The term wastewater refers to mixed water discharged in a wastewater pipe or sewer, where mixed water stands for the combination of sewage (from households, industry, and businesses) and meltwater and rainwater. The sewage portion can be composed of a variety of different components, which is why a distinction is made between sewage from private households (toilets, washing and rinsing water) and from industry and businesses (wastewater produced during manufacturing processes, etc.). The following graphic clearly shows the most important differences:
Wastewater can contain very different types of contaminants. These can be divided into the following main pollutant and contaminant groups:
- Dissolved and undissolved substances
- Easily biodegradable organic substances
- Poorly biodegradable organic substances
- Heavy metal compounds
- Plant nutrients
- Used and unused medications
To protect water bodies, all pollutants must be reduced as much as possible through wastewater treatment and various purification measures.
Wastewater Disposal
Wastewater disposal and treatment is an absolute necessity for human coexistence, just like the supply of drinking and utility water, as well as the general supply of food.
Historically, all settlements have exclusively emerged in places where water supply, as the most important component, was guaranteed: primarily near flowing waters or in areas with sufficiently large lakes or oases.
Along river courses, in addition to supply, there were almost equally valuable advantages of disposal as well as additional benefits for nutrition (fishing), goods transport, etc. There are thousands of examples of this from antiquity to modern times, as a single glance at a map shows. Settlements away from water bodies require supply through wells.
Disposal was and still is, in principle, carried out in such a way that the wastewater is returned to the natural water cycle, directed into the nearest stream or river.
After that, river water is used again as drinking water, today mostly as bank filtrate and after appropriate treatment. In Germany, for example, along the Rhine corridor between Basel and the Netherlands, in dozens of water extraction plants.
In agricultural land use, disposal also occurs through spreading wastewater (and animal products like manure and slurry) on fields for fertilization. This was and is fine as long as both the quantities are in a suitable ratio to the areas to be fertilized, and the wastewater is of ‘natural’ origin.
A ‘regulated’ water/wastewater cycle is therefore essential for the functioning of human coexistence.
This was already recognized in antiquity. All major settlements of that time were equipped with sophisticated water supply and wastewater disposal systems. The ancient Romans, among others, accomplished magnificent engineering feats.
Where this was not the case or where this engineering knowledge was lost in the meantime or was never present in the first place, disease hotspots and epidemics could form, sometimes to a considerable extent. Most recently, the city of Hamburg in Germany was affected by this. In 1892, more than 8,500 people died there from cholera.
From Hamburg, the development of sewerage and wastewater treatment plants then began in Germany and in Central Europe, supported by important doctors/scientists, e.g., Robert Koch and Max von Pettenkofer.
It became clear that wastewater, increasing in quantity parallel to population growth, could no longer simply be discharged into rivers, but had to be cleaned beforehand.
The development of wastewater treatment plants has since undergone rapid technological advancement, especially considering that, particularly since the second half of the 20th century, a multitude of chemical substances used in households and businesses ultimately end up in wastewater.