Organic matters, which are degraded comparatively easily by microorganisms contained among them in effluent, are usually called biodegradable organic matters. The water quality index is expressed as Biological Oxygen Demand (BOD). Much of the wastewater from industrial effluent contains organic matter. In order to remove such organic matter, decomposition and mineralization can be efficiently performed by microorganisms, specifically bacteria.
Bacteria are classified broadly into two types: aerobic bacteria, which require oxygen for survival, and anaerobic bacteria, which thrive in the absence of oxygen. The treatment system of industrial effluent differs depending on which bacterial medium is mainly employed. Although treatment by aerobic bacteria is conducted at a high speed, the supply of oxygen (usually air) is indispensable. Electrical expenses is provided under administrative and maintenance expense. Likewise, the drawback of the treatment method is the mass generation of sludge. Further expenses remain for the industry to deal with. On the other hand, in the case of anaerobic treatment using bacteria, the overall activity is slow, the entire duration of the treatment process is longer, and the rate of removal of organic matter is low, as well. However, the benefit of the system is the minimal generation of sludge only. As a result, the device for the increase of processing efficiency has so far been tried tremendously. Thus, one point of view being considered is the combination of aerobic and anaerobic treatment processes.
The consideration of both aerobic and anaerobic treatments has both merits and demerits. It is a general fact that anaerobic biochemical treatment by using anaerobic bacteria is better for high-concentration organic effluent. A familiar example is that human excrement and sewer sludge, which are highly organic in concentration, are treated anaerobic. Whereas municipal wastewater containing lower organic content, is treated aerobically. It is the usual way of treating common wastewater. The decomposition reaction of organic matter, which is conducted under oxygen-free environment, is quite complicated as compared with the treatment system under the presence of oxygen. The primary feature is the production of many kinds of substances. The main products are methane and carbon dioxide. Other by-products include ammonia, hydrogen, and hydrogen sulfide. Especially, since natural fuel sources, such as methane and hydrogen, are generated, the viewpoint of bio-energy comes in. There are various practical examples for production of methane as fuel source.
The type of bioreactor in anaerobic treatment is a big factor which influences reaction efficiency. In the conduct of design and operation management, understanding about a reactor is important. There are several types of reactors. The UASB (Upflow Anaerobic Sludge Blanket) method developed in the Netherlands increases bacterial concentration per unit capacity dramatically as compared with the previous methods. That is, this method receives a high assessment in that it can treat effluent efficiently with compact equipments. Especially, case examples in food and beverage effluent fields using the method are increasing. The feature of this system is the utilization of self-granulating sludge by contriving the structure in a reactor or the flow of water without supplying a carrier. While development of such a reactor advances, the efficiency of anaerobic treatment has been improved by solving the problems of operation management. Above all, regarding the application of the solubilization technology to solid waste or wastewater containing much SS, remarkable researches and developments are also reported.
In this special edition of anaerobic treatment of industrial effluent, food with high BOD concentration, beverage, and effluent from chemistry facilities have been taken as typical examples. It goes without saying that other components, be it organic or inorganic, are also contained in effluent. Since there are some components, which inhibit the activities of bacteria, a prior examination is required if anaerobic treatment can apply to all organic wastewater. Based on the background mentioned above, significant information from the fundamentals of anaerobic treatment to application is covered here. I hope that this will help people who are engaged in practical business, not only in their research and development but also in their design and operation.