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Rapid achievement of nitritation using aerobic starvation Wenlong Liu, Qing Yang, Bin Ma, Jun Li, Linna Ma, Shuying Wang, and Yongzhen Peng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04598 • Publication Date (Web): 06 Mar 2017 Downloaded from http://pubs.acs.org on March 7, 2017
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Rapid achievement of nitritation using aerobic starvation
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Wenlong Liu,† Qing Yang,*, ‡ Bin Ma,‡ Jun Li,§ Linna Ma,‡ Shuying Wang,‡ Yongzhen Peng*, †, ‡
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†
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China
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‡
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Research Center of Beijing, Beijing University of Technology, Beijing 100124, China
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§
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090,
Key Laboratory of Beijing Water Quality Science and Water Environment Recovery Engineering, Engineering
College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China
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ABSTRACT: Rapid start-up of partial nitrification is of great significance for subsequent
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denitrification and anammox process, however slow nitritation hinders the application of these
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processes. The current study presents a novel strategy for achieving the nitritation using aerobic
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starvation and controlling sludge retention time (SRT). Activated sludge with high level of complete
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nitrification was introduced into an aerated reactor without feeding to start the aerobic starvation.
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The results showed that nitritation was rapidly achieved, while the shorter SRT (15 days) guaranteed
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the stability of nitritation with an average nitrite accumulation ratio (NAR) of more than 95%. The
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activity recovery rates of ammonium-oxidizing bacteria (AOB; from 0.20±0.00 d-1 to 0.29±0.08 d-1)
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were higher than those of nitrite-oxidizing bacteria (NOB; -0.11±0.02 d-1 to 0.16±0.05 d-1) during
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the reactivation periods. Furthermore, the transcriptional responses of amoA and hao mRNA after
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aerobic starvation were faster than that of nxrB gene, which explained the fast occurrence of
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nitritation after aerobic starvation period. The quantitative real-time PCR (qPCR) analysis showed
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that the cell number of nitrifying bacteria remained stable during the starvation process, whereas
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AOB population gradually became dominant over that of NOB in the reactivation period. These
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observations strongly supported the feasibility of accelerating the establishment of nitritation using
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aerobic starvation.
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Keywords: Nitritation; Aerobic starvation; Sludge retention time; Cell decay; Recovery.
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Table of Contents
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Introduction Nowadays, several novel biological nitrogen removal (BNR) processes such as short-cut
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nitrification and denitrification, anaerobic ammonium oxidation (Anammox), completely autotrophic
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nitrogen removal over nitrite (Canon) process and oxygen-limited autotrophic
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nitrification-denitrification (Oland) process, have been developed to reduce energy consumption and
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to improve total nitrogen removal capacity.1–4 Due to the nitrite as substrate or intermediary media
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for these processes, partial nitrification only oxidized ammonium to nitrite by AOB plays a
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significant role in achieving these novel BNR processes.5 Compared to the conventional
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nitrification/denitrification processes, these processes not only reduce 25% of the aeration
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consumption in nitritation but also save 40% and 100% of the organic matter requirement for the
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subsequent denitrification and anammox processes, respectively.1,6
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The key to attain nitritation lies in achieving the suppression or wash-out of NOB (those which
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oxidize nitrite to nitrate) and retaining AOB (those which oxidize ammonia to nitrite). Several studies
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have reported that nitritation can be achieved by adjusting the operational parameters, such as
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temperature,7,8 dissolved oxygen (DO),9,10 pH,11 free ammonia (FA) and free nitrous acid (FNA),12
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inorganic carbon (IC),13 intermittent aeration,14,15 and real-time control strategy.16,17 The adjustment
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of these parameters produces ammonia oxidation rates which outcompete that of nitrite oxidation,
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even stops the nitrite oxidation rate.
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A long wash-out period, however, is essential to enhance the number of AOB over NOB, which
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would restrict the rapid start-up of nitritation. For instance, the alkalinity source changed from NaOH
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to NaHCO3 in 30 days and during the time transition of nitrate to the nitrite is required.13 When
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domestic wastewater is treated by either real time aerobic duration control18 or low DO control,10,19
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the start-up times for partial nitrification become longer than 40 days. Furthermore, a two-fold
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start-up time (76 days) was required for achieving nitritation by using real-time control when
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municipal wastewater was treated in a pilot-plant having sequencing batch reactor (SBR).16
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Simulation studies17 using two-step nitrification model indicated that substantial time (approximately
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300 days) was required to achieve high nitritation (greater than 80%) when aerobic duration control
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was the sole selection factor.
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Studies have shown that the initial nitrite accumulation caused by the addition of NOB inhibitor
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(such as formic acid) could shorten the time required for nitritation.17 For example, salt inhibition
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could accelerate the achievement of nitritation, whereas the start-up time while using a combination
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of salt inhibition and on-line control strategy was only 10 days.20 Nevertheless, the addition of formic
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acid or sodium chloride would increase the cost of wastewater treatment, while the toxic effects
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towards other functional bacteria present in the wastewater treatment system still remain unclear.
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Others researchers observed the accumulation of temporary nitrite in the start-up phase after
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long-term idle periods.21,22 This led to the possibility of using starvation to accelerate the
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achievement of nitritation. To the best of our knowledge, most of the published work deals with the
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effects of starvation on the activity of nitrifiers under different oxidation-reduction potential (ORP)
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conditions23,24 or with the modeling of the decaying process of AOB and NOB.25,26 The pretreatment
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through starvation to achieve nitritation has not yet been reported in the literature. Furthermore,
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majority of investigations have focused on the physiological responses (such as specific substrate
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removal rate) of nitrifiers upon exposure to starvation conditions, little is known about the functional
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gene transcriptional responses of AOB and NOB during the starvation and reactivation periods.
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The objective of this study was to investigate the feasibility of accelerating the achievement of
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nitritation by aerobic starvation, which was achieved using a laboratory-scale SBR process. The
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decay rates and the activity recovery rates of AOB and NOB were evaluated using batch tests. The
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impact of aerobic starvation on the nitrifying performance, microbial activity and population quantity
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of AOB and NOB were also studied. Additionally, the transcription of genes amoA, hao and nxrB
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present in nitrifying bacteria were measured in response to aerobic starvation by using reverse
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transcriptase-quantitative PCR (RT-qPCR) assays. Furthermore, the mechanisms responsible for
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achieving nitritation were discussed in terms of the transformation of nitrification activity,
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functional-gene transcript levels and population dynamics between AOB and NOB.
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Materials and methods
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Activated sludge
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The activated sludge was collected from a laboratory pilot-scale step-feed repeated anoxic/oxic
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(A/O) process (Figure S1). The process has a working volume of 54 L and has been operated with
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real domestic wastewater having low C/N ratio (C/N
