Careless youngsters and drunkards throw plastic empties
and mar the splendour of streets. Cut grass and the fallen leaves in the garden are removed depriving the soil of natural fertilizer. In a small way plastic bottles may be re-used while the  organic waste may be decomposed to obtain a fuel and compost for agriculture.  

Fig.1.  Scenic streets marred by the litter..

All organic waste matter, vegetable peelings, food remains, dead leaves and flowers decompose mainly due to the action of bacteria.This is a process similar to burning, which takes place at an exceedingly slow pace. (anaerobic respiration) The speed depends on the type of substance, availability of water, pH value (acidity) , temperature and the type and amount of decomposers such as bacteria and fungi present.

Fig.2 A Model Bio- gas Generator.

Fig.2 gives a suitable method to  decompose waste matter and collect the gas given out. This is not an experiment that can be completed in a day or two.  It may take two to three months, or even more depending on the environment, but it works. To start with the tall bottle will not have any air. As time goes bubbles will come up and a gas will be collected. When the tall bottle gets filled , the water there will come out into the outer container . When this is full water will flow out. You have to be prepared for this. The bottle also will try to get lifted. In order to keep the tall bottle in place rubber bands may be used.

WARNING-  Do not attempt to burn the gas without the help of  a trained scientist. 

As the gas will be inflammable, just like Hydrogen,  or fuel gases, no flame should be brought close to it. Especially if the gas is mixed with air a dangerous explosion can take place. In order to get a flame there are certain safety measures that have to be followed.

Fig.3  A safety device.

The gas bubbles through the water to enter the burning area. So there is no way for the flame to get sucked back into the main generator. If at all it comes back there can only be a minor explosion sending the top of the bottle up . The experiment has to be done in the open in the presence of a teacher or a qualified person. 

Accelerating Decomposition.
As decomposition is a very slow process it is worthwhile to  discover methods to accelerate it. If you just keep the dry leaves in a clean sterile environment they may not decay. Bacteria has to be introduced from some source. Soil is a good source of many bacteria. So is cow dung. Here is a simpler method to do the experiment. If you do not have test tubes you may use a narrow bottle.

Fig.4.  Comparing Rates of Reaction.