Assessment of denitrification by the ordinary heterotrophic organisms in an NDBEPR activated sludge system.

The purpose of this study was to isolate and characterise the ordinary heterotrophic organisms (OHOs) present in a NDBEPR system in order to gain a better understanding of the organisms involved in denitrification as well as a more holistic and accurate evaluation of the OHO fraction attributable to denitrification in such a system. Heterotrophic bacteria were isolated from the pre- and secondary anoxic zones of the Darvill NDBEPR process and characterised according to their ability to reduce nitrates and/or nitrites under anoxic conditions. Results showed that the OHO fraction is more complex than currently accepted and, with respect to denitrification, can be more accurately subdivided into five functional groups, four of which interactively contribute to denitrification occurring in the system and one group that are non-denitrifying. These groups were defined as true denitrifiers (bacteria capable of both nitrate and nitrite reduction), incomplete denitrifiers (bacteria that reduced nitrates to nitrites with no further reduction of the nitrites produced), incomplete-nitrite reducers (bacteria capable of both nitrate and nitrite reduction, however, exhibiting severe inhibition of nitrite reduction by nitrates), exclusive nitrite reducers (bacteria only capable of reducing nitrites) and non-denitrifiers (bacteria not capable of nitrate or nitrite reduction).

Intracellular bioaccumulation of zinc by an Enterobacter species.

Bacterial strains tolerant to the presence of 100 mg/l zinc ions were isolated from a water reclamation system. Each of the organisms were screened for their ability to accumulate zinc at the above mentioned concentration. The organism capable of maximum zinc accumulation was identified as an Enterobacter species and intracellular zinc deposition by this micro-organism was determined using energy dispersive X-ray analysis, transmission electron microscopy and a metal-staining technique at the light microscopy level. Further studies revealed that growth and glucose utilization by this isolate were inhibited in the presence of zinc, compared to a control culture grown in the absence of zinc.

Bacterial bioabsorption of nickel from industrial cooling water.

Three bacterial strains tolerant to the presence of 100 mg litre(-1) nickel ions were isolated from a water reclamation system. Each organism was tested for ability to accumulate nickel at the above-mentioned concentration. The organism capable of maximum nickel accumulation was identified as an Enterobacter sp. and intracellular nickel deposition by this microorganism was determined using energy dispersive X-ray analysis (EDAX) and transmission electron microscopy. A metal-staining technique for light microscopy was developed. Further studies revealed that growth and glucose utilisation by this isolate was inhibited in culture by nickel.