Recycling is the third of the three R of waste reduction : Reduce, Reuse and Recycle.
A colony on Mars uses a number of materials to build everything they need for living. Mining or ISRU in the main way of adding materials to the settlement. Importation from Earth or other planets is another.
To reduce the need for production or importation of materials, Recycling can be used. If the waste consists of products including just a few materials recycling is simplified. The concept requires manufacturing that takes care to use the simplest materials possible or that designs products for easy disassembly at end of life.
Products made from single materials
- Bottles from glass.
- Boxes from plastics (e.g. polyethylene).
- Cans from aluminum.
- Insulating foam from melted and expanded regolith or plastics.
Products made from multiple materials
The following products need more than one material, but the materials can be separated easily for recycling. Alternatively, some may be re-used directly.
- Electric cable from metal and plastics (e.g. polyethylene).
- Insulating mat from mineral fiber and plastics casing (e.g. polyethylene).
- Laminated safety glass.
Economics of Recycling
As the colony grows in size and population, the economics of the colony starts. The free market will determine whether it costs more to extract new material or recycle the existing materials in products. Recycling will be cheaper than mining in many cases. This is already obvious on Earth, where plastics, lead, aluminum and steel have higher and higher recycled content as the recycling systems develop.
List of recyclable materials
This list comprises recyclable materials, that are really needed by an autonomous colony, by order of importance and mass.
- Water - Water is typically recycled for most services using water treatment. Some water will be consumed for propellant production and for energy storage.
- CO2 - For propellant production and plants. CO2 is one of the rare products than can return to the environment before re-use.
- Ammonia and nitrogen - Nitrogen is an essential part of the life cycle and the settlement atmosphere. Ammonia availability may be a limitation to settlement development so recycling will be important.
- Concrete - for structures and infrastructures. Concrete can be recycled as aggregate on back into concrete.
- Steel - for digging machines, pipes, equipment, structures, buildings and infrastructure.
- Plastics - for greenhouses, space suits and industrial products as well as infrastructure (wiring and piping).
- Glass - for windows and recipients. As silica is the most common elements in the Martian crust, recycling may not always be advantageous compared to new production.
- Silicon - for solar panels and microprocessors.
- Metals: Aluminum, copper, chromium and Lithium, lead.