Sulfur Autotrophic Denitrification Process Research Articles

Salt stimulates sulfide−driven autotrophic denitrification: Microbial network and metagenomics analyses

Sulfur autotrophic denitrification (SADN) is a promising biological wastewater treatment technology for nitrogen removal, and its performance highly relies on the collective activities of the microbial community. However, the effect of salt (a prevailing characteristic of some nitrogen−containing industrial wastewaters) on the microbial community of SADN is still unclear. In this study, the response of the sulfide−SADN process to different salinities (i.e., 1.5 % salinity, 0.5 % salinity, and without salinity) as well as the involved microbial mechanisms were investigated by molecular ecological network and metagenomics analyses. Results showed that the satisfactory nitrogen removal efficiency (>97 %) was achieved in the sulfide−SADN process (S/N molar ratio of 0.88) with 1.5 % salinity. In salinity scenarios, the genus Thiobacillus significantly proliferated and was detected as the dominant sulfur−oxidizing bacteria in the sulfide−SADN system, occupying a relative abundance of 29.4 %. Network analysis further elucidated that 1.5 % salinity had enabled the microbial community to form a more densely clustered network, which intensified the interactions between microorganisms and effectively improved the nitrogen removal performance of the sulfide−SADN. Metagenomics sequencing revealed that the abundance of functional genes encoding for key enzymes involved in SADN, dissimilatory nitrate reduction to ammonium, and nitrification was up−regulated in the 1.5 % salinity scenario compared to that without salinity, stimulating the occurrence of multiple nitrogen transformation pathways. These multi−paths contributed to a robust SADN process (i.e., nitrogen removal efficiency >97 %, effluent nitrogen <2.5 mg N/L). This study deepens our understanding of the effect of salt on the SADN system at the community and functional level, and favors to advance the application of this sustainable bioprocess in saline wastewater treatment.

Effect of phosphorus on the performance of sulfur autotrophic denitrification

Autotrophic denitrification, recognized as a biological denitrification method, has garnered increasing interest in the field of ecological water environment denitrification technology. This study focuses on the utilization of the sulfur autotrophic denitrification process for the deep denitrification treatment of wastewater. Furthermore, it investigates the impact of phosphorus on nitrogen removal efficiency and bacterial community structure of sulfur autotrophic denitrification. In the experiment, a column containing an autotrophic denitrification filter with a carbon-sulfur filler was constructed. This study aimed to examine the impact of phosphorus on the initiation and denitrification efficiency of the autotrophic denitrification filter column. High-throughput sequencing was used to examine alterations in the structure of the bacterial community. The experimental findings indicated that the absence of phosphorus in the influent considerably extended the initiation period of the autotrophic denitrification filter column. The average Total Inorganic Nitrogen (TIN) removal rate was determined to be 80.26%, while the effluent exhibited an accumulation concentration of NO2−-N ranging from 7 to 11 mg/L. After the addition of phosphate, the removal rate of NO3−-N in the autotrophic denitrification process increased to more than 97%, with no2−-N accumulation. As the influent phosphorus concentration increased, the ability of the sulfur autotrophic denitrification filter column to resist hydraulic impact load improved. At a NO3−-N concentration of 30 mg/L and Hydraulic Retention Time (HRT) = 2 h, the mean NO3−-N removal rate increased from 73.22% to 81.71%. The concentration of phosphorus affected the quantity and variety of primary bacteria in the sulfur autotrophic denitrification system, as their domination changed from Pseudomonas to Ferritrophicum and Thiobacillus, and from a mixed culture to complete autotrophy.

Advance in the sulfur-based electron donor autotrophic denitrification for nitrate nitrogen removal from wastewater.

In the field of wastewater treatment, nitrate nitrogen (NO3--N) is one of the significant contaminants of concern. Sulfur autotrophic denitrification technology, which uses a variety of sulfur-based electron donors to reduce NO3--N to nitrogen (N2) through sulfur autotrophic denitrification bacteria, has emerged as a novel nitrogen removal technology to replace heterotrophic denitrification in the field of wastewater treatment due to its low cost, environmental friendliness, and high nitrogen removal efficiency. This paper reviews the advance of reduced sulfur compounds (such as elemental sulfur, sulfide, and thiosulfate) and iron sulfides (such as ferrous sulfide, pyrrhotite, and pyrite) electron donors for treating NO3--N in wastewater by sulfur autotrophic denitrification technology, including the dominant bacteria types and the sulfur autotrophic denitrification process based on various electron donors are introduced in detail, and their operating costs, nitrogen removal performance and impacts on the ecological environment are analyzed and compared. Moreover, the engineering applications of sulfur-based electron donor autotrophic denitrification technology were comprehensively summarized. According to the literature review, the focus of future industry research were discussed from several aspects as well, which would provide ideas for the application and optimization of the sulfur autotrophic denitrification process for deep and efficient removal of NO3--N in wastewater.

Unlocking the potential of elemental sulfur autotrophic denitrification through inorganic nutrient optimization

Elemental sulfur packed-bed (S0PB) bioreactors are increasingly employed to treat secondary effluents from wastewater treatment plants. Limited availability of inorganic nutrients, such as ammonium, phosphate, and inorganic carbon, significantly determines the growth of autotrophic microorganisms and the denitrification efficiency. This study investigated the constraining thresholds of inorganic nutrients on the elemental sulfur autotrophic denitrification process. In the absence of ammonium, phosphate, and bicarbonate, the denitrification rate decreased. Specifically, the ammonium assimilation process could be replaced by nitrate assimilation pathways, resulting in a 29.5 % decline in denitrification efficiency when the ammonium-N feed was reduced from 2.0 to 0 mg-N/L. However, the absence of phosphate-P and bicarbonate-C led to substantial drops in denitrification efficiency by 66.7 % and 77.5 %, respectively. This was primarily attributed to diminished biomass yield, as evidenced by reductions of 77.8–82.6 % in ATP and 35.7–44.3 % in protein content, along with a 12.4 %–14.7 % decrease in the relative abundances of dominant sulfur-oxidizing bacteria. Correlation analyses established specific thresholds for desired nitrate removal amounts: 0.131 for ammonium-N, 0.053 for phosphate-P, and 0.597 for bicarbonate-C. These thresholds provided valuable guidance for adjusting real-life wastewater through external supplementation when employing a pilot-scale S0PB bioreactor, leading to a significant enhancement of denitrification efficiency. This study emphasizes the significance of considering the concentrations of inorganic nutrients in wastewater when implementing S0PB bioreactors, which is a context that frequently neglects potential negative consequences.

Effect of ibuprofen on the sulfur autotrophic denitrification process and microbial toxic response mechanism

The effect of ibuprofen (IBU) on the sulfur autotrophic denitrification (SAD) process and microbial toxic response mechanism were investigated. Nitrate removal performance was inhibited by high IBU concentrations (10 and 50 mg/L), and the effect of low IBU concentrations (1 mg/L) on nitrate removal performance was negligible. The low IBU concentration induced basal oxidative stress for microbial self-protection, while the high IBU concentration induced high-intensity oxidative stress to damage the microbial cell membrane structure. Electrochemical characterization showed that the low IBU concentration stimulated the electron transfer efficiency, which was inhibited at the high IBU concentration. Moreover, the variation content of nicotinamide adenine dinucleotide (NADH) and nitrate reductase showed that metabolic activity increased at low IBU concentrations and decreased at high IBU concentrations during the sulfur autotrophic nitrate reduction process. This study proposed the hormesis toxic response mechanism of the SAD process to IBU exposure.

Determination of the Acute and Chronic Toxicity of Sulfate from the Sulfur Autotrophic Denitrification Process to Juvenile Zebrafish (Danio rerio).

Sulfur-based materials are widely used as electron donors for denitrification to enhance nitrogen removal from water. This leads to an increased sulfate concentration in the effluent or sulfate accumulation in recirculating aquaculture systems. This study explored acute and chronic toxicity of sulfate to juvenile zebrafish (Danio rerio) and investigated the histopathological changes in the gills of juvenile zebrafish exposed to sulfate. Results show that zebrafish had a high tolerance to sulfate, with no acute toxicity at sulfate concentrations from 250 to 3200 mg/L. For the chronic toxicity study, it was found that zebrafish mortality decreased with the increase in sulfate concentrations ranging from 250 to 1500 mg/L. In contrast, when the sulfate concentration was 1500-3000 mg/L, zebrafish mortality increased with the increasing sulfate concentration. In addition, in the ion balance test, KCl was added to balance the effects of Na+ from the Na2SO4 used to obtain the desired sulfate concentrations, showing that fish mortality correspondingly increased with increasing KCl addition. Furthermore, when living in an environment with elevated sulfate concentrations for a long period, changes were observed in the morphology, behavior, and gill tissue of the zebrafish, including slow and lateral swimming; bottom settling; and large opening and closing, lamellar fusion, and necrosis of gills. This research reveals the toxicity of sulfate to aquatic organisms, providing a scientific basis for the promotion and application of sulfur or sulfur-based materials in autotrophic reduction processes for wastewater treatment.

Effects of salinity on nitrite and elemental sulfur accumulation in a double short-cut sulfur autotrophic denitrification process

Double short-cut sulfur autotrophic denitrification (DSSADN) coupled with Anammox is of great significance in the low-carbon treatment of nitrogen-containing wastewater. In order to achieve high salinity autotrophic nitrogen removal, the effects of different salinities on the accumulation characteristics of NO2−-N and S0 and microorganisms in DSSADN process were studied. The results showed that the effect of salinity on the DSSADN process could be categorized into the stimulation, stable, and inhibition. When the salinity gradually increased to 2.5 %, the highest NO2−-N production rate (NiPR) and S0 production rate (S0PR) of DSSADN were 0.54 kg/(m3·d) and 1.1 kg/(m3·d) respectively. NiPR and S0PR gradually decreased as the salinity increased to more than 3 %. However, salinity had a relatively low impact on nitrite accumulation efficiency and S0 accumulation efficiency, which were 80 % and 81.5 %, respectively, when the salinity reached 5 %. Salinity has a great influence on the structure and abundance of microbial communities in the system.

Simultaneous removal of ammonia nitrogen and sulfide by coupled anammox and sulfur autotrophic denitrification process from industrial wastewater

This work presents an experimental study on the coupling between anammox and sulfur autotrophic denitrification for simultaneous removal of ammonia nitrogen and sulfide in industrial wastewater, leading to less environmental pollution. In a low-load continuous operation mode hybrid anaerobic baffled reactor (HABR) was started with 7 <pH<8.2 and temperature 30–35 °C. After 60 d of continuous operation successful enrichment of methanogenic granular sludge (MGS) size 7 and 5 mm was achieved. In the mature granular sludge phase (HRT 10 h), with influent chemical oxygen demand (COD) 1100 mg/L, the effluent COD 90 mg/L and removal efficiency was 90%. The MLSS, MLVSS, and f values were 9520, 6980, and 0.7. After 42 d of continuous operation with influent COD 600–700 mg/L, NO3−-N 250-300 mg/L, and COD/NO3−-N 2 to 2.8 (temperature 30–35 °C and pH 6.5–7.5) successful enrichment of denitrifying granular sludge (DGS) was achieved. In the research, the anammox start-up periods in MGS and DGS reactors are 86 and 118 d. An experimental comparative analysis to explore the influence of COD/TN 1:1,1:1.8,1:4.5, and 1:8.5 on the two reactors was performed. For COD/TN 1:1.8, the NH4+-N, NO2−-N, and TN removal efficiency were 54%, 73%, and 52%. The removal efficiency of the #2 reactors NH4+-N, NO2−-N, and TN were 50%, 60%, and 55%. S2−/NO3−-N of 2:5, 3.5:5, 5:5, 6.5:5 were investigated. Influent pH 7.5–8.0, temperature 30–35 °C and HRT 6.5 h, with average influent NH4+-N, NO3−-N, S2−, COD concentration 60, 25, 75, and 25 mg/L, the maximum removal efficiency of #1 reactor was 70%, 97%, 82%, and 100%. For 2# reactor 82%, 99%, 84%, and 100%. When MGS as carrier, the NH4+-N, NO3−-N, and S2− removal efficiency reached 67.67%, 98.59%, and 99.1%. With DGS as carrier, the NH4+-N, NO3−-N, and S2− removal efficiency reached 81.82%, 98.69%, and 84.18%. However, the coupling phase S0 production and productivity results showed that the DGS reactor was significantly better than the MGS reactor. Under the same hydraulic conditions the two reactors successfully coupled after 54 d of operation. Additionally, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis, revealed that the microbial community change is related to the concentration of organic matter, nitrogen and sulfur in the water. Building on these findings, future study will focus on the optimization of the mix design to provide practical engineering guidance.

A sulfur-limestone bioretention system for stormwater treatment: Nitrogen removal performance and microbial community

A lab-scale sulfur-limestone based bioretention system with a submerged zone was used to remove nitrate–nitrogen (NO3−-N) from stormwater. The results indicated that denitrification mainly occurred during the first 5 d of drying period. With the NO3−-N concentration in the influent increasing from 20 to 50 mg/L, after 5 d of drying period 93.99–97.26% NO3−-N was removed, and the effluent sulfate (SO42−) concentration ranged from 170.28 to 359.87 mg/L. When the NO3−-N content in the influent was lower than 30 mg/L, the effluent SO42− concentration met the Chinese Quality Standard for Ground Water (GB/T 14848-2017). Compared with the woodchips bioretention, there was no organic matter leakage problem. Sulfur autotrophic denitrification process followed first-order kinetic model, and the reaction kinetic parameters (k) were 0.7392–1.1472 d−1. The dominant genera in the submerged zone were Thiobacillus and Halothiobacillus (>63.69%) which participated in the sulfur autotrophic denitrification process.

Efficient nitrogen removal from stormwater runoff by bioretention system: The construction of plant carbon source-based heterotrophic and sulfur autotrophic denitrification process

The plant carbon source and sulfur were selected as the denitrification electron donors and filled in the internal water storage zone (IWSZ) of bioretention system to establish excellent mixotrophic denitrification system, which was beneficial to waste recycling and showed very high nitrate nitrogen removal efficiency (approximately 94%). The ammonia nitrogen, total nitrogen, and chemical oxygen demand removal efficiencies could reach 79.41%, 85.89%, and 74.07%, respectively. Mechanism study revealed the synergistic degradation effect was existed between acetic acid released from plant carbon source and the generated sulfate, which improved the S/CH3COOH mediated nitrate nitrogen removal reactions. Autotrophic denitrification occurred mainly in the upper layer of IWSZ, and the dominant bacteria were Thiobacillus. While in the lower layer, the dominant bacteria were mainly related to organic matter utilization and heterotrophic denitrification. The abundance of narG, nirK, nirS, and nosZ functional genes in the upper layer was significantly higher than the lower layers.

Alkalinity regulation in a sulfur autotrophic denitrifying filter substantially reduced total dissolved solids and sulfate in effluent

Sulfur autotrophic denitrification (SAD) filters are considered a promising technology due to their stable and excellent performance in nitrogen removal, affordable costs, and operational advantages. In this work, a novel operational strategy that employed sodium bicarbonate as an alkalinity source in the autotrophic denitrification filter (S-SAD) was established. With the sufficient supply of alkalinity, the S-SAD reached an excellent denitrification performance (98.01%±0.43%) with a nitrate concentration of 10 mg/L in influent and hydraulic retention time of 3 hrs. The total dissolved solids increment and sulfate concentration in effluent were significantly reduced by one-third, compared with that of the traditional SAD process under the same conditions. The analysis of microbial community indicated that Thiobacilhus, typical species with the functions of simultaneous sulfur oxidation and denitrification, was evidently enriched in the S-SAD. Thus, this present work demonstrated a feasible, relatively cost-effective and environmentally friendly approach to operate SAD towards further application.

Effect of current on biofilm-electrode reactor coupled with sulfur autotrophic denitrification process (BER-SAD) for nitrate removal from wastewater

The biofilm-electrode reactor coupled with sulfur autotrophic denitrification process (BER-SAD) was used to remove nitrate in groundwater, and the effect of current intensity on the denitrification characteristics of the coupled process was explored. Current intensity had a great influence on the denitrification effect of the coupled process, the maximum nitrate removal efficiency of 99.9% and lowest nitrite production were gained under the optimum current density of 100 mA. Moreover, the accumulation concentration of SO42- increased gradually with the increase of current intensity. With the increase of current intensity, the proportion of hydrogen autotrophic denitrification decreased, while the proportion of sulfur autotrophic denitrification increased.

A novel coupling process with partial nitritation-anammox and short-cut sulfur autotrophic denitrification in a single reactor for the treatment of high ammonium-containing wastewater

In this study, a novel coupling process with partial nitritation-anaerobic ammonium oxidation (anammox) (PNA) and sulfur autotrophic denitrification (SAD) was studied using an upflow biofilm reactor with mechanical vibration. At a lower dissolved oxygen (DO) concentration (0.40 ± 0.20 mg L−1), ammonia could be efficiently removed from synthetic wastewater by the coupling system with a total nitrogen removal efficiency (NRE) of 98% and an influent NH4+-N concentration of 600 mg L−1. In this system, the nitrate, which was produced during the anammox reaction, could be timely reduced by the SAD reaction. Compared with the conventional PNA and SAD processes, coupling the PNA and SAD processes in a single reactor prevented nitrite accumulation in the SAD reaction and reduced the total sulfate production by 59%. The high-throughput sequencing analysis supported that the SAD bacteria (Thiobacillus) and anammox bacteria (Candidatus Kuenenia) could coexist on the elemental sulfur stone. Additionally, sulfur consumption and sulfate production were increased under a high DO concentration. The sulfate production/nitrate reduction ratio and changing profile of the substrate suggested that the short-cut SAD process mainly occurred in this coupling system. Otherwise, batch experiments also suggested that the nitrite removal rate in the anammox process was 34.5 times higher than that in the SAD process. The outcomes of these experiments revealed that most of the nitrite, as an intermediate product in the SAD reaction, served as an electron acceptor for the anammox reaction. A stoichiometric calculation of this coupling process indicated that the novel reaction scheme with a high NRE was successfully achieved. Under an ideal short-cut SAD process, almost 55% of the sulfur consumption could be reduced in this coupling system. The coupling system provides a new perspective for nitrogen removal in a single reactor and further promotes anammox and SAD performance in wastewater treatment processes.

DL-cysteine and L-cystine formation and their enhancement effects during sulfur autotrophic denitrification

Sulfur autotrophic denitrification has been proved feasible for nitrate removal from aquatic environments and it utilizes elemental sulfur as the electron donor. A maximum denitrification rate of 194.57 mg N/L·d was achieved with biogenic sulfur as electron donor in a mixed culture collected from sulfur packed bed reactors; this rate was considerably higher than that delivered by α-S8 or μ-S in the same mixed culture. The elemental sulfur was also tested in the pure culture of Thiobacillus denitrificans, while a lower denitrification rate was noted than in the mixed culture, bio-S (4.86 mg N/L·d) again outperformed other two elemental sulfur's. X-ray absorption near edge structure spectra were collected to examine possible metabolic intermediates during the sulfur autotrophic denitrification process. The analysis revealed the existence of two major intermediates: DL-cysteine and L-cystine. They were found to not only provide electrons but also play a critical role in promoting the elemental sulfur-mediated sulfur autotrophic denitrification process. In general, we investigated the formation and enhancement effects of sulfur intermediates in the sulfur autotrophic denitrification process.

Selectivity control of nitrite and nitrate with the reaction of S0 and achieved nitrite accumulation in the sulfur autotrophic denitrification process

The characteristics of reaction between S0 and NO2−-N or NO3−-N in the sulfur autotrophic denitrification (SADN) process were studied using S0 as an electron donor and NO2−-N and NO3−-N as electron acceptors. The effect of changes in pH and temperature on the processes of NO2−-N and NO3−-N reduction were also studied to identify the optimum control parameters for strengthening the preference of S0 on NO3−-N; thus, achieving the efficient accumulation of NO2−-N. The results showed that the affinity of S0 for NO3−-N was considerably higher than that for NO2−-N. The optimum pH values for the reductions of NO2−-N and NO3−-N were 7.0 and 8.5, respectively, and both optimum temperatures were 35 °C. By controlling different pH, the NO3−-N conversion efficiency reached 90%, at which time the accumulation of NO2−-N was more than 95%. Microbial community analysis showed that Thiobacillus, Sulfurimonas, and Thioahalobacter were the main genera in the S0-SADN process.

Phosphorus Removal Mechanism of Sulfur/Sponge Iron Composite Fillers Based on Denitrification

In order to improve the phosphorus removal effect in the denitrification and phosphorus synchronous removal process by sulfur/sponge iron composite fillers, the phosphorus removal effect by different fillers with the coupling microorganisms was studied to analyze the denitrifying phosphorus removal mechanism of the microbial coupling sulfur/sponge iron composite fillers. The research result showed that the phosphorus removal ratio of sponge iron/sulfur composite fillers was over 95%, which was increased by 30% as compared to only sponge iron filler. In addition, the effluent TP concentration was reduced to less than 0.1 mg·L-1. The analysis of X-ray diffraction(XRD)and total iron concentration indicated that the main phosphorus removal system products which were produced in the corrosion and phosphorus removal process of sponge iron were FeOOH, FeS and Fe4 (PO4)3 (OH)3 deposits and dissolved iron ions; FeS and FeOOH which were the hydrolysis products of Fe2+ and Fe3+ converted PO43- to Fe4(PO4)3(OH)3 by adsorption and deposition so that phosphorus removal could be achieved. After the reactor of microbial coupling sulfur/sponge iron carbon composite fillers became stable, the removal efficiency of TN and TP could reach 90% and more than 83%, respectively; Corrosion of sponge iron and phosphorus removal process could also be promoted by biological iron and H+ that was produced in the sulfur autotrophic denitrification process, the system could realize the combination of "heterotrophic synergy autotrophic" composite denitrification and chemical phosphorus removal, and efficient denitrifying denitrification synchronous phosphorus removal process could be achieved in the urban sewage treatment plant.

Operational Characteristics of the Simultaneous Nitrogen and Phosphorus Removal and Removal of Phthalate Esters by Three-dimensional Biofilm-electrode Coupled with Iron/Sulfur Reactor

In order to explore the technological characteristics of the simultaneous removal of phthalate esters (PAEs) as well as nitrogen and phosphorus by the novel technology of three-dimensional biofilm-electrode coupled with iron/sulfur reactor (3DBER-S-Fe), the changes of the total nitrogen (TN),total phosphorus (TP),DBP,DEHP,NO3--N, SO42- and pH value were analyzed under the hydraulic retention time (HRT) of 8 h, 6 h and 4 h respectively. The results showed that 3DBER-S-Fe could remove nitrogen, phosphorus and PAEs effectively. Under the HRT of 8 h, 6 h and 4 h, the removal rates of TN were 80.99%, 78.85% and 64.76%; TP were 65.18%, 67.17% and 43.44%; DBP were 96.72%, 97.32% and 96.53%; DEHP were 91.89%, 81.57% and 74.30%, respectively. There were heterotrophic denitrification, hydrogen autotrophic denitrification and sulfur autotrophic denitrification processes in the 3DBER-S-Fe, the elemental sulfur could compensate for the relative shortage of denitrification electron donor caused by the increase of NO3--N load in the influent as a result of maintaining a high efficiency of the denitrification system when the HRT was shortened from 8h to 4h; the iron ions produced by the corrosion of the sponge iron filler in the system had a sustainable and efficient function of removing phosphorus by precipitation; the 3DBER-S-Fe process combined the interactions of physical adsorption, biological degradation and electrochemical processes which supported its high removal rates of DBP and DEHP under the different HRT conditions.

Efficient biological nitrogen removal by Johannesburg-Sulfur autotrophic denitrification from low COD/TN ratio municipal wastewater at low temperature

A novel system integrating Johannesburg (JHB) and sulfur autotrophic denitrification (SAD) process was proposed to enhance nitrogen removal in treating low COD/TN ratio (COD 129 mg/L, TN 29 mg/L on average) municipal wastewater at low temperature (12.2 ± 0.5 °C). The results showed that under an HRT of 11.3 h, the JHB process effluent COD, TN, and NH\( _{4}^{ + } \)–N were 32, 13.8, and 1.6 mg/L on average, respectively. Since NO\( _{3}^{ - } \)–N was the prominent compound of TN (average 80.6 %) and COD was low in JHB effluent, the SAD process utilized sulfur granule as electron donor for autotrophic denitrification was employed to remove the rest NO\( _{3}^{ - } \)–N of the JHB process. In JHB-SAD system, heterotrophic denitrification cooperated with autotrophic denitrification to enhance nitrogen removal. It was found that 87.0 % JHB effluent nitrogen was removed by SAD process under the most efficient nominal hydraulic retention time (HRT) of 0.32 h. The SAD process effluent of COD, TN, and NH\( _{4}^{ + } \)–N were 21, 1.8, and 1.0 mg/L, respectively. Most importantly, the JHB-SAD system could achieve complete nitrogen removal theoretically as long as the NH\( _{4}^{ + } \)–N was sufficiently oxidized. The nitrogen removal performance of JHB-SAD system is attractive in treating low COD/TN ratio municipal wastewater at low temperature. Moreover, SAD process was well adapted for limited space because of the efficient NO\( _{3}^{ - } \)–N removal, which was propitious to upgrade wastewater treatment plant.

Simultaneous heterotrophic and sulfur-oxidizing autotrophic denitrification process for drinking water treatment: Control of sulfate production

A long-term performance of a packed-bed bioreactor containing sulfur and limestone was evaluated for the denitrification of drinking water. Autotrophic denitrification rate was limited by the slow dissolution rate of sulfur and limestone. Dissolution of limestone for alkalinity supplementation increased hardness due to release of Ca 2+. Sulfate production is the main disadvantage of the sulfur autotrophic denitrification process. The effluent sulfate concentration was reduced to values below drinking water guidelines by stimulating the simultaneous heterotrophic and autotrophic denitrification with methanol supplementation. Complete removal of 75 mg/L NO 3–N with effluent sulfate concentration of around 225 mg/L was achieved when methanol was supplemented at methanol/NO 3–N ratio of 1.67 (mg/mg), which was much lower than the theoretical value of 2.47 for heterotrophic denitrification. Batch studies showed that sulfur-based autotrophic NO 2–N reduction rate was around three times lower than the reduction rate of NO 3–N, which led to NO 2–N accumulation at high loadings.

Study of a combined heterotrophic and sulfur autotrophic denitrification technology for removal of nitrate in water

A combined two-step process of heterotrophic denitrification in a fluidized reactor and sulfur autotrophic denitrification processes (CHSAD) was developed for the removal of nitrate in drinking water. In this process, the advantage of high efficiency of heterotrophic denitrification with non-excessive methanol and the advantage of non-pollution of sulfur autotriphic denitrification were integrated in this CHSAD process. And, this CHSAD process had the capacity of pH balance and could control the concentration of SO 4 2− in effluent by adjusting the operation condition. When the influent nitrate was 30 mg NO 3 −–N/L, the reactor could be operated efficiently at the hydraulic retention time (HRT) ranging from 20 to 40 min with C:N ratio (mg CH 3OH:mg NO 3 −–N) of 2.0 (methanol as carbon source). The nitrate removal was nearly 100% and there was no accumulated nitrite or residual methanol in the effluent. The effluent pH was about 7.5 and the sulfate concentration was lower than 130 mg/L. The maximum volume-loading rate of the reactor was 2.16 kg NO 3 −–N/(m 3 d). The biomass and scanning electron microscopy graphs of biofilm were also analyzed.