Various methods are available for the elimination of organic pollutants, micro-pollutants, drug residues and anthropogenic trace substances. These can be divided into four groups: "Oxidative" with ozone or AOP, "Adsorptive" with PAH in the activation, before a flake filter or as a PAH stage consisting of a contact reactor, sedimentation after secondary clarification with internal recycling of the coal, "Adsorptive" with GAK in our DynaSand carbon filter and "Physical", where the DynaSand protects the downstream technology.
The German Association for Water Management, Wastewater and Waste e. V. (DWA) publishes a new leaflet series DWA-M 285 "Trace substance elimination in municipal sewage treatment plants". As part of research projects and the implementation of pilot plants in operation, numerous cleaning systems for the elimination of trace substances have now been implemented in Germany. In the meantime, processes with ozone and/or activated carbon are already being operated at more than 20 sewage treatment plants in German-speaking countries, so that in the meantime there is experience with the planning, construction and operation of some processes. Ozonation and activated carbon adsorption are currently considered to be suitable processes for the elimination of trace substances in municipal sewage treatment plants. According to the current status, taking into account the results of the stakeholder dialogue of the Federal Environment Ministry on the "Federal Strategy for Trace Substances", it can be assumed that in the coming years further sewage treatment plants will have to be expanded to include processes for the targeted elimination of trace substances. Until now, the processes have been dimensioned on the basis of characteristic values derived from semi-industrial and large-scale tests. At present, there is no document in the DWA set of rules for the interpretation of these procedures or a decision-making aid when selecting the procedure. With the creation of the new leaflet series, these gaps should be closed. The first three parts of the series are: Part 1: Criteria for process selection with selected examples Part 2: Use of activated carbon - process principles and dimensioning Part 3: Ozonation - process principles and dimensioning.
The treated wastewater from conventional municipal sewage treatment plants contains a residual load of organic compounds of artificial origin. Such "anthropogenic trace substances" can then be detected in very low concentrations in water bodies. They come, for example, from the use of household and industrial chemicals, detergents and cleaning agents, or the use of pharmaceuticals and pesticides. Because of their stability, they are only partially broken down in sewage treatment plants. Some of these substances can affect aquatic organisms or drinking water production. This gave rise to the consideration of retrofitting, for precautionary reasons, especially larger sewage treatment plants with water-sensitive discharge conditions with a 4th cleaning stage to eliminate trace substances.
The city of Weißenburg in Bavaria has set up a 4th cleaning stage on its sewage treatment plant. A two-stage process combination of ozonation and filtration was implemented. The Free State of Bavaria funded the pilot project with 75 percent of the eligible costs. The Weissenburg sewage treatment plant discharges into the low-flow Swabian Rezat. Due to this sensitive water management situation, the sewage treatment plant was selected as the location for a Bavarian pilot project. The following goals were pursued:
From the start of planning until about a year after commissioning, the construction of the 4th cleaning stage was accompanied scientifically and technically as part of the project "Elimination of anthropogenic trace substances in municipal sewage treatment plants". Furthermore, an extensive measurement program was carried out. After a project period of around five years, commissioning was completed in spring 2019 and the knowledge gained was summarized in a final report.
In order to gain further insights into regular operation and to further optimize the energy use of the 4th cleaning stage, the follow-up project “4. Cleaning stage at the Weißenburg sewage treatment plant, experiences in regular operation”.
With the project for the sewage treatment plant in Weißenburg, an extensively examined "best practice" example is now available, which provides valuable knowledge for the conception and planning as well as for the operation of further plants for the elimination of trace substances.
There is a lot of plastic waste in the environment and in our waters: beverage bottles, plastic bags, packaging, straws and much more. Less recognizable with the naked eye, but not rarer, is so-called microplastic. This page provides information on what exactly microplastic is and what quantities occur in Swiss waters.
Plastic, also known as plastic, is a persistent organic material or POP (persistent organic pollutant). It will be through the polymerization from monomers manufactured, which are generated based on petroleum, coal, natural gas. Typical types of plastic are
In addition, there are essentially two types of bioplastics.
Plastic usually contains additional chemicals such as bisphenol A or plasticizers to give the plastic special properties.
In science, plastic particles are usually classified according to their size and origin.
Macroplastics: Plastic particles larger than 200 millimeters
Mesoplasty: plastic particles between 5 and 200 millimeters
Microplastics: plastic particles between 5 and 0.0001 millimeters (=100 nanometers)
Nanoplastic: Plastic particles smaller than 100 nanometers
Primary microplastics: Microplastic particles that are industrially produced in this size for a specific application, for example
Secondary microplastics: Microplastic particles that are only formed through the decay or decomposition of larger plastic parts, for example
There are large amounts of microplastics in street water. It comes from the abrasion of car and truck tires, from polymers and bitumen from the asphalt, from shoe soles and road markings. Especially when it rains heavily, the plastic particles are often washed off the road not only into the sewage system, but also onto fields and bodies of water. On roads with little traffic, there is also the fact that the street sewage does not always go through the sewage system into a Road sewage treatment plant SABA, but is fed unfiltered into the next body of water or seeps into the subsoil.
Empa researchers have taken a closer look at the abrasion of tires - the micro-rubber. They calculated that between 1988 and 2018 around 200,000 tons of micro-rubber could have accumulated in the environment in Switzerland. According to these calculations, about three quarters remain in a five meter wide strip on the right and left of the road, 5 percent end up in the soil on the other side of the strip and 20 percent in the water
(Source: "rubber in the environment», Empa, 2019).
In a study by the Fraunhofer Institute UMSICHT, the researchers identified tire abrasion as the biggest cause of microplastics in the environment in Germany. Abrasion from asphalt is third, shoe soles seventh and road markings ninth.
(Source: "Plastics in the environment: micro- and macroplastics», Fraunhofer Institute UMSICHT, 2018).
350 million tons of plastic are produced worldwide every year. This corresponds to an average of 50 kilograms of plastic per person per year. About half of this gets into the environment via various processes, i.e. around 20 to 30 kilograms per person and year. The main sources of microplastics - around 1 kilogram per person and year - are
Viewed worldwide, primary microplastics hardly contribute to the pollution of the environment with plastic. More than 99.95 percent of the microplastics in the environment are secondary microplastics, i.e. the smallest plastic particles that only arise through the decay or decomposition of larger plastic parts.
On behalf of the Federal Office for the Environment (FOEN), Empa used calculations to estimate how much plastic gets into the environment in Switzerland. The seven most commonly used plastics were recorded: polyethylene (LD-PE and HD-PE), polypropylene, polystyrene and expanded polystyrene, PVC and PET. It is estimated that around 5100 tons of plastic are released every year: 4500 tons of macroplastics and 615 tons of microplastics. Of this, around 600 tons of microplastics end up in the soil and almost 15 tons in the water. (Source: "More than 5000 tons of plastic released into the environment annually», Empa, 2019)
In the EU, only around 7 percent of the microplastics released flow into ARA wastewater treatment plants via domestic and commercial wastewater. There, between 80 and over 99 percent is removed and disposed of with the sewage sludge. There are still 1 to 5 micrograms of microplastics per liter in the treated wastewater.
In the Canton of Zurich, the Office for Waste, Water, Energy and Air (AWEL) examined 28 ARA wastewater treatment plants. They release about 18 billion microplastic particles, or 330g, into the environment every day. Extrapolated to all 64 Zurich WWTPs, this results in a quantity of 31 billion particles or 600 g entering Zurich's waters every day. No microplastics could be detected in groundwater or drinking water. (Source: Specialist article «Microplastics in waste water and bodies of water», Aqua&Gas No 7/8, 2016)
The main source of microplastics in the environment is discarded plastic waste. In order to protect surface water and the environment from microplastic pollution, it is particularly important to reduce plastic and microplastics at the source and to properly dispose of the remaining plastic waste.
If one counts microrubber among microplastics, tire abrasion becomes the main source of microplastics. (Source: "rubber in the environment», Empa, 2019)
In Switzerland, an average of 100 to 2,000 cubic meters of wastewater per person per year enter the ARA wastewater treatment plants. There, between 80 and 99 percent of the microplastics are removed from the wastewater. With additional sand and membrane filters, processes that are already well established in Central Europe, the rate can be increased to over 99 percent. The microplastics removed from the wastewater collect in the sewage sludge, which is usually incinerated in Switzerland. According to model calculations, only about 0.01 percent of the plastic entering the environment in Switzerland comes from the ARAs.
However, in countries that do not yet have a functioning wastewater treatment system, WWTPs are a good starting point for using cleaning technologies to remove microplastics from wastewater.
Photos of dead seabirds and fish with a belly full of plastic are well known. The dangers of large pieces of plastic in the environment are obvious. When plastic parts are mistaken for food and eaten by animals, they enter the digestive tract and can lead to abrasions, ulcers and constipation, and eventually starvation and death.