Reducing sulfide and methane production in gravity sewer sediments through urine separation, collection and intermittent dosing.

Sulfide and methane production are a major concern in sewer management. Many solutions with the use of chemicals have been proposed yet incurring huge costs. Here, this study reports an alternative solution to reduce sulfide and methane production in sewer sediments. This is achieved through integration of urine source separation, rapid storage, and intermittent in situ re-dosing into a sewer. Based on a reasonable capacity of urine collection, an intermittent dosing strategy (i.e. 40 min per day) was designed and then experimentally tested using two laboratory sewer sediment reactors. The long-term operation showed that the proposed urine dosing in the experimental reactor effectively reduced sulfidogenic and methanogenic activities by 54% and 83%, compared to those in the control reactor. In-sediment chemical and microbial analyses revealed that the short-term exposure to urine wastewater was effective in suppressing sulfate-reducing bacteria and methanogenic archaea, particularly within a surface active zone of sediments (0-0.5 cm) likely attributed to the biocidal effect of urine free ammonia. Economic and environmental assessments indicated that the proposed urine approach can save 91% in total costs, 80% in energy consumption and 96% in greenhouse gas emissions compared to the conventional use of chemicals (including ferric salt, nitrate, sodium hydroxide, and magnesium hydroxide). These results collectively demonstrated a practical solution without chemical input to improve sewer management.