Swine wastewater is one of the most serious pollution sources, and it has attracted a great public concern in China. Anaerobic digestion technology is extensively used in swine wastewater treatment. However, the anaerobic digestion effluents are difficult to meet the discharge standard. The results from batch experiments showed that plenty of refractory organic matter remained in the effluents after mesophilic anaerobic digestion for 30 days. The effluent total COD (tCOD) and soluble COD (sCOD) were 483 and 324 mg/L, respectively, with the sCOD/tCOD ratio of 0.671. Fluorescence excitation–emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) revealed that the dissolved organic matter in the effluents was tryptophan-like substance, humic acid substance, and fulvic acid substance. Based on the appearance time during anaerobic digestion, tryptophan-like substance and humic acid substance were inferred to originate from the raw swine wastewater, and the fulvic acid substance was inferred to be formed in the anaerobic digestion. This work has revealed the source of residual organic matter in anaerobic digestion of swine wastewater and has provided some valuable information for the post-treatment.

•A novel Hanbon was established for simultaneously treating NH4+-N and NO3−-N.•High nitrogen removal rate of 9.0 ± 0.1 kgN·m−3·d−1 was achieved in Hanbon.•Potential capacity of Hanbon process to treat municipal wastewaters was achieved.•Microflora in Hanbon were revealed at both high and low nitrogen loading rate.A novel Heterotrophic Ammonia and Nitrate Bio-removal Over Nitrite (Hanbon) process, combining Short Nitrate Reduction (SNR) with Anaerobic Ammonia Oxidation (Anammox), was developed in a lab-scale continuous up-flow reactor. The substrate effects were investigated to characterize the performance of Hanbon process, and the corresponding microflora information was also revealed. Our results showed that the optimal substrate ratio of NH4+-N:NO3−-N:COD for the Hanbon process was 0.65:1:2.2. The volumetric nitrogen removal rate was up to 9.0 ± 0.1 kgN·m−3·d−1 at high influent substrate concentrations of NH4+-N 375 mg L−1, NO3−-N 750 mg L−1 and COD 1875 mg L−1, which was superior to the reported values of analogous processes. Moreover, the effluent total nitrogen concentration was able to meet the strict discharge standard (less than 10 mg L−1) at low influent substrate concentration of NH4+-N 26 mg L−1, NO3−-N 40 mg·L−1and COD 88 mg L−1. Illumina-based 16S rRNA gene sequencing results showed that Halomonas campisalis and Candidatus Kuenenia stuttgartiensis were the dominant bacteria in the SNR section and Anammox section at high substrate concentration condition. However, Halomonas campaniensis and Candidatus Brocadia brasiliensis were raised significantly at low substrate concentration condition. Hanbon process provided in the present work was flexible of treating wastewater with various nitrogen concentrations, deserving further development.

•VLR and VRR for Fe-CAD reactor were 0.26 ± 0.01 kg-N/(m3·d) and 0.09 ± 0.03 kg-N/(m3·d).•Fe-CAD sludge was dominated by Rhodanobacter, Mizugakiibacter, and Sulfuricella.•Maximum removal rate of NO3− by Fe-CAD sludge was 4.68 mg-N/(L·gVSS·h).•Iron-encrustation caused sludge activity dropping and reactor deterioration.Aiming at treatment of wastewaters with low C/N ratio, a novel ferrous iron-based chemoautotrophic denitrification (Fe-CAD) reactor was developed with inoculum sludge from a municipal sewage plant in Hangzhou, China. The efficiency of the Fe-CAD reactor was remarkable. The volumetric loading rate (VLR) and volumetric removal rate (VRR) of NO3− were 0.26 ± 0.01 kg-N/(m3·d) and 0.09 ± 0.03 kg-N/(m3·d), while the VLR and VRR of Fe2+ were 3.10 ± 0.24 kg-Fe/(m3·d) and 1.69 ± 0.26 kg-Fe/(m3·d), respectively. By means of next generation sequencing, the Fe-CAD sludge was found to be rich in ferrous iron-oxidizing nitrate-reducing bacteria including Rhodanobacter, Mizugakiibacter, Sulfuricella, Comamonas and Gallionella. Reaction dynamics of the Fe-CAD sludge were determined by batch experiments. After fitted by Haldane Model, the maximum specific activity (μmax), the saturation concentration (Ki) and the half inhibition concentration (Ks) of NO3− to the Fe-CAD sludge were calculated as 0.24 mg-N/(h·gVSS), 72.82 mg-N/L and 2722.97 mg-N/L, while the μmax, Ki, Ks of Fe2+ were 2.28 mg-Fe/(h·gVSS), 203.09 mg-Fe/L and 229159.38 mg-Fe/L, respectively. The produced ferric iron formed an brilliant yellow iron-encrustation with irregular shape around the functional microorganisms, and the iron-encrustation resulted in a dropped specific activity of the Fe-CAD sludge. Removal or prevention of the iron-encrustation around microbial cells were suggested to be the key to improve the performance of the Fe-CAD reactor.Download high-res image (75KB)Download full-size image

•A new method was developed to obtain volume fractal dimension of granular sludge.•A fractal settling model was established with only a small deviation of 0.8% from the experimental data.•90% confidence interval of settling velocity was calculated to further modify the settling model.The settling performance of ANAMMOX granular sludge determines the biomass retention in reactors, and finally determines the potential reaction capacity. In this paper, Stokes equation was modified by fractal dimensions to describe the settling performance of ANAMMOX granular sludge. A new method was developed to obtain fractal dimensions, and a fractal settling model was established for ANAMMOX granular sludge. The fractal settling model was excellent with only a small deviation of 0.8% from the experimental data. Assuming normal distribution of all Feret diameters, 88% experimental data fell into the 90% confidence interval of settling velocities. Further assuming logarithmic normal distribution, 95% experimental data fell into the 90% confidence interval. The fractal settling model is helpful for the prediction of settling velocities of granular sludge and the optimization of bioreactor performance.Download high-res image (139KB)Download full-size image

Electrotrophic denitrification is a novel nitrogen removal technique. In this study, the performance and the mechanism of electrotrophic denitrification were investigated at different nitrate concentrations and current intensities. The results showed that the performance of electrotrophic denitrification was good with a sludge loading of 0.39 kg N/kg VSS day. The half-saturation constant for nitrate-N was 1894.03 mg/L. The optimal nitrate-N concentration and current intensity were 1500 mg/L and 20 μA, respectively. Electrotrophic denitrification was defined as the process of direct use of electron for nitrate reduction, and electrotrophic denitrifier was proposed to be the microbe of using electricity as energy source directly. The present work will benefit the development and application of electrotrophic denitrification.

•NAFO sludge possessed high settleability with settling velocity of 390.1 ± 161.3 m/h.•The increasing particle size and density contribute to the excellent settleability.•NAFO sludge had unique morphology profiles for high content of iron oxide compounds.•Microbial succession was supposed to occur during the NAFO cultivation process.The nitrate-dependent anaerobic ferrous oxidizing (NAFO) is a newly discovered bioprocess, which is valuable to develop autotrophic denitrifying technology. In this work, the physicochemical characteristics and microbial community of the cultivated sludge (NAFO sludge) from a lab-scale reactor operating for over 200 days were investigated. A comparison between the seeding sludge and NAFO sludge was also carried out. The results showed that the NAFO sludge possessed distinctly high settleability, and the average settling velocity was 390.1 ± 161.3 m/h. The increasing particle size and density, with average values of 1469 ± 65 μm (surface area-weighed mean diameter, SMD)/2389 ± 132 μm (volumetric-weighed mean diameter, VMD) and 1580 ± 80 kg/m3, were revealed to the main factors causing the profile of excellent settleability. High content of iron with peak value of 87.5% (wt) was detected in NAFO sludge, which was mainly in the form of oxide compounds, such as hematite and magnetite, endowing unique morphology characteristics of NAFO sludge. After the long-term operation, a microbial succession was supposed to occur in the granular sludge, and the dominant bacterial communities in the NAFO sludge were Gamma-proteobacteria, Thermoleophilia, Clostridia and Alpha-proteobacteria classes. The present work will benefit the development of NAFO technology, and also the separation and iron-recycling processes of the NAFO sludge.

•Performance stability of PN–ANAMMOX was evaluated in a new ILAB reactor.•Performance of ILAB reactor depended on shock magnitude and exposure time.•Recovery time of reactor was proportional to shock intensity and shock duration.•PN–ANAMMOX revealed robust performance in ILAB reactor under concentration shocks.Autotrophic nitrogen removal from ammonium-rich wastewaters by partial nitrification–anaerobic ammonia oxidation (PN–ANAMMOX) offers advantages such as energy and resources saving compared with conventional treatment. In view of substrate fluctuations in real applications, performance stability of PN–ANAMMOX was investigated in a new lab-scale internal-loop airlift bio-particle (ILAB) reactor. The response of steady-state reactor to substrate concentration shocks was evaluated at 439.49 mg N/L (shock A) and 489.49 mg N/L (shock B) for 0.5 hydraulic retention time (HRT) and 1.0 HRT respectively. Higher substrate concentrations such as 613.09 mg N/L (shock C) and 629.00 mg N/L (shock D) were also tested for 0.5 HRT and 1.0 HRT respectively. The intensity and duration of shocks (A–D) proportionately affected the disturbance, inertial and recovery phase of the reactor. However, the reactor showed resilience to substrate concentration shocks by tolerating higher pH and maintaining its primary functions in shocks. The inhibition of bio-reaction triggered by substrate concentration shocks was totally reversible and performance indicators returned to steady-state level soon after the end of shocks. The reactor demonstrated full recovery from all shocks with respective recovery time of 13 h, 18 h, 19 h and 23 h and it was capable of recovering 100% even from most disturbing shock D (629.00 mg N/L; 1.0 HRT). The effluent ammonium was sensitive parameter which shot up to 20.5 times the steady-state value and it could be used to monitor the reactor performance. The study results revealed that PN–ANAMMOX was robust and it was not prone to temporary adverse effects of substrate concentration shocks.

•Effect of electrodes on simultaneous sulfide and nitrate removal was studied in MFC.•The MFCs with graphite felt or rod as electrodes were shown to remove substrate.•Higher steady current densities of MFCs with graphite felt as electrodes were obtained.•Better catalytic activity of graphite felt was displayed by CV curves.The effect of electrode types on simultaneous sulfide and nitrate removal were studied in two-chamber microbial fuel cells (MFCs). Graphite rod and graphite felt as electrodes were compared and evaluated in terms of substrate removal and electricity generation. When the influent sulfide concentration elevating from 60 mg L−1 to 780 mg L−1 gradually, the MFCs both showed good capacities to remove substrate, no matter what material used as electrodes. Nitrogen and sulfate were the main end products. The steady current densities of the MFC with graphite felt as electrodes were nearly twice as large as that with graphite rod. It could be explained by the linear relationship between the electrons released by substrates and the accepted by electrodes. The CV curves also showed that the graphite felt has a higher catalytic activity than the graphite rod. The graphite felt was more suitable as electrodes for the MFCs treating sulfide and nitrate simultaneously.

Heterotrophic denitrifying enriched culture (DEC) from a lab-scale high-rate denitrifying reactor was discovered to perform nitrate-dependent anaerobic ferrous oxidation (NAFO). The DEC was systematically investigated to reveal their denitrification activity, their NAFO activity, and the predominant microbial population. The DEC was capable of heterotrophic denitrification with methanol as the electron donor, and autotrophic denitrification with ferrous salt as the electron donor named NAFO. The conversion ratios of ferrous-Fe and nitrate-N were 87.41 and 98.74 %, and the consumption Fe/N ratio was 2.3:1 (mol/mol). The maximum reaction velocity and half saturation constant of Fe were 412.54 mg/(l h) and 8,276.44 mg/l, and the counterparts of N were 20.87 mg/(l h) and 322.58 mg/l, respectively. The predominant bacteria were Hyphomicrobium, Thauera, and Flavobacterium, and the predominant archaea were Methanomethylovorans, Methanohalophilus, and Methanolobus. The discovery of NAFO by heterotrophic DEC is significant for the development of wastewater treatment and the biogeochemical iron cycle and nitrogen cycle.

The effect of operating modes on the simultaneous sulfide and nitrate removal were studied in two-chamber microbial fuel cells (MFCs). The batch and continuous operating modes were compared and evaluated in terms of substrate removal and electricity generation. Upon gradual increase in the influent sulfide concentration from 60 to 1,020 S mg L−1, and the hydraulic retention time decrease from 17.2 to 6 h, the MFC accomplished a good substrate removal efficiency whereby nitrogen and sulfate were the main end products. The removal efficiency of the MFC in the continuous mode was much higher than that in the batch mode, and its current densities in the continuous mode were more stable and higher than in the batch mode, which could be explained by the linear relationship between electrons released by the substrates and accepted on the electrodes. The electricity output in the continuous mode of the MFC was higher than that in the batch mode. MFC's operation in the continuous mode was a better strategy for the simultaneous treatment of sulfide and nitrate.

•Two innovative concepts were proposed to reveal the process characteristics.•The mechanisms of Fe(II)/P ratio and pH effects on phosphorus removal were clarified.•A function was established to predict the ferrous salt dose for phosphorus removal.•The optimal parameters of Fe(II)/P ratio and pH were obtained.Phosphorus pollution is one of the main factors causing water eutrophication. Phosphorus removal by ferrous salt is one of the common methods for phosphorus removal from wastewater. The effects of Fe(II)/P ratio and pH were investigated and new concepts of “balance reaction” and “unbalance reaction” were proposed to reveal their mechanisms. The results showed that the Fe(II)/P ratio had a significant influence on phosphorus removal by ferrous salt with optimal ratio of 2.25. A relationship between residual phosphorus concentration and total Fe(II)/P ratio was established to predict the dose of ferrous salt. pH also had a significant influence on phosphorus removal by ferrous salt with optimal range of 7.0–8.0, and it was found to be the key factor to regulate the competition between Fe3(PO4)2 precipitation and Fe(OH)2 precipitation. The process of phosphorus removal by ferrous salt was an unbalance reaction. And it was ascribed partly to the requirement for a higher residual Fe(II) concentration to get a lower concentration of residual phosphorus in the solution, and partly to the competition between Fe3(PO4)2 precipitation and Fe(OH)2 precipitation.Graphical abstract

•We developed an Ammonia-Oxidation Microbial Fuel Cell (AO-MFC).•The AO-MFC could convert most (99.7%) of the fuel (ammonium).•The AO-MFC showed good performance of electricity generation.•DO concentration could greatly affect the performance of electricity generation.•Oxygen played a key role in the electron distribution among electron accepters.Based on inorganic fuel, an Ammonia-Oxidation Microbial Fuel Cell (AO-MFC) had been developed, and the influence and mechanism of dissolved oxygen (DO) on the performance of nitrification and electricity generation were investigated. The results showed that the maximum conversion percentage of ammonium–nitrogen (NH4+–N) was 99.7%. The output voltage and the power density were 98.5 ± 1.41 mV and 9.70 ± 0.27 mW m−2 in the stable phase of electricity generation. In the AO-MFC, the electrons originated from ammonia and flowed to ammonia monooxygenase (AMO, which catalyzes the conversion of ammonia to hydroxylamine), Cyt aa3 oxidase (which catalyzes the reduction of oxygen) and electrode, which were used for triggering ammonia oxidation, synthesizing ATP and generating electricity. Molecular oxygen played a key role in the electron distribution among these three acceptors. DO concentration too high (>6.45 mg L−1) or too low (<0.5 mg L−1) could exert a great negative influence on the performance of electricity generation.

Anaerobic ammonium oxidation (anammox) is the microbial conversion of ammonium and nitrite to dinitrogen gas. The functional microbes of anammox reaction are anammox bacteria, which were discovered in a wastewater treatment system for nitrogen removal. Anammox bacteria are prevalent in anoxic ecosystems and play an important role in both biological nitrogen cycle and nitrogen pollution control. In this paper, we reviewed the investigation on ecological characteristics of anammox bacteria, and tried to figure out their complicated intraspecies and interspecies relationships. As for intraspecies relationship, we focused on the quorum sensing system, a cell density-dependent phenomenon. As for interspecies relationship, we focused on the synergism and competition of anammox bacteria with other microorganisms for substrate and space. Finally, we discussed the great influence of environmental factors (e.g., dissolved oxygen, organic matters) on the constitution, structure and function of anammox bacteria community.

Ammonium and nitrite are two substrates of anammox bacteria, but they are also inhibitors under high concentrations. The performance of two anaerobic ammonium-oxidizing (anammox) upflow biofilm (UBF) reactors was investigated. The results show that anammox UBFs become unstable under nitrogen loading rate (NLR) applied higher than 1.0 g/(L·d). The consumptions of acidity in the anammox reaction lead to the increase of pH, which is as high as 8.70–9.05. Free nitrous acid concentration is accompanied to be lower than the affinity constant of anammox bacteria, and then starvation effect appears. Moreover, free ammonia concentration increases to 57–178 mg/L, resulting in inhibitory effect on the anammox bacteria. Both negative effects contribute to the instability of the anammox bioreactors.

Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor (SAB) were performed based on bed expansion ratio (E), maximum bed sludge content (Vpmax), and maximum bed contact time between sludge and liquid (Tmax). Bed expansion behavior models were established under bed unfluidization, fluidization, and transportation states. Under unfluidization state, E was 0, Vpmax was 4 867 ml, and Tmax was 844-3 800 s. Under fluidization state, E, Vpmax, and Tmax were 5.28%–255.69%, 1 368-4 559 ml, and 104-732 s, respectively. Under transportation state, washout of granular sludge occurred and destabilized the SAB. During stable running of SAB under fluidization state, E correlated positively with superficial gas and liquid velocities (ug and ul), while Vpmax and Tmax correlated negatively. For E and Vpmax, the sensitivities of ug and ul were close to each other, while for Tmax, the sensitivity of ul was greater than that of ug. The prediction from these models was a close match to the experimental data.

The granulation of Anammox sludge plays an important role in improving the efficiency of high-rate Anammox bioreactors. The present study involved the use of anaerobic granular sludge to start up the Anammox process to accomplish granulation in Anammox reactor. The accumulation of nitrogen gas and subsequent slugging behavior were observed in the upflow Anammox granular sludge bed (AGSB) reactor, resulting in deteriorated effluent quality. Based on shear force analysis of the gas column under the quasi-steady state, the liquid-induced shear force was increased by progressively shortening of hydraulic residence time (HRT) and implementing effluent recycling. It appeared to be the right strategy to eradicate the slugging behavior which disappeared completely when HRT was shortened to 1.10 h with liquid upflow velocity of 1.30 cm min−1. The application of high shear stress enhanced the nitrogen removal performance to 15.40 kg-N m−3 d−1. Thus the amendments in the liquid-induced shear force by shortening HRT may be an appropriate strategy to overcome slugging behavior of the Anammox reactor.

The longer start-up period of the Anammox process is due to the very low cellular yield and growth rates of Anammox bacteria. Nitrite inhibition is considered to be the key factor in the instability of the Anammox process during the operation. However, little attention was paid to the inhibitory effect of pH and free ammonia. This paper presents start-up and inhibition analysis of an Anammox biofilm reactor seeded with anaerobic granular sludge. Results showed that the start-up period could be divided into the sludge lysis phase, lag phase, propagation phase, stationary phase and inhibition phase. Optimization control could be implemented correspondingly to accelerate the start-up of Anammox bioreactors. Effluent pH increased to 8.7–9.1 when the nitrogen removal rate was higher than 1,200 mg l−1 day−1. The free ammonia concentration was accompanied with a higher level of 64–73 mg l−1. Inhibitory effects of high pH and free ammonia on Anammox bacteria contributed to the destabilization of the Anammox bioreactor during the first 125 days with influent KHCO3 of 0.5 g l−1. Increasing the suffering capacity in the inlet by dosing 1.25 g KHCO3 l−1 effectively reduced the pH variation, and the nitrogen removal performance of the reactor was further developed.

The performance of sulfate-dependent anaerobic ammonium oxidation was studied. The results showed that both SO42− and NH4+ were chemically stable under anaerobic conditions. They did not react with each other in the absence of biological catalyst (sludge). The anaerobic digested sludge cultivated in an anaerobic reactor for three years took on the ability of oxidizing ammonium with sulfate anaerobically. The average reduction of sulfate and ammonium was 71.67 mg·L−1 and 56.82 mg·L−1 at high concentrations. The reaction between SO42− and NH4+ was difficult, though feasible, due to its low standard Gibbs free energy change. The experiment demonstrated that high substrate concentrations and low oxidation-reduction potential (ORP) may be favourable for the biological reaction.

Since nitrification is the rate-limiting step in the biological nitrogen removal from wastewater, many studies have been conducted on the immobilization of nitrifying bacteria. A laboratory-scale investigation was conducted to examine the effectiveness of a continuous-flow airlift reactor (ALR) on the granulation of nitrifying sludge and the nitrification efficiency of the reactor after granulation. The results showed that the granular sludge began to appear on day 30 and matured in 75 days. The mature granules had an average diameter of 1.54 mm, settling velocity higher than 82.4 m h−1 and specific gravity of 1.07. The granules cultured in the present study had aerobic ammonia oxidation activity of 13.3 mg NH4+-N (g VSS)−1 day−1 and anaerobic ammonium oxidation (ANAMMOX) activity of 3.22 mg NH4+-N (g VSS)−1 day−1, which demonstrated that the nitrifying granules possessed the potential to be used as seed sludge for ANAMMOX and CANON (completely autotrophic nitrogen-removal over nitrite) reactors. After granulation, the ALR exhibited an excellent nitrification performance. It had strong tolerance to influent NH4+-N of 1100 mg L−1. When operated at influent NH4+-N concentration of 546 mg L−1, the reactor could remove over 94.4% of ammonium even at a nitrogen loading rate (NLR) of 2.37 f m−3 day−1 with a short hydraulic retention time (HRT) of 5.4 h. With the influent NH4+-N concentration of 547 mg L−1, HRT 6.9 h and NLR of 1.90 kg m−3 day−1, superior effluent quality could be achieved robustly, with an effluent NH4+-N of less than 5 mg L−1, satisfying the national primary discharging standard of China (GB 8978-1996).

The concept of anaerobic ammonium oxidation (ANAMMOX) is presently of great interest. The functional bacteria belonging to the Planctomycete phylum and their metabolism are investigated by microbiologists. Meanwhile, the ANAMMOX is equally valuable in treatment of ammonium-rich wastewaters. Related processes including partial nitritation-ANAMMOX and completely autotrophic nitrogen removal over nitrite (CANON) have been developed, and lab-scale experiments proved that both processes were quite feasible in engineering with appropriate control. Successful full-scale practice in the Netherlands will accelerate application of the process in future. This review introduces the microbiology and more focuses on application of the ANAMMOX process.

Isolation of new bacterial strains and recognition of their metabolic activities are highly desirable for sustainability of natural ecosystems. Biodegradation of dimethyl phthalate (DMP) under anoxic conditions has been shown to occur as a series of sequential steps using strain CW-1 isolated from digested sludge of Sibao Wastewater Treatment Plant in Hangzhou, China. The microbial colony on LB medium was yellowish, 3∼5 mm in diameter, convex in the center, and embedded in mucous externally. The individual cells of strain CW-1 are irregular rods, measuring (0.6∼0.7)×(0.9∼1.0) μm, V-shaped, with clubbed ends, Gram positive and without any filaments. 16S rDNA (1438 bp) sequence analysis showed that the strain was related to Arthrobacter sp. CW-1 and can degrade PAEs utilizing nitrate as electron acceptor, but cannot mineralize DMP completely. The degradation pathway was recommended as: dimethyl phthalate (DMP)→monomethyl phthalate (MMP)→phthalic acid (PA). DMP biodegradation was a first order reaction with degradation rate constant of 0.3033 d−1 and half-life 2.25 d. The DMP conversion to PA by CW-1 could be described by using sequential kinetic model.

•The PN was started up with ammonium conversion rate of 4.74 kg-N m−3 day−1.•The RSM with CCD was applied to optimize the parameters of DO and HRT.•Good PN performance was ascribed to the high sludge activity (3.69 g-N g−1 VSS day−1).•The transition of predominant microorganisms was investigated by DGGE.•Nitrosomonas was predominant functional microorganisms.Partial nitritation (PN) is the controllable bottleneck of the combined PN-anaerobic ammonium oxidation process, because it has a low nitrogen conversion rate. In this study, a “co-culture and screening” technology was developed to start up PN, and a dual dissolved oxygen-hydraulic retention time (DO-HRT) control strategy was developed to regulate the NH4+-N/NO2−-N ratio. The results showed that PN could be successfully started up and it had a high nitrogen loading rate and ammonium conversion rate (9.42 kg-N m−3 day−1 and 4.74 kg-N m−3 day−1), respectively. A response surface methodology (RSM) with a central composite design (CCD) was used to optimize the parameters of DO and HRT. When DO and HRT satisfied the relationships 0.66–0.5 × DO ≤ HRT ≤ 0.79–0.53 × DO and 0.5 mg L−1 ≤ DO ≤ 0.75 mg L−1, the performance of PN was excellent with an NH4+-N/NO2−-N ratio ranging from 1:1.04 to 1:1.47, an ammonium conversion efficiency of 53.6–62.1% and a nitrite accumulation efficiency greater than 90%. The excellent performance of PN process was attributed to the high specific activity of sludge (3.69 g-N g−1 VSS day−1), the predominance of ammonia-oxidizing bacteria, Nitrosomonas, and the inhibition of nitrite-oxidizing bacteria, Nitrospira.Download high-res image (307KB)Download full-size image

Vigorous anaerobic ammonium oxidation (anammox) activity was realized by seeding with diverse sludge contents. Granules taken from a 2-year old methanogenic reactor loaded with high organic and methanol contents were used as inoculum to enrich anammox biomass in a 1.1 L upflow anaerobic sludge blanket reactor. Anammox activity appeared after an operation of 83 d resulting in the final nitrogen removal rate of 11.7 kg N m−3 d−1 with the efficient granulation of anammox sludge. The analysis based on 16S rDNA sequencing confirmed that Candidatus “Brocadia” was the dominant population in the enriched biomass.

The biodegradation of dimethyl phthalate (DMP) was investigated under fermentative conditions in this study. The nature of the intermediate compounds and the extent of mineralization were probed using high-pressure liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) methods. The fermentative bacteria were able to biodegrade the DMP under anaerobic conditions, with the biodegradation rate of 0.36 mg DMP/(L·h). The results demonstrated that the DMP degradation under fermentative conditions followed the modifed Gompertz model with the correlation coefficient of 0.99. Monomethyl phthalate (MMP) and phthalic acid (PA) were detected as the intermediates of DMP biodegradation. During the experiment, MMP was rapidly produced and removed; however, PA accumulated as the biodegradation was slower throughout the course of the experiment. The CODCr concentration decreased from 245.06 to 72.01 mg/L after the experimental operation of 20 d. The volume of methane produced was 3.65 ml over a period of 20 d and the amount of methane recovered corresponded to 40.2% of the stoichiometric value. The CODCr variation and methane production showed that the DMP could not be completely mineralized under the fermentative conditions, which implied that the fermentative bacteria were not able to biodegrade DMP entirely.

•An acid-tolerant nitrifying sludge was successfully enriched at pH 6.0.•It had a high volumetric ammonia removal rate of 1.13 kg-N m−3 day−1 at pH 6.0.•It had a high specific ammonia conversion rate (0.29 g-N g−1 VSS day−1) at pH 6.0.•It tolerates acid due to the dominant Nitrosospira and ammonia-oxidizing archaea.Nitrification is an acidifying process that requires the addition of external alkalinity because of the alkaliphilic nature of the most ammonia-oxidizing bacteria. In this study, aerobic activated sludge was used as inoculum in an internal loop air-lift reactor, which resulted in successful enrichment of acid-tolerant nitrifying (ACIN) sludge at pH 6.0 by sequential addition of tea orchard soil suspension. The results showed that ACIN sludge had a remarkable acid tolerant capability with a volumetric ammonia conversion rate of 1.13 kg N m−3 day−1. ACIN sludge showed a higher maximum specific ammonia conversion rate (0.29 g N g−1 VSS day−1) than neutrophilic nitrifying sludge (0.14 g N g−1 VSS day−1) at pH 6.0 and had good resistance against pH fluctuations, with a maximum specific ammonia conversion rate (0.584 g N g−1 VSS day−1) at pH 7.5. Microbial community analysis indicated that the higher abundance of acid tolerant Nitrosospira and ammonia-oxidizing archaea laid a solid foundation for the remarkable acid-tolerant capability of ACIN sludge.