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• VS reduction showed exponential decrease as sludge age extended from 5 to 40 d. • Decline in protein degradation accounted for 80.4% of the decrease of VS conversion. • Changed amount and components of EPS correlated little to degradability of sludge. • Increased molecular weight of EPS strongly correlated to the declined degradability. • More stable secondary structure of protein in EPS determined decreased degradation. Long sludge age (10 ~ 30 d) is prevalent in the operation of wastewater treatment plants of China, leading to big challenge to subsequent anaerobic digestion of sewage sludge because of low degradability and poor methane production. In order to overcome the low sludge degradability and promote the directional enhancement, the effects of sludge age on anaerobic digestion performance, especially the corresponding influencing mechanism in terms of distribution, occurrence state and structure of organic compounds in sludge driven by different sludge age were investigated. It was found that when the sludge age during wastewater treatment extended from 5 d to 40 d, the VS reduction of sludge showed an "exponential" decrease, and the degradability of protein, polysaccharides and lipids in sludge all declined. Among them, the degradation of protein was the most affected (down-regulated by 35.8%), and the decrease in degradation of protein accounted for 80.4% of the decrease of VS conversion. Sludge age during wastewater treatment impact the distribution, occurrence state and structure of organic compounds in activated sludge. And it was clarified that instead of the changed amount and components of EPS, the increased molecular weight of EPS and more stable secondary structure of protein driven by α-helix and β-turn in EPS were mainly responsible for the declined degradability of protein and sludge. [ABSTRACT FROM AUTHOR]

Biomass detachment generally occurred in granular sludge systems. However, little is known about the influence of biomass detachment on the granules performing nitritation. Here, a granular sludge reactor with high loading rates (6.8 ± 0.4 kg N·m−3·d−1) was achieved at mainstream conditions. Though the low ratio control strategy was maintained, the deterioration of nitritation performance was observed after the further increase of air supply rates to 3.4 ± 0.2 L min−1. In parallel with that, the loss of AOB and the proliferation of NOB was observed. Additionally, with the decrease of granules size and biomass concentration, the incomplete stratification of nitrifiers in the granules was confirmed by batch tests. All these results suggested that granules abrasion under the high shear stress conditions caused the detachment of external AOB and hence resulted in the deteriorated stratified structure of nitrifiers, which subsequently contributed to the proliferation of the internal NOB and the deterioration of nitritation. These findings highlight that the granules abrasion should be well controlled in the development of high-rate nitritation process with granular sludge. • High-rate nitritation with granular sludge was achieved at mainstream conditions. • Granules abrasion-based deterioration of nitritation was firstly observed. • Detachment of AOB resulted in incomplete stratification of nitrifiers in granules. • Granules abrasion must be well controlled in high-rate granular nitritation system. [ABSTRACT FROM AUTHOR]

To investigate the effect of temperature on the recovery of aerobic granule stability, two continuous-flow reactors inoculated with disintegrated partial nitritation granules were operated at different temperatures for organic-free wastewater treatment. Granules disintegration and partial nitritation deterioration further occurred in the reactor (R1) operating at 25–28 °C. However, successful sludge re-granulation with a decrease of sludge volume index (SVI5) from 73 mL/g to 35 mL/g was observed in the reactor (R2) operated with the decreasing temperature from 20 °C to 12 °C. The reduced temperatures decreased the activity and growth rate of nitrifiers (from 47.2 mg/g VSS/h to 21.3 mg/g VSS/h), and selected the extracellular polymeric substance (EPS) producing bacteria (e.g., Flavobacterium and Rhodobacteraceae sp.). Correspondingly, an enhanced secretion of tightly-bound EPS (200.3–224.6 mg/g VSS in R2 vs 166.8–152.5 mg/g VSS in R1), particularly proteins, and an increased expression of quorum sensing-related enzyme genes (2.98% in R2 vs 2.75% in R1) were obtained. All of this contributed to the cold temperature-driven sludge re-granulation. The recovery of granular structure promoted the stable maintenance of efficient partial nitritation at low temperatures. Overall, this study gives insights into the positive role of cold temperatures on the stability of partial nitritation granules. [Display omitted] • Temperature effects on nitrifying granules were studied in continuous-flow reactors. • Granule disintegrated at 25–28 °C, but regranulation occurred at low temperatures. • Cold temperature enriched extracellular polymeric substance-producing microbes. • The mechanism of cold temperature-driven sludge regranulation was proposed. [ABSTRACT FROM AUTHOR]

As a by-product of industry, waste iron scraps (WIS) are low-cost and widely available, which was potential for the development of iron-assisted anammox. In this study, the feasibility of adding WIS to enhance the nitrogen removal of the anammox process (also called WIS-assisted anammox) was demonstrated. Results indicated that the WIS-assisted anammox reactors performed a 15–35% higher nitrogen removal efficiency than that of the control. Compared to the sludge from the control, the sludge from the WIS-assisted anammox reactors had a higher iron content (78–113 g kg−1 SS) and a better specific anammox activity (10.8–15.5 mg N g−1 VSS h−1). The enhanced growth of the anammox bacteria (related to Ca. Kuenenia stuttgartiensis with 99% similarity) in the WIS-assisted anammox reactors was also confirmed by high-throughput sequencing and qPCR. Furthermore, the functional genes predicted by PICRUSt2 revealed a higher level of hydroxylamine oxidoreductase (hao)-like proteins expression of the biomass from the WIS-assisted anammox reactors, implying that the hydroxylamine-related anammox pathway was promoted. Additionally, the observation of cytoplasmic nitrate reductase (narG), copper-containing nitrite reductase (nirK), and nitric oxide reductase (norB) suggested that the introduction of WIS might promote the denitrification ability. This was correlated to the lower ΔNO 3 -/ΔNH 4 + ratio observed in these WIS-assisted anammox reactors. Overall, the WIS-assisted anammox offers a sustainable nitrogen removal process for wastewater treatment with waste iron recycling. [Display omitted] • The feasibility of the WIS-assisted anammox process was demonstrated. • WIS enhanced the nitrogen removal of the anammox process by 15–35%. • WIS promoted the activity and growth of the anammox bacteria. [ABSTRACT FROM AUTHOR]

Achieving mainstream nitritation with aerobic granules is attractive based on increasing evidence but generally treating artificial low-ammonium wastewater. Real municipal wastewater is much more complex in composition, the behavior of the nitritation granules would be different when treating real municipal wastewater. Herein, the response of nitritation granules to influent shift from artificial low-ammonium (35–40 mg/L) wastewater to anaerobically pre-treated municipal wastewater (MWW pre-treated) was investigated at low temperatures. Results showed that MWW pre-treated caused the outgrowth of filamentous bacteria on the granule surface and developed into finger-like structures, which in turn resulted in the decrease of the overall granular sludge settleability. Batch-tests and microbial analysis indicated the functional and microbial differentiation between the newly formed fluffy exterior and the original compact granule. The fluffy exterior was dominated by genus Flavobacterium (66.6%) and primarily functioned as COD removal, whereas the nitrifiers (mainly Nitrosomonas) were still located in the compact core and performed nitritation. Moreover, the heterotrophs-dominated fluffy exterior hindered the oxygen transfer towards nitrifiers located in the compact granule and thereby facilitated the stable NOB repression in the granule particularly at low temperatures (<10 °C). Finally, gradual recovery of the granular sludge morphology and settleability occurred after the influent reverted to synthetic low-ammonium wastewater. Overall, this work demonstrated that the feeding of MWW pre-treated only caused morphological changes of the nitritation granules, but its structural and functional stability could be maintained stably. [Display omitted] • Granule-based nitritation was maintained treating anaerobically pretreated sewage. • COD removal occurred primarily in external flocs, while nitritation in compact core. • External flocs promoted NOB repression by increasing oxygen transfer resistance. [ABSTRACT FROM AUTHOR]

Abstract: A pilot-scale submerged membrane bioreactor (MBR) for the treatment of real municipal wastewater was operated in this study under various sludge retention time (SRT) in order to verify the correlations of fluorescent dissolved organic matter (DOM) with membrane fouling. The fluorescent DOM determined by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy and the trans-membrane pressure (TMP) under different SRT operation were investigated, and the correlations between them were analyzed. The results showed that the variations of fluorescent DOM (Peaks B and C) in the sludge supernatants correlated well with the variations of EEM spectra signal of bound extracellular polymeric substances (EPS) even though they were different in nature, i.e., the bound EPS were found to be more non-biodegradable than DOM. The fluorescent intensity (FI) variations of Peaks A and B in the EEM spectra of DOM were closely related to the TMP increase rate (membrane fouling) in the MBR, suggesting that they might be used to monitor the DOM variations and to indicate MBR performance. Through the EEM spectra analysis, it was confirmed in this work that the DOM in the sludge supernatants was not only originated from the bound EPS but also from the influent wastewater. [Copyright &y& Elsevier]

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH 4 + <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 25-15 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008–0.013 d−1 at 15 °C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N·m−3·d−1 and 68% treating low-strength ammonium (∼50 mg N·L−1) wastewater under such aggressive conditions (DO = 0.8–1.5 mg/L, HRT< 1.0 h, and T = 15 °C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum. • A high-rate CANON process was started up at 15 °C treating low-strength wastewater. • Aerobic granules provided a habitable niche for in-situ enriching anammox bacteria. • Residual ammonium control and small granules wash-out contributed to NOB repression. [ABSTRACT FROM AUTHOR]

To elucidate how high dissolved oxygen (DO) favors the startup of nitritation with aerobic granular sludge, two granular reactors were operated under low (1–2 mg O 2 ·L−1) and high DO (3–5 mg O 2 ·L−1) conditions with similar effluent ammonium concentrations (>20 mg N·L−1). The results showed that though nitritation with an average nitrite accumulation ratio of above 95% was finally achieved in both reactors, a five-fold start-up time (eleven weeks) was required for the low DO reactor compared to the high DO reactor. Moreover, the nitritation performance was positively correlated with the extent of nitrifiers stratification in granules. The faster startup of nitritation under high DO conditions mainly resulted from the faster formation of well-stratified nitrifiers, with ammonium oxidizing bacteria (AOB) dominating granule surface. High DO operation combined with sufficient ammonium supply ensured the faster growth of AOB, which should provide a competitive advantage to AOB in competing for habitable space (i.e., granule surface). Besides, the lower porosity, larger size, and more active extracellular polymeric substances (particularly proteins) production of granules was observed under the high DO condition. Overall, these findings supported the proposition that the switch from mixed to stratified distribution of nitrifiers in granule was primarily driven by their competition for habitable space rather than by oxygen-limitation. Image 1 • Faster startup of granular nitritation under higher DO concentrations. • The startup of nitritation linked with the development of stratified nitrifiers. • Habitable space competition between AOB and NOB led to stratification of nitrifiers. [ABSTRACT FROM AUTHOR]

The inhibitory effects of calcium ion (Ca2+) on ammonium (NH 4 +) exchange by zeolite were investigated in the long-term exchange and sodium hypochlorite - sodium chloride (NaClO–NaCl) regeneration process, and alleviation measure was developed and validated in this study. The batch experiments indicated that NH 4 + removal efficiency, exchange kinetics and equilibrium isotherms were significantly dependent on the coexisting Ca2+. The exchange capacity decreased from 0.58 to 0.40 mg g−1 by increasing initial Ca2+ concentration from 0 to 100 mg L−1. The inhibitory effect of Ca2+ on NH 4 + exchange efficiency was fitted to the competitive inhibition Monod model with half-saturation rate constant of 134.7 mg L−1. Ca2+ addition reduced the NH 4 + removal rate and lengthened the exchange equilibrium time of zeolite. Periodic precipitation of Ca2+ in the form of calcium carbonate from the used regenerant maintained the removal efficiency of NH 4 + commendably by alleviating inhibition effect of Ca2+ and extended the working life of zeolite. The major chemical compositions of natural and regenerated zeolite were basically unchanged. Compared to Bohart-Adams model and Thomas model, the Dose-Response model could predict the breakthrough curve well, and the fitted parameter further confirmed that NaClO–NaCl regeneration with periodic Ca2+ removal is an effective method to maintain efficient NH 4 + from wastewater by zeolite. Image 1 • Ca2+ inhibition on NH 4 + exchange by zeolite with NaClO–NaCl regeneration was studied. • The exchange capacity decreased from 0.58 to 0.40 mg g−1 with Ca2+ from 0 to 100 mg L−1. • Inhibition of Ca2+ on NH 4 + exchange matched with the competitive Monod model. • Periodic Ca2+ removal as CaCO 3 from the used regenerant alleviated Ca2+ inhibtion. • Dose-Response model predicted NH 4 + breakthrough curve well and validated alleviation. [ABSTRACT FROM AUTHOR]

Biomass segregation between granules/biofilm and flocs is widespread in anammox-based processes. The segregation of biomass allows for easy control of processes stability. The goal of this study is to understand the biomass segregation in two anoxic anammox reactors respectively operated in nitrite-limited (R NO2) and ammonium-limited (R NH4) modes treating low-strength wastewater at 20 °C. Results showed that size-based biomass segregation was developed in both reactors. But the functional and population heterogeneity was more significant in the ammonium-limited anammox reactor. The activity and abundance of anammox bacteria in large granules were significantly higher than that in flocs under the ammonium-limited conditions. The large granules played a major role in nitrogen removal in R NH4. By contrast, both large granules and small flocs contributed significantly to the nitrogen loss in the nitrite-limited anammox reactor, since a large number of anammox bacteria existed in both granules and flocs. Besides, a number of Nitrospira -like NOB were also detected in both anoxic anammox reactors, which primarily inhabited in flocs seemingly droved by the availability of oxygen. But the abundance of Nitrospira in R NH4 was much higher than that in R NO2. All these results suggested that selective flocs removal would be necessary for R NH4 to improve its anammox performance but non-essential for R NO2. The two anammox reactors shared the predominant anammox species with the closest relative to Ca. Brocadia sp. 40 (98%). Unexpectedly, the anammox species grew faster in R NH4. But the microbial diversity and evenness was much greater in R NO2 , suggesting its higher functional stability. • The ammonium-limited and nitrite-limited anammox reactors were compared. • Anammox bacteria mainly enriched in granules, NOB preferred to live in flocs. • Anammox bacteria grew faster in the ammonium-limited reactor. • The nitrite-limited reactor possessed the higher microbial diversity and evenness. [ABSTRACT FROM AUTHOR]