Many people don’t worry about what happens to the wastewater they produce. They are not aware that it has to be clean in a complex process before it can be used again. In this post, we explain what is mean by wastewater treatment and what the aim of wastewater treatment is.
What is wastewater treatment?
Wastewater treatment is the name given to all techniques that aim to purify wastewater. It also includes the discharge of the treated water and the recycling of the substances extracted from the wastewater (phosphorus, sewage sludge). Wastewater that is fed to the sewage treatment plant or another wastewater treatment plant comes from
- private households
- commercial use (industrial wastewater)
According to state water laws, wastewater treatment is the responsibility of the municipalities. According to EU Directive 91/271 / EEC, this only applies to municipalities with at least 2,000 inhabitants. These carry out their wastewater treatment in a municipal sewage treatment plant. Municipalities with fewer inhabitants and sparsely populated areas have had to have private small wastewater treatment plants since 2015. One or more households are connected to this, depending on the size of the wastewater tank and the number of houses in the vicinity. The small wastewater treatment plants also include plant-based wastewater treatment plants.
Public sewage treatment plants
The wastewater from private households and businesses is fed separately from the rainwater or. together with it into the public sewage treatment plant. The former is referred to as a separate sewer system, the latter as a mixed sewer system. In the sewage treatment plant, devices (mechanical wastewater treatment) and special processes remove solids, suspended matter, organic and chemical compounds from the wastewater. The wastewater is transport from one clarifier to the next using pumps.
Biological processes cause the breakdown of organic substances and heavy metals by microorganisms. The resulting sewage sludge is pumped out and reuse when a certain level is reached. The wastewater, which has been clarifying twice using bacteria, is then subject to chemical wastewater treatment. The amount of phosphorus in the wastewater is reduced to an acceptable level through precipitation.
Small sewage treatment plants
In contrast to the sewage collection pit, in which allotment gardeners collect their sewage, and later have it remove by specializing disposal companies, private sewage treatment plants can purify the sewage themselves. Like the septic tanks, the mini sewage treatment plants are located on their own property. Depending on the certification of the underground plant made of concrete or plastics. The wastewater is partially or almost completely clean. The legal minimum requirement is partial clarification (cleaning class C). In this case, bacteria take over the degradation of the carbon compounds in the dirty water. Anyone who wants or has to do more to protect water can choose a class N, D, P, or even H system.
The cleaning classes N (nitrification) and D (denitrification) deal with the biological reduction of nitrogen in polluted water. The breakdown of nitrates protects surface waters and groundwater from a lack of oxygen. The elimination of phosphorus (P) and the killing of germs using ozone (H, sanitation) can often be retrofit. The former helps to avoid over-fertilization of the water and thus an excessive growth of algae. Home sewage treatment plants function fully automatically and mostly with electricity according to their pre-setting. They have several separate chambers and work like public sewage treatment plants, mechanical restraint devices, and bacteria that consume biological substances. So that the wastewater treatment works optimally, oxygen is supply to it from the outside.
Herbal sewage treatment plants
There are also root space disposal systems in rural areas. In these plant treatment plants, the wastewater, which has been collect and pre-clean in an underground multi-chamber tank is direct in gushes onto a mostly sloping surface. There certain plants or reeds grow on a bed of gravel of different grain sizes. The microorganisms living in the root area clean the wastewater by breaking down nitrogen and carbon compounds and binding heavy metals. The gravel removes the phosphates that are present. The task of the plants is to supply the bacteria with the oxygen they need. A pipe leads the purified water from the mud biotope into a drainage basin, which is usually also planted. Occasionally, the sludge collect in the underground multi-chamber pit has to be disposed of.
In addition, a sufficiently dimensioned plant-based sewage treatment plant provides a similarly high cleaning performance as other private sewage treatment plants at least in frost-free time. Reed beds with vertical wastewater treatment must be at least 4 m² per inhabitant and a total of at least 16 m². Infiltration basins should have an area of at least 4 m² for four residents. Different legal requirements apply to commercial wastewater and drinking water protection areas.
What is the goal of wastewater treatment?
The primary goal of wastewater treatment is the treatment of the resulting wastewater into service and drinking water. Process water that you use to water your garden, for example, does not have to be as pure as drinking water. That is why wastewater is treat using special processes so that the water quality achieve after wastewater treatment complies with environmental protection regulations.
The patent processes ensure that the water discharged into streams and seep into the groundwater is relatively clean. If this is not the case, the bacteria are present in the water will multiply too much due to the oversupply of food. They then need far more oxygen than is available in the water and ultimately die. The microorganisms sink to the bottom of the water and form a layer of digested sludge there, which leads to the death of fish and a strong odor nuisance.
The sewage sludge that arises in the course of must also only be slightly contaminated with pollutants. Since untreated and dewater digest sludge from the sewage treatment plant usually does not meet this requirement, it has not been allowing to be transported to landfills since 2005: The questionable residues contain therein would otherwise seep into the groundwater and pollute the drinking water. In addition, the methane gas escaping from the open sewage sludge would increase the already high methane content of the earth’s atmosphere.