Questions being raised today by the Green movement and by environmentalists apply to sanitation. From the Green perspective the issue is energy use:
How much energy is used in various sanitation approaches?
What kind of energy is used?
How much carbon emission is being generated?
From an environmental standpoint the issue is environmental impact:
How many and how much environmentally damaging emissions and by-products are created?
How much of the earth's natural resources are being used or contaminated?
Can these resources be replenished?
On a continuum from worst to best, in this writer's view, the worse would be waste treatment plants. The best would be non-discharge onsite systems. In the middle would be septic systems.
The worst: waste treatment plans use fossil energy, a great deal of energy. They use chemicals, a great deal of chemicals. The give out treated water that still has nutrients. Chemicals and nutrients being dumped into bodies of water are an invitation to environmental trouble.
Septic systems, on the other hand, use very little energy. They put nutrients into the ground but under ideal circumstances these nutrients are integrated by the earth and do not get into the groundwater.
The concern with septics is that when conditions are not ideal these systems can damage the environment as well as endanger human health. Floods and system malfunctions are the culprits. Reports of e-coli and sanitation nutrients leeching into creeks, streams, lakes and the ocean abound. These reports increase during times of heavy precipitation and flooding. Every state reports a certain percentage of failed or failing septic sytems.
Systems that treat water borne sanitation also use energy but they put nothing into the ground except safely treated water.
The best marks go to waterless systems. With the exception of incinerating systems, these use little energy and put nothing into the ground. The best types of these systems are evaporative. They harness the wind and sun for energy and require no electricity or fossil fuel.
Waste treatment plants are a necessary and very expensive evil for cities with large concentrations of people. Underground collection lines and plant construction pose environmental and financial costs. Operation and maintenance require energy. The emissions are environmentally undesirable. Improvement to the quality of treatment will increase the costs. But for the forseeable future we live with it. So long as our civilization uses water for sanitation these plants will be a necessity. Septic systems will also be with us as long as we use water for sanitation.
It is beginning to strike some people as odd that we would use perfectly good well water and very expensively treated rinking water to flush our urinals and toilets. Good water is becoming scarce and treated water is becoming increasingly expensive. So why do we then proceed to flush it down the toilet? 'Makes no sense from the Green perspective or environmental perspective! About twenty percent of the water used in an average household in the United States gets flushed down the toilet. Somebody go figure!
The future, logically speaking, belongs with waterless sanitation. But culturally speaking we want to flush. How expensive that preference becomes is a guess. It certainly will become more expensive. And only time will tell how long cultural preference prevails over logic.