Biodegradable domestic waste — kitchen scraps, vegetable peels, leftover food, garden trimmings and similar organic matter — can be broken down naturally by microorganisms. The most appropriate primary method of managing it after collection is conversion into compost, which is the correct answer.

Composting is the controlled biological decomposition of organic waste by bacteria, fungi and other decomposers under managed conditions of moisture and aeration. Over time the material turns into a dark, crumbly, humus-rich product that can be returned to the soil. Its benefits include:

• reducing the volume of waste sent to landfills;
• producing a natural, nutrient-rich fertiliser that improves soil structure and fertility;
• cutting greenhouse-gas emissions that would arise if the same waste rotted anaerobically in a dump; and
• closing the nutrient loop by recycling organic matter back to the land.

The other options are unsuitable for biodegradable waste:

• Recycling is meant for non-biodegradable materials such as plastic, glass and metal, not for wet organic waste.
• Throwing it into sewers would clog drainage systems and pollute water bodies.
• Burning in open air releases smoke, harmful gases and particulate pollution, and wastes the nutrients the waste could have returned to the soil.

Because composting safely converts organic waste into a useful resource, it is the preferred primary treatment.