Microbiology of high-sodium-nitrite-wastewater treatment

Abstract

A microbiological study conducted as a complement to kinetic studies of biological denitrification as a process for treating high-sodium-nitrite wastewaters generated from ship-boiler-tube cleaning is described. The number, genera, and denitrifying capabilities of the organisms inhabiting anoxic suspended-growth reactors used in the kinetic studies were evaluated for four experimental phases. The results regarding the enumeration of bacteria supported the findings of the kinetic studies as follows: (i) the better nitrite-removal efficiencies observed in the nitrification/denitrification system as compared with direct denitrification were confirmed by the presence of larger populations of organisms capable of completely reducing nitrate or nitrite; (ii) the presence of metals in concentrations associated with boiler-tube wastewater did not affect removal performance in the nitrification/denitrification systems, nor did it affect the density of complete denitrifiers; (iii) increasing sludge ages resulted in increasing nitrite-removal efficiencies as well as populations of complete denitrifiers; and (iv) a decrease in nitrate-removal efficiencies when the actual wastewater was introduced to a system that had been acclimated to the synthetic wastewater coincided with a reduction in the number of complete denitrifiers. Regarding the types of organisms found in this study, denitrifying strains of Alcaligenes and Pseudomonas were always present in the anoxic reactors along with other denitrifying and non-denitrifying bacteria of the same genera, or other genera such as Acinetobacter and Flavobacterium. However, members of the genus Alcaligenes were the only complete denitrifiers found in the anoxic reactors, and hence they are likely to play a key role in the denitrification process.