KLEBSIELLA AND NITROGEN-FIXATION IN PULP AND PAPER-MILL EFFLUENTS AND TREATMENT SYSTEMS

Many Enterobacteriaceae, such as Klebsiella pneumoniae are capable of fixing atmospheric nitrogen for growth. This paper describes a study aimed at establishing the significance of bacterial nitrogen fixation to the effective operation of a kraft mill aerated lagoon. The aerated lagoon treatment system at Tasman Pulp and Paper Ltd, Kawerau, New Zealand, was the focus of experimental work; results clearly show that nitrogen fixation is a significant activity in this system. Relatively high Klebsiella concentrations are present and some isolates can readily fix nitrogen under anaerobic conditions. It appears that Klebsiella spp. are not the major nitrogen fixing bacteria. Most of the activity seems to occur in the first aerated lagoon. In this lagoon alone about 1 tonne of nitrogen per day is being fixed by bacteria. It appears that elevated dissolved oxygen concentrations may inhibit nitrogen fixation. This may be a very important constraint on lagoon operation, especially for the first aerated lagoon, and represents a change to 'current thinking' on aerated lagoon operation. Nitrogen supplementation may also not have the desired effect. The presence of added ammoniacal nitrogen may simply displace bacterially-fixed nitrogen and give no overall benefit.