November 19 marks the date for the UN initiative the World Toilet Day, which draws attention to the fact that 3.6 billion people live without access to safe, secure and dignified sanitation, and the social and ecological problems connected. But research on bacteria can contribute to positive change!
– A well-functioning sewage system where wastewater is transported and treated in an efficient, hygienic, and environmentally friendly way is fundamental to protect the environment and human health, says Professor Britt-Marie Wilén, Department of Architecture and Civil Engineering.
Climate change causes droughts, floods and rising sea levels, which threatens our sanitation systems in various ways. Floodwaters can spread human waste to drinking water sources and food crops and cause disease. Discharges of wastewater can also lead to eutrophication, which causes fish and aquatic plants and animals to die.
For Sweden’s part, increasing amounts of precipitation effect society as pipes and treatment plants aren’t dimensioned for an inflow that sometimes increases tenfold, which leads to an overflow in the sewage systems where polluted wastewater is discharged into the environment.
– In countries that do not have sewage systems to the same extent, dry latrines can even be a better solution. In Sweden we have functioning systems that purify to a very high degree. What we are studying is how we can improve the processes further in terms of emission quality and energy consumption. Already today we extract energy from wastewater in the form of biogas, and in the future we may even be able to develop energy-neutral treatment plants. If we can find environmentally friendly, compact and resource-efficient processes, we can in the long run contribute to better sewage treatment and applications in countries with less developed systems, Britt-Marie Wilén comments.
Bacteria do the job
With her promotion in 2021, Britt-Marie Wilén became Chalmers first female professor in the water and sanitation area**. She has a solid background at Chalmers and is part of the research theme of wastewater treatment and resource recovery (Bioresource Labs) in the Division of Water Environment Technology, with “Bio” being the key to sustainable wastewater treatment, according to Britt-Marie.
– Purification with biological processes is based on bacteria doing the work of purifying the water. We don’t add any bacteria but create conditions in the treatment plant to make the bacteria from human faeces, as well as those that come in with stormwater and leakage into the pipe network, thrive and flourish.
A common method for purification where bacteria play an important role is the so called” activated sludge process”, where dissolved organic and inorganic substances in the wastewater, such as nitrogen and phosphorus, are converted into particles that can be separated. The bacteria grow and become sludge, and the sludge can, after purifying the wastewater, be used for biogas by digestion.
Compact and efficient cleaning processes create sustainability
The goal for the researchers is thus to develop as resource-efficient, compact and environmentally friendly purification processes as possible. Like minimizing the use of chemicals and energy by reducing the amount of pumping and adding of oxygen, and to build less space-consuming purification processes. Through research, one can understand the processes better and make them more efficient, and thus move forward on the road to a more sustainable sewage management.
– We try to understand what affects which bacteria can be found in the treatment plant and what they do. In this way, we can create conditions that make them thrive. We know, for instance, that bacteria like to grow together to assimilate nutrients in an easier way. We test different growth environments and growing methods such as granular sludge and biofilm where the bacteria grow close together. If you understand which bacteria do the job and how, then you can also understand how to control different parameters in a treatment plant, explains Britt-Marie.
The researchers at Chalmers collaborate with the municipal company Gryaab in the treatment plant Ryaverket in Gothenburg. The group is also looking at how to generate energy from wastewater, through so-called microbial electrochemical cells, a technique still at a research level, but in the long run could enable for treatment plants to generate their own energy in an even more efficient way, compared to current technology with digestion of sludge to biogas.
Other important research is about understanding how drug residues can be taken care of in the treatment plant – and also for this purpose, bacteria can be part of the solution.
– We consume more and more drugs, which means that drug residues end up in the wastewater. This is a real problem because it has been shown to be related to hormonal disorders in fish and aquatic organisms, and cause antibiotic resistance says Britt-Marie.
All water in nature is connected and becomes part of the natural cycle, and sewage treatment is thus important to protect all water in society.
By: Catharina Björk
*3.6 billion people do not have access to a safely managed sanitation service (WHO/UNICEF 2021)
** Ann Mattsson is employed by Gryaab AB and was appointed adjunct professor in water and sewage technology in Chalmers by 2013.
Read more about the research in the wastewater treatment area