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