 20.23%, and 13.27% when the substrates were treated with ultrasonic, autoclave, and microwave, respectively, compared to the untreated substrate. The optimized condition for the highest biogas production during anaerobic co-digestion of food waste and cow manure is a temperature of 35 °C, a pH of 7 and a mixing ratio (CM:FW = 1.5:0.5). ANOVA showed that temperature is the most important input parameter affecting biogas production, followed by mixing ratio.

Acidogenic gas utilization improves methane production in high-load digestion: Underlying mechanisms

High-load reactors face a significant challenge with fatty acid accumulation. Although injecting acidogenic gas (H2 and CO2) into methanogenic reactors improves biogas production, its mechanisms and stability enhancement remain unclear. Therefore, this study investigated the potential of using acidogenic gas to enhance methane production and system stability in a high substrate-loading co-digestion system with decreasing hydraulic retention time (HRT) and its regulatory role by considering biological pathways. Acidogenic gas injection effectively managed volatile fatty acid accumulation, with a concomitant increase in methane production from 0.042 to 0.066 L/L h as HRT decreased (16–8 days). However, the methane yield decreased from 611 to 460 mL/g volatile solids. Microbial community analysis revealed an increased abundance of hydrogenotrophic methanogens, along with several acidogenic and syntrophic fatty acid oxidizing consortia with decreasing HRT. The HRT10.67 sample exhibited the highest microbial species diversity and richness in the methanogenic reactor. Metabolomics analysis showed acidogenic gas reduced energy synthesis related to the tri-carboxylic acid cycle and oxidative phosphorylation while profoundly regulating the metabolism of amino acids, lipids, fatty acids, membrane transporters and inhibitory substances, thereby strengthening methane metabolism pathways. This study provides valuable insights into the roles of acidogenic gas in regulating energy metabolism to enhance methane production and offers potential opportunities for improving lipid and protein degradation.

Study on Co-Digestion of Palm Oil Mill Effluent and Empty Fruit Bunches to Improve Biogas Production in Palm Oil Mill

Study on Co-Digestion of Palm Oil Mill Effluent and Empty Fruit Bunches to Improve Biogas Production in Palm Oil Mill

Enhancement of Biodegradability of Chicken Manure via the Addition of Zeolite in a Two-Stage Dry Anaerobic Digestion Configuration.

Leach bed reactors (LBRs) are dry anaerobic systems that can handle feedstocks with high solid content, like chicken manure, with minimal water addition. In this study, the chicken manure was mixed with zeolite, a novel addition, and packed in the LBR to improve biogas production. The resulting leachate was then processed in a continuous stirred tank reactor (CSTR), where most of the methane was produced. The supernatant of the CSTR was returned to the LBR. The batch mode operation of the LBR led to a varying methane production rate (MPR) with a peak in the beginning of each batch cycle when the leachate was rich in organic matter. Comparing the MPR in both systems, the peaks in the zeolite system were higher and more acute than in the control system, which was under stress, as indicated by the acetate accumulation at 2328 mg L-1. Moreover, the presence of zeolite in the LBR played a crucial role, increasing the overall methane yield from 0.142 (control experiment) to 0.171 NL CH4 per g of volatile solids of chicken manure entering the system at a solid retention time of 14 d. Zeolite also improved the stability of the system. The ammonia concentration increased gradually due to the little water entering the system and reached 3220 mg L-1 (control system) and 2730 mg L-1 (zeolite system) at the end of the experiment. It seems that zeolite favored the accumulation of the ammonia at a lower rate (14.0 mg L-1 d-1) compared to the control experiment (17.3 mg L-1 d-1). The microbial analysis of the CSTR fed on the leachate from the LBR amended with zeolite showed a higher relative abundance of Methanosaeta (83.6%) compared to the control experiment (69.1%). Both CSTRs established significantly different bacterial profiles from the inoculum after 120 days of operation (p < 0.05). Regarding the archaeal communities, there were no significant statistical differences between the CSTRs and the inoculum (p > 0.05).

Anaerobic digestion of spoiled milk from dairy industry for biogas production – optimization of operating parameters and kinetic modeling of the pilot scale study

BackgroundSpoiled milk from the dairy industry was subjected to anaerobic treatment to produce biogas at 37℃ in this experiment. Parameters such as inoculum dosage, pH, Chemical Oxygen Demand (COD), and retention time were optimized in a laboratory-scale batch reactor for 90 days.MethodsThe anaerobic digestion of spoilt milk was carried out in a laboratory setting using a batch reactor. Then, using the recognized protocols of the APHA, the characteristics of the spoilt milk were assessed. In order to enhance the accuracy of predicting the reactor's performance, the research adopted two different models for kinetic analysis: the Stover-Kincannon model and the Grau second-order multi-component model. The reactor's improved performance, as indicated by evaluated kinetic parameters, was shown by the superior results from both of these models.ResultsThe results attained from the reactor’s performance were then used as a reference to improve biogas production in a 100 L Anaerobic Sequential Batch Reactor (ASBR) for 45 days. The ASBR achieved a high COD removal efficiency of 92.4% and produced a maximum of 70.4 L of biogas per liter of spoiled milk, equivalent to 69.6% methane content.ConclusionThe Stover-Kincannon model yielded kinetic parameters of Umax = 0.295 gCOD/L and KB = 12.87 gCOD/L, whereas the Grau second-order model presented kinetic coefficients a = 6.744 and b = 2.578. The results obtained from the two models suggest that the investigated kinetic coefficients could be improved upon to increase the reactor's capability for handling different substrates during the AD process.

Insight into physico-chemical properties and microbial community structure of biogas slurry from household biogas plants of sub-Himalaya for its implications in improved biogas production.

Numerous metagenomics studies, conducted in both full-scale anaerobic digesters and household biogas plants, have shed light on the composition and activity of microbial flora essential for optimizing the performance of biogas reactors, underscoring the significance of microbial community composition in biogas plant efficiency. Although the efficiency of household biogas plants in the sub-Himalayan region has been reported, there is no literature evidence on the microbial community structure of such household biogas plants in the sub-Himalayan region. The current study evaluated the physico-chemical properties and bacterial community structure from the slurry samples of household biogas plants prevalent in the sub-Himalayan region. The slurry samples were observed to be rich in nutrients; however, their carbon and nitrogen contents were higher than the recommended standard values of liquid-fermented organic manure. The species richness and diversity indices (Chao1, Shannon, and Simpson) of household biogas plants were quite similar to the advanced biogas reactors operating at mesophilic conditions. 16S rRNA gene amplicon sequencing reveals microbial diversity, showing a higher abundance of Firmicutes (70.9%) and Euryarchaeota (9.52%) in advanced biogas reactors compared to household biogas plants. Microbial analysis shows a lack of beneficial microbes for anaerobic digestion, which might be the reason for inefficient biogas production in household biogas plants of the sub-Himalayan region. The lack of efficient bacterial biomass may also be attributed to the digester design, feedstock, and ambient temperatures. This study emphasized the establishment of efficient microbial consortia for enhanced degradation rates that may increase the methane yield in biogas plants.

Impacts of free nitrous acid on stabilizing food waste and sewage sludge for anaerobic digestion

This work investigated the effectiveness of free nitrous acid (FNA) in enhancing organic waste solubilization to improve biogas production in anaerobic digestion (AD). The results indicated that FNA pretreatment can enhance soluble organic content and control H2S odor in tested organic wastes, including food waste, sewage sludge, and their combination. However, a significant decrease (>50 %) in FNA concentration was found in the reactors, possibly due to denitrifier-driven NO2– consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH4 production in the reactors fed with mixed substrate pretreated with 2.9 mg FNA-N/L. However, the presence of NO2– (325.6–2368.0 mg N/L) in some BMP reactors, due to carryover from FNA pretreatment, adversely affected CH4 production (>55 %) and prolonged lag time (>4.2 times). These findings are valuable for researchers and practitioners in waste management, offering insights for implementing FNA pretreatment to enhance the biodegradability of organic wastes in AD.

Design, fabrication, automation, and scaleup of anaerobic reactors for waste management and bioenergy recovery

AbstractDigitally controlled reactors can optimize biological reactions and process control through a neural network system. This study reports on the design, fabrication, and automation of a laboratory‐scale anaerobic reactor for the management of agrifood byproducts and bioenergy recovery. The process described here can digitally control the operational parameters, which is beneficial for stable methane production. The proposed process comprises the digital measurement of temperature, pH, humidity, biogas volume, and methane composition by integrating the data in a processor module. The proposed automated reactor can assist significantly in controlling and monitoring the anaerobic digestion process, providing decision making during waste management and bioenergy recovery. A case study is described with the application of automated reactors in a pilot‐scale plant, operated with the flow of 8 m3 slaughterhouse wastewater per day and a biogas production of 10 m3 h−1. The automated pilot‐scale process presents many advantages, including a continuous mode of operation and a faster adaptation of the microorganisms to the substrate, improving biogas production.

Biological Pretreatment of Cassava Husk with Aspergillus Niger ATCC 1004 to Improve Biogas Production

Biological Pretreatment of Cassava Husk with Aspergillus Niger ATCC 1004 to Improve Biogas Production

Preparation of iron oxide-modified digestate biochar and effect on anaerobic digestion of kitchen waste

Two kinds of Fe2O3-modified digestate-derived biochar (BC) were prepared and their effects on anaerobic digestion (AD) of kitchen waste (40.0 g VS/L) were investigated, with BC and Fe2O3 addition used as a comparison. The results showed that Fe2O3-modified BC (Fe2O3-BC1 prepared by co-precipitation and Fe2O3-BC2 by impregnation) significantly increased methane yield (20.8 % and 16.4 %, respectively) and reduced volatile fatty acid concentration (35.6 % and 29.6 %, respectively). Microbial high-throughput analysis revealed that Fe2O3-modified BC selectively enriched Clostridium (47.3 %) and Methanosarcina (72.2 %), suggesting that direct interspecies electron transfer contributing to improved biogas production performance was established and enhanced. Correlation analysis indicated that biogas production performance was improved by the larger specific surface area (83.4 m2/g), pore volume (0.101 cm3/g), and iron content (97.4 g/Kg) of the BC. These results offer insights for enhancing the efficacy of AD processes using Fe2O3-modified BCs as additives.

An Overview of Anaerobic Digestion of Cow Dung

In the past decade, governments and development agencies have contributed significantly to society through anaerobic digestion technology (ADT). Anaerobic digestion technology (ADT) has become an important tool in the fight against global poverty and environmental issues, leading to positive change in communities around the world. The technology works as a wet or dry process, depending on its classification. The process is complex and yields multiple benefits, such as creating a natural fertilizer that can be used to help crops grow, as well as generating renewable energy sources. It is common knowledge that many household-sized digesters installed in different areas are one-stage digesters. One-stage digesters do not require a separate pre-treatment stage before the digestion process. This makes them simpler and more cost-effective to install and operate than traditional two-stage digesters. Thus, some drawbacks are associated with these systems since they feed on just one type of feedstock. Many researchers fail to adequately address interactions critical to ADT’s operation, including interactions among growth factors and operating parameters. In a single-stage and one-substrate digester, researchers commonly neglect to study the digester feeding and operational conditions. Anaerobic digestion was the subject of this review, covering research conducted between 2001 and 2022. The study identified a significant drawback associated with mono-digestion and single-stage digestion. The findings illustrate that mono-substrate and single-stage digestion are worthwhile approaches, even though they have their challenges. However, adding a further digestion stage can significantly improve biogas production.

Comparative Environmental and Economic Analysis of Biomethane Production from Co-Digestion of Rice Straw and Spent Mushroom Compost: Application of Zero-Valent Iron Nanoparticles

Abstract Spent mushroom compost is one of the main potentials for biogas production. In recent years, several studies employed adding nanoparticles and alkaline pretreatment for improving biogas production. The present study is one of the pioneer studies that employ hybrid alkaline pretreatment (0, 5, and 15 mg of NaOH) and zero-valent iron nanoparticles (0, 10, 20, 30, and 40 mg) for improving the co-digestion of spent mushroom compost and rice straw. According to the results, retention time (RT) and nanoparticle (NP) concentrations have the most significant impact on biomethane production (significant at 1% probability level), while the NaOH concentration has the lowest impact on biomethane production (significant at 5% probability level) in comparison with RT and NP concentration. Also, the maximum biomethane production is related to NP40Na15 (about 200% higher than the control). The minimum cumulative biomethane production is related to NP0Na15 (about 30% lower than the control). The lowest relative environmental midpoint impact is related to NP40Na15, which was on average about 60% lower than the control. Adding NPs at high concentrations of NaOH reduces the midpoint impacts. The results of the study could lead to new, ecologically friendly biomethane production methods that make better use of agricultural and organic wastes.