Effect of Elodea nuttallii-Immobilized Nitrogen Cycling Bacteria on the Mechanism of Nitrogen Removal in Polluted River Water

Abstract

Surface water, Elodea nuttallii and undisturbed sediment cores from the Qinshui River in Gonghu Bay were collected to carry out a simulation experiment in a laboratory to study the effect of Elodea nuttallii-immobilized nitrogen-cycling bacteria on nitrogen removal mechanisms from the river water. In this study, the transformation and fate of ammonium among four different treatment groups were investigated by using a stable 15 N isotope pairing technique combined with high-throughput sequencing technology[Treatment A:bare sediment, Treatment B:sediment+immobilized nitrogen cycling bacteria (INCB), Treatment C:sediment+E. nuttallii, Treatment D:sediment+INCB+E. nuttallii]. The results of the 15 N mass-balance model showed that there were three pathways to the ultimate fate of nitrogen:precipitated with the sediments, absorbed by E. nuttallii, and consumed by microbial processes[denitrification and anaerobic ammonium oxidation (ANAMMOX)]. The percentages of E. nuttallii assimilated in the 15 NH4+ were 25.44% and 19.79% for treatments C and D. The sediment storage ratio of 15 NH4+ accounted for 7.94%, 5.52%, 6.47% and 4.86% in treatments A, B, C, and D, respectively. The proportion of 15 NH4+ lost as 15 N-labelled gas were 16.06%, 28.86%, 16.93% and 33.09% in the four different treatment groups, respectively. Denitrification and anammox were the bacterial primary processes in N2 and N2O production. The abundance and diversity of microorganisms was relatively higher in the treatment with E. nuttallii-immobilized nitrogen cycling bacteria (E-INCB) assemblage technology applied. Furthermore, the removal rates of 15 NH4+ were 24%, 34.38%, 48.84% and 57.74% in treatments A, B, C and D, respectively. These results show that the E-INCB assemblage technology may improve the capacity for nitrogen removal from the river water.