Environmental Engg.

Lesson-25 Composition to solid waste

Materials in solid wastes can be broadly categorized into three groups, Compostable, Recyclables and Inerts. Compostable or organic fraction comprises of food waste, vegetable market wastes and yard waste. Recyclables are comprised of paper, plastic, metal and glass. The fraction of solid wastes which can neither be composted nor recycled into secondary raw materials is called Inerts. Inerts comprise stones, ash and silt which enter the collection system due to littering on streets and at public places.

Waste composition dictates the waste management strategy to be employed in a particular location. Organics in municipal solid wates are putrescible, and are food for pests and insects and hence need to be collected and disposed off on a daily basis. The amount of recyclables like paper and plastic in solid wastes dictates how often they need to be collected. Recyclables represent an immediate monetary value to the collectors. Organics need controlled biological treatment to be of any value, however due to the general absence of such facilities, organics do not represent any direct value to informal collectors.

A major fraction of urban municipal solid wastes in India is organic matter (51%). Recyclables are 17.5 % of the municipal solid wates and the rest 31% is inert waste.  It has to be understood that this composition is at the dump and not the composition of the waste generated. The actual percentage of recyclables discarded as waste in India is unknown due to informal picking of waste which is generally not accounted. Accounting wastes collected informally will change the composition of municipal solid wastes considerably and help estimating the total waste generated by communities.

Waste composition varies with the socio-economic status within a particular community, since income, for example, determines life style, composition pattern and cultural behavior.

Factors affecting quantity and composition of solid waste

Geographic location

The geographical location is related primarily to different climate that can influence both the amount of solid wastes generated and the collection operation. For instance, substantial variations in the amount of yard and garden wastes generated in various parts of India are related to the climate. To illustrate, in the warmer southern areas, where the growing season is considerably longer compared to the northern areas, yard wastes are collected in considerably larger quantities and over a longer period of time.

Season

Seasons of the year have implications for the quantities and composition of certain types of solid wastes. For example, the growing season of vegetables and fruits affect the quantities of food wastes.

Collection frequency

A general observation is that in localities, where there are ultimate collection services, more wastes are collected. Note that this does not mean that more wastes are generated. For example, if a resident has access to only one or two containers per week, due to limited container capacity, he or she will store newspapers or other materials in some specified storage area. However, the same person will tend to throw them away, if there is access to unlimited container services. In this latter situation, the quantity of waste generated may actually be the same but the quantity collected, as it relates to the frequency of collection, is considerably different

Population diversity:

The characteristics of the population influence the quantity and composition of waste generated. The amount of waste generated is more in low-income areas compared to that in high-income areas. Similarly, the composition differs in terms of paper and other recyclables, which are typically more in high-income areas as against low-income areas

Typical waste composition based on income pattern of population

Characteristics	Low income	High income	Comments
Paper	1 to 4 %	20 to 50%	Low paper content indicates low calorific value
Plastics	1 to 6 %	5 to 10%	Plastic is low in low income areas as compared to high-income areas though the use of plastic has increased in recent years.
Ash and Fines	17 to 62 %	3 to 10%	Ash and fines do not contribute to combustion process

Extent of salvaging and recycling

The existence of salvaging and recycling operation within a community definitely affects the quantity of wastes collected.

Public attitude

Significant reduction in the quantity of solid waste is possible, if and when people are willing to change – on their own volition – their habits and lifestyles to conserve the natural resources and to reduce the economic burden associated with the management of solid wastes.

Legislation

This refers to the existence of local and state regulations concerning the use and disposal of specific materials and is an important factor that influences the composition and generation of certain types of wastes.

In a nutshell, elements that relate to waste generation include land use characteristics, population in age distribution, legislation, socio economic conditions, etc.

Changing composition of municipal solid wastes in India

It is rather interesting to study the changes in the composition of waste in India in the past.  The following table gives the changing composition of Municipal Waste over the last two decades and is attributed to the changing life styles and increasing consumerism.

Component	% of Wet Weight
	1971-73 (40 cities)	1995 (23 cities)
Paper	4.14	5.78
Plastics	0.69	3.90
Metals	0.50	1.90
Glass	0.40	2.10
Rags	3.83	3.50
Ash and Fine	49.20	40.30
Total Compostable Matter	41.24	41.80