I posted this before, but I will post it again. It is my write up on the different ways to generate ozone and the pros and cons of each. How long ozonation will take depend on the type of unit, ozone concentration and flow rate.
There are three ways to generate ozone: Ultraviolet (UV), hot corona and cold corona. Here are the pros and cons to each:
UV- Pros: The least expensive of the units averaging around $300. They will form higer allotropes of oxygen though, known as cascading ozone or polyatomic oxygen molecules. Cons: These units mimick sunlight, which means they also form nitrogen and sulfur oxides in the presence of air, which form the corresponding acids when reacted with water. The tubes deteriorate with time reducing output, and they are very difficult to regulate their output. They ARE NOT recommended for therapy internally.
Hot corona- Pros: A mid range priced machine, averaging $500-900. These machines are stronger than UV, and more easily regulated. Cons: They also form nitrogen and sulfur oxides in the presence of air. They only form O3, which is not as strong as the higher allotropes. They are not recommended for therapy internally.
Cold corona- Pros: Can be regulated and does not form acidic precursors in the presence of air. Forms O3 - Ozone and the higher allotropes. This is the type of ozone generator recommended by German doctors for therapy. Cons: The most expensive units and hardest to find. Average cost for these units is $1500-15,000.
One of the biggest problems with trying to find a cold corona unit is that many manufacturers selling "cold corona" units actually have hot corona units. The confusion comes from the tube design. In general a hot corona design has one dielectric between the electrodes. Cold corona tubes use two dielectrics preventing exposure of the gas to either of the electrodes. The problem is that is all based on the older pig iron high voltage transformers. With the introduction of the newer high frequency solid state transformers all of the above gets thrown out. The higher frequency drops the resistance of the dielectrics in essence converting the cold corona tube back in to a hot corona design. Manufacturers use these transformers because they are lighter, smaller and allow for wider spacing between the electrodes. So unles you know what you are looking at it is hard to tell if a "cold corona" device is really a cold corona device.
As far as building them, it is a really simple thing to do, just very tedious. It is basically two metal electrodes insulated with two pieces of glass encased in a tube with hose barbs on each end to allow passage of the oxygen. The metal electrodes are connected to a high voltage transformer (pig iron type)with a voltage of 7500-9000V 20-30ma. You can use neon transformers for this.
As for the oxygen, welding supply companies provide the tanks through either purchase or rental. All oxygen sold has to be medical grade regardless of its use under Federal law. You will have to buy a regulator though since they do not rent these. But a hose barb for the regualtor to fit your tubing for the unit. Altogether the tank, regulator and hose barb should run just under $200.