Team:EPFL/Proof Of Concept
Proof of Concept
Introduction
CuRe has always been an ambitious project, attempting to solve a large issue, that of copper contamination, all the while involving various stakeholders throughout the project. Indeed, copper contamination in the soil is not an issue only in vineyards, but in many other different crops, mainly caused by persistent use of copper-containing fungicides or fertilisers. Furthermore, copper may also accumulate due to application of sewage sludge, pig slurries or mine slag. Therefore, our second aim was to make our solution scalable and extendable, reaching all affected sectors. While the involvement of stakeholders helped us to better understand the issue at hand, we also had to take into account various physical constraints. Nevertheless, we managed to design a system that proves our concept : treating copper contaminated wastewater using yeast, beads and a bioreactor.
Design
Our design is a comprehensive one, designed with the help of numerous affected parties and taking into account their needs and wishes. If you are interested in our engagement with these parties, visit our Integrated Human Practices page. Our design is also an interdisciplinary one, involving processes from chemistry, physics, microtechnology, computer science and, of course, synthetic biology. Below, we showcase for each component of our design the main results we obtained, as well as describe why we think CuRe would be a possible solution for solving this always more diffused environmental issue.
Capturing rainwater
Thanks to multiple vineyard visits, we determined that the most practical way to treat copper contaminated rainwater was to capture it and introduce into a bioreactor. The way we would do this is via carpet system running along the vine ranks. It would be made in a flexible material to be able to adapt to the irregular terrain often present in vineyards. Ridges ensure that all of the rainwater enters the drain and is guided towards the treatment facility. A great advantage of this concept is that it would additionally inhibit the growth of weeds, decreasing labour for the winemakers and increasing our solution’s economic viability.
Functional biomass – yeast
Through our copper assays, we proved that S. Cerevisiae (EBY100), absorbed copper, and could effectively reduce the copper concentration of rainwater by 75% in only 120 minutes. The starting copper concentrations used in this experiment were those experimentally confirmed to occur in rainwater recuperated from the vineyards. For more information on how we obtained these numbers, consult our Background page.
The specific details of this experiment can be found on the Results page.
This low-maintenance organism would thus be the perfect choice for functional biomass to introduce into our bioreactor. Given its great capacity to accumulate copper in extremely short times, once implemented in the correct proportions in our hardware system, it could probably represent a suitable solution for our issue, easily implementable and extendable in every scale and sector.
A substrate to support yeast - beads
As we discovered when speaking to representatives of water treatment facilities during our integrated human practices work, they rarely work with suspended organisms. Rather, they use a substrate to bind their organisms to, such as beads. We emulated this idea, opting for alginate beads. As described on the Implementation page, these beads are nano-porous, meaning they let ions in but keep yeast from escaping out. During our project, we made alginate beads containing yeast. We also began testing the ability of these yeast filled beads to retrieve copper. However, due to lack of time, we were unable to achieve conclusive results. For this reason, we do not consider our findings as supported sufficiently to add to the wiki.
A bioreactor capable of treating the water
So far we proposed a physical system that captures the copper concentrated rainwater and a biological system to filter the metal ions out of solution. To bring them together, we designed and built a physical bioreactor prototype in which filtration can occur. The design is simple including a touchscreen GUI (Graphical User Interface) is easy to use. We decided to introduce electronics and automation into our bioreactor prototype, but such a simple design incorporating beads could be entirely mechanical. This may be interesting in areas that rely mainly on manual labour in agriculture and that need a cheap solution to copper pollution.
Recuperating copper from the yeast
Once we have empirically shown that our biomass works and that the hardware and bead system can reintroduce clean water back into the environment, the last step to close our recycling loop is recovering copper and recycling it for several possible applications.
In order to make this last step feasible and realizable, we designed and developed an experiment tailored to retrieve copper from the saturated yeast. This experiment, through a combination of chemical processes and compounds, showed excellent results in performing the retrieving copper.
The principle behind is based on exploiting the properties of the Ethylenediaminetetraacetic acid (EDTA), an aminopolycarboxylic acid widely used to bind to iron and calcium ions as a chelating agent.
We thus tested this chemical compound loading it (1 g/l) on saturated wild type yeast with different times of reaction as a function of EDTA concentration. The results are shown below.
From this result, we found it extremely effective to use EDTA for copper retrieval, observing the best profitability using a 20 min reaction time with 20 mM.
Moreover, during our second meeting with Ludovic Vincent, the CEO of Biomede, we shared these results with him.
It seemed that EDTA was indeed a great option for what we were trying to do. However, it is difficult to subsequently remove EDTA from the copper containing water. We must take this into account when thinking about the future uses of this copper.
Thus a rather complicated chemical question arises : we would need to find an effective chelating ligand (a compound that provokes complex formation), that is not too expensive and not too harmful to the environment.
In our case, if we consider this copper solution to be reusable by wine growers, EDTA at a low concentration is not in itself a major problem as it is already used as a fertilizer. However, other options should be considered, such as separating EDTA from the copper-filled water to avoid further contamination of plants and soils.
Through these experiments, we have successfully shown that our project provides a proof of concept for the treatment of contaminated rainwater from agricultural fields. For each aspect of our project, we have designed and built most of the corresponding parts required. Moreover, since our system is broadly applicable, we can envision it applied to various domains of agriculture, not only vineyards. Although CuRe focused mainly on polluted rainwater, our project could be generalized to treat all copper-contaminated water. Indeed, most of the water contamination by copper happens either in the water delivery system or by untreated industrial wastewater1, and such pollution can be very dangerous to anyone who comes in contact with this water2. We hope to have demonstrated a realistic path toward a solution to solve agricultural soil pollution - one that is sustainable, realistic and impactful.
References
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Water pollution: Major issue in urban areasInternational Journal of Water Resources and Environmental Engineering
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Heavy metal water pollution - A case studyRecent Research in Science and Technology