Overview
In today's world, human society as we know it will have to change and adapt in order to respond to the various issues it will face. Indeed, the increase in populations, the decrease in resources or ecological problems are all subjects that lead to controversy and require answers.
It is within this framework that the iGEM Orléans team has positioned itself to propose through our project an idea to address some of these issues and particularly the recovery of our waste.
Today, domestic and industrial wastewater must be treated, representing a total of 21,474 collective wastewater treatment plants (in France in 2016). The average daily load of biodegradable organic matter contained in the water entering the plant during a week, up to 79 million population equivalents (p.e.) for a purification capacity of 103 million p.e. per day. (1)
1 p.e. = 60 g of BOD5/day at the station entrance, i.e. 21.6 kg of BOD5/year.
The European Directive of 21 May 1991 defines the inhabitant equivalent as the biodegradable organic load with a biochemical oxygen demand in five days (BOD5) of 60 grams of oxygen per day (2)
This organic waste, therefore, has a high potential for waste recovery, and although some processes are already in place, the use of modified bacteria could make it possible to recover sewage sludge more efficiently.
Thus, the development of our bacterial model was carried out on "summer" sludge.
Sludge contains many toxic compounds, mainly heavy metals and is also very rich in cellulose. About 30% of the sludge is currently spread, the rest being incinerated or buried. Although the legislation regulates the use of sludge in agriculture (in order to avoid fertilization with sludge rich in heavy metals), costly controls are carried out only a few times during the year, which is not sufficient given the variability of the sludge. There is, therefore, a risk to public health.
The cellulose is highly present in sludges and responsible for the most part of the material damages in water treatment plants. Cellulose form a glue that clogs the pumps. Cellulose is basically a sugar polymer and sugar can be transformed through a fermentation process into Ethanol. Bioethanol can be used in cars or industry as a substitute for oil and its production from sewage cellulose will allow reducing at the same time the need of dedicated crops for the production of bioethanol, crops can be used for food production instead.
Orléans la source's water treatment plant
sewages sludges
Sewage sludge is a very heterogeneous environment. Indeed, their composition may vary over time depending on the releases from industries or populations.
Waste water sludge we ttok from the sewage station to work on
heavy metals
Heavy metals are highly toxic and they are partially responsible for the inability of sludges as fertilizer. Even is the heavy metal rates can change in the time or in the location depending on the city size and on the industries, we designed our bacteria to resist and capt this heavy metals in order to purify the sludge and can spread them from one side and from the other side we want to re-use this metal in industry.
cellulose
Circular economy and waste valorization
Waste recovery makes it possible to set up circular economy systems. The aim is to use the resources already available that different human activities produce to reduce the extraction of new raw materials from the environment.
Thanks to the development of our super-bacteria, heavy metals found in sludge can be captured and reused in the industry, which will reduce pollution and environmental damage caused by mining. In addition, the "purified" sludge could be more widely spread in the fields as a fertilizer due to its high nitrogen and nitrate content and thus reduce the use of chemical fertilizers.
Finally, the considerable quantity of toilet paper found in the purification basins constitutes a very large reserve of cellulose that could be used by our bacteria to produce bioethanol, which will offer a more ecological and renewable alternative to oil, which will disappear in a few decades. Bioethanol production is currently made from crop waste or dedicated crops, this new production from sewage cellulose could allow using bioethanol crops to produce human food.
From local application to national development
Locally, the University of Orléans is located in an agricultural region: Beauce. Sludge recycling could have a direct impact on local agriculture, in particular by increasing the spreading rate of sludge in order to fertilize the soil.
It can be observed that only between 2 and 5% of sludge is used for spreading in the region (Agreste-2010)(3), this rate tends to be stable, particularly through the tightening of sludge use laws and waste statutes (4). The rest of the sludge considered toxic is therefore mainly burned or buried (5), polluting the air, soil, and water through the diffusion of heavy metals contained in the sludge. The use of Cupriavidus metallidurans, which is a naturally metal-resistant bacterium, would allow the sludge to be seeded to allow the bacteria (which we will have previously modified to allow them to increase their ability to capture and internalize or aggregate heavy metals such as cadmium or lead on their membranes) to remove pollution from the sludge. Heavy metals can then be reused in the industry while purified sludge could be used more widely as a natural fertilizer to increase agricultural yields. In addition, heavy metals will no longer be found in soil, water or air, which would reduce the health risk of contamination of populations by heavy metals.
Faced with various environmental problems such as pollution or the increasing scarcity of non-renewable fossil fuels such as oil, more and more countries are investing in the development of "greener" renewable energies. France is thus developing the production of bioenergy as a fuel, as demonstrated by the creation of industrial complexes for the production of bioethanol and biogas, as shown by the Cristanol plant near Reims (6). The current means of bioethanol production are vegetable waste and dedicated agricultural crops.
Throughout France, 3% of agricultural land is used for bioethanol production (7). This makes France the 9th largest producer of bioethanol in the world (in 2018 with 1 billion liters produced) and 2nd largest in Europe (25% of European production) (8).
As mentioned above, the use of cellulosic waste (such as toilet paper) found in sludge could increase bioethanol production through the use of our genetically modified bacterium by recycling unused waste in order to consolidate France's position as a leader in the production of this energy. In addition, this new production route could make it possible to substitute crops used specifically for bioethanol production with crops intended for human or animal consumption.
See more in inspiration and description.
Map of the % of sewage spreaded in the Région Centre crops
From lab application to reality
Visit of the Orléans la source water treatment plant
To improve our project, we visited the Orléans la Source wastewater treatment plant located next to the university several times. We were able to visit the plant, and thus better understand its operation as well as all the different stages of water and sludge treatment. This first allowed us to better understand the complexity and heterogeneity of the sludge we plan to clean up. Indeed, the composition of sludge is very variable, it can vary from one day to the next depending on industrial or domestic discharges and sludge with different characteristics can be found throughout the year. We also had the opportunity to meet with the various station staff members to discuss their working conditions and the recurring problems they encounter.
Thus, three major problems emerged:
- Sludge is heterogeneous, there are few controls to analyze its composition and possible pollutants (including heavy metals and components), which makes it a danger to populations and does not allow most of them to be spread in the fields.
- Toilet paper made mainly of cellulose is more or less dissolved in the plant's sludge and water. Despite the constant agitation of the basins, cellulose particles accumulate in the filter pumps forming molasses that eventually clog the pumps or even break them. This leads to regular maintenance, which may sometimes require emptying a basin for several weeks in order to remove the cellulose agglomerate or change a pump, which represents a significant cost for the station.
- The lack of awareness among people about the operation of a wastewater treatment plant, and about the problems that can arise from the release of toxic products or objects into the pipes.
The METAL'OSE project team has taken all these problems into account in order to solve them and thus improve the functioning and performance of the treatment plants. The problem of heavy metals and cellulose will be addressed through our modified bacterium Cupriavidus metallidurans which will capture heavy metals while producing ethanol from digested cellulose. Awareness-raising among people of all ages and conditions will be carried out through our various actions ( see the Education and commitment page ).
Finally, an application in industrial conditions was discussed, in the sense that our system could be integrated into the existing purification process by creating an extension to the plant.
Alexandre and Mr Z a worker from the Station
Hypothetical application in the future
In order to go further in our approach, we collaborated with Ronan Galinier, an engineer-architect student at the INSA in Strasbourg.
With his expertise, we imagined what the Orléans wastewater treatment plant could look like if we installed our sludge recovery system using our Cupriavidus metallidurans bacteria.
The building we have designed is a natural extension of the existing ones. The sludge coming out of the tanks will first be transported to different incubators in order to be brought into contact with our bacteria. After a certain incubation period, the latter is transferred to industrial centrifuges to allow the separation of the cleaned sludge pellet, bacteria that have aggregated the metals and the supernatant.
The supernatant will then be treated by distillation to recover the bioethanol, and the lysed bacteria to recover the various metals.
Our various products (Metals, healthy sludge and ethanol) will then be stored in different silos before being sent to their different recycling sites.
Sludge will be spread in the fields, ethanol will be sent to gas stations to be used as fuel and metals will be sent to different industries.
Global visualization of our potential structure for sewage bioremediation
Details of the structure of our potential extension for sewage bioremediation
Improve the system
To go further, we can imagine extending the application of our system. For example, specified our bacterium has other heavy metals that we can find in the sludge from treatment plants. But also to propose other systems to better purify molecules such as hormones or drugs.
We can also design the recovery and recovery of recoverable grease in the waste treatment chain.
References
1. https://www.eaufrance.fr
2. https://www.actu-environnement.com
3. http://agreste.agriculture.gouv.fr/IMG/pdf/R2412A16-2.pdf
4. http://www.loiret.gouv.fr/Politiques-publiques/Environnement-eau-foret-chasse-peche/Eau/Projets-soumis-a-la-loi-sur-l-eau/Rejets/Assainissement-eaux-usees/Epandage-des-boues-d-epuration
5. http://www.amorce.asso.fr/fr/eau/actualites/epandage-des-boues-depuration-eclairages-sur-la-reglementation-relative-au-retour-au-sol/
6. https://www.cristal-union.fr/sites-de-production/distillerie-cristanol/
7. https://www.ecologique-solidaire.gouv.fr/biocarburants
8. https://fr.statista.com/statistiques/753650/production-d-ethanol-par-pays-monde/