Waste Management

Wastes are any unwanted or discarded material from residential, commercial, industrial, or agricultural activities that may cause environmental problems. Not necessarily pollutants. Through recycling it might even possible to make it usable. Waste management is a problem in both urban and rural areas in our country as elsewhere in the world.

Waste management is the collection, transport, processing or disposal, managing and monitoring of waste materials. The goals of waste management are to minimize waste quantity, reduce the amount of raw materials consumed, dispose of non-hazardous waste cost-effectively, and dispose of hazardous waste with minimal risk to human health and the environment. 

 How Pollutants Enter the Environment

Hazardous-waste pollutants from a solid-waste disposal site may enter the environment by as many as six paths:

1.        Methane, ammonia, hydrogen sulfide, and nitrogen gases may enter the atmosphere through emission

2.       Heavy metals, such as lead, chromium, and iron may be retained in the soil

3.       Soluble materials, such as chloride, nitrate, and sulfate may reach the groundwater system through seepage and leakage

4.      Overland runoff may transport leachate into streams and rivers

5.       Heavy metals and other toxic materials may enter food chain via plant uptake growing near the disposal site

6.      Crop residue containing toxic substances returns these to the soil after decomposition.

Early Concepts of Waste Disposal

Early concept of waste disposal was “dilute and disperse” as the volume of waste produced was relatively small. Factories were located near rivers because the water provided a number of benefits, including easy transport of materials by boat, sufficient water for processing and cooling, and easy disposal of waste into the river. With a few factories and sparse population, dilute and disperse seemed to remove the waste from the environment.

As industrial and urban areas expanded, the concept of dilute and disperse became inadequate and a new concept “concentrate and contain” is giving way to concepts of waste management focusing on managing materials and eliminating waste. It has become apparent; however, that containment was and is not always achieved. Containers, whether landfills or drums, natural or artificial, may leak or break and allow waste to escape.

Modern Trends

The environmentally preferable concept with respect to waste management is to consider wastes as resources out of place. It seems apparent that the cost of raw materials, energy, transportation, and land will make it economically feasible to reuse and recycle more resources. Moving toward this objective is moving toward an environmental view that there really is no such thing as waste, only resources. Under this concept, waste would not exist, because it would not be produced or, if produced, would be a resource to be used again. This concept is referred to as the “Zero waste” movement where waste from one part of the system would be a resource for another part.

Integrated Waste Management

The dominant concept today in managing waste is known as the integrated waste management (IWM), which is best defined as a set of management alternatives including the three R’s (reduce, recycle, reuse) of waste prevention, incineration, composting, and landfill.

Reduce, Recycle, Reuse

The three R’s of IWM are reduce, recycle, and reuse. The ultimate objective of the three R’s is to reduce the amount of urban and other waste that must be disposed of in landfills, incinerators, or other waste management facilities.

A 50% reduction by weight of urban waste could be facilitated by:

• Better design of packaging to reduce waste, an element of source reduction (10% reduction);
• Establishment of recycling programs (30% reduction) and
• Large scale composting programs (10% reduction).

Above mentioned list suggests that recycling is a major player in the reduction of the urban waste stream. There are two types of recycling for materials such as glass, metals, paper, and plastics. One is closed-loop recycling. It occurs when wastes discarded by consumers are recycled to produce new products of the same type (such as newspaper into newspaper). This reduces pollution and use of virgin resources and saves energy.

The second type is down cycling in which waste materials are converted into different and usually lower quality products.

More realistic for many communities is partial recycling of a specified number of materials that can provide the 30% reduction.  

Composting

Composting is a biochemical process in which organic materials such as lawn clippings and kitchen scraps decompose to a rich, soil-like material. It is a process of rapid, partial decomposition of moist, solid, organic waste by aerobic organisms. As a waste management option large-scale composting is generally carried out in the controlled environment of mechanical digesters.  A major disadvantage of composting is the necessity to separate organic material from other waste. Therefore, it is probably economically advantageous only when organic material is collected separately from other waste.  Nevertheless, composting is an important component of IWM and can be used as an organic soil fertilizer, topsoil, or landfill cover.

Incineration

In incineration combustible waste is burned at temperatures high enough (900-1000 ⁰C) to consume all combustible material, leaving only ash and noncombustibles to dispose of in a landfill. Under ideal conditions, incineration may reduce the volume of waste by 75% to 95%. In practice, however, the actual decrease in volume is closer to 50%, because of maintenance problems as well as waste supply problems. Besides reducing a large volume of combustible waste to a much smaller volume of ash, incineration has another advantage is that the process of incineration can be used to supplement other fuels and generate electric power.

Incineration of urban waste is not necessarily a clean process. It may produce air pollution and toxic ash. Smokestacks from incinerators may emit oxides of nitrogen and sulfur that lead to acid rain; heavy metals such as lead, cadmium, and mercury; and carbon dioxide—a greenhouse gas. 

In modern incineration facilities, smokestacks are fitted with special devices to trap pollutants, but the process of pollutant abatement is expensive. Furthermore, plants themselves are expensive. Considering IWM principles it may be concluded that a combination of reusing, recycling, and composting may reduce the volume of requiring disposal at a landfill by at least as  much as incineration.

Solid waste management

Open Dumps (Landfill)

In the past, solid waste was usually accumulated in open dumps, where the refuse was piled up without being covered or otherwise protected. Common sites are natural low areas, such as swamps or floodplains; and hillside areas above or below towns. The waste is often piled as high as equipment allows.

Such dumping spoils scenic resources, pollute soil and water resources, and is a potential health hazard to plants, animals, and people. As a general rule, open dumps create a nuisance by being unsightly, providing breeding grounds for pests, creating a health hazard, polluting the air and sometimes polluting groundwater and surface water. A properly designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste materials.

Sanitary Landfills                

A sanitary landfill is designed to concentrate and contain refuse (contrast to open dumping) without creating a nuisance or hazard to public health or safety. It is covered with a layer of compacted soil at the end of each day of operation or more frequently if necessary. Covering the waste in landfill is what makes the landfill sanitary. The compacted layer restricts (not eliminate) continued access to the waste by insects, rodents, and other animals, such as seagulls. It also isolates the refuse, minimizing the amount of surface water entering into and gas escaping from the waste.

                                                       

Modern sanitary landfills are engineered to include multiple barriers (double-lined), such as clay and plastic liners to limit movement of leachate; surface and subsurface drainage to collect leachate; system to collect methane gas produced as waste decomposes; and groundwater-monitoring to detect leaks of leachate below and adjacent to the landfill.                  

                                               

The production of methane gas by the anaerobic decomposition of organic wastes in a landfill can present a very serious explosion hazard if the gas is not collected (and possibly burned as an energy source).

Environmental Impacts of Landfills

• A major concern with regard to landfills is the potential water pollution from the rainwater that percolates through the wastes, dissolving and carrying away all organic and inorganic contaminants
• Many of the contaminants in landfill leachate are highly toxic and would create a serious pollution problem if they reach the groundwater
• The production of methane gas by the anaerobic decomposition of of organic wastes in a landfill can present a very serious explosion hazard if the gas is not collected
• Possibly burned as an energy source
  

Hazardous Chemical Waste Management

About 70,000 chemicals are currently on the market. Although many of the chemicals have been beneficial to people, approximately 35,000 are classified as definitely or potentially hazardous to public health (Table W). The US currently generates about 250 million metric tons of hazardous chemical waste per year, referred to more commonly as hazardous waste.

Uncontrolled dumping of chemical waste pollutes soil, surface water and groundwater in several ways:

• Chemical waste stored in barrels, either stacked on ground or buried, eventually corrode and leak, polluting surface water, soil, and groundwater;
• Liquid chemical waste dumped in an unlined lagoon, from which contaminated water percolates through soil and rock to the groundwater table; and

Hazardous chemical waste management is one of the most serious environmental problems. Management of hazardous chemical waste involves several options, including recycling, on-site processing to recover by-products with commercial value, microbial breakdown, chemical stabilization, high temperature decomposition, incineration, and disposal by secure landfill or deep-well injection. A number of technological advances have been made in toxic-waste management, and as land disposal becomes more expensive, the recent trend toward on site treatment is likely to continue. However, on-site treatment will not eliminate all hazardous chemical waste; disposal of some waste will remain necessary. However, all available technologies cause some environmental disruption. There is no simple solution for all waste management issues.

Table W: Products and the Potentially Hazardous Waste they Generate  (Q)

Products we Use	Potentially Hazardous Waste
Leather	Heavy metals, organic solvents
Medicines	Organic solvents and residues, heavy metals (e.g., Hg, Zn)
Metals	Heavy metals, fluorides, cyanides, acid and alkaline cleaners, solvents, pigments
Oil, gasoline & other petroleum products	Oil, phenols and other organic compounds, heavy metals, ammonia, salts, acids
Paints	Heavy metals, pigments, solvents, organic residues
Pesticides	Organic chlorine compounds, organic phosphate compounds
Plastics	Organic chlorine compounds
Textiles	Heavy metals, dyes, organic chlorine compounds, solvents

Summary

Direct land disposal of hazardous waste is often not the best initial alternative. Even with extensive safeguards land disposal cannot guarantee that the waste is contained and will not cause environmental disruption in the future. This concern holds true for all land disposal facilities, including landfills, surface impoundments, land application, and injection wells. Pollution of air, land, surface water, and groundwater may result from failure of a land disposal site to contain hazardous waste.  Pollution of groundwater is perhaps the most significant risk, because groundwater provides a convenient route for pollutants to reach humans and other living things.

Urbanization and Urban Growth

Because the world is becoming increasingly urbanized, it is important to learn how to improve urban environments, to make cities more pleasant and healthier places in which to live and to reduce undesirable effects on the environment.

Urban Area

An urban area often is defined as a town or city plus its adjacent suburban fringes with a population of 2,500 or more. A rural area usually is defined as an area with a population of less than 2,500 people.

 Urbanization and Urban Growth 

Urbanization is the process in which people increasingly move from rural areas to densely populated cities; also involves the transformation of rural areas into urban areas. Historically, it has been closely connected with industrialization. A country’s degree of urbanization is the percentage of its population living in an urban area. Urban growth is the rate of increase of urban populations.

Urban areas grow in two ways: by natural increase (more births than deaths) and by immigration (mostly from rural areas).

Migration is influenced by ‘push factor’ and ‘pull factor’. People can be pushed from rural areas into urban areas by factors such as poverty, lack of land to grow food, declining agricultural jobs, famine, and war.

Rural people are pulled to urban areas in search of jobs, food, housing, health care, a better life, entertainment, and freedom from religious, racial, and political conflicts.

Cities are known to be places where money, services and wealth are centralized. Many rural inhabitants come to the city for reasons of seeking fortunes and social mobility. Businesses, which provide jobs and exchange capital are more concentrated in urban areas.

Trends Important in Understanding the problems and Challenges of Urban Growth

Several trends are important in understanding the problems and challenges of urban growth. First, the global proportion of urban population rose dramatically from 13%  in 1900, to 29% in 1950, to 49% in 2005.  

According to UN projections, by 2050 over 6 billion people, two thirds of humanity, will be living in towns and cities, with 93% of this urban growth occurring in developing countries.

Second, the number of large cities is mushrooming. In 1900, only 19 cities had a million or more people, and more than 95% of humanity lived in rural communities. In 2003, more than 400 cities had a million or more people (projected to increase to 564 by 2015). Also there were 19 megacities (up from 8 in 1985) with 10 million or more people—most of them in developing countries.

 As they grow and sprawl outward, separate urban areas may merge to form a megalopolis.

A third trend is that urbanization and the urban population is increasing rapidly in developing countries. Currently, about 40% of the people in developing countries live in urban areas.

Fourth, urban growth is much slower in developed countries (with 75% urbanization) than in developing countries. Still, developed countries are projected to reach 84% urbanization by 2025.

Finally, poverty is becoming increasingly urbanized as more poor people migrate from rural to urban areas. The UN estimates that at least 1 billion people live in crowded slums of central cities and in squatter settlements and shantytowns that surrounds the outskirts of most cities in developing countries.

Fig: Centre of Sao Paulo, one of the largest metropolises in the world.

Major Environmental Pros and Cons of Urban Areas

Because urbanization changes the landscape, it also changes the relationships between biological and physical aspects of the environment.

In terms of resource use, most of the world’s cities are not self-sustaining systems because of their high resource input and high waste output.

Traffic congestion, increased pollution, limited real estate, and decreasing resources are all possible side effects of urbanization.

Urbanization obviously destroys farmland where it occurs and concentrates pollution. Although urban dwellers occupy only about 2% of the Earth’s land area, they consume about 75% of the Earth’s resources. In addition, large areas of the Earth’s land area must be disturbed and degraded to provide urban dwellers with food, water, energy, minerals, and other resources. This decreases and degrades the Earth’s biodiversity.

When an area expands rapidly, it can cause great environmental damage. As cities expand they destroy rural croplands, fertile soil, forests, wetlands, and wildlife habitats.

Peoples' desire for more personal space is leading real-estate developers to buy up land and clear it for housing developments. The destruction of farm land is becoming more and more of an issue.

Habitat is changed and the wildlife with it. With urbanization comes more building, which means loss of habitat. Urbanization through habitat destruction reduces wildlife populations and can lead species to become endangered in certain areas.

Most cities have few trees, shrubs, or other plants that absorb air pollutants, give off oxygen, help cool the air as water transpires from their leaves, provide shade, reduce soil erosion, muffle noise, provide wildlife habitats, and give aesthetic pleasure.

Many urban areas have water resource problems. As cities grow their water demands increase.  Increased demand is met through heavy extraction of groundwater that depletes this resource faster than it is replenished. Many cities have water supply problems. In urban areas of many developing countries, 50—70% of water is lost or wasted because of leaks and poor management of water distribution systems.                                                

City pavement increases the chances of local flooding within the city by overloading the storm drains, and the increased runoff from the city to the countryside can increase the chances of flooding downstream. Paved city streets and city buildings prevent water infiltration. Flooding tends to be greater in cities. One reason is that many cities are built on floodplain areas or along low-lying coastal areas subject to natural flooding. Another reason is that covering land with buildings, asphalt, and concrete causes precipitation to run off quickly and overload storm drains.

Urbanization changes the type of pollution, more so than the amount. There is less nutrient pollution and siltation, more metals and petroleum pollution.

Urbanization increases both surface and ground water pollution as well.

Everything is concentrated in a city, including pollution. Because of their high population densities and high resource consumption, urban dwellers produce most of the world’s air pollution, water pollution, solid and hazardous wastes. Some of this comes from motor vehicles, which have contributed lead in gasoline, nitrogen oxides, ozone, carbon monoxide, and other air pollutants from exhaust. Stationary power sources also produce air pollutants. Home heating is a third source, contributing particulates, sulfur oxides, nitrogen oxides, and other toxic gases. Industries are a fourth source. In addition, high population densities in urban areas can increase spread of infectious diseases and physical injuries. This environment makes life riskier, causing hundreds and thousands of premature deaths each year.

Many urban areas of developing countries have no proper sewer facilities, meaning huge amounts of human waste are deposited in gutters and vacant lots everyday attracting armies of rats and swarms of flies. When the winds pick up dried excrement, a fecal snow often falls on parts of city. This bacteria-laden fallout leads to widespread salmonella and hepatitis infections, especially among children.  In general, life in a city is riskier because of higher concentrations of pollutants and pollutant-related diseases.

                                          

Fig: Massive urbanization in Dhaka resulted in tremendous strain on the city’s infrastructure.

Urban areas suffer from high unemployment, deafening noise, and a soaring rate of crime. Unwanted, disturbing, or harmful sound that impairs or interferes with hearing, causes stress, hampers concentration and work efficiency, or cause accidents. Noise levels above 65 dbA are considered unacceptable, and prolonged exposure to levels above 85 dbA can cause permanent hearing damage. Many of urban population (may be one-third) live in crowded slums or squatter settlements, without running water, or electricity.

An urban heat island is formed when industrial and urban areas are developed resulting in greater production and retention of heat. A large proportion of solar energy that affects rural areas is consumed evaporating water from vegetation and soil. In cities, where there is less vegetation and exposed soil, the majority of the sun’s energy is absorbed by urban structures and asphalt. Hence, during warm daylight hours, less evaporative cooling in cities results in higher surface temperatures than in rural areas. Vehicles and factories release additional city heat, as do industrial and domestic heating and cooling units. As a result, cities are often 2 to 10 °F (1 to 6 °C) warmer than surrounding landscapes. Impacts also include reducing soil moisture and a reduction in re-uptake of carbon dioxide emissions.

Finally, urban areas can intensify poverty and social problems. For example, rapid urban growth can increase urban poverty and inequality, which can increase civil unrest and undermine governments. Crime rates also tend to be higher in urban areas than in rural areas.

However, urban areas have better sanitation, public water supplies, and medical care that have slashed death rates and the prevalence of sickness from malnutrition and transmittable diseases such as measles, diphtheria, typhoid fever, pneumonia, and tuberculosis. Urban dwellers have better access to family planning, education, and social services than do people in rural areas. To many environmentalists and urban planners, the primary problem is not urbanization but our failure to make most cities more sustainable and livable.

City Planning

City planning has a long history. At various times city planners have taken environmental factors carefully into consideration. A city’s site and situation are both important. It is important to combine the physical and aesthetic needs of a city.

                                                      

A city grows at the expense of the surrounding countryside, destroying the surrounding landscape on which it ultimately depends. As the nearby areas are ruined for agriculture and as the transportation network extends, the use, misuse, and destruction of the environment increase.

One of the ways in which we can improve the management of a city environment is to analyze the city as an ecological system. Like any life-supporting system, a city must maintain a flow of energy, provide material resources, and have ways of removing wastes. These ecosystem functions are maintained in a city or urban area by transportation and communication with outlying areas.

Although it is impossible to eliminate exposure to pollutants in urban areas, it is possible to reduce the exposure by careful planning, design, and development. A practical solution to the problems associated with urbanization can be achieved by involving several specialized professions including urban forestry, landscape architecture, city planning, and city engineering. These professionals take into account climate, soils, and the general influences of the urban setting, such as the shading imposed by tall buildings and the pollution from motor vehicles.

An ideal city planning takes advantage of locally available renewable energy sources and requires that all buildings, vehicles, and appliances meet high energy-efficiency standards. Trees and plants adapted to the local climate and soils are planted throughout to provide shade and beauty, supply wildlife habitats, and reduce pollution, noise, and soil erosion. Abandoned lots and industrial sites and polluted creeks and rivers are cleaned up and restored. Nearby forests, grasslands, wetlands, and farms are preserved instead of being devoured by urban sprawl. Much of the city’s food comes from nearby organic farms, solar greenhouses, community gardens, and small gardens in rooftops, in yards, abandoned lots, and in window boxes.

Urban areas can be modified to provide additional habitats for wildlife that people can enjoy. They can provide if perfectly planned all the needs—physical structures and necessary resources such as food, minerals, and water—for many plants and animals.

Modern parks provide some of the world’s best wildlife habitats, and importance of parks will increase as truly wild areas shrink.

Urban drainage structures can be designed as wildlife habitats. Stream and marsh habitats should be maintained or created so that they can become habitats for fish and mammals.

Agriculture and the Environment

Primitive societies obtained food through hunting and gathering. Although some food is obtained from oceans and fresh waters, 95% of the human population’s protein and most of its calories are obtained from traditional land-based agriculture of crops and livestock. The major agricultural challenge facing us today is to achieve sustainable production of crops.       

                 

Crops

Most of the world’s food is provided by only 14 crop species. Of these 14, six species provide more than 80% of the total calories consumed by human beings either directly or indirectly. Other crops, called forage, are important food for domestic animals.

It is useful to group crops into cash crops and subsistence crops:

Cash crops are grown to be sold or traded in a large market. e.g., tea, tobacco, jute, etc.

Subsistence crops are used directly for food by the farmer or sold locally where the food is used directly. e. g., rice, wheat, etc.  Some cash crops may provide nonfood products (latex from rubber trees).

Seasonal Crop Species in Bangladesh

Cropping seasons in Bangladesh can be broadly divided into two: Rabi (dry period; October to February) and Kharif (wet; March to September). Although some of the crops are sown in one season they are harvested in another season, i.e., there is overlapping of seasons. Again crops are also divided into different groups as cereals, pulses, fibre crops, oilseeds, root crops, vegetables, spice crops, fruit crops, etc.  

Soil and Soil forming factors

Soils are earth materials modified over time by physical, chemical, and biological processes that support rooted plant life.  It can be defined as : “Soil is a collection of natural bodies occupying a portion of the Earth’s crust that support plant growth which have acquired properties due to the integrated action of climate and vegetation upon parent material as conditioned by relief over a period of time.”  

The four major components of soil are air (25%), water (25%), mineral matter (45% {sand, silt, and clay}), and organic matter (5%).

Soil forming factors

The type of a soil at a particular site depends on five factors such as

• Parent material (geological or organic precursors to the soil),
• Climate (primarily precipitation and temperature),
• Topography (relief) (slope, aspect, and landscape position),
• Biological activity (living organisms, especially native vegetation, microbes, soil animals, and human beings), and
• Time (the period of time since the parent materials became exposed to soil formation).

Soils are extremely important in many environmental considerations. As a result, the study of soils continues to be an important part of environmental sciences.

             Soil material  S = f(p+cl+r+v+t......)

Soil Fertility

Soil fertility refers to the capacity of a soil to supply the nutrients and physical properties necessary for plant growth. Ironically, agriculture depends heavily on soil quality, but agriculture can lead to a decline in that quality. A high-quality agricultural soil has all the chemical elements required for plant growth and a good physical structure that lets both air and water move freely through the soil, yet retains water well. Such a soil has high organic matter (Soil organic matter is the plant and animal residues, leaves, forest litter, etc. at various stages of decomposition, considered as the storehouse of nutrients) content. Organic matter in soil is rich in chemical nutrients and provides a physical structure conducive to plant growth.

Plowing (shattering of soil uniformly with partial to complete inversion) the soil and planting crops has been a way of life for several thousand years and continues today.                            

                       

                        Fig: Tillage operation in soil to receive the crop.