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The adsorption behavior of Zn2+ in four different biological sludge systems, i.e. activated sludge, denitrification sludge, short-cut nitrification sludge, and anammox granules, was investigated. The results indicated that all sludge samples possessed considerable potential for Zn2+ adsorption. Short-cut nitrification sludge possessed the highest Zn2+ maximum adsorption capacity (qm) of 36.4 mg g SS−1, which was much higher than other sludges applied (12.8-14.7 mg g SS−1). Besides, the adsorption rate for short-cut nitrification sludge was fastest among the four types of sludge after fitting with a pseudo-second-order rate equation. Comparing with the physicochemical properties of the four sludges, the soluble extracellular polymeric substances (EPS), especially soluble polysaccharide (PS), played a prior role in binding metal cations (i.e., Zn). The present study also showed that with less than 30% of Zn2+ trapped by EPS, 61.6-71.9% of Zn2+could be harvested directly by cells, indicating that the protecting capability by EPS was limited. Therefore, it is important to remove metal ions as early as possible if the activated sludge processes encountered high stress of heavy metal.ᅟ [ABSTRACT FROM AUTHOR]

The spread application of nanoparticles (NPs) would cause instability on anaerobic ammonium oxidation (anammox) process. The present study focused on the short-term evaluation of ZnO nanoparticles (NPs) on anammox process by batch tests. Results indicated that a significant inhibition occurred under ZnO NPs stress of 5–100 mg gVSS −1 . The half inhibitory concentration (IC 50 ) of ZnO NPs was found to be 11.6 mg gVSS −1 . The release of zinc ions from ZnO NPs dissolution was confirmed to be the main mechanism of inhibition on anammox activity. Haldane kinetic model simulation results confirmed that ZnO NPs imposed a non-competitive inhibition on nitrite conversion by decreasing maximum nitrogen removal rate ( q max ), while they showed a competitive inhibition on ammonium conversion kinetics with affinity constant ( K s ) increasing by 6 times. From the competitive inhibition results, it is suggested that the inhibition caused by ZnO NPs could be alleviated and recovered under higher ammonium concentrations. [ABSTRACT FROM AUTHOR]

A lab-scale UASB reactor was used to assess the high-rate performance of anammox process after long-term operation by shortening HRT. The nitrogen removal rate (NRR) was developed to 15.51 kg N m −3 d −1 with a relative high nitrogen removal efficiency (NRE) of 90.5% under the short HRT of 1.0 h. However, continuous granules’ flotation consequently initiated and was enhanced under the high nitrogen gas production condition, accompanying by the decrease in NRE to 69.8%. The physical, chemical and microbial characteristics of the settled and floated anammox granules were compared. Results indicated that the alternation of chemical properties (e.g. EPS over-secretion) of granules helped to prevent gas escaping out, thus decreasing sludge density. Therefore, granules’ flotation becomes inevitable in high-rate anammox reactors. Microbial analysis showed that “ Brocadiacea ” dominated in settled and floated granules with abundance of 42% and 36%, respectively. Whereas, the abundance of “ Chloroflexi ” in floated sludge (20.69%) was much higher than that in settled sludge (12.66%). [ABSTRACT FROM AUTHOR]

Batch experiments were conducted to investigate the short-term effects of Cd(II), Hg(II), Pb(II), As(III) and Cr(VI) on anammox activity, which are considered to be the top 5 toxic heavy metals in China. The IC 50 values of Cd(II), Hg(II), Pb(II) and Cr(VI) were calculated to be 7.00, 2.33, 10.40 and 9.84 mg/L, respectively, while As(III) caused only 29.67% decrease in SAA even at the dosage of 60 mg/L. The evaluation of metal concentrations in liquid and sludge revealed that anammox biomass hold a high heavy-metal accumulation ability, which was hypothesized to be the key reason of activity inhibition. The functional groups possessed by anammox biomass and the extracellular polymeric substance (EPS) might contribute to the attachment of heavy metals. Especially, microbial reduction of Cr(VI) to Cr(III) inside the granules was discovered, which was considered to relieve the Cr(VI) inhibition under concentrations lower than 8.96 mg/L. [ABSTRACT FROM AUTHOR]