YOUNG TALENTS
From Grey to Black
Elisabeth Bohnet: I became aware of "Arewa", with which you have been nominated for the Green Concept Award 2024, via your university's homepage. For your final project, you designed a water treatment system that can theoretically collect shower water in the bathroom at home and use it to flush the toilet. How did this product idea come about? Did you have any previous experience with sanitation?
Sophie Kling: We got together to do the final project together. We wanted to make a product with sustainable benefits. To do this, we started researching: What are the issues of the day and what is currently a waste of resources, what can be improved? From the areas of industry, agriculture and private households, we decided in favour of the latter and took a look: Where can we save water? Consumption is high in the garden, kitchen and bathroom. Through further research, we realised that the toilet is a major waster of drinking water. That's where we wanted to get involved, and we've continued to focus on the problem.
Helena Fricke: Personal hygiene is the number one water consumer. We looked at how we could combine consumption. Grey water is slightly soiled water that is produced when showering and in the washing machine. Drains containing faeces form black water. Grey water can also be used for black water production. I looked at sanitary products at the trade fair in Milan, but we had no practical experience with sanitary product design beforehand.
The idea behind "Arewa" sounds quite simple. You collect the grey water from the shower, treat it and use it to flush the toilet. But there were certainly many challenges on the way to developing the product.
Helena Fricke: The problem is when grey water is collected and reused for whatever purpose: it starts to stink or the system gets dirty. The main task was to ensure that the filter system doesn't break down after three months or five years. We didn't want to design a product that needs a filter change once a week. We have now designed it so that the filter has to be changed once a year. And that it is as maintenance-free and resistant as possible, so that it doesn't destroy itself.
Soap residue is certainly a big problem. How does the filtration system work?
Sophie Kling: We took our cue from existing grey water filter systems or small wastewater treatment plants. Ultimately, they do what our plant does, only on a larger scale. We have simply condensed it. The grey water flows into a first tank, which contains bacteria and the water is cleaned bacterially. This also happens in the sewage treatment plant. There is a strain of bacteria that always remains in the tank and purifies the water, or to be more precise, some bacteria eliminate the other bacteria.
The water remains in the first tank for around three quarters of an hour. A chemical sensor measures when the process is complete. A tablet compartment is then opened from which flocculant falls into the tank. It binds the larger particles in the water. A flap then opens and the water is channelled through an ultra-membrane filter into a second tank. The flocculant serves to hold back the dirt from the filter.
Helena Fricke: The water is now purified to operating water level, it is not yet drinking water quality, but it is so clean that it doesn't start to stink. The filter would naturally clog up after a while. That's why we've installed a suction cup in the elongated pipe, and every time water runs through it, it pushes water upwards and flushes the membrane filter against and into the drain.
This is the standard scenario when everything is running smoothly. We have built in mechanisms if this is not the case: if there is too much showering, we have the drain from which the water runs off with the remains of the filter. Excess water is also drained there when the tank is full. If too little water is used, there is a fresh water inlet. If showers are taken in succession, the chemical sensor helps to ensure that water is not transferred to the second tank too early.
What are the guidelines for water treatment in Germany and other countries?
Sophie Kling: In Germany, the guidelines are stricter than in other countries. Above all, the fresh water pipe must not protrude into a tank containing contaminated water. This is a problem with cisterns. We haven't worked this out yet, but we would orientate ourselves on solutions such as those used for cisterns.
Helena Fricke: In Spain and Portugal, and I think also in Italy, the rules are more relaxed due to the scarcity of water.
What happens if I am not at home for three months and no water runs through? Does something dry up or is fresh water flushed in to keep the bacteria alive?
Helena Fricke: There is a small hollow in the first tank. This is a small bacteria tank to ensure that there is always enough water to keep the bacteria alive.
Are you worried about blockages in the pipes?
Helena Fricke: You actually need smaller pipes to avoid blockages. We haven't looked into the issue in depth because all the specialists have told us that there are no concerns.
Sophie Kling: We have the coarse filter in the shower tray, which can be removed and cleaned at any time. Hair and larger particles get stuck there. Another filter is integrated into the shower pump, which can also be cleaned if necessary. On the way to the bacteria tank, the water is so clean that nothing should happen.
And the flocculant, can it run out?
Helena Fricke: The flakes have to be refilled once a year. We have integrated a light strip into the front of "Arewa". It not only shows the water level in white, but also lights up red if something is wrong with the filter, for example if flocculant needs to be topped up.
Is there then an indication of what the problem is?
Helena Fricke: No, open it up and have a look. It's pretty low-tech, we wanted to go without screens and keep it simple.
The light strip involves the end user in the process. What does this effect?
Sophie Kling: You automatically become aware of your water consumption. You realise straight away whether you've been showering for a long time or not so long. Or if you have a lot of people over, you realise how much flushing up you do. You become much more aware of grey water production, but also black water production.
I have seen that you have also designed a solution for the washbasin.
Sophie Kling: The basic solution is based on the shower. We also developed the washbasin solution, where the water would come from the washbasin, but washing hands doesn't produce that much grey water. We also decided against it because you have to bear in mind that "Arewa" will be added during a bathroom renovation. New pipes would have to be laid, and the cost would probably be too high for the benefit of the washbasin wastewater.
What is the intended usage scenario? And what is the status quo of the product, are you in contact with manufacturers?
Sophie Kling: We made the product as part of our bachelor's thesis and we also applied for competitions. We carried out tests, but it was theoretical for the time being.
Our product is designed for private households, possibly also for gyms or hotels, because people shower and wash up there. We wanted a solution that would work in a room. It would also be conceivable for swimming pools that are next to a school, but in such cases small sewage treatment plants are more appropriate.
Helena Fricke: We have already had various discussions with manufacturers, but so far they have come to nothing and life has intervened. As a result, the project is currently on hold, but we would still like to pursue the product.
What distinguishes your product from existing endeavours for a "greener bathroom" by renowned manufacturers?
Helena Fricke: The existing ideas are primarily dreams of the future and are shown to demonstrate: "We are thinking in this direction." As far as we know, these ideas are currently not realisable. We wanted to design a product that could be launched on the market now, with existing, functioning technology.
Do you see any difficulties on the way to production?
Sophie Kling: We have done a lot of research into the technical implementation, but it will be a matter of carrying out tests. There would still be work and time involved. We have made sure that our system fits into all possible bathrooms.
Helena Fricke: For me, the costs are an issue. We want to keep the product affordable. For example, we chose bacteria because it is cheaper than a chlorine filter, for example. The ultra-membrane filter is a standard filter used in small wastewater treatment plants. Our aim is for "Arewa" to pay for itself after 5 years, and that's how cost-effective we want the product to be. Water savings: According to Statista, each person uses 34 litres of water per day to flush the toilet. On average, 46 litres are used for personal hygiene. This is slightly more than is used for flushing the toilet.
Theoretically, a lot is possible in water treatment using membrane filters, right up to drinking water quality.
Sophie Kling: Yes, it's very fascinating. We have looked into it, but we wanted to make a product that is feasible, also at the mindset level. Our research has shown that the disgust factor is actually too great, even with the idea of using treated grey water to wash your hands, for example. On a technical level, it wouldn't be a problem at all, but mentally we're not quite there yet.
Helena Fricke currently works at the Diez Office in Munich. Sophie Kling is currently working at Scala Design in Stuttgart. After completing their Bachelor's degree in summer 2023, they both want to gain practical experience before deciding what path to take next.
