Variation in biofilm structure and activity along the length of a rising main sewer

Sewers systems are dynamic in nature, with periodic variation of hydraulic flow and wastewater substrate concentrations. While various models are currently available for predicting hydrogen sulfide (H2S) production in rising mains, they assume constant biofilm activities along the length and ignore the effect of substrate availability on biofilm development. To investigate variation in rising main biofilm structure and activity, detailed studies were carried out on a Robbins device setup, which was established in parallel to a real rising main that it simulated. The changes in wastewater characteristics, as wastewater traveled through both the experimental setup and the real sewer system, were monitored. The study revealed that the biofilm activities varied significantly with locations, with biofilm corresponding to the start of the rising main capable of greater sulfide and volatile fatty acid production than biofilm downstream. Analysis of microbial community composition of these biofilms showed a difference in diversity and abundance, both with regard to general bacterial populations and sulfate reducers. These differences were hypothesized to be a consequence of varying substrate types and availability along the sewer line. The results suggest that the biofilm structure and activity may vary considerably along the length of rising mains and should be taken into consideration for improved sewer modeling and when considering the overall effect of different hydrogen sulfide management options.