Ecology of nitrification in oil refinery wastewater treatment systems

Abstract

The diversity and abundance of ammonia oxidizing bacteria (AOB) and Archaea (AOA) were investigated in five oil refinery wastewater treatment plants in the UK using culture-independent molecular techniques. The AOB found in the plants were phylogenetically associated with the Nitrosomonas oligotropha and Nitrosomonas marina lineages and clones related to the Nitrosomonas oligotropha lineage may represent novel AOB species. Putative AOA were found in a trickling filter system and in two activated sludge systems and were phylogenetically placed within marine group 1.1a and terrestrial group 1.1b, Crenarchaeota. Evidence suggests that these are most closely related to AOA from other wastewater treatment systems. Only three of the refinery wastewater treatment plants were nitrifying. AOB numbers quantified through real-time PCR of amoA ranged from 1.54 x 105 cells/mL to 9.49 x 105 cells/mL in the trickling filter system. In contrast, AOB numbers in one of the activated sludge systems ranged from 1.24 x 104 cells/mL to 1.68 x 106 cells/mL, while in the other, AOB numbers ranged from 7.14 x 103 cells/mL to 9.56 x 104 cells/mL, despite showing good nitrification. Conversely, AOA were detected in the trickling filter system at 1.54 x 107 cells/mL. In the activated sludge systems AOA were more abundant than AOB. In the activated sludge system with the higher AOB numbers, AOA abundance ranged from 4.32 x 106 cells/mL to 1.77 x 108 cells/mL, and in the activated sludge system with the lower AOB numbers, AOA abundance ranged from 6.15 x 106 cells/mL to 2.69 x 108 cells/mL. The high abundance of AOA in the nitrifying refinery wastewater treatment systems suggested that AOA may play an important role in nitrification in these reactors. However microautoradiography coupled with CARD-FISH (conducted by Dr Marc Muβmann, University of Vienna) indicated that the AOA were not chemoautotrophic ammonia-oxidizers. Assessment of AOA and AOB abundance in relation to ammonia removal in the treatment plants indicated that ammonia removal was consistent with the AOB numbers detected and thus, AOB are probably responsible for most of the nitrification observed and the overall contribution of putative AOA to nitrification in these wastewater treatment plants appears to be relatively minor. Keywords: Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA), nitrite oxidizing bacteria (NOB), diversity, phylogeny, abundance, real-time PCR, CSAOR (cell specific ammonia oxidizing rate or rates), fluorescence in situ hybridization (FISH), oil refinery wastewater treatment plants.