Water Pasteurization with Heat Regeneration

I wasn't sure where to put this discussion. I did a search on water pasteurization, and it seems there is very little information beyond a few discussions on using solar heat for this purpose.

I wanted to point out that it's possible to pasteurize water very efficiently by setting up a counterflow heat exchanger to preheat the cool unpasteurized water with the hot pasteurized water leaving the heater. It's a solution that many people seem to miss that can increase yields 5 fold or more. My calculations show that 1 pound of dry biomass burned in a small efficient furnace such as a rocket furnace or updraft gasifier furnace can easily pasteurize 20 gallons of water. Many sources of otherwise wasted heat can be used for this purpose as well. For example, use the exhaust from a wood stove, or use the heat given off a stationary generator during operation. This principle could also be applied to a solar water heating system to increase the yield of pasteurized water many fold. Also, note that this process can be used not only to pasteurize water from a nearby body of fresh water, but also used to process water taken from very shallow wells that would otherwise not be potable. Finally, passing the pasteurized water through a simple filter system such as sterilized sand followed by crushed charcoal should make for good quality potable water.

Again, it's a simple solution, but we often miss the obvious.

The system needs to ensure that the water is "pasteurized" if you are counting on safe drinking water. Therefore, the system needs to be well designed in regards to residence time/heat to kill the bio hazards etc. If you have a little extra electricity a UV filter can do a great job on biological risks with very little energy. What your talking about sounds like a batch type operation which could be okay if you didn't need much drinking water. Also is the approach practical in the none heating season when you don't need to use the stove?

J Abatis wrote:The system needs to ensure that the water is "pasteurized" if you are counting on safe drinking water. Therefore, the system needs to be well designed in regards to residence time/heat to kill the bio hazards etc. If you have a little extra electricity a UV filter can do a great job on biological risks with very little energy. What your talking about sounds like a batch type operation which could be okay if you didn't need much drinking water. Also is the approach practical in the none heating season when you don't need to use the stove?

Sorry, I missed this question. A thermal mass can be used with a thermostat to control a pump that sends water through the heat exchangers. A pump that operates at a fixed rate and with heat exchangers sized for this flow rate will ensure the water is properly pasteurized. Let's say a mass of water is heated to 200F to actuate a thermostat that starts a water pump. The water flows through the heat exchangers that are sized to take the water to the proper temperature for the required time. As long as the thermal mass is sufficient, the temperature high enough, heat exchangers large enough, and water flow rate not excessive, then it should work just fine.