Anammox Granules Acclimatized to Mainstream Conditions Can Achieve a Volumetric Nitrogen Removal Rate Comparable to Sidestream Systems.

The implementation of mainstream anammox has gained increasing attention. In this study, the feasibility of using sidestream anammox granules to start up mainstream reactors was investigated by comparing two switching strategies. A maximum nitrogen removal potential of 3.6 ± 0.2 kg N m-3 d-1 was obtained for the reactor after direct switching to mainstream conditions (70 mg TN L-1, 15 °C). Nevertheless, the reactor preacclimatized to 25 °C (Ma) exhibited a higher nitrogen removal potential of 7.0 ± 0.3 kg N m-3 d-1 at 15 °C, which is the highest volumetric nitrogen removal rate of mainstream anammox reactors to date. Candidatus Kuenenia stuttgartiensis was identified as the dominant anammox bacterium, and its relative abundance in two reactors remained stable throughout the whole operation (200 days). Moreover, with the aid of acclimatization, the activation energy was reduced and the specific growth rate became higher. These results indicated that the physiological evolution of the dominant anammox bacterium instead of interspecies selection was the main reason for the high potential during the switch to mainstream conditions. Therefore, using sidestream anammox granules as seed sludge to start up mainstream reactors was demonstrated to be feasible, and a switching strategy of acclimatization at 25 °C was recommended.

Long-term effects of copper nanoparticles on granule-based denitrification systems: Performance, microbial communities, functional genes and sludge properties.

The widespread use of copper nanoparticles (CuNPs) has attracted increasing concern because of their potential effects on biological wastewater treatment. However, their effect on granule-based denitrification systems is unclear. Hence, the effects of CuNPs on denitrifying granules were investigated during long-term operation. The results showed that 51.9% of nitrogen removal capacity was lost after exposure to 5 mg L-1 CuNPs, with the amount of Cu(II) gradually increasing with elevating CuNP levels. Moreover, the relative abundance of denitrifying bacteria (Castellaniella) and denitrifying functional genes (nirK, napA, narG and nosZ) obviously decreased. Meanwhile, the specific denitrification activity, the content of extracellular polymeric substances and dehydrogenase activity decreased by 44.0%, 15.2% and 99.9%, respectively, compared to their values in the initial sludge. Considering the downtrend in the abundance of copper resistance genes, it was deduced that the toxicity of CuNPs was mainly or at least partially due to the release of Cu(II).