The variation of nitrifying bacterial population sizes in a sequencing batch reactor (SBR) treating low, mid, high concentrated synthetic wastewater

Abstract

The purpose of this study was to correlate the population size of ammonia-oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) with nitrification performance under various operational conditions (chemical oxygen demand (COD) concentration, dissolved oxygen (DO), and hydraulic retention time (HRT)) and influent allylthiourea (ATU) shock. The AOB (genera Nitrosomonas and Nitrosospira) and NOB (genera Nitrobacter and Nitrospira) communities were analyzed using fluorescent in situ hybridization (FISH). Ammonia-oxidizing bacteria and NOB accounted for 6.2 ± 0.9% and 2.5 ± 0.3% in total biomass, respectively. The population sizes of AOB and NOB varied with different levels of COD, DO, and HRT. Nitrosomonas and Nitrospira were dominant under conditions favorable for nitrification, while Nitrosospira outcompeted Nitrosomonas under adverse conditions (low [NH4 + ], low DO, short HRT, and ATU shock), and Nitrobacter outcompeted Nitrospira at high substrate concentrations (COD and [NH 4 + ]). Under ATU shock that inhibited the oxidation of NH 4 + to NO 2 -, AOB population was substantially reduced with the stepwise increase of ATU dosage, and led to a corresponding decrease of NOB population. There was a discrepancy between nitrifying bacterial populations and their functions. Although AOB outnumbered NOB in all tests and became more dominant at low DO and short HRT, NH 4 + oxidation, instead of NO 2oxidation, was the rate-limiting reaction for nitrification and susceptible to the adverse conditions. The study demonstrated the importance of elucidating the shifts of nitrifying bacterial population to optimize process design and operation at different influent characteristics, aeration intensity, retention time, and potential influent toxic shock.

Nitrogen removal from an AAO pilot plant with nitrifier bioaugmentation after seasonal deterioration

“…The pilot-scale WWTP had a higher nitrifying activity (Table 4) and lower bacterial numbers (Table 7) than the full-scale WWTP, indicating that the activity of single bacteria in the pilot-scale (bioaugmented) WWTP was higher than the activity in the full-scale WWTP. The lower bacterial number of the pilot-scale WWTP can be attributed to shorter HRT of 10 h compared with the full-scale one with a HRT of 14 h. As reported by Li et al [27], both AOB and NOB populations were reduced at short HRT. In addition, the short SRT of 15 d compared with 20 d of the full-scale one may be another reason for the lower nitrifier number because a longer SRT may have certain impact on the physiological state of the AOB community [28].…”

Diversity of nitrifying bacteria in a full-scale petroleum refinery wastewater treatment plant experiencing unstable nitrification

“…Considerable numbers of AOB cells have been reported previously under conditions of nitrification failure [37,41,42]. This has been attributed to the adaptation ability of AOB to survive periods of energy-source deprivation, when they cannot perform their normal task [41].…”

Nitrite oxidizing bacteria (NOB) dominating in nitrifying community in full-scale biological nutrient removal wastewater treatment plants

“…Although nitrifying bacteria populations are generally within the range of 4–6% of biomass for adequate nitrification in nutrient removal facilities (Nielsen et al 2004), a wide variation of the fraction of nitrifying bacteria in microbial communities has been reported. It varies from 0.39% in activated sludge (Dionisi et al 2002), to 9% in a nitrifying activated sludge SBR reactor (Li et al 2007), and even to over 18% in a combined activated sludge and rotating biological contactor (You et al 2003). The difference of the percentage of nitrifying bacteria may be affected by operational conditions and influent qualities.…”