This article is based in large part on the excellent work of Abby Rockefeller, President of the ReSource Institute for Low Entropy Systems, 179 Boylston St., Boston, MA USA 02130; telephone (617) 524-7258. Unreferenced facts and sources are from her original work.
How It All Began
Humans began to lead a settled life, growing crops to supplement hunting and gathering, only about 10,000 years ago. For all time before that, humans "deposited their excreta - urine and faeces - on the ground, here and there, in the manner of all other land creatures." 
The advent of modern sewers, in the 19th century, changed everything. The Mary Evans Picture Library.
The soil and its communities (including plants, small animals and micro-organisms) captured almost all of the nutrients in animal excrement and recycled them into new components for soil. In this way, the nutrients were endlessly recycled within the soil ecosystem and largely kept out of surface water.
As a result, what we call 'pure water' is low in nutrients, particularly the major nutrients nitrogen and phosphorus. Because these conditions have existed for a very long time, life in lakes, rivers and oceans is accustomed to the relative absence of these nutrients. Over the past couple of billion years, life has flourished in this low-nutrient environment, growing complex and interdependent in the process - an aquatic condition we call 'clean' and 'healthy'.
When a body of water is suddenly inundated with nutrients - especially nitrogen and phosphorus - things change drastically. One or a few organisms flourish and begin to crowd out the others. We can all recall seeing a body of water that is pea-soup green from overgrowth of algae. Such a water body is clearly sick, choked, its diversity vastly diminished.
Today, much of the surface water of the planet is in a state of ill health because of misplaced nutrients. And a main contributing culprit is misplaced human excreta.
East and West: Conflicting Views on Sewage Management
Long ago, human civilisations split into two camps regarding the management of excreta. Many Asian societies recognised the nutrient value of 'night soil' (as it became known). For several thousand years, and up until very recently, Asian agriculture flourished by recycling human wastes into croplands.
The opposing camp, particularly in Europe, had ambiguous feelings about human waste - was it valuable fertiliser or was it a nasty and embarrassing problem to get rid of?
In Europe, a pattern evolved: the first stage was urinating and defecating on the ground near dwellings. As population density increased, this became intolerable and the community pit evolved. For privacy, this evolved into the pit privy or 'outhouse' - a structure for privacy atop a hole in the ground. Despite what many people may think, the pit privy is not environmentally sound - it deprives the soil of the nutrients in excrement, and by concentrating wastes it promotes pollution of groundwater by those same nutrients.
Before the advent of piped water in the late 18th century, European towns stored excreta in cesspools (lined pits with some drainage of liquids) or in vault privies (tight tanks without any drainage). The 'night soil' was removed by 'scavengers' and was either taken to farms, or dumped into pits in the ground or into rivers. In general, Europeans never developed a clear and consistent perception of the nutrient value of excrement, as Asians had done.
In ancient Rome, the wealthy elite had indoor toilets and running water to remove excrement via sewers. Later, European cities developed crude sewer systems - usually open gutters but sometimes covered trenches along the centre or sides of streets - though they had no running water until the 18th or 19th century. The putrefying matter in these stagnant ditches did not move until it rained - thus the name 'storm sewers' - and many cities prohibited the dumping of human wastes into them.
The Birth of the Modern Sewage System
With the advent of piped water, things changed dramatically. In the USA, the first waterworks was installed in Philadelphia in 1802, and by 1860, 136 cities were enjoying piped water systems. By 1880, the number was up to 598. With piped water, per-capita water use increased at least 10-fold, from 3-5 gallons per person per day to 30-50 gallons per person per day or even more.
But as with every new technology, the piping of water brought new and unforeseen problems of its own. Water piped into homes had to be piped out again and this caused cesspools to overflow, increasing the problems of odours and of water-borne diseases. To solve these problems, cesspools were connected to the cities' crude sewer systems which ran along the streets. The result was epidemics of cholera. In Paris in 1832, 20,000 people died of cholera. Around the world, the combination of piped water and open sewers has consistently led to outbreaks of cholera.
To solve this problem, engineers designed closed sewer systems, pipes using water as the vehicle for carrying away excrement. This solution engendered a debate among engineers: some wanted to return sewage to agricultural land, others argued that 'water purifies itself' and wanted to pipe sewage straight into lakes, rivers and oceans. By 1910, the debate was over and sewage was being dumped into water bodies on a grand scale. This decision - taken for short-term reasons - was to prove extremely damaging in the long run.
Industry Changes the Rules
In the cities, the cholera epidemics abated. However, cities drawing their drinking water downstream from sewage discharges began having outbreaks of typhoid, caused by the emptying of sewage into clean water. This engendered another debate: whether to treat sewage before dumping it into water bodies used for drinking, or whether to filter drinking water. Public health officials favoured treating sewage before dumping it; sanitary engineers favoured dumping sewage raw and filtering water before drinking. Again, the engineers prevailed, again largely for reasons of ease and convenience. And again, this created unforeseen problems.
As cities began to filter and disinfect their drinking water, typhoid began to abate. But throughout the 20th century, as the West industrialised rapidly, industry developed a huge demand for low-cost waste disposal. Because sewers already existed, and because the public was paying for them, they were the obvious places for dumping industrial waste. As the pressure for greater waste disposal capacity increased, industrialised nations allocated vast sums of money to construct centralised sewer systems to serve the combined needs of homes and factories.
But sewers had been designed for natural human wastes, not industrial chemicals, and as industries began to use them as giant drains for their poisonous wastes, new and virulent dangers emerged. The nutrients in the excrement became mixed with industrial wastes, many of them toxic. So by the 1950s, essentially every body of water receiving piped wastes was badly polluted with a combination of excessive nutrients and toxicants. This led to a new demand: to treat wastes before dumping them into water. Thus began the 'treatment' phase of the 'get rid of it' approach to human waste: the latest stage in the adulterating of a clean, natural and even beneficial waste product by unnatural poisons.
The Failure of Sewage Treatment
The first stage in the process of modern sewage treatment is 'primary treatment - screening out the dead cats and other 'floatables' from the sewage. All other nutrients and toxic chemicals remain in the waste water that is discharged to a river or ocean. Next comes 'secondary treatment' which speeds up the biological decomposition of wastes by forcing oxygen into them, by promoting bacterial growth, and by other means. This is an energy-intensive process and therefore expensive. Unfortunately it, too, leaves many of the nutrients and toxic chemicals in the discharge water.
This two-stage treatment process ends up by creating a new form of combined nutrients and toxins known as 'sludge'. Sludge is the de-watered, sticky black "cake" created in large quantities by modern sewage treatment plants. It contains everything that can go down the drains in homes and industries and which a treatment plant is able to get back out. In the US Federal Register of November 9, 1990, the US Environmental Protection Agency (EPA) describes sludge this way:
"The chemical composition and biological constituents of the sludge depend upon the composition of the wastewater entering the treatment facilities and the subsequent treatment processes. Typically, these constituents may include volatiles, organic solids, nutrients, disease-causing pathogenic organisms (e.g. bacteria, viruses, etc.), heavy metals and inorganic ions, and toxic organic chemicals from industrial wastes, household chemicals, and pesticides."
Industry is currently using 70,000 different chemicals in commercial quantities; any of these may appear in sludge. About 1,000 new chemicals come into commercial use each year, so any of these, too, may appear in sludge. A description of the toxicants that may be found in sludge would fill several books. The US General Accounting Office has reported - not surprisingly - that municipal sludge regularly contains radioactive wastes (from both medical and military sources). 
With hundreds of sewage treatment plants now producing toxic sludge in mountainous quantities, the next question was what in the world to do with it? For many years, coastal cities had dumped sewage sludge into the oceans, where it created large "dead zones" that could not support marine life. New York dumped its sewage sludge 12 miles offshore; when that place developed obvious contamination problems, the dumping was moved to a spot 106 miles offshore, where, to no one's surprise, contamination soon developed.
Other communities dumped their sludge into landfills, where it polluted their groundwater. Still others incinerated their sludge, creating serious air pollution problems, then dumped the remaining ash into landfills, or simply heaped it on the ground for the wind to disperse.
In 1988, the US Congress, in line with other government authorities across the industrialised world, outlawed the ocean dumping of sewage sludge. At this point, many communities faced a real waste crisis. There was no safe (or even sensible) place to put the mountains of toxic sludge that are generated every day by centralised sewage treatment systems.
It was at this point in history that US EPA - feeling tremendous pressure to 'solve' the sludge disposal problem - discovered that sewage sludge is really 'night soil' after all - the nutrient-rich product that has fertilised crops in Asia for several thousand years. The EPA, the latest in the long line of authorities tackling a serious problem in a short-sighted way, decided that the expedient thing to do with sewage sludge was to plough it into the land. Shortly after 1992, when the ban on ocean dumping went into effect, the EPA renamed toxic sludge 'beneficial biosolids', and began aggressively campaigning to sell it to the American people as fertiliser. 
The Official Poisoning of the Soil
The increasingly complicated methods of dealing with human wastes and industrial wastes combined had thus, in the USA, come full circle. The fertiliser value of human wastes had been officially recognised. What had been officially unmentioned was that the 'night soil' being spread on the fields typically contained thousands of industrial poisons. The EPA had overlooked, perhaps deliberately, two important differences between modern sewage sludge and unadulterated human waste.
Firstly, most of the nitrogen in human waste is in the urine and is water-soluble, so it is not captured in the sludge. Therefore, if sludge is going to substitute for commercial fertiliser, you have to use a lot of it to get enough nitrogen. And, secondly, when you add a lot of sludge to soil, you are also adding a lot of toxic metals and a rich (though very poorly understood) mixture of organic chemicals and, very likely, radioactive wastes as well.
In sum, ploughing sewage sludge into soils is almost guaranteed to harm many of those soils as time passes.  And as we know from the ancients who poisoned their soils with irrigation salts, a nation that poisons its farmland is a nation that doesn't have a long-term future.
Rethinking the Sewage Problem
It is time that we in the West began to think again about how we deal with human waste. The present systems were not designed to produce useable products and therefore the design of present systems is the root of the problem.
I would suggest that three policy goals are needed. Firstly, where possible, the individual should practise 'sewer avoidance' -stay off or get off centralised sewer systems. Secondly, governments should promote low-cost, on-site resource-recycling technologies, such as composting toilets, that avoid polluting water and preclude wasting resources. Thirdly, water should be priced right - i.e. higher than at present - so that the market works to keep it clean, rather than contaminates it with excreta. 
None of this is as difficult as it might sound. For individual households, for example, real solutions are already available. An excellent new book by David del Porto and Carol Steinfeld, The Composting Toilet System,  will dispel any fears you may have that composting toilets are a step backward. And with microflush toilets and vacuum-flush toilets now readily available, you can compost your household wastes into an odour-free product that is entirely satisfactory as agricultural fertiliser. And for larger buildings, the technology already exists for manufacturing building-scale waste systems based on 'anaerobic digesters', which produce methane gas and fertiliser. As human waste expert Abby Rockefeller said recently in an interview, "Surely, human ingenuity can do this."
The challenge before us is clear. We must find ways, such as those above, to deal with human wastes in a way that allows their potential to be realised. At the same time, we must keep those wastes apart from the industrial poisons they are currently mixed with. It is time that industries realised that dumping their toxic by-products into the nearest sewer will never be a sustainable way of dealing with them. Toxic industrial wastes should be managed by the industries that make them, not dumped into the environment that sustains all life.
You may say that none of this is 'realistic' - that we can't do any of it because we've been doing it another way for 100 years. But ask yourself what kind of people would dump their excreta into their drinking water in the first place. And what kind of people, faced with workable, cheaper, more environmentally sound alternatives would continue to insist that soiling their food, water and environment is still the best way of dealing with a problem that many of us prefer not to think about, in the hope that it will go away?
1. Abby Rockefeller, "Civilization and Sludge: Notes on the History of the Management of Human Excreta", Current World Leaders, Vol. 39 No. 6, December 1996, pp.99-113.
2. Gary O. Krauss and Albert L. Page, "Wastewater, Sludge and Food Crops", Bicycle (February 1997), pp 74-82. Krauss was staff director for the National Research Council Study.
3. Rachel's' Environment and Health Weekly, No.561.
5. Robert Goodland and Abby Rockefeller, "What is Environmental Sustainability in Sanitation?", Insight [newsletter of the United Nations Environment Programme, International Environmental Technology Centre) Summer, 1996, pp.5-8. The International Environmental Technology Centre can he reached at: UNEP-IETC, 2-1110 Ryokuchikoen, Tsurumi-ku, Osaka 538, Japan. Telephone: (81-6) 915 4580; Fax: (81-6) 915-0304.
6. David Del Porto and Carol Steinfeld, The Composting Toilet System Book, Concord, Mass, Center for Ecological Pollution Prevention, 1999. ISBN 0-9666783-0-3. $29.95 plus $3.30 shipping ($12 overseas shipping) front: Center for Beological Pollution Prevention, 50 Beharrell St., P.O. Box 1330, Concord. Mass. USA 01742. Phone (978) 369-9440. Fax: (978) 368-2484. E-mail: firstname.lastname@example.org.