Enrichment and retention of key functional bacteria of partial denitrification-Anammox (PD/A) process via cell immobilization: A novel strategy for fast PD/A application

Abstract Cell immobilization was used to enrich and retain functional bacteria within partial denitrification-Anammox (PD/A) process to achieve its fast start-up for the first time. To do so, residue sludge and Anammox sludge were immobilized in poly (vinyl alcohol)/sodium alginate (PVA/SA) gel for PD cultivation and Anammox bacteria inoculation, respectively. Stable PD with NO3−-N to NO2−-N transformation ratio (NTR) of 72.0% was achieved within 13 days at 25 °C and successfully combined with Anammox on 14th day. The hydrous porous PVA/SA gel matrix played the role of extracellular polymeric substance (EPS) and thus protected the microbes against low temperature. Satisfactory nitrogen removal rate (NRR) (301.6 ± 6.1 g N/(m3·d)) was achieved even when temperature decreased to 13 °C. The contribution of nitrogen removal via Anammox was as high as 77.10%. Abundance of Thauera and Candidatus Kuenenia increased from 0.9% and 1.1% to 30.6% and 2.1%, respectively.