Rapid start-up of a nitrifying reactor using aerobic granular sludge as seed sludge

Abstract

In this study, the effectiveness of aerobic granular sludge as seed sludge for rapid start-up of nitrifying processes was investigated using a laboratory-scale continuous stirred-tank reactor (CSTR) fed with completely inorganic wastewater which contained a high concentration of ammonia. Even when a large amount of granular biomass was inoculated in the reactor, and the characteristics of influent wastewater were abruptly changed, excess biomass washout was not observed, and biomass concentration was kept high at the start-up period due to high settling ability of the aerobic granular sludge. As a result, an ammonia removal rate immediately increased and reached more than 1.0 kg N/m(3)/d within 20 days and up to 1.8 kg N/m(3)/d on day 39. Subsequently, high rate nitritation was stably attained during 100 days. However, nitrite accumulation had been observed for 140 days before attaining complete nitrification to nitrate. Fluorescence in situ hybridization analysis revealed the increase in amount of ammonia-oxidizing bacteria which existed in the outer edge of the granular sludge during the start-up period. This microbial ecological change would make it possible to attain high rate ammonia removal.

Efficient and automated start-up of a pilot reactor for nitritation of reject water: From batch granulation to high rate continuous operation

“…The applied automated SBR-type strategy for starting-up nitritation systems treating reject water is an attractive alternative for full scale installations, because (i) a short period of operation was required if compared with continuous-type start-up strategies 13 based on AC addition and (ii) the absence of nitrate in the effluent was assured by the control strategy.…”

“…Once the selection pressure applied with the shear stress and the short settling times is relaxed, heterotrophic bacteria could trigger the development of non-compact biomass which leads to a reduction of the settling velocity, which in turn produce the eventual washout of the biomass. Nevertheless, if the granules are colonized by slow-growing bacteria, like for instance nitrifying bacteria, the possibilities of destabilization of the granular sludge are rather reduced and stable operation is usually reported [11][12][13]. Therefore the operation mode with such 3 granular reactors might be switched to continuous, just after convenient granule formation under sequencing batch mode operation.…”