Using static magnetic field to recover ammonia efficiently by DNRA process

Abstract Dissimilatory nitrate reduction to ammonium (DNRA) has garnered attention due to its ability to recover ammonia and reduce greenhouse gas emissions simultaneously. In this study, the potential of using static magnetic field (SMF) to improve DNRA process was explored from the sight of molecular biology. Functional genes, microbial community structure, and metabolism pathways were discussed. SMF of 40 mT shortened the start-up time of DNRA from 75 days to 41 days, while 80 mT SMF delayed it to 103 days. On day 80, DNRA potential rate under 40 mT SMF, reached 174 ± 11 μmol kg−1 h−1, significantly surpassing 0 mT (88 ± 6 μmol kg−1 h− 1) and 80 mT SMF (52 ± 4 μmol kg−1 h−1). SMF of 40 mT also accelerated community succession and the enrichment of functional bacteria like Geobacter (from 15.71% to 32.11%). qPCR results suggested that 40 mT SMF promoted the rapid enrichment of DNRA functional gene nrfA and 80 mT SMF promoted the enrichment of nirS gene on day 40. Dynamic responses of Thauera sp. RT1901, Stutzerimonas stutzeri, Shewanella oneidensis MR-1, and Shewanella loihica PV-4 to SMF at transcriptional levels confirmed SMF could improve the nitrogen removal and electron transfer of DNRA and denitrification bacteria. Consequently, this work validated the possibility of using SMF to improve DNRA process for ammonia recovery and investigated the underlying mechanisms, which could promote the application of DNRA in full-scale.