As a retired "Coastie", during my time on ships the mess-deck (dining facility for land-lubbers) is the "town square" where off-duty crew hangs out. When I was operating my lean-to greenhouse-nursery, the wife and daughter typically declined to visit me there, because to them it was such a mess. I was looking for an acronym other than NASA's CELSS, so I figured why not. (Ok, so I tend toward corny names.) The purpose of this appendix is to look at the limits on closing the loop for the safe recycling of human effluents to a growing medium which is a micro-environment optimized for growth of food.
Our present population of 6+ billion is dependent on the present global socio-economic-industrial infrastructure not only for economic purposes, but also for "life support" such as food. That infrastructure is itself dependent on cheap, abundant fossil fuels, in particular oil. It is becoming clear that we are approaching the peak of oil production. Prior to the point where oil ceases to be cheap, or abundant, we need alternatives.
Organisms live in many different kind of habitats, which MUST contain a minimum of every life support limiting factor for each species. As the eagle's habitat is more that a nest, including both land and air, so the habitat for a human is not just a house, it is the rest of the local ecosystem that provides the overall life support for not just the present generation of humans, but for the indefinite future.
The human food chain is the simple progression from plants that absorb sunlight, to the human table. A downward example of a food chain is: The human eats the dog, the dog ate several cats, the cats ate lots of mice, the mice ate fields of grass which grew by absorbing the sunlight. After the table though, all waste must somehow, eventually, become "food" for something else and be recycled. Small organisms such as insects, bacteria, mold, & mushrooms fill a vital niche in an ecology in that they eat dead biological materials and make the atoms and molecules again available as nutrients to grow plants. This takes us to the food web, which is the blend of the overlapping food chains in an ecosystem. A food web is from one celled organisms to bugs, to humans, and everything in-between.
Scientifically a community is all of the population that lives together in the same place and interacts. In reality a minimal human food production area is a specialized niche, requiring some particular mix of organisms and physical factors. What are the minimums for such?
If overall loss is minimized, a community of organisms, interacting with each other and the nonliving things in the environment can provide a long term localized ecosystem. A limiting factor is any living or nonliving part of an ecosystem that effects the survival of an organism, such as heat, light, particular atoms or molecules, and water.
Introduction[edit | edit source]
As far as the physical atoms incorporated into living organizations are concerned, the Earth is essentially a closed system, with the energy of sunlight as the only input and the power source for essentially all life on the surface of the Earth. Much of this document is "generic", based on the theory that once the major nutrient loops are closed further augmentation should not be required. However, my personal focus is "high desert", in Arizona, USA, where water is a significant limiting factor. Every area will have it's on local limiting factor, potentially for most locations the limiting factor may be sunlight and growing season. I've also got to deal with the natural heat, and very low typical humidity.
The optimal human centered ecosystem is physically different from, and essentially incompatible with, any "natural" environment, and must be kept separate. This document combines personal theory, web research into programs such as NASA's CELESS, the Biosphere II project, the work of Ecology Action, and other closed loop food systems, as well as research on optimal food growing methods (hydroponics, aquaponics & aeroponics) and recycling of human effluent, and personal container garden experiments.The area needed to grow food for a fully grown human to survive should, logically, match the area which can be fertilized by human effluents (solid, liquid & gas). Urine, feces, and eventually our physical bodies can all be readily returned to the growing medium.
It is vital to ensure optimal growing conditions for crops, to include exclusion of plant pathogens, as well as those that may infect humans. The growing area will receive both gray water and black water, which must be handled in a safe manner.
Absent a sealed environment, we lose water vapor, CO2, and other gases. It is obvious that when we grow a crop of which humans eat only a portion, the rest of the plant must be recycled by animals or microorganisms before the nutrients are again available for plant growth. Think of the kernels eaten on an ear of corn, vs the total mass of the plant. This makes crop selection a critical element.
With a typical "first world" diet the upper fertilizing limit for humanure looks to be around 1600 ft. sq. and a potential "minimum" area of 600 ft. sq. as touched on below. Of course, our diets are horrible. If we ate food with greater vitamin content, we would excrete a greater concentration, which would fertilize a larger area. I solicit feedback on vitamin / nutrition standards and what the upper limit is for safe human consumption of various minerals if they are in high concentration in plants.
Every square yard (9 sq. ft.) on the earth's surface with direct, perpendicular un-shaded exposure to the sun receives energy at the rate of around 1kwh (3412 BTU or 859,845 heat calories). The value of a food calorie is 1,000 heat calories, so at 100% conversion each square yard could generate 859 "food" calories per hour. An "average" person needs 2,000 food calories per day. Therefore, if humans were directly solar powered with 100% efficiency, each of us would only need around 22 sq. ft. /hours per day of solar exposure. But of course, we are not directly solar powered, nor are our plants 100% efficient.
If limited to fertilizing 1600 ft. sq., and 6 hour/day of light, the garden must have an overall average efficiency of something just over .225%. But crops for nutrition rather than mere calories do not approach this level of efficiency.
Various health guides indicate humans should "aim" for having our daily calorie intake fulfilled by 40% carbohydrates (1 g = 4 calorie), 30% protein (1 g = 4 calorie), and 30% fats (1 g = 9 calorie).
