Advanced Ammonia Oxidation by Adding Metabolic Mediator

Abstract

In ammonia-oxidizing autotrophic bacteria, coenzymes such as NAD⁺ and NADP⁺ act as intermediates linking the electron transfer system in the cell membrane and the CO₂- fixing Calvin cycle in the cytoplasm. The influence of these physiologically active substances on the growth of ammonia-oxidizing bacteria (AOB) and their nitrification ability was examined by adding a trace amount of NAD⁺ or NADP⁺ into a wastewater treatment system. In pure cultures of Nitrosomonas europaea IFO 14298, when NAD⁺ or NADP⁺ were added in the wastewater oxidation of ammonia increased comparing a control culture, and the strain grew 1.6-1.9 times faster than that of the control. Similarly, in activated sludge, both the rate of formation of NOx-N and the growth of AOB increased when NAD⁺ or NADP⁺ were added. Furthermore, ammonia monooxygenase-coding mRNA (amoA-mRNA), an estimate of ammonia oxidation activity, increased over time only in the presence of these physiologically active substances. When activated sludge previously exposed to NAD⁺ or NADP⁺ was used for new sewage, these desirable effects continued. The types of AOB affected by adding NAD⁺ or NADP⁺ were characterized using TaqI -based T-RFLP (terminal restriction fragment length polymorphism) of amoA-mRNA. The results indicated that AOB with fragment sizes of 219 bp and 491 bp were the active species in the NAD⁺ and NADP⁺-containing systems, respectively. These results suggest that the simple technique of adding a trace amount of NAD⁺ or NADP⁺ into activated sludge can result in increased nitrification and the selective growth of a particular AOB.