Feasibility study of complete nitrogen removal from domestic wastewater byconsequent nitrification-denitrification using immobilized nitrifiers in gel beads

A two-stage process for complete removal of nitrogen from domestic wastewat er is proposed in this paper. The two stages of this process are an aerobic stage using nitrifying microorganisms immobilized in gel beads and a conve ntional anoxic stage. The possible application of gel-entrapped biomass for high-rate, complete nitrogen removal from domestic wastewater was verified through theoretical and experimental work. Two assumptions were confirmed in the present work: (a) substances present in domestic wastewater do not i nhibit nitrification, and (b) heterotrophic biomass that builds up on the s urface of nitrifying beads is not expected to affect ammonium oxidation or remove a significant part of the biochemical oxygen demand required for den itrification. The effect of the attached heterotrophic layer on system perf ormance was evaluated through theoretical prediction and short-term experim ents. Calculations indicated that complete nitrogen removal could be achiev ed if the heterotrophic layer on 2-mm gel beads is less than 12 mu m thick. The heterotrophic biofilm observed in the experiments did not homogeneousl y spread over the entire bead surface. it was found that attached growth of heterotrophs is affected by mixing intensity and type of carrier material.