My employer operates a biological water filtration plant. The first stage of filtration has the raw water passing through a filter embedded with bacteria, the processes used here is aerated biological treatment where oxidizing processes (bio-oxidation) are used and the microbes gain energy when they transform the ions from a reduced to an oxidized state. Specifically in the first filter the bacteria oxidize all ferrous oxide to ferric oxide (Fe^+2 to Fe^+3) which is caught in the filter and when the water moves on to the next stage it is completely free of iron. The large amount of rust build up in the first filter must be periodically cleansed by backwashing. When water is pumped backward through the filter it comes out with both a very very high concentration of Fe^+3 and a portion of the bacteria population. What I am looking for is a way to reduce the iron in a sample of this backwash water back to Fe^+2. It has been suggested that perhaps an alternative energy source such as glucose could be added then the sample sealed so the bacteria would use all of oxygen present and create anaerobic conditions. In this environment might the very same bacteria that oxidized the iron begin to reduce it? If not, are there other suggestions on how to accomplish this?