Microbiology of Solid Waste Treatment

In addition to ridding our environment of wastes in water, we must dispose of the solid wastes that are generated each day. Some of it is inert materials such as glass, metals, and plastics, but a large amount is organic material that is affected by microorganisms. Eliminating waste products from the environment has become an increasingly complex problem.

Sanitary Landfills for Solid Waste Disposal

Sanitary landfills are widely used to dispose of non-hazardous solid wastes in a manner that minimizes damage to human health and the environment. Before sanitary landfills were developed, solid wastes were often piled up on the ground in open-burning dumps, attracting insects and rodents and causing aesthetic and public health problems.

Federal standards dictate that sanitary landfills must be located away from wetlands, faults, flood plains or other sensitive areas. The excavated site is lined with plastic sheets or a special membrane atop a thick layer of clay, which minimizes leaching of contaminates from the wastes into the surrounding area. Next comes a layer of sand with drainage pipes; above this the wastes are compacted and covered with a layer of soil every day. When a landfill is finished, it is covered with soil and plants, and it can be used for recreation and eventually as a site for construction. Methane and other gases are vented, and the methane is burned or recovered for use.

There are several disadvantages to this type of waste management. First, only a limited number of sites are available for use near urban and suburban areas. Second, the organic content of landfills anaerobically decomposes very slowly, over a period of at least 50 years. During this time, the methane gas that is produced must be removed. If buildings are constructed before the methane is removed, disastrous gas explosions can occur. Pollutants such as heavy metals and pesticides can leach from landfill sites into the underground aquifers. It is very difficult to purify these aquifers once they have become contaminated.

Sanitary landfills have traditionally been a low-cost method of handling large quantities of solid waste. Because of increased costs and decreased availability of land, however, many cities are

31.3 Microbiology of Solid Waste Treatment 795

looking for ways to decrease the amount of solid waste dumped in landfills. In some cities, the fees charged to people for garbage collection are based on the size of the container collected. The smaller the can, the lower the cost. Waste disposal companies are also considering weighing garbage and charging people accordingly to further reduce the amount of solid waste generated. Both of these methods are intended to raise people's awareness of how much solid waste they are generating as well as to offer an incentive to recycle. Companies in some areas offer lower costs for garbage collection to people who recycle. Programs to recycle paper, plastics, glass, and metal are being implemented in many cities and counties with great success. Through these programs, landfill areas can be expected to be available for a longer period of time.

Commercial and Backyard Composting— Alternative to Landfills

Commercial and home composting programs are becoming popular in many areas and are succeeding in reducing the amount of organic waste added to landfills. Composting is the natural decomposition of organic solid material.

Backyard composting involves mixing garden debris with kitchen organic waste, excluding meats and fats (figure 31.8). If proper amounts of warmth, water, and air are provided to the mix, the bulk of the waste is reduced by two-thirds in a matter of months. The black organic material generated by composting can then be used to fertilize garden beds. This material is rich in organic compounds and improves the soil for growing plants. Figure 31.9 shows the steps involved in composting.

A backyard compost pile usually starts with a supply of organic material such as leaves and grass clippings, as well as kitchen wastes. Often, some soil and water are added. In a few days, the inside of the pile heats up. At 55°C to 66°C, pathogens are killed but thermophilic organisms are not affected. When the pile cools down, it is aerated by physically stirring it up and turning it. If a compost pile is turned frequently and other conditions

Figure 31.8 A Backyard Compost Heap

Nester-Anderson-Roberts: I V. Applied Microbiology I 31. Environmental I I © The McGraw-Hill

Microbiology, A Human Microbiology: Treatment of Companies, 2003 Perspective, Fourth Edition Water, Wastes and

Polluted Habitats

796 Chapter 31 Environmental Microbiology: Treatment of Water,Wastes, and Polluted Habitats Commercial Compost

Pick up yard waste from private homes and city parks.

Hauled to transfer station

Hauled to transfer station

Screened

Ground material is put in curing piles for approximately 18 months

Screened

Compost sold by the bulk or by the bag

Figure 31.9 Industrial and Backyard Composting

Compost sold by the bulk or by the bag

Garden and yard use

Backyard Compost

Yard waste (no heavy branches)

Compost bin

Ground material is put in curing piles for approximately 18 months

Backyard Compost

Yard waste (no heavy branches)

Compost bin

Kitchen waste (no meats or fats)

Turning compost

-cri

Kitchen waste (no meats or fats)

Turning compost

-cri

Garden and yard use

Figure 31.9 Industrial and Backyard Composting are good for aerobic digestion, the composting can be completed in as little as 6 weeks. ■ thermophile, p. 87

Composting on a large scale offers cities a way to reduce the amount of garbage sent to their landfills. In some cities, yard wastes are collected separately from the main garbage. These wastes are then composted and used in various ways, including improving soils in city parks. Special machinery is used to compost on a large scale, and the composting can be accomplished in a very short time (see figure 31.9).

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  • Askalu
    What is microbiological and soild waste in medical.in?
    3 years ago
  • Sirkka
    What is wastes in microbiology wikipedea?
    2 years ago
  • palmira romano
    How to disposse solid waste of microbiology?
    1 year ago

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