Sulfur-based Autotrophic Denitrification Research Articles

Impact of multi-ionic stress on sulfur-based autotrophic denitrification process

Nitrite accumulation poses a significant challenge in treating highly saline nitrogenous wastewater biologically, and the nitrite-based sulfide autotrophic denitrification (NiSAD) process has shown outstanding effectiveness in nitrite removal. Nevertheless, its capacity to withstand salinity in the presence of diverse salt ions remains uncertain. Therefore, this study investigated the individual and combined stresses of NaCl, KCl and MgCl2 on NiSAD process. Denitrification performance was found susceptible to high salinity, and its inhibition was significantly correlated with the type of ions exposed, while IC50 of specific denitrification activity were 5.14% (NaCl), 6.48% (KCl) and 2.03% (MgCl2), respectively. Dual and triple stresses exposure indicate that combined influence of NaCl, KCl and MgCl2 on denitrification performance was characterized by antagonism. Specifically, the order of inhibition intensity was Mg2+>K+>Na+, highlighting the more pronounced impact of ion strength on denitrification inhibition. Metagenomic analysis suggests that the system contains multiple genes associated with osmotic adaptation, indicating its potential for salt tolerance. It would enhance the understanding of the NiSAD process's response to multi-ionic stresses, thereby expanding its potential applications to a wider range of complex salt-containing wastewaters.

Sulfur-based mixotrophic denitrification: A promising approach for nitrogen removal from low C/N ratio wastewater.

Sulfur-based mixotrophic denitrification has significant potential as a promising denitrification technology for treating low ratio of carbon-to‑nitrogen (C/N) wastewater. This paper provided an in-depth and comprehensive overview of the sulfur-based mixotrophic denitrification process and discussed the underlying mechanisms and functional microorganisms. Possible electron transfer pathways involved in the sulfur-based mixotrophic denitrification process are also analyzed in detail. This review focused on the various sulfur-based electron donors used in the sulfur-based mixotrophic denitrification process, including S0, S2-, S2O32-, and pyrite (FeS2), and their performances when combined with various carbon sources (such as methanol, ethanol, glucose, and woodchips) were also explored. The analysis of the contribution proportion between autotrophic and heterotrophic denitrification suggested an appropriate C/N ratio can emphasize the dominance of autotrophs, thus exerting synergistic effects and reducing the consumption of carbon sources. Additionally, three strategies, including developing new composites, new bioreactors, and new sulfur sources, were proposed to improve the performance and stability of the sulfur-based mixotrophic denitrification process. Finally, the applications (such as secondary effluent, groundwater, and agricultural/urban storm water runoff), challenges, and perspectives of the sulfur-based mixotrophic denitrification were highlighted. This review provided an in-depth insight into the coupling mechanism of sulfur-based autotrophic and heterotrophic denitrification and guidance for the future implementation of the sulfur-based mixotrophic denitrification process.

A novel sulfur-based fiber carrier fixed-bed reactor for nitrate-contaminated wastewater treatment: Performance, operational characteristics and cold-tolerant mechanism

In the view of the serious prejudice of nitrates, sulfur-based autotrophic denitrification filter (SADF) has been widely used for deep nitrate removal from electron-donor-deficient water. However, it faces many challenges like slow start-up, reliance on backwashing, and poor low-temperature tolerance. For these challenges, a novel sulfur-based fiber carrier fixed bed reactor (SFFR) was developed in this study. It was found that SFFR had great film-forming ability and flow field characteristics, which promoted it to obtain superior denitrification performance, and the maximum nitrogen removal rate of 0.53 kg-N/m3/d. Meanwhile, SFFR shows significant cold tolerance, and alleviating the acidification problem of effluent to a certain extent. To sum up, the SFFR possesses the potential to be widely used in real-world wastewater treatment applications, especially as a promising solution for nitrate removal in cold regions. This study can provide an important reference for the improvement of the elemental sulfur autotrophic denitrification process.

Unraveling the impact of perfluorooctanoic acid on sulfur-based autotrophic denitrification process

PFOA has garnered heightened scrutiny for its impact on denitrification, especially given its frequent detection in secondary effluent discharged from wastewater treatment plants. However, it is still unclear what potential risk PFOA release poses to a typical advanced treatment process, especially the sulfur-based autotrophic denitrification (SAD) process. In this study, different PFOA concentration were tested to explore their impact on denitrification kinetics and microbial dynamic responses of the SAD process. The results showed that an increase PFOA concentration from 0 to 1000 μg/L resulted in a decrease in nitrate removal rate from 9.52 to 7.73 mg-N/L·h. At the same time, it increased nitrite accumulation and N2O emission by 6.11 and 2.03 times, respectively. The inhibitory effect of PFOA on nitrate and nitrite reductase activity in the SAD process was linked to the observed fluctuations in nitrate and nitrite levels. It is noteworthy that nitrite reductase was more vulnerable to the influence of PFOA than nitrate reductase. Furthermore, PFOA showed a significant impact on gene expression and microbial community. Metabolic function prediction revealed a notable decrease in nitrogen metabolism and an increase in sulfur metabolism under PFOA exposure. This study highlights that PFOA has a considerable inhibitory effect on SAD performance.

Achieving Long-Term Stability of Partial Nitrification and Autotrophic Denitrification in an MABR via Sulfide Dosing.

While partial nitrification (PN) has the potential to reduce energy for aeration, it has proven to be unstable when treating low-strength wastewater. This study introduces an innovative combined strategy incorporating a low rate of oxygen supply, pH control, and sulfide addition to selectively inhibit nitrite-oxidizing bacteria (NOB). This strategy led to a stable PN in a laboratory-scale membrane aerated biofilm reactor (MABR). Over a period of 260 days, the nitrite accumulation ratio exceeded 60% when treating synthetic sewage containing 50 mg NH4+-N/L. Through in situ activity testing and high-throughput sequencing, the combined strategy led to low levels of nitrite-oxidation activity (<5.5 mg N/m2 h), Nitrospira species (relative abundance <1%), and transcription of nitrite-oxidation genes (undetectable). The addition of sulfide led to simultaneous PN and autotrophic denitrification in the single-stage MABR, resulting in over 60% total inorganic nitrogen removal. Sulfur-based autotrophic denitrification consumed nitrite and inhibited NOB conversion of nitrite to nitrate. The combined strategy has potential to be applied in large-scale sewage treatment and deserves further exploration.

Manganese sulfide-sulfur and limestone autotrophic denitrification system for deep and efficient nitrate removal: Feasibility, performance and mechanism

Despite the great potential of sulfur-based autotrophic denitrification, an improvement in nitrate removal rate is still needed. This study used the desulfurized products of Mn ore to develop the MnS-S0-limestone autotrophic denitrification system (MSLAD). The feasibility of MSLAD for denitrification was explored and the possible mechanism was proposed. The nitrate (100 mg/L) was almost removed within 24 h in batch experiment in MSLAD. Also, an average TN removal of 98 % (472.0 mg/L/d) at hydraulic retention time of 1.5 h in column experiment (30 mg/L) was achieved. MnS and S0 could act as coupled electron donors and show synergistic effects for nitrate removal. γ-MnS with smaller particle size and lower crystallinity was more readily utilized by the bacterium and had higher nitrate removal efficiency than that of α-MnS. Thiobacillus and Sulfurimonas were the core functional bacterium in denitrification. Therefore, MnS-S0-limestone bio-denitrification provides an efficient alternative method for nitrate removal in wastewater.

Rapid conversion of heterotrophic denitrification to autotrophic denitrification in mariculture wastewater treatment: Denitrification performance and microbial communities under antibiotic stress

Mariculture wastewater, characterized by a low COD/Nitrogen (C/N) ratio and the occurrence of antibiotics, is commonly treated by a heterotrophic denitrification (HD) process with supplying substantial carbon sources. Compared to HD, sulfur-based autotrophic denitrification (AD) requires less external carbon sources and is more favorable for low-carbon wastewater treatment. However, the AD process often consumes more startup time. Thus, the present study was designed to explore a rapid startup strategy for the AD process by switching from HD to AD, treating mariculture wastewater. A rapid transformation from HD to AD was achieved by inoculating mixotrophic denitrifying sludge, reducing carbon sources and adding sulfur sources under the antibiotic sulfamethoxazole (SMX). From the functional microbial community point of view, our results showed that autotrophic bacteria exhibited greater adaptability to sulfamethoxazole than heterotrophic bacteria. During the transition from HD to AD, nitrate removal improved from 53.13 % to 68.57 %, and the secretion of tightly bound extracellular polymeric substances (TB-EPS) increased by 29.94 mg/g VSS. Meanwhile, in the heterotrophic phase, the presence of sulfate in mariculture wastewater maintained a high abundance of sulfate-reducing bacteria such as Desulfuromusa (0.8 %) and sulfur-based autotrophic denitrifying bacteria such as Sedimenticola (36.7 %) and Thiogranum (15.2 %). This increases the activity of sulfur metabolism during the heterotrophic phase and ensures a rapid transition from HD to AD. The rapid shift from HD to AD in seawater under antibiotic stress provides theoretical support for the improvement of mariculture wastewater treatment processes.

Establishment and optimization of sulfur-based autotrophic-heterotrophic denitrification biofilters for advanced post-anaerobic treatment of effluent from kitchen wastewater and landfill leachate under low temperature

Landfill leachate treatment is a major challenge in wastewater treatment. In this study, two sulfur-based autotrophic-heterotrophic denitrification biofilters (Ra biofilter with room-temperature molded filler and Rb biofilter with melt molded filler) were used to treat kitchen-landfill leachate at low temperatures. The effects of reflux ratio, concentrations of NaHCO3, and Na2S2O3 on the total nitrogen removal efficiency were analyzed, and based on response surface methodology, the optimum parameters were determined. After optimization, the total nitrogen removal efficiency for the Ra and Rb biofilters increased by 83% and 81%, respectively. Moreover, sulfur-based autotrophic denitrification accounted for more than 70% of the nitrogen removal in both biofilters. Based on high-throughput sequencing results, the functional bacteria exhibited high abundance in the Ra biofilter, indicating that the room-temperature molded filler favored the enrichment of functional bacteria. These findings were important for optimizing the operation of sulfur autotrophic-heterotrophic denitrification biofilters at low temperatures.

Ultra-stable mixotrophic denitrification coupled with anammox under organic stress for mainstream municipal wastewater treatment

Sulfur-based autotrophic denitrification (SAD) coupled with anammox is a promising process for autotrophic nitrogen removal in view of the stable nitrite accumulation during SAD. In this study, a mixotrophic nitrogen removal system integrating SAD, anammox and heterotrophic denitrification was established in a single-stage reactor. The long-term nitrogen removal performance was investigated under the intervention of organic carbon sources in real municipal wastewater. With the shortening of hydraulic retention time, the nitrogen removal rate of the mixotrophic system dominated by the autotrophic subsystem reached 0.46 Kg N/m³/d at an organic loading rate of 0.57 Kg COD/m³/d, with COD and total nitrogen removal efficiencies of 82.5 % and 94 %, respectively, realizing an ideal combination of autotrophic and heterotrophic systems. The 15NO3−-N isotope labeling experiments indicated that thiosulfate-driven autotrophic denitrification was the main pathway for nitrite supply accounting for 80.6 %, while anammox exhibited strong competitiveness for nitrite under the dual electron supply of sulfur and organic carbon sources and contributed to 65.1 % of nitrogen removal. Sludge granulation created differential functional distributions in different forms of sludge, with SAD showing faster reaction rate as well as higher nitrite accumulation rate in floc sludge, while anammox was more active in granular sludge. Real-time quantitative PCR, RT-PCR and high-throughput sequencing results revealed a dynamically changing community composition at the gene and transcription levels. The decrease in heterotrophic denitrification bacteria abundance indicated the effectiveness of the operational strategy for introduction of thiosulfate and maintaining the dominance of SAD in denitrification process in suppressing the excessive growth of heterotrophic bacteria in the mixotrophic system. The high transcriptional expression of sulfur-oxidizing bacteria (SOB) (Thiobacillus and Sulfurimonas) and anammox bacteria (Candaditus_Brocadia and Candidatus_Kuenenia) played a crucial role in the stable nitrogen removal.

Intensified denitrification in a fluidized-bed reactor with suspended sulfur autotrophic microbial fillers

Sulfur-based autotrophic denitrification (SAD) is a promising low-carbon approach to tackle nitrate pollution. However, practical SAD reactor implementation faces challenges of slow denitrification rates and prolonged start-up periods. In this work, a fluidized-bed denitrification reactor with suspended composite fillers immobilized with elemental sulfur and SAD bacteria was constructed. The reactor reaches a steady state within the first day of operation. A denitrification rate of 0.61 g N L−1 d−1 was realized, which is 2.4-fold higher than that in the packed-bed reactor. Mixotrophic denitrification prevailed during the start-up period, while the SAD process became the predominant pathway (>70%) after several days of operation. The prevailing bacteria in the fillers, notably Thiobacillus, are enriched during denitrification operations. Overall, this study highlights the impressive denitrification capabilities of the fluidized SAD reactor with microbial fillers, providing valuable insights for enhancing denitrification techniques.

Co-removal of P-nitrophenol and nitrate in sulfur-based autotrophic and methanol-fed heterotrophic denitrification bioreactors

P-nitrophenol (PNP) can co-occur with nitrate (NO3-) in industrial and municipal wastewater due to effluent discharges from industry and agricultural activities. In this study, the simultaneous removal of PNP and NO3- was investigated under autotrophic and heterotrophic denitrifying conditions in two bioreactor columns at laboratory scale. Autotrophic denitrification with elemental sulfur showed efficient elimination of both PNP (85 % on average for 5–50 mg/L) and NO3- (99 % on average) even at feed PNP concentration of 50 mg/L. In contrast, the heterotrophic column showed significantly lower PNP removal (53 % on average for 5–50 mg/L) despite denitrification efficiency being ≥ 95 %. ORP was identified as a possible control parameter to modulate PNP removal efficiency. The autotrophic column showed better resiliency than the heterotrophic one under intermittent feeding of 50 mg/L of PNP. Absorbance spectra and HPLC results revealed no accumulation of PNP by-products, i.e., aminophenol, in the autotrophic column during transient feeding conditions.

A novel pattern of coupling sulfur-based autotrophic disproportionation and denitrification processes for achieving high-rate and precisely adjustable nitrogen removal

Sulfur-based autotrophic disproportionation (SADP) has been accidentally discovered during employing sulfur-based autotrophic denitrification (SADN) bioreactor to treat low C/N ratio wastewater. The SADP products, including sulfide (SADP-S2−) and polysulfide (SADP-Sn2−), can supply additional electrons to improve the denitrification efficiency. However, the in-situ SADP process was challenging to control, resulting in the unstable enhancement efficiency and excessive sulfide emissions, thereby impeding its scalability in practical engineering. In this study, an independent SADP process was achieved in a sulfur-packed bed bioreactor, with a controllable sulfide production rate ranging from 0.24 ± 0.02 to 0.83 ± 0.03 kg-S/m3/d by adjusting the empty bed contact time between 1 and 5 h. Subsequently, the SADP bioreactor was connected upstream of a SADN bioreactor to create a sulfur-based autotrophic disproportionation-denitrification (SAD2) system. The SAD2 system realized an enhanced denitrification rate by up to 2.38 times, with flexibility to adjust between 0.65 ± 0.06–1.55 ± 0.20 kg-N/m3/d. One reason for this enhancement was that SADP-S2− provided additional electrons to the SADN process and exhibited higher biocompatibility than chemical-S2− (Na2S) at similar doses. Additionally, it stimulated the sulfur bioavailability by 1.66 times as a result of stoichiometry matrix calculation. SADP-Sn2− was only detected in the biofilm, as indicated by a linear increase in the Sn proportion from 8.1 % to 30.1 %, but with minimal releases (352 μg-S/L) into the water. Another reason for the enhancement was bioaugmentation, with increases in protein (30.0 %), ATP (6.9 %), live cells proportion (10.1 %) and total relative abundance of denitrificans (87.7 %). These findings imply that the novel SAD2 system facilitates adjustable and high-rate nitrogen removal without the risk of sulfide emission, surpassing the capabilities of the independent SADN system. This offers a new pattern for practical applications.

Mixotrophic denitrification process driven by lime sulfur and butanediol: Denitrification performance and metagenomic analysis

Heterotrophic sulfur-based autotrophic denitrification is a promising biological denitrification technology for low COD/TN (C/N) wastewater due to its high efficiency and low cost. Compared to the conventional autotrophic denitrification process driven by elemental sulfur, the presence of polysulfide in the system can promote high-speed nitrogen removal. However, autotrophic denitrification mediated by polysulfide has not been reported. This study investigated the denitrification performance and microbial metabolic mechanism of heterotrophic denitrification, sulfur-based autotrophic denitrification, and mixotrophic denitrification using lime sulfur and butanediol as electron donors. When the influent C/N was 1, the total nitrogen removal efficiency of the mixotrophic denitrification process was 1.67 and 1.14 times higher than that of the heterotrophic and sulfur-based autotrophic denitrification processes, respectively. Microbial community alpha diversity and principal component analysis indicated different electron donors lead to different evolutionary directions in microbial communities. Metagenomic analysis showed the enriched denitrifying bacteria (Thauera, Pseudomonas, and Pseudoxanthomonas), dissimilatory nitrate reduction to ammonia bacteria (Hydrogenophaga), and sulfur oxidizing bacteria (Thiobacillus) can stably support nitrate reduction. Analysis of metabolic pathways revealed that complete denitrification, dissimilatory nitrate reduction to ammonia, and sulfur disproportionation are the main pathways of the N and S cycle. This study demonstrates the feasibility of a mixotrophic denitrification process driven by a combination of lime sulfur and butanediol as a cost-effective solution for treating nitrogen pollution in low C/N wastewater and elucidates the N and S metabolic pathways involved.

Effect of Sulfur Autotrophic Denitrification Sludge on the Start-Up Characteristics of Anaerobic Ammonia Oxidation

In this study, we used a two-stage experiment in order to investigate the effect of the inoculation with elemental sulfur-based autotrophic denitrification (S0-SADN) sludge on the start-up characteristics of Anaerobic ammonia oxidation (ANAMMOX). In the first stage, we attempted direct enrichment with an elemental sulfur and pyrite filler in a S0-SADN reactor, which retained stable operation, and adjusted the nitrogen source components of the influent at different times. In the second stage, we replaced the original filler with Kaldnes filler, and set the influent component to be divided into NH4+-N and NO2−-N. The ANAMMOX process could not be started in the 80-day S0-SADN stage despite the 0.8% abundance of Candidatus Kuenenia; however, after changing the original filler, the reactor showed obvious ANAMMOX reaction characteristics after day 44, and under the condition of an influent TIN load of 0.36 kg(m3·d)−1, the reactor TIN removal rate was stable at more than 80% after day 55. The main ANAMMOX bacteria in the reactor were Candidatus Brocadia (1.08%) and Candidatus Kuenenia (0.96%). The results show that it is feasible to initiate the ANAMMOX process by inoculating the S0-SADN sludge; however, it is not suitable to start the ANAMMOX and the stable operation of the S0-SADN simultaneously. The ANAMMOX process can be started first under the condition of no sulfur source, which takes little time. After initiating the ANAMMOX process, the coupling S0-SADN process can be re-considered given an excessive accumulation of S0-SADN bacteria in the system.

Denitrification performance and mechanism of a novel sulfur-based fiber carrier fixed-bed reactor: Co-existence of sulfur-based autotrophic denitrification and endogenous denitrification

Sulfur autotrophic denitrification becomes a research hotspot in recent years, but traditional packed bed reactor has several disadvantages, including small sulfur specific surface area, easy blockage, and sulfur loss when using small sulfur grains. A sulfur-based fiber carrier fixed-bed reactor (SFFR) was developed in the study, which had the advantage of higher denitrification efficiency due to the large sulfur specific surface area, and the nitrogen removal rate (NRR) of it could reach 0.304 kg (NO3−-N)/m3·d. Meanwhile, the sulfur-based fiber filler that used in SFFR had characteristics of high surface roughness and suitable for microbial attachment growth, which promoted the endogenous denitrification in the reactor. Therefore, SAD and endogenous denitrification were jointly involved in nitrate removal in SFFR, and the sulfate productivity gradual decreased to 5.58 mgSO42−/mgNO3−-N in this study, which decreased by 26 % compared with the theoretical value (7.54 mgSO42−/mgNO3−-N). The result of this research showed that compared with the traditional SAD process, the electron utilization rate of SFFR increased from 75.76 % to 91.8 %. Meanwhile, the higher electron utilization rate of SFFR indicated that the advantages of SFFR included lower elemental sulfur consumption, lower acid production and smaller sludge production. In addition, the maximum NRR of SFFR was further increased to 0.528 kg (NO3−-N)/m3·d with the assist of vibrating device because it could enhance the mass transfer during the process of wastewater treatment. Microbial analysis suggested that several autotrophic denitrifiers along with heterotrophs and endogenous denitrifiers, co-existed in the biofilm.

Long-Term Operation of a Pilot-Scale Sulfur-Based Autotrophic Denitrification System for Deep Nitrogen Removal

Sulfur-based autotrophic denitrification is a novel biological denitrification process characterized by the absence of an organic carbon source, a short reaction time, a high denitrification rate, a low treatment cost, and a small footprint. However, the technique is facing challenges with respect to engineering applications. In this study, a pilot-scale sulfur-based autotrophic denitrification system was established with an optimal hydraulic retention time (HRT) of 0.21 h, which achieved the highest denitrification load of 1158 mg/(L·d) and a denitrification rate of 164 gNO3−-N/(m3·h). Effective backwashing is the basis for the long-term stable and efficient nitrogen removal performance, which recovered its normal nitrogen removal performance within 0.5 h. In addition, the operation cost is merely 0.013 $/t, indicating that the sulfur-based autotrophic denitrification process presents good economic applicability, and the relatively low operation cost will lay a foundation for practical application.

High-rate iron sulfide and sulfur-coupled autotrophic denitrification system: Nutrients removal performance and microbial characterization

Iron sulfides-based autotrophic denitrification (IAD) is a promising technology for nitrate and phosphate removal from low C:N ratio wastewater due to its cost-effectiveness and low sludge production. However, the slow kinetics of IAD, compared to other sulfur-based autotrophic denitrification (SAD) processes, limits its engineering application. This study constructed a co-electron-donor (FeS and S0 with a volume ratio of 2:1) iron sulfur autotrophic denitrification (ISAD) biofilter and operated at as short as 1 hr hydraulic retention time (HRT). Long-term operation results showed that the superior total nitrogen and phosphate removals of the ISAD biofilter were 90–100% at 1–12 h HRT, with the highest denitrification rate up to 960 mg/L/d. Considering low sulfate production, HRT of 3 h could be the optimal condition. Such superior performance in the ISAD biofilter was achieved due to the interactions between FeS and S0, which accelerated the denitrification process and maintained the acidity-alkalinity balance. Metagenomic analysis found that the enriched nitrate-dependent iron-oxidizing (NDFO) bacteria (Acinetobacter and Acidovorax), sulfur-oxidizing bacteria (SOB), and dissimilatory nitrate reduction to ammonia (DNRA) bacteria likely supported stable nitrate reduction. The metabolic pathway analysis showed that completely denitrification and DNRA, coupled with sulfur oxidation, disproportionation, iron oxidation and phosphate precipitation with FeS and S0 as co-electron donors, were responsible for the high-rate nitrate and phosphate removal. This study provides the potential of ISAD as a highly efficient post-denitrification technology and sheds light on the balanced microbial S-N-Fe transformation.

Effect of salinity on the denitrification of the sulfur-based autotrophic denitrification system

This study investigated the effect of gradual salt concentration increases on the nitrogen removal performance from a sulfur-based autotrophic denitrification (SAD) process. A continuous operation reactor was used to study the adaptability of sulfur-based autotrophic denitrifying bacteria to changes in salinity. The study focused specifically on the effects of SO42− and Cl− on the activity of SAD bacteria. When the concentration of SO42− was 0∼4 ​g/L, NO3−-N was removed at more than 97%. When the concentration of SO42− increased to 15 ​g/L, the removal of NO3−-N decreased to 51%. When the concentration of NaCl was 0∼30 ​g/L, the removal rate of NO3−-N was all greater than 97%. When the concentration of NaCl increased to 80 ​g/L, the removal rate of NO3−-N decreased to 34.6%. When the NaCl concentration was 50 ​g/L, the removal rate of NO3−-N decreased to 80.59% at first, and the removal rate of NO3−-N recovered to 98% after 16 days of operation. When the NaCl concentration increased to 80 ​g/L, the NO3−-N removal rate decreased to 50%, and the reactor still could not recover its performance after long-term operation. The growth of halophilic heterotrophic bacteria with the increase of NaCl concentration leads to an increase in the abundance of Proteobacteria. The higher concentration of Cl− seriously inhibits the growth of Sulfurimonas and Thiobacillus, decreasing the effectiveness of bacteria to remove nitrogen.

Performance of sulfur-based autotrophic denitrification process for nitrate removal from permeate of an MBR treating textile wastewater and concentrate of a real scale reverse osmosis process

Textile is one of the industrial sectors generating the highest amount of wastewater with various polluting substances. Lately, water reuse in textile industries, especially, with the reverse osmosis (RO) process following membrane bioreactor (MBR) treatment has been applied more commonly. In this study, an autotrophic sulfur-based denitrifying column performance was evaluated, for the first time, for nitrate reduction from permeate of a lab-scale MBR receiving real textile wastewater and from the concentrate stream of a real scale-RO plant used for recovering water from textile wastewater. Nitrate concentration in the MBR effluent and RO concentrate averaged 35 ± 3 and 12 ± 2 mg-N/L, respectively. With the sulfur-based column bioreactor, quite high (≥90%) denitrification performances were attained both for MBR effluent and RO concentrate up to nitrate loadings of 0.432 and 0.12 g-N/(L.d), respectively. COD present in wastewater was not utilized in the column bioreactor, which illustrates no or minimal contribution of heterotrophic denitrification. Alkalinity concentration in the wastewater was enough to buffer the acid formation during autotrophic denitrification. Sulfate was generated accompanied by nitrate reduction and sulfide was formed at low nitrate loadings. In the batch tests, the denitrification rates for the MBR effluent and RO concentrate were 0.31 and 0.28 g-N/(g-VSS.d), respectively, which were relatively higher than the ones observed for the synthetic nitrate-contaminated groundwater. Autotrophic sulfur-based denitrification is a promising and robust process alternative even for textile RO concentrate with high concentrations of salinity, non-biodegradable COD, and color.

Element sulfur-based autotrophic denitrification constructed wetland as an efficient approach for nitrogen removal from low C/N wastewater

Constructed wetlands (CWs) integrated with sulfur autotrophic denitrification to stimulate high-rate nitrogen removal from carbon-limited wastewater holds particular application prospect due to no excessive carbon source addition, high efficiency, and good stability. In this study, we conducted elemental sulfur-based constructed wetland (SCW) and traditional constructed wetland (CW) under different C/N (2, 1, and 0.5) to explore the feasibility and mechanisms for nitrogen removal from low C/N wastewater. Compared with CW, SCW was demonstrated more robust in nitrogen removal in the case of low C/N influent. When the influent C/N control was at 0.5, SCW observed total nitrogen (TN) and nitrate removal efficiency of 69.36 ± 3.96% and 81.71 ± 3.96%, with the corresponding removal rate of 1.18 ± 0.66 and 1.70 ± 0.92 g-N·m–2·d–1, which were 2.11 and 10.03 times of CW, respectively. The nitrate removal rate constant k in the SCW was 1.05, 3.83, and 10.33 times higher than the CW with C/N of 2, 1 and 0.5. Furthermore, 14.40, 54.51, and 79.82% of nitrogen were removed by the sulfur autotrophic denitrification (SAD) in SCW, which also contributed 43.89, 73.68, and 71.70% of sulfate production. Moreover, the combined system of CW-SCW is proved be an efficient operation mode for simultaneously removing total ammonia nitrogen (TAN) and nitrate. In the SCW, the richness of the microbial community was improved and sulfur-oxidizing genera (e.g. Thiobacillus, Sulfurimonas) was selectively enriched, which affect the performance the elemental sulfur-based denitrification process. The nitrate reduction pathway was overwhelmed by denitrification and the dissimilatory nitrate reduction process. These findings offer elemental sulfur-based autotrophic denitrification constructed wetland has excellent potential to enhance nitrogen removal from carbon-limited wastewater.