Effect of COD:N ratio on biological nitrogen removal using full-scale step-feed in municipal wastewater treatment plants

Abstract

This study investigated the effect of low and high chemical oxygen demand (COD):N ratios on biological nitrogen removal and microbial distributions in full-scale step-feed (SF) municipal wastewater treatment plants (WWTPs) in Thailand (SF1) and Taiwan (SF2). The SF1 WWTP had a low COD:N (4:1) ratio, a long solids retention time (SRT) (> 60 d), and low dissolved oxygen (DO) conditions (0.2 mg L− 1 in anoxic tank and 0.9 mg L− 1 in aerobic tank). The total nitrogen (TN) removal efficiency was 48%. The SF2 WWTP had a high COD:N (10:1) ratio, a short SRT (7 d), and high DO (0.6 mg L− 1 in anoxic tank and 1.8 mg L− 1 in aerobic tank). The TN removal efficiency was 61%. The nitrification and denitrification rates from these two plants were inadequate. Using a quantitative polymerase chain reaction (qPCR) technique, the populations of ammonium oxidizing bacteria (AOB) and ammonium oxidizing archaea were quantified. Measurement of ammonia monooxygenase (amoA) gene abundances identified these AOB: Nitrosomonas sp., Nitrosospira sp., Nitrosoccus sp. and Zoogloea sp. Higher amounts of the archaeal-amoA gene were found with long SRT, lower DO and COD:N ratios. Abundance of Nitrobacter sp. was slightly higher than Nitrospira sp. at the SF1, while abundance of Nitrobacter sp. was two orders of magnitude greater than Nitrospira sp. at the SF2. More denitrifying bacteria were of the nirS-type than the nirK-type, especially at higher COD:N ratio. Most bacteria belong to the phyla Acidobacteria, Actinobacteria Bacteroidetes, Chloroflexi, Proteobacteria. The results from this work showed that insufficient carbon sources at the SF1 and high DO concentration in anoxic tank of SF2 adversely affected nitrogen removal efficiencies. In further research work, advanced techniques on the next generation sequencing with different variable regions should be recommended in full-scale WWTPs.

Comparison of Nitrogen Removal Efficiencies and Microbial Communities of Full-Scale Anaerobic, Anoxic and Aerobic Processes in Municipal Wastewater Treatment Plants having Low and High COD/TN Ratios

“…For WWTPs treating low COD/TN ratio (≤ 4) wastewater, maintaining longer SRT (≥ 60 day) is recommended to overcome the low TN removal e ciency [4] as the longer SRT would increase nitrifying bacteria abundancy. Meanwhile, long SRT could also enhance NH 4 + removal by increasing nitri cation activity [1].…”

“…Gao et al [6] studied the effects of DO levels on the growth of AOB-amoA and AOA-amoA, showing the former is much more abundance under high DO levels of 1.9-3.5 mg-O 2 L -1 . Phanwilai et al [4] analyzed the abundance of microorganisms in the step-feed aerobic tanks of a municipal wastewater treatment plant, reporting that AOA-amoA was the most abundance genes in the tank with low DO levels (0.9±0.5 mg-O 2 L -1 ) while AOB-amoA gene was higher than AOA-amoA genes in the tank with high DO level (1.8±0.5 mg-O 2 L -1 ). In this work, the result of AOB and AOA abundance at WWTPs TH2, SK1, and SK2, which are operated at high DO levels of 2.6-4 mg-O 2 L -1 , is inline with the results by Gao et al…”

“…Insu cient carbon source for denitri cation process occurs in municipal wastewater with low COD/TN ratio, resulting in low N removal performance [2]. External carbon source addition [3] or maintaining longer SRT [4] are the most effective approaches to improve biological N removal performance for wastewater with low COD/TN ratio. Investigating the effects of SRT on N removal e ciency, Liu et al [5] reported that system with SRT at 40 day outperformed those with shorter SRTs (5, 10, and 20 day).…”

“…Investigating the effects of SRT on N removal e ciency, Liu et al [5] reported that system with SRT at 40 day outperformed those with shorter SRTs (5, 10, and 20 day). Phanwilai et al [4] achieve excellent N removal with a step feed treatment process operated at SRT of 60 day. Biological N removal can be improved by optimizing DO levels.…”

Influence of Variations in Wastewater on Simultaneous Nutrient Removal in a Pre-anoxic Selector Attached Full-scale Sewage Treating SBR

“…Denitrifying bacteria requires an optimum carbon source for succeeding in excellent denitri cation, and therefore they have to contend with further heterotrophs. Lesser C/N ratio in the in uent effects in a rapid carbon discrepancy and consequences in unstable simultaneous nitri cation and denitri cation (SND) (Zhao et al 2008;Phanwilai et al 2020).…”