Denitrifying sulfur cycle-associated phosphorus removal in saline sewage

Abstract

Phosphorus (P) is an essential cause of eutrophication of receiving waters due to the excessive wastewater discharges from agriculture and domestic uses. The most effective eutrophication control approach is P removal from wastewater before discharge. However, in Hong Kong where the climate is warm, and seawater for toilet flushing is practiced, the saline wastewater increases the difficulty of the application of conventional enhanced biological P removal processes. Thus, to investigate the potential of P removal in saline water in subtropical areas, this study operated a sequential batch reactor (SBR) with 20-30% of seawater (by volume) in the influent at 30 ℃ to investigate the P-release and uptake. The long-term performance of the SBR demonstrated that the P-release and sulfate reduction had a negative correlation in the anaerobic phase and the P-uptake positively linked with the nitrate consumption in the anoxic phase. Microbial community analysis showed that sulfate-reducing bacteria (SRB) and colored sulfide-oxidizing bacteria (SOB) contributed to a significant proportion of total biomass. However, no conventional polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms were found. The long-term performance and the microbial community analysis in the SBR showed that the P removal was not conventional biological P removal, which P-release and uptake are contributed by PAOs, but instead, it was mainly related to sulfur conversion bacteria, especially in the anaerobic phase. Batch tests conducted for comparison of different stages in the anaerobic phase further revealed that the P-release had the positive correlation with the unbalance value between sulfate reduction and observed sulfide production, herein designated as “S-loss”, which might be poly-sulfur or elemental sulfur (i.e., poly-S/S⁰). Reaction kinetics of sulfur-related reactions proved that the synergistic effects of SRB and colored SOB were correlated with the P-release in this system.

Keywords: phosphorus removal; sulfate reduction; saline sewage; colored sulfide-oxidizing bacteria; sulfate-reducing bacteria.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology