A biofilm reactor utilizes colonies of bacteria in laboratory and industrial processes to produce substances such as vinegar and acetic acid. It is also used to make ethanol, lactic acid, butanol, fumaric acid, and succinic acid. Biofilm is also used regularly for wastewater treatment, and the bacteria can either absorb or break down toxic substances in the water. The different kinds of biofilm reactors include membrane, fluidized bed, packed bed, airlift, and upflow anaerobic sludge blanket reactors.
Inside a biofilm reactor, bacterial cells grow within a structural matrix and adhere to a surface. Individual cells must first attach to a surface, either by electrical charge or chemical attraction, or because of the concentration of nutrients near this surface. Cells must be irreversibly attached to the surface to form a biofilm, which happens when extracellular polymeric substances (EPS) are produced. Biofilms develop in the reactor as water channels form within them so nutrients can reach subsurface areas. As nutrients are depleted, cells that focus on producing EPS then break down the matrix for food and to escape.
Nutrients, temperature, and the nature of the cells affect the quality of a biofilm reactor. Membrane biofilm reactors, in which the film grows on a gas-transfer membrane, are one type. A gas-phase substrate, which can be either hydrogen, oxygen, or methane, ammonia, or carbon dioxide, is used by the bacteria. Contaminants, such as nitrates, nitrites, chlorates, bromate, arsenante, selenate, and chloroform, can be reduced into harmless products through this process.
Media are mechanically stirred in a continuous stirred tank reactor, but the mixture cannot be agitated when there is a supporting structure for the film. A packed bed reactor is first filled with support materials before the bacteria are introduced and is fed from the bottom up with nutrients. Bacterial cells tend to grow quickly in this type of biofilm reactor. Top bed reactors are fed from the top, but not every cell in the film gets the nutrients. Other reactors include fluidized bed, suitable for breaking down toxic phenolic chemicals, and airlift reactors, which mix air from the bottom with liquid in two tubes.
For water treatment, upflow anaerobic sludge blanket reactors process wastewater and industrial effluents. A biofilm reactor can also be used to break down gases as well as odors. Overall, it can treat large volumes of water or fluid at high rates, creating an efficient industrial process.
By Andrew Kirmayer