A novel sewer pipe with a double-deck structure was developed for in-sewer treatment. The upper deck is designed for the smooth transportation of wastewater, while the treatment is conducted by sponge media in the lower deck, which is intermittently exposed to wastewater and oxygen as with a trickling filter. The performance of the novel pipe was examined in the pilot-scale demonstration fed with domestic wastewater for 9 months. The indices of organic matter (BOD, COD, and SS) decreased for several hours of batch-mode recirculating tests. The removal rates ranged between 12 and 39 g-COD/(m•d) and were not significantly affected by temperature (18 -29°C) and flow rate (6 -15 m 3 /h). The estimated oxygen requirement was balanced with the intermittent oxygen supply, i.e., sum of reaeration with water flow and direct exposure without water flow. Furthermore, the performance of the novel pipe coupled with simple post-treatments was also examined. The coagulation was the most efficient: BOD was successfully decreased to below 20 mg/L by the in-sewer treatment for 3.5 h followed by the addition of 100 mg/L of polyaluminum chloride. The novel pipe, therefore, may be promising technology for both COD reduction (independent usage) and alternative secondary treatment (coupled with coagulation).

Various transformations in wastewater quality along sewers, such as that due to self-purification, have been reported. However, little is known about the contributions of the attached (sewer-wall) and suspended biomass originally existing in wastewater due to a lack of experimental fields. In this study, we examined the effects of attached and suspended biomass on the dynamics of the microbial communities in sewers by conducting recirculating batch tests in a pilot-scale sewer system equipped with sponge media and a lab-scale aerating batch test, respectively. The changes in the quantity and quality of organic matter indicated that the contribution of the attached biomass to self-purification was much larger than that of the suspended biomass, because the former was sufficiently acclimated to the wastewater. Moreover, the microbial community analysis by pyrosequencing suggested that there were two candidates responsible for self-purification: 1) Comamonadaceae and Rhodocyclaceae, which could immediately proliferate under attached conditions and become dominant (15% each) in the attached biomass, and 2) Pseudomonadaceae, which could proliferate under suspended conditions after a lag period of several hours and remain a small component (4%) of the attached biomass.