Solid Waste Management in Dhaka City
Solid Waste Management in Dhaka City
– A Review on the Present Status and Possible Solutions
A. H. M. Safayet Ullah Prodhan
Dept. of Biochemistry & Molecular Biology,
Jahangirnagar Univ., Savar, Dhaka-1342
Email : sapu.polock@gmail.com
Aflatun Kaeser
Dept. of Public Administration,
Jahangirnagar Univ., Savar, Dhaka-1342
Email : akzilany777@gmail.com
Abstract
Municipal Solid Waste Management (MSWM) is one of the main environmental problems in Dhaka, the capital city of Bangladesh. About 5000 tons of waste is being generated in Dhaka city every day among which only about more than half portion is properly collected and dumped. So, a huge amount of waste is being mistreated every day. In the present study an effort was made to represent the current waste management (WM) scenario of Dhaka city, how Dhaka City Corporation (DCC) is trying to cope with the WM problem, public concern about some WM practices, the problems created by improper WM system and some possible solutions to the WM problems.
Key words: Dhaka City Corporation; Solid waste; Recycling; Waste to energy.
- Introduction
Dhaka is one of the most densely populated cities in the world having a population of about 20 million in an area of just 360 km2. The total population is growing at a high rate of 1.4%; where as her urban population is growing at a faster rate of 3.4% per annum. The estimated population here by 2040 is 40 million. So, with the increasing rate of population, the rate of waste management problem of the city is also rising keeping a pace to it. In 1985 the total amount of solid waste in the city was 1040 tons/day, which rose to 3500tons/day in 1999 and might rise to 30000tons/day by the year 2020. Though a massive amount of municipal solid waste having 80% organic content and 50-70% moisture is generated every day, only about 50% of the waste is collected properly by DCC and dumped as landfill [1] [2] [3]. The improper management leaves behind a huge amount of uncollected waste, which has been creating environmental hazards in the city.
Dhaka City Corporations DCC, North, and South, have been trying to mitigate the problem taking new initiatives, but the problem seems to be aggravating more and more day by day. This huge waste seems to be beyond control of the DCC alone until the city dwellers come forward together to solve it.
The area required for land filling is increasing proportionally with the growth of waste. It is estimated that by 2020, the required area for landfill will be 206.31 acre to 309.46 acre with the collection efficiency of 50% to 75%.[3] Though from the definition of waste we know that “Waste is an unwanted material that lacks financial value regardless of the time or season because there is no demand for such an item in the market”[4]. But, this idea can be proved wrong by reusing and recycling the waste in a proper way. There are a number of recognized Waste-to-Energy (WtE) technologies in the world right now, which can turn the unwanted waste into energy. Moreover, the waste can be decomposed to create fertilizers. So, in lieu of being a burden, the waste of Dhaka city can become a blessing to the citizens if subjected to modern technology.
So, a comprehensive review on the scenario and problems of the waste management has been a demand of the time for a probable solution to the problem and at the same time turn this huge waste into resources. To perform the present work, we analyzed a number of research works, review articles, different online sources and reports of different government, non-government and international organizations on waste management on Dhaka city as well as other cities of the developed and developing countries. The aim of this review is to demonstrate the current waste management process in a proper way so that the existing problems related to it are minimized. At the same time, the work refers to possible ways and means to convert the municipal solid waste into resources. We strongly believe, if brought into practice, this could help the citizens of Dhaka and other cities to live a better life in an eco-friendly, congenial and sustainable environment, for present and future.
- Existing Waste Management of Dhaka City Corporation
Primarily The DCC (Dhaka City Corporation) is liable for collecting and managing waste in Dhaka, Bangladesh. In spite of limited waste management service of Dhaka, door-to-door community based waste collection from households to local dust bins is considered as a success. Informal waste recycling systems are also highly fruitful in waste recycling and job creations for the poor.
Wastes are normally collected in a non-segregated manner and placed into little containers at households. Wastes are then collected by organizations delegated by DCC in vans to the secondary collection points. Waste trucks then carry the wastes to the landfill sites. A significant portion of the solid waste is operated by an informal market to be recycled. Scavengers (Tokais) collect the recyclable items from landfills and open dustbins and then sell those to a waste recycling dealer (Bhangari). Besides, the Hawkers buy recyclables from door to door and trade with the Bhangari. The items are then washed, dried and sorted by the recycling dealers and traded in the market.
Figure 1: Existing solid waste management system in DCC [5]
DCC does not have the capability to perform regulatory administration of these wastes. Besides, there are no laws to regulate the management of these wastes. So, these wastes are constantly being mixed with solid waste. [7]
DCC is divided into DCC (North) having 36 wards and DCC (South) Having 56 wards. In Dhaka, all the wastes are sent for landfilling in Matuail and Amin Bazar dumping ground. Wastes from 55 wards of Dhaka city are dumped in Matuail, and wastes from 36 wards are dumped in Amin Bazar. 852391 ton waste has been transported by DNCC to the landfill in 2016-2017 which is 24.77% higher than 2015-2016. The typical features of open dump sites in Dhaka city and waste collection trend (in tonnes) in DNCC since 2014-15 are presented below:
Table. 1: Typical features of Landfill sites in Dhaka City [8]
| Salient Features | Landfills of Dhaka | |
| Matuail | Amin Bazar | |
| Area (hectares) | 40 | 20 |
| Condition | In operation | In operation |
| Landfilling Started | 2003 | 2007 |
| Height of MSW deposit | 7 meter | 6.4 meter |
| Distance from the city (km) | 6 | 8 |
| Closed/expected end of life | 2021 | 2023 |
| Average disposal per day | 2000 tons | 1200 tons |
| Current CH4 Status | No recovery | No recovery |
| Ward Covered | 55 | 36 |
DCC (North) might have to manage over 5637728 ton waste in next 5 years. Growth percentage of waste collection in 2015-17 and projected waste volume in DNCC between 2017-18 and 2021-22 is appended in charts below:
Figure 2: Waste collection trend in tones in DNCC from 2014-15
Figure 3: Projected waste volume in DNCC during the period between 2017-18 and 2021-22 [7]
Figure 4: Waste collection growth percentage in DNCC [7]
Figure 5: Projection of future landfill requirement of Dhaka [9]
Landfill demand for disposal of MSW of Dhaka assessed by projecting population and waste generation for the period 2007-2025 is represented in the table below:
| Year | Projected Population | Daily Waste Generation (tons) | Yearly waste generation (M tons) | Cumulative Waste (M tons) | Cumulative Landfill waste volume (Mm3) |
| 2007 | 13.50 | 6750 | 2.5 | 2.5 | 4.93 |
| 2008 | 13.87 | 6934 | 2.5 | 5.0 | 9.99 |
| 2009 | 14.24 | 7122 | 2.6 | 7.6 | 15.19 |
| 2010 | 14.63 | 7316 | 2.7 | 10.3 | 20.53 |
| 2011 | 15.03 | 7515 | 2.7 | 13.0 | 26.01 |
| 2012 | 15.44 | 7719 | 2.8 | 15.8 | 31.65 |
| 2013 | 15.86 | 7929 | 2.9 | 18.7 | 37.44 |
| 2014 | 16.29 | 8145 | 3.0 | 21.7 | 43.38 |
| 2015 | 16.73 | 8367 | 3.1 | 24.7 | 49.49 |
| 2016 | 17.19 | 8594 | 3.1 | 27.9 | 55.77 |
| 2017 | 17.66 | 8828 | 3.2 | 31.1 | 62.21 |
| 2018 | 18.14 | 9068 | 3.3 | 34.4 | 68.83 |
| 2019 | 18.63 | 9315 | 3.4 | 37.8 | 75.63 |
| 2020 | 19.14 | 9568 | 3.5 | 41.3 | 82.61 |
| 2021 | 19.66 | 9828 | 3.6 | 44.9 | 89.79 |
| 2022 | 20.19 | 10096 | 3.7 | 48.6 | 97.16 |
| 2023 | 20.74 | 10370 | 3.8 | 52.4 | 104.73 |
| 2024 | 21.30 | 10652 | 3.9 | 56.3 | 112.50 |
| 2025 | 21.88 | 10952 | 4.0 | 60.9 | 120.49 |
Table 2: Population, waste generation and waste volume in Dhaka city (2007 – 2025) [10]
- Initiatives taken by DCC for Solid Waste Management
Around six thousands mini bins were installed at different points of Dhaka in earlier 2016. But the bins were installed not for houses or business entities, but for pedestrians so that they can put light garbage into those instead of hither and thither. But the pedestrians do not use the bins as was expected. They throw wastes on the street or footpaths. However, the street vendors prefer the bins. [11]
Figure 6: A man discarding an empty water bottle in a bin set up by DCC [12]
DoE has introduced a program by building two waste management plants, which will use solid waste collected from different parts of Dhaka to create compost fertilizer. One such plant will be in Matuail under Dhaka South City Corporation (DSCC) and the other in Amin Bazar under Dhaka North City Corporation (DNCC). Each of the plants will be capable of producing 20 tones compost fertilizer per day from solid waste. DCC expects producing fertilizer out of those plants by early 2018.[13]
Figure 7.1: Before STS Construction
Figure 7.2: After STS Construction
Figure 7.3: Inside the STS
Construction STS in Dhaka has been a noticeable development in waste management. Construction of 52 STS in DNCC has enabled DNCC to remove great number of waste containers from the roads [7]. 45 STSs were planned to be built in DSCC by this time, but only 12 has been completed so far[14]. DNCC plans to build 2-4 STSs in each of 36 wards. In areas of primary collection, the Primary Waste Collection Service Provider (PWCSP), an NGO is coordinating collections from households to STS. In 2016-17, 340 private operators were registered with the PWCSPECIES There are also unregistered operators, who collect wastes from households to STS. Containers on the street were bottlenecks in traffic movements, which were also solved by the construction of STS.
- Public Concern about Waste Management in the City
Door-to-door service and waste dumping %: A study got some data showing that 88 % of upper group, 75 % of middle group and only 30 % of lower group received door-to-door collection service. 51 % of lower group households dumped their waste in vacant lands/river, while only 5% of upper group and 4% of middle group do that.
Figure 8: Door-to-door service and waste dumping % in Dhaka
Waste Segregation, Recycling & Composting: The same study shows that 70% of upper group, 68 % of middle group, and 75 % of lower group were not willing to participate in waste segregation activities. 88% of upper group, 95% of middle group and 100% of lower group were not willing to participate in recycling activities. 91% of upper group, 88% of middle group and only 29% of lower group give or sell recyclable waste. 80% of upper group, 83% of middle group and 96% of lower group were not participating in any community activities. 85% of upper group, 96% of middle group and 98% of lower group were not willing to participate in composting activities. 77% of all respondents replied that they were willing to participate in activities on solid waste management in their communities.[15]
Figure 9: Waste segregation, recycling, composting and community activity status of diff. group of people in Dhaka
Another study expresses that, people ranked natural environment as 6 among 8 sectors suggested for government funding and solid waste dumping as 3 among 8 environmental problems. On average the respondents in Dhaka were willing to pay only 13 TK (0.18 USD) waste collection service charge per month. [16]
- Physical Composition of DCC Solid Waste
Cultural tradition, food habitat socio-economic and climate conditions affect the composition of MSW. Typical characterization of MSW in Dhaka is reflected below:
Figure 10: Typical characterization of MSW in Dhaka [9]
6. Present status of Solid Waste in Dhaka City
The Dhaka City Cooperation estimated that, of the total daily generation of 3500 tons of solid waste (The value is found higher in some recent studies), among them 400 tons go to road side and open space.[6]That means about 11.5% waste remains untreated and these wastes pollute environment. The DCC clearly states that, its collection system cannot cope with the task of handling the large volumes of refuse produced by the ever-growing numbers of city dwellers, and that only 40-50% of the solid waste produced is being collected. 50% of the daily generated waste remains uncollected in the city and disposed at official dump sites. Only 14-17% of the total municipal budget is used for solid waste management which is approximately 0.5 USD per capita per year. As a result, the uncollected waste is primarily dumped illegally in the neighborhood’s streets, wastewater drains, ponds, lakes etc. or managed informally. Uncollected waste has been recognized as the root of inferior environment such as scattered garbage, offensive odor, drain clogging, water pollution and mosquitoes.[6]
- Probable solutions to present problem of Solid Waste Management in Dhaka City
To solve the existing problems regarding waste management in Dhaka city, we have to focus on three sectors:
- Smart dumping and transportation of waste
- Energy generation from waste
- Fertilizer generation from waste
7.1. Smart Dumping and Transportation of Waste
In existing waste management system, the dustbins are located on street and therefore when wastes are overflowed they fall on the street and thus cause environmental pollution. Besides, the dustbins cover a large area of street and hamper traffic movement resulting in traffic jam. Underground dust containers can be the best solution to such problems.
In this system, (like in India) the dustbin is kept underground in the form of a large bin, with a relatively narrow opening through which the wastes are deployed inside. By this process the waste is kept underground and thus there is almost no risk of pollution and street clogging. The process is shown below in systematic order:
Figure 11.1 – A personnel is deploying waste in the underground bin
Figure 11.2 – The waste is deployed from a Van
Figure 11.3 – Collection of waste from the Underground bin
Figure 11.4- Reinserting the bin in the Underground chamber
7.2. Energy Generation from the Waste
Waste to energy (WtE) option means waste treatment process generating energy in the form of electricity, heat, or transport fuels. WtE is considered as one of the eight technologies having significant potential to contribute to future low-Carbon energy system by the world economic forum report “Green Investing: Towards a Clean Energy Infrastructure” published in 2009.[8] It is interesting to note that the electrical energy generation potential increases from 456,900 MWh in 1995 to 1,894,400 MWh in 2025, and the electrical energy recovery from urban solid waste generation of Dhaka city can supply a significant portion of the consumption requirement of electrical energy of the city.[18] Various technologies can be utilized for energy conversion from waste. Each of these WtE solutions has specific features, and can be more or less feasible depending on many parameters. The following list gives an overall picture of the available options of WtE technologies:
Figure 12: Current waste to energy technologies [19]
7.2.1.1. Incineration
The complete oxidation of the combustible materials present in the solid waste is referred to as incineration of MSW. Initially, the moisture contained in the solid waste is evaporated and volatilized by the heat in the combustion chamber. The actual combustion process is then begun by the ignition of resulting gases in the presence of combustion air which converts waste fuel into heat, flue gas, and ash. A high-pressure superheated steam is produced from water by the heat, which is then sent either to the steam turbine to produce electricity which is incorporated with generator, or used to supply process steam.
Figure 13: Model of an incinerator [20]
C + O2↔ CO2; oxidation of Carbon
½ O2 + H2↔ H2O; oxidation of hydrogen
N + O2↔ NO2 (NOX); oxidation of Nitrogen
S + O2 ↔ SO2 (SOX); oxidation of sulfur [21]
Some of the generated gases are toxic. So, they should be removed before emission. SCR system is used for the reduction of NOX as well as PCDD/F. The main reactions involved are:
C12HnCl8 nO2 + (9 + 0.5 n) O2→ 12CO2 + (n-4)H2O + (8-n)HCl
and
C12HnCl8 nO + (9.5 + 0.5 n) O2→ 12CO2 + (n-4)H2O + (8-n)HCl
Volatile inorganic compounds and heavy metals are totally or partly evaporated. These substances are transferred from the input waste to the flue-gas and the fly ash it contains. A mineral residue fly ash (dust) and heavier solid ash (bottom ash) are created. [22] They affect the energy balance through its mean heat capacity, even though does not particularly participate in the combustion process. Ferrous and non-ferrous metals can be recaptured and the remaining ash can be enhanced to be used for building and road construction.[19]
A study shows that incineration of MSW from Chinese cities present some unique challenges because of its low caloric value (3000-6700 kJ/kg and high water percentage (~50%). So, MSW has to be co-fired with coal in a CFB incinerator. [23]
| Energy Production: | Specific power output per ton of waste generated from DCC at a thermal efficiency of 445 kWh/ton. Potential of electric power plant capacity from the waste in Dhaka city is 71 MW. |
| Cost: | 38 $/ton. [24] |
7.2.1.2. Thermal Gasification
Gasification plant thermally treats fuels without allowing enough oxygen for complete combustion. It is typically smaller and more flexible than combustion plants and typically consumes 25 to 350 thousand tonnes of waste per year. [25]Either the heat required for this process is provided by partial combustion to gasify the rest or heat energy is provided by using an external heat supply. The solid waste is broken down into useful byproducts that contain a mixture of hydrogen, Carbon Di-oxide and Carbon monoxide. The produced syngas can be used for various applications after syngas cleaning process. After cleaning,high quality fuels, synthetic natural gas (SNG) and chemicals can be produced by it. Syngas can be used in a more efficient gas turbines and/or internal combustion engines or it can be burned in a conventional burner that is connected to a boiler and steamturbine. [19] Some of the chemical reactions involved in thermal gasification are given below
CH4 + H2O → CO + 3H2O (CH4 decomposition – endothermic)
CO + H2O→CO2 + H2 (Water gas shift reaction – exothermic)
C + H2O → CO + H2 (Heterogeneous water gas shift reaction – endothermic)
C + CO2→ 2CO (Boudouard equilibrium – endothermic)
The overall equation of global gasification reaction is written as follows; waste material is described by its ultimate analysis (CHxOy):
CHxOy +wH2O +mO2 +3.76mN2→ aH2 +bCO +cCO2 +dH2O +eCH4 +fN2 +gC
Here w is the amount of water per mole of waste material, m is the amount of O2 per mole of waste, a, b, c, d, e, f and g are the coefficients of the gaseous products and soot (all stoichiometric coefficients in moles). [26]
| Energy production: | 1 ton of MSW can be used to produce up to 1,000 kilowatt-hours of electricity. |
| Cost: | Construction cost about $1 million to $300 million to implement. [27] |
Figure 14: Schematic of overall process for 100 TPD thermal plasma Gasification plant [26]
During Pyrolysis organic waste is heated in the absence of air in between 500-800°C to produce a mixture of gaseous (Syngas) and/or liquid fuels (Tar) and a solid (Char), inert residue (mainly Carbon).[28] The pyrolysis temperature and the rate of heating determines the quantity of H2, CO, CH4 and other hydroCarbons and their proportion.[19] The lower temperature pyrolysis processes are used for maximizing the production of bio-oil which is a potential precursor to the production of many other chemicals in a bio-refinery context. The higher temperature pyrolysis processes have been developed in order to maximize the production of syngas, which is more easily converted to electricity. [28]
Reactions involved in pyrolysis of MSW:
Primary reaction:
The primary decomposition reaction of the solid waste sample can be represented by equation 1. The decomposition is a single reaction with no competitive selectivity towards any of the products formed. Where, k is the reaction rate constant for decomposition of waste sample to form char (Sp), tar (Tp) and gaseous (Gp) products. a, b and c are the yield coefficients (kg of product formed/kg of reacted biomass).
Sample → kaGp + bTp + cSp … … … (1)
Secondary reaction:
The tar obtained from primary decomposition reactions cracks during the secondary decomposition reaction. Equation 2 correlated the thermal decomposition of tar.
bTp → kseGs + fSs … … … (2)
Here Gs is the representation of total gases and Ss is the total char and refractory tar produced during tar (produced from primary decomposition) decomposition. e and f are the corresponding yield coefficients (referring to the initial biomass since the coefficient b has been considered in the equation; and ks is the reaction rate constant. However, poly-ethylene (PE) cracking takes place through two parallel reactions as seen in Equation 3.
BTp → ks1 G s ,
BTp → ks2 S s … … … (3)
Here, B is the coefficient of tar containing PE; and k s1 and k s2 are the reaction rate constant for the two parallel decomposition reaction to form gaseous and solid (char and refractory tar) product respectively. [28]
| Energy production: | 44.30kJ/kg of end products.[29] |
| Cost: | Pyrolysis machine with 10ton capacity, costs about 45000-55000USD.[30] |
Figure 15: Fluidized bed pyrolysis reactor [31]
7.2.2.1. Fermentation
Fermantation is a process by which organic waste is converted into an acid or alcohol (e.g. lactic acid, ethanol) or hydrogen in the absence of oxygen by microorganisms (e.g. yeast, bacteria) leaving a nutrient-rich residue. There can be dark fermentation or photo fermentation. Fermentation leads to ethanol, biodiesel, and hydrogen which are good sources of energy. Methane can be produced from these substances by methanogenesis. [19] [20] [32]
Figure 16: Scheme of anaerobic metabolism pathways [32]
Production: An optimal sized bio-ethanol fermentation plant produces about 200,000-300,000 tons of ethanol per year.[19]
7.2.2.2. Anaerobic Digestion
Micro-organisms in controlled conditions convert biomass into biogas comprising primarily of methane and Carbon Di-oxide , and a stabilized residue known as digestate, a source of nutrients used as fertilizer. This process is called anaerobic digestion.[34]As MSW is normally rich in carbohydrates, proteins, and minerals, it has been widely used as raw material for anaerobic digestion.[33] The overall conversion method can be described as a three-stage procedure which may occur simultaneously in an anaerobic digester. These stages are: (i) hydrolysis of insoluble biodegradable organic substance; (ii) generation of acid from small soluble organic molecules; and (iii) methane synthesis. The three-stage scheme involving various microbial Species can be presented as follows: (1) hydrolysis and liquefaction; (2) acidogenesis and (3) methane fermentation.[32] The time of operation per cycle, meaning how long it takes for the organic waste to be processed by an AD plant, is usually 15 to 30 days.[19]Efficiency of an AD process depends on the type of waste used as feedstock and the vessel used to host the procedure. [35]
The synthesis of methane, which is the final product of anaerobic digestion, happens by two major ways. Acetic acid, hydrogen, formic acid, and methanol can be used as energy sources by the various methanogens. The overall reaction is:
CH3COOH → CH4 + CO2
Bacteria that utilize acetic acid are from acetoclastic group which comprises two main genera: Methanosarcinaand Methanothrix. Some methanogens use hydrogen to reduce Carbon Di-oxide to methane (hydrogenophilic methanogens) according to the following overall reaction:
4H2+ CO2 → CH2 + 2H2O[32]
Biogas can be used to generate electricity, process steam, or in the transportation sector as fuels and consists of 60%-70% methane (CH4), 30%-40% Carbon Di-oxide (CO2). [35]The bio-fertilizer is generated which is pasteurized to make it pathogen free and can be applied twice a year on farmland. The technology is widely used to treat wastewater and can also be effectively employed to treat organic wastes from domestic and commercial food waste, to manures and biofuel crops.[19]
| Production: | An AD plant having capability of processing 12000 ton wet organic waste and 3000 ton sewage sludge feedstock can produce around 9000000 kWh energy and worth of 35000$ fertilizer every year. |
| Cost: | Investment cost is about $4-6 million. Operation and maintenance cost is about 300000-350000$ per year.[36] |
7.2.2.3. Landfill Gas Capture
Landfills are a significant source of greenhouse gas emissions, and methane in particular can be captured and utilized as an energy source. Organic materials that decompose in landfills produce a gas comprised of roughly 50% methane and 50% Carbon Di-oxide , called landfill gas (LFG). Methane is a potent greenhouse gas with a global warming potential that is 25 times greater than CO2. Capturing methane emissions from landfills is not only beneficial for the environment as it helps mitigate climate change, but also for the energy sector and the community.
Applications for LFG include direct use in boilers, thermal uses in kilns (cement, pottery, bricks), sludge dryers, infrared heaters, blacksmithing forges, leachate evaporation and electricity generation to name a few. LFG is increasingly being used for heating of processes that create fuels such as biodiesel or ethanol, or directly applied as feedstock for alternative fuels such as compressed natural gas, liquefied natural gas or methanol. The projects that use cogeneration (CHP) to generate electricity and capture the thermal energy are more efficient and more attractive in this sense.
The process of capturing LFG involves partially covering the landfill and inserting collection systems with either vertical or horizontal trenches. Both systems of gas collection are effective, and the choice of design will depend on the site-specific conditions and the timing of installation. They can also be employed in combination and an example is the utilization of a vertical well and a horizontal collector. As gas travels through the collection system, the condensate (water) formed needs to be accumulated and treated. The gas will be pulled from the collection wells into the collection header and sent to downstream treatment with the aid of a blower. Depending on the gas flow rate and distance to downstream processes, the blowers will vary in number, size, or type. The excess gas will be flared in open or enclosed conditions to control LFG emissions during start up or downtime of the energy recovery system, or to control the excess gas, when the capacity for energy conversion is surpassed.
Figure 17: Landfill gas system[38]
| Production: | LFG is considered a good source of renewable energy, and has a heating value of about 500 British thermal units (Btu) per standard cubic foot.[19] |
| Cost: | A 1.6MW power plant based on landfill gas costs around $9 to $10 million.[37] |
7.2.3. Chemical Conversion
7.2.3.1. Esterification
The Esterification process involves the reaction of a triglyceride (fat/oil) with alcohol in the presence of an alkaline catalyst such as sodium hydroxide. A triglyceride has a glycerin molecule as its base with three long fatty acids attached. The alcohol reacts with the fatty acids to form a mono-alkyl ester, or biodiesel, and crude glycerol, used in the cosmetic, pharmaceutical, food and painting industries. The alcohol used is usually either methanol, which produces methyl esters, or ethanol, with ethyl esters. The base applied for methyl ester is potassium or sodium hydroxide, but for ethyl ester the former base is more suitable.
Figure 19: Base Catalyzed Transesterification reaction [40]
Figure 18: Biodiesel production process [39]
Waste Concern says, if recyclable materials including organic waste for composting is seperated, the total waste can be reduced upto 60-70%. Only 15% of total waste which are recyclabe items is being collected by 87000 waste pickers leaving behind a large amount organic waste from which a huge amount of organic fertilizer can be generated. They conducted a survey in Dhaka and surrounding areas which says that 94% of the farmers are willing to buy compost but the yeild is so little that the organic matter in soil was found less than 1% against the critical level of 3%. [40]
Figure 20: Fertilizer generation process from waste
Fertilizer can be produced by biologial treatment of waste like anaerobic digestion and composting. Anaerobic digestion is discussed earlier. Various types of composting methods can be used to generate organic manure from municipal solid waste. Static pile and contained pile composting, vermi composting, bin composting, windrow composting, rotatory drum composting, tunnel composting and in-vessel composting are some of the common composting procedures. An overview of the composting procedures is represented in the table below:
| Table 3: An overview of different commonly used composting systems [42] |
|||||||
| Criteria | Static and contained pile | Vermi | Bin | Windrow | Rotator drum | Tunnel | In-vessel |
| Size and form of the heap/ container | Waste is laid out in parallel rows; considerably taller and wider rows can be had compared to windrows; especially in contained pile systems | Can be done in pits, concrete tanks, well rings, or in wooden or plastic crates appropriate to a given situation. |
Bins of different sizes and materials are used | The waste is laid out in parallel rows; 2–3 m high and 3–4 m wide across the base; acquires trapezoidal shape. | Rotary drum with 3 m or larger diameter is used for pretreating the waste; the waste is then windrowed | Long perforated heavy-duty conveyor enclosed inside a sealed casing of approximately square cross section moves the waste though a tunnel; the system approximates a plug flow reactor | Consist of vessels (reactors) of different shapes and sizes; most approximate the characteristics of plug-flow (tubular) reactors or of continuously stirred tank reactors which are common in process industry |
| Preprocessing | Material is mixed using standard agricultural equipment | Washing, precomposting, macerating or mixing. Precomposting is particularly beneficial. | Material is hand-sorted to prevent noncompostables from getting into the composting bin. | Material is shredded and screened. | The drum itself is a precomposting unit; it homogenizes the waste and sets its decomposition process going | Material is shredded | Material is sorted to remove uncompostables |
| Turning/ aeration | No turning is done; to speed up the composting process, agrid of aeration or exhaust piping is used, over which substrate piles are formed. | No need for mechanical or forced aeration. | The composting mass is either left to natural aeration or turning is done at periodic intervals with simple garden equipment. | Frequency of turning is high during the early stages; progressively lesser with time Turning is accomplished using machines according to the scale of operation. | As in the windrows | Air is blown through the conveyor or pan, and is exhausted from the casing top | A variety of mechanical and forced aeration systems are used |
| Composting period | 3–4 weeks | 6-7 weeks | 6–8 weeks | 3–4 weeks | 3–4 weeks | 2–3 weeks | 2–3 weeks |
| Curing period | 4 weeks or longer | 6-7 weeks | 3–4 weeks | 3–4 weeks without turning | 3–4 weeks | 3–4 weeks | 3–4 weeks |
| Operation site | Contained pile systems can be used anywhere | Large area is required. | Ideal for household composting | Carried out in the outskirts of towns and cities to avoid disturbance to public. Operated as an addition to existing landfill operations. | As in the windrows | Suitable only where adequate land area is available |
Can be installed everywhere at widely varying scales of operation |
| Major features |
Since turning is not done, it is less dependent on labor. Low odor emission. |
Organic matter is converted to more bioavailable forms. Can be done in various types of places or containers. | Being small scale, very effective hand sorting of material is possible; hence can ensure good quality product. | Thorough mixing of material is possible | Ability to co-compost a mixture of sewage sludge and municipal waste, which is otherwise difficult to achieve by other methods | Highly efficient at low-to-medium scales of operation Overcomes traditional compaction problems |
Enable large masses of waste to be composted within much shorter land spaces Better public acceptance due to less forbidding appearance of the composting site Less manpower requirements Consistent compost quality Better odor control |
|
Draw backs |
Decomposition progresses at slower rate, causing the material to remain on site for a longer period. Decreased ability to adjust moisture in composting mass after initial mix Potential for drying in the immediate vicinity of the aeration systems. Composted material can be heterogeneous. |
Large area and long time is needed for composting. | The potential of bin composting can be realized only by ensuring public participation, which until now has been difficult to achieve. |
Require large land area; can cause odor problems, particularly when windrows are turned during periods of calm air and temperature inversion. Likely to release fungal spores and other bioaerosols. |
As in windrows | Pose serious feasibility problems at larger scales; occupy more floor surface, since they are long rather than high | High capital and operational cost. Episodes of odor release can occur due to equipment failure or system design limitations |
- Concluding Remarks
Though a number of possible ways are discussed to eradicate the waste management problem from Dhaka city and turn the waste into resources, we couldn’t discriminate between the waste-to-energy techniques. Each of the waste-to-energy process has great potential to convert the hidden power of municipal solid waste into resources because of greater organic portion in the waste of Dhaka. But as there are financial boundaries for the govt. of a developing country like Bangladesh, it’s better implementing the biochemical and chemical procedures initially as well as steps to generate fertilizers by composting as these processes are cost-effective. The practice of proper, scientific, and hygienic management of waste and at the same time turning it into energy or resource, could ensure a safer life of people and at the same time ensure a sustainable healthy atmosphere for our future generations. There is a huge gap between the researchers, policy makers and the public, who are the main executives of the target. So, the research findings should not be poorly considered in policy making like that is going on now. At the same time, researches should be public benefit oriented as well as the research paper’s language should be up to an understandable level of the policy makers, stake holders and the public. The policy makers should build a bridge between the researcher and the public by formulating sustainable and practicable policies. Only this trio joint-venture can solve the monumental waste management problem in our country and likewise all over the globe. At the same time the Government and the public should come forward with enthusiasm to time to time to support and modify the policy to make it more time worthy and eco-friendly.
- Limitations
Though our target was to publish a complete article with the most recent information about the solid waste management of different developed cities in the world, but due to certain limitations and insufficiency of time, it could not be fully possible. So, we had to depend on some earlier publications in cases. Moreover, latest data of different topics and places on waste management are lacking. We also observed major deviations of the same value in different articles in some cases and could not have enough time to confirm with those publications. But, our next target is to prepare a complete scientific paper with latest substantial data with reference about all aspects of Solid Waste Management of the city and the recommendations for the way out of such environmental problems.
- Acknowledgement
Authors are grateful to Nature Study Society of Bangladesh (NSSB) for the active cooperation and support rendered for the review work.
- Abbreviation
AD – Anaerobic digestion
CFB – Circulating Fluidized Bed
CHP – Combined Heat and Power
DCC – Dhaka City Corporation
DNCC – Dhaka North City Corporation
DoE – Department of Environment
DSCC – Dhaka South City Corporation
JICA – Japan International Cooperation Agency
LFG – Landfill Gas
MSW – Municipal Solid Waste
MSWM – Municipal Solid Waste Management
MW – Mega Watt
MWh – Mega Watt Hour
NGO – Non-government Organization
PCBs – Polychlorinated Biphenyls
PCDD/F – Polychlorobenzodioxins / polychlorodibenzofurans
PWCSP – Primary Waste Collection Service Provider
SCR – Selective Catalytic Reduction
SNG – Synthetic Natural Gas
STS – Secondary Transfer Station
USD – United States Dollar
VOCs – Volatile Organic Compounds
WM – Waste Management
WtE – Waste to Energy
[N.B.-This article was earlier published in the Journal Book – Environmental Thoughts, Part-1, 2019; (ISBN: 978-984-93766-2-0)]
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