Yanlong Zhang

Process stability and the recovery control associated with inhibition factors in a UASB-anammox reactor with a long-term operation.

A UASB-anammox reactor was operated for 900 days to study its process stability. The negative effects of free ammonia (FA) and free nitrous acid (FNA) were investigated over three separate inhibitions and recoveries. The IC10, IC50 and IC90 (inhibitory concentration/a 10%, 50% and 90% activity loss) of FNA and FA responding to the NH4(+)-N, NO2(-)-N and TN removal efficiency were evaluated. In the 1st inhibition, the average FNA-IC10 observed was 0.67 μg L(-1) and the FA-IC10 for TN removal was 4.85 mg L(-1). In the 2nd inhibition, an FNA-IC10 of 0.44μ g L(-1) and an FA-IC10 of 3.56 were found. In the 3rd inhibition, however, both the FNA-IC10 and FA-IC10 were found to have increased, with values of 0.50 μg L(-1) and 4.42 mg L(-1), respectively. A clear control region was established for multiple inhibitions and the recoveries, which followed (pH 7.5-8.5, FA below 10mg/100mg NH4(+)-N and an FNA below 0.005 mg/100 mg NO2(-)-N) for the purpose of optimizing the operation conditions of the UASB-anammox reactor.

Long-term operation performance and variation of substrate tolerance ability in an anammox attached film expanded bed (AAFEB) reactor.

An anammox attached film expanded bed (AAFEB) reactor was operated to study the long-term performance and the variation of substrate tolerance ability. The results indicated that the nitrogen loading potential (NLP) was significantly enhanced from 13.56gN·(L·d)(-)(1) to 20.95gN·(L·d)(-)(1) during the stable operation period. The inhibitory concentration of 10% (IC10) for free ammonia (FA), free nitrous acid (FNA) and SNinf (diluted substrate concentration) increased from 18mg/L, 12μgL(-1) and 370mgNL(-)(1) to 31mg/L, 19μgL(-1) and 670mgNL(-)(1), respectively. However, the substrate shock of 2500mgNL(-)(1) for 24h terribly weakened the treatment performance and substrate tolerance ability of the reactor. The results of batch tests indicated that the existence of lag phase made the AAFEB reactor more vulnerable to substrate variation. The SNinf was accurate to be used to monitor the reactor performance and should be maintained below 320mgNL(-)(1) to ensure the absolute stable operation.

Substrate inhibition and concentration control in an UASB-Anammox process

An UASB-Anammox reactor was operated for more than one year to study the process performance variations respond to the nitrogen loading rate (NLR) and substrate concentration. The IC10 (451.1mg/L), IC50 (725.3mg/L) and the prospected threshold of influent total nitrogen (TN) concentration were simulated. A stable TN removal efficiency was obtained when the TN influent was controlled. The disequilibrium distribution of the substrate following the plug flow with the height of the reactor resulted in significant variations in specific Anammox activity from the bottom to the top of the reactor (348→3mgN/gVSS/d). With long term acclimation, the nitrogen removal capacity of Anammox sludge varied significantly, with the most activated sludge obtained in the bottom part a 100 times capacity greater than that of the top. A stable performance with high removal efficiency in the constructed UASB-Anammox reactor was obtained when the influent TN concentration was below 451.1mg/L.

The Treatment Performance and the Bacteria Preservation of Anammox: A Review

Because of the low energy costs in the absence of the need for aeration, the non-requirement of a carbon source and alkali, and the reduced production of excess sludge, anaerobic ammonia oxidation (Anammox) has been extensively studied as an alternative to the conventional nitrification–denitrification pathway for biological nitrogen removal from wastewater. However, many challenges remain which need to be overcome to prepare the process for engineering application. These include the long doubling time of Anammox bacteria/autotrophic ammonia-oxidizing bacteria (AAOB), the low tolerance capacity to substrate concentration, and high sensitivity to various environmental factors. This review article focuses on the main drawbacks of the Anammox process and evaluates the progress made to date with regard to the enrichment of AAOB and the treatment performance of the Anammox process itself. The factors affecting the nitrogen removal performance of the Anammox process, such as substrate concentration, organic matters, and variation of temperature, are also reviewed and discussed. Finally, the need for the development of long-term storage methods for AAOB is addressed.

Bio-kinetics evaluation and batch modeling of the anammox mixed culture in UASB and EGSB reactors: batch performance comparison and kinetic model assessment

To predict the performance and evaluate the optimized process operation, a number of kinetic models were conducted in batch experiments for UASB-anammox biomass and EGSB-anammox biomass. Following a time series with substrate variations, the reaction of the mixed culture was separated into three phases: the anammox reaction, denitrification and cell lysis. Among the six selected kinetic models, the Hanlev and Luong models were found to be the most appropriate, with a prospected rmax of 0.28, 0.30 gN gVSS−1 d−1, a Ks of 53.38, 52.52 mg NH4+-N L−1 and inhibition coefficient of 900 and 928 mg N L−1, respectively. Significant differences were found in the simulated specific anammox activity (SAA) in the two reactors following longitudinal distribution. The EGSB-anammox biomass had the highest rmax of 0.30 gN gVSS−1 d−1, and a Ks of 53.38 mg NH4+-N L−1 (123.84 mg TN L−1), both validated in the models and experimentally. In contrast, a large variation was found in the UASB-anammox biomass, from 0.1 to 0.6 gN gVSS−1 d−1 from the top to the bottom of the reactor, and the removal efficiency of the whole system was lower. It was also found that a second feeding tended to increase the SAA for higher purity anammox biomass.

Influence of four antimicrobials on methane-producing archaea and sulfate-reducing bacteria in anaerobic granular sludge.

The influence of Cephalexin (CLX), Tetracycline (TC), Erythromycin (ERY) and Sulfathiazole (ST) on methane-producing archaea (MPA) and sulfate-reducing bacteria (SRB) in anaerobic sludge was investigated using acetate or ethanol as substrate. With antimicrobial concentrations below 400mgL(-1), the relative specific methanogenic activity (SMA) was above 50%, so that the antimicrobials exerted slight effects on archaea. However ERY and ST at 400mgL(-1) caused a 74.5% and 57.6% inhibition to specific sulfidogenic activity (SSA) when the sludge granules were disrupted and ethanol used as substrate. After disruption, microbial tolerance to antimicrobials decreased, but the rate at which MPA utilized acetate and ethanol increased from 0.95gCOD·(gVSS⋅d)(-1) to 1.45gCOD·(gVSS⋅d)(-1) and 0.90gCOD·(gVSS⋅d)(-1) to 1.15gCOD·(gVSS⋅d)(-1) respectively. The ethanol utilization rate for SRB also increased after disruption from 0.35gCOD·(gVSS⋅d)(-1) to 0.46gCOD·(gVSS⋅d)(-1). Removal rates for CLX approaching 20.0% and 25.0% were obtained used acetate and ethanol respectively. The disintegration of granules improved the CLX removal rate to 65% and 78%, but ST was not removed during this process.

Effects of soluble microbial products (SMP) on the performance of an anammox attached film expanded bed (AAFEB) reactor: Synergistic interaction and toxic shock

The accumulation of soluble microbial production (SMP) in an anammox attached film expanded bed (AAFEB) and its effect on the reactor performance were investigated in this study. During the long-term experiment, an extended HRT resulted in the accumulation of SMP and the change of treatment performance. When the SMP increased from 10.5±1.5mgL-1 to 31.7±6.4mgL-1 with the increase of influent TN concentration from 313mgL-1 to 2500mgL-1, the TN removal efficiency was stable. However, when the influent TN concentration was 3500mgL-1, the SMP concentration increased higher than 100mgL-1, the reactor soon became inhibited. Bath tests indicated that both the specific anammox activity (SAA) and the substrate tolerance ability decreased during the stable operation phases, whereas the specific denitrification activity (SDA) was significantly enhanced. In addition, N2O emissions in the anammox-denitrifier symbiotic system were greater than in the conventional nitrogen removal process.

Effects of substrate shock on extracellular polymeric substance (EPS) excretion and characteristics of attached biofilm anammox granules

Environmental stresses are assumed to significantly impact the content and concentration of produced extracellular polymeric substances (EPS) and therefore influence the performance of an ananmmox attached film expanded bed (AAFEB) reactor. In this study, a transient high substrate concentration of 2500 mg N L−1 (calculated as the sum of NN4+–N and NO2−–N) for 24 hours stimulated abundant EPS excretion as well as deterioration of anammox granules. The results indicated that a high EPS concentration of 89.6 ± 48.3 mg g−1 VSS resulted in 35.0 ± 0.8% decrease in the granule settling properties and 30.5 ± 0.9% reduction in the total VSS amount. The production of EPS was reasonably attributed to the impact of utilization-associated and stress-associated effects by the substrate. The results of a series of batch experiments indicated that a rapid increase of loosely-bound EPS (LB-EPS) from 41.2 to 114.6 mg g−1 VSS occurred when the substrate concentration steadily increased from 400 to 1000 mg N L−1, in contrast, the tightly-bound EPS (TB-EPS) remained stable at 32.5 ± 2.8 mg g−1 VSS. Thus, the LB-EPS was considered the key factor for the deterioration of granule stability and the substrate concentration should be controlled below 400 mg N L−1 to avoid triggering the accumulation of LB-EPS. Furthermore, the formation and disintegration mechanisms of attached film anammox granules were also elucidated in this study.