Inhibitory Effect Of Free Ammonia Research Articles

Nitritation Performance of Zeolite Moving Bed Biofilm Reactor for Ammonium Wastewater Treatment

A new type of zeolite-suspended packing was developed by using zeolite as an important raw material, which was then used to start the zeolite moving bed biofilm reactor (ZMBBR). ZMBBR was compared with the ceramsite moving bed biofilm reactor (CMBBR) packed with ordinary ceramsite-suspended packing to investigate the different nitritation performance. The results showed that stable nitritation was successfully achieved in two reactors by the inhibitory effect of free ammonia (FA), and both of their nitrite accumulation rates (NAR) reached 90%; due to the adsorption of zeolite to ammonium, ZMBBR relieved the inhibition of FA on AOB faster than CMBBR and achieved nitritation earlier; CMBBR and ZMBBR could maintain long-term stable nitrosation when ρ(NH4+-N) was 350 mg·L-1 and 1050 mg·L-1 and NPRAVG was 0.43 kg·(m3·d)-1 and 1.26 kg·(m3·d)-1, respectively, and ARECMBBR=82.21% and AREZMBBR=88.85%. In the process of the influent ρ(NH4+-N) gradually increasing from 250 mg·L-1 to 1250 mg·L-1, the maximum nitrite production rate (NPR) of CMBBR was 0.5634 kg·(m3·d)-1; when ρ(FA) reached 166 mg·L-1 at the influent ρ(NH4+-N) of 750 mg·L-1, CMBBR broke down for the heavy inhibition of FA. The maximum NPR of ZMBBR was 1.800 kg·(m3·d)-1, and the performance of ZMBBR was getting worse after the ρ(FNA) reached the peak value of 1.9611 mg·L-1 at the influent ρ(NH4+-N) of 1250 mg·L-1. Subsequently, the ρ(FA) of ZMBBR reached 158 mg·L-1 rapidly, the NPR dropped significantly to 0.9028 kg·(m3·d)-1, and the performance of ZMBBR became significantly worse. It was demonstrated by high-throughput sequencing analysis that the dominant strain of ZMBBR and CMBBR was Nitrosomonas_europaea, and the relative abundances of N._europaea in ZMBBR and CMBBR were 11.15% and 10.92%, respectively.

Free ammonia inhibition in microalgae and cyanobacteria grown in wastewaters: Photo-respirometric evaluation and modelling

The inhibitory effects of free ammonia (FA) on microalgae/cyanobacteria in wastewater-treating photobioreactors (PBR) can strongly reduce their treatment efficiency, increasing the operational costs and undermining the stability of the system. Although FA-promoting conditions (high pH, temperature and ammoniacal nitrogen concentration) are commonly met in outdoor PBRs, photosynthesis inhibition from FA has been scarcely explored and is rarely considered in microalgae-bacteria growth models. Two pilot systems and a series of lab-scale monocultures were tested using a photo-respirometry approach, to evaluate the effects of FA (8.5–136 mg NH3 L−1) on photosynthesis. Two mathematical inhibition models were compared, with the aim of selecting best-fitting equations to describe photo-respirometric experiments. A set of calibrated inhibition parameters was obtained for microalgae and cyanobacteria, growing in monocultures or in mixed algae-bacteria consortia. Cyanobacteria were more sensitive to FA than green microalgae and mixed phototrophs-bacteria consortia showed a higher resistance compared to monocultures. Estimated inhibition parameters were used to describe common operational/environmental conditions in algae-bacteria systems, demonstrating the potential drop in photosynthetic activity under those relevant operational conditions.

Effects of Alkalinity on Partial Nitrification in a Zeolite Sequencing Batch Reactor

Stable partial nitrification was successfully achieved in a zeolite sequencing batch reactor (ZSBR) with an excellent nitrite accumulation ratio of over 90.0%, and the effects of four alkalinity concentrations (calculated by CaCO3) on the nitritation in the ZSBR were investigated at an influent ammonia nitrogen concentration of 500 mg·L-1. The results showed that the key for the partial nitrification achieved in ZSBR was that the inhibitory effect of free ammonia (FA) on nitrite oxidizing bacteria (NOB) was much greater than that on ammonia oxidizing bacteria (AOB). Additionally, the wastewater containing ammonia nitrogen converted by this process can be used as the influent for anaerobic ammonium oxidation to further remove ammonia nitrogen and total nitrogen in wastewater. When the dosage of alkalinity was 2500 mg·L-1 in the ZSBR, the best nitritation efficiency was obtained with an average ammonia nitrogen conversion efficiency of 66.7%, nitrite accumulation ratio of 98.1%, and nitrite production rate of 0.74 kg·(m3·d)-1. It was demonstrated by high-throughput sequencing analysis that significant microbial community variations occurred after a long period of operation, and these changes involved an enrichment of AOB and inhibition of NOB in the ZSBR.

Effect of free ammonia inhibition on process recovery of partial nitritation in a membrane bioreactor

Long-term inhibitory effect of free ammonia (FA) on the catabolic and anabolic activities of an enriched Nitrosomonas culture was investigated. Ammonia oxidizing bacteria (AOB) was inhibited at FA concentration of 34.34 ± 6.85 mg NH3-N/L while threshold inhibitory FA concentration was likely 23.64 ± 4.51 mg NH3-N/L. Below the latter, cell-specific ammonia oxidation rate (AOR), cell number and extracellular polymeric substances (EPS) increased. The calculated yield showed AOB had tended to increase cell mass under FA inhibition. Nitrite concentration increased by 58.6% 12 days after FA decreased to 8.89 ± 0.95 mg NH3-N/L. However, AOB cells became more sensitive to free nitrous acid (FNA) after 70 days of FA inhibition. Long-term FA inhibition changed AOB cell morphology and this could have increased AOB vulnerability to FNA. This study indicated FA inhibited catabolic and anabolic activities, and that long-term FA inhibition had adverse impact on process recoverability and subsequent failure threshold.

The inhibitory effects of free ammonia on ammonia oxidizing bacteria and nitrite oxidizing bacteria under anaerobic condition

The free ammonia (FA) inhibition on ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) under anaerobic condition was investigated in this study. The results indicated that NOB was more sensitive to the FA anaerobic treatment than AOB. The FA anaerobic inhibition on nitrifier gradually heightened with the increase of FA concentration. Accompanied with FA concentration increase from 0 to 16.82mgNH3–N·L−1 (the highest concentration adopted in this study), the activity of AOB reduced by 15.9%, while NOB decreased by 29.2%. After FA anaerobic treatment, nitrite was accumulated during nitrification. However, the nitrite accumulation disappeared on the sixth cycle of activity recovery tests with excessive aeration. Based on this result, a novel strategy for achieving nitritation is proposed, which involves recirculating a portion of the activated sludge through a side-line sludge treatment unit, where the sludge is subjected to treatment with FA under anaerobic condition.

Performance, limitations and microbial diversity of a biotrickling filter for the treatment of high loads of ammonia

In this work, limits and capacities of biotrickling filtration as a technique to compete with chemical scrubbing for the treatment of ammonia loads above 40gNm−3h−1 are investigated. Long-term operation of a lab-scale biotrickling filter under different inlet NH3 concentrations (100–1400ppmv) and gas contact times (2–46s) was performed to study the influence of operating parameters such as the make-up water flowrate and to assess biological and mass transfer limitations. The effect of the ammonia load over nitritation and nitratation rates was analyzed. At the same ammonia load, nitrification rates at gas velocities of 38.4mh−1 (large gas contact times) were 2-fold higher compared to those at gas velocities of 844mh−1 (short gas contact time) due to a better distribution of the NH3 along the packed bed, thus reducing the inhibitory effect of free ammonia (FA) and free nitrous acid (FNA) accumulation. Microbial diversity was compared between low and high-ammonia load conditions through tag-encoded FLX amplicon pyrosequencing showing that accumulation of FA and FNA promoted the growth of nitrifiers. Also, a large fraction of denitrifying species was found demonstrating that denitrification occurs also in aerobic biotrickling filters.

Effects of free ammonia on volatile fatty acid accumulation and process performance in the anaerobic digestion of two typical bio-wastes

The effect of free ammonia on volatile fatty acid (VFA) accumulation and process instability was studied using a lab-scale anaerobic digester fed by two typical bio-wastes: fruit and vegetable waste (FVW) and food waste (FW) at 35°C with an organic loading rate (OLR) of 3.0kg VS/(m3·day). The inhibitory effects of free ammonia on methanogenesis were observed due to the low C/N ratio of each substrate (15.6 and 17.2, respectively). A high concentration of free ammonia inhibited methanogenesis resulting in the accumulation of VFAs and a low methane yield. In the inhibited state, acetate accumulated more quickly than propionate and was the main type of accumulated VFA. The co-accumulation of ammonia and VFAs led to an “inhibited steady state” and the ammonia was the main inhibitory substance that triggered the process perturbation. By statistical significance test and VFA fluctuation ratio analysis, the free ammonia inhibition threshold was identified as 45mg/L. Moreover, propionate, iso-butyrate and valerate were determined to be the three most sensitive VFA parameters that were subject to ammonia inhibition.

Advanced nitrogen removal using bio-refractory organics as carbon source for biological treatment of landfill leachate

A combined system was developed to enhance the chemical oxygen demand (COD) and total nitrogen (TN) removal from landfill leachate. The system consists of an up-flow anaerobic sludge blanket (UASB), anoxic/aerobic (A/O) reactor, and the denitrifying UASB (DUASB). The influent used in our study was a mixture of 1:2 raw leachate and domestic wastewater. Because of the inhibitory effect of free ammonia (FA) on the nitrite-oxidizing bacteria (NOB), stable partial nitrification occurred, with a consistent nitrite accumulation ratio in the A/O reactor. In the DUASB, the nitrite and nitrate nitrogen (NOX−-N) were removed efficiently by denitrification by utilizing the carbon source of refractory organics under anoxic condition, which were likewise degraded. The organic matter, total nitrogen and ammonia nitrogen in the final effluent were 80–90, 39, and 14 mg/L, respectively, with respective removal efficiencies of 95, 98, and 95%. The respective COD removal efficiencies in the UASB, A/O and denitrifying-UASB were 76.8, 2.8, and 16.3%. The proposed process is an advanced technique that accomplishes the removal of organic matter and nitrogen in a single step.

Effect of influent nitrogen concentration on feasibility of short-cut nitrification during wastewater treatment in activated sludge systems

AbstractThe inhibitory effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria (NOB) was studied in a laboratory-scale sequencing batch reactor with a suspended microbial culture. The reactor was operated at 15°C, with a dissolved oxygen concentration in excess of 5 mg L

Improving anaerobic digestion of pig manure by adding in the same reactor a stabilizing agent formulated with low-grade magnesium oxide

Struvite precipitation and pig manure anaerobic digestion were coupled in the same reactor in order to mitigate the inhibitory effect of free ammonia and avoid precipitator costs. The stabilizing agent used to facilitate struvite precipitation was formulated with low-grade magnesium oxide by-product; an approach that would notably reduce struvite processing costs. The interaction between pig manure and stabilizing agent was analyzed in batch experiments, on a wide range of stabilizing agent additions from 5 to 100 kg m−3. The monitoring of the pH and ammonia removal during 24 h showed the high capacity of the stabilizing agent to remove ammonia; removal efficiencies above 80% were obtained from 40 kg m−3. However, a long-term anaerobic digester operation was required to assess the feasibility of the process and to ensure that the stabilizing agent does not introduce any harmful compound for the anaerobic biomass. In this vein, the addition of 5 and 30 kg m−3 of the stabilizing agent in a pig manure continuous digester resulted in a 25% (0.17 m3 kg−1) and a 40% (0.19 m3 kg−1) increase in methane production per mass of volatile solid, respectively, when compared with the reference digester (0.13 m3 kg−1). Moreover, the stability of the process during four hydraulic retention times guarantees that the stabilizing agent did not exert a negative effect on the consortium of microorganisms. Finally, scanning electron microscopy and X-ray diffraction analysis confirmed the presence of struvite as well as two precipitation mechanisms, struvite precipitation on the stabilizing agent surface and in the bulk solution.

Modeling the pH effect on sulfidogenesis in anaerobic sewer biofilm

Wastewater pH affects the transfer of H2S from liquid to gas and hence impacts on the extent of odour and corrosion. Sewage pH may change significantly in sewer networks due to, for example, the fermentation of organic compounds, particularly when the hydraulic retention time is long, the discharge of trade wastes that are organic-rich or with extreme pH, and the intentional addition of alkali to raise the sewage pH. Such a variation of pH is expected to affect sulfate reduction by sewer biofilms. In this work, experimental studies were carried out to reveal the detailed effects of pH on sulfidogenesis by anaerobic sewer biofilms developed in a laboratory sewer reactor fed with real sewage, and the potential causes for the inhibitory effects observed under both high and low pH conditions. The data clearly showed that the sewer biofilm had the highest sulfate reduction rate at around neutral pH (6.5–7.5), and the activity decreased when pH was higher or lower. The data also suggested that the inhibiting effect at a higher pH is likely due to the inhibitory effects of free ammonia, while at a lower pH it is more likely due to the pH itself. An inhibition model formulated based on the above hypotheses was able to adequately describe the measured sulfide production rates under different pH levels and different free ammonia concentrations, as well as data previously reported in literature. The calibrated model was used to simulate sulfide production in a sewer network receiving alkali dosage. The model adequately predicted sulfide production in the network, which could not be achieved with a model not considering the pH effect.

Achieving nitrogen removal via nitrite pathway from urban landfill leachate using the synergetic inhibition of free ammonia and free nitrous acid on nitrifying bacteria activity

In this study, a biological system consisting of an up-flow anaerobic sludge blanket (UASB) and anoxic-oxic (A/O) reactor was established for the advanced treatment of high ammonium urban landfill leachate. The inhibitory effect of free ammonia (FA) and free nitrous acid (FNA) on the nitrifying bacterial activity was used to achieve stable nitritation in the A/O reactor. The results demonstrated that the biological system achieved chemical oxygen demand (COD), total nitrogen (TN) and NH(4)(+)-N removal efficiencies of 95.3, 84.6 and 99.2%, respectively at a low carbon-to-nitrogen ratio of 3:1. Simultaneous denitritation and methanogenesis in the UASB could improve the removal of COD and TN. Nitritation with above 90% nitrite accumulation was successfully achieved in the A/O reactor by synergetic inhibition of FA and FNA on the activity of nitrite oxidizing bacteria (NOB). Fluorescence in situ hybridization (FISH) analysis showed that ammonia oxidizing bacteria (AOB) was dominant and was considered to be responsible for the satisfactory nitritation performance.

Biological Treatment of High Ammonium Content Urban Landfill Leachate Using an Anaerobic-Aerobic Process

Biological system consisting of an up-flow anaerobic sludge blanket (UASB) and anoxic-oxic (A/O) reactor was applied to treat high ammonium content urban landfill leachate. Inhibitory effect of free ammonia (FA) and free nitrous acid (FNA) on nitrifying bacteria activity was used to achieve nitrogen removal via nitrite pathway in the A/O. Results demonstrated that removed efficiencies of COD, total nitrogen (TN) and NH4+-N were 95.3%, 84.6 %and 99.2%, respectively. Stable nitrite pathway with above 90% nitrite accumulation was successfully achieved in the A/O reactor by synergetic inhibition of FA and FNA on the activity of nitrite oxidizing bacteria (NOB). Moreover, Fluorescence in situ hybridization (FISH) analysis showed that AOB was dominant microorganism.

Bio-electrochemical post-treatment of anaerobically treated landfill leachate

Bio-electrochemical treatment of anaerobically pre-treated landfill leachate was investigated in batch and continuous-flow two-chambered microbial fuel cells (MFCs). A high strength young landfill leachate was pre-treated using an upflow anaerobic sludge blanket reactor and the effluent resembling medium-aged landfill leachate was fed to the anode chamber of MFCs. The highest maximum current and power densities achieved in continuous-flow MFC with hydraulic retention time (HRT) of five days were 525mA/m2 (8227mA/m3) and 158mW/m2 (2482mW/m3), respectively. Increase of HRT from one day to five days resulted in the occurrence of partial nitrification, where influent ammonia was converted into nitrite presumably due to the inhibitory effects of free ammonia. The maximum power and current densities obtained in this study were higher compared to other studies with similar leachate characteristics. The results of this study suggest that MFCs can be exploited as a polishing step for anaerobically pretreated landfill leachate.

Inhibitory effects of free ammonia on Anammox bacteria

Anammox bacteria can effectively treat high ammonia and nitrite concentrations under anoxic environments. However, the presence of high ammonia and nitrite concentrations may cause free ammonia and nitrous acid inhibition at high pH and temperature environments. In this study, the inhibitory effect of free ammonia on Anammox bacteria was investigated in a lab-scale upflow fixed-bed reactor with Kaldnes biofilm carriers. Results of continuous operation showed that inhibition was not observed in the Anammox reactor when the free ammonia concentration gradually increased up to 150mg/L. However, Anammox activity suddenly dropped to 10 % when the free ammonia concentration reached to 190mg/L. Nevertheless, high influent ammonia and nitrite concentrations up to 1,500 and 500mg/L, respectively, did not noticeably inhibit the Anammox activity. Gradually decreasing Anammox activity was also supported by fluorescent in situ hybridization (FISH) analysis. FISH and 16S rRNA gene analysis results revealed that main Anammox organisms were phylogenetically related to Candidatus Kuenenia stuttgartiensis, Candidatus Jettenia asiatica and Candidatus Brocadia anammoxidans.

Combined effect of inorganic carbon limitation and inhibition by free ammonia and free nitrous acid on ammonia oxidizing bacteria

The inhibitory effect of free ammonia (NH 3 or FA) and free nitrous acid (HNO 2 or FNA) on the ammonia oxidizing bacteria (AOB) and the dependence of the AOB activity on the concentration of total inorganic carbon (TIC) are well-established. In contrast, less is know about the effect of high FA and FNA concentrations in combination with TIC limitation. Respirometric tests performed with an enriched AOB sludge (81% of AOB as measured with fluorescent in situ hybridization) established that AOB inhibition by FA under TIC limitation was higher than under non-limiting TIC conditions (Haldane inhibition coefficients of 139 and 376 mg NH 3 L −1). AOB affinity for FA decreased under TIC limitation conditions (half-saturation coefficient of 0.28 mg NH 3 L −1 without TIC limitation and 4.3 mg NH 3 L −1 with TIC limitation). Higher inhibition by FNA was observed when TIC was limited since the non-competitive inhibition coefficient decreased from 1.31 mg HNO 2 L −1 (without TIC limitation) to 0.21 mg HNO 2 L −1 (with TIC limitation). This study demonstrates that AOB inhibitions by FA and FNA are amplified with TIC limitation and consequently, AOB dynamics are strongly modified under TIC limitation conditions.

Free ammonia and free nitrous acid inhibition on the anabolic and catabolic processes of Nitrosomonas and Nitrobacter

The inhibitory effects of free ammonia (FA) and free nitrous acid (FNA) on the catabolic and anabolic processes of Nitrosomonas and Nitrobacter were investigated using a method that allows decoupling the growth and energy generation processes. Lab-scale sequencing batch reactors (SBRs) were operated for the enrichment of Nitrosomonas and Nitrobacter. Fluorescent In-Situ Hybridization (FISH) analysis showed that the reactors were 82% and 73% enriched with Nitrosomonas and Nitrobacter, respectively. Batch tests were carried out to measure the oxygen uptake rate (OUR) by the enriched cultures at various FA and FNA levels, in the presence (OUR with CO2 ) or absence (OUR without CO2) of inorganic carbon (CO2, HCO*3 and CO 2*3). FA up to 16.0 mgNH3-N.L(-1) was not found to have any inhibitory effect on either the catabolic or anabolic processes of the Nitrosomonas culture, but both these processes were inhibited by FNA. While an FNA level of 0.40-0.63 mgHNO2-N.L(-1) inhibited the energy production capability of Nitrosomonas by 50%, the growth process of the culture was completely inhibited by FNA at a concentration of 0.40 mgHNO2-N.L(-1). Both FA and FNA were found to have strong inhibition on the anabolic processes of Nitrobacter, but with limited inhibitory effects on the catabolism of this culture. The biosynthesis of Nitrobacter was totally inhibited at an FA level of 6.0 mgNH3-N.L(-1) (or above) or an FNA level of 0.02 mgHNO2-N.L(-1) (or above). At the same level of FA, the energy production capability of Nitrobacter was only inhibited by 12%, whereas an FNA level of up to 0.024 mgHNO2-N.L(-1) did not show any inhibition on the energy production of Nitrobacter. Further, these inhibitory effects appears to be much stronger on Nitrobacter than on Nitrosomonas, supporting that FA and FNA inhibition may play a major role in the elimination of nitrite oxidizing bacteria in processes treating wastewater containing a high level of nitrogen.

Effect of free ammonia on the respiration and growth processes of an enriched Nitrobacter culture

The inhibitory effect of free ammonia (FA;NH 3) on the metabolism of Nitrobacter is investigated using a method that allows decoupling energy generation from growth processes. A lab-scale sequencing batch reactor (SBR) was operated for the enrichment of Nitrobacter. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population in the reactor was Nitrobacter, while no Nitrospira was detected. Batch tests were carried out to measure the oxygen uptake rate (OUR) by the culture at various FA levels, in the presence ( OUR withCO 2 ) or absence ( OUR withoutCO 2 ) of inorganic carbon (CO 2, HCO 3 − and CO 3 2−). The FA inhibition on the respiration initiated at below 1 mgNH 3–N L −1 in both cases. OUR withoutCO 2 gradually decreased by 12% when the FA concentration increased from 0 to approximately 4 mgNH 3–N L −1 and remained at the same level till an FA level of 9 mgNH 3–N L −1 (the highest FA concentration applied in this study). This indicates that FA has a limited inhibitory effect on the respiratory capability of Nitrobacter. Starting from a level that is 15% higher than OUR withoutCO 2 when no FA was present, OUR withCO 2 decreased more rapidly than OUR withoutCO 2 reaching the same level as OUR withoutCO 2 when FA was between 6–9 mgNH 3–N L −1. This implies that in this range of FA the presence of inorganic carbon did not cause any increase in the respiration activity of Nitrobacter. The results suggest that, while still oxidizing nitrite at approximately 75% of the non-inhibited rate, Nitrobacter likely ceased to grow at an FA level of above 6 mgNH 3–N L −1. While the real mechanisms remain to be identified, this study indicates that the FA inhibition on Nitrobacter is likely much more serious than suggested by previous studies where OUR withCO 2 (or the equivalent nitrite oxidation rate) was used as the sole measure of the inhibitory effects.