Free nitrous acid-based suppression of sulfide production in sewer sediments: In-situ effect mechanism.

Abstract

Sulfide production control in gravity sewer sediments is more complex and difficult due to the greater spatial complexity of biological processes as a result of the abundant microflora inside the sediments. In this study, a promising and cost-effective free nitrous acid (FNA)-based suppression strategy for sulfide production in sewer sediments was proposed. Novel in-situ measurement methods were implemented by incorporating the diffusive gradients in thin films (DGT) technique and high-resolution dialysis (HR-Peeper) with microbial characterization analysis along the vertical sediment profile to examine the effect mechanism of the FNA-based inhibition process on sulfide production in the sediments. The results revealed that the FNA-based exposure strategy could effectively suppress the sulfidogenic activity across the whole shallow active layer (approximately 0.5cm below the surface) in the sediments. An initial high FNA concentration up to 2.5mg HNO2-N/L was required to maintain a critical inhibition level (24-h average concentration>0.2mg HNO2-N/L) across the whole active sediment zone. The FNA concentration decreased sharply deeper than 0.5cm with a significant pH increase, resulting in FNA inactivation only reducing the microbial live/total ratio and shifting the microbial community structure near the sediment surface. Maintaining a low pH is the critical factor for the FNA-based suppression strategy of the sulfidogenic activity in the shallow sediment zone.