Piped-slow-release calcium nitrate dosing: A new approach to in-situ sediment odor control in rural areas.

Calcium nitrate addition is economically viable and highly efficient for the in-situ treatment of contaminated sediment and enhancement of surface water quality, particularly in rural areas. However, conventional nitrate addition technologies have disadvantages such as excessive nitrate release, sharp ammonium increase, and weakened sulfide oxidation efficiency owing to rapid nitrate injection into the sediment. To resolve these defects, we propose a piped-slow-release (PSR) calcium nitrate dosing method and investigate its treatment efficiency and underlying mechanisms. The results illustrated that PSR dosing had a longer half-life (t1/2 = 5.08 days) and a lower maximum apparent nitrate escape rate of 1.28 % than conventional nitrate injection and other dosing methods. In addition, the PSR managed the inorganic nitrogen release into the overlying water, and after the treatment, the nitrate, ammonium, and nitrite concentrations of 0 mg/L, 8.60 mg/L, and 0 mg/L on day 28 were close to those of the control group (0 mg/L, 8.76 mg/L, and 0 mg/L, respectively). Moreover, the PSR method maintained a moderate nitrate concentration of approximately 3000 mg/L in sediment interstitial water by its controlled-release design, thus greatly enhancing the sulfide oxidation efficiency by relieving the inhibitory effects of high nitrate concentrations, with 83.0 % sulfide being eradicated within 5 days. Sulfide-ferrous nitrate reduction (denitrification and dissimilatory nitrate reduction to ammonium) genera (e.g., Sulfurimonas, Thiobacillus, and Thioalkalispira) were successively enhanced and dominated the microbial community, and the related functional genes displayed high relative abundances. These results imply that the PSR dosing method for calcium nitrate, characterized by flexible operation, high efficiency, low cost, and controllable processes, is appropriate for remediating black-odorous sediment in rural areas.

Response of microbial communities to exogenous nitrate nitrogen input in black and odorous sediment.

Since nitrate nitrogen (NO3--N) input has proved an effective approach for the treatment of black and odorous river waterbody, it was controversial whether the total nitrogen concentration standard should be raised when the effluent from the sewage treatment plant is discharged into the polluted river. To reveal the effect of exogenous nitrate (NO3--N) on black odorous waterbody, sediments with different features from contaminated rivers were collected, and the changes of physical and chemical characteristics and microbial community structure in sediments before and after the addition of exogenous NO3--N were investigated. The results showed that after the input of NO3--N, reducing substances such as acid volatile sulfide (AVS) in the sediment decreased by 80 % on average, ferrous (Fe2+) decreased by 50 %, yet the changing trend of ammonia nitrogen (NH4+-N) in some sediment samples increased while others decreased. High-throughput sequencing results showed that the abundance of Thiobacillus at most sites increased significantly, becoming the dominant genus in the sediment, and the abundance of functional genes in the metabolome increased, such as soxA, soxX, soxY, soxZ. Network analysis showed that sediment microorganisms evolved from a single sulfur oxidation ecological function to diverse ecological functions, such as nitrogen cycle nirB, nirD, nirK, nosZ, and aerobic decomposition. In summary, inputting an appropriate amount of exogenous NO3--N is beneficial for restoring and maintaining the oxidation states of river sediment ecosystems.

A new strategy for the enrichment of ammonia-oxidizing archaea in wastewater treatment systems: The positive role of quorum-sensing signaling molecules.

Ammonia-oxidizing archaea (AOA) play an important role in natural nitrogen cycle, but are difficult to be enriched in wastewater treatment systems. In this experiment, under ambient temperature and high dissolved oxygen, different types of acyl-homoserine lactones (C6-HSL, C8-HSL, C10-HSL, C14-HSL and 3-oxo-C14-HSL) were added to five wastewater nitrification systems to achieve AOA enrichment. Results showed that AOA couldn't be detected in the blank group without the addition of signaling molecules, while the AOA could be detected in all the reactors with the addition. The enrichment effect of AOA was not obvious with added 100 or 200 nmol/L signaling molecules, while the enrichment effect was both obvious with added C8-HSL of 400 nmol/L and C10-HSL of 800 nmol/L. And relative abundance of AOA increased from undetected in the control group to 1.10 % and 0.96 %, respectively. The exogenous signaling molecules may provide new view for AOA enrichment in wastewater treatment systems.

The optimum particle size of anaerobic ammonia oxidation granular sludge under different substrate concentrations.

The nitrogen removal performance of anaerobic ammonia oxidation granular sludge (AnGS) varies widely among particle sizes. In this paper, the nitrogen removal performance, extracellular polymeric substances (EPS) secretion level and microbial community of AnGS with different particle sizes were investigated to select the optimal particle size for different substrate concentrations. The results showed that the optimal particle size migrated from 0.6-1.6 mm to 1.6-2.5 mm and then to 2.5-3.2 mm as the substrate concentration increased. When the influent concentration of NH4+-N was 110 mg/L, granular sludge with particle size of 1.6-2.5 mm showed excellent nitrogen removal performance with the highest EPS secretion, while the highest EPS secretion gradually migrated to smaller particles as the substrate concentration decreased. The nitrogen removal performance of AnGS with different particle sizes depends on different proportions of anaerobic ammonium-oxidizing (anammox) bacteria (Candidates_Jettenia, Candidates_Kuenenia, Candidatus_Brocadia), heterotrophic nitrification aerobic denitrifying bacteria (Acinetobacter) and denitrifying bacteria (Denitratisoma). The optimum particle size range for AnGS has been clarified for different influent nitrogen concentrations, which can provide some new understanding for the application of anammox reactors.

Efficient treatment of digested piggery wastewater via an improved anoxic/aerobic process with Myriophyllum spicatum and bionic aquatic weed.

The traditional anoxic/aerobic process (A/O) process is widely used for treating digested piggery wastewater, but the lack of carbon sources leads to poor efficiency. Therefore, the process needs optimization to achieve high-efficiency and low-cost operation mode. In this study, an improved A/O system with bionic aquatic weed and Myriophyllum sp. was established to decontaminate digested piggery wastewater. The average removal efficiencies of chemical oxygen demand (COD), NH4+-N, and total nitrogen (TN) by the improved A/O system was satisfactory. The average removal efficiencies of COD, NH4+-N, and TN were 62.1%, 87.5%, and 61.9%, respectively. High-throughput sequencing identified a number of dominant microorganisms. The relative abundance of Nitrosomonas (ammonia-oxidizing bacteria) and Nitrospira (nitrite-oxidizing bacteria) was 0.07%-3.52% and 0.32%-1.30%, respectively. Combining bionic aquatic weed and Myriophyllum sp. altered the microbial community structure and metabolic pathways. The results demonstrate a cost-effective method for treating digested piggery wastewater.

Coupling oxidation of acid volatile sulfide, ferrous iron, and ammonia nitrogen from black-odorous sediment via autotrophic denitrification-anammox by nitrate addition.

The coupling removal of acid volatile sulfide (AVS), ferrous iron, and ammonia nitrogen has been applied for black-odorous sediment remediation. In this study, calcium nitrate with different N/(S + Fe) ratios (0.45, 0.90, 1.20 and 1.80) was added into black-odorous sediment in four systems named R1, R2, R3, and R4. Results showed that the removal rate of AVS was 76.40% in the R1, which was lower compared with rates in R2-R4 around 96.70%. The ferrous oxidation rate was approximately 87.00% in R2-R4, which was considerably higher than that in the R1 (24.62%). And the ammonia was reduced by 81.02%, 88.00%, 100%, and 57.18% in R1, R2, R3 and R4, respectively. During the reaction, nitrite accumulation was observed, indicating partial denitrification. Moreover, microbes related to autotrophic denitrification (e.g., genus Thiobacillus, Dok59, GOUTA19, Gallionella, with the highest abundance of 15.40%, 13.21%, 8.79%, 9.44%, respectively) were detected in all systems. Furthermore, the anammox bacteria Candidatus_Brocadia with the highest abundance of 3.44% and 4.00% in R2 and R3, respectively was also found. These findings confirmed that AVS, ferrous iron, and ammonia nitrogen could be simultaneously removed via autotrophic denitrification coupled with anammox in black-odorous sediment by nitrate addition.

Effects of high ammonia loading and in-situ short-cut nitrification in low carbon­nitrogen ratio wastewater treatment by biocathode microbial electrochemical system.

The microbial electrochemical system (MES) has great advantages in wastewater treatment for rapid chemical oxygen demand (COD) removal and low sludge yield rate. Herein, biocathode MES was proposed to remove COD from high-ammonia wastewater with low carbon­nitrogen ratio and regulate the nitrogen forms in effluent for ANAMMOX process. The biocathode was more sensitive to ammonia nitrogen (NH4+-N) than anode and determined the power generation of MES. With COD of 500-550 mg L-1 in influent, increasing NH4+-N from 50 to 150 mg L-1 improved maximum power output (Pmax) from 3.0 ± 0.2 to 3.4 ± 0.1 W m-3, which was then reduced with further increase of NH4+-N from 300 to 600 mg L-1. However, for the cathodic reductive current, the negative effects of ammonia only revealed with NH4+-N ≥ 450 mg L-1. The cathodic equilibrium potential drop determined the power degradation, because the increased reductive compounds (NH4+ and COD) in catholyte. The high NH4+-N reduced the abundance of denitrifiers, exoelectrogens and organic-degrading bacteria on electrodes, while that of nitrogen-fixing bacteria increased. External alkalinity addition achieved in-situ short-cut nitrification and nitrite accumulation. With comparable NH4+ and NO2-, limited NO3- and low COD, the biocathode MES effluent was then suitable for subsequence ANAMMOX process.

Impacts of the heavy metals Cu (II), Zn (II) and Fe (II) on an Anammox system treating synthetic wastewater in low ammonia nitrogen and low temperature: Fe (II) makes a difference.

In this study, the impacts of heavy metals (1 mg L-1) on the nitrogen removal, bioactivity of anaerobic ammonia-oxidizing bacteria (AAOB) and the microbial community of anaerobic ammonium oxidation (Anammox) process were investigated. It was observed that short-term exposure in Cu (II) and Zn (II) both improved AAOB bioactivity, while long-term exposure significantly lowered the nitrogen removal to 0.218 and 0.302 kg m-3 d-1, when treated the wastewater with 100 mg L-1 nitrogen under 14-16 °C. Fe(II) had slight impact on Anammox in short-term experiment but deeply enhanced nitrogen removal during the long-term contact, and finally increased the that to 0.58 kg m-3 d-1. The impact on Anammox was Cu(II) > Zn(II) > Fe(II). Cu(II) and Zn(II) lowered the share of Candidatus Kuenenia to 3.32% and 3.80%, while Fe(II) improved that to 11.30% from 7.99%. Extracellular polymeric substance in biofilm had prominent iron adsorption capacity, which was the key factor that help AAOB resist Fe(II).

Index for nitrate dosage calculation on sediment odor control using nitrate-dependent ferrous and sulfide oxidation interactions.

Nitrate-driven sulfide and ferrous oxidation have received great concern in researches on sediments odor control with calcium nitrate addition. However, interrelations among sulfide oxidation, ferrous oxidation and their associated microbes during the nitrate reduction process are rarely reported. In this work, a nNO3/n(S+Fe) ratio (mole ratio of NO3- concentration to S2- and Fe2+ concentration) was first introduced as an index for calcium nitrate dosage calculation. Then certain amount of calcium nitrate was added to four sediment systems with various sulfide and ferrous initial concentration to create four gradients of nNO3/n(S+Fe) ratio (0.6, 0.9, 1.5 and 2.0) for treatment. Furthermore, the significant variations of sulfide and ferrous oxidation, microbial diversity and community structure were observed. The results revealed that at low nNO3/n(S+Fe) ratio (0.6 and 0.9) systems, sulfide seemed prior to ferrous to be oxidized and no obvious ferrous oxidation occurred. Meanwhile, sulfide oxidizing associated genus Sulfurimonas sp. became dominant in these systems. In contrast, sulfide and ferrous oxidation rate increased when nNO3/n(S+Fe) ratio reached 1.5 and 2.0 (two and three times of theoretically required amount for sulfide and ferrous oxidation), which made Thiobacillus sp. more dominant than Sulfurimonas sp. Hence, when nNO3/n(S+Fe) ratio of 1.5 and 2.0 were used, sulfide and ferrous could be simultaneously oxidized and no sulfide regeneration appeared in two months. These results demonstrated that for sulfide- and ferrous-rich sediment treatment, the nitrate consumed by ferrous oxidation should be taken into account when calculating the nitrate injecting dosage. Moreover, nNO3/n(S+Fe) ratio was feasible as a key parameter to control the oxidation process and as an index for calcium nitrate dosage calculation.

Degeneracy-analogous femtosecond dual-wavelength optical parametric oscillator at non-degenerate wavelengths.

Synchronously pumped optical parametric oscillator (OPO) at degeneracy is ideal for generating ultrafast laser pulses. Normally, however, group velocity mismatch (GVM) is ubiquitous among the interacting pulses at widely separated wavelengths. A versatile quasi-phase-matching (QPM) technique is proposed for temporal synchronizing of the signal and idler pulses relied on a less common Type-II QPM (oe-o interaction). The proposed group-velocity regulation technology is advantageous to constructing a degeneracy-analogous femtosecond OPO for dual-wavelength operation. Qualitative prediction for the proposed design is conducted based on a commercial femtosecond pump source at 1064 nm while the signal/idler wavelengths are 3.2 µm and 1.59 µm respectively. Compared with the conventional Type-0 QPM based counterpart (ee-e interaction), the uncompensated temporal distortion caused by temporal walk-off is strongly suppressed while the idler spectrum gets significantly broader. The versatility of the proposed scheme is also clearly demonstrated by its fairly stable performance within a broad tuning range of 2.9-3.5 µm and 1.68-1.53 µm. The demonstrated configuration might be promising for synchronously obtaining dual-wavelength ultrafast pulses with higher spectral and temporal qualities.

Reactor performance and microbial characteristics of CANON process with step-wise increasing of C/N ratio.

In this study, the nitrogen removal performance and microbial characteristics of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated with a step-wise increasing of C/N ratio (0.5, 1, 2 and 4) in a membrane bioreactor. The microbial distribution of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic AOB (AAOB) was analysed by fluorescence in situ hybridization (FISH). Results showed that the denitrification ratio rose up correspondingly with the increase of influent C/N, and nitrogen removal rate (NRR) reached the maximum when C/N was 1 due to the harmonious work of denitrification and CANON. However, NRR decreased when influent C/N was more than 2. The threshold C/N ratio of CANON process was 2.2; so the sewage with a high C/N ratio should be pretreated by combining with pre-oxidation of organics or anaerobic-energy-producing process. FISH results showed decreasing numbers of both AOB and AAOB with the addition of organics.

Rapid start-up and microbial characteristics of partial nitrification granular sludge treating domestic sewage at room temperature.

The successful suppression of nitrite-oxidizing bacteria in the partial nitrification (PN) stage was the main challenge for the application of autotrophic nitrogen removal process treating mainstream sewage. In this study, two identical PN granular reactors (P1 and P2) were rapid started-up using the simultaneous PN and granulation strategy, for treating the domestic sewage. P1 was seeded with 30% PN granular sludge to induce nucleation, in which the granule size achieved to more than 400µm in 12d, with ammonia oxidation rate and nitrite accumulation rate of 80% and 95%, respectively, while P2 realized granulation in 42d. The presence of organic matters and specific structure of granules were profitable for the stability of PN for treating sewage with low ammonia. High-throughput pyrosequencing results indicated the biodiversity of both reactors decreased after start-up, and Nitrosomonas was the predominant specie of aerobic ammonia-oxidizing bacteria in PN granular sludge.

Nitrate removal by organotrophic anaerobic ammonium oxidizing bacteria with C2/C3 fatty acid in upflow anaerobic sludge blanket reactors.

In anaerobic ammonium oxidation (Anammox) process, a harsh ratio of nitrite to ammonia in influent was demanded, and the max nitrogen removal efficiency could only achieve to 89%, both of which limited the development of Anammox. The aim of this work was to study the nitrate removal by organotrophic anaerobic ammonium oxidizing bacteria (AAOB) with C2/C3 fatty acid in upflow anaerobic sludge blanket (UASB) reactors. In this study, organotrophic AAOB was successfully enriched by adding acetate and propionate with the total organic carbon to nitrogen (TOC/N) ratio of 0.1. In the condition of low substrate, the TN removal efficiency reached 90%, with the effluent TN of around 11.8 mg L(-1). After the addition of acetate and propionate, the predominant species in Anammox granular sludge transformed to Candidatus Jettenia that belonging to organotrophic AAOB from the Candidatus Kuenenia relating to general AAOB.

Performance and influence factors of completely autotrophic nitrogen removal over nitrite (CANON) process in a biofilter packed with volcanic rocks.

Completely autotrophic nitrogen removal over nitrite (CANON) process was considered as one of the most efficient and economical nitrogen removal processes, which was suitable for treating wastewater with low ratio of carbon to nitrogen. In this study, an enlarging start-up strategy for CANON process was proposed, and a 40-L CANON reactor was successfully started by seeding 2-L mature biofilm containing both aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB). The effects of dissolved oxygen (DO), ammonia loading rate and the ratio of air inflow to water inflow (Qair/Qwater) on nitrogen removal performance were investigated. The distribution of AerAOB and AnAOB was analysed using fluorescence in situ hybridization (FISH) technique. The system reached a maximum NRR of 3.11 kg N m(-3) d(-1) with a removal efficiency of 89.5%, and the average value in steady state was 2.42±0.26 and (83.07 ± 6.89)%, respectively. Analysis of influence factors showed the important role of high DO (around 5 mg L(-1)), for the high-rate nitrogen removal, and the Qair/Qwater should be controlled at 28-40 for stable operation. FISH results suggested that AerAOB and AnAOB predominated in the reactor, with proportions of 46.8% and 39.3%, respectively. This study demonstrated that the biofilter operated with high effluent DO was a feasible setup for CANON process.

Stability and nitrite-oxidizing bacteria community structure in different high-rate CANON reactors.

In completely autotrophic nitrogen removal over nitrite (CANON) process, the bioactivity of nitrite-oxidizing bacteria (NOB) should be effectively inhibited. In this study, the stability of four high-rate CANON reactors and the effect of free ammonia (FA) and organic material on NOB community structure were investigated using DGGE. Results suggested that with the increasing of FA, the ratio of total nitrogen removal to nitrate production went up gradually, while the biodiversity of Nitrobacter-like NOB and Nitrospira-like NOB both decreased. When the CANON reactor was transformed to simultaneous partial nitrification, anammox and denitrification (SNAD) reactor by introducing organic material, the denitrifiers and aerobic heterotrophic bacteria would compete nitrite or oxygen with NOB, which then led to the biodiversity decreasing of both Nitrobacter-like NOB and Nitrospira-like NOB. The distribution of Nitrobacter-like NOB and Nitrospira-like NOB were evaluated, and finally effective strategies for suppressing NOB in CANON reactors were proposed.

Autotrophic nitrogen removal process in a potable water treatment biofilter that simultaneously removes Mn and NH4(+)-N.

Ammonia (NH4(+)-N) removal pathways were investigated in a potable water treatment biofilter that simultaneously removes manganese (Mn) and NH4(+)-N. The results indicated a significant loss of nitrogen in the biofilter. Both the completely autotrophic nitrogen removal over nitrite (CANON) process and nitrification were more likely to contribute to NH4(+)-N removal. Moreover, the model calculation results demonstrated that the CANON process contributed significantly to the removal of NH4(+)-N. For influent NH4(+)-N levels of 1.030 and 1.749mg/L, the CANON process contribution was about 48.5% and 46.6%, respectively. The most important finding was that anaerobic ammonia oxidation (ANAMMOX) bacteria were detectable in the biofilter. It is interesting that the CANON process was effective even for such low NH4(+)-N concentrations.

Nitrogen removal and microbial characteristics in CANON biofilters fed with different ammonia levels.

The nitrogen removal performance and microbial characteristics of four completely autotrophic nitrogen removal over nitrite (CANON) biofilters were investigated. These four reactors were simultaneously seeded from a stable CANON biofilter with a seeding ratio of 1:1, which were fed with different ammonia levels. Results suggested that with the ammonia of 200-400 mg L(-1), aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) could perform harmonious work. The bioactivity and population of the two groups of bacteria were both high, which then resulted in excellent nitrogen removal, while too low or too high ammonia would both lead to worse performance. When ammonia was too high, the bioactivity, biodiversity and population of AerAOB all decreased and then resulted in the lowest nitrogen removal. Nitrosomonas and Candidatus Brocadia were detected as predominant functional microbes in all the four reactors. Finally, strategies for treating sewage with different ammonia levels were proposed.

Microbial characteristics and nitrogen removal of simultaneous partial nitrification, anammox and denitrification (SNAD) process treating low C/N ratio sewage.

Simultaneous partial nitrification, anammox and denitrification (SNAD) process was successfully realized for treating low C/N ratio sewage, nitrogen and COD removal achieved to 3.26 kg m(-3) d(-1), 81%, respectively. The nitrogen removal performance, microbial community and distribution of the functional microorganisms were investigated. Results suggested that the presence of COD performed activity inhibition on both aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB), and led to the number decreasing of both AerAOB and AnAOB. Even though COD presence resulted in the biodiversity increasing of AerAOB and decreasing of AnAOB, the dominant species were always Nitrosomonas and Candidatus brocadia during the whole experiment. Clone-sequencing of 16S rRNA results suggested the emergence of five different denitrifying species, which then led to a higher nitrogen removal. Results in this study demonstrated that the applied start-up strategy was feasible for SNAD process treating low C/N ratio sewage.

Performance and microbial community of completely autotrophic nitrogen removal over nitrite (CANON) process in two membrane bioreactors (MBR) fed with different substrate levels.

To study the influence of substrate on completely autotrophic nitrogen removal over nitrite (CANON) process, two membrane bioreactors (MBR) with identical setup but fed with different substrate levels (R1 with low ammonia, R2 with high ammonia), were adopted in this study. The nitrogen removal performance, bioactivity, biodiversity and distribution of the functional microorganisms in two reactors were investigated. Both the aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) in R2 showed higher bioactivity than those in R1, while nitrite-oxidizing bacteria (NOB) showed the contrary result. Nitrosomonas and Candidatus Kuenenia stuttgartiensis were detected as predominant functional microbes in the two reactors while Nitrobacter only existed in R1. High influent ammonia possibly led to the higher biodiversity of AerAOB and the more densely packed distribution. Meanwhile, this study has demonstrated the feasibility of increasing ammonia for rapid start-up, and decreasing HRT for high-rate nitrogen removal in CANON process.

Application of membrane bioreactor for completely autotrophic nitrogen removal over nitrite (CANON) process.

A membrane bioreactor (MBR) was adopted for completely autotrophic nitrogen removal over nitrite (CANON) process at ambient temperature. CANON was rapidly started-up within around 50d under oxygen-limited condition. The average nitrogen removal rate reached to 0.70kgNm(-3)d(-1) with a removal efficiency of 88%. The ratio of air flow rate to volumetric ammonium loading rate should be maintained below 0.28Lairmin(-1)kg(-1)Nm(3)d for stable CANON. The feasibility of MBR for CANON process was proved in batch experiments. FISH results showed that aerobic ammonium-oxidizing bacteria predominated in the reactor sludge, whereas anaerobic ammonium-oxidizing bacteria predominated in the membrane biofilm. This study demonstrated that MBR was a suitable experimental setup for the operation of CANON process.