Further characterization of the biochar was carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The aim of the study is to suggest the optimum way to manage MSW in Bangladesh.
Municipal Solid Waste in Bangladesh
- MSW Management in Dhaka City
- MSW Management in Chittagong City
- MSW Management in Khulna City
- MSW Management in Sylhet City
- MSW Management in Rajshahi City
- MSW Management in Barisal City
- MSW Management in Narayanganj City
The waste collection structure in Dhaka can be divided into primary and secondary collection. Various sources have reported different amounts regarding the waste generated in Khulna city.
MSW Valorization Technologies
Landfilling and Anaerobic Digestion
- Anaerobic Digestion Reactions
- Anaerobic Digestion of MSW in Bangladesh
Anaerobic digestion reactions are carried out in reactors or chambers called digesters in the absence of oxygen. In Bangladesh, especially in rural areas, there is a significant amount of small-scale anaerobic digestion processes for biogas production [57].
Composting
- Types of Composting Systems
- Composting System Implementation
- Composting in Bangladesh
- Negative Impacts of Composting
In the United States (US), many homeowners are establishing individual composting systems and cooperating with each other to provide kitchen and yard waste, manage the composting system, and use the compost [60]. Various communities in the USA have implemented and benefited from community composting systems [65].
Incineration and Combustion
- Combustion/Incineration Technologies
- Environmental Impacts of MSW Combustion/Incinera-
- MSW Combustion Potential in Bangladesh
The released flue gas from a fluidized bed reactor is passed through a boiler for heat recovery. Particles can also be removed using electrostatic precipitators and cyclone separators, which use electrostatic force on electric plates and centrifugal force, respectively, to separate particles from the flue gas [85]. In SCR, ammonia is used to reduce NOx gases in the presence of vanadium oxide or titanium oxide catalyst; SCR can remove up to 90% of NOx from the flue gas.
In SNCR, ammonia is injected into the hot flue gas at high temperatures (870–1150◦C) to reduce NOxto N2and H2O [73] without the use of any catalyst.
Hydrothermal Treatment
- Hydrothermal Carbonization (HTC)
- Hydrothermal Liquefaction (HTL)
- Hydrothermal Gasification (HTG)
The study considered the price of biocrude to be expensive and recommended changing the HTL plant to reduce the final fuel price. It is difficult to understand whether HTL plants will be feasible to produce bio-oil from municipal waste in the future. However, the use of alkaline catalysts makes more sense because solid catalysts can be easily poisoned by the alkalis and sulfur present in the system [109, 112].
At this point, there are only a limited number of studies on the HTG of MSW in the literature, and it is expected that more studies will be conducted in the future to improve the understanding of the process.
Pyrolysis
- Pyrolysis Types and Heating Methods
- Pyrolysis of MSW
- MSW Pyrolysis in Bangladesh
Heat for the pyrolysis process can be provided from the exothermic reactions that take place in pyrolysis; initially, part of the feedstock is burned to produce hot gases that can sustain the pyrolysis reactions by transferring heat through the heat transfer surface. All pyrolysis processes produce solids, liquids and gases in proportions that depend on the type of pyrolysis performed [115]. A fluidized bed furnace uses facility D; The LHV obtained from volatiles and char is lower than that of char obtained from rotary kilns [119].
However, pyrolysis processes for MSW treatment are inefficient and they draw more energy into the carbon production than the energy that can be extracted from the carbon produced [119].
Gasification
- Gasification Reactions and Types of Gasifiers
- MSW Gasification Technologies
- Environmental Concerns of MSW Gasification Plants . 48
- Gasification in Bangladesh
Increasing the steam supply shifts the equilibrium position to the right in the shift conversion reaction, increasing the yield of carbon dioxide and hydrogen; However, in the gasifier the concentration of carbon monoxide decreases. A boiler is used to recover the thermal energy from the hot flue gas and the charcoal produced in the primary chamber is oxidized to provide thermal energy for subsequent gasification [132]. Tar produced during gasification is a concern for gasification plants because tar can cause blockages and inefficiencies in the process [130, 133].
It was possible to completely remove the tar and significantly increase the gas yield by maintaining the gasifier temperature at 800 °C and the steam to MSW ratio at 0.42 [133].
MSW Valorization Technology Selection
As far as the author knows, gassing is not an established process in Bangladesh. Articles propose the use of rice husks and sugar cane bagasse as raw materials in gasification processes to generate electricity. Although rice husk gasification is not financially viable compared to utility-supplied electricity, it is an attractive alternative to diesel-generated electricity [140].
Sugarcane production in Bangladesh was 5.15 million tons in 2010–2011, and sugar factories in Bangladesh produced about 1.29 million tons of sugarcane [141].
Experimental Setup
The heat gun has two settings at level “I” and level “II” for air outlet temperatures of 350◦C and 500◦C respectively. The height of the reactor from the top of the table (see Figure 3.1) was changed to control the distance between the air duct and the reactor. The design shield (2f t×2f t×2f t) was designed using SpaceClaimR software and built using BUET foil-on-metal.
The front of the shield has a sliding glass panel that is used to access the inside of the shield.
Temperature Calibration
However, due to the presence of a large amount of water in the reactor and the high specific heat capacity of water, the temperature increase due to the overall exothermic reaction is negligible and will not affect the temperature calibration. For the final experiments in this study, only the surface temperature is recorded and therefore the surface temperature is reported. However, it should be emphasized that for purposes of reaction conditions, the internal temperature of the reactor should be referred to Table 4.1 in Section 4.2.
MSW Sampling and Proximate Analyses
Where is the number of samples, t∗ is the student statistic corresponding to the desired confidence level, is the standard deviation, is the desired precision level, and ∗ is the mean. Where V M is volatile matter, Wc is the weight of the lid and cap, Wi is the initial weight, Wf is the final weight, and Bis the moisture percentage. The HHVs for biochar products were calculated using the established empirical correlation based on the literature [146].
HHV = [(T)(E)−e1−e2−e3−e4]/g (3.5) Where, T is the corrected temperature rise, E is the energy equivalent obtained from calorimeter standardization, e1 is the correction for heat of formation of nitric acid, e2 is the correction for the heat of formation of sulfuric acid, e3 is the correction for the heat of combustion of the ignition wire, and e4 is the correction for the ignition energy and sample mass.
Factorial Design
Experimental Method
Elemental analysis of the parent MSOW and produced biochar was carried out using the Energy Dispersive X-ray Spectroscopy (EDS) technique at the Department of Glass and Ceramics Engineering at BUET; Scanning electron microscopy (SEM) was also performed on the samples. A Schottky field emission scanning electron microscope (Model: JEOL JSM-7600F, Japan) equipped with an energy dispersive X-ray spectrometer was used.
Introduction
Temperature calibration
MSW Sampling and Proximate Analyses Data
From Table 4.5, it can be seen that the HHV of MSOW determined in this study is almost double the literature value reported from 2005 in Bangladesh and 2007 in USA. This may be due to the change in the composition (higher percentage of carbon) of the waste in recent times and different locations.
Experimental Evaluation
The solids yield and HHV of the biochar product are shown in Figure 4.1 and Figure 4.2 respectively. From the ash analysis of each biochar product and the EDS data, dry ash-free elemental compositions of the biochar products were determined using Equation 4.1 and are listed in Table 4.7. The result of experiments in the literature revealed that the percentage of ash and solid carbon in the initial MSOW sample is almost doubled in biochar or hydrochar and the percentage of volatile matter is almost halved due to the volatile matter leaving the solid matter [91].
The ash content, measurements of the biocoal and direct analysis of the mother sample were used to determine the.
Energy Retention in Biocoal
The calculated calorific value (HHV) for the biochar produced in this study ranged from MJ/kg. 90% of the water load, the most (83%) of the energy was retained in the biochar relative to the MSOW parent sample.
SEM Analysis
The presence of significant amount of ash in MSOW of Bangladesh lowers the calorific value of the produced biochar. Biochar obtained from DNCC MSOW had significant amounts of ash compared to other literature reports. Based on the factorial model of the HTC experiments in MSOW, the optimal condition was determined.
Moreover, the biochar produced in the optimum condition retained about 83% of the energy content of the parent MSOW.
Recommendations
Experimental setup for hydrothermal carbonization
The experimental setup was housed within a draft shield to minimize heat loss and fluctuations in the convective heat transfer rate.
Design of the draught shield
Temperature calibration experiment
However, due to the size limitation of the reactor, it was not possible to produce 1 g of biochar product. The biochar product was fired at 600 °C for 30 minutes in a muffle furnace (Nabertherm, L/5/12/P330, Germany) to obtain the ash content. We used about 1g of samples; the experiments were repeated and the average values were taken.
The biocoal product was then dried overnight at 105◦C in an oven (Model: DIGISYSTEM, DSO-D, Taiwan), followed by determination of the percent solids yield.
Process Flow Diagram
26] International PC and Limited YEC, The Study on Solid Waste Management in Dhaka City, Technical Report, 2005. Effects of Solid Waste in Barisal City of Bangladesh, in Proceedings of the Waste Safe 20154th International Conference on Solid Waste Management in the Developing Countries . 73] WASTE TO ENERGY A Technical Review of Municipal Solid Waste Thermal Treatment Practices, Technical Report, Stantec Consulting Ltd., 2011.
78] Grillo LM, Municipal Solid Waste (MSW) Combustion Plants, in Waste to Energy Conversion Technology, Woodhead Publishing Limited, 2013. 84] Yusoff MHM and Zakaria R, Incineration of Municipal Solid Waste in a Fixed Bed Incinerator for Energy Recovery, Journal of Applied Sciences , 2012. 119] Hwang IH and Kawamoto K, Research on Carbonization Facilities for the Treatment of Municipal Solid Waste in Japan, Waste Management pp.
Solid yield percentage (dry basis) of HTC experiments at 90% water loading 66
EDS image of biocoal sample from experiment 12A
EDS image of parent MSOW
The moisture content of each of the solid HTC samples is analyzed using a moisture analyzer (Model: RADWAG MA 110.R., Poland). The amount of volatile matter can be calculated by subtracting the moisture content from the balance between 100 and solids yield. Figure 4.5(c) shows that the highest amount of flammable organic substances was obtained at 300◦C, 40 minutes and 90% water.
Composition of solids obtained via HTC at 90% water loading
3] Khan D, Kumar A and Samadder SR, Influence of socio-economic status on municipal solid waste generation rate, Waste Management, 2016. 18] Alamgir M and Ahsan A, Municipal solid waste and recovery potential: Bangladesh Perspective, Iranian Journal of Environmental Health Science and Engineering p. 48] Nguyen P, Kuruparan P and Visvanathan C, Anaerobic digestion of municipal solid waste as pre-landfill treatment, Bioresource Technology, 2007.
134] Luo S, Zhou Y and Yi C, Syngas production by catalytic steam gasification of municipal solid waste in a fixed bed reactor, Energy, 2012. 139] Zhang Q, Dor L, Fenigshtein D, Yang W and Blasiak W, Gasification of solid municipal waste in plasma gasification melting process, Applied Energy, 2011. 150] Lariviere M, Methodology for sorting municipal solid waste into biogenic and non-biogenic energy, technical report May, 2007.
Energy retention by biocoals obtained at various conditions with 90% wa-
SEM images of the parent and hydrothermally carbonized samples (dried) 74
Sorting and weighing of different MSW fractions from sample
Experiment to determine inside and surface temperature of the reactor
Experiment to determine inside and surface temperature of the reactor
Determining height of the reactor from the table top before an experiment 105
SwageLok valve in use to purge the reactor with nitrogen gas
Parent MSOW organic fraction EDS (1)
Parent MSOW organic fraction EDS (2)
Parent MSOW organic fraction EDS (3)
Parent MSOW organic fraction EDS (4)
Experiment 3 biocoal EDS (1)
Experiment 3 biocoal EDS (1)
Experiment 6 biocoal EDS
Experiment 9 biocoal EDS
Experiment 12A biocoal EDS
Experiment 13A biocoal EDS (1)
Experiment 13A biocoal EDS (2)
Experiment 14 biocoal EDS (1)
Experiment 14 biocoal EDS (2)
Experiment 15A biocoal EDS
Experiment 18B biocoal EDS
Experiment 21 biocoal EDS
Experiment 24A biocoal EDS
Experiment 27 biocoal EDS
Per capita MSW generation rates around the world
Urban population and urban population percentage in Bangladesh in 2001
Per capita waste generation in Bangladesh according to socio-economic
Various MSW Components Generated in Bangladesh in tons/day and as a
MSW physical and chemical properties in Bangladesh
Dhaka City Corporations manpower and equipment
Waste generation and collection trend in Chittagong
MSW Percent Composition in Chittagong in 2009
Landfill or dump sites at major cities of Bangladesh
Anaerobic Digestion Reactions
Typical anaerobic digester parameters
Characteristics of composting systems
Pollutants in flue gas of MSW incineration plants and their treatment
Commercial-scale HTC plants in operation around the world
HTL plant biocrude price reduction strategies
Different types of pyrolysis processes
Char obtained from four Japanese facilities
MSW Plasma Gasfication Plants
Factor levels chosen for factorial design
Full factorial experiment design for three variable factors
Partial factorial design of experiments
Temperature difference on the outer surface and inside of the reactor
MSW composition in Dhaka North City Corporation (wet basis)
HHV obtained for parent MSOW (dry basis)
Proximate analysis of MSOW from DNCC (dry basis)
HHV of MSOW Comparison
Solid yield (dry basis) obtained from the experiments carried out
Elemental composition of biocoal product and parent MSOW sample (dry
Proximate analyses of biocoal products
DNCC MSW Sampling Data
