Guang-Feng Yang

The effect of nitrite inhibition on the anammox process

The negative effect of nitrite on anammox activity has been reported widely during the past decade. Although the adverse effect is clear, conflicting reports exist on the level at which it occurs and its reversible/irreversible nature. An in depth study on nitrite inhibition therefore was performed in which the influence of environmental factors was evaluated. Anammox activity was measured in anammox granules by continuously monitored standardized manometric batch tests extending the interpretation by evaluation of lag times, maximum conversion rates during the tests and substrates/product conversion ratios. The granules where obtained from a one-stage anammox reactor, the dominant anammox organisms belonged to the Brocadia type. The observed 50% activity inhibition for nitrite (IC(50)) was 0.4 g N L(-1). The activity recovered fully after removal of the nitrite. Conversion in fresh medium after exposure to up to 6 g NO(2)(-)-N L(-1) for 24 h showed less then 60% loss of activity. Presence of ammonium during nitrite (2 g N L(-1)) exposure resulted in a stronger loss of activity after nitrite exposure (50% and 30% in presence and absence of ammonium respectively). Presence of oxygen during nitrite incubation led to a maximum activity reduction of 32%. The recovery after exposure indicates that the adverse effect of nitrite is reversible and thus inhibitory rather than toxic in nature. Similarities between exposure at three different pH-values indicate that nitrite rather than nitrous acid is the actual inhibiting compound.

Impacts of transient salinity shock loads on Anammox process performance

The effect of salinity shock (5-60 g l(-1) NaCl) on anaerobic ammonium oxidation (Anammox) process performance was investigated. The response to the shock loads can be divided into three stages: a sensitive period, an interim stable period and a recovery period which lasted 6-26 d. When exposed to NaCl shocks for 12h, the sludge retention time (SRT) of the reactor decreased with increasing NaCl shock loads, ranging between 2.9 and 22.5d, meanwhile the biomass decreased by 0.8-37.4%. When shock loads were higher than 10 g l(-1) NaCl, the reactor was at risk of losing too much biomass. The granular surface was rough due to rapid growth of filamentous bacteria and extracellular polymeric substances (EPS), also the EPS amount changed during all NaCl shock loads. In the latter of shocks, the microorganisms in the reactor showed a little adaption to the NaCl shock.

The joint inhibitory effects of phenol, copper (II), oxytetracycline (OTC) and sulfide on Anammox activity.

A batch test was employed to analyze the joint toxicity of copper (II) and oxytetracycline (OTC), OTC and sulfide, phenol and sulfide (S(2-)), phenol and copper (II), and OTC, copper (II) and substrate on an Anammox mixed culture. The joint toxicity of OTC and copper (II) on the Anammox mixed culture was antagonistic, whereas the interaction between OTC and S(2-) and between phenol and S(2-) was generally synergistic. The joint toxicity of phenol and copper (II) was dependent on the level of phenol: the joint toxicity was antagonistic at a high phenol level of 300 mg L(-1), whereas the joint toxicity was synergistic at a low phenol level of 75 mg L(-1). The joint toxic effect of OTC, copper (II) and NO(2)(-)-N on the Anammox activity can be ranked in the following order: NO(2)(-)-N>copper (II)>OTC.

Changes in the nitrogen removal performance and the properties of granular sludge in an Anammox system under oxytetracycline (OTC) stress.

The short- and long-term effects of oxytetracycline (OTC) on the anaerobic ammonium oxidation (Anammox) process were evaluated. The OTC inhibition of Anammox was substrate-, and especially nitrite-, dependent. The IC50 of OTC in the batch tests on an Anammox mixed culture was calculated to be 517.5 mg L(-1). The long-term effects of OTC on the Anammox process were examined in a continuous-flow upflow anaerobic sludge blanket reactor. Fifty milligrams per liter of OTC significantly decreased the nitrogen removal rate from 12.4 to 2 kg N m(-3) d(-1) within 26 days. The recovery of Anammox performance after OTC inhibition was accelerated by adding biocatalyst. In contrast to the modified Stover-Kincannon model, the modified Boltzmann model accurately simulated the recovery of Anammox performance. OTC presented in the influent led to sludge hardening and cell lysis. A poor settling property of Anammox sludge was also observed.

The evolution of Anammox performance and granular sludge characteristics under the stress of phenol.

The short- and long-term effects of phenol on anaerobic ammonium oxidation (Anammox) were evaluated. The short-term impact of phenol on Anammox activity was determined by a batch test, and an IC50 value of 678.2 mg L(-1) was calculated. Anammox granular sludge was equally seeded into two identical upflow anaerobic sludge blanket reactors (R0 and R1); synthetic wastewater without phenol was fed to R0 while with varied phenol was fed to R1 to study the long-term effects. The performance of R0 was stable, with a steadily rising nitrogen removal rate of 10.5-21.3 kg N m(-3)d ay(-1). However, the performance of R1 was significantly suppressed by an influent phenol concentration of 50 mg L(-1), and was recovered and stabilized by applying one or more control strategies. The phenol-mediated inhibition depressed the Anammox activity and biomass, and caused a change of stoichiometric ratios and granule characteristics.

Evaluating the recovery performance of the ANAMMOX process following inhibition by phenol and sulfide.

In this study, the recovery performance of two anaerobic ammonium oxidation (ANAMMOX) reactors (R1, R2) that were previously subjected to phenol and sulfide for nearly 200 days with respective levels of 12.5-50 and 8-40 mg L(-1) and then operated in the absence of these suppressors was investigated. High nitrogen removal rates of greater than 36 kg-Nm(-3)d(-1) were achieved through the 81 and 75 days restoration of R1 and R2, respectively. The recovery performance was determined by specific sludge removal rate, heme c contents, specific ANAMMOX activity, settling properties and morphology of ANAMMOX granules. In addition, the modified Boltzmann model, the modified Gompertz model and the modified Logistic model were applied to simulate recovery performance. The modified Boltzmann model was found to be appropriate for predicting recovery performance of the phenol-inhibited reactor, while the modified Logistic model effectively simulated the recovery performance of the sulfide suppressed reactor.

Performance and robustness of an ANAMMOX anaerobic baffled reactor subjected to transient shock loads.

The impacts of transient overloads on the performance of a laboratory-scale anaerobic ammonium oxidation (ANAMMOX) anaerobic baffled reactor was studied by increasing the substrate concentration or inflow rate to 1.5-3.0 times above normal values. These shocks, with the exception of the highest substrate shock, weakened the nitrogen removal efficiency (NRE) but improved the nitrogen removal rate by 0.01-0.18 g l(-1) h(-1). The communities and the location of the sludge may be altered by distinct types of shocks. The substrate vibration data showed that the reactor was unresponsive to hydraulic shocks but sensitive to substrate shocks and the former compartments were more susceptible to the shocks. In the inhibition period, the pH and NRE of the reactor were related to the residual ammonium and free ammonia (FA) and FA was a factor in the reactor fluctuations. The Gaussian model proposed to describe the shocks response fits the experimental data well.

Floatation of flocculent and granular sludge in a high-loaded anammox reactor.

The floatation of flocculent and granular sludge was investigated in this study. An anaerobic ammonium oxidation (anammox) upflow anaerobic sludge blanket (UASB) reactor was operated for 665 days. During this time, the maximum nitrogen removal rate was 52.6 kg Nm(-3) d(-1). Floccule floatation occurred between days 100 and 140, which potentially resulted from the sudden increase in gas yield and the poor settling ability of the floccules. Increasing the shear rate from 0.084 to 0.135 s(-1) was effective at eliminating floccule floatation. In addition, granule floatation occurred between days 572 and 665, which likely resulted from the formation of hollows within the granules. Floatation may be effectively prevented by maintaining a shear rate of more than 0.778 s(-1). Furthermore, the mechanisms of granule floatation and the floatation processes were proposed. Overall, controlling the shear force may effectively overcome sludge floatation.