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In order to explore the performance, kinetics characteristics and enhancement mechanisms in anammox process under ferrous iron enhanced conditions, a laboratory-scale UASB anammox reactor has been built up and operated for 534 days. Experimental results showed that the Anammox process was successfully started up in a short operation period and the TNRE reached 83.34 ± 2.96% with a maximum total nitrogen removal rate of 14.4 kg m−3 d−1 after long-term operated under influent Fe(II) concentration of 5.3 mg L−1. Simulation results using different kinetic models showed that the Stover–Kincannon model and the Grau second-order model were useful for describing the anammox performance under Fe(II) enhanced conditions. Extracellular polymeric substance (EPS) act a pivotal part in the granulation of Anammox sludge and the improvement of anammox activity. Iron improved the hydrophobicity of the sludge by reducing the PN/PS ratios, and also increased the Anammox granular diameter. The granular diameter of higher than 2.00 accounted for 58.3% of the total sludge. At the same time, the presence of iron decreased EPS levels, and also decreased the iron adsorption ability to sludge. More iron was transported into Anammox, which improved the nitrogen removal ability in the Anammox reactor. [ABSTRACT FROM AUTHOR]

Here, we review the possible reasons responsible for the occurrence, maintenance and proliferation of antibiotic resistance genes (ARGs) in the environment, as well as the corresponding mechanisms of their development, diffusion and transfer. Additionally, elimination strategies are also discussed. The factors that influence the development of ARGs are selection pressure, including that from antibiotics, metal and multiple other factors, co-resistance and cross-resistance, microbial consortium structure, nutrients in the environment and oxidative stress responses. Process parameters, transport pathways, and elimination strategies to reduce the health risk caused by ARGs are also reviewed in detail. Moreover, knowledge gaps and future opportunities of ARGs are addressed. [ABSTRACT FROM AUTHOR]

The anaerobic ammonium oxidation (anammox) process is a promising wastewater treatment method for biological nitrogen removal. A sufficient amount of active anammox sludge as a seed is crucial to the fast establishment and stability of the anammox process. Anammox bacteria is a kind of microorganism which is sensitive to the environmental conditions, e.g., oxygen, temperature. The optimum temperature and pH for the growth of the anammox bacteria are 30-40 °C and 6.7-8.3. A proper preservation technique allows fast start-up of the anammox process, overcoming the long doubling time of anammox biomass. The preservation of the anammox sludge is influenced by various factors, e.g., preservation techniques, duration, temperature, substrates, and protective agents. During preservation, the characteristics of the anammox biomass, including the bioactivity, heme c content, extracellular polymeric substances (EPS), and sludge morphology, change with time. The optimum preservation technique is not invariable and it depends on the purpose of preservation (precedence of bioactivity or quantity), the bacterial community, and other parameters. It is important for the preserved anammox biomass to achieve reactivation so that stable anammox reactors can be established as soon as possible. However, because the preservation process is complicated, the knowledge regarding preservation is far from complete, and much future work will be required to increase the understanding of preservation. [ABSTRACT FROM AUTHOR]

This study evaluated the individual and interactive effect of phenol and thiocyanate (SCN) on partial nitritation (PN) activity using batch test and response surface methodology. The IC of phenol and SCN on PN sludge were 5.6 and 351 mg L, respectively. The PN sludge was insensitive to phenol and SCN at levels lower than 1.77 and 43.3 mg L, respectively. A regression model equation was developed and validated to predict the relative specific respiration rate (RSRR) of PN sludge exposed to different phenol and SCN concentrations. In the range of independent variables, the most severe inhibition was observed with a valley value (17%) for RSRR, when the phenol and SCN concentrations were 4.08 and 198 mg L, respectively. An isobole plot was used to judge the combined toxicity of phenol and SCN, and the joint inhibitory effect was variable depending on the composition and concentration of the toxic components. Furthermore, the toxic compounds showed independent effects, which is the most common type of combined toxicity. [ABSTRACT FROM AUTHOR]

Preserving active anaerobic ammonium oxidation (anammox) biomass is a potential method for securing sufficient seeding biomass for the rapid start-up of full-scale anammox processes. In this study, anammox granules were cultured in an upflow anaerobic sludge blanket (UASB) reactor (R), and then the enriched anammox granules were preserved at 35, 20, 4, and −30 °C. The subsequent reactivation characteristics of the granules were evaluated in four UASB reactors (denoted R, R, R, and R, respectively) to investigate the effect of preservation temperature on the characteristics of anammox granules and their reactivation performance. The results demonstrated that 4 °C was the optimal preservation temperature for maintaining the biomass, activity, settleability, and integrity of the anammox granules and their cellular structures. During the preservation period, a first-order exponential decay model may be used to simulate the decay of anammox biomass and activity. The protein-to-polysaccharide ratio in the extracellular polymeric substances and the heme c content could not effectively indicate the changes in settleability and activity of the anammox granules, respectively, and a loss of bioactivity was positively associated with the degree of anaerobic ammonium-oxidizing bacteria cell lysis. After 42 days of storage, the anammox granules preserved at 4 °C (R) exhibited a better recovery performance than those preserved at 20 °C (R), −30 °C (R), and 35 °C (R). The comprehensive comparison indicated that 4 °C is the optimal storage temperature for anammox granular sludge because it promotes improved maintenance and recovery performance properties. [ABSTRACT FROM AUTHOR]

The feasibility of the anaerobic ammonium oxidation (anammox) process to treat synthetic swine wastewater containing antibiotics and heavy metals was studied in this work. Nitrogen removal performance and granule characteristics were tracked by continuous-flow monitoring to evaluate the long-term joint effects of Cu and Zn and of Cu and oxytetracycline (OTC). Cu and Zn with a joint loading rate (JLR) of 0.04 kg m day did not affect the performance, while a JLR of 0.12 kg m day caused a rapid collapse in performance. Cu and OTC addition with a JLR of 0.04 kg m day for approximately 2 weeks induced significant nitrite accumulation. Granule characteristic analysis elucidated the disparate inhibition mechanisms of heavy metals and antibiotics: the internalization of heavy metals caused metabolic disorders, whereas OTC functioned as a growth retarder. However, anammox reactors could adapt to a JLR of 0.04 kg m day via self-regulation during the acclimatization to subinhibitory concentrations, which had a stable nitrogen removal rate (>8.5 kg m day) and removal rate efficiency (>75 %) for reactors with Cu-OTC addition. Therefore, this study supports the great potential of using anammox granules to treat swine wastewater. [ABSTRACT FROM AUTHOR]

In the present study, the short- and long-term effects of Zn(II) on the anaerobic ammonium oxidation (anammox) performance and sludge characteristics were evaluated. The anammox activity decreased with increasing Zn(II) concentration and pre-exposure time in short-term tests. The half maximal inhibitory concentration (IC) of Zn(II) was found to be 25.0 mg L. The 24 and 48-h pre-exposure time was a restricted factor impacting the anammox activity, and washing the inhibited sludge with buffer solution only worked under 0 and 24-h pre-exposure time. The anammox sludge could tolerate 5 mg L Zn(II) but was suppressed at 8 mg L. The inhibited performance could be remitted, as the combination strategies were applied, and after the short term of recovery period, the inhibited sludge characteristics were remitted to the normal. [ABSTRACT FROM AUTHOR]

In this study, the effects of both transient and long-term inorganic carbon (IC) addition on the anaerobic ammonium oxidation (ANAMMOX) process under pseudo-steady-state and substrate inhibitions were analyzed using reactor performance and measures of sludge activity. Compared with the nitrogen removal rate (NRR) of 3.42 kg N m day in the control bioreactor (ICDR) without IC, the peak NRR reached 21.0 kg N m day in the reactor (ICAR) with sufficient IC added. It was revealed that the long-term addition of bicarbonate significantly enhanced the performance of the ANAMMOX reactor. The optimum HCO/TN ratio was considered to be 1.20, which is lower than that in normal conditions. The IC concentration affected biomass activity, and the transient addition or removal of IC to differing sludge media caused a significant loss of activity. Sufficient addition of IC alleviated the inhibition of excess substrates, while the inhibition was aggravated by the IC limitation. The half-maximal (50 %) inhibitory concentrations of substrate for the sludge were 295 mg L NO-N and 361 mg L NH-N with 120 mg L of fixed HCO and 346 mg L NO-N and 456 mg L NH-N with unlimited IC, respectively. Changing the HCO/TN (in milligrams per milligram) ratio resulted in the variation of ANAMMOX stoichiometric ratios. Sludge characterization parameters in the ICDR, including biomass, extracellular polymeric substances, heme C, and so on, were lower than those in ICAR. Filamentous bacteria and spherical bacteria were also observed in the reactor with limited IC. [ABSTRACT FROM AUTHOR]

The present study reports the operation of a laboratory-scale anoxic sulfide oxidizing (ASO) reactor to investigate the effects of influent nitrite to bisulfide molar ratios of 0.58, 1.45, and 1.75 upon the simultaneous bisulfide and nitrite removal rates from the synthetic wastewater. For all tested ratios, very high bisulfide removal percentages (above 99 %) were observed. The mass balance analysis suggested that the bisulfide oxidation was incomplete. The sulfate formation decreased with the increasing influent sulfide concentrations. An influent bisulfide concentration above 1400 mg S / 1 accompanied by high effluent nitrite might have some inhibitory effect on the complete sulfide oxidation to sulfate. Nitrite removal percentage for the 0.58 ratio was in the range of 71.89-86.86 %, showing some fluctuations in the working performance of the ASO reactor. Nitrite removal at the 1.45 ratio ranged from 72.70-87.30 %. Comparatively higher nitrogen removal (78-94 %) was observed for the 1.75 ratio. The application of an influent nitrite to sulfide molar ratio of 1.75 would be a better choice for higher nitrite and bisulfide removal efficiencies in an ASO reactor. [ABSTRACT FROM AUTHOR]