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Question 1186

Could microwave heating be used to treat sewage to wipe out disease organisms in it? — KO
While microwave heating could be used to sterilize sewage, it's not the most energy efficient or inexpensive technique. Microwave heating is really only worthwhile in cases where you can't reach the inside of an object directly—as is the case in most solid foods. Since sewage is essentially liquid, it can be heated quickly and efficiently by passing it close to a hot surface. Just about anything can be used to heat that surface—electricity, natural gas, coal, you name it.

But to be even more energy efficient, the sewage that was just sterilized a minute ago and is still hot can be used to heat the sewage that is about to be treated! A well designed thermal treatment facility could employ "counter-current exchange"—that is it could pass the hot, treated material through a heat exchanger to allow it to transfer most of its excess heat to the cooler, untreated material that is about to be sterilized. By recycling the heat in this manner, the facility could avoid having to burn so much fuel. The only drawback with this technique is that the heat exchanger must be leak-proof—it must keep the sterilized material from touching and being contaminated by the unsterilized material.


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