Characteristics of solid waste

Solid waste means any garbage, refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility and other discarded materials including solid, liquid, semi-solid, or contained gaseous material, resulting from industrial, commercial, mining and agricultural operations, and from community activities.

1. Characteristics Of Solid Waste KULVENDRA PATEL 2K19/ENE/05 Delhi Technological University

2. Introduction Solid waste means any garbage, refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility and other discarded materials including solid, liquid, semi-solid, or contained gaseous material, resulting from industrial, commercial, mining and agricultural operations, and from community activities. Solid waste management is defined as the discipline associated with control of generation, storage, collection, transport or transfer, processing and disposal of solid waste materials in a way that best addresses the range of public health, conservation, economic, aesthetic, engineering, and other environmental considerations. The primary goal of solid waste management is reducing and eliminating adverse impacts of waste materials on human health and the environment to support economic development and superior quality of life.

3. Characteristics of solid waste Physical Characteristics Chemical Characteristics Biological Characteristics

4. 1. Physical Properties of MSW Specific Weight (Density) Moisture Content Size of Waste Constituent Field Capacity Permeability of Compacted Waste Important for the selection and operation of equipment and for the analysis and design of disposal facilities. Physical properties includes:-

5. Specific Weight (Density) Specific weight is defined as the weight of a material per unit volume (e.g. kg/m3, lb /ft3) Usually it refers to uncompacted waste. It varies with geographic location, season of the year, and length of time in storage. Any normal compaction equipment can achieve reduction in volume of wastes by 75%

6. Typical Specific Weight Values

7. Moisture Content The moisture in a sample is expressed as percentage of the wet weight of the MSW material. A typical range of moisture content is 20 to 40%, representing the extremes of wastes in an arid climate and in the wet season of a region of high precipitation. Analysis Procedure : Weigh the aluminum dish Fill the dish with SW sample and re-weigh SW + dish in an oven at 105°C. Remove the dish from the oven, allow to cool in a desiccator, and weigh. Record the weight of the dry SW + dish. Calculate the moisture content ( M ) of the SW.

8. Typical Moisture Contents of Wastes

9. Q:- A residential waste has the following components and moisture content:- Component Percentage Moisture Content Paper 50% 6% Glass 20% 2% Food 20% 70% Yard waste 10% 60% Estimate its moisture concentration. Assume a wet sample weighing 100 kg. Solution:- Component Percent Moisture wet weight (based on 100 kg) Paper 50 6 3 Glass 20 2 0.4 Food 20 70 14 Yard waste 10 60 6 Total = 23.4 kg wet Moisture content (M)  

10. Size of Waste Constituent The size and distribution of the components of wastes are important for the recovery of materials, especially when mechanical means are used, such as trommel screens and magnetic separators. For example, ferrous items which are of a large size may be too heavy to be separated by a magnetic belt or drum system.

11. Field Capacity The total amount of moisture that can be retained in a waste sample subject to the downward pull of gravity.

12. Field Capacity Field capacity is critically important in determining the formation of leachate in landfills It varies with the degree of applied pressure and the state of decomposition of wastes, but typical values for uncompacted commingled wastes from residential and commercial sources are in the range of 50 - 60%.

13. Determination of Field Capacity of Solid Waste To carry out the test, Lysimeters were constructed and these were filled with a homogeneous sample of refuse recovered from the front of the disposal. To fill the lysimeter a steel frame which has a perforation is placed inside the steel drum at the bottom and the voids was filled with gravel to prevent the passage of fine matter that might have obstructed the drainage device. A geotextile mesh is laid on top of the false bottom to act a type of filter. Then the device is packed with drop hammer until the desired density is obtained. Then water is added until level with the top of the compacted waste. The drainage operations depend on the characteristics of the solid waste. With certain tpes of solid waste, water can accumulate at the bottom of the lysimeter after only a few minutes, whereas with other types, it might take as long as several hours.

14.   Field capacity is given by :- Where, Cc = filed capacity in Kg of water per Kg of dry waste H = percentage of relative moisture in the solid waste Si = Vol. of water in Liters added to the Lysimeter Di = vol. of water in liters extracted from lysimeter d = density of water in kg/L PV = weight density of solid waste in Kg/L V = Vol. of lysimeter in Liter

15. Permeability of Compacted Waste The permeability (hydraulic conductivity) of compacted solid waste is an important physical property because it governs the movement of liquids & gases in a landfill. Permeability depends on:- Pore size distribution Surface area Porosity

16. Chemical properties of MSW are very important in evaluating the alternative processing and recovery options. If solid wastes are to be used as fuel, or are used for any other purpose, we must know their chemical characteristics, including the following :- Chemical: Chemical characteristics include pH, Nitrogen, Phosphorus and Potassium (N-P-K), total Carbon, C/N ratio, calorific value. Bio-Chemical: Bio-Chemical characteristics include carbohydrates, proteins, natural fibre , and biodegradable factor. Toxic: Toxicity characteristics include heavy metals, pesticides, insecticides, Toxicity test for Leachates , etc. 2. Chemical Properties of MSW

17. Methods of Chemical Analysis:- Proximate analysis Fusing point of ash Ultimate analysis (major elements) Energy content

18. Proximate Analysis Proximate analysis for the combustible components of MSW includes the following tests: Moisture (drying at 105 ° C ) Ash (weight of residue after combustion in an open crucible) Volatile combustible matter (ignition at 950 ° C in the absence of oxygen) Fixed carbon (combustible residue)

19. Typical Proximate Analysis Values (% by Weight)

20. Fusing Point of Ash Fusing point of ash is the temperature at which the ash resulting from the burning of waste will form a solid (clinker) by fusion and agglomeration. Typical fusing temperatures: 1100 - 1200 ° C Ash Fusion Furnace

21. Ultimate Analysis Involves the determination of the percent C (carbon), H (hydrogen), O (oxygen), N (nitrogen), S (sulfur) and ash. The determination of halogens are often included in an ultimate analysis. The results are used to characterize the chemical composition of the organic matter in MSW. They are also used to define the proper mix of waste materials to achieve suitable C/N ratios for biological conversion processes.

22. Chemical composition of typical MSW

23. Typical data in elemental analysis (% by weight)

24. Methods for Calculating the Calorific Value of a waste (Dulong Equation) BTU/ lb = 145 C + 610 (H - ) + 40 S + 10 N   Where C, H, O, S, N are percent of those elements respectively

25. Example:- What is the calorific value of PVC PVC   %C = = 39.7%   %H = = 1.65%   BTU/ lb = 145(39.7) + 610(1.65) = 6763 = 15730.74 Kj /kg

26. Energy Content of Solid Waste Energy content can be determined by; 1. By using a full scale boiler as a calorimeter 2. By using a laboratory bomb calorimeter 3. By calculation Most of the data on the energy content of the organic components of MSW are based on the results of bomb calorimeter tests.

27. Equation for internal energy change Where Z = Heat capacity of calorimeter system T = Rise in temp. M = molecular mass of substance w = Mass of Substance taken Δ E = -Z x Δ T x  

28. Q:- A sample of MSW is analyzed and found to contain 10% moisture content. The energy content of the entire mixture is measured in a calorimeter and is found to be 9300 kJ/kg. A 1.0 g sample is placed in the calorimeter, and 0.2 g ash remains in the sample cup after combustion. What is the comparable moisture-free energy content (kJ/kg) and moisture & ash-free heat value? Solution:- Energy on Dry basis = 9300 = 10333.33 KJ/kg Energy on ash and moisture free basis = 9300 x = 13285.71 KJ/kg  

29. 3. Biological Properties of MSW The organic fraction of MSW (excluding plastics, rubber and leather) can be classified as: Water-soluble constituents - sugars, starches, amino acids and various organic acids Hemicellulose - a product of 5 and 6-carbon sugars Cellulose - a product of 6-carbon sugar glucose Fats, oils and waxes - esters of alcohols and long-chain fatty acids Lignin - present in some paper products Lignocellulose - combination of lignin and cellulose Proteins - amino acid chains

30. Biodegradability of MSW The most important biological characteristic of the organic fraction of MSW is that almost all the organic components can be converted biologically to gases and relatively inert organic and inorganic solids. The production of odours and the generation of flies are also related to the putrescible nature of the organic materials. Volatile solids (VS), determined by ignition at 550 , is often used as a measure of the biodegradability of the organic fraction of MSW. Some of the organic constituents of MSW are highly volatile but low in biodegradability (e.g. Newsprint) due to lignin content. The rate at which the various components can be degraded varies markedly. For practical purposes, the principal organic waste components in MSW are often classified as rapidly and slowly decomposable.  

31. Biodegradable fraction of selected organic waste components Biodegradable Fraction (BF) = 0.83 - 0.028 LC Where BF = Expressed on a volatile solids basis LC = Lignin content of volatile solids expressed as a percent of dry weight

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