For long-term missions, it will not be economically feasible to resupply these life support elements from Earth, explained NASA Agricultural Engineer Dr. John C. Sager. Humans will need to develop systems to produce food, purify their water supply, and create oxygen from the carbon dioxide they expel. Physicochemical processes can perform the two latter tasks, but only biological processes can perform all three. The BPC was retrofitted for plant growth and now contains four levels for growing crops, including potatoes and wheat. Humans need oxygen, food, and water, and expel carbon dioxide and organic waste.
Plants utilize carbon dioxide, produce food, release oxygen, and purify water.
Inedible plant material and human waste are degraded by microorganisms to recycle nutrients for plants processes. The project's key is integration of these component systems. The initial phase of the project was baseline crop production. Phase II, the integration of resource recovery with crop production, started in 1994 with the growth of plants on a recycled solution. In 1996, a 3-year continuous operation of the breadboard began.