Organic Fraction Of Municipal Waste Research Articles

Economic Feasibility Study of the Production of Biogas, Coke and Biofuels from the Organic Fraction of Municipal Waste Using Pyrolysis

The objective of this study is to analyze the economic viability of municipal household solid waste (organic matter + paper) for the production of gas, coke and biofuel through the pyrolysis and distillation process. The waste was collected in the city of Belém do Pará-Brazil and pretreated at the Federal University of Pará. The analyzed fraction (organic matter + paper) was subjected to the pretreatment of drying, crushing, and sieving and was subsequently subjected to proximate characterization and, finally, pyrolysis of the organic fraction (organic matter + paper) in a fixed bed reactor. Initially, it was necessary to review the literature, and with the yields obtained by pyrolysis of the fraction, economic feasibility analyses were carried out. The economic indicators for evaluating the most viable pyrolysis process were basic payback, discounted payback, net present value, internal rate of return, and profitability index, which are all financial metrics commonly used in investment analysis and decision making. These metrics provide valuable insights into the financial viability and attractiveness of investment projects. They are essential tools for assessing the feasibility and profitability of various ventures, helping decision-makers make informed choices in allocating resources. The analysis of the indicators showed the economic viability considering an analysis horizon of 10 years of materials based on organic material and paper. The breakeven point obtained was USD 0.96/dm3 and the minimum biofuel sales price found in this project was USD 1.30/dm3. The sensitivity research found that material costs (organic matter + paper), bio-oil yield, total project investment and electricity, respectively, are the variables that most affect the minimum biofuel sales price.

Implementation of anaerobic digestion for valorizing the organic fraction of municipal solid waste in developing countries: Technical insights from a systematic review

Anaerobic digestion (AD) as a waste management strategy for the organic fraction of municipal waste (OFMSW) has received attention in developed countries for several decades, leading to the development of large-scale plants. In contrast, AD of OFMSW has only recently drawn attention in developing countries. This systematic review was carried out to investigate the implementation of AD to treat the OFMSW in developing countries, focusing on assessing pilot and full-scale AD plants reported in the last ten years. Studies that met the selection criteria were analyzed and data regarding operating parameters, feedstock characteristics, and biogas, digestate, and energy production were extracted. As outlined in this systematic review, AD plants located in developing countries are mostly one-stage mesophilic systems that treat OFMSW via mono-digestion, almost exclusively with the aim of producing electrical energy. Based on the analysis done throughout this systematic review, it was noted that there is a large difference in the maturity level of AD systems between developing and developed countries, mainly due to the economic capacity of developed countries to invest in sustainable waste management systems. However, the number of AD plants reported in scientific papers is significantly lower than the number of installed AD systems. Research articles regarding large-scale implementation of AD to treat OFMSW in developed countries were analyzed and compared with developing countries. This comparison identified practices used in plants in developed countries that could be utilized in the large-scale implementation and success of AD in developing countries. These practices include exploiting potential products with high market-values, forming partnerships with local industries to use industrial wastes as co-substrates, and exploring different biological and physical pretreatment technologies. Additionally, the analysis of capital and operational costs of AD plants showed that costs tend to be higher for developing countries due to their need to import of materials and equipment from developed countries. Technical, economical, and political challenges for the implementation of AD at a large-scale in developing countries are highlighted.

Pilot-Scale Anaerobic Co-Digestion of Food Waste and Polylactic Acid

Bioplastics are frequently utilized in daily life, particularly for food packaging and carrier bags. They can be delivered to biogas plants through a separate collection of the organic fraction of municipal waste (OFMSW). The increased demand for and use of bioplastics aimed at mitigating plastic pollution raises significant questions concerning their life cycle and compatibility with waste management units. Anaerobic digestion (AD) in OFMSW is a valuable resource for biogas production. In this work, the valorization of poly-L-lactic acid (PLLA) composed of food waste within the Biowaste to Bioplastic (B2B) Project framework was studied in laboratory and pilot-scale anaerobic liquid conditions. Taking into account that the addition of PLLA to biowaste can increase biogas production, we performed laboratory-scale anaerobic tests on food waste enriched with different molecular-weight PLLAs produced from food waste or commercial PLLA at a mesophilic temperature of 37 °C. PLLA with the highest molecular weight was subjected to AD on the pilot scale to further validate our findings. The addition of PLLA increased biogas production and had no apparent negative impact on the operation of the reactors used in the laboratory or on the pilot scale. Biogas production was higher when using PLLA with the lowest molecular weight. In the pilot-scale experiments, co-digestion of FW with PLLA increased biogas production by 1.1 times. When PLLA was added to the feed, biomethane was 8% higher, while volatile solids (VS) and total chemical oxygen demand (TCOD) removal were almost the same. Importantly, no effect was observed in the operation of the digesters.

Dynamic Simulation and Thermoeconomic Analysis of a Novel Hybrid Solar System for Biomethane Production by the Organic Fraction of Municipal Wastes

The anaerobic digestion of the organic fraction of municipal solid waste and the biogas production obtained from its stabilization are becoming an increasingly attractive solution, due to their beneficial effects on the environment. In this way, the waste is considered a resource allowing a reduction in the quantity of it going to landfills and the derived greenhouse gas emissions. Simultaneously, the upgrading process of biogas into biomethane can address the issues dealing with decarbonization of the transport. In this work, the production of biogas obtained from the organic fraction of municipal solid wastes in a plug flow reactor is analyzed. In order to steer the chemical reactions, the temperature of the process must be kept under control. A new simulation model, implemented in the MatLab® environment, is developed to predict the temperature field within the reactor, in order to assess how the temperature affects the growth and the decay of the main microbial species. A thermal model, based on two equilibrium equations, is implemented to describe the heat transfer between the digester and the environment and between the digester and the internal heat exchanger. A biological model, based on suitable differential equations, is also included for the calculation of the biological processes occurring in the reactor. The proposed anaerobic digestion model is derived by the combination of these two models, and it is able to simultaneously simulate both thermal and biological processes occurring within the reactor. In addition to the thermal energy demand, the plant requires huge amounts of electricity due to the presence of a biogas upgrading process, converting biogas into biomethane. Therefore, the in-house developed model is integrated into a TRNSYS environment, to perform a yearly dynamic simulation of the reactor in combination with other renewable technologies. In the developed system layout, the thermal energy required to control the temperature of the reactor is matched by a solar thermal source. The electrical demand is met by the means of a photovoltaic field. In this work, a detailed thermoeconomic analysis is also proposed to compare the environmental impact and economic feasibility of a biomethane production plant based on a plug flow reactor and fed by renewables. Several economic incentives are considered and compared to determine the optimal solution, both in terms of energy and economic savings. The plant is designed for the treatment of a waste flow rate equal to 626.4 kg/h, and the biomethane produced, approximately 850 tons/years, is injected into the national gas grid or supplied to gas stations. In the proposed plant, a solar field of an evacuated tube collector having a surface of approximately 200 m2 is able to satisfy 35% of the thermal energy demand while over 50% of the electric demand is met with a photovoltaic field of 400 m2. A promising payback time of approximately 5 years was estimated.

Community composting strategies for biowaste treatment: methodology, bulking agent and compost quality

The European Union’s commitment to increase recycling and recovery rates of municipal solid waste requires significant changes in current waste management. Local governments are developing various strategies for treating the organic fraction of municipal waste (biowaste) via composting. Community composting centres (CCC), green waste collection, treatment points and community gardens are some of these new approaches. Population density and spatial distribution, together with the existence of community green areas, determine the location of the various infrastructures for recycling local biowaste. The composting process consumes high amounts of bulking agent (BA) necessary to provide the structure that allows, amongst other uses, biowaste aeration and microbial surface colonisation. Shredded green waste from parks, gardens and households can be used as BA in community composting and home composting. In this study, a total of 46 compost samples obtained from CCC with two types of handling were analysed: 22 samples treated by vertical flow (VF) and 24 samples treated by horizontal flow (HF). The HF model allowed better use of the volume of modular composting units and the VF model required less effort and time for the CCC operator. Mature, stable and high-nutrient-content composts were obtained with both models. These composts met the legal requirements to be used as an organic amendment, and they can be delivered to the participants or used in community gardens in the municipality.

Strategies for the Sustainable Management of the Organic Fraction of Municipal Waste

The organic fraction of municipal waste, OFMW, management is one of the main concerns for urban waste managers in developed countries. Composting this biodegradable urban waste and using the compost in agricultural activities is a quickly growing method and is a viable option to manage urban waste in both the developed and the developing world. This research presents the example of the management proposal for Cartagena city in Spain, in which the technical and environment feasibility has been studied. This work aimed to evaluate the composting of a mixture of different residues, namely organic waste, pruning, and Posidonia oceanica (L.) Delile, which was collected from the beaches of the municipality while cleaning. Mixtures 1, M1 (composed of 20% OFMW and 40% pruning and seaweed) and 3, M3 (composed of 30% OFMW and 70% pruning) proved to be the best to reach the ideal compost (1.23-0.08-1.28 NPK and 2.22-0.33-3.45 NPK, respectively). An extreme mixture, M2, was evaluated (50% PO; 50% pruning) but poor results were obtained due to a non-optimal initial C/N by not containing OFMW. At the same time, the volumes by urban nucleus and the viability of different composting strategies have been studied, proposing that 180,000 inhabitants use the centralized composting plant and almost 31,000 inhabitants use self-composting and community composting. Considering the carbon footprint of this management, the value was 50% lower than the total management in a centralized plant. Moreover, the final use of compost is optimum with self-composting and community composting because it is nearest to agricultural consumptions, also reducing the transport of the final product.

Barriers in biogas production from the organic fraction of municipal solid waste: A circular bioeconomy perspective

Biogas-based circular bioeconomy can provide a long-term way out of the organic fraction of municipal solid waste. The barriers to biogas production are obstructing the growth of the biogas-based circular bioeconomy. This study provides a comprehensive analysis of the barriers to biogas in developing countries for the wider implementation of biogastechnology. Twenty barriers are identified and categorized into technical, logistical, institutional, and social dimensions. The analytical hierarchy process is applied to rank the barriers. The result of barrier ranking shows that the lack of appropriate segregation facilities is the most crucial barrier, followed by waste characteristics variation, and inconsistent supply. This study will provide an outline for rational decision-making in the sustainable organic fraction of municipal waste management.

Assessment of the Possibilities for the Use of Selected Waste in Terms of Biogas Yield and Further Use of Its Digestate in Agriculture.

The utilization of municipal waste and sewage sludge as a source of energy is technically very difficult due to high variability of their physical and chemical properties. The aim of this study was to evaluate the efficiency of the conversion of biomass contained in the whitewater fraction of municipal waste and sewage sludge by means of methanogenesis. The second objective was to assess the chemical composition of the digestate in the context of its use for fertilizer purposes. The whitewater fraction of municipal waste and sewage sludge was subjected to methanogenesis under static experimental conditions, according to DIM DIN 38414 methodology. The methanogenesis of concentrated substrates used in agricultural biogas plants was taken as a reference to evaluate the efficiency of the process. The organic fraction of the municipal waste was characterized by approximately 30% lower value of the soluble COD, with a comparable level of total COD compared to other materials. The total biogas yield, i.e., 404 dm3 per 1 kg of dry weight of the batch, was measured in the facility with sewage sludge. In COD value, this is 0.232 dm3·g O2 COD. In the case of corn, these values were, respectively, 324 dm3 and 0.193, and for the organic sub-sieve fraction of municipal waste, 287 dm3·kg−1 dw or 0.178 dm3·g O2 COD, respectively. The type of fermented material did not affect the intensity of biogas production. The maximum level of biogas production occurred between the 13th and 15th day of the process. The digestate obtained in the process of methanogenesis of corn silage and the organic fraction of municipal waste was characterized by good parameters in terms of possible use for fertilization purposes.

Impacts of gasification biochar and its particle size on the thermal behavior of organic waste co-composting process

This work investigates the effects of gasification biochar on the thermal behavior of organic municipal waste composting. Two different biochar granulometries were mixed in a 3% w/w share with the organic fraction of municipal waste and tested in nine (three per thesis and three as control) reactors of 1 m3 of volume, designed to simulate full-scale aerated static piles. The temperatures of each composter were monitored for 31 days of the active composting phase and used as key parameters for air flow tuning. After the active phase was completed, the air was turned off and the temperatures were monitored for an additional 31 days during compost maturation. Results show that biochar-aided composters run 4 °C hotter and are more stable in temperature compared to the control thesis. Experimental data were used as a basis for thermal energy modeling: the addition of fine biochar to composting material increased the thermal energy production by 0.5 MJ kg−1 compared to the control thesis; coarse biochar increased the thermal energy production by 0.4 MJ kg−1. The standard composting process, without biochar, produced 2.5 MJ kg−1. Results might serve as a starting point for further considerations in terms of composting time reduction, improvement of the final product and reduction of process related issues, such as undesired anaerobic decomposition, leachate production and temperature instability.

Solid state anaerobic digestion of water poor feedstock for methane yield: an overview of process characteristics and challenges

Solid state anaerobic digestion (SSAD) of water poor feedstock may be a promising technology for energy recovery. Feedstocks having high solid concentration like lignocellulosic biomass, crop residues, forestry waste and organic fraction of municipal waste may be the appropriate feedstock for its biochemical conversion into energy carries like biomethane through SSAD. Compared to liquid state anaerobic digestion (LSAD), SSAD can handle higher organic loading rates (OLR), requires less water and smaller reactor volume and may have lower energy demand for heating or stirring and higher volumetric methane productivity. Besides these, pathogen inactivation may also be achieved in SSAD of biodegradable waste. Around 60% of recently built AD systems have adopted SSAD technology. However, the process stability of an SSAD system may have several constraints like limited mass transfer, process inhibitors and selection of digester type and should be addressed prior to the implementation of SSAD technology. In this article, a comprehensive overview of the key aspects influencing the performance of SSAD is discussed along with the need for mathematical modelling approaches. Further to this, reactor configuration for SSAD and digestate management requirement and practice for solid-state condition are reviewed for a better insight of SSAD technology

Municipal waste generation in Heilongjiang Province (People’s Republic of China) in 2010–2018: the impact of urbanization and the level of well being of the population

In this paper, the authors consider the conceptual issues of creating an effective regional model of solid municipal waste management in Heilongjiang Province (China). The article substantiates the principles and defines the conditions for the implementation of an integrated solid municipal waste management system in Heilongjiang Province, based on the formation of an organized recycling system through the development of territorial production clusters. The authors analyzed the changes in the rate of generation of solid municipal waste from 2010 to 2018, the impact on the amount of generation of the level of well-being and population size. The paper shows that the amount of municipal solid waste generation per capita had a maximum value in 2010–2011 — 204.1–207.8 kg/year, but by 2018 it had decreased to 139.1 kg. A decrease in the intensity of solid municipal waste generation was observed against the background of an increase in GRP: studies have not confirmed the link between waste generation and increased well-being of residents. The correlation analysis of the relationship between the total population and the formation of municipal solid waste revealed an average direct relationship. The authors made a forecast of solid municipal waste generation in the province and the Harbin Industrial Corridor cluster. The expediency of creating a cluster for the management of solid municipal waste on the territory of the «Harbin industrial corridor» is noted. The main problem that needs to be justified in the regional concept of solid municipal waste management is the segregated collection of the organic fraction of municipal waste, which in the foreseeable future will account for more than 50 % of the total waste flow. The optimization of the spatial and logistics scheme for the placement of infrastructure facilities in Heilongjiang province will allow achieving the sustainable functioning of the system and will lead to a significant increase in the use of the resource potential of solid municipal waste.

Solid-state anaerobic co-digestion of organic fraction of municipal waste and sawdust: impact of co-digestion ratio, inoculum-to-substrate ratio, and total solids.

Municipal solid waste contains mainly organic wastes that can be a good source for anaerobic digestion. Solid-state anaerobic digestion is an affordable and suitable technique to mitigate the organic fraction of municipal solid waste (OFMSW). However, as the organic loading of OFMSW is high, co-digestion with other materials can improve the system's performance. This study aimed to investigate the performance of the co-digestion of OFMSW and sawdust and study the parameters affecting its performance. Based on the experiments, the optimum sawdust/OFMSW ratio was achieved 1:2 with the methane production of 0.3L/g VS. In addition, the inoculum-to-substrate ration (I/S) was investigated at 1:4, 1:2, 1:1, 2:1 ratios. The best result was obtained at 2:1 ratio with a total methane yield of 0.28 L/g VS. The results also indicated that I/S ratios less than 1:1 led to fatty acid accumulation and acidic pH condition. The effect of total solids content on the co-digestion process was also examined in this study. According to the results, as the total solids increased, the biomethane yield decreased while the biogas content increased.

Evaluation of the performance of integrated bioreactors for anaerobic digestion of organic wastes to biogas

The evaluation of the performance of an integrated bioreactor was carried out using organic municipal waste as the substrate. The test rig of the coupled bioreactor was designed and fabricated for experimented studies of anaerobic digestion of organic fraction of municipal waste. The first module up-flow bioreactor (UASB), has volume of 76 liter, the second module which was designed as twin in bioreactor with central dispensing unit has a total void volume of 76 liters. The test rig has a control panel which can be switch off and on from the experiment the maximum biogas yield was obtained in OLR3 module 11 with 1577 ml/stp followed by OLR1 module 1 with 1572 ml/stp. The least was noticed from the twin reactor OLR2 module 11 with 895 ml/stp. The accumulative biogas yield and R-values obtained show close agreement between observed and theoretical postulate.

Environmental consequences of the treatment of corn contaminated by aflatoxin B1 with co-digestion and co-composting in a life cycle perspective.

Global environmental performances of anaerobic co-digestion and co-composting of aflatoxin B1 (AFB1) contaminated corn were investigated by a life cycle assessment approach. Anaerobic co-digestion of pig slurry and corn with 25 μgkg-1 ww AFB1 concentration resulted able to generate 627 NLkgVS-1 of biogas with a reduction of the AFB1 concentration in the digestate of 44%. At AFB1 concentration of 100 μg kg-1 ww, the process resulted strongly inhibited with a biogas generation of 122 NLkgVS-1 and AFB1 concentration reduction in the digestate of 25%. Co-composting of 100 μg kg-1 dw AFB1 contaminated corn with other substrates as organic fraction of municipal waste, pig slurry, and other lignin-cellulosic residues showed a removal efficiency of AFB1 ranging from about 80 up to 95% depending on the different mixtures adopted. Environmental consequences associated to the removal of 1 mg of AFB1 in different scenarios investigated, including also the use on land of the digestate and of the compost, indicated that global warming was affected equally by co-digestion and co-composting, about 95 kgCO2eq. Co-digestion showed also the possibility of achieving avoided emissions of about - 0.007 kgNMVOCeq, - 2.5E-3 kgPeq, and - 30CTUe. Benefits concerning resource depletion resulted higher for co-composting due to the high amount of mineral fertilizer replaced. Contribution of AFB1 in the determination of human health (DALY) resulted lower than about 4% for co-digestion and practically negligible for co-composting.

Sequential bioethanol and methane production from municipal solid waste: An integrated biorefinery strategy towards cost-effectiveness

The organic fraction of municipal waste (OFMW), source-sorted (SS-OFMW) and non-sorted (NS-OFMW), was used as raw material for the sequential production of bioethanol and biogas. Non-isothermal and simultaneous saccharification and fermentation (NSSF) resulted in maximum ethanol concentrations of 51 g/L and 26 g/L for SS-OFMW and NS-OFMW samples, showing overall process yields of up to 80 % and 59 %, respectively, even without subjecting substrate to hydrothermal pretreatment. Subsequently, the solid residues resulting from the fermentation were further subjected to anaerobic digestion (AD), showing a methanogenic potential of 384 ± 6 mL CH4/g of volatile solids (VSin) and 322 ± 3 mL CH4/g VSin, respectively. These methane yields were similar or even higher to those obtained when using non-fermented OFMW substrates (SS-OFMW: 380 ± 18 mL CH4/g VSin and NS-OFMW: 239 ± 4 mL CH4/g VSin), highlighting NSSF as a beneficial step to enhance methane yields during AD. Overall, bioconversion of OFMW would benefit from coupling bioethanol and biogas production since the biogas produced might be further employed as bioenergy source to compensate operational costs.

Elemental concentration and migratability in bioplastics derived from organic waste

In line with the Circular Economy approach, the production of polyhydroxyalkanoate (PHA) with organic waste as the feedstock may a biotechnological application to reduce waste and recover high-value materials. The potential contaminants that could transfer from bio-waste to a PHA include inorganic elements, such as heavy metals. Hence, the total content and migratability of certain elements were evaluated in several PHA samples produced from different origins and following different methods. The total content of certain elements in PHA ranged between 0.0001 (Be) and 49,500 mg kg−1 (Na). The concentrations of some alkaline (Na and K) and alkaline earth (Ca and Mg) metals were highest, which are of little environmental concern. The feedstock type and PHA stabilisation and extraction procedures affected the element contents. Several sets of experiments were conducted to evaluate the migration of elements from the PHA samples under different storage times, temperatures, and pH levels. The total contents of some heavy metals (As, Cd, Fe, Hg, Ni, Pb, and Zn) in PHA produced from fruit waste or crops (commercial PHA) were lower than those in the PHA samples produced from the mixture of the organic fraction of municipal waste and sludge from wastewater treatment. Both the PHA obtained by extraction from wet biomass (acid storage) with aqueous phase extraction reagents and commercial PHA were below the migration limits stipulated by the current Toy Safety Directive and by Commission Regulation (EU) October 2011 on plastic materials and articles intended to come into contact with food under frozen and refrigerated conditions.

Mesophilic and Thermophilic Anaerobic Digestion of Organic Fraction Separated during Mechanical Heat Treatment of Municipal Waste

The objective of this study was to investigate the effect of process temperature on semi-continuous anaerobic digestion of the organic fraction separated during autoclaving of municipal waste. Tests were carried out in reactors with full mixing. Biogas production was higher in thermophilic conditions than in mesophilic conditions (0.92 L/g volatile solids at 55 °C vs. 0.42 L/g volatile solids at 37 °C, respectively). The resulting methane yields were 0.25-0.32 L CH4/g VS and 0.56–0.70 L CH4/g VS in mesophilic and thermophilic conditions, respectively. In both variants, the methane share was over 70% v/v. This work also discusses the potential impact of Maillard compounds on the efficiency of the fermentation process, which were probably produced during the process of autoclaving of municipal waste. These results indicate that, after autoclaving, the organic fraction of municipal waste can be an effective substrate for anaerobic digestion in thermophilic conditions.

Economic and Environmental Analysis of Small-Scale Anaerobic Digestion Plants on Irish Dairy Farms

The European Union’s (EU) climate and energy package requires all EU countries to reduce their greenhouse gas (GHG) emissions by 20% by 2020. Based on current trends, Ireland is on track to miss this target with a projected reduction of only 5% to 6%. The agriculture sector has consistently been the single largest contributor to Irish GHG emissions, representing 33% of all emissions in 2017. Small-scale anaerobic digestion (SSAD) holds promise as an attractive technology for the treatment of livestock manure and the organic fraction of municipal wastes, especially in low population communities or standalone waste treatment facilities. This study assesses the viability of SSAD in Ireland, by modelling the technical, economic, and environmental considerations of operating such plants on commercial Irish dairy farms. The study examines the integration of SSAD on dairy farms with various herd sizes ranging from 50 to 250 dairy cows, with co-digestion afforded by grass grown on available land. Results demonstrate feedstock quantities available on-farm to be sufficient to meet the farm’s energy needs with surplus energy exported, representing between 73% and 79% of the total energy generated. All scenarios investigated demonstrate a net CO2 reduction ranging between 2059–173,237 kg CO2-eq. yr−1. The study found SSAD systems to be profitable within the plant’s lifespan on farms with dairy herds sizes of >100 cows (with payback periods of 8–13 years). The simulated introduction of capital subvention grants similar to other EU countries was seen to significantly lower the plant payback periods. The insights generated from this study show SSAD to be an economically sustainable method for the mitigation of GHG emissions in the Irish agriculture sector.

Anaerobic Co-digestion of Food Waste with Cow Manure

The composition of waste generated in urban areas of Nepal is primarily decomposable which provides scope to convert the waste into energy. In addition, organic fraction of municipal waste is a serious environmental and economic burden in Nepal. In this study, samples from food waste were taken from household of Biratnagar Metropolitan city and Kathmandu University Canteen, Dhulikhel. The samples were analyzed for physical and chemical properties and biogas production. The feed containing 6% TS were analyzed for the potential of biogas production from the canteen food waste (CFW) of Kathmandu University (KU) and household food waste (HFW) from Biratnagar in ambient and control temperature (35 ℃) in a batch reactor. This was also conducted for food waste mixed with 30% cow manure in both the conditions. The average total solid and volatile solid for BFW were 17.7 and 93.2% of TS and CFW were 19.9 and 90.2% of TS, respectively. In every run of the experiment, the volume changes of gas were monitored. Both in the ambient and the controlled temperature, biogas production and yield were higher when 30% cow dung as inoculum was added in both samples. Moreover, the biogas production and yield of CFW was also higher than the BFW at different conditions. This shows that food wastes characteristics and biogas production potential varies depending on the source of the food waste, inoculum added and operating condition for the anaerobic digestion process.

OPTIMIZATION OF THE ANAEROBIC DIGESTION PROCESS BY USING MULTI-CRITERIA ANALYSIS

Anaerobic co-digestion (AcD) of various fractions of organic wastes (OW) is a good method to solve the problem of OW management and energy recovery. The process is influenced by many factors, such as physical and chemical characteristics of the waste. This study is engaged with optimization of AcD process investigation; a mathematical model was developed, on the basis of characteristics of OW with the aim to achieve a maximum biogas production. Different fractions of OW available at the territory of the city of Niš, organic fractions of municipal waste (OFMSW), cow manure (CM), pig manure (PM), wheat straw (WS), maize silage (MS), hen manure (HM) and a theory-calculated amount of sludge from wastewater treatment plant (WWS) were observed. By applying a multi-criteria optimization and observing a carbon, nitrogen, lipid and lignin content in OW, a mathematical model was developed. The criteria for the model were to achieve a maximum carbon and lipid content and minimize nitrogen and lignin content. Two different mixtures of OW were also examined. The first mixture included OFMSW, CM, PM, MS, HM, WS, whereas the second one included the fractions from the first mixture and sludge from the wastewater treatment plant. The results show that in the first optimal mixture there is 10% of HM, 10% PM and 10%MS, 24% OFMSW, 34%CM, and 12%WS. The share of carbon is 44.1%, nitrogen 2.4%, lipid 5.8%, and lignin 3.9%, while the C/N ratio is 17.7. The content of the second optimal mixture involves 10% of HM, 10% of PM, 10% of MS, and 10% of WWS, 23% of OFMSW, 26% of CM, and 11% of WS. Carbon content is 43.2%, nitrogen 2.7%, lipid 6.1% and lignin 4.1%, while the C/N ratio is 15.6. From the aspect of biogas production, the results showed that the first optimal mixture had 17.6% higher production than the second optimal mixture.