Study on microbial reactions in high salinity sanitary sewage and modelling wastewater quality changes in a municipal gravity sewer

Previous studies showed that the municipal sewage with low salinity could achieve self-purification by microbial reactions in sewer. However, the salinity in Hong Kong is distinctly high because seawater is routinely supplied for toilet flushing, and the study on high saline sewage was not presented yet. Thus, we conducted 2 sets of lab-experiments to evaluate the capacity of self-purification and the main microbial reactions in high saline sewage. Three reactors for each set experiment were used to simulate difference conditions in sewers. Continues sampling and measurement were done to determine the oxygen uptake rate (OUR), dissolved organic carbon (DOC), ammonium (NH₃) and nitrate/nitrite (NO_x) in 72h experiment. The result from data analysis showed that the high saline sewage was also capable to achieve self-purification in sewer. In high saline sewage, the main microbial reactions to pollutant degradation were aerobic growth of heterotrophs and hydrolysis of organic particulate, which was similar to that in low saline sewage. But differing from low saline sewage, nitrification and denitrification in high saline sewage could not be ignored. Based on these conclusions, a mathematical ASM3-based sewer process model was built for simulate the wastewater transformation in sewage. By full-scale verification, the result showed that the model within modules of hydraulics, re-aeration and temperature effect, could well predict the DO, DOC, NH3 and NOX variation in sewer