COUPLED NITRIFICATION-DENITRIFICATION PROCESSES IN A MIXED CULTURE OFCOIMMOBILIZED CELLS - ANALYSIS AND EXPERIMENT

In this work we suggest, analyze and test a novel design of nitrogen r emoval system that utilizes coupled nitrification - denitrification re actions in a mixed culture of immobilized cells. Two practical designs are considered: the technologically -simple pellet with uniform distr ibution of mixed cultures and the more complex scheme of a core and a shell structure with segregated populations. First, we analyze the rea ction-diffusion model of cell growth and substrate consumption in an i mmobilized commensalystic system. Detaled kinetics, that account for p H-effect within the pellet and self-inhibition of the nitrification an d denitrification rates by their substrates, has been employed. Next, we demonstrate the technology by comparing the performance of alginate gel pellets that were seeded either with nitrifiers or with a mixed c ulture, of nitrifiers and denitrifiers, or with segregated cultures. M easurements of ammonium and nitrate concentrations in parallel sequenc ing batch reactors demonstrate that while the nitrification rates are similar in the three pellets, there is no build-up of nitrates in the mixed or segragated culture processes: there were no significant diffe rences between the latter two processes.