Review of Earthquake Contingency Plan of Dhaka City Corporation
Solid Waste Management in Dhaka City
– A Review on the Present Status and Possible Solutions
A. H. Yard. Safayet Ullah Prodhan
Dept. of Biochemistry & Molecular Biological science,
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 1 of the main environmental problems in Dhaka, the capital city of Bangladesh. About 5000 tons of waste is being generated in Dhaka city every twenty-four hour period among which only almost more than than half portion is properly collected and dumped. Then, a huge corporeality of waste product is beingness mistreated every day. In the present study an attempt was made to stand for the current waste matter direction (WM) scenario of Dhaka metropolis, how Dhaka City Corporation (DCC) is trying to cope with the WM problem, public concern about some WM practices, the bug created by improper WM system and some possible solutions to the WM bug.
Key words: Dhaka City Corporation; Solid waste; Recycling; Waste to energy.
- Introduction
Dhaka is one of the most densely populated cities in the globe having a population of about twenty million in an area of just 360 km2. The total population is growing at a high charge per unit of 1.4%; where equally her urban population is growing at a faster rate of three.iv% per annum. The estimated population hither by 2040 is 40 million. And so, with the increasing charge per unit of population, the rate of waste management problem of the city is as well rising keeping a footstep to it. In 1985 the total corporeality of solid waste in the metropolis was 1040 tons/day, which rose to 3500tons/twenty-four hours in 1999 and might rise to 30000tons/twenty-four hours past the year 2020. Though a massive amount of municipal solid waste having 80% organic content and fifty-lxx% wet is generated every day, only about 50% of the waste is collected properly by DCC and dumped equally landfill [i] [2] [3]. The improper management leaves behind a huge amount of uncollected waste matter, which has been creating environmental hazards in the city.
Dhaka Urban center Corporations DCC, North, and Southward, have been trying to mitigate the problem taking new initiatives, but the problem seems to be aggravating more and more day past twenty-four hour period. This huge waste seems to be beyond command of the DCC alone until the metropolis dwellers come forrard together to solve it.
The surface area required for land filling is increasing proportionally with the growth of waste product. It is estimated that past 2020, the required area for landfill will exist 206.31 acre to 309.46 acre with the collection efficiency of 50% to 75%.[iii] Though from the definition of waste nosotros know that "Waste material is an unwanted material that lacks financial value regardless of the time or flavor because there is no need for such an item in the market"[4]. But, this idea can exist proved wrong by reusing and recycling the waste in a proper way. At that place are a number of recognized Waste-to-Energy (WtE) technologies in the globe right at present, which can plough the unwanted waste into energy. Moreover, the waste can exist decomposed to create fertilizers. And 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 direction has been a demand of the time for a likely solution to the problem and at the aforementioned fourth dimension plow this huge waste into resource. To perform the nowadays piece of work, we analyzed a number of research works, review manufactures, dissimilar online sources and reports of different government, not-government and international organizations on waste management on Dhaka city equally well as other cities of the developed and developing countries. The aim of this review is to demonstrate the current waste material direction process in a proper way so that the existing problems related to information technology are minimized. At the same time, the piece of work refers to possible ways and means to catechumen the municipal solid waste material into resources. We strongly believe, if brought into practice, this could assist the citizens of Dhaka and other cities to live a better life in an eco-friendly, congenial and sustainable environment, for nowadays 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 matter drove from households to local dust bins is considered as a success. Informal waste recycling systems are also highly fruitful in waste recycling and chore creations for the poor.
Wastes are normally collected in a not-segregated way and placed into lilliputian containers at households. Wastes are then nerveless by organizations delegated by DCC in vans to the secondary collection points. Waste trucks and so carry the wastes to the landfill sites. A significant portion of the solid waste is operated by an informal market to exist recycled. Scavengers (Tokais) collect the recyclable items from landfills and open dustbins and then sell those to a waste material recycling dealer (Bhangari). As well, the Hawkers purchase 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 marketplace.
Figure i: Existing solid waste direction system in DCC [five]
The process of waste management of city streets is dissimilar. Cleaners from DCC cleans public places (drains, streets, parks etc.) regularly. All the wastes nerveless from the urban center is dumped to the land filling sites. A massive amount of waste matter in Dhaka is not collected because of lack of funds, infrastructure, and transportation vehicles.[half dozen]In addition to solid waste, electronic waste, construction waste matter, medical waste product, nutrient waste and various forms of industrial wastes are produced in the metropolis.
DCC does not have the adequacy to perform regulatory assistants of these wastes. Besides, at that place are no laws to regulate the management of these wastes. So, these wastes are constantly existence 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 past 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 |
| Status | In functioning | In operation |
| Landfilling Started | 2003 | 2007 |
| Height of MSW deposit | vii meter | half dozen.4 meter |
| Altitude from the urban center (km) | 6 | 8 |
| Closed/expected end of life | 2021 | 2023 |
| Average disposal per day | 2000 tons | 1200 tons |
| Current CH4 Condition | No recovery | No recovery |
| Ward Covered | 55 | 36 |
DCC (Due north) might accept to manage over 5637728 ton waste material in next v years. Growth percentage of waste collection in 2015-17 and projected waste book in DNCC between 2017-18 and 2021-22 is appended in charts beneath:
Effigy 2: Waste material drove trend in tones in DNCC from 2014-15
Effigy 3: Projected waste matter book in DNCC during the period betwixt 2017-eighteen and 2021-22 [vii]
Figure 4: Waste product drove growth percentage in DNCC [seven]
Effigy five: Projection of future landfill requirement of Dhaka [ix]
75% composting landfill requirement will be around just 400 acres by the yr 2050. The landfill requirement without composting will exceed chiliad acres by the same twelvemonth. Futurity landfill requirement of Dhaka without composting and with composting is projected in the nautical chart beneath:
Landfill demand for disposal of MSW of Dhaka assessed by projecting population and waste material generation for the period 2007-2025 is represented in the tabular array below:
| Yr | Projected Population | Daily Waste matter Generation (tons) | Yearly waste generation (M tons) | Cumulative Waste (M tons) | Cumulative Landfill waste product volume (Mm3) |
| 2007 | 13.l | 6750 | 2.v | 2.5 | 4.93 |
| 2008 | 13.87 | 6934 | 2.5 | five.0 | 9.99 |
| 2009 | xiv.24 | 7122 | two.6 | vii.half-dozen | 15.xix |
| 2010 | fourteen.63 | 7316 | two.7 | ten.iii | 20.53 |
| 2011 | 15.03 | 7515 | 2.seven | thirteen.0 | 26.01 |
| 2012 | 15.44 | 7719 | two.eight | 15.8 | 31.65 |
| 2013 | 15.86 | 7929 | two.9 | 18.7 | 37.44 |
| 2014 | sixteen.29 | 8145 | 3.0 | 21.vii | 43.38 |
| 2015 | xvi.73 | 8367 | three.ane | 24.7 | 49.49 |
| 2016 | 17.xix | 8594 | iii.1 | 27.nine | 55.77 |
| 2017 | 17.66 | 8828 | iii.2 | 31.ane | 62.21 |
| 2018 | 18.fourteen | 9068 | 3.3 | 34.iv | 68.83 |
| 2019 | eighteen.63 | 9315 | 3.four | 37.eight | 75.63 |
| 2020 | 19.14 | 9568 | 3.5 | 41.iii | 82.61 |
| 2021 | 19.66 | 9828 | 3.vi | 44.9 | 89.79 |
| 2022 | 20.19 | 10096 | 3.7 | 48.6 | 97.xvi |
| 2023 | 20.74 | 10370 | 3.viii | 52.4 | 104.73 |
| 2024 | 21.30 | 10652 | 3.ix | 56.3 | 112.50 |
| 2025 | 21.88 | 10952 | 4.0 | 60.9 | 120.49 |
Tabular array two: Population, waste generation and waste volume in Dhaka urban center (2007 – 2025) [ten]
- Initiatives taken by DCC for Solid Waste matter Management
Around half dozen 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 low-cal garbage into those instead of hither and thither. But the pedestrians practice not use the bins as was expected. They throw wastes on the street or footpaths. However, the street vendors adopt the bins. [11]
Figure 6: A man discarding an empty water canteen in a bin set upwards by DCC [12]
Two of import initiatives have been undertaken for Solid Waste Management in Dhaka. One was undertaken by Japan International Cooperation Agency (JICA) in 2005 with the objectives of formulating a master plan of Dhaka City and to develop capabilities and management skills of DCC. Some other initiative, 3R Strategy (The principle of reducing, reusing and recycling of resources and products is often called the 3Rs) was undertaken in 2010 by the Department of Surroundings (DoE), Ministry of Environment and Forestry of the Regime. Towards sustainable waste direction, 3Rs tin play an of import office protecting environs from greenhouse gas emission and convert waste into invaluable resource.[12]
DoE has introduced a program by edifice ii waste product management plants, which volition use solid waste product collected from different parts of Dhaka to create compost fertilizer. One such establish will exist in Matuail nether Dhaka South City Corporation (DSCC) and the other in Amin Bazar under Dhaka North City Corporation (DNCC). Each of the plants will exist capable of producing 20 tones compost fertilizer per 24-hour interval from solid waste. DCC expects producing fertilizer out of those plants by early 2018.[13]
Figure 7.1: Before STS Construction
Figure vii.ii: Afterwards STS Construction
Figure 7.three: Inside the STS
Construction STS in Dhaka has been a noticeable development in waste product direction. Structure of 52 STS in DNCC has enabled DNCC to remove dandy number of waste material containers from the roads [7]. 45 STSs were planned to be built in DSCC by this fourth dimension, only just 12 has been completed and then far[fourteen]. DNCC plans to build ii-4 STSs in each of 36 wards. In areas of chief drove, the Primary Waste Collection Service Provider (PWCSP), an NGO is analogous 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 likewise solved by the structure of STS.
- Public Concern about Waste Management in the City
Door-to-door service and waste matter dumping %: A study got some information showing that 88 % of upper grouping, 75 % of heart group and only 30 % of lower grouping received door-to-door collection service. 51 % of lower grouping households dumped their waste product in vacant lands/river, while only 5% of upper group and 4% of heart 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 centre group, and 75 % of lower group were not willing to participate in waste product segregation activities. 88% of upper group, 95% of centre group and 100% of lower group were non 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 grouping and 96% of lower group were non participating in any community activities. 85% of upper group, 96% of center group and 98% of lower grouping were non willing to participate in composting activities. 77% of all respondents replied that they were willing to participate in activities on solid waste direction in their communities.[15]
Figure 9: Waste segregation, recycling, composting and community activity status of diff. group of people in Dhaka
Another report expresses that, people ranked natural environment as 6 among 8 sectors suggested for government funding and solid waste dumping equally three among 8 environmental problems. On average the respondents in Dhaka were willing to pay only 13 TK (0.18 USD) waste material collection service accuse per month. [sixteen]
- Physical Limerick of DCC Solid Waste
Cultural tradition, food habitat socio-economic and climate weather affect the composition of MSW. Typical characterization of MSW in Dhaka is reflected below:
Figure ten: Typical label of MSW in Dhaka [9]
6. Present status of Solid Waste in Dhaka City
The Dhaka City Cooperation estimated that, of the full 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 eleven.5% waste remains untreated and these wastes pollute surround. The DCC clearly states that, its collection organisation cannot cope with the task of handling the large volumes of pass up produced past the ever-growing numbers of city dwellers, and that simply 40-l% of the solid waste matter produced is being nerveless. 50% of the daily generated waste remains uncollected in the city and disposed at official dump sites. Merely 14-17% of the total municipal budget is used for solid waste material direction which is approximately 0.5 USD per capita per year. Equally a consequence, the uncollected waste is primarily dumped illegally in the neighborhood's streets, wastewater drains, ponds, lakes etc. or managed informally. Uncollected waste matter has been recognized equally the root of inferior environment such as scattered garbage, offensive odour, drain clogging, water pollution and mosquitoes.[6]
- Probable solutions to present problem of Solid Waste Management in Dhaka Metropolis
To solve the existing problems regarding waste management in Dhaka metropolis, we have to focus on three sectors:
- Smart dumping and transportation of waste
- Energy generation from waste product
- 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 ecology pollution. Likewise, the dustbins cover a big area of street and hamper traffic movement resulting in traffic jam. Hole-and-corner dust containers can exist the best solution to such problems.
In this system, (like in Republic of 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 at that place is well-nigh no risk of pollution and street clogging. The procedure is shown below in systematic order:
Effigy 11.1 – A personnel is deploying waste in the surreptitious bin
Effigy 11.2 – The waste is deployed from a Van
Figure eleven.3 – Collection of waste from the Secret bin
Effigy 11.iv- Reinserting the bin in the Hole-and-corner chamber
seven.2. Energy Generation from the Waste
Waste material to free energy (WtE) option means waste material handling procedure generating energy in the form of electricity, estrus, or transport fuels. WtE is considered equally one of the eight technologies having significant potential to contribute to hereafter depression-Carbon energy organization by the world economic forum report "Green Investing: Towards a Make 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 ane,894,400 MWh in 2025, and the electric energy recovery from urban solid waste product generation of Dhaka city can supply a significant portion of the consumption requirement of electrical free energy of the city.[xviii] Diverse technologies can be utilized for free energy conversion from waste product. Each of these WtE solutions has specific features, and tin can exist more than or less viable depending on many parameters. The post-obit list gives an overall picture of the bachelor options of WtE technologies:
Figure 12: Current waste to free energy technologies [nineteen]
7.2.i. Thermo-chemical Conversion
7.2.i.i. 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 oestrus in the combustion chamber. The bodily combustion process is and so begun past the ignition of resulting gases in the presence of combustion air which converts waste matter fuel into heat, flue gas, and ash. A loftier-pressure level superheated steam is produced from water by the heat, which is and so 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]
Smaller amounts of CO, HCl, HF, HBr, Howdy, NO10, SOX, VOCs, PCDD/F, PCBs and heavy metal compounds (among others) are formed or remain depending on the composition of the waste material incinerated. Formation of some of the common gases is shown by reactions given below:
C + Otwo↔ CO2; oxidation of Carbon
½ O2 + Htwo↔ H2O; oxidation of hydrogen
North + Otwo↔ NO2 (NOX); oxidation of Nitrogen
Due south + Oii ↔ Sotwo (So10); oxidation of sulfur [21]
Some of the generated gases are toxic. And 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:
C12HnorthwardCl8 nO2 + (nine + 0.5 due north) O2→ 12COii + (n-4)HiiO + (8-n)HCl
and
C12HnorthCl8 nO + (nine.5 + 0.5 northward) O2→ 12CO2 + (n-4)HiiO + (eight-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 impact the energy residuum through its mean heat capacity, fifty-fifty though does not peculiarly participate in the combustion process. Ferrous and non-ferrous metals tin be recaptured and the remaining ash can be enhanced to exist used for building and road structure.[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 (~l%). 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 electrical power plant capacity from the waste in Dhaka city is 71 MW. |
| Cost: | 38 $/ton. [24] |
7.2.1.2. Thermal Gasification
Gasification institute 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 m tonnes of waste per year. [25]Either the heat required for this process is provided by partial combustion to gasify the rest or heat free energy is provided by using an external rut supply. The solid waste matter is broken down into useful byproducts that contain a mixture of hydrogen, Carbon Di-oxide and Carbon monoxide. The produced syngas can exist used for various applications subsequently syngas cleaning procedure. Afterwards cleaning,loftier quality fuels, constructed natural gas (SNG) and chemicals can be produced by information technology. Syngas tin can be used in a more efficient gas turbines and/or internal combustion engines or information technology can exist 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 + HiiO → CO + 3H2O (CH4 decomposition – endothermic)
CO + H2O→ CO2 + H2 (Water gas shift reaction – exothermic)
C + HiiO → 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):
CH10Oy +wHtwoO +mO2 +3.76mNtwo→ aH2 +bCO +cCO2 +dH2O +eCHiv +fN2 +gC
Here west is the amount of water per mole of waste material material, g is the amount of Oii 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 tin be used to produce upward to 1,000 kilowatt-hours of electricity. |
| Toll: | Construction cost about $1 million to $300 million to implement. [27] |
Figure fourteen: Schematic of overall process for 100 TPD thermal plasma Gasification plant [26]
vii.2.1.3. Pyrolysis
During Pyrolysis organic waste is heated in the absenteeism of air in betwixt 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, CHiv and other hydroCarbons and their proportion.[nineteen] 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 college temperature pyrolysis processes accept 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 principal decomposition reaction of the solid waste sample can exist represented past equation one. The decomposition is a single reaction with no competitive selectivity towards any of the products formed. Where, 1000 is the reaction charge per unit abiding for decomposition of waste product sample to class char (Southwardp), tar (Tp) and gaseous (Gp) products. a, b and c are the yield coefficients (kg of product formed/kg of reacted biomass).
Sample → yardaG p + bT p + cS p … … … (i)
Secondary reaction:
The tar obtained from primary decomposition reactions cracks during the secondary decomposition reaction. Equation 2 correlated the thermal decomposition of tar.
b T p → kseThou south + fS due south … … … (2)
Here One thousand south is the representation of total gases and S s is the total char and refractory tar produced during tar (produced from primary decomposition) decomposition. due east and f are the corresponding yield coefficients (referring to the initial biomass since the coefficient b has been considered in the equation; and thousands is the reaction rate constant. However, poly-ethylene (PE) slap-up takes identify through two parallel reactions every bit seen in Equation iii.
B T p → ks1 G s ,
B T p → ks2 Due south south … … … (3)
Here, B is the coefficient of tar containing PE; and grand s1 and one thousand s2 are the reaction rate abiding for the ii parallel decomposition reaction to form gaseous and solid (char and refractory tar) product respectively. [28]
| Energy production : | 44.30kJ/kg of terminate products.[29] |
| Price: | Pyrolysis machine with 10ton chapters, costs nearly 45000-55000USD.[xxx] |
Figure 15: Fluidized bed pyrolysis reactor [31]
7.two.2. Biochemical Conversion
7.2.ii.i. Fermentation
Fermantation is a process by which organic waste material is converted into an acid or alcohol (e.g. lactic acid, ethanol) or hydrogen in the absenteeism of oxygen past microorganisms (due east.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] [xx] [32]
Figure 16: Scheme of anaerobic metabolism pathways [32]
During ethanol fermentation, the sugar portion of MSW (e.one thousand., glucose, fructose, cellulose, and starch) is converted to ethanol, whereas the proteins and minerals nowadays in MSW are needed for the growth of the fermenting microorganisms. A diversity of commercial enzyme solutions are estimated for the transformation of the food waste toglucose, with the most effective amalgamation being carbo-hydrase (from Aspergillus aculeatus) or gluco-amylase (from Aspergillus niger) supplemented with protease (from Bacillus licheniformis).[33]
Production: An optimal sized bio-ethanol fermentation establish produces most 200,000-300,000 tons of ethanol per year.[19]
seven.2.two.2. Anaerobic Digestion
Micro-organisms in controlled conditions convert biomass into biogas comprising primarily of methyl hydride and Carbon Di-oxide , and a stabilized residue known as digestate, a source of nutrients used every bit fertilizer. This process is chosen anaerobic digestion.[34]Every bit MSW is commonly rich in carbohydrates, proteins, and minerals, it has been widely used equally raw material for anaerobic digestion.[33] The overall conversion method can be described as a 3-phase 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; (two) acidogenesis and (3) methane fermentation.[32] The time of functioning per cycle, meaning how long it takes for the organic waste to be candy past an Advertizement plant, is usually 15 to 30 days.[19]Efficiency of an Advertizing process depends on the type of waste material used as feedstock and the vessel used to host the procedure. [35]
The synthesis of methane, which is the concluding product of anaerobic digestion, happens by two major ways. Acetic acrid, hydrogen, formic acid, and methanol can be used as energy sources past the various methanogens. The overall reaction is:
CH3COOH → CHfour + CO2
Bacteria that utilise acerb acid are from acetoclastic group which comprises two master genera: Methanosarcinaand Methanothrix. Some methanogens use hydrogen to reduce Carbon Di-oxide to methane (hydrogenophilic methanogens) according to the post-obit overall reaction:
4H2+ CO2 → CH2 + 2HiiO [32]
Biogas can be used to generate electricity, process steam, or in the transportation sector as fuels and consists of 60%-70% marsh gas (CH4), xxx%-40% Carbon Di-oxide (COii). [35]The bio-fertilizer is generated which is pasteurized to make it pathogen costless and tin be applied twice a year on farmland. The technology is widely used to treat wastewater and can besides be effectively employed to treat organic wastes from domestic and commercial food waste material, to manures and biofuel crops.[19]
| Production: | An AD plant having adequacy of processing 12000 ton wet organic waste and 3000 ton sewage sludge feedstock tin can produce around 9000000 kWh energy and worth of 35000$ fertilizer every twelvemonth. |
| Cost: | Investment toll is almost $four-6 one thousand thousand. Operation and maintenance cost is about 300000-350000$ per yr.[36] |
7.2.two.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 fifty% methane and 50% Carbon Di-oxide , called landfill gas (LFG). Methyl hydride is a potent greenhouse gas with a global warming potential that is 25 times greater than COii. Capturing methane emissions from landfills is not only benign for the environment as it helps mitigate climate modify, just also for the free energy sector and the customs.
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 proper name a few. LFG is increasingly being used for heating of processes that create fuels such as biodiesel or ethanol, or directly practical equally feedstock for culling fuels such every bit 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 bonny 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 pattern will depend on the site-specific weather and the timing of installation. They tin can as well be employed in combination and an example is the utilization of a vertical well and a horizontal collector. Every bit gas travels through the collection system, the condensate (water) formed needs to exist 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 menstruum rate and distance to downstream processes, the blowers will vary in number, size, or type. The excess gas will exist flared in open or enclosed conditions to control LFG emissions during kickoff upward or reanimation of the energy recovery system, or to control the excess gas, when the chapters for energy conversion is surpassed.
Effigy 17: Landfill gas system[38]
The LFG treatment of moisture, Particulates and other impurities is necessary, but the type and the extent will depend of the sort of energy recovery used and the site-specific characteristics. Minimal treatment can be employed for boilers and well-nigh internal combustion systems, while other internal combustion systems, gas turbines and micro-turbine applications will require more sophisticated procedures with absorption beds, biological scrubbers and others, to remove substances such equally siloxane and hydrogen sulphide.
| Product: | LFG is considered a practiced source of renewable free energy, and has a heating value of most 500 British thermal units (Btu) per standard cubic foot.[19] |
| Cost: | A ane.6MW power plant based on landfill gas costs around $9 to $ten million.[37] |
7.ii.3. Chemic Conversion
7.two.iii.1. Esterification
The Esterification process involves the reaction of a triglyceride (fat/oil) with alcohol in the presence of an alkali metal goad such as sodium hydroxide. A triglyceride has a glycerin molecule as its base with three long fat acids attached. The alcohol reacts with the fat 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 practical for methyl ester is potassium or sodium hydroxide, but for ethyl ester the former base is more suitable.
Figure xix: Base Catalyzed Transesterification reaction [40]
The Esterification reaction is afflicted by the chemic structure of the booze, the acid and the acrid catalyst. Biodiesel is used in the transportation sector and can be produced from oils and fats through 3 methods: base catalyzed transesterification of oil; directly acid catalyzed transesterification of oil and; conversion of the oil to its fatty acids and and then to biodiesel. Base catalyzed transesterification is the near economical process to produce biodiesel.
Effigy eighteen: Biodiesel product process [39]
vii.3. Fertilizer Generation from Waste product:
Waste Business concern says, if recyclable materials including organic waste for composting is seperated, the total waste can be reduced upto 60-70%. But 15% of total waste which are recyclabe items is beingness nerveless past 87000 waste pickers leaving backside a large amount organic waste material 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 purchase compost but the yeild is so little that the organic affair in soil was found less than one% against the critical level of three%. [40]
Figure 20: Fertilizer generation procedure from waste
Fertilizer tin can be produced by biologial treatment of waste material like anaerobic digestion and composting. Anaerobic digestion is discussed earlier. Various types of composting methods tin exist 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 mutual composting procedures. An overview of the composting procedures is represented in the table beneath:
| Table 3: An overview of different commonly used composting systems [42] | |||||||
| Criteria | Static and contained pile | Vermi | Bin | Windrow | Rotator pulsate | Tunnel | In-vessel |
| Size and form of the heap/ container | Waste material is laid out in parallel rows; considerably taller and wider rows tin be had compared to windrows; especially in contained pile systems | Can be done in pits, physical tanks, well rings, or in wooden or plastic crates appropriate to a given situation. | Bins of different sizes and materials are used | The waste matter is laid out in parallel rows; 2–three k loftier and 3–4 m wide across the base; acquires trapezoidal shape. | Rotary drum with 3 thou or larger diameter is used for pretreating the waste material; the waste is and so windrowed | Long perforated heavy-duty conveyor enclosed inside a sealed casing of approximately square cross section moves the waste product though a tunnel; the arrangement approximates a plug flow reactor | Consist of vessels (reactors) of different shapes and sizes; about approximate the characteristics of plug-flow (tubular) reactors or of continuously stirred tank reactors which are mutual in process manufacture |
| Preprocessing | Textile is mixed using standard agricultural equipment | Washing, precomposting, macerating or mixing. Precomposting is particularly benign. | Material is mitt-sorted to foreclose noncompostables from getting into the composting bin. | Textile is shredded and screened. | The drum itself is a precomposting unit of measurement; it homogenizes the waste and sets its decomposition process going | Fabric is shredded | Textile is sorted to remove uncompostables |
| Turning/ aeration | No turning is done; to speed upwards the composting process, agrid of aeration or exhaust pipage 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 washed at periodic intervals with unproblematic 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 functioning. | Equally in the windrows | Air is blown through the conveyor or pan, and is exhausted from the casing summit | A diversity of mechanical and forced aeration systems are used |
| Composting period | 3–4 weeks | 6-seven weeks | 6–8 weeks | iii–4 weeks | 3–4 weeks | ii–3 weeks | two–3 weeks |
| Curing period | four weeks or longer | 6-7 weeks | three–4 weeks | 3–4 weeks without turning | 3–four weeks | iii–4 weeks | 3–4 weeks |
| Operation site | Contained pile systems tin can be used anywhere | Large area is required. | Ideal for household composting | Carried out in the outskirts of towns and cities to avert disturbance to public. Operated every bit an addition to existing landfill operations. | As in the windrows | Suitable merely where adequate land area is available | Can be installed everywhere at widely varying scales of operation |
| Major features | Since turning is not washed, information technology is less dependent on labor. Low odor emission. | Organic matter is converted to more than bioavailable forms. Can be washed in various types of places or containers. | Being small calibration, very effective hand sorting of fabric 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 product, which is otherwise difficult to accomplish by other methods | Highly efficient at low-to-medium scales of functioning Overcomes traditional compaction bug | Enable large masses of waste material to exist composted within much shorter country spaces Ameliorate public acceptance due to less forbidding appearance of the composting site Less manpower requirements Consequent compost quality Better odor control |
| Draw backs | Decomposition progresses at slower rate, causing the textile 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 tin be heterogeneous. | Big surface area and long fourth dimension is needed for composting. | The potential of bin composting can be realized only by ensuring public participation, which until now has been hard to achieve. | Require large country expanse; can cause olfactory property problems, peculiarly when windrows are turned during periods of at-home air and temperature inversion. Likely to release fungal spores and other bioaerosols. | Every bit in windrows | Pose serious feasibility problems at larger scales; occupy more flooring surface, since they are long rather than high | High capital and operational cost. Episodes of odor release can occur due to equipment failure or organisation design limitations |
- Concluding Remarks
Though a number of possible means 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 material-to-energy procedure has great potential to convert the hidden power of municipal solid waste into resource because of greater organic portion in the waste of Dhaka. But as there are financial boundaries for the govt. of a developing country similar Bangladesh, it'due south better implementing the biochemical and chemical procedures initially besides as steps to generate fertilizers past composting as these processes are toll-effective. The do of proper, scientific, and hygienic management of waste material and at the same time turning it into energy or resources, could ensure a safer life of people and at the same time ensure a sustainable good for you temper for our future generations. In that location is a huge gap betwixt the researchers, policy makers and the public, who are the main executives of the target. And then, the enquiry findings should not be poorly considered in policy making like that is going on now. At the aforementioned time, researches should exist public benefit oriented likewise every bit the research paper's language should exist 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 past formulating sustainable and practicable policies. Simply this trio joint-venture tin can solve the monumental waste management trouble in our state and likewise all over the globe. At the same time the Authorities and the public should come forward with enthusiasm to time to fourth dimension to support and alter the policy to make it more fourth dimension worthy and eco-friendly.
- Limitations
Though our target was to publish a complete article with the most recent information well-nigh the solid waste management of different adult cities in the world, merely due to certain limitations and insufficiency of time, it could not be fully possible. And then, nosotros had to depend on some before publications in cases. Moreover, latest data of different topics and places on waste management are lacking. We also observed major deviations of the aforementioned value in different articles in some cases and could not take enough fourth dimension to ostend with those publications. But, our side by side target is to fix 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 mode out of such ecology issues.
- Acknowledgement
Authors are grateful to Nature Study Society of Bangladesh (NSSB) for the agile cooperation and support rendered for the review work.
- Abridgement
Ad – Anaerobic digestion
CFB – Circulating Fluidized Bed
CHP – Combined Rut and Power
DCC – Dhaka Urban center Corporation
DNCC – Dhaka North City Corporation
DoE – Department of Surroundings
DSCC – Dhaka South Metropolis Corporation
JICA – Japan International Cooperation Agency
LFG – Landfill Gas
MSW – Municipal Solid Waste
MSWM – Municipal Solid Waste Direction
MW – Mega Watt
MWh – Mega Watt Hour
NGO – Non-regime Organization
PCBs – Polychlorinated Biphenyls
PCDD/F – Polychlorobenzodioxins / polychlorodibenzofurans
PWCSP – Master 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 Free energy
[N.B.-This article was earlier published in the Periodical Book – Environmental Thoughts, Part-1, 2019; (ISBN: 978-984-93766-2-0)]
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