Autotrophic Denitrification Reactor Research Articles

Microbial enhanced manganese-autotrophic denitrification in reactor: performance, microbial diversity, potential functions

Autotrophic denitrification technology has gained increasing attention in recent years owing to its effectiveness, economical, and environmentally friendly nature. However, the sluggish reaction rate has emerged as the primary impediment to its widespread application. Herein, a bio-enhanced autotrophic denitrification reactor with modified loofah sponge (LS) immobilized microorganisms was established to achieve efficient denitrification. Under autotrophic conditions, a nitrate removal efficiency of 59.55 % (0.642 mg/L/h) and a manganese removal efficiency of 86.48 % were achieved after bio-enhance, which increased by 20.92 % and 36.34 %. The bioreactor achieved optimal performance with denitrification and manganese removal efficiencies of 99.84 % (1.09 mg/L/h) and 91.88 %. ETSA and 3D-EEM analysis reveled manganese promoting electron transfer and metabolic activity of microorganisms. High-throughput sequencing results revealed as the increase of Mn(II) concentration, Cupriavidus became one of the dominant strains in the reactor. Prediction of metabolic functions results proved the great potential for Mn(II)-autotrophic denitrification of LS bioreactor.

Study on the removal of high nitrate-nitrogen concentration from pig farm wastewater by heterotrophic and sulphur autotrophic synergistic denitrification filter process

Following the anaerobic fermentation process in a lagoon, the effluent from pig wastewater exhibited elevated levels of total nitrogen and nitrate nitrogen. The utilization of simple sulphur-limestone autotrophic denitrification resulted in a sluggish reaction rate and relatively moderate removal load. To enhance the efficacy of the sulphur autotrophic denitrification process, a strategy was implemented involving the introduction of a limited quantity of corncobs as a slow-release carbon source. This addition was made to a sulphur-limestone autotrophic denitrification reactor that was being operated continuously and stably. Furthermore, the volume ratio of the corncobs added was progressively increased. This study examines the alterations in nitrate nitrogen, chemical oxygen demand (COD), sulphate, and alkali consumption within the sulphur-limestone autotrophic denitrification reactor, both prior to and after the introduction of corncobs. This study examines the operational efficiency and reaction mechanism of a sulfur-limestone autotrophic denitrification reactor that is enhanced by the utilization of corncobs as a slow-release carbon source. The findings of the study indicate that the inclusion of maize cob carbon source in the sulphur limestone autotrophic denitrification process resulted in improved effectiveness in removing nitrate and nitrogen. Additionally, when considering the three different ratios of corncob carbon source, the process exhibited a chemical oxygen demand (COD) removal rate exceeding 42%. The observed trend in the consumption of alkalinity in both the pure sulphur limestone autotrophic denitrification process and the sulphur limestone autotrophic denitrification process augmented by the three types of corncob slow-release carbon sources indicated an increase with time. The concentration of nitrate-nitrogen in the influent water exhibited a negative correlation with the length of the reactor flow-through. The addition of a slow-release carbon source derived from corncob greatly enhanced the autotrophic denitrification and denitrification impact in the three reactors. Moreover, there was an observed increase in the trend of heterotrophic denitrification as the amount of carbon source added increased. The efficacy of the mixotrophic denitrification process surpassed that of the sulphur-limestone autotrophic denitrification method in the treatment of nitrate-nitrogen wastewater characterized by a high concentration of nitrate-nitrogen. The former exhibited a higher denitrification rate and resulted in lower levels of sulphate ions and alkalinity production.

Impact of organic carbon on sulfide-driven autotrophic denitrification: Insights from isotope fractionation and functional genes

Additional organics are generally supplemented in the sulfide-driven autotrophic denitrification system to accelerate the denitrification rate and reduce sulfate production. In this study, different concentrations of sodium acetate (NaAc) were added to the sulfide-driven autotrophic denitrification reactor, and the S0 accumulation increased from 7.8% to 100% over a 120-day operation period. Batch experiments revealed a threefold increase in total nitrogen (TN) removal rate at an Ac−-C/N ratio of 2.8 compared to a ratio of 0.5. Addition of organic carbon accelerated denitrification rate and nitrite consumption, which shortened the emission time of N2O, but increased the N2O production rate. The lowest N2O emissions were achieved at the Ac−-C/N ratio of 1.3. Stable isotope fractionation is a powerful tool for evaluating different reaction pathways, with the 18ε/15ε values in nitrate reduction ranging from 0.5 to 1.0. This study further confirmed that isotope fractionation can reveal denitrifying nutrient types, with the 18ε (isotopic enrichment factor of oxygen)/15ε (isotopic enrichment factor of nitrogen) value approaching 1.0 for autotrophic denitrification and 0.5 for heterotrophic denitrification. Additionally, the 18ε/15ε values can indicate changes in nitrate reductase. There is a positive correlation between the 18ε/15ε values and the abundance of the functional gene napA, and a negative correlation with the abundance of the gene narG. Moreover, 18ε and 15ε were associated with changes in kinetic parameters during nitrate reduction. In summary, the combination of functional gene analysis and isotope fractionation effectively revealed the complexities of mixotrophic denitrification systems, providing insights for optimizing denitrification processes.

Sulfur-pyrite-limestone biological filter for simultaneous nitrogen and phosphorus removal from wastewater treatment plant effluent: Interaction mechanisms of autotrophic and heterotrophic denitrification

To efficiently remove nitrogen(N) and phosphorus(P) from wastewater treatment plant effluent (WWTPE) with insufficient carbon, sulfur-pyrite-limestone autotrophic denitrification (SPLAD) reactor and gravel heterotrophic denitrification (GHD) reactor were constructed. Results showed that SPLAD was successfully started after 8 days and was faster than GHD. Under optimal hydraulic retention time (30 min) and backwash cycle (2 d), SPLAD achieved higher removal rates for TP, TN, NO3−-N, NH4+-N at 70.49 %, 90.35 %, 92.82 %, 79.66 %, respectively, surpassing those of GHD. The N removal primarily occurred through nitrification and denitrification with a proportion of 2.42–2.51 between heterotrophic and autotrophic denitrification, while P removal predominantly relied on the combination with Fe2+/Fe3+ generated by FeS2 autotrophic denitrification. Microbial community analysis revealed that Thiobacillus (17.86 %), Thioalbus (7.30 %) and Geothrix (0.81 %), belonging to autotrophic denitrification bacteria using S0/FeS2 as electron donors to reduce NO3−-N, were existed exclusively in SPLAD. Besides, the denitrification genes, such as nitrate reduction (narG, narZ, nxrA, and narH, narY, nxrB) and nitrite reduction (nirB and nirD), were higher in PSLAD than that in GHD. High abundance of sulfur oxidation genes (soxA, soxX, soxB, soxY and soxZ) and iron oxidation gene (ccoN) for autotrophic denitrification were also found in SPLAD. This study highlights the practical engineering application potential of the sulfur/pyrite/limestone involved mixotrophic denitrification process due to its simplicity, cost-effectiveness, and efficient N and P removal.

Nano-α-Fe2 O3 for enhanced denitrification in a heterotrophic/biofilm-electrode autotrophic denitrification reactor.

In this study, a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER) was constructed and nano-ɑ-Fe2 O3 was coated on granular activated carbon (GAC) as a third electrode to enhance the nitrate removal performance. The introduction of nano-ɑ-Fe2 O3 could stimulate microorganisms to secrete more extracellular polymeric substances (EPS), accelerating the electron transfer. Moreover, more denitrification bacteria were enriched on the particle electrodes, especially Pseudomonas and Thermomonas, which played a significant role in denitrification. The denitrification performance at different COD/N ratios (0.65-3.23) and current intensities (0-150 mA) was investigated in depth. When the nitrate concentration of the influent was 60 mg/L, nitrate was almost completely removed at the optimal current intensity (60 mA) and COD/N ratio (1.29). At the same time, there was almost no nitrite (<0.10 mg/L) and ammonia nitrogen (0 mg/L) accumulation in the effluent. This study provided a new direction for the advancement of HAD-BER and accelerated its implementation. PRACTITIONER POINTS: By introducing nano-a-Fe2O3 into HAD-BER, more denitrification bacteria were enriched on the particle electrodes. The increased contents of polysaccharide and protein content could accelerate the electron transfer. Almost completely denitrification could be achieved at current = 60 mA and COD/N = 1.29. The study provided a new direction for the further development of HAD-BERs.

Deciphering the influence of S/N ratio in a sulfite-driven autotrophic denitrification reactor.

Sulfur-based autotrophic denitrification is a cost-effective alternative to heterotrophic denitrification for nitrate removal due to no need of external organic carbon supply. Herein, sulfite-driven autotrophic denitrification (SDAD) was firstly established in a sequencing batch biofilm reactor treating high-strength nitrate-containing wastewater added by the sulfite. The nitrogen removal performance was mainly investigated under a molar ratio of sulfur-to‑nitrogen (S/N) ranging from 0.44 to 3.07 in a total of 180-day operation. Long-term experiment showed the optimal of S/N was found to be 2.63, much close to the stoichiometric value, achieving the highest autotrophic denitrification rate and complete total nitrogen removal efficiency (TNRE) with 92.4 ± 0.3%. Cyclical trial confirmed nitrate reduction and sulfite oxidation simultaneously occurred along with sulfate formation. Meanwhile, nitrite accumulation was observed at a very low S/N conditions. Microbial community analysis identified that Sulfurovum, Thiobacillus, and Thermomonas as key denitrifying sulfur-oxidizing bacteria responsible for SDAD. Moreover, the dynamic shift in functional microorganisms affected by influent S/N was also detected. Finally, the metabolic pathway of SDAD process was unraveled via the cooperative encoding of sulfite oxidases (Sor, Apr, Sat) and nitrate-reducing genes. This study sheds light on a new sulfur-cycle autotrophic denitrification process for the bioremediation of nitrate-contaminated wastewater.

Exploration and Comparison of the Effects of Vibration and Backwashing Methods on the Process of the Sulfur-Based Autotrophic Denitrification

Both the vibration and backwashing methods are efficient pathway to improve the denitrification ability in reactors. However, the comparison of the effects of vibration and backwashing on the sulfur-based autotrophic denitrification (SAD) reactor is still lacking. In this study, two SAD reactors were compared under various conditions, and the results showed that the use of the oyster shell powder could lower the sulfate productivity with better denitrification ability, and the denitrifiers could be more enriched due to the use of the oyster shell powder. In addition, vibration method performs better than backwashing in improving SAD denitrification ability, reasonable vibration intensity can not only help to reduce energy consumption, but also improve the ability of denitrification of the SAD reactors to a greater extent. Overall, the results of the experiments in this study are helpful for improving the ability of SAD reactors at low temperature and could provide the possibility for wider application of SAD technology.

A new inoculation method of sulfur autotrophic denitrification reactor for accelerated start-up and better low-temperature adaption

Elemental sulfur (S0) autotrophic denitrification (SAD) has been proved feasible for nitrate removal from aquatic environments. The long start-up period up to weeks of the SAD reactor impedes its industrial application. To accelerate the start-up process, this study employed S0 powder packed sequencing batch reactor operated for 10 days to obtain a seed biofilm, which was inoculated into a regular S0 flake packed bed reactor afterwards. Merely two days after inoculation, the reactor inoculated with seed biofilm was well started up and outperformed the control reactor, which was inoculated with regular anaerobic sludge and operated for more than 10 days, delivering much increased denitrification rate of 126 ± 0.68 mg N/(L·d) and a high nitrate removal efficiency of 93.0%. Batch tests during the start-up period showed that the seed biofilm developed well on S0 flakes and delivered improved nitrate removal performance than the control. Extracellular polymeric substance (EPS) analysis revealed an abundant content of protein in tightly bound EPS in the biofilm developed from the seed biofilm, which was recognized as a major contributor to facilitate the biofilm's attachment and growth onto S0 flakes. After operating under moderate temperature, the reactors were tested at a reduced temperature of 15 °C. Results indicated that the reactor inoculated with seed biofilm showed stronger adaptation ability towards low temperature and sustained better denitrification performance than the control, which was attributed to increased protein content in tightly bound EPS produced by the microbes against low-temperature. Determination of the microbial communities in tested reactors when the whole experiment was closing found that sulfur-related genera were dominating in the packed-bed reactor inculcated with seed biofilm, which played an important role in the S0-based denitrification process.

Achieving rapid thiosulfate-driven denitrification (TDD) in a granular sludge system

Sulfur-oxidizing bacteria (SOB) can drive a high level of autotrophic denitrification (AD) activity with thiosulfate (S2O32−) as the electron donor. However, the slow growth of SOB results in a low biomass concentration in the AD reactor and unsatisfactory biological nitrogen removal (BNR). In this study, our goal was to establish a high-rate thiosulfate-driven denitrification (TDD) system via sludge granulation. Granular sludge was successfully cultivated by increasing the nitrogen loading rate stepwise in thiosulfate-oxidizing/nitrate-reducing conditions in an upflow anaerobic blanket reactor. In the mature-granular-sludge reactor, a nitrate removal rate of 280 mg N/L/h was achieved with a nitrate removal efficiency of 97.7%±1.0% at a hydraulic retention time of only 15 minutes, with no nitrite detected in the effluent. Extracellular polymeric substance (EPS) analysis indicated that the proteins in loosely bound and tightly bound EPS were responsible for maintaining the compact structure of the TDD granular sludge. The dynamics of the microbial-community shift were identified by 16S rRNA high-throughput pyrosequencing analysis. The Sulfurimonas genus was found to be enriched at 74.1% of total community and may play the most critical role in the high-rate BNR. The batch assay results reveal that no nitrite accumulation occurred during nitrate reduction because the nitrate reduction rate (75.90±0.67 mg N/g MLVSS/h) was almost equal to the nitrite reduction rate (66.06±1.28 mg N/g MLVSS/h) in the thiosulfate-driven granular sludge reactor. The results of this study provide support for the establishment of a high-rate BNR system that maintains its stability with a low sludge yield.

Biological conversion of sulfamethoxazole in an autotrophic denitrification system

Sulfamethoxazole (SMX) is a common antibiotic prescribed for treating infections, which is frequently detected in the effluent of conventional wastewater treatment plants (WWTPs). Its degradation and conversion in a laboratory-scale sulfur-based autotrophic denitrification reactor were for the first time investigated through long-term reactor operation and short-term batch experiments. Co-metabolism of SMX and nitrate by autotrophic denitrifiers was observed in this study. The specific SMX removal rate was 3.7 ± 1.4 μg/g SS-d, which was higher than those reported in conventional wastewater treatment processes. The removal of SMX by the enriched denitrifying sludge was mainly attributed to biodegradation. Four transformation products (three known with structures and one with unknown structure) were identified, of which the structures of the two transformation products (TPs) were altered in the isoxazole ring. Additionally, the presence of SMX significantly shaped the microbial community structures, leading to the dominant denitrifier shifting from Sulfuritalea to Sulfurimonas to maintain the stability of system. Collectively, the sulfur-based autotrophic denitrification process could effectively remove SMX in addition to efficient nitrate removal, and further polish the effluent from conventional WWTPs.

Operational Performance and Microbiological Characteristics of an Iron-Salt Denitrification Reactor in Co-substrate Mode

When iron salt is used as an autotrophic denitrification electron donor, the high iron yield generated by oxidation is easy to precipitate, resulting in "iron encrustation" on the surface of denitrifying microorganisms, which inhibits their activity and even leads to their death. In order to solve the degradation of the efficiency of the autotrophic ferric denitrification reactor caused by the "iron encrustation" coating, this paper adopted the co-substrate mode to cultivate the ferric denitrification reactor; that is, a small amount of sodium acetate was added into the water of the reactor as an organic electron donor, to realize the efficient and stable operation of the ferric denitrification reactor. The results showed that adding an appropriate amount of organic matter could make the iron salt denitrification reactor run efficiently and stably, with an efficiency of up to 0.51 kg·(m3·d)-1, for more than 30 days. Heterotrophic bacteria could always be detected during the operation of the reactor in the co-substrate mode. Combined with the transmission electron microscopy (TEM) test results of the sludge, it was found that during the stable operation of the iron-salt denitrification reactor, heterotrophic bacteria were the main cause of iron-salt denitrification, and their unique iron-salt metabolism mode could effectively avoid the formation of iron encrustation. This study effectively solved the problem of microbial "iron encrustation" coating in the process of iron-salt denitrification, and will contribute to the development and application of autotrophic denitrification technology.

PH control and microbial community analysis with HCl or CO2 addition in H2-based autotrophic denitrification

H2-based autotrophic denitrification is promising to remove nitrate from water or wastewater lacking organic carbon sources, and pH is one of its most important process parameters. HCl and CO2 addition are known as adequate pH control methods for practical purposes. However, because of H2, added CO2 may participate in microbial metabolisms and affect denitrification mechanisms. Here, a combined micro-electrolysis and autotrophic denitrification (CEAD) reactor, in which H2 is generated based on galvanic-cell reactions between zero-valent iron and carbon, was optimized and continuously operated for 233 days by adding HCl or CO2 to control pH in the range of 7.2–8.2. Microbial communities were compared between the two pH-control methods through high-throughput sequencing of 16S rRNA, nirS, and nirK genes. Under a low COD/N ratio of 0.5 in the influent (with ∼36 mgNO3-–N/L), when adding HCl, the total nitrogen (TN) removal efficiency reached 91.4% ± 0.9% with a 28-h hydraulic retention time (HRT). When adding CO2, the TN removal efficiency was improved to 96.5% ± 1.7% with 24-h HRT. Significant differences of 16S rRNA and nirS genes between the two pH-control stages indicated the variation of microbial communities and nirS-type denitrifiers. With HCl addition, Thiobacillus, unclassified Comamonadaceae, Arenimonas, Limnobacter, and Thermomonas, which were reported previously as likely autotrophic or heterotrophic denitrifiers, were most dominant in the biofilms. With CO2 addition, the biofilms became dominated by Anaerolineaceae and Methylocystaceae (related to organic carbon metabolism), Denitratisoma (likely heterotrophic denitrifier), and uncultured bacteria TK10 and AKYG587. The results suggest that the added CO2 not only contributed to pH control but also participated in microbial metabolisms. This study provides useful insights into microbial mechanisms and further optimization of H2-based autotrophic denitrification in water and wastewater treatment.

Study on key influencing factors of magnetic autotrophic denitrification reactor

Under the condition of inoculating autotrophic denitrification sludge cultured earlier in the laboratory by constructing a magnetic autotrophic nitrogen removal reactor, the effect of the change in the range of Influent ammonia nitrogen loading at 0.05KgN·m-3 d-1-0.2KgN·m-3 d-1, pH = 6 ~ 8, COD concentration in 0-300mg/L on the treatment efficiency of autotrophic nitrogen removal process was investigated. Research shows that, magnetic autotrophic denitrification reactor has better resistance to ammonia-nitrogen shock load. When the influent ammonia nitrogen concentration was 400mg / L (ammonia nitrogen loading was 0.2 KgN·m-3 d-1, the autotrophic nitrogen removal efficiency could be ensured. PH had obvious effects on short-cut nitrification and anaerobic ammonia oxidation in magnetic autotrophic denitrification reactor. Too high or too low pH had great effect on nitrogen removal efficiency of the reactor. At pH=8, the removal efficiency of total nitrogen is up to 60%, and the efficiency of autotrophic nitrogen removal is the best. The presence of appropriate organic carbon source is helpful to improve the efficiency of nitrogen removal. When the influent COD concentration is 100mg/L, the nitrogen removal efficiency of the reactor is the highest, and the removal rate of total nitrogen is 74%.

Microbial Community Analysis and Effect of nZVI on Autotrophic Denitrification in a Biological Reactor

Abstract This study investigates the influence of dosage of nanoscale zero-valent iron (nZVI) on an immobilized biological autotrophic denitrification reactor. Effects of hydraulic retention time (...

Impact of phenol on the performance, kinetics, microbial communities and functional genes of an autotrophic denitrification system.

Nitrate and phenol often co-occur in wastewater because of the complex industrial and agricultural processes, while the impacts of phenol on autotrophic denitrification remain unclear. Here, a sulfur and hydrogen-oxidizing autotrophic denitrification reactor was established, and the effects of different concentrations of phenol on the nitrate removal performance, kinetics, microbial communities, and functional genes were investigated. Increasing concentrations of phenol significantly decreased the denitrification efficiency in the reactor. The kinetic data indicate the limitation of nitrate diffusion may be one of reasons. Increasing phenol concentrations declined the activities of nitrate and nitrite reductases and induced the production of reactive oxygen species (ROS) and the release of lactate dehydrogenase (LDH), suggesting potential toxicity to the denitrifying consortium. Denitrifying gene nirK was most sensitive to phenol stresses in the reactor. In addition, Thauera was the predominant genus in system with and without phenol, Bacillus was enriched under high phenol concentrations.

Nitrite accumulation in continuous-flow partial autotrophic denitrification reactor using sulfide as electron donor

The nitrite accumulation in handling nitrate and sulfide-laden wastewater in a continuous-flow upflow anaerobic sludge blanket reactor was studied. At sulfide/nitrate-nitrogen ratio of 1:0.76 and loading rates of 1.2kg-Sm−3d−1 and 0.4kg-Nm−3d−1, the elemental sulfur and nitrite accumulation rates peaked at 90% and 70%, respectively, with Acrobacter, Azoarcus and Thauera presenting the functional strains in the studied reactor. The accumulated nitrite was proposed a promising feedstock for anaerobic ammonia oxidation process. An integrated partial autotrophic denitrification-anaerobic ammonia oxidation-aeration process for handling the ammonia and sulfide-laden wastewaters is proposed for further studies.

Impact of Starvation Conditions on Biological Community Structure in Sulfur Autotrophic Denitrification Reactor

Sulfur/dolomite and pyrite/dolomite autotrophic denitrification reactors were applied to treat the secondary effluent of wastewater treatment plant to explore the removal effect, the changes of microbial community, and recovery time of reactors after starvation period. It was shown in the results that after 30 d non-water starvation endurance, the effluent concentrations of NO3--N in sulfur/dolomite and pyrite/dolomite reactors increased from 1.78 mg·L-1, 11.32 mg·L-1 to 27.87 mg·L-1, 26.56 mg·L-1 respectively at the low temperature of 12-14℃. In addition, sulfur/dolomite and pyrite/dolomite reactors recovered within 5 d and 11 d since restarted and could maintain a good effect of nitrogen removal at low temperature. MiSeq high throughput sequencing results showed that the abundance and diversity of the bacterial communities in starvation period in both reactors were lower than those in recovery period. The dominating phylum was Proteobacteria in both reactors while the dominating class was β-Proteobacteria. Thiobacillus was identified as the main genus for denitrification in sulfur/dolomite reactor.

Granulation of sulfur-oxidizing bacteria for autotrophic denitrification

Sulfur-oxidizing bacteria (SOB) was successfully employed for effective autotrophic denitrification and sludge minimization in a full-scale application of saline sewage treatment in Hong Kong. In this study, a Granular Sludge Autotrophic Denitrification (GSAD) reactor was continuously operated over 600 days for SOB granulation, and to evaluate the long-term stability of SOB granules, microbial communities and denitrification efficacy. Sludge granulation initiated within the first 40 days of start-up with an average particle size of 186.4 μm and sludge volume index (SVI5) of 40 mL/g in 5 min. The sludge granules continued to grow reaching a nearly uniform size of mean diameter 1380 ± 20 μm with SVI5 of 30 mL/g during 600 days of GSAD reactor operation at hydraulic retention time of 5 h and nitrate loading rate of 0.33 kg-N/m3/d. The GSAD reactor with SOB granular sludge achieved 93.7 ± 2.1% nitrogen and complete sulfide removal with low sludge yield of 0.15 g-volatile suspended solids (VSS)/g-N, and much lower nitrous oxide (N2O) emission than the heterotrophic denitrifying process. Microbial community analysis using fluorescence in situ hybridization (FISH) technique revealed that granules were enriched with SOB contributing to autotrophic denitrification. Furthermore, 16S rRNA analysis showed diverse autotrophic denitrification related genera, namely Thiobacillus (32.6%), Sulfurimonas (31.3%), and Arcobacter (0.01%), accounting for 63.9% of total operational taxonomic units at the generic level. No heterotrophic denitrification related genera were detected. The results from this study could provide useful design and operating conditions with respect to SOB sludge granulation and its subsequent application in a full-scale autotrophic denitrification in the Sulfate reduction-Autotrophic denitrification-Nitrification Integrated (SANI) process.

Characteristics of a Combined Heterotrophic and Sulfur Autotrophic Denitrification Technology for Removal of High Nitrate in Water

A combined heterotrophic and sulfur autotrophic denitrification technology for NO3--N wastewater treatment was started up by adding elemental sulfur in the heterotrophic denitrifying reactor, and the characteristics of pH constant and sludge reduction were studied. The results showed that the sulfur autotrophic denitrification bacteria in heterotrophic denitrifying reactor could achieve rapid growth. After running for 65d, TOC/N was controlled between 0.65 and 0.75, and the combined denitrification process did not require external alkalinity supplementation as the alkalinity need of autotrophic denitrifiers was supplemented by the heterotrophic denitrifiers. After running for 116d, the total nitrogen removal rate reached above 85%, and the denitrification efficiency was kept steady at 2.5 kg·(m3·d)-1. Compared to heterotrophic denitrification, the sludge production was greatly reduced, which was only 60% of that produced in combined heterotrophic and sulfur autotrophic denitrification reactor. NO2--N accumulated by using collaborative denitrification treatment of high concentration of NO3--N wastewater, the concentration reached 20 mg·L-1 even at the eventual plateau stage, which would require deep processing.

Effect of Element Sulfur Particle Size and Type of the Reactor on Start-up of Sulfur-based Autotrophic Denitrification Reactor

The effect of element sulfur particle size and type of the reactor on sulfur autotrophic denitrification reactor start-up was researched at room temperature(19-24℃) by using sulfur autotrophic denitrification bio-membrane reactor and anaerobic sludge bed biofilm reactor and inoculating anaerobic sludge. The research indicated that after 65 d operation, the bio-membrane reactor gained steady denitrification efficiency. With an influent NO3^--N of 150 mg·L^-1, and an HRT of 3.3 h, the removal efficiencies of NO3^--N and TN were 91% and 77%, and the removal rate of TN was 0.67-0.83 kg·(m³·d)^-1. The increase of volumetric loading rate of NO3^--N and production of nitrogen gas led to the floating of sludge in the anaerobic sludge bed biofilm reactor. With an influent NO3^--N of 185 mg·L^-1 and an HRT of 3.3 h, the maximum removal rate of NO3^--N of 1.1 kg·(m³·d)^-1 was attained in anaerobic sludge bed biofilm reactor. But the increase of effluent NO3^--N and NO2^--N lowered the quality of effluent water seriously, and the floating of sludge affected the steady operation of the anaerobic sludge bed biofilm reactor. Sulfur particles with particle size of 0.8 mm and 3.0 mm were used as electron donors for start-up of two batch reactors. The experiment results indicated that the reactor which used sulfur particle size of 0.8 mm attained higher removal efficiency of NO3^--N and TN, and its effluent accumulated less NO2^--N compared with the reactor which used particle size of 3.0 mm.