Transportation and disposal of solid waste

TRANSPORTATION & DISPOSAL OF SOLID WASTE

Solid waste management can be thought of as a chain of linked stages beginning with generation of waste by individual households, institutions and workplaces. Solid waste is a major problem for cities in developing countries.

•  It requires major financial investment as well as infrastructure development. 
• A well-planned collection and transfer process can lead to significant reductions in the overall cost of waste management.
• Primary collection is the collection of waste from the point where it is placed by the person or organisation that has produced it. These collection points could be located outside each individual household and business
• Depending on the collection vehicle and the distance to the waste treatment/disposal site, the waste at this stage may be taken to the final disposal site or to a transfer station
• Secondary collections are where the waste from a number of primary collections is taken from the transfer station to the final disposal site.
• The waste is taken off the primary collection vehicle and loaded onto secondary collection vehicles. 
• This is done at a transfer station. Waste can also be stored at a transfer station for a short time period where recyclable material is extracted from the mixed waste.
• Transfer stations should be located conveniently close to all the communities they serve and should have access to major roads leading to the treatment or disposal sites.
• In urban locations, there are a number of transfer stations distributed around the town. 
• The site for final treatment and disposal, to which the waste must be transported, and this is usually situated at the edge of the town. Hence the routes for the waste collection vehicle should be properly planned to make the best use of resources.

DISPOSAL OF SOLID WASTE

The following methods are adopted for discarding wastes:

• Landfill
• Incineration and
• Composting

LANDFILL: 

• Solid wastes are placed in a sanitary landfill in which alternate layers of 80 cm thick refuse is covered with selected earth-fill of 20 cm thickness. 
• After 2-3 years solid waste volume shrinks by 25-30% and land is used for parks, roads and small buildings. 

This is the most common and cheapest cheapest method of waste disposal and is mostly employed in Indian cities.

Advantages:

• It is simple and economical
• Segregation of wastes is not required
• Landfilled areas can be reclaimed and used for other purposes
• Converts low-lying, marshy waste-land into useful areas.
• Natural resources are returned to soil and recycled.

Disadvantages:

• Large area is required
• Land availability is away from the town, transportation costs are high
• Leads to bad odour if landfill is not properly managed.
• Land filled areas will be sources of mosquitoes and flies requiring application of insecticides and pesticides at regular intervals.
• Causes fire hazard due to formation of methane in wet weather.

INCINERATION:

• It is a hygienic way of disposing solid waste. 
• It is suitable if waste contains more hazardous material and organic content. 
• It is a thermal process and very effective for detoxification of all combustible pathogens. 
• It is expensive when compared to composting or land-filling.
• In this method municipal solid wastes are burnt in a furnace called incinerator. 
• Combustible substances such as rubbish, garbage, dead organisms and non-combustible matter such as glass, porcelain and metals are separated before feeding to incinerators. 
• The non-combustible materials can be left out for recycling and reuse. 
• The leftover ashes and clinkers may account for about 10 to 20% which need further disposal by sanitary landfill or some other means.
• The heat produced in the incinerator during burning of refuse is used in the form of steam power for generation of electricity through turbines. 
• Municipal solid waste is generally wet and has a high calorific value. 
• Therefore, it has to be dried first before burning. 
• Waste is dried in a pre-heater from where it is taken to a large incinerating furnace called "destructor" which can incinerate about 100 to 150 tonnes per hour. 
• Temperature normally maintained in a combustion chamber is about 700 C which may be increased to 1000 C when electricity is to be generated.

ADVANTAGES

• Residue is only 20-25% of the original and can be used as clinker after treatment
• Requires very little space
• Cost of transportation is not high if the incinerator is located within city limits
• Safest from hygienic point of view
• An incinerator plant of 3000 tonnes per day capacity can generate 3MW of power.

DISADVANTAGES

• Its capital and operating cost is high
• Operation needs skilled personnel
• Formation of smoke, dust and ashes needs further disposal and that may cause air pollution.

COMPOSTING

It is another popular method practiced in many cities in our country. In this method, bulk organic waste is converted into fertilizer by biological action.

• Separated compostible waste is dumped in underground trenches in layers of 1.5m and finally covered with earth of 20cm and left for decomposition. 
• Sometimes, actinomycetes are introduced for active decomposition. Within 2 to 3 days biological action starts. 
• Organic matter is destroyed by actinomycetes and lot of heat is liberated increasing the temperature of compost by 75C and the refuse is finally converted into powdery brown coloured odourless mass called humus that has a fertilizing value and can be used in agriculture. 
• Humus contains lot of Nitrogen essential for plant growth apart from phosphates and other minerals.

ADVANTAGES

• Manure added to soil increases water retention and ion-exchange capacity of soil.
• This method can be used to treat several industrial solid wastes.
• Manure can be sold thereby reducing cost of disposing wastes
• Recycling can be done

DISADVANTAGES

• Non-consumables have to be disposed separately
• The technology has not caught-up with the farmers and hence does not have an assured market.