Influent Ammonia Research Articles

The evolution of bacterial community structure and function in microalgal-bacterial consortia with inorganic nitrogen fluctuations in piggery digestate

The inorganic nitrogen concentrations in full-scale anaerobic digestion plants always vary seasonally, challenging the removal stability of microalgal-bacterial consortia in treating piggery digestate. Using a continuous photobioreactor, this study revealed the evolution of bacterial community under inorganic nitrogen fluctuations with influent nitrate loading ranged from 11 to 90 mg-N L−1 and influent ammonium loading ranged from 130 to 550 mg-N L−1. The loading of gradient nitrogen concentrations demonstrated that the optimal removal rate of total inorganic nitrogen was 45.62 mg-N L−1 d−1 along with the total chlorophyll concertation of 19.27 mg L−1, when introducing 240 mg-N L−1 of ammonium and 11 mg-N L−1 of nitrate. High throughput sequencing indicated that the dominant community members for nitrogen removal were shifted from prokaryotic algae to nitrifying and denitrifying bacteria, with nitrate being changed to ammonium. With the increasing influent ammonium loading, the suspended microalgal bacterial consortia gradually changed to microalgal bacterial biofilm, which was attributed to the biofilm-producing prokaryotes Thauera Comamona and Arenimonas. Co-occurrence network analyses illustrated that more functional bacterial modules were formed under ammonium fluctuation. Further correlation test identified influent ammonium loading as the important functional parameter shaping the bacterial community. Overall, this study expands our understanding of the homeostasis in microalgal-bacterial system in the cleaner production of piggery digestate.

Study of Biofilter Planted with Basil for Removal of Ammonia in Aquaponic Water

Abstract This experimental investigation of a laboratory scale aquaponic system included testing of a biofilter with basil plant as the biofilter part on aquaculture water quality. Irridescent shark was selected as aquaculture species. The biofilter consist of natural biomaterials such as coconut husk, coco peat, and coarse aggregates. The experiment was carried out for three short water recirculation durations of 2, 3, and 4 h/day. The influent and effluent ammonia NH3, total ammonia nitrogen (TAN), nitrites NO2 and nitrates NO3 levels were measured and analysed. The results showed that the biofilter effectively removed NH3 (65 - 71 %), TAN (34 - 58 %), and NO2 (60 - 67 %) from the aquaculture water. The dissolved oxygen (DO) levels were maintained between 3 - 7.0 mg/l during all the recirculation durations. The significance of water recirculation period was assessed by calculating the differences between the means of water quality parameters with a statistical test named one-way analysis of variance (ANNOVA) with significant level P taken as 5 %, i.e., P ≤ 0.5. The effluent mean NH3 levels 0.030 mg/l, 0.033 mg/l, and 0.022 mg/l exhibited significant difference at 4 h/d periods while effluent TAN levels 0.81, 0.77, and 0.77 showed no difference with varying periods.

Achieving superior nitrogen removal performance in low-strength ammonium wastewater treatment by cultivating concentrated, highly dispersive, and easily settleable granule sludge in a one-stage partial nitritation/anammox-HAP reactor

In low-strength ammonium wastewater (LSAWW) treatment, the application of anammox-based process is still limited due to extreme instability and the poor nitrogen removal rate (NRR). In this work, granule sludge, comprised of functional microbes and hydroxyapatite (HAP), was inoculated and cultivated in a one-stage partial nitritation/anammox (PNA) reactor for LSAWW treatment. The results showed that at the hydraulic retention time (HRT) of about 1.0 h and the influent ammonium concentration of 63.0 mg/L, an average NRR of 1.28 kg/m3/d was achieved, which far exceeds that reported in similar studies. The main inorganic matter in sludge was identified as HAP through the X-ray diffractometer and Raman spectrum analysis. The tomographic images of wet granule created through computed tomography revealed that the interior density of the granules was uneven and many hollow structures existed in the granule interior. Combined with the Scanning Electron Microscope images of dry granules, it was found that the granules were comprised of hollow sub-granules. Since the biomass in the reactor increased with no obvious increase in the granule size, it was inferred that the hollow sub-granules had fragile connections with each other and that granules division occurred easily, resulting in the high dispersity of sludge. Florescence in situ hybridization results also showed that the ammonium-oxidizing bacteria and anammox bacteria were mainly distributed in the two sides of the sub-granule shells and the HAP in the middle. This kind of structure raised the density of granules and improved the settleability of sludge, which made it possible to achieve a high biomass in the reactor at a short HRT. Therefore, the sludge formed in the reactor was concentrated, highly dispersive and easily settleable. These factors appear to be crucial for achieving the desired nitrogen removal performance. This study marks a big leap in LSAWW treatment through the one-stage PNA process and has great potential in actual applications.

Seasonal Effects of Influent Ammonia Oxidizing Bacteria of Municipal Wastewater Treatment Plants on Activated Sludge System

The specific ammonia uptake rates (SAUR) and ammonia oxidizing bacteria (AOB) community of influent sewage and activated sludge in the 2nd wastewater treatment plant (WWTP) of Xi'an without the primary settling tank were analyzed over multiple years to explore the seasonal effects of the influent AOB on the activated sludge systems. During the experiment, the SAUR of the raw sewage and activated sludge were 0.48-3.02 mg·(g·h)-1 and 0.68-2.25 mg·(g·h)-1, respectively. Meanwhile, the correlation analysis indicated that the monthly SAUR of the raw sewage was highly correlated with that of the activated sludge of the following month (r=0.862,P<0.05), which indicated that influent nitrifiers had a significant effect on the nitrification performance of activated sludge. Considering that the estimated AOB seeding intensities based on the ammonia oxidizing activity were 0.21-0.92 g·(g·d)-1, the nitrifier immigration from the raw sewage should added to the design of WWTP and the activated sludge modeling. Moreover, the qPCR results revealed that the AOB abundance of activated sludge in winter decreased but remained at 1010 cells·g-1, indicating that the immigration of influent nitrifiers could partially compensate for the reduction of the AOB abundance in the activated sludge caused by decreasing temperatures. Finally, the Illumina MiSeq sequencing demonstrated that the shared dominant AOB between the raw sewage and activated sludge were Nitrosomonas sp. Nm58, Nitrosomonas sp. JL21, and bacterium CYCU-0253. These findings can provide theoretical support for the design and operation of a WWTP.

Ammonia stripping using a continuous flow jet loop reactor: mass transfer of ammonia and effect on stripping performance of influent ammonia concentration, hydraulic retention time, temperature, and air flow rate.

When wastewater containing ammonia is discharged into the receiving environment without any kind of treatment, it causes both environmental problems and negatively affects human health. In this study, the aim was to strip ammonia using air in a continuous flow jet loop reactor (JLR) and investigate the effects of ammonia concentration, hydraulic retention time (HRT), air flow rate, and temperature on ammonia removal within this scope. By changing the ammonia concentration in the influent, no significant change was observed in ammonia removal efficiency. With air flow rate 45 L min-1, temperature 50 °C, pH 11, and HRT 7.5 h, mean 88.1% ammonia removal was achieved. Increasing the HRT, air flow rate, and temperature increased the ammonia removal efficiency. Later the ammonia stripping process in the continuous flow JLR was modeled and the volumetric mass transfer coefficient (KLa) for each parameter was calculated from the model equation. While the experimental parameters of air flow rate and temperature had a significant effect on the mass transfer coefficient, influent ammonia concentration and HRT were determined to have no effect.

Performance and onsite regeneration of natural zeolite for ammonium removal in a field-scale non-sewered sanitation system

Natural zeolite clinoptilolite was used as the primary ammonium removal method from the permeate of an anaerobic membrane bioreactor (AnMBR) treating high-strength blackwater generated from a community toilet facility. This zeolite-based nutrient capture system (NCS) was a sub-component of a non-sewered sanitation system (NSSS) called the NEWgenerator and was field tested for 1.5 years at an informal settlement in South Africa. The NCS was operated for three consecutive loading cycles, each lasting 291, 110, and 52 days, respectively. Both blackwater (from toilets) and blackwater with yellow water (from toilets and urinals) were treated during the field trial. Over the three cycles, the NCS was able to remove 80 ± 28%, 64 ± 23%, and 94 ± 11%, respectively, of the influent ammonium. The addition of yellow water caused the rapid exhaustion of zeolite and the observed decrease of ammonium removal during Cycle 2. After Cycles 1 and 2, onsite regeneration was performed to recover the sorption capacity of the spent zeolite. The regenerant was comprised of NaCl under alkaline conditions and was operated as a recycle-batch to reduce the generation of regenerant waste. Modifications to the second regeneration process, including an increase in regenerant contact time from 15 to 30 h, improved the zeolite regeneration efficiency from 76 ± 0.7% to 96 ± 1.0%. The mass of recoverable ammonium in the regenerant was 2.63 kg NH4-N and 3.15 kg NH4-N after Regeneration 1 and 2, respectively. However, the mass of ammonium in the regenerant accounted for only 52.8% and 54.4% of the estimated NH4-N originally sorbed onto the zeolite beds after Cycles 1 and 2, respectively. The use of zeolite clinoptilolite is a feasible method for ammonium removal by NSSS that observe variable nitrogen loading rates, but further research is still needed to recover the nitrogen from the regenerant waste.

Minimization of N2O Emission through Intermittent Aeration in a Sequencing Batch Reactor (SBR): Main Behavior and Mechanism

To explore the main behavior and mechanism of minimizing nitrous oxide (N2O) emission through intermittent aeration during wastewater treatment, two lab-scale sequencing batch reactors operated at intermittently aerated mode (SBR1), and continuously aerated mode (SBR2) were established. Compared with SBR2, the intermittently aerated SBR1 reached not only a higher total nitrogen removal efficiency (averaged 93.5%) but also a lower N2O-emission factor (0.01–0.53% of influent ammonia), in which short-cut nitrification and denitrification were promoted. Moreover, less accumulation and consumption of polyhydroxyalkanoates, a potential endogenous carbon source promoting N2O emission, were observed in SBR1. Batch experiments revealed that nitrifier denitrification was the major pathway generating N2O while heterotrophic denitrification played as a sink of N2O, and SBR1 embraced a larger N2O-mitigating capability. Finally, quantitative polymerase chain reaction results suggested that the abundant complete ammonia oxidizer (comammox) elevated in the intermittently aerated environment played a potential role in avoiding N2O generation during wastewater treatment. This work provides an in-depth insight into the utilization of proper management of intermittent aeration to control N2O emission from wastewater treatment plants.

Robust Nitritation Sustained by Acid-Tolerant Ammonia-Oxidizing Bacteria

Oxidation of ammonium to nitrite rather than nitrate, i.e., nitritation, is critical for autotrophic nitrogen removal. This study demonstrates a robust nitritation process in treating low-strength wastewater, obtained from a mixture of real mainstream sewage with sidestream anaerobic digestion liquor. This is achieved through cultivating acid-tolerant ammonia-oxidizing bacteria (AOB) in a laboratory nitrifying bioreactor at pH 4.5-5.0. It was shown that nitrite accumulation with a high NO2-/(NO2- + NO3-) ratio of 95 ± 5% was stably maintained for more than 300 days, and the obtained volumetric NH4+ removal rate (i.e., 188 ± 14 mg N L-1 d-1) was practically useful. 16S rRNA gene sequencing analyses indicated the dominance of new AOB, "Candidatus Nitrosoglobus," in the nitrifying guild (i.e., 1.90 ± 0.08% in the total community), with the disappearance of typical activated sludge nitrifying microorganisms, including Nitrosomonas, Nitrospira, and Nitrobacter. This is the first identification of Ca. Nitrosoglobus as key ammonia oxidizers in a wastewater treatment system. It was found that Ca. Nitrosoglobus can tolerate low pH (<5.0), and free nitrous acid (FNA) at levels that inhibit AOB and nitrite-oxidizing bacteria (NOB) commonly found in wastewater treatment processes. The in situ inhibition of NOB leads to accumulation of nitrite (NO2-), which along with protons (H+) also produced in ammonium oxidation generates and sustains FNA at 3.0 ± 1.4 mg HNO2-N L-1. As such, robust PN was achieved under acidic conditions, with a complete absence of NOB. Compared to previous nitritation systems, this acidic nitritation process is featured by a higher nitric oxide (NO) but a lower nitrous oxide (N2O) emission level, with the emission factors estimated at 1.57 ± 0.08 and 0.57 ± 0.03%, respectively, of influent ammonium nitrogen load.

The call for regional design code from the regional discrepancy of microbial communities in activated sludge.

Discerning the differences in activated sludge (AS) microbial community due to geographic location and environmental and operational factors is of great significance for precise design and maintenance of wastewater treatment plants (WWTPs). Hence, in this study, 150 AS samples collected from WWTPs in South China and North China were analyzed by 16S rRNA gene sequencing. In general, AS microbial community in North China had lower diversity, higher proportions of stochastic assembly (35.7% v.s. 15.8%) and more network keystone species (19 v.s. 5) compared with southern AS community. Conductivity and SRT had significant effects on AS community in both regions. Latitude, annual mean temperature, and influent BOD, COD, and ammonia influenced South China community significantly, while pH and influent total phosphorus affected North China community. To achieve stable performance, southern WWTPs should carefully monitor fluctuations in wastewater characteristics, while northern WWTPs should monitor AS communities for shifts in the dominant taxa from immigrant strains brought in through the influent. Additionally, WWTPs in North China should be aware of the need to proactively control sludge bulking because of the high abundance and occurrence of Haliscomenobacter in these AS communities. MAIN FINDING: The call for regional design based on the regional discrepancy of microbial communities in activated sludge is uncovered and according suggestions were given.

Prediction of biogas production from food waste in a continuous stirred microbial electrolysis cell (CSMEC) with backpropagation artificial neural network

In this study, a three-layer backpropagation neural network (BPNN) model was utilised as an estimation model of biogas production from a continuous stirred microbial electrolysis cell (CSMEC) and a continuous stirred tank reactor (CSTR) treating food waste. The study focuses on the effects of several factors, such as chemical oxygen demand removal, oxidation reduction potential (ORP), volatile fatty acids (VFAs), organic loading rate (OLR), influent pH, effluent pH, and influent ammonium on biogas production. The biogas recovery target for the model was set at 75–85%. Levenberg Marquardt backpropagation algorithm was chosen as the algorithm for the model out of the seven-benchmark comparison. Determination coefficient (R2), index of agreement (IA) and fractional variance (FV) used for the exactitude of optimal BPANN model were 0.8902, 0.925 and 0.0715 in the CSMEC and 0.9414, 0.966 and 0.0484 in the CSTR, respectively. The results of this study showed a higher accuracy and dependability of BPANN in modelling and optimizing the process parameter interactions in relation to biogas production in both the CSMEC and CSTR.

Achieving simultaneous nitritation, anammox and denitrification (SNAD) in an integrated fixed-biofilm activated sludge (IFAS) reactor: Quickly culturing self-generated anammox bacteria

In this study, by inoculating nitritation suspended sludge, simultaneous nitritation, anammox and denitrification (SNAD) was established quickly in an integrated fixed-biofilm activated sludge (IFAS) reactor to treat high-ammonia municipal wastewater. Results showed that, deep-level total nitrogen and chemical oxygen demand removal efficiencies (92.8% and 78.8%, respectively) were achieved, and their effluent concentrations were 13.2 and 39.3 mg/L, respectively. Excess generation of nitrate was once occurred under continuous aerobic condition, but it could be solved by suppressing nitrite oxidizing bacteria activity stably via switching to intermittent aeration mode (alternate 7 min of aerobic and 21 min of anoxic) and rising influent ammonium concentration temporarily (lasted 31 days). High-throughput sequencing analysis revealed that, Candidatus_Brocadia, as dominant anammox bacteria, was self-generated in flocs (2.93%) but mainly biofilm (7.67%), whereas uncultured_f_Nitrosomonadaceae as ammonia oxidizing bacteria was mainly found in flocs (2.4%). This work not only demonstrated that anammox bacteria could be self-generated and retained in the SNAD-IFAS system, but also suggested a promising application of the SNAD-IFAS in wastewater treatment plants.

Effect of influent ammonia nitrogen concentration on microbial community in MBBR reactor.

The purpose of this study is to explore the nitrogen removal efficiency of the moving bed biofilm reactor (MBBR) under different ammonia nitrogen concentrations (states P1-P5), especially the composition of various forms of nitrogen, related genes and microbial community structure and succession law in the effluent of the reactor. The results show that the average efficiency of MBBR effluent denitrification is 63.63%. The concentration dynamics of NO3--N and NO2--N in the effluent indicated a relatively short-range nitrification and denitrification reaction in the MBBR. The results of 16SrDNA sequencing of P1-P5 microbial samples found that changes in the concentration of ammonia nitrogen in the influent produced significant changes in the composition of the microbial community in the MBBR. The genera Ottowia and Flavobacterium played an important role in the nitrogen removal of the MBBR system.

Performance analysis of four-stage rotating biological contactor in nitrification and COD removal from petroleum refinery wastewater

The petroleum refining process generates large quantities of wastewater that discharge of untreated wastewater into water bodies results in environmental and human health effects due to the release of toxic containments. In this study, the biological removal of ammonia from petroleum refinery wastewater in a bench-scale rotating biological contactor (RBC) under continuous operation was investigated. The experiments were conducted base on a central composite design to evaluate the effect of four significant independent variables on the performance of the system. Response surface methodology was applied to minimize the number of runs and investigating the interactive effects of variables on ammonia and chemical oxygen demand (COD) removals. The RBC was operated at different hydraulic loading rates of 0.005, 0.008, and 0.016 m3/m2d. The optimum conditions were the temperature of 32.19 °C, influent ammonia concentration of 20.54 mg/l, the flow rate of 5.57 mL/min, and discs rotational speed of 4.58 rpm for ammonia and COD removal efficiency simultaneously. The maximum removal efficiency of ammonia and COD were obtained at 99.07 % and 85.76 % respectively. Finally, our results suggest that RBC may be considered as a promising method for petroleum refinery wastewater treatment, especially in simultaneously COD and ammonia removal.

Enhancement of static magnetic field on nitrogen removal at different ammonium concentrations in a sequencing batch reactor: Performance and biological mechanism

This study aimed to investigate the effects and biological mechanism of external static magnetic fields (SMFs) on enhancing nitrogen removal at different influent ammonium nitrogen (NH4+) concentrations. Four sequential batch reactors (SBRs) with SMFs of 0, 15, 30, and 50 mT were operated continuously for 196 days, during which the influent NH4+-N concentration increased stepwise as 50, 100, 350, and 600 mg L−1. The results showed that 50 mT had optimum effects on enhancing nitrogen removal, especially at high NH4+-N concentrations (350 and 600 mg L−1). The biological mechanism by which SMF influences nitrogen removal varies depending on the NH4+ concentration. At low NH4+-N concentrations (50 and 100 mg L−1), a field of 50 mT increased key enzyme activities and corresponding functional gene abundances. Additionally, it further improved functional bacterial abundances, which involved nitrifying and denitrifying bacteria at high NH4+ concentrations. These findings could provide guidance for the selection of optimum SMF intensity at different influent NH4+ concentrations.

The Influence of Sulfate on Anaerobic Ammonium Oxidation in a Sequencing Batch Reactor

Anaerobic ammonia-oxidizing bacteria have a more comprehensive metabolism than expected - there may be other electron acceptors that oxidize ammonium nitrogen under anaerobic conditions, in addition to the well-known nitrite nitrogen, one of which is sulfate in the sulfammox process. Sulfate-containing compounds are part of the medium for the anammox process, but their concentrations are not particularly high (0.2 g MgSO4 ∙ 7H2O/dm3 and 0.00625 g FeSO4/dm3). They can react to some extent with influent ammonium nitrogen. In this work, tests were carried out in two sequencing batch reactors with granular sludge. The first reactor (R1) operated in a 6 h cycle, and the concentration of the inflowing sulfate was kept at 44 mg/dm3∙d. The second reactor (R2) was operated until the 36th day in a 6 h cycle; the influencing concentration was 180 mg SO42−/dm3∙d from the 37th to 64th day in a 3 h cycle, with an influencing concentration of 360 mg SO42−/dm3∙d; and from the 65th to 90th day, the reactor was operated again in a 6 h cycle with an influencing concentration of 180 mg SO42−/dm3∙d. Along with the increased share of sulfate, both the ammonium utilization rate and specific anammox activity showed an increasing trend. As soon as the sulfate dosage was reduced, the ammonium utilization rate and specific anammox activity values dropped. Therefore, it can be concluded that sulfate-containing compounds contribute to the efficiency and rate of the anammox process.

Hydroxyapatite crystallization-based phosphorus recovery coupling with the nitrogen removal through partial nitritation/anammox in a single reactor

For digestion effluent treatment, while the anammox-based process has been successfully applied for nitrogen removal, in most cases, phosphorus (P) represents another major concern. In this study, a novel process, integrating the partial nitritation/anammox and hydroxyapatite crystallization (PNA-HAP) in a single airlift reactor, was developed for the simultaneous nitrogen removal and P recovery from synthetic digestion effluent. With a stable influent P concentration of 20.0 mg/L, an HRT of 6 h, and alternating increases of influent calcium and ammonium, the final achieved nitrogen removal rate was 1.2 kg/m3/d and the P removal efficiency was 83.0%. The settleability of sludge was desirably enhanced with the calcium addition and a high biomass concentration was achieved in reactor. Quantitative and qualitative analyses confirmed that HAP was the main inorganic content in sludge, which could be harvested for P recovery. According to the Scanning Electron Microscope observation and the Energy Dispersive X-ray spectrometry analysis, the microbes were mainly distributed on the outer layer of the sludge aggregate, while the HAP mainly in the interior. The relevant theoretical calculation also revealed that the sludge discharge manipulation has direct effect on the sludge composition and aggregate structure. In sum, the results are evidence of the feasibility of simultaneous nitrogen removal and P recovery through one-stage PNA-HAP process for digestion effluent.

Biological pre-treatment system for ammonia removal from slightly contaminated river used as a drinking water source

A pilot-scale biological pre-treatment reactor filled with porous polyurethanes carriers (BioNET) was operated over 500 days under different hydraulic retention times (HRT) (1.3 to 0.5 h) to evaluate the feasibility and efficiency of ammonia removal for a slightly contaminated source water. Under 0.5 h HRT, 84 % nitrification efficiency and 0.42 kg-N/m3/day ammonia removal rate could be achieved with influent ammonia concentration of 10.4 mg N/L. Results of batch tests indicated that the effect of aeration on nitrification of BioNET was more significant than temperature and components in raw water. Specific ammonia oxidization rate for batches with aeration were 4.5–9.1 times higher than those without aeration. In addition, simultaneous nitrification and denitrification were observed with batch tests using BioNET obtained from the reactor. Ammonia monooxygenase subunit A (amoA) gene of ammonia oxidizing archaea and bacteria (AOA and AOB) and 16S rRNA gene of total bacteria, Nitrospira, and Nitrobacter were quantified using real time quantification polymerase chain reaction (qPCR). AOB and Nitrospira were dominant in the bioreactor. Higher nitrification efficiency (>60 %) could be achieved at AOB abundance higher than 1.25 × 108 copy/BioNET and AOB/TB higher than 1.2. This study demonstrated that the BioNET system can be a promising technology for removing ammonia from slightly polluted river water at a low HRT condition.

Suppression of nitrite-oxidizing bacteria under the combined conditions of high free ammonia and low dissolved oxygen concentrations for mainstream partial nitritation

Abstract The possibility of nitrite-oxidizing bacteria (NOB) suppression in mainstream wastewater (COD/N of 6.0, ammonia of approximately 50 mg N L−1) was investigated by controlling the ratio of dissolved oxygen to total ammoniacal nitrogen (DO/TAN) in a continuous suspended sludge reactor without prior COD removal. It was found that a combination of high free ammonia (FA) of approximately 20 mg N L−1 and low dissolved oxygen (DO) of 0.3 ± 0.1 mg L−1 (DO/TAN ratio of 0.003) established in the start-up period was an efficient way to inhibit the growth of NOB. The activity of NOB was more inhibited as FA concentration increased, particularly at the initial ammonia concentration of 175 mg N L−1 (FA of about 20 mg N L−1) Then, the influent ammonia was lower to 50 ± 2 mg N L − 1 (FA of 4.9 ± 0.2 mg N L−1), a typical nitrogen concentration of mainstream wastewater. After four months of operation, mainstream partial nitritation (PN) became stable with nitrite accumulation ratio over 87% and COD removal of above 94% (effluent COD of 18.4 mg L−1). Besides, the effluent NO 2 − -N/NH3-N ratio was 1.22 ± 0.12, which was suitable for the subsequent anaerobic ammonium oxidation (anammox) reaction. The relative abundance of ammonia-oxidizing bacteria (AOB) (e.g., Nitrosomonas) was 15 times higher than NOB. The abundance (0.3%) of Nitrospira (k-strategist NOB) was insignificant, while Nitrobacter (r-strategist NOB) and Nitrotoga (NOB) were not detected during the steady state of PN under low nitrogen load because NOB was suppressed and washed out of the reactor by the condition of extremely low DO/TAN ratio in the start-up period. Thus, it was noted that NOB suppression for stable PN could be accomplished by providing high FA and low DO concentrations, especially in the early stage.

Effect of transient substrate shock on performance and granules properties in single-stage partial nitritation-anammox system

The stability of single partial nitritation and anammox (SPNA) granular system at different nitrogen loads was evaluated in two laboratory-scale continuous stirred tank reactor (CSTR) reactors (R1with lower influent ammonium concentration, R2 with higher concentration). The effects of different transient substrate shock (50 mg N/L and 100 mg N/L) on the bacteria population structure, nitrogen removal and granular sludge properties of the system were studied. Results showed that R1 had a better resilience, and the average removal efficiencies of TN and ammonium can recover to 66.5 % and 73.9 % after two shocks, while nitrogen performance of R2 deteriorated. The inhibition of free nitrous acid (FNA) to functional bacteria was the key factor influencing reactor performance. When FNA concentration exceeded 2 μg/L, FNA/MLVSS > 1.5 μg/g VSS, the inhibition was irreversible. Moreover, excessive substrate shock changed extracellular polymeric substances (EPS) production and composition, which led to granules disintegration. The formation and disintegration mechanism of SPNA micro-granules were also investigated.

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater.

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCordTM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94–100%) and CSTR (72–100%), and BioCordTM SBR (96–100%) and CSTR (92–100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93–94% in both the MBBR SBR and BioCordTM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20–35%) and BioCordTM SBR (45–54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.