Due to disease risks caused by faecal wastewater, in large European cities sewers were constructed to drain the wastewater away from the people’s surroundings to the nearby water courses, and ultimately into the sea. Later it was found that discharging raw wastewater had deteriorated aquatic Environment of the receiving water body, and at the same time it caused diseases to the people, who received their drinking water from the same river downstream. Because of drinking water contamination, epidemics of cholera had periodically caused heavy losses of life in large European cities. The outbreak of cholera in 1892 for instance, took place all over in Hamburg, where drinking water supply was extracted from the river Elbe. To protect these rivers from the pollution as well as the public health from water borne diseases, the wastewater was since then treated at the end of the sewer before discharging it into the river. This tradition has been widely established as a standard way of managing wastewater world wide. However, most of the wastewater is discharged without any treatment mostly in developing countries.

Centralised wastewater management systems have been built and operated for more than hundred years. In the mean time, because of advanced technological development, the wastewater management has reached a high standard in many industrialised countries. However, in developing countries the present situation is still similar to that of the currently industrialised countries in the 19^th century in many respects. About 95 % of wastewater in developing countries is still discharged without any treatment into the aquatic Environment . This contributes largely about 1.2 billion people without access to clean drinking water. Almost 80 % of diseases throughout the world are water-related. Water-borne diseases account for more than 4 million infant and child deaths per year in developing countries.

Figure 3: Conventional Sanitation System (source Otterwasser GmbH)

In conventional sanitation systems, a huge amount of fresh water is used as a transport medium and a sink to dispose of wastes (see figure 3). In this process a small amount of human faeces is diluted with a huge amount of water. Therefore, it is hardly possible to prevent contaminants from emitting into surface and ground water bodies. As a result a huge amount of fresh water is contaminated and deemed unfit for other purposes. Moreover, due to the pollution and hygienic problems in receiving waters, surface water can no longer be used as a source for drinking water supply. Huge investments have to be made to improve the surface water quality in order to use it as drinking water.

Conventional sanitation systems show clear deficiencies in recovery of nutrients and organic matter, which are valuable fertiliser and soil conditioner respectively. Even the best affordable treatment plants discharge those to the aquatic Environment, where they are lost for ever and cause severe problems. Those nutrients, which are captured in sludge, are often contaminated with heavy metals such as Cadmium (Cd) and organic compounds such as PCB (polychlorinated Biphenyl), which pose potential toxic risks to plants, animals and humans. Therefore, large amounts of Sewage sludge are disposed of in landfills or incinerated. Only a smaller part is applied to agricultural land.

Also decentralised sanitation systems, such as pit toilets, septic tanks, etc. cause pollution i.e. nutrients and pathogens seeping from these systems contaminate the groundwater and nearby surface water - they cannot destroy pathogens. Basically septic tanks are designed only to collect household wastewater, settle out the solids and anaerobically digest them to some extent, and then leach the effluent into the ground, not to destroy pathogens contained in wastewater. Therefore, septic tank systems can be highly pathogenic, allowing the transmission of disease causing bacteria, viruses, protozoa and intestinal parasites through the system. It is reported that there are 22 million septic system sites in the USA issuing contaminants such as bacteria, viruses, nitrate, phosphate, chloride, and organic compounds into the Environment. Another problem is home chemicals with hazardous constituents, which are discharged to toilets and contribute to severe groundwater contamination in sanitation using septic tanks. According to the EPA, states of the USA reported septic tanks as a source of groundwater contamination more than any other source, with 46 states citing septic systems as sources of groundwater pollution (see figure 4), and nine of them to be the primary source of groundwater contamination in their state. It has to be noted that occasionally problems with broken septic tanks occur leading to infiltration of nearly untreated wastewater.

Figure 4: Reported sources of groundwater contamination in the United States (Jenkins, 1994)