Jin-Jin Yu

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.

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.

Enhancement of ANAMMOX activity by low-intensity ultrasound irradiation at ambient temperature

This paper aims to investigate the enhancement effect of low intensity intermittent ultrasound irradiation on the efficiency of anaerobic ammonium oxidation (ANAMMOX) process at ambient temperature. With intermittently irradiated (ultrasound intensity of 0.19 w/cm(2), exposure time of 0.2 min), the reactor (RU) had a nitrogen removal rate (NRR) of 5.49 kgTN/m(3)/d at 14.8°C, while the NRR was 1.53 kgTN/m(3)/d in the control reactor (RC). At the end of operation, the contents of polysaccharide, protein, TTC-dehydrogenase and VSS were 6.82 mg/mgVSS, 26.79 mg/mgVSS, 0.58 mgTF/L/H and 10.11 gVSS/L in RU, higher than the levels in the RC. These results demonstrated that it is possible to achieve stable and highly efficient operation in an ANAMMOX reactor at low ambient temperature by implementation of ultrasonication.

The ANAMMOX reactor under transient-state conditions: Process stability with fluctuations of the nitrogen concentration, inflow rate, pH and sodium chloride addition

The process stability of an anaerobic ammonium oxidation (ANAMMOX) was investigated in an upflow anaerobic sludge blanket reactor subjected to overloads of 2.0- to 3.0-fold increases in substrate concentrations, inflow rates lasting 12 or 24h, extreme pH levels of 4 and 10 for 12h and a 12-h 30 g l(-1) NaCl addition. During the overloads, the nitrogen removal rate improved, and the shock period was an important factor affecting the reactor performance. In the high pH condition, the reactor performance significantly degenerated; while in the low pH condition, it did not happen. The NaCl addition caused the most serious deterioration in the reactor, which took 108 h to recover and was accompanied by a stoichiometric ratio divergence. There are well correlations between the total nitrogen and the electrical conductivity which is considered to be a convenient signal for controlling and monitoring the ANAMMOX process under transient-state conditions.