Mumbai University > CIVIL > Sem 7 > Solid Waste Management

Marks: 10 M

Year: Dec 2011

Physical Characteristics

• Moisture content:
  • Moisture content is a critical determinant in the economic feasibility of waste treatment by incineration since energy must be supplied for evaporation of water and in raising the temperature of the water vapour.
  • Moisture content also plays an important role in other processing methods such as composting and anaerobic digestion.
• Particle size:
  • The measurement of the size distribution of particles in the waste stream is important because of its significance in the design of mechanical separators and shredders.
  • The results of the analysis are expressed in the manner used for the particle analysis of soils namely a plot of particles size against % less than a given value.
• Density:
  • Knowledge of the density of waste i.e. mass per unit volume is essential for the design of all elements of the solid waste management system.
  • For example, in high income countries, considerable benefit is derived through the use of compaction vehicles on collection routes, because the waste is typically of low density.
  • However, in India and other developing countries such as Thailand, Indonesia etc. due to higher initial density the compaction ratio obtained rarely exceeds 1.5.
• Field capacity:
  • Field capacity of solid waste is total amount of moisture that can be retained in waste sample subject to downward pull of gravity.
  • Field capacity of critically important in determining the formation of leachate in landfills.
  • Water excess of field capacity can be released as leachate and field capacity varies with degree of applied pressure and state of decomposed moisture of waste.
• Permeability: The Hydraulic conductivity of compacted waste is an important physical property to a large extent governs movement of liquid and gases in landfill.

Chemical Characteristics

• pH: A 5 gm portion of the powdered sample is mixed with 50 ml of distilled water by stirring and pH is then measured by a pH meter. The pH of fresh solid waste is normally around 7. During decomposition it tends to become acidic and stabilized solid waste has an alkaline pH.
• Organic content: A 10 gm portion of the dried ground sample is placed in a silica dish and slowly heated in an electric furnace to 700 degree Celsius for 30 min. The residue is weighed and the loss of weight represents the organic content and is expressed as percent by weight. The knowledge of organic content helps assess the feasibility of biological processing-composting and anaerobic digestion.
• Carbon content: The carbon is determined by using the New Zealand formula in which the percent organic matter is divided by 1.724.
• Nitrogen content: Total nitrogen is obtained by Kjeldahl method and the phosphorous and potassium are estimated by using phosphomolybdic and flame photometric method. Nitrogen, phosphorous and potash values are important in composting.
• Toxicity: Toxicity characteristics include heavy metals, pesticides, insecticides etc. Heavy metals are present in municipal solid waste due to the waste from small scale industries. As some of the heavy metals leach out, testing for heavy metals is often carried out. Toxicity Characteristics Leaching Procedure (TCLP) test is invariably carried out if the waste is suspected to be toxic in nature.
• Ultimate analysis
• Proximate analysis.

The composition and quantities of a typical sample of solid waste are: