Solid Waste Management

Solid waste is dry refuse: It includes garbage, ashes, rubbish, dust etc. Density varies from 300 to 600 Kg/Cum

• Garbage: It includes all sorts of putrescible organic wastes.
• Rubbish: Includes all non-putrescible wastes, includes all combustible and non- combustible wastes such as rags, paper pieces, broken pieces of glass and furniture, card-boards etc.

Disposal of Refuse: Various methods are as follows.

• Sanitary land filling
• Burning or incineration
• Barging it out into the sea
• Pulverization and
• Composting, i.e. digestion by bacterial agency.

Disposal of Refuse by Sanitary Land Filling: Refuse is carried and dumped into the low lying area and it is covered by good earth layer, so that the refuse is not directly exposed- The waste is stabilized by aerobic as well anaerobic bacterial processes.The -refuse, in managed landfills, may usually get stabilized, generally within a period of 2 to 4 months. About 90% of Indian refuse- is disposed of in this manner.

Leachate: During rainy season, when excess water seeping through the area, may come out of the dump, as a coloured liquid, called leachate. This is highly poisonous and polluted. 

Gas Production: In most cases, over 90% of the gas volume produced from the decomposition of solid wastes, consists of methane and carbon dioxide. in large sized landfills, the gases evolved due to decomposition of refuse may be collected through installing gas recovery wells.

Disposal of refuse by Incineration and thermal Pyrolysis: It consists of burning of refuse at high temperatures in furnace. called incinerators. Large sized incinerators are called destructors.

Pyrolysis: Upon heating in an oxygen free atmosphere, most of the organic substances can

be split through a combination of thermal cracking and condensation reactions into gaseous, liquid and solid fractions. This process is known as Pyrolysis or Thermal Pyrolysis.

This process is also known as destructive distillation.

When the organic solid waste is pyrolysed, the following three types of products are produced at different stages or temperatures.

• A gas stream, primarily contains hydrogen, methane, CO, CO2.
• A Liquid fraction, consisting of a tar and / or an oil steam.
• A solid fraction., consisting of charcoal like product of almost pure carbon.

Disposal of Refuse by Barging it out into the sea at reasonable distance from the coast

Disposal of Refuse by Pulverization: Refuse is pulverized in grinding machines, so as to reduce its volume and to change its physical character it has, therefore, to be further disposed of by filling in trenches, or digested in open windows or closed digestors.

Disposal of Refuse by Composting: This decomposition can be effected either under aerobic condition, or under anaerobic condition or both. The final end product. is a manure,

called compost or humus, as fertilizer for farms. Composting is considered to be an aerobic process.

In India, the composting is practiced in rural areas on the mixture of night soil and refuse.

Two methods, which are generally adopted here are:

• Indore Process 
• Bangalore Process

Indore Method: It uses manual turning of piled up mass (refuse + night soil), for its decomposition under aerobic conditions.

Bangalore Method: It is primarily anaerobic in nature, and does not involve any turning or

handling of the mass, and is hence more clean than the indore method. This method is therefore widely adopted by municipal authorities throughout the country. The refuse and night soil, in this method, are therefore pilled up in layers ¡n an underground earthen trench. This mass is covered at its top by layer of earth of about 15 cm depth, and is finally left over for decompositions. After about 4 to 5 months the refuse gets fully stabilized and changes into a brown,, coloured odourleš;

innocuous powdery mass, called humus.

Additional Terms Related to Sanitary Engineering:

Elutriation: Elutriation which literally means washing. h is a unit operation in which a solid

or a solid-liquid mixture is intimately mixed with a liquid for the purpose of transferring certain components to the liquid.

Eutrophication: Eutrophication results from the enrichment of a body of water with fertilizing

elements when in the presence of sunlight stimulate the growth of algae and other aquatic plants. Both treated and untreated domestic have high concentration of these fertilizing elements and contribute to the rate of Eutrophication of waters into which they are discharged.

Energy content: Energy values may be converted to a dry basis by the following equation.

KJ/ kg(dry basis) = KJ/ kg (as discarded) x 100/ (100 - % mc)

The corresponding equation on an ash - free dry basis is:

KJ/kg (ash free dry basis) KJ/kg (as described) x  100/100 - %ash - % mc