EcoEng Newsletter No. 9, June 2004


What you must know about turning waste into compost

By R. Shanthini, EcoEng-Correspondent and K.S. Walgama, Sri Lanka

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2.1 Why should we turn waste into compost?

Roses grown on compost from the authors garden

Almost all the waste generated in the urban and suburban households in Sri Lanka end up in the dumping grounds. All dumping grounds are similar in many aspects. Every one of them is a disgusting sight, gives out an intolerable stench, and breeds flies and mosquitoes, including the infamous dengue mosquitoes.

Besides, the people who have no alternatives but to live by these repulsive dumping grounds, are forced into living their lives without dignity. They live in a continual mental and physical agony caused by the presence of dumping grounds so close to their homes. The sad fact is that dumping grounds have become an integral part of the modern way of life. What is worst is that we all believe that there is no alternative but to accept the dumping grounds.

The amount of waste that reaches the dumping ground can be reduced to at least half the present amount, if we all make an attempt to not let the waste generated in our own homes to reach the dumping grounds. The only pleasant and environmentally friendly way in which we could achieve that is to turn our own kitchen and garden waste into compost in our own gardens.


2.2 What is special about compost?


Organic matter is broken down to stable end products, collectively known as compost. Unlike the waste, the compost resulting from the waste is a pleasant material to work with. Mature compost is dark in color and uniform in its texture. It gives off a clean, earthy smell. Besides, compost is a soil conditioner and a natural fertilizer.

Suppose your garden soil is sandy and therefore it does not retain wetness well. As a result, your plants dry quickly unless you water your plants very often. If compost is added to this dry soil, compost will help the soil retain wetness for a considerably longer period of time than otherwise. And, therefore, frequent watering of the plants in your garden will not be a necessity.

On the other hand, you may have a clay-like soil in your garden, which does not permit good air and water circulations within the soil. As a result, you are unable to grow anything in your garden. Compost added to this soil helps improve the air spaces within the soil, and thereby improving the air and water circulations within the soil.

Moreover, spreading the compost on the soil surface around the plants in your garden prevents the surface soil from drying out. Besides, the dark color of the compost around the plants gives an improved, and well-cared for, look to your garden.

Healthy growth of the plants in your garden, as you may already know, depends heavily upon the availability of nutrients, such as nitrogen (N), phosphorus (P) and potassium (K), for the plants. The very purpose of adding artificial fertilizers to the plants is to provide these nutrients. The major problem with the application of artificial fertilizers is that the nutrients present in them dissolve readily in water, and therefore get washed away easily.

The washed away fertilizers ending up in fresh water ponds and lakes accelerate the growth of plants in these fresh water systems. This overgrowth causes severe water pollution, including bad smell emanating from these water bodies and death of fish and other lives in these water bodies. The washed away fertilizers ending up in the ground water system also cause environmental pollution, but of a different kind.

The interesting point to note is that compost also has the nutrients that the artificial fertilizers have, but of course in smaller amounts than what the artificial fertilizers have. However, the nutrients present in the compost do not dissolve easily, and therefore do not get washed away even by a heavy rain.

Besides, the nutrients in compost are released very slowly, thereby providing the plants and soil organisms with the nutrients as and when they require the nutrients. Moreover, compost applied to the plants causes absolutely no environmental pollution.

Compost also contains calcium, iron, magnesium, manganese, silicon, and the 'trace' minerals such as boron, cobalt, zinc and iodine. These minerals, in limited amounts, are essential for preventing many deficiency diseases of the plants.

It is also important to note that compost, unlike the artificial fertilizers, adds organic matter and beneficial microorganisms to the soil.

Compost is therefore definitely the best and the most eco-friendly fertilizer for the plants in our gardens and elsewhere. It is also the most inexpensive fertilizer when you make it in your own garden.


2.3 Does all waste turn into compost?


Since the conversion of waste into compost is a natural process, only the matter that are of natural origin turns into compost. For instance, banana skins turn into compost, as does goat dung, leaves and grass clippings. Coconut shells and paper also turn into compost, but slowly. It is important to know that the numerous polythene bags that reach our homes with almost every item that we shop, the so-called lunch sheets, the yoghurt and ice cream cups, and the broken and discarded plastic items, all of these technological innovations of the modern times, never turn into compost.

When we decide to turn our kitchen and garden waste into compost, the first thing we must do is to separate the waste that could be composted from the waste that could not be composted. The most difficult part of implementing the process of turning our waste into compost in our own gardens is just this.

For many, many years, we have been disposing of our household waste by the roadside, which the sanitary workers have been taking away from us to let them rot away from our eyes and nose. We know very well that such methods of waste disposal are not honorable methods, but they are very convenient methods for us.

And, therefore, we find it very difficult to adjust to the fact that we must collect in one place the waste that can be composted, and in another place, collect the waste that cannot be composted. That means every time we throw something away, we must think for a minute, and that is hard for us.

It is hard for us because we don't want to waste our precious time thinking about garbage. Once we get over this difficult phase, turning our waste of natural origin into compost in our own gardens becomes a rewarding experience.


2.4 How does waste turn into compost?


Natural organic matter has been turning into compost for millions and millions of years. That is, composting was occurring even before there was human in this world. Composting is Mother Nature's way of recycling matter on earth. She uses billions and billions of microorganisms, the tiniest creatures in her empire, to convert organic matter of natural origin into stable end products, broadly known as compost. The principle character of compost is that it is in a form most suitable to be synthesized into fresh organic matter once again by Nature.

No single microorganism can ever be seen with naked eyes. Very powerful microscopes are necessary to be able to look at a microorganism, because they are so tiny in their sizes. Millions of microorganisms, such as bacteria, fungi and others, may be found attached to every piece of organic matter. They feed on the organic matter, during which the organic matter is broken down to compost. For instance, microorganisms are responsible for converting nitrogen into ammonia, and then the ammonia into nitrates, which the plants happily use as natural fertilizers.


2.5 How do the microorganisms convert waste into compost?


Conversion of waste into compost by microorganisms is a natural process, and therefore it is a very complex process as well. Here an attempt is made to give a simplified picture of how the microorganisms convert waste into compost.

Organic matter can be as complex as carbohydrates, proteins and fats. Microorganisms, mainly bacteria and fungi, start the process of composting by breaking down the complex organic matter for their own food. During this process, most of the carbon in the organic matter gets converted into carbon dioxide.

A lot of heat is released during the conversion of carbon into carbon dioxide. Since the composting mass is a natural insulator, the heat generated gets trapped within the composting mass. As a result, the temperature of the composting heap increases.

Once the composting heap is reasonably hot, say about 40 to 50oC, the family of moderately heat-loving (known as mesophilic) microorganisms that has been turning the waste into compost cannot continue to live in the composting heap any more. They either leave the hotter parts of the composting heap and move to the cooler parts, or die in the heap, adding to the mass to be composted.

The composting action within the composting heap, however, does not stop at that point, since there are those heat-loving (known as thermophilic) microorganisms in Nature that come to populate the composting heap and continue the composting action. Their actions also involve the conversion of carbon into carbon dioxide, and therefore still more heat is produced, which makes the composting heap hotter than before.

If the temperature of the heap rises above 70oC or so, then the thermophilic microorganisms will either work slowly or leave the composting heap. But, it is very seldom the temperatures of the composting heap in our garden would rise above 70oC. What happens is that the thermophilic microorganisms degrade all the matter so rapidly in the temperature range of 50 to 70oC that the microorganisms themselves will soon be left with no food in the heap to survive on. At this point, they die of starvation, or they leave the heap.

When there is nothing much left to degrade in the composting heap, the temperature of the heap goes down. The cooling heap attracts the mesophilic microorganisms, which may have been living in the cooler parts of the composting heap, to the other parts of the composting heap to compost any remaining material. This phase is known as the curing stage of the compost.

The curing stage of the compost is dominated by microorganisms, such as fungi and actinomycetes, which give finishing touches to the compost. At the end of this stage, what we have is mature compost. You may now add the 'waste' that the microorganisms have turned into compost free of charge for you in your garden, to the plants in your garden.


2.6 How do we know that compost has reached maturity?


A good sign of the maturity of the compost is that it attracts earthworms and other similar life forms to populate it. The presence of earthworms in the compost indicates that the temperature of the compost is reasonable, aeration within the compost is good, wetness in the compost is balanced, the compost is neither acidic nor alkaline, and toxicity of the compost is either low or nil. At this point, the compost is full of nutrients needed for healthy plant growth, and microorganisms that are beneficial for plant growth.


2.7 Good composting requires air.


The microorganisms that do the composting are known as aerobic microorganisms, which means they love air. The aerobic microorganisms use the oxygen in air in the same way as we do. They breathe air, and without air they simply die. The products of aerobic degradation are carbon dioxide, water vapor, a lot of heat, and compost. Therefore, it is a pleasant process to work with in our garden.

Suppose that a situation arises in which the air supply to the composting mass is reduced or cut off. In the absence of adequate oxygen, the aerobic microorganisms die. But, the waste continues to degrade. The degradation process of waste under conditions of inadequate air supply is similar to the processes that take place in a toilet pit or in a biogas plant.

As you know, no air is supplied to a toilet pit or to a biogas plant. Nevertheless, the waste in these units degrade. The fact is that the degradation in these units is carried out by a different group of microorganisms, known as anaerobic microorganisms. These are microorganisms that hate air, and therefore they thrive when there is no air.

The problem, however, is that the gases produced during the anaerobic degradation of the waste smell extremely bad. The foul-smelling lakes in some of the Sri Lankan cities do so because the major part of the degradation taking place within the lake is anaerobic in nature. And, therefore it is very important to make sure that the composting heap in your garden gets plenty of air, and that it never goes anaerobic.

If the composting heap gets too much air, however, it would cool off, and thereby discouraging the efficient thermophilic microorganisms taking over the composting action in the heap.


2.8 Good composting requires the right amount of wetness of the composting heap.


Wetness of the composting heap is usually referred to as the moisture in the composting heap. The composting heap must be moist (that is moderately wet) in order for the microorganisms to live in, since they require water to survive as we do. If the moisture content of the composting heap is lower than 30 to 40% by weight, then the microorganisms will be dehydrated, and their cells will be damaged, leading to the death of microorganisms.

If the moisture content of the composting heap is above 60% by weight, then the presence of excessive amount of moisture in the heap will lead to clogging of the pores. As a result, aerobic microorganisms in certain locations of the composting heap may not get adequate oxygen for their survival. Consequently, anaerobic zones would be created within the composting heap, leading to a bad smell emanating from the composting heap.

It is therefore very important to ensure that the moisture content within the composting heap is maintained in the range of 40 to 60% by weight. If a stick inserted into the composting mass comes out somewhat wet but clean, it will mean that the heap is wet, but not sticky. That is, the moisture content of the composting mass is within the right range for good composting.

Since the moisture content of kitchen waste is very high, a compost heap made up of kitchen waste alone has excessive amount of moisture, which leads to a sticky, smelly composting heap. To avoid this, it is necessary to add some dry materials, such as dried leaves, paper torn into pieces, and sawdust, to the composting heap in which kitchen waste is degraded.


2.9 The composting heap should have a proper balance of carbon and nitrogen.


Nearly every natural organic matter is built from the basic elements known as carbon and nitrogen. The relative amounts of carbon and nitrogen present however change from one organic matter to another. In general, kitchen waste is rich in nitrogen and the garden waste is rich in carbon. For example, the carbon/nitrogen ratio (abbreviated to C/N ratio) of vegetable waste is known to be in the range of 15 to 20, of fruits waste in the range of 30 to 50, and of dried leaves and dried grass clippings in the range of 50 to 70.

In order to maintain a healthy composting heap in our gardens and to obtain the best compost from our waste, we need to maintain the optimum C/N ratio of 25 to 30 in our composting heap. We may wonder how to ensure that the correct C/N ratio is maintained in our composting heap without carrying out scientific measurements of our waste. Actually, it is very easy to ensure a proper balance of carbon and nitrogen in the composting heap. All what we need is a bit of common sense.

If the composting mass is sticky and smelly and if it attracts flies and rodents, then we know that the composting mass contains a lot of nitrogen. That means there is too much kitchen waste. To fix this condition, we must add dried garden waste to the sticky and smelly composting heap . If we do not have enough garden waste, then you may add shredded paper without color, straw, sawdust, or anything else that is dry and brownish. It is useful to know that the C/N ratios of paper and straw are in the range of 70 to 200, and of sawdust in the range of 200 to 500.

On the other hand, if the composted mass is light in color then we know that there is a lot of carbon and not enough nitrogen. To fix this condition, we have to add nitrogen-rich kitchen waste to the composting heap. Since we almost always have a fixed amount of kitchen waste, there is no way of increasing the amount of kitchen waste added to the composting heap, unless we invite our neighbors to add their kitchen waste to our composting heap.

Adding grass clippings while they are still fresh also helps improve the nitrogen content of the composting heap, since the C/N ratio of fresh grass clippings is in the range of 20 to 30. We may also add nitrogen-rich leaves from the trees such as Gliricidia sepium and Erythrina verigeta [1], as our forefathers would have done. Cow dung and goat dung which are rich in nitrogen, may also be added to the composting heap to increase the nitrogen content of the composting heap. It is useful to know that the C/N ratios of nitrogen-rich leaves and fresh cow dung are in the range of 10 to 15.

Some suggest that urea may be added to increase the nitrogen content of the composting heap in case it becomes nitrogen deficient, but we have strong objection to that. The goodness and tenderness of compost as a fertilizer lie in the very fact that composting involves only natural raw materials and natural processes. Addition of urea to the composting heap would introduce the illnesses associated with artificial fertilizers into compost, and would destroy the gentle naturalness of compost.


Footnote 1: Gliricidia sepium and Erythrina verigeta have the indigenous names "Giniseeriya"/ "Seemaikilluwai" and "Erabadu"/ "Mulmurungai", respectively.


© 2004, International Ecological Engineering Society, Wolhusen, Switzerland