1. Microbial fuel cells (MFCs) use living microorganisms such as bacteria as catalysts to generate electricity from certain substrates. The microorganisms in the anode chamber of an MFC oxidize the organic matter in the substrate and produce electrons and protons. The electrons are transferred to the cathode chamber through an external circuit, generating electricity. This process is sustainable because the microorganisms can be replenished, and the substrates can be sourced from renewable sources such as wastewater, agricultural waste, and food waste.

2. MFCs can use a variety of inorganic materials as substrates, including metals, minerals, and salts. Some MFCs have been shown to generate electricity from inorganic substrates such as acetate, formate, and hydrogen gas. This widens the scope of substrates that can be used to generate electricity in MFCs and makes them more versatile as a sustainable energy source.

3. MFCs can be installed in wastewater treatment plants to cleanse water and produce electricity simultaneously. In such systems, the wastewater acts as a substrate for the microorganisms, which break down the organic matter in the water and produce electricity in the process. This not only generates sustainable energy but also helps to clean up wastewater, which is a significant environmental concern.

Therefore, all the statements are correct, and together they provide a strong case for the suitability of MFCs as a source of sustainable energy.