Qian-Qian Chen

Successful start-up of the anammox process: Influence of the seeding strategy on performance and granule properties

Successful start-up of the anaerobic ammonium oxidation (anammox) process in up-flow sludge blanket reactor was achieved by seeding denitrifying (R0) or mixed denitrifying-anammox granular sludge at a 3:1 volume ratio (R1). The results demonstrated that R1 was successfully started-up on day 40 and had a nitrogen removal rate (NRR) of 0.55kgNm(-3)d(-1). By contrast, it took 98days to start up R0 (0.54kgNm(-3)d(-1)). R0 and R1 achieved maximum NRRs of 5.70 and 12.02kgNm(-3)d(-1), respectively. The biogranules from R1 generally possessed greater specific anammox activity (SAA), higher extracellular polymeric substance (EPS) and heme c content, larger granules and greater settling velocity. Quantitative PCR (qPCR) and high-throughput sequencing techniques were used to monitor the evolution of the bacterial community. These results demonstrated the feasibility of seeding mixed denitrifying-anammox granular sludge to start-up an anammox reactor.

Anaerobic ammonium-oxidizing bacteria gain antibiotic resistance during long-term acclimatization.

Three broad-spectrum antibiotics, amoxicillin (AMX), florfenicol (FF) and sulfamethazine (SMZ), that inhibit bacteria via different target sites, were selected to evaluate the acute toxicity and long-term effects on anaerobic ammonium oxidation (anammox) granules. The specific anammox activity (SAA) levels reduced by approximately half within the first 3 days in the presence of antibiotics but no nitrite accumulation was observed in continuous-flow experiments. However, the SAA levels and heme c content gradually recovered as the antibiotic concentrations increased. Extracellular polymeric substances (EPS) analysis suggested that anaerobic ammonium-oxidizing bacteria gradually developed a better survival strategy during long-term acclimatization, which reduced the antibiotic stress via increased EPS secretion that provided a protective cocoon. In terms of nitrogen removal efficiency, anammox granules could resist 60 mg-AMX L(-1), 10 mg-FF L(-1) and 100 mg-SMZ L(-1). This study supported the feasibility of using anammox granules to treat antibiotic-containing wastewater.

Influence of preservation temperature on the characteristics of anaerobic ammonium oxidation (anammox) granular sludge

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 (R0), and then the enriched anammox granules were preserved at 35, 20, 4, and −30xa0°C. The subsequent reactivation characteristics of the granules were evaluated in four UASB reactors (denoted R1, R2, R3, and R4, respectively) to investigate the effect of preservation temperature on the characteristics of anammox granules and their reactivation performance. The results demonstrated that 4xa0°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 42xa0days of storage, the anammox granules preserved at 4xa0°C (R3) exhibited a better recovery performance than those preserved at 20xa0°C (R2), −30xa0°C (R4), and 35xa0°C (R1). The comprehensive comparison indicated that 4xa0°C is the optimal storage temperature for anammox granular sludge because it promotes improved maintenance and recovery performance properties.

Effects of thiocyanate on granule-based anammox process and implications for regulation.

The feasibility of using anaerobic ammonium oxidation (anammox) process to treat industrial wastewater containing thiocyanate (SCN-) was examined in this study. Anammox activity decreased with increasing thiocyanate concentration and pre-exposure time in batch tests. A typical noncompetitive model was used to fit the data for thiocyanate inhibition, and the 50% inhibition concentration (IC50) of thiocyanate on anammox was 620.4mgL-1 at 200mgL-1 total nitrogen level. The influent thiocyanate concentration of test reactor (R1) in phase II gradually increased from 10 to 120mgL-1, and the average nitrogen removal efficiency (NRE) of R1 was maintained at 83.0±7.82%. This robustness was attributed to the self-adaptation ability of anammox biomass through long-term acclimatization. The NRE was decreased to 57.1% under 130mgL-1 thiocyanate within two days. However, the NRE of control reactor (R0) in absence of thiocyanate was 91.23±4.11% in this phase. Under thiocyanate stress, the specific anammox activity, settling velocity and heme c content of the granules significantly decreased, and the extracellular polymeric substances content slightly increased. The short- and long-term performance inhibition could be reversed in the presence of 10mgL-1 Fe(III).

The short- and long-term effects of Mn2+ on biogranule-based anaerobic ammonium oxidation (anammox)

The short- and long-term effects of Mn2+ on the performance of anaerobic ammonium oxidation (anammox) granules were investigated in the present study. Anammox activity was determined at various Mn2+ concentrations in batch assays, and the 50% inhibition concentration value was determined to be 7.33mgL-1. However, no obvious deterioration of reactor performance was observed during the 150-day continuous-flow operation, and the nitrogen removal efficiency of the test reactor (R1) fluctuated between 91% and 92% as the Mn2+ concentration was increased from 1 to 200mgL-1. Additionally, the specific anammox activity, heme c content and the amounts of extracellular polymeric substances in the anammox biomass increased and then subsequently decreased. The results demonstrated that short-term exposure to Mn2+ has a negative effect on anammox biomass, but the biomass could tolerate Mn2+ stress after acclimation to a high concentration of 200mgL-1 at the end of the continuous-flow experiment.

Inhibitory effects of sulfamethoxazole on denitrifying granule properties: Short- and long-term tests

The broad-spectrum antibiotic sulfamethoxazole (SMX) was chosen to assess its short- and long-term effects on denitrifying granules. The SMX concentration and pre-exposure time in batch testing influenced the denitrifying granule activity. In the continuous-flow experiments, no inhibitory effects on the upflow anaerobic sludge blanket performance were observed at SMX concentrations up to 100mgL-1, probably because of functional redundancy and long-term acclimation. The specific denitrifying activity first decreased to a minimum of 49.3% and then recovered to a level comparable to the initial level as the SMX concentration increased. The changing trend of the extracellular polymer content was consistent with the specific denitrifying activity throughout the process, and relatively high EPS loss ratios (maximum loss of 61.8%) were observed. Additionally, the diameter of the denitrifying granules monophonically increased to a final value of 35.0%. This research provided the application of denitrifying granules to treat wastewater that contained antibiotic.

Insight into the short- and long-term effects of Cu(II) on denitrifying biogranules.

This study aimed to investigate the short- and long-term effects of Cu(2+) on the activity and performance of denitrifying bacteria. The short-term effects of various concentrations of Cu(2+) on the denitrifying bacteria were evaluated using batch assays. The specific denitrifying activity (SDA) decreased from 14.3 ± 2.2 (without Cu(2+)) to 6.1 ± 0.1 mg N h(-1)g(-1) VSS (100 mg Cu(2+)L(-1)) when Cu(2+) increased from 0 to 100 mg L(-1) with an increment of 10 mg Cu(2+)L(-1). A non-competitive inhibition model was used to calculate the 50% inhibition concentration (IC50) of Cu(2+) on denitrifying sludge (30.6 ± 2.5 mg L(-1)). Monod and Luong models were applied to investigate the influence of the initial substrate concentration, and the results suggested that the maximum substrate removal rate would be reduced with Cu(2+) supplementation. Pre-exposure to Cu(2+) could lead to an 18.2-46.2% decrease in the SDA and decreasing percentage of the SDA increased with both exposure time and concentration. In the continuous-flow test, Cu(2+) concentration varied from 1 to 75 mg L(-1); however, no clear deterioration was observed in the reactor, and the reactor was kept stable, with the total nitrogen removal efficiency and total organic carbon efficiency greater than 89.0 and 85.0%, respectively. The results demonstrated the short-term inhibition of Cu(2+) upon denitrification, and no notable adversity was observed during the continuous-flow test after long-term acclimation.

Insight into the short- and long-term effects of quinoline on anammox granules: Inhibition and acclimatization

The short- and long-term influence of quinoline on the properties of anaerobic ammonium oxidation (anammox) biogranules was evaluated. During batch tests, the bioactivity of anammox granules in the presence of different quinoline concentrations was monitored, and the IC50 of quinoline was calculated to be 13.1u202fmgu202fL-1 using a non-competitive inhibition model. The response of anammox granules to pre-exposure to quinoline was dependent on metabolic status, and the presence of both quinoline and NO2--N had a rapid detrimental effect, resulting in a 64.5% decrease within 12u202fh. During continuous-flow experiments, the nitrogen removal rate (NRR) of the reactor decreased sharply within 3u202fdays in the presence of 10u202fmgu202fL-1 quinoline and then was restored to 2.6u202fkgu202fNu202fm-3u202fd-1. In the presence of quinoline-induced stress, the specific anammox activity and levels of extracellular polymeric substance and heme c were decreased, while settling velocity persistently increased. After cultivation and acclimation obtained by adding a medium level of quinoline to the influent, the anammox granule sludge was able to tolerate 10u202fmgu202fL-1 quinoline in 178u202fdays.