Question

QUESTION 2

(a) In your opinion, what are the contributing factors for the generation of leachate in a landfill sites. [6 marks]

(b) Properties of solid wastes are important to determine, develop and design proper integrated solid waste management system. List FOUR physical properties of solid wastes. [4 marks]

subject: enviromental engineering

Answer 1

(a) Leachate is the chemical fluid which is formed due to decomposition of waste dumped into the landfills and this substance constitutes different components like dissolved organic matter, heavy metals and inorganic compounds. The Leachate may be very useful in nature and sometimes can take shape of toxic substance all these characteristics depend on the constituents of the solid waste dumped in the landfill.

The factors which contribute to the formation of Leachate are the organic matter in the waste, thermal property of the waste, liquid composition in the waste, bacteria present in the waste, chemicals present in the waste and metals in the waste .

The organic matter present in the waste is the biggest contributor to the formation of Leachate as the entire Leachate formed is in one or the other way the transformed form of the organic matter or the resultant of decomposition of organic matter and even its percentage influences the amount of Leachate formed and higher the organic matter higher is the formation of Leachate. The thermal property present is waste will increase the rate of Leachate formation and even help in dissolving metals which are reactive to temperature in the form of Leachate therefore, Leachate has got very high concentration of different elements by which the metals get into existence. The liquid composition in the waste facilitates mobility and dilution in the chemical concentration of Leachate and the Leachate thus formed is highly fluidic in nature thus liquid forms the major chunk in the Leachate.

The bacteria present in the waste helps in decomposition of waste and the Leachate so formed is highly nutritious in nature and can be used as a fertilizer in the agricultural fields as the bacteria gives results only for the decomposable matter present in the overall waste. The chemicals present in waste act as a catalyst in increasing the rate of decomposition and they also constitute the resulting Leachate and their composition is also explore for determining the use of resulting Leachate. Lastly the metals or inorganic or non-biodegradable waste also constitutes Leachate as these components settle down with the decomposed matter and can mix up with the Leachate formed in the underlying strata making the Leachate toxic in nature. Thus, these non-decomposable matters should be avoided in the landfills where the Leachate formed is used for agricultural purpose and these materials can be subjected to incineration for avoiding the erosion of soil.

(b) The physical properties of solid waste which influence the design of solid waste management techniques are as follows:

1. Moisture content

The amount of water present in the waste influences the design of solid waste disposal technique as this will lead to formation of Leachate in the landfills, reduce suitability for incineration process and even can increase rate of chemic reactions leading to development of toxic gases in the transfer period itself and even gives rise to unacceptable odour creating uncomfortable conditions to the people handling the waste.

2. Density   

The density helps in design of landfills as the density determines the space required for the dumping of solid waste. Higher the density lower the space occupied by waste and vice-versa. It even influences the vehicles used for transportation and also the collection mechanisms involved in the solid waste collection.

3. Compressibility

Compressibility is the physical property through which a material can be subject to compacting so as to reduce the size of the space the waste is taking in the sanitary landfills and if the waste constitutes incompressible matter like fluid it will be really difficult to allot the required space to the waste.

4. Material size of Waste constituents

The size distribution helps in primary separation of waste as the waste is subjected to mechanical separators and shredding prior to disposal to the treatment process. This will help in design of these equipments and also in the efficient functioning of treatment process as heavy metals cannot be treated at a single instance.

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