Insights into the Response of Anammox Sludge to the Combined Stress of Nickel and Salinity

Anaerobic ammonium oxidation (Anammox) is a promising technology being applied to treat industry wastewater, while the commonly coexistent heavy metals and salinity usually become the challenging issue to be addressed. In this study, the responses of anammox sludge to the combined stress of Ni(II) and high salinity(20‰), in terms of performance, activity, functional enzyme and EPS were investigated in a holistic manner. It turned out that low Ni(II) concentration (0.2 mg·L -1 ) together with high salinity(20‰) showed insignificant effect on the performance of Anammox process, while a decreased nitrogen removal by 46.96% was observed when the Ni(II) concentration further increased to 1 mg·L -1 . It should be pointed out that the Anammox process exhibited a good robustness evidenced with rapid recovery to achieve 89.13% of nitrogen removal efficiency and 1.21 kg·m -3 ·d -1 of nitrogen removal rate within 40 days. Ni(II) concentration was revealed to play a more important role in the combined stress of Ni(II) and salinity to the specific activity of anammox sludge. The functional enzymes related to nitrogen removal, e.g. nitrite reductase (NIR), hydrazine oxidase (HZO) and heme c were found to be inhibited by the combined stress of Ni(II) and salinity, with decreased activity by 49.54%, 39.39% and 45.88%, respectively. However, the enzyme related to growth, e.g. alkaline phosphatase (AKP) and nitrate reductase (NAR) appeared to be enhanced. The EPS content was found to decrease by 55.19% under the combined stress, while the decreased PN/PS ratio indicated an enhancement of physical stability of the sludge. Detailed analysis of 3D-EEM and FTIR spectra analysis further revealed that the combined stress of Ni(II) and salinity could change both the quantity and composition of EPS in anammox sludge. This study is expected to offer new insights into the combined effect of nickel and salinity on anammox sludge