Environment, Sewage Disposal

The history of civilization, especially urban civilization, is the history of water—of the fundamental need to supply clean, fresh, disease-free drinking water while simultaneously disposing of vast quantities of disease-ridden, foul human and animal waste. From at least the time of the Phoenicians up to the present day, the growth of the world's major metropolitan centers—Rome, Paris, London, New York, Beijing—has been defined by how well they solved that dilemma of water supply and waste disposal.

The challenge of water supply and disposal is directly related to population density. In prehistoric time, and in many impoverished areas even today, “night fertilization” of open field and cropland is not uncommon and may not pose an unwarranted risk of [Page 313]disease to the population or a heavy burden to the environment. Under rural farm conditions, both the supply of potable water and the safe disposal of waste are only minor difficulties. More often than not, nature itself, without the need of human intervention, provides the mechanisms by which water is filtered and cleansed of contaminants. Simple precautions such as keeping the outhouse far from the water well are adequate to ensure human health wherever population density is low.

Increasing population density demands increasingly complex treatment solutions. There are at least three major environmental issues that have to be addressed when disposing of human and animal waste: (1) reducing organic and inorganic solids, (2) reducing the demand for oxygen in wastewater that is a consequence of its dissolved and suspended load of organic matter, and (3) minimizing the concentration of nutrients and chemicals that always characterize waste materials.

As population density increases above rural, farm levels, some sort of engineered solution to the waste disposal problem must be found. Cesspools and septic systems have long provided such solutions in many suburban areas of the world. A cesspool is little more than an underground tank with many holes in it. Household waste enters one (settling) chamber of the tank from which overflow is allowed to escape into the soil surrounding the tank. Natural or introduced microbes and enzymes within the cesspool tank decompose the organic matter in the waste stream while the tank itself provides storage for any indigestible materials. Soil organisms and vegetation around and above the tank provide further filtering of the wastewater and take up some, if not all, of the chemical burden. Cesspools have the drawback of becoming clogged over time and require periodic cleaning and flushing to work efficiently. Septic systems are a slight improvement over cesspools—the overflow wastewater stream from a septic tank exits through a gridded system of perforated pipe that is laid out in soil at shallow depth. The slow flow of water through the septic-field grid enhances the decomposition of organic matter and the absorption of nutrients and chemicals by soil organisms and vegetation. Septic systems require less maintenance but demand large areas of lawn or open field not often available in urban centers.

Both cesspools and septic systems cannot remove 100 percent of the burden of organic matter, nutrients, and chemicals from typical household waste. The increasing use of detergents, soaps, and other chemicals in modern households has placed an additional and growing burden on the ability of house-specific waste disposal systems. At some point on the population growth curve of urban systems, cesspools and septic systems are no longer a viable alternative and some other approach has to be taken to sewage treatment. One of the most spectacular examples of this transition in modern times is provided by Nassau and Suffolk Counties on Long Island, New York. What was once rural farmland was rapidly suburbanized following World War II. Initially the waste disposal of homes was served by cesspools and septic systems—one or the other depending primarily on lot size. Over time, however, these house-specific systems dispensed an ever-increasing load of nutrients into the groundwater system of the island—a drinking water supply on which the suburban community was totally dependent. The concentration of one particular nutrient, dissolved inorganic nitrate, was the trigger that led to a complete reengineering of the two counties' waste disposal systems—a construction project of immense size that is still under way. High levels of nitrate had led to “blue-baby syndrome,” a condition under which newborns have difficulty breathing. The solution was to place the homes in every community in the two counties on sewerage systems connected to central processing plants. Nearly every street and highway had to be excavated, every household lawn dug up, and sewer lines installed. In addition, a place had to be found for the huge and not-always-welcome treatment plants.

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