Introduction
 

 Water pollution has been defined as “any impairment of the suitability of water for any of its beneficial uses, actual or potential, by man-caused changes in the quality of the water” (Warren 1971).  One of the first kinds of water pollution to cause alarm were changes rendering it unfit for human consumption.  In those countries that have modern facilities for treating water, the public is generally confident in the safety of water supplies.  However, in some parts of the world no such safety exists, and nowhere should it be taken for granted (Warren 1971).

 Water pollution as we know it today - a problem afflicting large regions - began with the Industrial Revolution. Advances in agricultural methods and the development of early factories in the eighteenth century increased the movement of people into cities, a trend which continues today.  The rapid growth of cities in England in the early nineteenth century resulted in large concentrations of people in areas having no adequate community organization.  Sir Edwin Chadwick, in his survey of English cities in the 1840’s, found water supply and waste disposal facilities almost indescribably foul.  Contaminated water supplies led to cholera and typhoid epidemics, and the enormous problems of providing safe water and adequate waste disposal were impediments to the correction of conditions leading to serious epidemics (Warren 1971).

Sanitary conditions in the United States did not become quite so intolerable, but they still had their own considerable problems of water supply and waste disposal.  For example, Chicago was disposing of wastes into Lake Michigan, which provided its water supply, even with prevalent epidemic typhoid (Warren 1971).

Sewers in the United States and Europe were originally designed for the removal of storm and drainage water; in fact, the discharge of human wastes into sewers was forbidden by law in London until 1815 and in Boston until 1833.  Although the introduction of wastes into sewers improved living conditions around houses, it led to foul conditions in rivers and streams.  Odors rising from the Thames during 1858 and 1859 made life in London almost intolerable, and the Chicago Drainage Canal became known as “Bubbly Creek”, with a thick scum that people could safely walk on (Warren 1971).

 Studies leading to the development of waste treatment practices were undertaken primarily to control these pollutional conditions in rivers and streams.  Over the past 150 years various processes have been developed to reduce the amount of organic pollution reaching fresh and marine waters.  One of the first processes tested was land treatment, in which sewage was sprayed directly onto areas of land where microbial action degraded the organic matter as the waste waters trickled through the soil.  However, these “sewage farms” were not efficient enough to deal with the ever-increasing quantities of domestic and industrial waste waters.  The process generally used now occurs in large sewage-treatment plants and involves two and sometimes three stages (Curds 1992).

 Primary treatment is purely physical and involves the removal of coarse solids and the sedimentation of most suspended solids.  All forms of secondary treatment are biological and rely on the growth of micro-organisms to remove dissolved and suspended materials or to convert them to more acceptable compounds.  Tertiary treatment includes any additional processing of the waste water.  It can involve the further removal of suspended particulate matter, the reduction in the number of enteric bacteria, or a decrease in nitrate and phosphate concentrations.  The resulting effluent is generally released into the nearest above-ground water source (Curds 1992).

 These sewage treatment facilities are predominantly found in developed countries, and most people in those countries never give a thought towards the quality of the effluent released or its effects on the water quality of the receiving water body.  We watch television and learn of the epidemics raging in undeveloped countries as a result of polluted water sources, and think: “I don’t need to worry, that would never happen here.”  But it does happen.  And there are many other effects caused by the sewage effluent being pumped into our rivers and oceans.  Most are negative impacts from anyone’s point of view, but there are also some positive impacts for both humans and the aquatic environment.

 A lot of the negative effects are a result of the characteristics of the area, the sensitivity of the aquatic community, the contaminants that are not removed during the treatment process, or spills of mostly untreated sewage from treatment plants.  As well, sewage contaminated water is implicated in incidences of epidemic cholera and other such diseases.  Most of the positive effects are the result of the large amount of nutrients in the effluent and its subsequent ability to support larger and more diverse aquatic communities.  However, taken together, the negative impacts of dumping sewage effluent into our water sources far outweigh the positive.  The potential risks are too great to continue our present practices.  Fortunately, some new, and old, strategies have recently been employed that reduce the negative impacts while creating additional benefits.

Negative Effects

 The location in which sewage effluent is discharged is important because, for example, it affects the degree to which the effluent is diluted or the distance over which the suspended solids in the effluent are distributed.  Bascom (1989) states that an ocean outfall should be located where the water movement is sufficient to cause rapid dilution, dispersion, and mixing with open-ocean water.  Novitsky and Karl (1985) found that these requirements limit the effect on sediment microbiota to an area immediately adjacent to the diffuser ports.  To illustrate, samples taken from within 10m of the outfall at Barber’s Point showed a rate of DNA synthesis of 1759.8 pmol/g/hr while samples taken between 90 and 120m had a rate of 171.7 pmol/g/hr (see Table 1).  Conversely, an ocean outfall located in an area with insufficient water current would see a build-up of suspended solids around the discharge site and therefore an increased impact on the benthic community.  On the bottom, wastes alter the physical and chemical nature of sediments and, in turn, increase the likelihood of chronic responses in bottom-dwelling organisms and produce changes in the composition of benthic communities (Swanson and Mayer 1989).

 Although it is reasonable to assume that some species or aquatic communities are not greatly affected by sewage outfalls, many are.  For instance, various pollution-associated fish and shellfish diseases have been reported from the New York Bight.  The incidence of blackening of the gills and carapaces of rock crabs has been tentatively linked to the presence of highly organic black mud and silt in areas where bottom sediments have been permanently altered by sewage sludge deposition.  As well, significant changes in the nature of the benthos have been noted in the inner portions of New York Bight.  Areas adjacent to discharges are dominated by pollution tolerant organisms, while pollution-sensitive organisms are restricted to areas distant from the pollution source (Swanson and Mayer 1989).  As well, sewage effluent has been seen to alter the structure of aquatic communities.  In a study by Bascom (1989), it was found that the marine organisms that usually live on rocky bottoms were present on a sewage outfall pipe in large numbers.  Sea anemones (Metridium senile) almost covered the end of the pipe and sea stars and gastropods were very common on the surrounding soft bottom.  As well, several species of fish were common around the pipe, and fish were generally more abundant in the sludge field.  The individuals present and the biomass were about twice that at control sites; however, the number of species was reduced to the few that could utilize the food (see Figure 1).
 Perhaps the most negative effects of sewage effluent are caused by the contaminants that are not removed during treatment.  These include organic materials, plant nutrients, and heavy metals.  One very destructive kind of pollution occurs when relatively large amounts of organic materials, which require oxygen for their decomposition, are introduced into waters.  The oxidation of such materials by micro-organisms depends largely on dissolved oxygen already present in the waters, oxygen entering from the atmosphere, and oxygen made available through plant photosynthesis.  When the rate of oxidation is greater than the rate of oxygen replenishment, anoxic conditions result.  These anoxic conditions can be very harmful to other aquatic organisms which can be suffocated by the lack of oxygen in the water.   Secondary waste treatment reduces the amount of organic materials in effluents; it does not, however, prevent the enrichment of these waters with nitrates, phosphates, and other inorganic plant nutrients made available through the decomposition of organic materials.  These plant nutrients can lead to increased production of micro-organisms, particularly algae.  Thus in lakes, rivers, and estuaries, even treated effluents can lead to blooms of algae that can change the aquatic environment in ways harmful to some valuable species (Warren 1971).  Small amounts of metals are also added to aquatic environments in sewage sludge (Table 2) (Clark 1992).  In the study by Hamlett (1986), a salt marsh bacterial community was significantly altered when fertilized by sewage sludge.  There was reduced diversity and changes in species distribution as a result of selection for mercury-resistant bacteria.  Although the biological effects of metal contamination are many and often severe, a discussions of them would go beyond the limit of this paper.

 Today, each of us generates about sixty gallons of waste water daily.  The greater wasteloads pouring into treatment plants require more cleansing steps before disposal.  The whole process creates risks of larger and dangerous accidental spills from giant plants.  Some coastal cities build big disposal plants but then forget to expand and maintain lines that bring in the raw sewage.  Aging sewer lines clogged with roots and inadequate pump stations contribute to San Diego’s infamous rate of sewage spills.  In 1989, the EPA charged the city with discharging raw or only partially treated sewage into the ocean and local bays on 1,814 occasions since 1983 (Marx 1991).

 There are many types of diseases that can be harbored in and contracted from sewage contaminated water.  In one circumstance, cholera unexpectedly reappeared in the Americas in January 1991, after a 100 year absence.  The first confirmed cases occurred in Peru, and by mid-February more than 10,000 patients were being treated weekly.  The epidemic spread to involve a new country almost every month, and by the end of the year 391,000 cases and nearly 4,000 deaths had been reported.  Once introduced, fecal contamination of a municipal water supply serving several large urban areas becomes an efficient means to amplify the organism while producing a massive epidemic.  It is likely that cholera could become epidemic in the Americas as it has in Asia and Africa through the establishment of reservoirs of cholera vibrios in the environment - in plankton, shellfish, water, and humans (Anon. 1992).

Positive Effects

 There are cases, though, in which sewage effluent can cause positive impacts.  Nevertheless, these are a matter of degree; that is, low levels of sewage effluent can be beneficial but high levels are generally harmful.  As discussed above, the study by Bascom (1989) found that above the canyon sludge area there were more species of fish, greater biomass, and larger individual fish (Table 3).  As well, Campbell’s (1984) study showed that the presence of sewage outfalls in the Firth of Forth, Scotland, created wintering habitat for several types of sea-ducks.  The introduction of sewage treatment in 1978 and the removal of the outfalls significantly decreased the numbers of birds using the area; for example, the peak number of scaup in 1975-76 was 10, 280, while in 1979-80 the peak number had decreased to 675 (Table 4).

 Although the evidence to support my argument that the potential negative impacts of dumping sewage effluent into water systems far outweigh the positive is limited in this paper, my point should be clear.  Even in developed countries where sewage treatment plants are believed to produce “safe” effluent, there are many cases in which our waters are becoming polluted and we are making the water unsuitable for use by humans and many aquatic organisms.  The compounds present in sewage effluent not only changes the structure of aquatic communities, they also cause harmful algae blooms, can deplete the amount of oxygen in the water, and poison the environment with metals and other harmful chemicals.  Furthermore, water can become contaminated by spills from treatment plants and cause widespread epidemics in the human population.

Alternative Sewage Treatment Methods

 The idea of treatment plants is over a hundred years old, and you would think that, with our advanced technology, we could come up with something that produces a less harmful effluent and is more reliable.  In fact, some of the alternatives being developed and implemented rely more on the power of nature to detoxify waste water, rather than advanced technology.
 The town of Arcata on the northern Califoria coast has used just such a solution to replace a failing sewage treatment plant.  Instead of building an expensive new plant, they built a marsh instead.  Through a three-year pilot project to demonstrate the marsh system’s effectiveness, it was found that wetlands improve water quality with a mix of physical, chemical, and biological processes.  Marsh vegetation obstructs water flow, enhancing sedimentation.  The vegetation also provides an environment for algae, fungi, protozoa, and bacteria which break down or remove substances from waste water.  As well, the marshes serve as important wintering grounds for birds, as habitat for other animals and plants, and as a recreational and educational facility for the community (MacDonald 1994).  No solution is perfect, however.  Marshes require large tracts of land, are labour intensive to build, can be costly, and still necessitate some treatment of sewage.  Nevertheless, in areas where they can be effectively implemented, marshes are far more preferable to just dumping the waste water into the nearest river or ocean.

 Another alternative solution that has been practiced for centuries is the use of sewage for fertilizer.  This road carries some cautions though.  In many developed countries, wastes are processed by technologies designed to dispose of them, rather than reuse them.  Safe reuse is best ensured by shifting away from disposal technologies, such as conventional treatment plants or sewers that mix industrial and domestic waste, and toward technologies engineered to produce clean fertilizer (Gardner 1997).  When this is done, a waste product that has been a problem for years will become a valuable resource.

Conclusion

 Humans pollute the water resources of this planet in uncounted ways.  Many of them are more harmful to the quality of water than sewage effluent, but, at least, it is a problem that could be easy to fix.  People should take this opportunity to implement some of the new, and old, solutions to the sewage effluent problem.  The risks to human health, as well as the health of the aquatic environment, should be incentive enough to take action.

References Cited

Anonymous. 1992. Epidemic cholera in the Americas. Science 256:1524-1527.

Bascom, Willard N. 1989.  Disposal of sewage sludge via ocean outfalls.  pp. 25-34 In: Michael A. Champ and P. Kilho Park (ed.) Oceanic Processes in Marine Pollution, vol. 3: Marine Waste Management: Science and Policy. Krieger Publishing Company, Malabar, Florida. 534 pp.

Campbell, L.H. 1984. The impact of changes in sewage treatment on seaducks wintering in the Firth of Forth, Scotland. Biological Conservation 28: 173-180.

Clark, R.B. 1992. Marine Pollution. Clarendon press, Oxford. 172 pp.

Curds, C.R. 1992. Protozoa in the Water Industry. Cambridge University Press, Cambridge. 122 pp.

Gardner, G. 1997. Recycling Organic Waste: From Urban Pollutant to Farm Resource. Worldwatch Institute, Library of Congress. 59 pp.

Hamlett, N.V. 1986. Alteration of a salt marsh bacterial community by fertilization with sewage sludge. Applied and Environmental Microbiology 52: 915-923.

MacDonald, L. 1994. Pollution Solution: Build a Marsh. American Forests 100: 26-29.

Marx, W. 1991. The Frail Ocean: A Blueprint for Change in the 1990’s and Beyond. The Globe Pequot Press, Chester, Connecticut. 204 pp.

Novitsky, J.A. and D.M. Karl. 1985. Influence of deep ocean sewage outfalls on the microbial activity of the surrounding sediment. Applied and Environmental Microbiology 50: 1464-1473.

Swanson, R.L. and G.F. Mayer. 1989. Ocean dumping of municipal and industrial wastes in the United States. pp. 35-52 In: Michael A. Champ and P. Kilho Park (ed.) Oceanic Processes in Marine Pollution, vol. 3: Marine Waste Management: Science and Policy. Krieger Publishing Company, Malabar, Florida. 534 pp.

Warren, C.E. 1971. Biology and Water Pollution Control. W.B. Saunders Company, Toronto. 434 pp.