Microbial fuel cells are considered a source of sustainable energy. Why? 1. They use living organisms as catalysts to generate electricity from certain substrates. 2. They use a variety of inorganic materials as substrates. 3. They can be installed in waste water treatment plants to cleanse water and produce electricity. Which of the statements given above is/are correct?

1. Statement 1 is correct: Microbial fuel cells (MFCs) function by utilizing living organisms (typically bacteria) as biological catalysts. These microbes oxidize substrates (fuel) and transfer electrons to an electrode, thereby enabling the generation of electricity. 2. Statement 2 is incorrect: MFCs primarily utilize *organic* matter as substrates for the microbes to metabolize. While some inorganic compounds might be involved in the electrochemical processes, the main fuel source is typically organic, not a variety of inorganic materials. 3. Statement 3 is correct: A significant potential application of MFCs is their installation in waste water treatment plants. The microorganisms can utilize the organic pollutants present in the waste water as their substrate, simultaneously helping to cleanse the water (bioremediation) and produce electricity, making the treatment process more sustainable. Therefore, statements 1 and 3 are correct.