Ethanol is a biomass which is a cleaner fuel. It can burn completely so, it reduces air pollution and global warming. Ethanol was produced by raw materials from agricultural crops. It classified into three types include sugar (sugar from beets and molasses), starch (tapioca, potatoes, and whole grains) and byproducts from agriculture (bagasse, rice straw, and corn). In the production of ethanol, it causes wastewater which has BOD and COD around 40000-70000 and 100000-150000 mg/l, respectively. Moreover, wastewater has high concentrations of nitrogen and phosphate and has dark brown to black. Those things affect to water quality and scenery of water source thus, it cannot be released into water bodies.
The process for decolorization of wastewater was divided into three processes. First is the Physical process such as, adsorption with activated carbon which is high porosity and ability to absorb color. But, the problem of this process is a blockage at the surface layer of charcoal and high cost of recycling. Second is a chemical process such as coagulation and flocculation by using alum, lime and iron compounds. This method is highly effective, but it will be much sludge cause to find a way to dispose of the sludge. The last is the biological process which was applied to remove the color of wastewater, such as using algae, bacteria and fungus. Algae are effective to reduce colors and not add chemicals to the environment, but there are limits on the temperature, pH, nutrients, and inhibitors. The using of bacteria is the effective process but it cannot withstand the high concentrations of toxic while the fungus has a few limitations and has durable than bacteria. So, it is appropriate to reduce color. From this capability, the fungus has been applied in the treatment of waste water from the production of ethanol.
Microorganisms can use free cells or immobilized cells for reducing the color. When comparing it, free cells have a leakage and obstruction of cells while immobilized cells have a high effective and no leakage and obstruction problems. The popular technique used is Entrapment which is available to all microorganisms but it has the limitation of cell loading and cell leakage. The other technique is Encapsulation. It has not the limitation of cell loading but it causes to be the weak beads. The problem of Entrapment and Encapsulation cause the development a new technique for immobilization cells by integration two methods together which is Hybrid Immobilization. Beads from this technique are highly effective, no limitation of cell loading and can protect the leakage of cells.