The household wastes (or rubbish) are called garbage. Every household produces a lot of garbage (or wastes) daily. This garbage includes left-over food, fruit and vegetable peels, fallen leaves of potted plants, waste paper, unwanted plastic objects (such as plastic bottles, polythene bags, toys, etc.), glass articles (like glass bottles, broken window panes, etc.), metal objects (like aluminium foils, rusted iron grills, etc.), old wooden objects, rags (old, torn clothes), discarded shoes, and sewage. Some of the garbage (or waste) is biodegradable whereas a major part of it is nonbiodegradable. If the household garbage or waste is not disposed of properly, it can pollute the environment like soil, water and air.
'Disposal of waste' means 'to get rid of waste'. The disposal of waste should be done in a scientific way. There are different methods of waste disposal. The method to be used depends on the nature of the waste. Some of the important modes of waste disposal are:
(ii) Preparation of compost
(v) Sewage treatment
We will now describe all these methods of waste disposal (or garbage disposal) briefly, one by one. Let us start with recycling.
The solid wastes like paper, plastics and metals, etc., are recycled. For example, waste paper is sent to paper mills where it is reprocessed to form new paper once again. The broken plastic articles like plastic
bags, buckets, bowls, cups, plates, etc., are sent to plastic processing factories where they are melted and remoulded to make new articles. Similarly, waste metal articles are sent to metal industries where they are melted and recycled as solid metal for various purposes.
Biodegradable domestic wastes such as left-over food, fruit and vegetable peels, and leaves of potted plants, etc., can be converted into compost by burying in a pit dug into ground, and used as manure.
'Incineration' means 'reducing to ashes'. The burning of a substance at high temperature (of more than 1000°C) to form ash is called incineration. Incineration is used to destroy household waste, chemical waste and biological waste (like that from hospitals). Incineration greatly reduces the volume of the waste. This is because when the large volume of waste material is burned, then only a small amount of ash is left behind which can be disposed of by landfill. Incineration is carried out in an incinerator (which is a kind of furnace). The waste disposal on large scale by using incinerators is done by the Municipality of a City. The solid waste is burned at a high temperature in the incinerator. All the organic matter present in waste is removed as carbon dioxide and water vapour. The ash left behind is removed from time to time.
The disposal of wastes by putting it in low-lying areas of ground and covering it with earth is called landfill. Most of the solid waste in urban areas (which cannot be disposed of by other methods) is dumped in low-lying areas of ground and covered with earth to level the uneven ground. A big landfill site can be used to dispose of waste materials (or garbage) for a considerable time.
The dirty drain water containing urine and faeces which is carried from our homes by the underground pipes (called sewers) is called sewage. If untreated sewage is dumped into a river, it can pollute the river water. Thus, sewage is disposed of by treating it at the sewage treatment plant (or sewage works). The treatment of sewage produces clean water which is discharged into the river. The organic matter present in sewage is 'digested' in the digesters of sewage treatment plant to produce 'sewage gas' (which is a kind of biogas), and 'manure'.
We will now give an example to illustrate how the use of biodegradable and non-biodegradable materials can make a difference to our environment. There was a time when tea in trains was served in plastic glasses which had to be returned to the vendor. This was, however, not a hygienic thing to do.
Later on disposable plastic cups were introduced (which are used 'once' and then 'thrown away'). Though it was hygienic to use a disposable plastic cup for drinking tea but the disposal of millions of plastic cups on daily basis posed a big problem.
Sometime back 'kulhads' (disposable cups made of clay) were introduced for serving tea in trains. It was, however, soon realised that the use of a lot of clay for making millions of kulhads daily led to the loss of fertile top soil from fields (which was used for making kulhads).
So, the practice of using 'kulhads' has also been discontinued. These days, disposable paper cups are being used. The use of disposable paper cups has the following advantages over the plastic cups:
(i) Paper cups are biodegradable. So, even if paper cups are thrown away after use, they will decompose (break down) automatically by the action of micro-organisms in due course of time. On the other hand, plastic cups are non-biodegradable. They will remain as such and pollute the environment.
(ii) Paper cups can even be disposed of by burning without causing much air pollution. On the other hand, burning of plastic cups produces toxic gases (poisonous gases) which cause too much air pollution.