Anaerobic Digestion, Codigestion of Food Waste, and Chicken Dung: Correlation of Kinetic Parameters with Digester Performance and On-Farm Electrical Energy Generation Potential

Valorization of agro-food waste through anaerobic digestion (AD) is gaining prominence as alternative method of waste minimization and renewable energy production. The aim of this study was to identify the key parameters for digester performance subjected to kinetic study and semicontinuous operation. Biochemical methane potential (BMP) tests were conducted in two different operating conditions: without mixing (WM) and continuous mixing (CM). Three different substrates, including food waste (FW), chicken dung (CD), and codigestion of FW and CD (FWCD) were used. Further kinetic evaluation was performed to identify mixing’s effect on kinetic parameters and correlation of the kinetic parameters with digester performance (volatile solid removal (VS%) and specific methane production (SMP)). The four models applied were: modified Gompertz, logistic, first-order, and Monod. It was found that the CM mode revealed higher values of Rm and k as compared to the WM mode, and the trend was consistently observed in the modified Gompertz model. Nonetheless, the logistic model demonstrated good correlation of kinetic parameters with VS% and SMP. In the continuous systems, the optimum OLR was recorded at 4, 5, and 7 g VS/L/d for FW, CD, and FWCD respectively. Therefore, it was deduced that codigestion significantly improved digester performance. Electrical energy generation at the laboratory scale was 0.002, 0.003, and 0.006 kWh for the FW, CD, and FWCD substrates, respectively. Thus, projected electrical energy generation at the on-farm scale was 372 kWh, 382 kWh, and 518 kWh per day, respectively. Hence, the output could be used as a precursor for large-scale digester-system optimization.

Numerical Demonstration of an Unconventional EGS Arrangement

A new EGS arrangement, Robust EGS (REGS), is studied for its potential benefits for wide-spread applications for clean, carbon-free, electrical energy generation. Numerical simulations are carried out to prove the key benefit of REGS in a simple, but effective, geologic heat exchanger arrangement with large, stabilized fracture aperture and controlled flow zones. The numerical model results show the estimated potential energy capacity and the converted value to electrical energy generation over a 30-year operation time period for two simple REGS arrangements. The results may assist EGS investors and drilling companies in deciding whether the investment and operation can be made profitable for the wide-scale application of REGS for green energy generation.

Energy potential and economic feasibility of biogas: case study of a landfill in Minas Gerais, Brazil

The final disposal of solid waste in landfills may result in the production of a clean and renewable energy through the exploitation of biogas generated in these locations. This study aims to estimate the methane production in a landfill, with a total population of 237,298 inhabitants, and a total generation of waste of 83,561.78 ton/year, in the last year of operation, located in the state of Minas Gerais and evaluate the economic feasibility of a biogas exploitation project in this place, for electrical energy generation. The methane production was estimated by the Intergovernmental Panel on Climate Change (IPCC) methodology, obtaining the maximum methane production value of 6,692,590 mÑ in the last year of operation of the landfill. For economic feasibility analysis, the tools, such as net present value, discounted payback, and internal rate of return, were used with values of R$ 1,323,684.90 for 8 years, 4 months, and 12 days, and 9% per annum, respectively, demonstrating that the implementation of the project for the use of biogas at the landfill was viable, with positive economic return.

Evaluation of Gas Composition Obtained from Gasification of Pellets and Blends with Agricultural Wastes

The gas produced by gasification is more versatile than the original solid biomass and can be applied as raw material for chemical industry and as fuel for the electrical and thermal energy production. Small gasification plants are being considered as an option for electrical energy generation in remote areas where agriculture wastes can be found easily. In this way, the aim of this work was to evaluate the characteristics of the gas composition of co-gasification using pine pellets and blends with agricultural wastes. The experiments were carried out in duplicate in a pilot scale fixed bed downdraft gasifier, GEK Power Pallet 20kW. It was performed experimental runs with 100 % pine pellets, 80 % pine pellets and 20 % agriculture wastes, and 80 % pine pellets with 15.4 % agriculture wastes and 4.6 % of glycerol used as an agglutinant agent. The samples were analyzed by GC-FID/TCD. The moisture of different feedstocks varied between 8.00 and 10.88. The results of the produced gas show an average composition of 37.45% CO and 15.79% H2, and LHV 7,155 kJ/kg for gasification of 100 % pine pellets. While the mixture of pine pellets and agriculture wastes resulted in a gas with 32.13% CO and 20.10% H2, and LHV of 6,663.4 kJ/kg. When added glycerol, the gas composition to CO was 20.52 % and to H2 11.21 % with LHV of 4,507.4 kJ/kg. The results indicate that the gasifier is compatible with the mixture of agricultural residues and pines pellets in co-gasification.

Evaluation of Gas Composition Obtained from Gasification of Pellets and Blends with Agricultural Wastes

The gas produced by gasification is more versatile than the original solid biomass and can be applied as raw material for chemical industry and as fuel for the electrical and thermal energy production. Small gasification plants are being considered as an option for electrical energy generation in remote areas where agriculture wastes can be found easily. In this way, the aim of this work was to evaluate the characteristics of the gas composition of co-gasification using pine pellets and blends with agricultural wastes. The experiments were carried out in duplicate in a pilot scale fixed bed downdraft gasifier, GEK Power Pallet 20kW. It was performed experimental runs with 100 % pine pellets, 80 % pine pellets and 20 % agriculture wastes, and 80 % pine pellets with 15.4 % agriculture wastes and 4.6 % of glycerol used as an agglutinant agent. The samples were analyzed by GC-FID/TCD. The moisture of different feedstocks varied between 8.00 and 10.88. The results of the produced gas show an average composition of 37.45% CO and 15.79% H2, and LHV 7,155 kJ/kg for gasification of 100 % pine pellets. While the mixture of pine pellets and agriculture wastes resulted in a gas with 32.13% CO and 20.10% H2, and LHV of 6,663.4 kJ/kg. When added glycerol, the gas composition to CO was 20.52 % and to H2 11.21 % with LHV of 4,507.4 kJ/kg. The results indicate that the gasifier is compatible with the mixture of agricultural residues and pines pellets in co-gasification.

Generation of Electricity by Microbial Fuel Cells using Industrial Effluent

A microbial fuel cell (MFC) is a device that converts bio-chemical energy into electrical energy during substrate oxidation with the aid of microorganisms (bacteria). The energy contained in waste water is converted to the electrical power by the action of bacteria. The principle of MFC is to transfer electrons from the microorganisms to electron acceptor at a higher electrochemical potential. An experimental study was performed to find the most efficient industrial waste water that can produce highest and stable electrical power by the MFC and to determine the removal rate of pollutant from the waste water by the MFC. Two MFC, namely one PEM MFC and two PEM FMC, has been fabricated for this study. The three different waste water samples used were Dyeing Waste Water-1 (DWW-1), Dairy Industry Waste Water (DIWW) and Dyeing Waste Water-2 (DWW-2). The highest rate of voltage generation is achieved when the MFC was operated with DWW-1 (1.06 V), DIWW (0.95 V) and DWW-2(0.644 V), respectively. Based on the graph pattern the DWW-1 provided the best record in terms of electrical energy generation.