Composting is the aerobic breakdown of organic waste by microorganisms. The product is a stable, humus-rich material used to improve soil.

What carbon to nitrogen ratio suits composting?

A carbon to nitrogen ratio of about 25–30 to 1 suits composting microbes. Woody “browns” supply carbon and fresh “greens” such as grass supply nitrogen.

Why does a well-managed compost heap become hot?

Microbial respiration releases heat faster than it escapes from the heap. Thermophilic microbes then raise the temperature to around 55–70°C.

Why is the hot, thermophilic stage of composting important?

Sustained high temperatures kill pathogens and weed seeds. The heat also speeds up the breakdown of organic matter.

CCEA A-Level Environmental Technology 3930

Fossil Fuels

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Global Action on Energy Conservation and Climate Change

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Macrogeneration

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Microgeneration

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Energy From Wind

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Energy Storage

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Plastics for the Future

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Renewable Energy Investigations

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Sustainable Development

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Waste Management

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Waste to Energy Technologies

Topic overview Embodied energy Incineration with energy recovery Digester design: solids content, residence time and staging Stages of anaerobic digestion and biogas CHP Composting and catering waste

Land Contamination and Remediation

Topic overview Contaminated land, risk and traditional remediation Bioremediation principles and bioreactor systems Micro-organisms that degrade named pollutants Bioremediation benefits and genetically engineered microbes Phytoremediation of metals and other elements Phytoextraction with Indian mustard and alpine pennycress Biohydrometallurgy and phytomining of ores

Hydrogen Fuel Cells

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Transport System Challenges

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Energy Performance of Buildings

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Emerging Technologies

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Sustainable Urban and Rural Communities

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The Code for Sustainable Homes

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Waste to Energy Technologies

Composting and catering waste

3 things to know
A2 1

Overview

How composting works, aeration and the carbon to nitrogen ratio, the thermophilic stage, windrow and in-vessel composting, catering waste and the animal diseases it can spread, where it must go, and composting against anaerobic digestion.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is composting?

Key term

What types of waste can be treated by composting?

Key term

Why must a compost heap be turned or aerated?

Questions from this subtopic

Each one with the model answer underneath.

1
What is composting?
Model answer
Composting is the aerobic breakdown of organic waste by microorganisms. The product is a stable, humus-rich material used to improve soil.
2
What types of waste can be treated by composting?
Model answer
Garden waste such as grass cuttings, leaves, hedge trimmings and prunings composts well. Straw, wood chips, shredded card and plant residues from farms can also be composted.
3
Why must a compost heap be turned or aerated?
Model answer
Compost microbes need oxygen, and turning lets fresh air into the heap. An airless heap turns anaerobic and gives off foul-smelling gases.
4
What carbon to nitrogen ratio suits composting?
Model answer
A carbon to nitrogen ratio of about 25–30 to 1 suits composting microbes. Woody “browns” supply carbon and fresh “greens” such as grass supply nitrogen.
5
Why does a well-managed compost heap become hot?
Model answer
Microbial respiration releases heat faster than it escapes from the heap. Thermophilic microbes then raise the temperature to around 55–70°C.
6
Why is the hot, thermophilic stage of composting important?
Model answer
Sustained high temperatures kill pathogens and weed seeds. The heat also speeds up the breakdown of organic matter.

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Fossil Fuels

Global Action on Energy Conservation and Climate Change

Macrogeneration

Microgeneration

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