Disposal of refuse - Environmental Engineering

Disposal of refuse and Sewage sickness of Land

Method of disposal of refuse

Landfill or Burying:

• Landfill refers to the disposal of waste material by burying it.
• It is an extended storage area for non-biodegradable waste.
• Landfill is an area, which prevent contamination from the waste entering the area surrounding by soil and water and it also helps to reduce odor and pests

Incineration: 

• This method involves burning of solid wastes in a furnace until the wastes are turned into ashes
• In this process, the combustible portion of the waste is combined with oxygen forming carbon dioxide and water, which are released into the atmosphere
• Incinerators are made in such a way that they do not give off extreme amounts of heat when burning solid wastes
• Suitable temperature and operating conditions are required to achieve for incineration
• It reduces the volume of waste up to 20 or 30% of the original volume
• This method of solid waste management can be done by individuals, municipalities and even institutions

• It involves of two stages involved such as drying and combustion. Drying and combustion may be accomplished either in separate units or successively in same units depending upon the temperature constraints or control parameter. It is an exothermic process.

Fluidized bed incineration:

• It is a combustion technology used to burn solid fuels. 
• In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which jets of air are blown to provide the oxygen required for combustion or gasification. 
• The resultant fast and intimate mixing of gas and solids promotes rapid heat transfer and chemical reactions within the bed

Pulverization 

• It refers to the action of crushing and grinding heavier solids into the lighter solids.

Composting 

• It is a natural biological process, carried out under controlled aerobic conditions (requires oxygen).
• In this process, various microorganisms, including bacteria and fungi, break down organic matter into simpler substances.
• The effectiveness of the composting process is dependent upon the environmental conditions present within the composting system i.e. oxygen, temperature, moisture, material disturbance, organic matter and the size and activity of microbial populations.

process of composting

Bangalore method

• It is an anaerobic method conventionally carried out in pits. 
• In the Bangalore method of composting, dry waste material of 25 cm thick is spread in a pit and a thick suspension of cow dung in water is sprinkled over for moistening.

Indore method

• It is an aerobic method. 
• The Indore method of composting in pits involves filling of alternate layers of similar thickness as in the Bangalore method.
• However, to ensure aerobic condition the material is turned at specific intervals for which a 60 cm wide strip on the longitudinal side of the pit is kept vacant.

There are mainly two methods (Indore and Bangalore method) adopted in India for the decomposition of Solid wastes generated. 

The main difference between Indore Method and Bangalore Method for decomposition of MSW is given below:

Indore Method	Bangalore Method
Decomposition of MSW by composting is done aerobically.	Decomposition of MSW by composting is done an-aerobically.
Decomposition takes 2 - 3 Months	Decomposition takes 5 - 6 Months
Mixing is ensured either Mechanically or manually	No mixing is done.

• In Composting with a combination of proper environmental conditions and adequate time, microorganisms turn raw putrescible organic matter into a stabilized product.

• Through composting, readily available nutrient and energy sources are transformed into carbon dioxide, water, and a complex form of organic matter compost. 

• Process management can be optimized for a number of criteria, including the rate of decomposition (to reduce residence time in reactors and thus minimize facility size requirements), pathogen control, and odour management.

• The key parameters are the available carbon to nitrogen (C: N) ratio, moisture, oxygen, and temperature.

• Decomposition slows dramatically in mixtures under 40 to 45 percent moisture, which can lead facility operators to prematurely assume compost is stabilized and ready to sell.

• A minimum moisture content of 50 to 55 percent is usually recommended for high rate composting of MSW.

• During the active composting phase, additional water usually needs to be added to prevent premature drying and incomplete stabilization. MSW compost mixtures usually start at about 52 percent moisture and dry to about 37 percent moisture prior to final screening and marketing.

C/N ratio is an important factor in composting

• since bacteria use nitrogen for their cell structure building and carbon for food.
•  The optimum composting C/N ratio should be in range (30 - 50)
•  So, If C/N ratio is more, Nitrogen is utilized prior to that of carbon, which results in incomplete digestion of organic matter.

gases produced from a land fill site

• Sanitary landfill involves dumping the waste in layers and compacting them after each layer, hence tractor can be used very effectively for this purpose.It is simple and economical.

• But there is continuous evolution of foul gases which may be explosive in nature. The major constituent gases produced from a land fill site are carbon dioxide and methane.

• It also causes leachate in landfills which pollutes the nearby ground water thereby impacting the ecology of the area.

Sewage sickness of  Land: 

• When sewage is applied continuously on a piece of land, the soil pores or voids may get filled up and clogged with sewage matter retained in them. This phenomenon of soil getting clogged is known as sewage sickness of the land.

The following preventive measures may be adopted to avoid sewage sickness:

Pre-treatment of sewage	Sewage should be given some pre-treatment before it is applied on land.
Rotation of crops	It is desirable to grow different types of crops on a piece of land instead of one single crop. Rotation of crops minimizes the chances of sewage sickness.
Drainage of soil	Subsoil drain pipes should be laid in sufficient number to collect the percolated effluent.
Depth of sewage	The depth of sewage on land should be carefully decided by keeping in view the climatic conditions, drainage facilities, nature of crops, and characteristics of the soil.
Alternative arrangement	There should be ample provision of extra land so that land with sewage sickness can be given the desired rest.
Intermittent application	Sewage should be applied on land at intervals. The period between successive applications depends on the general working of sewage farms and the permeability of the soil. Depending on the nature of the soil, this period between successive applications varies from few hours to few weeks.
Treatment to land	The land affected by sewage sickness should be properly treated before it is put up in use again. Clogged surfaces should be broken by suitable equipment.