Enhancement of anaerobic ammonia oxidation process composed of mixed sludge without additional deoxidation by sulfur autotrophic denitrification under mainstream conditions

Abstract

The practical application of anaerobic ammonia oxidation (anammox) process is hindered because of its strict demand of an anaerobic environment. Due to the slow growth cycle of anammox bacteria and the high cost of wastewater deoxidation, it is difficult to improve the contribution rate of denitrification in anammox pathway. Sulfur oxidizing bacteria (SOB) consume oxygen in the process of oxidizing sulfur elements to provide a better anaerobic environment for anammox bacteria, and sulfur autotrophic denitrification can also remove nitrate produced during the anammox process for deep nitrogen removal. The analysis of cell hydrophobicity and EPS secondary structure were consistent, which showed that the biofilm of A-SAD (anammox- sulfur autotrophic denitrification) system exhibited stronger adhesion and a more stable structure. The functional genes of ammonia oxidation (amoA) and nitrite oxidation (nxrA) were reduced by more than 90 %, implying that SAD provided a favorable anaerobic environment for anammox and reduced the cost of deoxidation in actual operation. The relative abundance of Candidatus_Kuenenia increased nearly threefold, becoming the dominant anammox bacteria in low substrate environment, while other anammox bacteria almost disappeared. The increase of the relative abundance of Thiobacillus and Desulfovibrio were beneficial to the transformation of S0 into bio-sulfur (Bio-S0) through redox, which provided the possibility for the recovery and utilization of sulfur. This experiment provides a comprehensive understanding of the nitrogen and sulfur conversion mechanism for the deoxidation and sulfur recovery of anammox in practical applications.