Yijing Shi

Sorption and biodegradation of tetracycline by nitrifying granules and the toxicity of tetracycline on granules

This paper examines the simultaneous sorption and biodegradation performance of tetracycline (TC) by the nitrifying granular sludge as well as the short-term exposure toxicity of TC. The removal of TC was characterized by a quick sorption and a slow process of biodegradation. The adsorption process fits pseudo-second-order kinetic model, with a complex mechanism of surface adsorption and intra-particle diffusion. Both temperature and mixed liquor suspended solid (MLSS) influenced TC sorption to the granules. TC biodegradation was enhanced with the increase of COD and NH(4)(+)-N concentrations, with except of the NH(4)(+)-N concentrations higher than 150 mg/L. With the ATU addition, TC degradation was weakened remarkably, indicating a synergistic effect of multiple microbes. Results of the short-term exposure (12h) effects showed that the respirometric activities of the microbes decreased greatly. The addition of TC also decreased the rate of NH(4)(+)-N utilization considerably, with the half saturation constant (K(s)) increasing from 297.7 to 347.2 mg/L.

Changes of the reactor performance and the properties of granular sludge under tetracycline (TC) stress

In this study, the response of nitrifying granules (NG) and conventional granules (CG) to tetracycline (TC) was compared. The presence of TC made granules break down into small fractions and led to nitrite accumulation in nitrifying system; while it had little toxic effect on CG system. Specific oxygen uptake rate tests showed 3.3% inhibition of ammonium oxidizing bacteria and 25.7% inhibition of nitrite oxidizing bacteria in the NG system. Granules produced more extracellular polymeric substances (EPS) to protect themselves from the TC stress, with higher production of proteins compared to polysaccharides. FTIR data also revealed significant changes of protein functional groups, while only small changes in polysaccharides functional groups were found. Three dimensional excitation-emission matrix fluorescence spectroscopy showed a decrease of peak intensity, indicating quenching effect of TC on EPS fluorescence, and also a blue shift of peak position, indicating chemical changes of EPS components.

Aerobic granulation for nitrogen removal via nitrite in a sequencing batch reactor and the emission of nitrous oxide.

In this study, the granulation of nitrifying-denitrifying via nitrite process in a sequencing batch reactor (SBR) as well as N(2)O emission patterns was investigated. After 60 days of operation, 0.8 mm granules were obtained, and partial nitrification was achieved after NH(4)(+)-N was raised to 350 mg/L. Fluorescence In-Situ Hybridization (FISH) analysis indicated that a fairly large proportion of ammonia-oxidizing bacteria (AOB) was close to the surface but nitrite-oxidizing bacteria (NOB) were rarely found. Batch experiments showed that 64.0% of NH(4)(+)-N in influent was transformed into NO(2)(-)-N, which showed the granules had excellent partial nitrification ability. Inhibition of free ammonia (FA) and limited DO diffusion within granules may contribute to the development and stabilization of partial nitrification. This process did not simultaneously lead to increased N(2)O production. N(2)O emissions at the anoxic and aerobic phases were 0.06 and 13.13 mg N(2)O/cycle, respectively.

Enhanced aerobic nitrifying granulation by static magnetic field

One of the main challenging issues for aerobic nitrifying granules in treating high strength ammonia wastewater is the long granulation time required for activated sludge to transform into aerobic granules. The present study provides a novel strategy for enhancing aerobic nitrifying granulation by applying an intensity of 48.0mT static magnetic field. The element analysis showed that the applied magnetic field could promote the accumulation of iron compounds in the sludge. And then the aggregation of iron decreased the full granulation time from 41 to 25days by enhancing the setting properties of granules and stimulating the secretion of extracellular polymeric substances (EPS). Long-term, cycle experiments and fluorescence in-situ hybridization (FISH) analysis proved that an intensity of 48.0mT magnetic field could enhance the activities and growth of nitrite-oxidizing bacteria (NOB). These findings suggest that magnetic field is helpful and reliable for accelerating the aerobic nitrifying granulation.

Characterization of the interactions between tetracycline antibiotics and microbial extracellular polymeric substances with spectroscopic approaches

The antibiotics have attracted global attentions for their impact on aquatic ecosystem. The knowledge about the fate of antibiotics encountering extracellular polymeric substances (EPS) is, however, limited. In this study, we investigated the interacting mechanisms of tetracycline (TC) to EPS extracted from aerobic activated sludge. The contributions of the main components of EPS, extracellular proteins, and polysaccharides were evaluated using bovine serum albumin and alginate sodium, respectively. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nuclear magnetic resonance indicated that hydroxyl, carboxyl, and amino groups were the domain chemical groups involved in the interaction between TC and EPS, and the binding of TC onto EPS changed the structure of these chemical groups, thus causing shifts in their UV–visible absorption spectra. In addition, we found that extracellular proteins, rather than polysaccharides, were the major active contents involved in the interaction. Three-dimensional excitation–emission matrix fluorescence spectroscopy showed that the fluorophores in EPS were clearly quenched by TC and the static quenching process was observed, implying the complex formation of TC and EPS. Furthermore, thermodynamic analysis indicated that the binding of TC with EPS is spontaneous and dominated by electrostatic forces.

Fluoride adsorption on carboxylated aerobic granules containing Ce(III)

Aerobic granules (AG) were carboxylated and Ce(III) was incorporated to obtain modified granuels (Ce(III)-MAG) for removal of fluoride from aqueous solutions. The Ce(III)-MAG was characterized by SEM, FTIR, XRD and pH(pzc), and the introduction of carboxyl groups and Ce(III) was confirmed. The adsorption capacity of Ce(III)-MAG for fluoride was 45.80 mg/g at neutral pH, an increase of 359% compared to the capacity of pristine AG. Adsorption was highest at pH range of 3.0-5.0. A positive effect on fluoride removal in the order of K(+) ≈ Mg(2+) > Ca(2+) > Na(+) and a negative effect in the order of NO(3)(-) > Cl(-) > SO(4)(2-) > HCO(3)(-) > PO(4)(3-) was observed. Fluoride adsorption followed the Redlich-Peterson model and the pseudo-first order model with correlation factors of 0.999 and 0.950, respectively. Ce(III)-MAG held up to 790 bed volumes and the effluent fluoride concentration remained below 1.0mg/L (influent fluoride 10mg/L).

Effects of step-feed on granulation processes and nitrogen removal performances of partial nitrifying granules

Two anoxic/oxic sequencing batch reactors (A/O SBRs) were operated to investigate the effects of step-feed on granulation processes and performances of partial nitrifying granules (PNG). R1 was operated in a traditional single-feed mode, while a two-step-feed strategy was used in R2. Results showed that R1 had a faster granulation process and better performance in maintaining partial nitrification compared with R2, indicating that the step-feed mode had a negative effect of on formation of PNG. However, after full granulation, PNG in both reactors had similar properties in terms of suspended solids (MLSS), sludge volume index (SVI) and granule size. Moreover, mature granules in R2 had a higher nitrite accumulation rate than that in R1. Step-feed strategy was also observed to enhance denitrification and TN removal, as well as ammonia oxidation. It can be concluded that step-feed was unfavorable for cultivating PNG, but it significantly improved the nitrogen removal performance of PNG.

Microbial activity balance in size fractionated suspended growth biomass from full-scale sidestream combined nitritation-anammox reactors

The purpose of this study was to determine the abundance, distribution and activity of aerobic ammonia-oxidizing bacteria (AOB) and anammox in size fractionated aggregates from full-scale suspended growth combined nitritation-anammox sidestream reactors. Plants with or without a cyclone device were also studied to assess a purported enrichment of anammox granules. Specific aerobic ammonium oxidation rates (p=0.01) and specific oxygen uptake rates (p=0.02) were significantly greater in flocs than in granules. AOB abundance measured using quantitative FISH was significantly higher in flocs than in granules (p=0.01). Conversely, anammox abundance was significantly greater in granules (p=0.03). The average ratio of anammox/AOB in systems employing hydrocyclone separation devices was 2.4, significantly higher (p=0.02) than the average ratio (0.5) in a system without a hydrocyclone. Our results demonstrate substantial functional and population-level segregation between floccular and granular fractions, and provide a key corroboration that cyclone separation devices can increase anammox levels in such systems.

Comparing the Resistance, Resilience, and Stability of Replicate Moving Bed Biofilm and Suspended Growth Combined Nitritation–Anammox Reactors

Combined partial nitritation-anammox (PN/A) systems are increasingly being employed for sustainable removal of nitrogen from wastewater, but process instabilities present ongoing challenges for practitioners. The goal of this study was to elucidate differences in process stability between PN/A process variations employing two distinct aggregate types: biofilm [in moving bed biofilm reactors (MBBRs)] and suspended growth biomass. Triplicate reactors for each process variation were studied under baseline conditions and in response to a series of transient perturbations. MBBRs displayed elevated NH4+ removal rates relative to those of suspended growth counterparts over six months of unperturbed baseline operation but also exhibited significantly greater variability in performance. Transient perturbations led to strikingly divergent yet reproducible behavior in biofilm versus suspended growth systems. A temperature perturbation prompted a sharp reduction in NH4+ removal rates with no accumulation of NO2- and rapid recovery in MBBRs, compared to a similar reduction in NH4+ removal rates but a high level of accumulation of NO2- in suspended growth reactors. Pulse additions of a nitrification inhibitor (allylthiourea) prompted only moderate declines in performance in suspended growth reactors compared to sharp decreases in NH4+ removal rates in MBBRs. Quantitative fluorescence in situ hybridization demonstrated a significant enrichment of anammox in MBBRs compared to suspended growth reactors, and conversely a proportionally higher AOB abundance in suspended growth reactors. Overall, MBBRs displayed significantly increased susceptibility to transient perturbations employed in this study compared to that of suspended growth counterparts (stability parameter), including significantly longer recovery times (resilience). No significant difference in the maximal impact of perturbations (resistance) was apparent. Taken together, our results suggest that aggregate architecture (biofilm vs suspended growth) in PN/A processes exerts an unexpectedly strong influence on process stability.