Effect of carbon-to-nitrogen ratio on high-rate nitrate removal in an upflow sludge blanket reactor for polluted raw water pre-treatment application

• Main Authors: How, Seow Wah, Ting, Choo Xiang, Yap, Jing Ying, Kwang, Ching Yi, Tan, Chee Keong, Yoochatchaval, Wilasinee, Syutsubo, Kazuaki, Chua, Adeline Seak May
• Format: Article
• Published: BMC 2021
• Subjects: GE Environmental Sciences; Q Science (General); T Technology (General)
• Online Access: http://eprints.um.edu.my/33941/

The drinking water treatment plants (DWTPs) in the developing countries urgently need an efficient pre-treatment for nitrate (NO3-) removal to cope with the increasing NO3- pollution in raw water. An upflow sludge blanket (USB) reactor applied for NO3- removal from domestic wastewater may be adopted by the DWTPs. However, studies on the optimal carbon-to-nitrogen ratio (C/N) and operation of USB reactor at short hydraulic retention times (HRT) for high-rate polluted raw water pre-treatment are lacking. In this study, we first investigated the optimal C/N for biological NO3- removal in a sequencing batch reactor (SBR). An USB reactor was then operated with the optimal C/N for pre-treating synthetic raw water contaminated with NO3- (40mgNL(-1)) to monitor the NO3- removal performance and to examine opportunities for reducing the HRT. After operating the SBR with designed C/N of 4, 3 and 2g C g(-1) N, we selected C/N of 3g C g(-1) N as the optimal ratio due to the lower carbon breakthrough and nitrite (NO2-) accumulation in the SBR. The USB reactor achieved complete NO3- and NO2- removal with a lower designed C/N of 2g C g(-1) N due to the longer sludge retention time when compared with that of SBR (10 d). The high specific denitrification rate (18.7 +/- 3.6mgNg(-1) mixed liquor volatile suspended solids h(-1)) suggested a possible HRT reduction to 36min. We successfully demonstrated an USB reactor for high-rate NO3- removal, which could be a promising technology for DWTPs to pre-treat raw water sources polluted with NO3-.