Development of Simple Denitrification System With Autotrophic Bacteria for Developing Countries

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A simple denitrification process suitable for developing countries was proposed by employing autotrophic Thiobacillus dentrificans. The effect of nitrate concentration, phosphorus concentration, alkalinity and inhibitants on the rate of denitrification was investigated with a column packed with sulfur and limestone particles involving denitrification bactaeria, and the following results were obtained.1) The denitrification proceeded without substrate inhibition up to 1,000 g-nitrate-N/m^3, which demonstrated that most of the wastewater cold be treated without dilution.2) The minimum phosphorus concentration was evaluated under constant pH controlled by borate-buffer showing that 1 mg-P/m^3 was enough for the present process. However, higher phosphorus concentration was necessary when borate buffer was not used. This was because pH at the reaction site, probably the boundary between biofilm and surface of sulfur particles, may drop due to the release of proton as a result of denitrification.3) The minimum alkalinity was found as 600g-CaCO_3/m^3 for load of 420g-N/(m^3/d). The inhibition with fluoride and Ni was not observed until 90 and 3 g/m^3, respectively.It was concluded that the present system was suitable for developing countries because it was simple without any special instruments or technical care and it offered stable performance with slight request for phosphorus even in concentrated wastewater.