Stable denitrification performance of a mesh rotating biological reactor treating municipal wastewater
Shehani Sharadha Maheepala, Shunji Fuchigami, Masashi Hatamoto, Takumi Akashi, Takahiro Watari, Takashi Yamaguchi
Abstract
The mesh rotating biological reactor (MRBR) is one of the advanced modifications of the rotating biological contactor. MRBRs have a high specific surface area for biomass in order to achieve efficient nutrient removal performance. This study evaluated the denitrification performance of an MRBR during municipal wastewater treatment. A laboratory-scale MRBR was continuously operated for approximately 550 days under ambient conditions, fed with actual sewage. Influent NO3−-N concentration was decreased from 27.8 ± 6.0 mg-N L−1 to an effluent value of 8.4 ± 4.8 mg-N L−1 at ≥20 ºC under 2 h of hydraulic retention time. The total nitrogen removal was 190 ± 130 g N m−3 d−1, compared to 860 ± 310 g N m−3 d−1 with added nitrate at ≥20 ºC and 100 ± 47 g N m−3d−1 compared to 830 ± 220 g-N m−3d−1 with added nitrate at ≤15 ºC. A batch test showed that soluble chemical and biological oxygen demand removal efficiencies were 87% and 93%, respectively, after 2 h of operation. While NO3−-N remained after 2 h, adding methanol to enhance denitrification resulted in 93% removal after 8 h. Microbial analysis was performed on samples taken from the surface and inside the mesh carrier. Comamonadaceae, Thiotrichaceae, and Rhodocyclaceae denitrifying bacteria dominated the bacterial community and accelerated the performance of the MRBR. The study revealed that water temperature changes have an insignificant effect on denitrification and that the process can be performed stably throughout the year.