Using decades of experience to help the environment
One of the great success stories of the 20th century in terms of environmental protection is the treatment of wastewater – or more specifically, the wastewater treatment plant. In the 1950s, pollution of lakes and rivers by residential, commercial and industrial wastewater was commonplace. Foaming, stinking streams, dying fish and waste in bodies of water were the order of the day. Swimming was largely forbidden for health reasons, and no wonder, since most of the wastewater entered these bodies of water untreated.
By comparison, we have a much firmer grip on the situation today, but more knowledge also brings more complexity – and that includes our approach to wastewater. Modern analysis shows that wastewater treatment plants cannot completely remove many micropollutants, such as endocrine disruptors, household chemicals, cosmetics and pharmaceuticals. These continue to enter our waters, as do substances from commercial and industrial processes.
Fighting Micropollutants with Ozone
What to do? Wastewater treatment plants must be retrofitted so that micropollutants can also be removed from wastewater. That’s where Eawag’s expertise can help, and not just on the technical side. Environmental chemist Urs von Gunten, Eawag group leader in the Water Resources and Drinking Water department, has decades of experience in treating drinking water with ozone. When applying “ozonation”, which is now also used in wastewater, two questions were key: Are the problematic chemicals reliably “defused”, and does the ozone really not produce any un wanted substances? This is important to consider, since the “organic matrix” naturally also reacts with the ozone.
Process engineering and analytics were important in this context. It is at this point that the expertise of chemist Christa McArdell, group leader in the Environmental Chemistry department, comes into play. She calls it “backbreaking work to find out what is in the wastewater and what exactly is produced in the ozonation process”. However, it is impossible to capture everything that occurs in the complex reaction of ozone with various substances and the matrix. Ecotoxicology tests are used to assess the effects: Can the known effects of micropollutants be minimised or might new, unexpected ones emerge? It has been shown that ozone is a very reliable oxidising agent for rendering a large number of micropollutants “harmless”. The ozone causes small changes in their chemical structure, which means that the molecules lose their biological effect. Moreover, there is also a solution for what is produced from the matrix during ozonation (e.g. aldehydes): biological posttreatment also purifies these, as they are usually broken down easily by microorganisms.
Putting the process into practice
Process and analytical aspects were immediately convincing; the challenge then was putting the process into practice. “To implement something like this, you need additional expertise,” says McArdell, adding that an interdisciplinary approach, such as that cultivated at Eawag, is crucial. In collaboration with engineers, ozonation and activated carbon treatment, another method for removing micropollutants, and combinations thereof were tested in pilot plants and later in a largescale operation. The methods were evaluated by means of tests in cooperation with the Environmental Toxicology department. Finally, the costs of retrofitting plants must also be kept in mind if the aim is not only to prove the theoretical effectiveness, but also to implement it in wastewater treatment plants.
The "Swiss model"
For a viable proposal, politicians also need to be on board early on. The Federal Office for the Environment (FOEN) and the traditionally wellfunctioning network of Eawag researchers with authorities and practitioners played an important role here. Social sciences were also involved in order to assess the economic benefits and acceptance among the population. The strategy is now considered exemplary, has been enshrined in the Waters Protection Act since 2016 and is known as the “Swiss model”. It is also being followed with interest internationally and has already been implemented in some cases, for example by the EU and in the USA, where some of the wastewater is recycled into drinking water.
As the retrofitting of all 700 or so wastewater treatment plants was originally estimated to be too expensive, it was agreed that the aim should be to halve the residues. This is possible with the retrofitting of around 120 plants at the most critical locations. The Federal Government is currently working on an amendment to the law on behalf of Parliament, according to which all wastewater treatment plants whose discharges currently lead to limit values being exceeded must be retrofitted. According to initial estimates, this would affect a further 300 or so wastewater treatment plants.
The two Eawag experts are justifiably proud of what they have achieved in such a short time. Their efforts were also recognised by the Swiss Chemical Society, which presented them and other team members with the Sandmeyer Award.
From wastewater to clean rivers
Ten years after the start of the pilot trials, the new Waters Protection Act came into force, and more and more plants are being upgraded. The political will to make further improvements remains a key factor, although micropollutants are less of a problem for people. “Very few of these wastewaterborne substances are found in drinking water,” says von Gunten. The aim is to protect the aquatic environment. In future, residues from commercial and industrial processes are likely to become more of a focus again. Often, however, we first have to develop an awareness of this type of environmental pollution. Here, too, advances in analytics play a major role. After all, you can’t clean what you can’t see.
