A modern state-of-the-art wastewater treatment is based on the principle of downstream treatment steps. The domestic, industrial or agricultural wastewater is mechanically pre-treated in a physical manner, biologically purified, and finally mechanically purified before being released into a receiving water body. This natural way of wastewater treatment does not require chemical additives. In some cases however, certain qualities can be achieved with an additional chemical purification step. For some wastewaters, a chemical treatment step can also support the biological processes.
For in-depth requirements, downstream treatment steps, such as disinfection, are also available. The modular concept of System S&P® offers a wide variety of combinations of above mentioned technologies.
The mechanically performed physical pre-treatment of domestic treatment plants is normally achieved by multi-chamber pits or by a similar technology like septic tanks. For bigger plants, state-of-the-art technologies such as screening systems, grit chambers or drum sieves are being used. In many cases it is important to foresee a grease trap. The aim of such technologies is to remove all kinds of particular matters, otherwise they might have a negative influence on the biological step. With these technologies, a treatment efficiency of up to 35% can be achieved in the mechanical pre-treatment.
The main part of the wastewater treatment is controlled by the biological step, where micro organisms degrade the organic load. This load consists mainly of carbon compounds with a specific oxygen consumption. By adequate process conception it is possible to biologically transform the ammonia nitrogen into the more environmentally friendly nitrate-nitrogen. This process is called nitrification. The next step within the biological treatment consists in the removal of the nitrogen through an anoxic process called denitrification.
Highly loaded wastewaters can be treated by additional biological anaerobe steps that are used for phosphate elimination.
Basic activated sludge processes are common technologies for such a biological treatment. Such systems suspend the biomass in the wastewater, where it is supplied with vital oxygen by aerators. In contrast to this, the biomass remains fixed with fixed film technologies. The biomass adheres to the basic fixed film technology by growing on provided surfaces. These surfaces are continuously or periodically surrounded by wastewater and an oxygen atmosphere. Combinations of both above mentioned technologies are also possible, for example a high load fixed film zone followed by an activated sludge process.
The final clarification step becomes necessary since the biologically treated wastewater still contains degradation products from the biological step, the so-called excess sludge. The sludge has to be separated. This is done by a mechanically performed physical process. Adequate technologies to use for this application are gravity separators such as Emscher Tanks or floatation separators.
A special kind of gravity separator is the specific lamella separator, which is an approved technology in combination with a fixed film biology.
A certain amount of sludge needs to be separated and recycled into the pre-treatment step where it is used as an innocollum. This so called fecal sludge cannot be used as a fertilizer due to its consistency and stabilization grade. However, the excess sludge of the fixed film technologies is widely stabilized and can be used as valuable fertilizer in agriculture. Other possibilities for sludge disposal are composting, sludge-to-soil technology and incineration.
Further amelioration of the quality of the treated wastewater can be achieved through several tertiary treatment steps. This is especially recommended if the wastewater will be used for irrigation, or if the process water will be recycled for air conditioning or toilet flushing. Common technologies are chemical precipitation for phosphate elimination or heavy metal removal. Mechanical filtration in sand filters can remove the finest suspended particles. By activated carbon filtration, non-biodegradable organic compounds can be removed. UV-disinfection or chlorination removes bacterial contamination of the treated wastewater.
By the single use of these tertiary treatment technologies, existing surface or ground water bodies can be treated to a degree as high as drinking water or process water qualities.
For gaining drinking water quality from wastewater, ultra and nano filtration, reverse osmosis, and membrane technology are used along with the above mentioned technologies. The aim of these technologies is to provide drinking water for mankind without noxious side effects.
In particularly sensitive fields such as hospitals or hotels, an additional installation of air filters is recommended in order to avoid all unpleasant smells. Despite the aerobic processes available, it’s still a wastewater treatment plant. For this purpose biofilters are mainly in use.