Transformation of sulfur in the sediment-water system of the sewage pipeline under different hydraulic retention time.

Transformation of sulfur in sewage pipeline was affected by water flow, and the transformation laws at different locations in the sediment-water system were different. This work studied the changes of sulfur in sediments, sewage, and upper space of the sewage pipeline, analyzed the differences in microbial community under different hydraulic retention time (HRT) and depth, and focused on the transformation law of sulfur. Results showed that sulfate and sulfide concentrations in sewage were higher than those in sediments under anaerobic conditions. Moreover, sulfate and sulfide concentrations in sediments decreased with depth. When HRT decreased from 3 h to 1 h, H2S concentration increased evidently, whereas sulfate concentration decreased in the sewage and sediment, and sulfide concentration increased in sewage and surface sediment. Those differences were related to the relative abundances of the two microbial communities. The relative abundances of sulfate-reducing bacteria (SRB), such as Desulfobacter, Desulfovibrio, and Desulfomicrobium, were higher in surface sediment. Correspondingly, those of Thiobacillus, Bacillus, and other sulfur-oxidizing bacteria (SOB) and Smithella were higher in deep sediment. The decrease of HRT might worsen the mass transfer effect of dissolved oxygen, thereby increasing the production rate of sulfur and causing H2S to easily escape from sewage.