Faculty of Agricultural Engineering
Assignment
Name: Dabeer-UlMulk Reg.No: 2K17AE-42
Topic:
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Classification of solid waste.
Brief on Solid Waste Management in Pakistan
Classification of Solid waste
Biomass
Waste Processing
Benefits of utilization energy from
Agricultural waste:
Course title: Solid Waste
Management Course code: EE601
Submitted to: Sir Ghulam Shabir Keerio
Solid waste management:
Solid waste management is a term that is used to refer to the process of collecting and treating
solid wastes. It also offers solutions for recycling items that do not belong to garbage or trash.
As long as people have been living in settlements and residential areas, garbage or solid waste
has been an issue. Waste management is all about how solid waste can be changed and used
as a valuable resource.Solid waste management should be embraced by each and every
household, including the business owners across the world. The industrialization has brought a
lot of good things and bad things as well. One of the adverse effects of industrialization is the
creation of solid waste.
Solid-waste management, the collecting, treating, and disposing of solid material that is
discarded because it has served its purpose or is no longer useful. Improper disposal of
municipal solid waste can create unsanitary conditions, and these conditions in turn can lead to
pollution of the environment and to outbreaks of vector-borne disease that is, diseases spread
by rodents and insects.
Physical Characteristics
This includes the determination of percent contents of various ingredients of the solid waste.
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Specific Weight (Density)
Moisture Content
Particle Size and Distribution
Field Capacity
Permeability of Compacted Waste
Specific Weight:
Specific weight is defined as the weight of a material per unit volume (e.g. kg/m3, lb/ft3) usually it
refers to uncompact waste. It varies with geographic location, season of the year, and length of
time in storage.
Moisture Content:
The moisture in a sample is expressed as percentage of the wet weight of the MSW material.
The wet- weight method is most commonly used in the field of solid waste management.
• Wet- weight Moisture content is expressed as follows:
�−�
�=
∗ 100
�
• Where, M= wet-weight moisture content, %
• w= initial mass of sample as delivered, kg (or
lb.)
• d= mass of sample after drying at 77°C, kg (or lb.)
Particle Size and Distribution
The size and distribution of the components of wastes are important for the recovery of
materials, especially when mechanical means are used, such as trommel screens and magnetic
separators.
• The size of waste components can be determined using the following equations:
• SC = L
• SC = (L+w)/2
• SC = (L+w+h)/3
• SC: size of component, mm
• L: length, mm
• W: width, mm
• h: height, mm
Field Capacity
The total amount of moisture that can be retained in a waste sample subject to the downward
pull of gravity. Field capacity is critically important in determining the formation of leachate in
landfills. It varies with the degree of applied pressure and the state of decomposition of wastes,
but typical values for uncompact commingled wastes from residential and commercial sources
are in the range of 50 -60%
Permeability of Compacted Waste:
The permeability (hydraulic conductivity) of compacted solid waste is an important physical
property because it governs the movement of liquids & gases in a landfill.
Permeability depends on:
• Pore size distribution, Surface area and Porosity
Chemical Characteristics:
Chemical properties of SW are very important in evaluating the alternative processing and
recovery options. Used primarily for combustion and waste to energy (WTE) calculations but
can also be used to estimate biological and chemical behaviors. Waste consists of combustible
(i.e. paper) and non- combustible materials (i.e. glass). If solid wastes are to be used as fuel,
the four most important properties to be known are:
Proximate Analysis:
Loss of moisture (temp held at 105 C)
Volatile Combustible Matter (VCM) (temp increased to 950 C, closed
crucible) Fixed Carbon (residue from VCM)
Ash (temp = 950C, open crucible)
Typical Proximate analysis values
Fusing Point of Ash:
Clinker (agglomerations of carbon and metals) formation temperature, 2000 to 2200 F (1100-1200 C)
Typical data on ultimate analysis of combustible materials found in SW
Ultimate Analysis:
Molecular composition (C, H, N, O, P, etc.)
Energy Content:
• Knowledge of the energy content of an organic fraction of solid waste is essential for
evaluating its potential for use as a fuel in a combustion system.
• Depends on the constituents of a sample
• Can be estimated by modified Dulong formula
Energy Content (KJ/Kg) = 338.2C+1430 (H-O/8)
+ 95.4S
Inert Residue and energy content of typical MSW
Brief on Solid Waste Management in Pakistan
Solid waste collection by government owned and operated services in Pakistan's cities
currently averages only 50 percent of waste quantities generated; however, for cities to be
relatively clean, at least 75 percent of these quantities should be collected
Unfortunately, none of the cities in Pakistan has a proper solid waste management system
right from collection of solid waste up to its proper disposal. Much of the uncollected waste
poses serious risk to public health through clogging of drains, formation of stagnant ponds,
and providing breeding ground for mosquitoes and flies with consequent risks of malaria
and cholera. In addition, because of the lack of adequate disposal sites, much of the
collected waste finds its way in dumping grounds, open pits, ponds, rivers and agricultural
land.
Urbanization Pattern:
According to the 1981 census, of the 5.92 million persons who had migrated within the
country, 87.6% moved from rural to urban areas, while only 12.4% moved in the opposite
direction. Over 50% of them permanently settled in cities.
During the last several decades, migration has occurred from rural to urban areas. The
chief factors responsible for this migration are: slow progress in the agriculture sector, low
crop yields, lack of alternate employment opportunities and environmental degradation due
to water logging/salinity, deforestation and desertification.
The large rural influx has, in turn, contributed to the overburdening of urban infrastructure
and urban services. There has not only been a rapid decline in the quality and availability
of basic urban resources and amenities, such as housing, potable water, transportation,
electricity, gas, drainage and sewage but also mushrooming of katchi abadis (squatter
settlements), often located on the most marginal land. Today, squatter settlements account
for about 25 to 30% of Pakistan’s overall urban population. The municipal institutions do not
have sufficient resources and technical capacity to accommodate the needs of increasing
urban population.
According to a study1, the selected cities are growing at a growth rate from 3.67% to 7.42%
which is much higher than the overall growth rate of Pakistan, i.e. 2.8%. Major cities in
Pakistan are estimated to double their population in next ten years. These cities are
generating high amounts of solid waste which is increasing annually with the respective
population growth.
Growth in Solid Waste Generation
Presently it is estimated that, 54,888 tons per day of solid waste is generated in Pakistan.
The Ministry of Environment undertook a study during 1996 on “Data Collection for
Preparation of National Study on Privatization of Solid Waste Management in Eight Selected
Cities of Pakistan”. The study revealed that the rate of waste generation on average from
all type of municipal controlled areas varies from 0.283 kg/capita/day to 0.613
kg/capita/day or from 1.896 kg/house/day to 4.29 kg/house/day in all the selected cities. It
shows a particular trend of waste generation wherein increase has been recorded in
accordance with city's population besides its social and economic development. Table 2
presents city wise waste generation rate with respective daily and annual estimate of solid
waste.
Table 2.
S.
No
Waste Generation Estimates
Cities
Waste
Generation
Rate
Kg/c/day
Kg/h/day
Generate
d Tons/day
Tons/ye
1
2
3
4
5
6
7
8
Gujranwala
Faisalabad
Karachi
Hyderabad
Peshawar
Bannu
Quetta
Sibi
Total
0.469
0.391
0.613
0.563
0.489
0.439
0.378
0.283
3.424
2.737
4.291
3.941
3.423
2.941
2.646
1.896
ar
824.0
924.3
6,450.0
975.7
809.3
36.0
378.0
17
10,414.3
300,760
337,370
2,354,250
356,131
295,395
13,140
137,970
6,205
3,601,22
1
Keeping in view the population growth of 2.61 % per year, an estimate of solid waste
generation has been made as presented in table 3.
Table 3. Solid waste Generation on the basis of population for 2004
City
Urban Areas
Karachi
Faisalabad
Hyderabad
Gujranwala
Peshawar
Quetta
Bannu
Sibi
Remainin
g urban
areas
Rural Areas
Sub-Total
Add 3 % for
hazardo
us
waste
G Total
Population
(Million)
1998
Census
Populatio
n
(Million)
2004
Solid Waste Waste
Generation Generated
Tons/day
Rate
Kg/C/da
y
Tons/year
9.269
1.977
1.151
1.124
0.988
0.560
0.046
0.082
27.261
10.818
2.307
1.343
1.312
1.153
0.654
0.054
0.095
31.818
0.613
0.391
0.563
0.469
0.489
0.378
0.439
0.283
0.453
6,632
902
756
615
564
247
24
27
14,414
2,420,680
329,230
275,940
224,475
205,860
90,155
8,760
9,855
5,261,110
88.121
102.85
3
152.40
9
0.283
29,108
10,624,420
53,289
19,450,485
1,599
583,635
54,888
20,034,120
130.579
It is important to note there is a big difference in Pakistan between solid waste generation and the
amounts reaching final disposal sites. In developed countries, the two figures are usually
much the same since most waste arising must be disposed of formally (although) there are
moves towards the segregation of some components of waste at the source in a number of
countries
The situation is made worse in Pakistan as there are no weighing facilities at disposal sites
and no tradition of waste sampling and analysis. Furthermore, the types and quantities of
wastes arising and reclaimed vary with the locality and, to some extent, with the season;
and areas with more traditional lifestyles tend to generate relatively small quantities of
waste, and segregation and reclamation practices are more widespread.
Solid Waste Management Scenario – Strategic Challenges
Solid waste in Pakistan is generally composed of plastic and rubber, metal, paper and
cardboard, textile waste, glass, food waste, animal waste, leaves, grass, straws and
fodder, bones, wood, stones and fines to various extents. The detailed physical
compositions of waste are given in Table 4III.
Table 4 Physical Composition of Waste (% weight) in selected Cities
Cities
Faisalabad
Karachi
Hyderabad
Peshawar
Quetta
Plastic &
Rubber
Metals
Paper
Card board
Rags
Glass
Bones
Food Waste
4.80
6.40
3.60
3.70
8.20
0.20
2.10
1.60
5.20
1.30
2.90
17.20
0.75
4.10
2.40
8.40
1.50
3.00
21.00
0.75
2.40
1.50
4.70
1.60
2.00
20.00
0.30
2.10
1.90
4.30
1.30
1.70
13.80
0.20
2.20
1.30
5.10
1.50
2.00
14.30
Animal Waste
Leaves, grass
etc.
Wood
Fines
0.80
15.60
3.00
14.00
5.80
13.50
7.50
13.60
1.70
10.20
0.70
43.00
2.25
29.70
2.25
38.90
0.60
42.00
1.50
44.00
Stones
4.60
3.50
3.00
7.30
7.80
The typical composition of municipal solid waste in Pakistan is shown in Table 5
Table 5. Typical Composition of Solid Waste in Pakistani Cities (%)
Composition
Food Waste
%
8.4% to 21 %
Leaves, grass, straw,
Fodder
Fines
Recyclables
10.2 % to 15.6 %
29.7 % to 47.5 %
13.6 % to 23.55 %
Presently domestic waste in Pakistan has not been carried out in a sufficient and proper
manner in collection, transportation and disposal regardless of the size of the city. Solid
waste management by municipalities as a whole is quite inefficient as it collects only 5169% of the total waste generated. No weighing facilities are installed at disposal sites. The
scavengers play an important role as they separate recyclable at various steps of existing
solid waste management. Hazardous hospital and industrial wastes are being simply
treated as ordinary waste. Open burning of waste especially non- degradable components
like plastic bags are adding to air pollution. Municipalities have been reported to spend
considerable portion of their budgets on solid waste management but as a return receive
nothing (no tax) from the population being served.
Institutional, Legal and Management Aspects
The Planning & Development Division at the federal level and Planning & Development
Departments at the provincial levels are responsible for the preparation of development
plans and allocation of resources. At the federal level, the Ministry of Environment is
responsible for the development of policies and programmers under the environment
theme. The Pakistan Environmental Protection Agency (PEPA) and provincial EPAs are
the main regulatory bodies for the implementation of Pakistan Environmental Protection
Act, 1997. In Pakistan, municipal governments are usually responsible agency for solid
waste collection and disposal, but magnitude of the problem is well beyond the ability of
any municipal government. Under the recently devolved local government system, the
Town/Tehsil Municipal Administration (TMAs) are responsible for the solid waste collection,
transportation and disposal. However, TMAs are unable to cope with continuously
increasing volumes of municipal waste due to inadequate funds, lack of rules, regulations
and standards, lack of knowhow on the subject, lack of expertise and lack of collection
vehicles and equipment.
Solid Waste Management Policy
The Government of Pakistan enacted the Pakistan Environmental Protection Act (PEPA) in
1997-- which is the most recent and updated legislation on environment. It provides a
framework for establishing federal and provincial Environmental Protection Agencies
(EPAs). One of the functions of Pak-EPA is to assist the local councils, local authorities,
Government Agencies and other persons to implement schemes for the proper disposal of
wastes so as to ensure compliance with the standards established by it.
Presently the legal rules and regulations dealing with solid waste management in Pakistan
are as follows:
Current
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Section 11 of the Pakistan Environmental Protection Act prohibits discharge of
waste in an amount or concentration that violates the National Environmental
Quality Standards.
Draft Hazardous Substances Rules of 1999.
Islamabad Capital Territory Bye Laws, 1968 by Capital Development Authority
Islamabad
“Section 132 of the Cantonment Act 1924 deals with Deposits and disposal of
rubbish etc.
Provisions contained in the Local Government Ordinance, 2001
Required
The rules and guidelines that are yet to be introduced include:
 Basic Recycling rules
 Waste Management rules
 E-Waste Management rules
 Development of Environmental Performance Indicators (EPI)
 Eco-Labeling guidelines and its promotion
 Adoption of Life Cycle Assessment Approaches
 Guidelines for Environmentally Sound Collection and Disposal
 Guidelines for model landfill site
Classification of Solid waste:
Some of the major various classification of solid waste are as follows:
1. Municipal Waste
2. Domestic I Residential Waste
3. Commercial Waste
4. Garbage
5. Rubbish
6. Institutional Waste
7. Ashes
8. Bulky Wastes
9. Street Sweeping
10. Dead Animals
11. Construction and Demolition Wastes
12. Industrial Wastes
13. Hazardous Wastes
14. Sewage Wastes
15. Biomedical/Hospital Waste
16. Plastics.
Solid waste is the material generated from various human activities and which is normally disposed
as useless and unwanted.
1. Municipal Waste:
Municipal waste includes waste resulting from municipal activities and services such as street
wastes, dead animals, market wastes and abandoned vehicles. However, the term is commonly
applied in a wider sense to incorporate domestic wastes and commercial wastes.
2. Domestic I Residential Waste:
This category of waste comprises the solid wastes that originate from single and multi-family
house hold units. These wastes are generated as a consequence of house hold activities such as
cooking, cleaning, repairs, hobbies, redecoration, empty containers packaging, clothing, old
books, paper and old furnishings.
3. Commercial Waste:
Included in this category are solid wastes that originate in offices, wholesale and retail stores,
restaurants, hotels, markets, warehouses and other commercial establishments. Some of these
wastes are further classified as garbage and others as rubbish.
4. Garbage:
Garbage is the term applied to animal and vegetable waste resulting from the handling, storage,
sale, cooking and serving food. Such wastes contain putrescible organic matter, which produces
strong odors and therefore attracts rats, flies and other vermin. It requires immediate attention in
its storage, handling and disposal.
5. Rubbish:
Rubbish is general term applied to solid wastes originating in households, commercial
establishments and institutions, excluding garbage & ashes.
6. Institutional Waste:
Institutional wastes are those arising from institutions such as schools, universities, hospitals and
research institutes. It includes wastes, which are classified as garbage and rubbish, as well as
wastes, which are considered to be hazardous to public health and to the environment.
7. Ashes:
Ashes are the residues from the burning of wood, coal, charcoal, coke and other combustible
materials for cooking and heating in houses, institutions and small industrial establishments. When
produced in large quantities at power generation plants and factories, these wastes are classified
as industrial wastes. Ashes consist of a fine powdery residue, cinders and clinker often mixed with
small pieces of metal and glass.
8. Bulky Wastes:
In this category are bulky household wastes, which can’t be accommodated in the normal storage
containers of households. For this reason, they require special collection. In developed countries
residential bulky wastes include household furniture and “white goods” appliances such as stoves,
washing machines and refrigerators, mattresses and springs, rugs, TV sets, water heaters, tires,
lawn mowers, auto parts, tree and brush debris, and so forth. Commercial bulky wastes include
packaging and containers in a wide range of sizes, including corrugated cardboard, and wood
boxes, fiber, plastic and steel drums usually under 40 gallons (0.15m3), loose and bundled paper
(office, printouts), bundles of textiles and plastics, bales of corrugated and paper, furniture and
equipment, and flat and wire banding. Industrial bulky waste includes dunnage, including crates,
cartons, pallets, skids; large and small steel, fiber, and plastic drums; bales and rolls of paper,
plastics, and textiles; miscellaneous metal boxes, tubing, rod, punching’s, and skeleton; wire, rope,
and metal banding; and paper, textile, and plastic streamers (William D. Robinson, 1986).
9. Street Sweeping:
This term applies to wastes that are collected from streets, walkways, alleys, parks and vacant
lots. In the more affluent countries manual street sweeping has virtually disappeared but it still
commonly takes place in developing countries, where littering of public places is a far more
widespread and acute problem. Street wastes include paper, cardboard, plastic, dirt, dust, leaves
and other vegetable matter.
10. Dead Animals:
This is term applied to dead animals that die naturally or accidentally killed. This category does not
include carcass and animal parts from slaughterhouses, which are regarded as industrial wastes.
Dead animals are divided into 2 groups, large and small. Among the large animals are Horses,
Cows, Goats, Sheep and the like. Small animals include dogs, cats, rabbits and rats. The reason
for this differentiation is that large animals require special equipment for lifting and handling during
their removal. If not collected promptly, dead animals are a threat to public health because they
attract flies and other vermin as they putrefy. Their presence in public places is particularly
offensive and emits foul smell from the aesthetic point of view.
11. Construction and Demolition Wastes:
Construction and demolition wastes are the waste materials generated by the construction,
refurbishment, repair and demolition of houses, commercial buildings and other structures. It
mainly consists of earth, stones, concrete, bricks, lumber, roofing materials, plumbing materials,
heating systems and electrical wires and parts of general municipal waste stream, but when
generated in large amounts at building and demolition sites, it is generally removed by contractors
for filling low lying areas and by urban local bodies for disposal at landfills. While retrievable items
such as bricks, wood metal are recycled, the concrete and masonry waste accounting for 50% of
the waste from construction and demolition activities, are not been currently recycled in India.
Concrete and masonry waste can be recycled by sorting, crushing and sieving into recycled
aggregates. These recycled aggregates can be used to make concrete for road construction and
building material. This category waste is complex due to the different types of building materials
being used but in general may comprise of major components like: Cement concrete, Bricks,
Cement plaster, Steel (from RCC, door/ window frames, roofing support etc., Rubble, Stone
(marble, granite, sand stone), Timber/wood and a few minor components like Conduits (iron,
plastic), Pipes (GI, iron, plastic), Electrical fixtures (copper/ aluminum wiring, wooden baton,
Bakelite, wire insulation, plastic switches), Panels (wooden, laminated), Others (Glazed tiles, glass
panels).
12. Industrial Wastes:
In this category are the discarded solid material of manufacturing processes and industrial
operations. They cover a vast range of substances which are unique to each industry. For this
reason, they are considered separately from municipal wastes. However, solid wastes from small
industrial plants and ash from power plants are frequently disposed of at municipal landfills. The
major generators in the industrial solid wastes are the thermal power plants producing coal ash,
the integrated Iron and steel mills producing blast furnace slag and steel melting slag, non-ferrous
industries like aluminum, zinc, and copper producing red mud and tailings, sugar industries
generating press mud, pulp and paper industries producing lime and fertilizer and allied industries
producing gypsum. The source and quantum of generation of some major industrial wastes are:
13. Hazardous Wastes:
Hazardous wastes may be defined as wastes of industrial, institutional or consumer origin which
because of their physical, chemical or biological characteristics are potentially dangerous to
human and the environment. In some cases, although the active agents may be liquid or gaseous,
they are classified as solid waste because they are confined in solid containers. Typical examples
are solvents, paints and pesticides whose spent containers are frequently mixed with municipal
wastes and become part of urban waste stream. Table 5.10 lists typical hazardous products found
in co-mingled with municipal solid waste. Certain hazardous wastes cause explosions in
incinerators and fires at landfill sites. Others, such as pathological wastes from hospitals and
radioactive wastes, require special handling at all time. Good management practice should ensure
that hazardous wastes are stored, collected, transported and disposed of separately, preferably
after suitable treatment to render them innocuous.
Hazardous products found in co-mingled with municipal solid waste:
Product
Concern
Household cleaners:
Corrosive, Flammable and Irritants
Chlorine bleach, Furniture polish, Glass cleaners, Outdated
medicines, Shoe polish, Silver polish, Spot remover, Drain
openers etc.
Personal Care products:
Poisonous and Flammable
Hair waving lotions, Medicated shampoos, Nail polish remover,
Rubbing alcohol
Automotive Products:
Flammable, Poison and Corrosive
Antifreeze, Brake and transmission fluid, Car batteries, Diesel
fuel, Kerosene, Gasoline and Waste oil
Paint Products: Enamel, Paints and paint solvents and thinners
Flammable
14. Sewage Wastes:
The solid by-products of sewage treatment are classified as sewage wastes. They are mostly
organic and derive from the treatment of organic sludge from both the raw and treated sewage.
The inorganic fraction of the raw sewage such as grit is separated at a preliminary stage of
treatment, but because it entrains putrescible organic matter which may contain pathogens, must
be buried/disposed of without delay.
The bulk of treated dewatered sludge is useful as a soil conditioner but invariably its use for this
purpose is uneconomical. The solid sludge therefore enters the stream of municipal wastes unless
special arrangements are made for its disposal.
15. Biomedical/Hospital Waste:
Hospital waste is generated during the diagnosis, treatment, or immunization of human beings or
animals or in research activities in these fields or in the production or testing of biological. It may
include wastes like sharps, soiled waste, disposables, anatomical waste, cultures, discarded
medicines, chemical wastes, etc. These are in the form of disposable syringes, swabs, bandages,
body fluids, human excreta, etc. This waste is highly infectious and can be a serious threat to
human health if not managed in a scientific and discriminate manner. It has been roughly estimated
that of the 4 kg of waste generated in a hospital at least 1 kg would be infected.
These wastes are categorized into 10 different categories as:
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Human anatomical waste (tissues, organs, body parts etc.)
Animal waste
Microbiology and biotechnology waste, such as, laboratory cultures, microorganisms,
human and animal cell cultures, toxins etc.
Waste sharps such as, hypodermic needles, syringes, scalpels, broken glass etc.
Discarded medicines and cyto-toxic drugs
Soiled waste, such as dressings, bandages, plaster casts, material contaminated with blood etc.
Solid waste (disposal items like tubes, catheters etc., excluding sharps)
Liquid waste generated from any of the infected areas
Incineration ash
Chemical waste
16. Plastics:
Plastics, due to their versatility in use and impact on environment can be grouped under a different
category of solid waste. Plastic with its exclusive qualities of being light yet strong and economical,
has invaded every aspect of our day-to-day life. It has many advantages viz., durable, light, easy
to mold, and can be adapted to different user requirements. Once hailed as a ‘wonder material’,
plastic is now a serious worldwide environmental and health concern, essentially due to its nonbiodegradable nature.
Source of generation of waste plastics:
Household
Carry bags Bottles Containers Trash bags
Health and Medicare
Disposable syringes Glucose bottles Blood and uro bags Intravenous tubes Catheters ,Surgical gloves
Hotel and Catering
Packaging items, Mineral water bottles, Plastic plates, glasses, spoons
Air/Rail Travel
Mineral water bottles Plastic plates, glasses, spoons Plastic bags
Biomass:
Biomass is used for facility heating, electric power generation, and combined heat and power.
The term biomass encompasses a large variety of materials, including wood from various
sources, agricultural residues, and animal and human waste. Biomass can be converted into
electric power through several methods. The most common is direct combustion of biomass
material, such as agricultural waste or woody materials. Other options include gasification,
pyrolysis, and anaerobic digestion. Gasification produces a synthesis gas with usable energy
content by heatingthe biomass with less oxygen than needed for complete combustion. Pyrolysis
yields bio-oil by rapidly heating the biomass in the absence of oxygen. Anaerobic digestion
produces a renewable natural gas when organic matter is decomposed by bacteria in the absence
of oxygen.
Different methods work bet with different types of biomass. Typically, woody biomass such as
wood chips, pellets, and sawdust are combusted or gasified to generate electricity. Corn Stover
and wheat straw residues are baled for combustion or converted into a gas using an anaerobic
digester. Very wet wastes, like animal and human wastes, are converted into a medium-energy
content gas in an anaerobic digester. In addition, most other types of biomass can be converted
into bio-oil through pyrolysis, which can then be used in boilers and furnaces.
Image of a generation station with a large skip of woody
materials from the agricultural industry being loaded into it.
In Woodland, California, a generation station uses wood from
the agricultural industry.
This overview focuses on woody biomass used for generating electricity at a commercial-scale
facility rather than a utility-scale project. Biomass heat and biogas, including anaerobic digestion
and landfill gas, are covered in other technology resource pages in this guide:
 Biomass Heat
 Biogas
Compared to many other renewable energy options, biomass has the advantage of dispatch
ability, meaning it is controllable and available when needed, similar to fossil fuel electric
generation systems. The disadvantage of biomass for electricity generation, however, is that the
fuel needs to be procured, delivered, stored, and paid for. Also, biomass combustion produces
emissions, which must be carefully monitored and controlled to comply with regulations.
DESCRIPTION
Most bio power plants use direct-fired combustion systems. They burn biomass directly to
produce high- pressure steam that drives a turbine generator to make electricity. In some
biomass industries, the extracted or spent steam from the power plant is also used for
manufacturing processes or to heat buildings. These combined heat and power (CHP) systems
greatly increase overall energy efficiency to approximately 80%, from the standard biomass
electricity-only systems with efficiencies of approximately 20%. Seasonal heating requirements
will impact the CHP system efficiency.
A simple biomass electric generation system is made up of several key components. For a steam
cycle, this includes some combination of the following items:
 Fuel storage and handling equipment
 Combustor / furnace
 Boiler
 Pumps
 Fans
 Steam turbine
 Generator
 Condenser
 Cooling tower
 Exhaust / emissions controls
 System controls (automated).
Direct combustion systems feed a biomass feedstock into a combustor or furnace, where the
biomass is burned with excess air to heat water in a boiler to create steam. Instead of direct
combustion, some developing technologies gasify the biomass to produce a combustible gas,
and others produce pyrolysis oils that can be used to replace liquid fuels. Boiler fuel can include
wood chips, pellets, sawdust, or bio- oil. Steam from the boiler is then expanded through a
steam turbine, which spins to run a generator and produce electricity.
In general, all biomass systems require fuel storage space and some type of fuel handling
equipment and controls. A system using wood chips, sawdust, or pellets typically use a bunker or
silo for short-term storage and an outside fuel yard for larger storage. An automated control
system conveys the fuel from the outside storage area using some combination of cranes,
stackers, re-claimers, front-end loaders, belts, augers, and pneumatic transport. Manual
equipment, like front loaders, can be used to transfer biomass from the piles to the bunkers, but
this method will incur significant cost in labor and equipment operations and maintenance (O&M).
A less labor-intensive option is to use automated stackers to build the piles and re- claimers to
move chips from the piles to the chip bunker or silo.
Wood chip-fired electric power systems typically use one dry ton per megawatt-hour of electricity
production. This approximation is typical of wet wood systems and is useful for a first
approximation of fuel use and storage requirements but the actual value will vary with Most wood
chips produced from green lumber will have a moisture content of 40% to 55%, wet basis, which
means that a ton of green fuel will contain 800 to 1,100 pounds of water. This water will reduce
the recoverable energy content of the material, and reduce the efficiency of the boiler, as the
water must be evaporated in the first stages of combustion. System efficiency. For comparison,
this is equivalent to 20% HHV efficiency with 17 MMBtu/ton wood. The biggest problems with
biomass-fired plants are in handling and pre-processing the fuel. This is the case with both small
grate-fired plants and large suspension-fired plants. Drying the biomass before combusting or
gasifying it improves the overall process efficiency, but may not be economically viable in many
cases. Exhaust systems are used to vent combustion by-products to the environment. Emission
controls might include a cyclone or multi-cyclone, a baghouse, or an electrostatic precipitator.
The primary function of all of the equipment listed is particulate matter control, and is listed in
order of increasing capital cost and effectiveness. Cyclones and multi-cyclones can be used as
pre-collectors to remove larger particles upstream of a baghouse (fabric filter) or electrostatic
precipitator.In addition, emission controls for unburned hydrocarbons, oxides of nitrogen, and
sulfur might be required, depending on fuel properties and local, state, and Federal regulations.
How Does It Work?
In a direct combustion system, biomass is burned in a combustor or furnace to generate hot gas,
which is fed into a boiler to generate steam, which is expanded through a steam turbine or
steam engine to produce mechanical or electrical energy.
Illustration of how a direct combustion/steam turbine system operates. The biomass first goes
into storage, then preparation and processing, and on to simultaneously create ash and
exhaust. From there, the biomass becomes boiler fuel that produces steam to operate a steam
turbine and generator to make electricity.
In a direct combustion system, processed biomass is the boiler fuel that produces steam to
operate a steam turbine and generator to make electricity.
Types and Costs of Technology
There are numerous companies, primarily in Europe, that sell small-scale engines and combined
heat and power systems that can run on biogas, natural gas, or propane. Some of these systems
are available in the United States, with outputs from about 2 kilowatts (kW), and approximately
20,000 British thermal units (Btu) per hour of heat, to several megawatts (MW). In addition,
small-scale (100 to 1,500 kW) steam engine/gen-sets and steam turbines (100 to 5,000 kW) that
are fueled by solid biomass are currently available in Europe.
In the United States, direct combustion is the most common method of producing heat from
biomass. Small-scale biomass electric plants have installed costs of $3,000 to $4,000 per kW,
and a leveled cost of energy of $0.8 to $0.15 per kilowatt hour (kWh).
The two principal types of chip-fired direct combustion systems are stationary- and travelinggrate combustors, otherwise known as fixed-bed stokers and atmospheric fluidized-bed
combustors.
FIXED-BED SYSTEMS
There are various configurations of fixed-bed systems, but the common characteristic is that fuel
is delivered in some manner onto a grate where it reacts with oxygen in the air. This is an
exothermic reaction that produces very hot gases and generates steam in the heat exchanger
section of the boiler.
FLUIDIZED-BED SYSTEMS
In either a circulating fluidized-bed or bubbling fluidized-bed system, the biomass is burned in a
hot bed of suspended, incombustible particles, such as sand. Compared to grate combustors,
fluidized-bed systems generally produce more complete carbon conversion, resulting in reduced
emissions and improved system efficiency. In addition, fluidized-bed boilers can use a wider
range of feedstock’s. Furthermore, fluidized-bed systems have a higher parasitic electric load
than fixed-bed systems due to increased fan power requirements.
BIOMASS GASIFICATION SYSTEMS
Photo of a small, modular bio power system. Small,
modular bio power system by Community Power
Corporation
Although less common, biomass gasification systems are similar to combustion systems, except
that the quantity of air is limited, and thus produce a clean fuel gas with a usable heating value
in contrast to combustion, in which the off gas does not have a usable heating value. Clean fuel
gas provides the ability to power many different kinds of gas-based prime movers, such as
internal combustion engines, Stirling engines, thermos electric generators, solid oxide fuel cells,
and micro-turbines.
The efficiency of a direct combustion or biomass gasification system is influenced by a number of
factors, including biomass moisture content, combustion air distribution and amounts (excess
air), operating temperature and pressure, and flue gas (exhaust) temperature.
APPLICATION
The type of system best suited to a particular application depends on many factors, including
availability and cost of each type of biomass (e.g. chip, pellet, or logs), competing fuel cost (e.g.
fuel oil and natural gas), peak and annual electrical loads and costs, building size and type,
space availability, operation and maintenance staff availability, and local emissions regulations.
Projects that can make use of both electricity production and thermal energy from biomass energy
systems are often the most cost effective. If a location has predictable access to year-round,
affordable biomass resources, then some combination of biomass heat and electricity production
may be a good option. Transportation of fuel accounts for a significant amount of its cost, so
resources should ideally be available from local sources. In addition, a facility will typically need to
store biomass feedstock on-site, so site access and storage are factors to consider.
As with any on-site electricity technology, the electricity generating system will need to be
interconnected to the utility grid. The rules for interconnection may be different if the system is a
combined heat and power system instead of only for electricity production. The ability to take
advantage of net metering may also be crucial to system economics.
Waste Processing:
Waste processing means the physical alteration in waste to make it best suited for technology
adopted for its treatment. The processing of wastes helps in achieving the best possible benefit
from every functional element of the solid waste management (SWM) system. It requires
proper selection of techniques and equipment for every element to derive maximum
economical value. Various methods used in waste processing are baling, shredding,
compaction, drying, metal segregation etc.
Objectives of processing techniques:
Three major objectives of any processing done on waste are: Improving efficiency of SWM system: the technology should always help in making the waste
transport and storage effective.
Example – waste paper is baled to reduce transporting and storage volume requirements, compaction and
shredding of waste is done to improve the efficiency of the transportation and disposal.
Recovery of resources: materials with high market value and in sufficient quantity are
recovered from mixed waste by various segregation techniques
Example - paper, cardboard, plastic, glass, ferrous metal, aluminum and other residual metals
Recovering conversion products and energy: Combustible organic materials can be
converted to intermediate products and ultimately to usable energy. Incineration, pyrolysis,
composting or bio- digestion.
Shredding and drying is necessary before the waste material can be used for power generation
to reduce moisture content.
At the stage of storage and transportation, it is very important to store maximum waste in one
truck and small storage area. This reduces the fright of trucks and storage space thus reduces
the investment. Various methods are used to reduce the volume of waste. The most widely
used techniques are mechanical, chemical and thermal techniques of volume reduction.
Manure:
Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists
of animal feces; other sources include compost and green manure. Manures contribute to the
fertility of soil by adding organic matter and nutrients, such as nitrogen, that are utilized by
bacteria, fungi and other organisms in the soil. Higher organisms then feed on the fungi and
bacteria in a chain of life that comprises the soil food web.
History
According to a Byzantine tradition attributed to Cassian’s Bassus pig dung was generally not
usable as fertilizer, except for almond trees. Similar views recorded by Columella were
unrelated to the Islamic taboos of later centuries, though the medieval Andalusian writer Ibn
Bassal and some later writers from Yemen also recorded negative effects of pig dung "burning"
plants. Ibn Bassal described a sort of mixed manure with straw or sweeping mixed in as mudaf,
implying that was not composed of only manure.
The sweepings from hot baths included urine and human wastes, which Ibn Bassal describes
as dry and salty, unsuitable for use as fertilizer unless mixed with manure. Ibn Bassal gives two
recipes for composting pigeon (hamam) and possibly donkey (himar) manure, though the
translation is uncertain. Bassal says the excessive heat and moist qualities of pigeon dung
worked well for weaker and less hardy plants, especially those effected by cold temperatures.
Types
Skatole is the source of the foul smelling odor of manure.
There are in the 21st century three main classes of manures used in soil management:
1. Animal manure
2. Compost
3. Green manure
Animal manure:
Concrete reservoirs, one new, and one containing cow manure mixed with water. This is
common in rural Hainan Province, China.
Most animal manure consists of feces. Common forms of animal manure include farmyard
manure (FYM) or farm slurry (liquid manure).FYM also contains plant material (often straw),
which has been used as bedding for animals and has absorbed the feces and urine. Agricultural
manure in liquid form, known as slurry, is produced by more intensive livestock rearing systems
where concrete or slats are used, instead of straw bedding. Manure from different animals has
different qualities and requires different application rates when used as fertilizer. For example
horses, cattle, pigs, sheep, chickens, turkeys, rabbits, and guano from seabirds and bats all have
different properties. For instance, sheep manure is high in nitrogen and potash, while pig
manure is relatively low in both. Horses mainly eat grass and a few weeds so horse manure can
contain grass and weed seeds, as horses do not digest seeds the way that cattle do. Cattle
manure is a good source of nitrogen as well as organic carbon.[4]Chicken litter, coming from a
bird, is very concentrated in nitrogen and phosphate and is prized for both properties. Animal
manures may be adulterated or contaminated with other animal products, such as wool (shoddy
and other hair), feathers, blood, and bone. Livestock feed can be mixed with the manure due to
spillage. For example, chickens are often fed meat and bone meal, an animal product, which
can end up becoming mixed with chicken litter.
Compost
Compost containing turkey manure and wood chips from bedding material is dried and then
applied to pastures for fertilizer.
Compost is the decomposed remnants of organic materials. It is usually of plant origin, but
often includes some animal dung or bedding.
Green manure
Green manures are crops grown for the express purpose of plowing them in, thus increasing
fertility through the incorporation of nutrients and organic matter into the soil. Leguminous plants
such as clover are often used for this, as they fix nitrogen using Rhizobia bacteria in specialized
nodes in the root structure. Other types of plant matter used as manure include the contents of
the rumens of slaughtered ruminants, spent grain (left over from brewing beer) and seaweed.
Benefits of utilization energy from agricultural waste:
Energy utilization of agricultural waste is among the most effective methods for disposing of
agricultural waste. It refers to the conversion of agricultural waste into clean energy. This includes
the use of crop field residues such as crop straw, crop process residues such as rice husk and
corncob, livestock breeding waste such as farm bedding and manure, and slaughterhouse
waste such as carcasses and wastewater. Over the last decades, remarkable improvements
have been made in technology for energy utilization of agricultural wastes, including agricultural
wastes gasification technologies such as straw thermal cracking gas and biogas, agricultural
wastes liquefaction technologies such as hydrolysis, enzymolysis, Fischer–Tropic synthesis,
and water phase catalysis, agricultural wastes solidification technologies such as biomass
briquette technology and steam explosion pretreatment technologies, and power generation
technologies from agricultural wastes, such as straw directly burning, straw–coal co-firing and
biogas generate electric technologies. In addition, with the advancing energy utilization
technology of agricultural waste, the forms of energy utilization of agricultural waste have
become more and more diversified, and the major types include pyrolysis gas, biogas, biomass
molding fuel, fuel ethanol, bio- gasoline, bio-kerosene, bio-diesel, and electricity, and so forth.
Accordingly, a great variety of by-products are generated during the process of energy utilization
of agricultural waste, such as biogas residue. Of late, with the deepening of research on
energy utilization of agricultural waste, scholars started to devote themselves in the study of
biogas residue disposal, in order to prevent secondary pollution. In recent years, the
importance of energy utilization of agricultural waste has been widely recognized by all sectors
of the community. First, large-scale farming creates a huge amount of agricultural waste that
aggravates environmental problems, widely existing in developing and developed countries
Energy utilization of agricultural waste is helpful to the release of fossil fuel shortage.
Researchers have found that agricultural wastes, including crop straw and livestock manure,
will be the most perspective energy source as an alternative of nonrenewable energy in the
near future [Energy utilization of agricultural waste is conducive to relieve the issues of global
resource waste. Great efforts have been done in resources utilization of agricultural waste in
some countries, and the comprehensive utilization ratio of agricultural waste has been
significantly increased. Energy utilization of agricultural waste contributes to environmental
improvement. With rapid economic development, energy consumption has gradually increased,
which causes a series of serious environmental problems. At present, environmental issues
have gradually become one of the biggest obstacles to economic development. Sustainable
development of the economy and environment is one of the most important issues for modern
society. The shortage of fossil energy has restricted the sustainable development of the
economy and environment. The combustion of fossil fuel (a nonrenewable resource) has been
seen as a major cause of global climate change. Energy utilization of agricultural waste in rural
areas has obvious advantages. A study on farm anaerobic digestion of agricultural waste
shows that, with anaerobic digestion, the Greenhouse Gas (GHG) emission reduction effect
can be strengthened by the increased CH4 production potential. Therefore, encouraging
energy utilization of agricultural wastes has been recognized as an important factor for
environmental problem improvement. Energy utilization of agricultural waste could not only
conduce to solving resource and environmental problems, but also bring great
economicbenefits.