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 drinkingwater contamination, epidemics of cholera had periodically caused heavy loss of life in the large European cities (Evans, 1987). 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 worldwide. However, most of the wastewater is discharged without any treatment mostly in developing countries.
In centralised wastewater management systems, household wastewater together with municipal and industrial wastewater, storm water as well as infiltration/inflow water is collected and transported a long way to central treatment plants where it is treated and disposed/reused (figure 3). This system has been built and operated for more than hundred years. In the mean time, because of advanced technological development, the wastewater management has reached 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 19th century in many respects. About 95 % of wastewater in developing countries is discharged without any treatment into the aquatic Environment (WIR, 1992). 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 (Lubis, A.-R., 1999). In New Delhi, India, more than 50 % of the raw wastewater is still discharged into the river Yamuna, from where the city draws its water supply (Narain, 2002).
Figure 3: Traditional centralized system of water supply and wastewater treatment
In households, the nutrients that are brought in in the form of food are converted into human excreta and kitchen waste. In conventional sanitation systems, a huge amount of fresh water is used as a transport medium and a sink to dispose of these wastes. 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 groundwater 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.
In the industrial countries, a large amount of money has been already spent to build up and maintain these conventional sanitation systems. In Germany it has been estimated that large investments are still necessary for repairing, rebuilding and extending existing systems in the coming years (Hiessl, 2000). About 80 % of the overall expenditures for sewerage systems go to the collection and transportation of wastewater to the central treatment plant, where only about 20 % of the overall expenditures is spent.
Although construction, maintenance and operation of sewers are very costly parts of the centralised wastewater treatment systems, more than 90 % of the population in Germany are already connected to sewer systems (Wilderer and Schreff, 2000). Experience shows that centralised sewerage systems can be extremely expensive for regions with a low population density, since costs of construction, operation and maintenance of long sewers are to be covered by a small number of inhabitants. These costs are obviously unaffordable for the major part of the population mostly living in developing countries. Thus, it is irrational to plan central sewerage for all rural and peri-urban regions of developing countries. Even in the USA, the complete coverage with sewerage systems is not possible or desirable, for both geographical and economical reasons (Crites and Tchobanoglous, 1998).
Even with the high inputs of money for construction, maintenance and operation, this end-of-pipe concept is producing linear mass flows (figure 4). It shows clear deficiencies in recovery of nutrients and organic matter, which are valuable fertiliser and soil conditioner. As it is already mentioned that even the best affordable treatment plants discharge considerably large amount of nutrients 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 Biphenyle), 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.
Brown water as soil conditioner
Brown water as soil conditioner