Microbial characteristics in a fixed-biofilm BNR process for treatment of low organic sewage

Microbial characteristics of a fixed-biofilm process packed with hollow-type ceramic media were studied for treating low organic level sewage (average TCOD/NH4(+)-N ratio = 3.4), and an easy monitoring method such as a bio-index was suggested. The fractions of autotrophs and heterotrophs were directly affected by changing the organic surface loads in the aerobic reactors. After 90 days of operation, the amount of attached biomass was maintained constantly with a stable nitrification rate and low effluent NH4(+)-N concentration. At this point, the dominant diatoms observed were Fragilaria sp. in the second anoxic reactor, Cyclotella sp. in the second anoxic and aerobic reactors, and Navicula sp. in the first aerobic reactor. Specific protozoa (Euglypha sp., Arcella sp. and Colepus sp.), which were considered predators of nitrifiers, were observed under high nitrification rate and were used as a bio-index and indicators of nitrifying biofilm formation and low effluent NH4(+)-N concentration in the fixed-biofilm BNR process.