Municipal wastewater treatment via the two-stage partial nitrification-anammox (PN/A) process with gel immobilization

Abstract

This study focused on treating municipal wastewater using a novel two-stage partial-nitritation/anammox (PN/A) process by gel immobilization. The first stage employed a PN immobilized carrier reactor, in which the nitrite accumulation rate was 90.7–95.1 % and the COD removal rate was 33.2 ± 2.9 %. The second stage comprised an anammox-based sequencing batch reactor (SBR) fed with the effluent from the first stage. Two second stage SBRs were tested to compare their treatment effect, one contained anammox granules (AG-SBR) and one contained anammox immobilized carriers (AC-SBR). The AC-SBR exhibited better nitrogen removal performance than the AG-SBR during the PN/A process, with the nitrogen removal rate of AC-SBR being 83.4 ± 1.5 %. The gel immobilization technology effectively reduced the adverse effects of dissolved oxygen and organic matter in the PN reactor effluent on the anammox system. Aerobic denitrification was observed in the AG-SBR. In the PN immobilized carrier, Nitrospira was the dominant nitrite-oxidizing bacteria (NOB) with a relative abundance of 0.10 %, indicating that the growth of NOB was effectively inhibited in municipal wastewater. Candidatus Kuenenia was the dominant genus of anammox bacteria, exhibiting a relative abundance of 1.50 % and 19.26 % in the AG-SBR and AC-SBR, respectively. Thus, the PN/A process by gel immobilization is an effective treatment for municipal wastewater.