Phosphorus removal and denitrification using iron and wood as electron donors were examined in a laboratory-scale biological filter reactor. Phosphorus removal and denitrification using iron and wood continued for 1,200 days of operation. Wood degradation by heterotrophic denitrification and iron oxidation by hydrogenotrophic denitrification occurred simultaneously. In the biofilm inside the wood, not only heterotrophic denitrification activity but also sulfate reduction and sulfur denitrification activities were recognized inside the wood, indicating that a sulfur oxidation-reduction cycle was established. Sulfate reduction and denitrification were accelerated with the addition of cellulose. Microbial communities of sulfate-reducing bacteria by PCR primer sets could be amplified in the biofilm in the reactors. The dissimilatory sulfite reductase gene and the 16S rRNA gene of six phylogenetic groups of SRB in the reactors were analyzed. Some SRB group-specific primers-amplification products were obtained inside the wood and around iron.

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