Development of chitosan-magnetite aggregates containing Nitrosomonas europaea cells for nitrification enhancement

A cell suspension of the nitrifying bacterium Nitrosomonas europaea obtaine d after 96-h cultivation was subjected to magnetic separation using chitosa n-conjugated magnetite particles (chitosan-magnetite), which have the abili ty to form aggregates with microbial cells. An equilibrium condition was ob tained at room temperature after 30 min and over 90% of the cells were reco vered when the chitosan-magnetite concentration was 200 mg/l. The relations hip between the cell concentration in the supernatant in equilibrium and th e number of cells adsorbed per 1g chitosan-magnetite was expressed by a Fre undlich-type adsorption equation. A high nitrifying bacterium activity yiel d was obtained with a chitosan-magnetite concentration between 100 and 200 mg/l. Repeated batch culture resulted in more N. europaea cells accumulatin g on the aggregates and as a consequence their nitrification activity impro ved further. The chitosan-magnetite/cell aggregates were recovered and empl oyed to remove ammonia from artificial wastewater together with PVA-alginat e gel beads containing the denitrifying bacterium Paracoccus denitrificans. A higher ammonia removal rate was achieved under aerobic conditions in com parison with that obtained when N. europaea and P. denitrificans were coimm obilized in PVA-alginate gel beads.