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Writer's pictureMarysol Peña
13 min read

Environmental chemistry for everyone through the Microbial Fuel Cell


Keywords: Microbial Fuel Cell Environmental Chemistry Sustainable Energy Organic Waste Plants ABSTRACT The current energy demand has become a crisis whereby nations encourage the use of sustainable energy. Most of the technological systems that are proposed are only suitable, in terms of maintenance, for developed countries; on the other hand, for nations in inferior positions, this option does not exist, hence the importance of promoting renewable energies based on organic matter, which we produce every day; in this way, we foment the fight against the energy crisis. The usefulness of Organic Ingredients from plants is investigated for the functioning of a Microbial Fuel Cell, taking advantage of organic waste, and simultaneously demonstrating that anyone is capable to benefit the planet with the study and application of Environmental Chemistry.

1. INTRODUCTION Microbial Fuel Cells are devices that use microorganisms to convert the chemical energy present in a substrate, that is possible thanks to the fact that, under certain conditions, these microorganisms transfer electrons produced by their metabolic activity to an electron (anode) instead of to a natural electron acceptor, such as oxygen. The main factors influencing energy generation are the metabolic pathways that govern the flow of electrons and protons, the influence of the substrate, and the anode potential. At high anode potentials, bacteria can use the respiratory chain in oxidative metabolism and transfer electrons to the anode, however, if the anode potential decreases, the electrons are probably deposited on alternative electron acceptors (sulfate, nitrate, among others) and in its absence, fermentation will occur. [1, 3] ​ Regarding the amounts of electricity generated by microorganisms, in the advances of the last 10 years, the power density of the MFC's increased from 0.1 mW / m2 to 4.3 W / m2. [2] ​ The purpose of the invention of the study and use of CFMs is to gradually introduce renewable energies to combat the energy crisis that the planet is going through, knowing that renewable energies have clean origins, they become inexhaustible and competitive, and in effect, every substrate used in this research comes from organic plant ingredients and it is more than certain that they generate organic waste (compost) forming an endless cycle of plant life. This means the invention of a bioelectrochemical system. [13] ​ 1.2 Investigation Question. Can organic waste (in compost’s form) be used to react with plants and transform into electrical energy? ​ 1.3 Investigation Objective. Verify that the use of organic waste in the form of compost for plants works as a fuel and is effective to run a Microbial Fuel Cell (MFC), and thus obtain electrical energy. ​ 1.4 Significance of the study. By submitting the participation of plants and trees, we will verify their use as fuel and reducers of the emissions of gases that make up the greenhouse effect, the variety of this last form of life is so extensive that quantifying the species of plants that can be used is almost unlimited, leading us to the premise that, no matter where in the world you are, there will always be a possibility of obtaining a substrate to develop an MFC. ​ Finally, the role that environmental chemistry plays is of utmost importance because it allows us to know what are the reactions, evolutions, and interactions in the environment for each chemical process; therefore, the determination of the use and potential of each substrate is dictated by it and is closely linked to the use of the natural resources of our planet to live sustainably and surprisingly, the previous objective is part of one of the achievements of this investigation. ​ 1.5 Literature Review / Concept & Definition. Organic Waste is those materials, products, and waste of human and biological origin, they come from some live organisms where their nature has not been altered. These are organically degraded by the effect of bacteria; they proliferate in proportion to the environment in which they are found. There is a wide variety of wastes, but those that will be used to enhance the electrical activity of the substrates will be: eggshells, fruit, and vegetable remain, and animal waste (bones). [4] ​ The big issue they harbor is the pollution they produce because of their accumulation, which has consequences such as contamination of surface and underground water bodies, air pollution, soil contamination, the proliferation of infectious vectors, and greenhouse gases. [5] ​ That’s the reason why they will be used as compost for MFC substrates since an average person generates 0.63 kg of waste per day and 219 kg per year (According to SEMARNAT 2018, Mexico). We observe how much pollution is generated, knowing that it can be reduced if it is transformed into compost to improve the growth of plants and trees. The previous point leads us to explain the substrate that will be used in this investigation. For centuries the Earth has been dealing with the problem of the emission of gases in to the atmosphere, better known as Greenhouse Gases. If we analyze plant respiration, the tiny pores on the surface of the leaves, called “stomata”, are those that regulate the exchange of gases between plants and the atmosphere, as they absorb oxygen and release CO2 to breathe, and during photosynthesis, it happens otherwise. [6] ​ Now, we can see that the big questions have simple and perfect answers. That small particle that every day destroys our planet called "Carbon" is the food of magnificent creations called "Plants", which, in the last 200 years, we have been disappearing. That is why, by using plants as fuel in MFCs, we combat another major pollution problem, and yes, it is in small quantities, but success is the product of small efforts repeated day by day. ​ Selected plants: 1. Salvia Rosmarinus: It is a very common and abundant condiment for food all over the world, its optimal growth requires plenty of water and sun, so its use would not have many limitations, although in desert places it would have them, which leads to our second option. [9] ​ 2. Cactus Cereus: It was chosen to offer it as an option to people who live in regions lacking water (due to its ability to retain water) and rich in solar lighting. [15] ​ Four cells will be built, two with Salvia Rosmarinus plants and two with Cactus. Only one of each type of plant will have compost added, to study the double bacterial activity compared to the bacterial activity of a normal plant. [17] ​ 1.6 Critical analysis of the literature. The reason why it was decided to make use of the proposed plants, in addition to contributing to carbon emissions, [16] was to contemplate the two scenarios the planet presents. A geographical region where water is abundant and another where it is not, here we reinforce one of the premises of this research "No matter where in the world you are, there will always be a possibility of obtaining a substrate to develop an MFC." ​ And the purpose of the study of the CFM with compost is to demonstrate that the bacterial activity that degrades these organic waste contributes significantly to the increase of electricity generated, promoting its use and counteracting its accumulation on the planet, but at the same time, to certify the optimal conditions of the soil in its 3 components: physical factor (understood by the characteristics of the soil and textures), chemical (the nutrients that it contains and provides), and biological (microorganisms that, thanks to their activity, keep the soil fertile).[7] The appearance of this last member is due to the problems that arise in the agricultural industry worldwide, since population growth, industrialization, and climate change have caused it. [8] ​ According to the research advances, it will be defined if it is necessary to build the last MFC for the purification of wastewater and reduce the limitations of the use of the Salvia Rosmarinus plant as a substrate. [12] ​

2. RESEARCH METHOD 2.1 Investigation design (MFC set up with just one camera) [11]


2.2 Materials. Material specifications by models a) MFC with Herbaceous Plants Substrate and compost (compost of 3 months)

  • Salvia Rosmarinus Plant

  • Compost made from eggshells, fruit, and vegetable remains, and animal waste (bones) 100 gr.

b) MFC with just Herbaceous Plant Substrate

  • Salvia Rosmarinus Plant

c) MFC with Composted Desert Plants Substrate and compost (compost of 3 months)

  • Cactus Cereus Plant

  • Compost made from eggshells, fruit, and vegetable remains, and animal waste (bones) 50 gr.

d) MFC with just Desert Plant Substrate

  • Cactus Cereus Plant

​

3. RESULTS AND DISCUSSIONS 3.1 Investigation Data

3.2 RESULTS AND DISCUSSIONS According to sections 1 and 2 The results obtained after two weeks of constant voltage monitoring and measurement are the next: ​ (1) The hypothesis was approved. The addition of compost to the plant substrate of the Microbial Fuel Cells generates more electricity than proposed, due to the double degradation bacterial activity and improves the soil fertility conditions for the plant. That is, the MFC’s A and C models had the highest voltages. Being model A the highest voltage model. ​ Discussing: The care of each model was the same, all were given the proposed amount of water, all received sunlight in the same proportion and hours. Taking models, A and B. Model A started with a voltage of 0.18 (mW) on Monday, September 13, and in its last measurement, it presented a voltage of 0.87 (Mw) on Wednesday, September 22. On the other hand, model B started with a voltage of 0.13 (mW) and in its last measurement, it presented a voltage of 0.64 (mW). Turning to models C and D, we observe the same situation. Model C had an initial voltage of 0.15 (mW) and a final voltage of 0.84 (mW). Instead, Model D had an initial voltage of 0.11 (mW) and a final voltage of 0.64 (mW) according with the results showed in Investigation Data graphics. This leads us to analyze the bacterial activity in the presence of organic waste (compost).[18] We know that for a plant to obtain nutrients from soil biomolecules, made up of minerals, there must be a process of ingestion and digestion by bacteria, so they are finally delivered to the plants. [14] But what happens if we add compost? Well, let's remember that compost is an organic compost formed through the microbial degradation of materials arranged in layers and subjected to a composition process (oxidation-reduction reactions). [19] This means that there is already a previous existence of microorganisms stimulating the soils, causing the percentage of these to increase and give rise to greater bacterial activity. That is why models A and C produced higher chemical energy than the models that carried out a routine process without fortifiers. Now, focusing on the part of improving soil conditions, the compost promoted a process of "reigniting" (ISIA.21 BIOMUSA October 21st) of microorganisms involved in the nutrient cycle, proliferating better conditions for the development of the plant. This last point explains why during the 17th and 18th of September, where there were colder climates than usual, models A and C (better fortified) had very low consequences, instead of models B and D they suffered changes and voltage drops. ​ (2) The waste of 25% of organic waste generated by one person a day was avoided. ​ Discussing: (According to SEMARNAT 2018, Mexico) Initially, it was considered that one person generates 0.63 kg of waste per day, and 0.15 kg of compost was used in the construction of the MFCs, which mathematically indicates that 25% of organic waste is generated by a single person was rescued. If portions of compost are constantly added to the MFCs, the percentage of salvaged waste increases, and if it is contemplated that not only one person uses these cells, we would be counting on the sum of multiple people who reuse their organic waste in the form of compost, obtaining low pollution caused by the accumulation of organic waste, which was one more reason for the present investigation. (3) It was proven that the maintenance of an MFC can be carried out by anyone, is effective and sustainable. ​ Discussing: Why are MFCs sustainable energy sources?

  • Seeks to improve environmental quality (less pollution caused by organic waste) and combat the energy crisis (promoting clean technologies). [16]

  • Not only does it improve the life of a person, but it also does of a group of people, because the energy supply is not their own, it is shared.

  • Uses natural resources efficiently (soil and improves its conditions, that is, restores small damaged ecosystems)Promotes reuse (the construction material of an MFCs is reused, except for copper cable)

  • Encourages self-sufficiency.

  • Recognizes the importance of nature for the life of all living beings

​ Data collection procedure: The voltage was measured with a multimeter on a 20-volt scale. (mW and W as units) For models A and B, samples were taken every 6 hours from 6 a.m. to 6 p.m., since their highest activity of photosynthesis and metabolism is carried out in the hours where sunlight abounds. 6 For models C and D samples were taken every 6 hours from 6 p.m. until 12 a.m. since their highest activity of photosynthesis and metabolism is carried out during the night. [10] Data analysis techniques: The ambient temperature of the location of the cells was also taken into consideration (this to observe their behavior) and the amounts of water that were used to feed each cell (this to be able to make a judgment about how much is the demand for water). [21] ​ a) COMBINATION OF ANODE AND CATHODE

  • Taking the process of the MFC’s set explained in section 3, these MFCs are working with just one camera, the membrane separates the two cells (anode and cathode).

  • The low wire represents the cathode because it’s away from the plant roots.

  • The high wire represents the anode because it’s very close to the plant roots

  • The electrons flow works the same as a normal MFC with two cameras does. There’s no interference, that’s why I had to set the membrane thoroughly.

​ b) SUBSTRATE USED

  1. Salvia Rosmarinus

  2. Cactus Cereus

  3. Compost made for 3 months

​ c) AMBIENT TEMPERATURE

  • This parameter was taken in mind because the water for the plants is related to the temperature, so they won’t get dry or die. ​ d) QUANTITIES OF WATER USED

  • I watered the Salvia Rosmarinus plants with 100 millimeters once a day at 6 p.m.

  • I watered the Cactus plants with 50 millimeters every other day at 7 p.m.

3. CONCLUSION Environmental Chemistry. This field of science has allowed us to develop this investigation. It is born from the copulation of the environmental necessities we have created. As humans, we don’t overthink too much of those things we do day by day. We don’t take care of how our actions are going to reverberate in the wild. For decades the society has been self-absorbed, and what we have obtained? A world asking for help. This world full of necessities gives us many problems to solve, allows us to change, and the pertinence to revolutionize, but what is this, what is a revolution? Is the social and moral change that takes us to a new lifestyle, and what has changed us? Science. This powerful integration of knowledge plus studies gives us help to change. That’s why we have faculties to improve everything we can complex. ​ Environmental Chemistry is the voice that tells us what we are capable to do with two big things: knowledge and purpose. If we are kind of curious and we want to change the world, Science and specifically Chemistry, are the fields we should take in mind to make our objectives come true. This is revolution. This is Chemistry, this is Environmental Chemistry, that revolutionizes this needy world. If you want to modify your surroundings, this is the way. ​ The first purpose of this investigation was to show that little invents have the potential to transform all we know and that everyone is capable to do it, having in mind one of the biggest issues in the world: energy crisis, the innovation of the Microbial Fuel Cell used in this job increases electrical energy from chemical energy to help to deal with this crisis that we all are going through. ​ We used Environmental Chemistry to work up the plants and their microbial process as a substrate of the MFCs, also we added organic waste and take advantage of the energy they produce. ​ During the research periods we could realize how much these MFCs impact nature, because we didn’t just expose their benefits and advantages, we solved many problems joined to them, like helping to reduce the carbon emissions at using plants, reutilizing objects, and organic waste, improving soil conditions for the proper growth of a plant, and explaining why everyone has the opportunity to help the world by using MFCs. ​ As mentioned, many times before, success is the product of small efforts repeated day by day. This is a recent and new technology, which means, that if an interested group of people settles, as an objective, increasing the MFC’s voltage by building more than one, electricity levels will grow. And if its voltage levels become enough, many electrical devices can work with these cells. The last point will make us closer to the changes, and eventually, to the revolution. ​ The results obtained in this investigation of the use of plants as a substrate in the Microbial Fuel Cells show us another way to produce energy by sustainable sources where all of us are suitable to help the world with a little bit of science, chemistry, curiosity, and purpose.


ACKNOWLEDGEMENTS

I am deeply grateful to my Chemistry teacher, Dr. Irasema Leticia Islas García, for being my supervisor in this Olympiad, for sharing her knowledge in a professional way, her rigorous direction, and time invested. To my house of studies, CECyT 16 from the IPN, which inspires me to always put "Technique at the service of the Fatherland", the motto that prompted me to develop this project. To Incognity Academy instance, who saw in me the potential to represent my country in this Olympiad and allowed me to attest to the long period of preparation I worked. To my father and family, Antelmo Peña, who support and encourage me in every project I undertake. To my friends, who accompany me at all times and represent the greatest moral and human support, Paulina Baltazar, Claudia Pérez, and Tristán Mociño. Finally, to myself, for persisting, resisting, and never giving up since I decided to follow my dreams and live my passion.

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