Do you know how to deal with your discarded Printed circuit board?
2008-08-12

                                                                             Do you know how to deal with your discarded Printed circuit board?        There are three most important types of circuit boards: Breadboard¡¢Stripboard¡¢Printed Circuit Board£¨PCB£©.        During the three types of the circuit boards, Printed circuit board is the most commonly use nowadays.        A printed circuit board, or PCB, is a self-contained module of interconnected electronic components found in devices ranging from common beepers, or pagers, and radios to sophisticated radar and computer systems. The circuits are formed by a thin layer of conducting material deposited, or "printed," on the surface of an insulating board known as the substrate. Individual electronic components are placed on the surface of the substrate and soldered to the interconnecting circuits. Contact fingers along one or more edges of the substrate act as connectors to other PCBs or to external electrical devices such as on-off switches. A printed circuit board may have circuits that perform a single function, such as a signal amplifier, or multiple functions.        The substrate most commonly used in printed circuit boards is a glass fiber reinforced (fiberglass) epoxy resin with a copper foil bonded on to one or both sides. PCBs made from paper reinforced phenol resin with a bonded copper foil are less expensive and are often used in household electrical devices.        Because of the raw material of the printed circuit board—PCBS, While the printed circuit board take us much convenience, it also posed a problem to us which is the most important nowadays—environment pollution.        PCB pollution was once considered a problem of developed countries that have massively produced and used PCBs. However, recent surveys indicate that nations in the torrid zones of lower latitudes are also being polluted. One reason for this pollution is the export of PCB-polluted products from developed countries to the developing world. Exported products are still being used and some of them are discarded in inappropriate ways. PCB pollution is no longer a problem that can be addressed by the efforts of one single nation. Now, worldwide cooperation is required.        A survey of the year-to-year changes in the concentrations of PCBs in the environment indicates that there was a peak in the 1970s, and then after that, concentrations began to decline following the ban on production. Concentrations are still declining, but at a slower pace compared to other oregano-chlorine pesticides. A monitoring report on mink whales in the Antarctic Ocean shows that concentrations have not changed in the past 10 years, but rather have shown a tendency to increase. This suggests that pollution sources have not yet been completely removed and also indicates that PCBs are very slow to decompose.        Once PCBs are emitted into the natural environment, it takes a very long time for them to decompose. We must not allow any more release of PCBs into the environment.         PCB's are highly resistant to degradation, once these are in the environment, these are sorted onto the particles including sediments, suspended particulates and may bio-accumulate in organisms. Degradation of PCB's in the environment is dependent on the degree of chlorination of the biphenyl. The persistence of PCB's congeners increase as the degree of chlorination sets. In the atmosphere, the vapor phase reaction of PCB's with hydroxyl radicals (which are photo chemically formed by sunlight) may be the dominant transformation process. In the aquatic environment, hydrolysis and oxidation do not significantly degrade PCB's. Photolysis appears to be the only viable a biotic degradation process of PCB's in the water.        It has been established that microorganisms degrade mono, and tri-chlorinated biphenyls relatively rapidly and tetra-chore biphenyls slowly, whilst higher chlorinated biphenyls are resistant to biodegradation. Chlorine substitution positions on the biphenyl ring play an important role in determining the biodegradation rate. The PCB's containing chlorine atoms in the Para positions are preferentially biodegraded. Higher chlorinated congeners are bio-transformed an aerobically, by reductive dechlorination, to lower chlorinated PCB's, which may then be biodegradable by aerobic processes.        PCBs are now burned or buried, but there have been leaks. And if they are not burned at a high enough temperature, that burning can produce toxic by-products.        But if you use natural bacteria, you don't have to transport contaminated soil or burn PCBs, this would cost less and there would be no toxic by-products....In essence, we hope to be able to reduce pollution cleanly and affordably.