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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 N 2 O 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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Despite the promising potential of elemental sulfur-based denitrification (ESDeN) packed-bed progresses, challenges such as excessive biofilm growth and gas entrapment persist, leading to denitrification deterioration. Water flush (WF) is recognized as an effective strategy, yet its effects remain underexplored. To address this knowledge gap, this study systematically investigated WF effects on ESDeN packed-bed denitrification. Results demonstrated that controlling WF effectively regulated denitrification, achieving superior and stable rates. Compared to no WF (0.45 kgN·m -3 ·d -1 ), rates improved by 1.20 ∼ 1.56 times under low-frequency (weekly WF, 0.54 kgN·m -3 ·d -1 ) and low-intensity WF (0.54 ∼ 0.70 kgN·m -3 ·d -1 ). High-frequency (hours WF) and high-intensity WF (30 & 50 m/h) further amplified denitrification rates by 1.73 ∼ 2.29 times. The enhanced denitrifications under low-frequency/intensity WF were mainly attributed to prolonged actual hydraulic retention time (AHRT), while high-frequency/intensity WF improved both AHRT prolonging and biofilm thinning, facilitating mass transfer. This study offers a promising avenue for fine-tuning denitrification rates via strategic WF adjustments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Expanded granular sludge blanket (EGSB) is regarded as a promising reactor to carry out denitrifying sulfide removal (DSR) and elemental sulfur (S 0 ) recovery. Although the recirculation ratio is an essential parameter for EGSB reactors, how it impacts the DSR process remains poorly understood. Here, three lab-scale DSR-EGSB reactors were established with the different recirculation ratios (3:1, 6:1 and 9:1) to evaluate the corresponding variations in pollutant removal, S 0 recovery, anaerobic granular sludge (AGS) characteristics and microbial community composition. It was found that an intermediate recirculation ratio (6:1) could facilitate long-term reactor stability. Adequate recirculation ratio could enhance S 0 recovery, but an excessive recirculation ratio (9:1) was likely to cause AGS fragmentation and biomass loss. The S 0 desorbed more from sludge at higher recirculation ratios, probably due to the enhanced hydraulic disturbance caused by the increased recirculation ratios. At the low recirculation ratio (3:1), S 0 accumulation as inorganic suspended solids in AGS led to a decrease in VSS/TSS ratio and mass transfer efficiency. Although typical denitrifying and sulfide-oxidizing bacteria (e.g., Azoarcus, Thauera and Arcobacter) were predominant in all conditions, facultative and heterotrophic functional bacteria (e.g., Azoarcus and Thauera) were more adaptable to higher recirculation ratios than autotrophs (e.g., Arcobacter, Thiobacillus and Vulcanibacillus), which was conducive to the formation of bacterial aggregates to response to the increased recirculation ratio. The study revealed recirculation ratio regulation significantly impacted the DSR-EGSB reactor performance by altering AGS characteristics and microbial community composition, which provides a novel strategy to improve DSR performance and S 0 recovery., (Copyright © 2019. Published by Elsevier Inc.)

Micro-aerobic condition has proven to be effective in enhancing sulfide oxidation to elemental sulfur (S 0 ) during integrated simultaneous desulfurization and denitrification process (ISDD). In this study we investigated and compared the performance and microbial community of ISDD process operating under initially anoxic, then micro-aerobic and finally switch back to anoxic condition. For all the three tested scenarios, comparable bioreactor performance in terms of sulfate (95.0 ± 4.4%, 90.6 ± 3.8%, 89.8 ± 3.5%) and nitrate (∼100%) removal was achieved. However, a shift of ISDD bioreactor from micro-aerobic to anoxic environment clearly increased the S 0 production (30.6%), relative to that at initial anoxic condition (14.2%). Further anoxic bioreactor operation with different influent nitrate concentrations also obtained satisfactory performance particularly in terms of S 0 production. Microbial community analysis results showed that functional microorganisms selectively enriched at micro-aerobic condition, particularly sulfide-oxidizing bacteria (SOB), could also function well and enhance S 0 production when bioreactor switching from micro-aerobic to anoxic environment. We proposed that micro-aerobic strategy could function as a bio-selector and provide a new idea in functional microorganisms selectively enrichment for wastewater treatment., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Elemental sulfur (S 0 ) is always produced during bio-denitrification and desulfurization process, but the S 0 yield and purification quality are too low. Till now, no feasible approach has been carried out to efficiently recover S 0 . In this study, we report the S 0 generation and recovery by a newly designed, compact, biofilm formed membrane filtration reactor (BfMFR), where S 0 was generated within a Thauera sp. strain HDD-formed biofilm on membrane surface, and then timely separated from the biofilm through membrane filtration. The high S 0 generation efficiency (98% in average) was stably maintained under the operation conditions with the influent acetate, nitrate and sulfide concentration of 115, 120 and 100 mg/L, respectively, an initial inoculum volume of approximate 2.4 × 10 8  cells, and a membrane pore size of 0.45 μm. Under this condition, the sulfide loading approached 62.5 kg/m 3 ·d, one of the highest compared with the previous reports, demonstrating an efficient sulfide removal and S 0 generation capacity. Particular important, a solid analysis of the effluent revealed that the recovered S 0 was adulterated with barely microorganisms, extracellular polymeric substances (EPSs), or inorganic chemicals, indicating a fairly high S 0 recovery purity. Membrane biofilm analysis revealed that 80.7% of the generated S 0 was accomplished within 45-80 μm of biofilm from the membrane surface and while, the complete membrane fouling due to bacteria and EPSs was generally observed after 14-16 days. The in situ generation and timely separation of S 0 from the bacterial group by BfMFR, effectively avoids the sulfur circulation (S 2- to S 0 , S 0 to SO 4 2- , SO 4 2- to HS - ) and guarantees the high S 0 recovery efficiency and purity, is considered as a feasible approach for S 0 recovery from sulfide- and nitrate-contaminated wastewater., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

To characterize the impact of influent loading on elemental sulfur (S 0 ) recovery during the denitrifying and sulfide oxidation process, three identical, lab-scale UASB reactors (30cm in length) were established in parallel under different influent acetate/nitrate/sulfide loadings, and the reactor performance and functional community structure were investigated. The highest S 0 recovery was achieved at 77.9% when the acetate/nitrate/sulfide loading was set to 1.9/1.6/0.7kgd -1 m -3 . Under this condition, the genera Thauera, Sulfurimonas, and Azoarcus were predominant at 0-30, 0-10 and 20-30cm, respectively; meanwhile, the sqr gene was highly expressed at 0-30cm. However, as the influent loading was halved and doubled, S 0 recovery was decreased to 27.9% and 45.1%, respectively. As the loading was halved, the bacterial distribution became heterogeneous, and certain autotrophic sulfide oxidation genera, such as Thiobacillus, dominated, especially at 20-30cm. As the loading doubled, the bacterial distribution was relatively homogeneous with Thauera and Azoarcus being predominant, and the nirK and sox genes were highly expressed. The study verified the importance of influent loading to regulate S 0 recovery, which could be achieved as Thauera and Sulfurimonas dominated. An influent loading that was too low or too high gave rise to insufficient oxidation or over-oxidation of the sulfide and low S 0 recovery performance., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Organics,sulfide and nitrogen compounds in industrial wastewater are significant challenges for wastewater treatment. These pollutants could be removed simultaneously from wastewater treatment system using biological technologies. In this study, a heterotrophic denitrifying sulfur bacterial strain HDD1 was isolated from wastewater treatment bioreactor. Strain HDD1 was identified as Thauera sp. based on the 16S rRNA gene phylogenetic analysis and physiological characteristics. Acetate and sulfide could be utilized as electron donors and nitrate as electron acceptor for respiration in Thauera sp. HDD1. The acetate (300 mg·L -1 ), sulfide (200 mg·L -1 ) and nitrate (487 mg·L -1 ) were completely metabolized and removed within 15 hours. The main product of sulfide oxidation was elemental sulfur as identified by scanning electron microscope and energy dispersive spectrometer. These results suggest that the newly isolated Thauera sp. HDD1 could be used for simultaneous industrial wastewater treatment and elemental sulfur resource recovery.

A mathematical model of carbon, nitrogen and sulfur removal (C-N-S) from industrial wastewater was constructed considering the interactions of sulfate-reducing bacteria (SRB), sulfide-oxidizing bacteria (SOB), nitrate-reducing bacteria (NRB), facultative bacteria (FB), and methane producing archaea (MPA). For the kinetic network, the bioconversion of C-N by heterotrophic denitrifiers (NO 3 - →NO 2 - →N 2 ), and that of C-S by SRB (SO 4 2- ) was proposed and calibrated based on batch experimental data. The model closely predicted the profiles of nitrate, nitrite, sulfate, sulfide, lactate, acetate, methane and oxygen under both anaerobic and micro-aerobic conditions. The best-fit kinetic parameters had small 95% confidence regions with mean values approximately at the center. The model was further validated using independent data sets generated under different operating conditions. This work was the first successful mathematical modeling of simultaneous C-N-S removal from industrial wastewater and more importantly, the proposed model was proven feasible to simulate other relevant processes, such as sulfate-reducing, sulfide-oxidizing process (SR-SO) and denitrifying sulfide removal (DSR) process. The model developed is expected to enhance our ability to predict the treatment of carbon-nitrogen-sulfur contaminated industrial wastewater.2- ) and SOB (S 2- →S 0 ) was proposed and calibrated based on batch experimental data. The model closely predicted the profiles of nitrate, nitrite, sulfate, sulfide, lactate, acetate, methane and oxygen under both anaerobic and micro-aerobic conditions. The best-fit kinetic parameters had small 95% confidence regions with mean values approximately at the center. The model was further validated using independent data sets generated under different operating conditions. This work was the first successful mathematical modeling of simultaneous C-N-S removal from industrial wastewater and more importantly, the proposed model was proven feasible to simulate other relevant processes, such as sulfate-reducing, sulfide-oxidizing process (SR-SO) and denitrifying sulfide removal (DSR) process. The model developed is expected to enhance our ability to predict the treatment of carbon-nitrogen-sulfur contaminated industrial wastewater., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Sulfide biooxidation by the novel sulfide-oxidizing bacteria Pseudomonas sp. C27, which could perform autotrophic and heterotrophic denitrification in mixotrophic medium, was studied in batch and continuous systems. Pseudomonas sp. C27 was able to oxidize sulfide at concentrations as high as 17.66 mM. Sulfide biooxidation occurred in two distinct stages, one resulting in the formation of sulfur with nitrate reduction to nitrite, followed by thiosulfate formation with nitrite reduction to N2. The composition of end-products was greatly impacted by the ratio of sulfide to nitrate initial concentrations. At a ratio of 0.23, thiosulfate represented 100% of the reaction products, while only 30% with a ratio of 1.17. In the continuous bioreactor, complete removal of sulfide was observed at sulfide concentration as high as 9.38 mM. Overall sulfide removal efficiency decreased continuously upon further increases in influent sulfide concentrations. Based on the experimental data kinetic parameter values were determined. The value of maximum specific growth rate, half saturation constant, decay coefficient, maintenance coefficient and yield were to be 0.11 h(-1), 0.68 mM sulfide, 0.11 h(-1), 0.21 mg sulfide/mg biomass h and 0.43 mg biomass/mg sulfide, respectively, which were close to or comparable with those reported in literature by other researches.

In this study, two lab-scale UASB reactors were established to testify S(0) recovery efficiency, and one of which (M-UASB) was improved from the previous T-UASB by shortening reactor height once S(2-) over oxidation was observed. After the height was shortened from 60 to 30cm, S(0) recovery rate was improved from 7.4% to 78.8%, and while, complete removal of acetate, nitrate and S(2-) was simultaneously maintained. Meanwhile, bacterial community distribution was homogenous throughout the reactor, with denitrifying sulfide oxidization bacteria predominant, such as Thauera and Azoarcus spp., indicating the optimized condition for S(0) recovery. The effective control of working height/volume in reactors plays important roles for the efficient regulation of S(0) recovery during DSR process., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Biological treatment of sulfate-laden wastewater consists of two separate reactors to reduce sulfate to sulfide by sulfate-reducing bacteria (SRB) and to oxidize sulfide to sulfur (S(0)) by sulfide oxidation bacteria (SOB). To have SRB+SOB in a single reactor faced difficulty of low S(0) conversion. This study for the first time revealed that dissolved oxygen (DO) level can be used to manipulate SRB+SOB reactions in a single reactor. This work demonstrated successful operation of an integrated SRB+SOB reactor under micro-aerobic condition. At DO = 0.10-0.12 mg l(-1), since the activities of SOB were enhanced by limited oxygen, the removal efficiency for sulfate reached 81.5% and the recovery of S(0) peaked at 71.8%, higher than those reported in literature. At increased DO, chemical oxidation of sulfide with molecular oxygen competed with SOB so conversion of S(0) started to decline. At DO>0.30 mg l(-1) activities of SRB were inhibited, leading to failure of the SRB+SOB reactor., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

[Display omitted] • Self-acidification was mainly attributed to sulfur disproportionation. • Supplying alkalinity to bulk was essential to control self-acidification. • S0FB achieved 7–129 times higher of TN removal rate than S0PB. • S0FB achieved 26–65 times higher of TP removal rate than S0PB. The sulfur fluidizing bioreactor (S0FB) has significant superiorities in treating nitrate-rich wastewater. However, substantial self-acidification has been observed in engineering applications, resulting in frequent start-up failures. In this study, self-acidification was reproduced in a lab-scale S0FB. It was demonstrated that self-acidification was mainly induced by sulfur disproportionation process, accounting for 93.4 % of proton generation. Supplying sufficient alkalinity to both the influent (3000 mg/L) and the bulk (2000 mg/L) of S0FB was essential for achieving a successful start-up. Furthermore, the S0FB reached 10.3 kg-N/m3/d of nitrogen removal rate and 0.13 kg-PO 4 3-/m3/d of phosphate removal rate, respectively, surpassing those of the documented sulfur packing bioreactors by 7–129 times and 26–65 times. This study offers a feasible and practical method to avoid self-acidification during restart of S0FB and highlights the considerable potential of S0FB in the treatment of nitrate-rich wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SAD efficiency under high salinity could reach 70 %–80 % of salt-free condition. • Salt-tolerant SAD microbes were key to efficient SAD under high-salinity stress. • The salinity-tolerance abilities of difference SOBs were ranked. • High-salinity inhibited biomass yield rather than individual microbial function. This study investigated the performance of sulfur-dominated autotrophic denitrification (SAD) process under four different salinities of 0 %, 0.5 %, 3 %, and 6 %, simulating groundwater, sewage, seawater, and industrial wastewater scenarios, respectively. In terms of removal efficiency, the nitrate removal rates at 0.5 % and 3 % salinities decreased by 5.8 % and 16.8 %, respectively, compared to 0 % salinity. At 6 % salinity, the efficiency fluctuated during long-term operation, ranging from 56.0 % to 89.9 % of the value at 0 % salinity. According to the succession of microbial communities across time and salinity gradients, the dominant denitrification functional microorganisms were ranked by their salinity-tolerance ability as low-tolerant bacteria (0 %–0.5 %: Simplicispira , Herpetosipin , and Thermomonas), medium-tolerant bacteria (0 %–3 %: Thiobacillus and Sulfurimonas), high-tolerant bacteria (3 %–6 %: Thiogranum , Xanthomarina , and Vicingus), and halophilic bacteria (6 %: Aequorivita). Additionally, Aequorivita and Thiogranum , as the top 2 genera under 6 % salinity, presented positive and negative correlations with nitrate removal efficiency. The molecular ecological network revealed that increased positive interactions of 58.7 % among dominant genera occurred at 6 % salinity, confirming an effective cooperation coping with the high-salinity stress. In addition, the microbial responses to high-salinity primarily exhibited 22 %–45 % decrease in protein content, a 15 % decrease in live cells proportion, and a comparable level of individual functional gene expression. The results indicate that the efficiency of SAD by high salinity is determined by biomass amount and individual microbial capacity. This study offered new sights for understanding microbial succession and relationships in response to saltwater with diverse origins and varying water qualities in SAD systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The deficient inorganic N, P, and C sources induced decline in S0AD efficiency. • Specific thresholds for inorganic N, P, and C to robust S0AD were established. • Substantial reduction in SOBs occurred under deficient inorganic nutrients. • External supplying mitigated nutrient constraints in a pilot-scale S0PB bioreactor. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • SADP process was independently and controllably maintained in sulfur PBR. • SAD2 system achieved 2.38 times higher of SADN rate by the assist of SADP. • SADP-S2− had higher biocompatibility than chemical-S2− (Na 2 S). • Bioaugmentation and polysulfuration by SADP-S2− stimulated S0 utilization rate. • An applicable pattern of SAD2 system was supposed. 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-S n 2−), 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− (Na 2 S) at similar doses. Additionally, it stimulated the sulfur bioavailability by 1.66 times as a result of stoichiometry matrix calculation. SADP-S n 2− was only detected in the biofilm, as indicated by a linear increase in the S n 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. [ABSTRACT FROM AUTHOR]

• MS0D was induced in a pilot-scale S0PB reactor by reducing influent nitrate. • The absence of SHEAs was verified as primary inducing factor to MS0D. • Shortening EBCT and increasing reflux-ratio was proposed to effectively inhibit MS0D. • Strategy was provided for preventing S0PB reactor from the occurrence of MS0D. Elemental sulfur packed-bed (S0PB) bioreactors for autotrophic denitrification have gained more attention in wastewater treatment due to their organic carbon-free operation, low operating cost, and minimal carbon emissions. However, the rapid development of microbial S0-disproportionation (MS0D) in S0PB reactor during deep denitrification poses a significant drawback to this new technology. MS0D, the process in which sulfur is used as both an electron donor and acceptor by bacteria, plays a crucial role in the microbial-driven sulfur cycle but remains poorly understood in wastewater treatment setups. In this study, we induced MS0D in a pilot-scale S0PB reactor capable of denitrifying over 1000 m3/d nitrate-containing wastewater. Initially, the S0PB reactor stably removed 6.6 mg-NO 3 −-N/L nitrate at an empty bed contact time (EBCT) of 20 mins, which was designated the S0-denitrification stage. To induce MS0D, we reduced the influent nitrate concentrations to allow deep nitrate removal, resulted in the production of large quantities of sulfate and sulfide (SO 4 2−:S2− 3.2 w/w). Meanwhile, other sulfur-heterologous electron acceptors (SHEAs), e.g., nitrite and DO, were also kept at trace levels. The negative correlations between the SHEAs concentrations and the sulfide productions indicated that the absence of SHEAs was a primary inducing factor to MS0D. The microbial community drastically diverged in response to the depletion of SHEAs during the switch from S0-denitrification to S0-disproportionation. An evident enrichment of sulfur-disproportionating bacteria (SDBs) was found at the S0-disproportionation stage, accompanied by the decline of sulfur-oxidizing bacteria (SOBs). In the end, we discovered that shortening the EBCT and increasing the reflux ratio could inhibit sulfide production by reducing it from 43.9 mg/L to 3.2 mg/L or 25.5 mg/L. In conclusion, our study highlights the importance of considering MS0D when designing and optimizing S0PB reactors for sustainable autotrophic sulfur denitrification in real-life applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient nitrogen removal was achieved under influent nitrate and temperature variation. • Nitrate removal loading was more sensitive to temperature than other factors. • Nitrogen gas was the prominent inducement to clogging. • Using gas-venting could save 90% time and energy than conventional back-washing. • No functional instability or "treatment short-circuit" occurred in S0AD biofilter. Elemental sulfur autotrophic denitrification (S0AD) is viewed as a promising alternative to conventional heterotrophic denitrification due to lower running costs, zero carbon dioxide emission, and minimum excess sludge production. However, its scale-up capability and robustness in treating real-life wastewater have not been convincedly demonstrated. In this study, a pilot-scale S0AD packed-bed with over 1000 m3/d of actual wastewater treatment capacity was operated for 197 days. The S0AD packed-bed could effectively remove nitrate to below 12 mg-NO 3 −-N/L that is 20% stricter than China's national standard (15 mg-TN/L). The temperature effect coefficient Q 10 was calculated as 1.01, illustrating that denitrification efficiency could be doubled when the temperature increased every 10 °C. Mass balance calculations indicated that 85% of removed nitrate was contributed by S0AD process, and the rest 15% was by heterotrophic and assimilative processes. A total of 2684 kg sulfur was consumed during the course of the experiment which was attributed to 16.1% DO oxidation and 83.9% denitrification. Nitrogen gas produced through denitrification, could be trapped in the S0 packed-bed that was the primary causality of clogging. Daily gas venting instead of conventional back washing, could effectively recover the packed-bed flux and promote denitrification efficiency. In addition, a weekly thorough back washing was deemed necessary to deeply clean the trapped SS and sloughed overgrowing biofilm. The predominant S0AD bacteria belonged to the genus Thiobacillus, was enriched throughout the packed-bed providing robust and stable denitrification. Overall, we provided some guidance to the design and operation of S0AD packed bed in practical engineering. [ABSTRACT FROM AUTHOR]

Sulfur autotrophic denitrification (SAD) process, as an alternative to heterotrophic denitrification (HD) filter, receives growing interest in polishing the effluent from secondary sewage treatment. Although individual studies have indicated several advantages of SAD over HD, rare study has compared these two systems under identical condition and by using real secondary effluent. In this study, two small pilot scale filters (SAD and HD) were designed with identical configuration and operated parallelly by feeding the real secondary effluent from a WWTP. The results showed SAD filter can be started up without the addition of soluble electron donor, although the time (14 days) was about 3 times longer than that of HD filter. The nitrate removal rate of SAD filter at HRT of 1.4 h was measured as 0.268 ± 0.047 kg N/(m3∙d). Similar value was observed in HD filter with supplementing 90 mg/L COD. The COD concentration of effluent always kept lower than that of influent in SAD filter but not in HD filter. In addition, SAD filter could maintain a stable denitrification performance without backwash for 15 days, while decline of nitrate removal rate was observed in HD filter just 2 days after stopping the backwash. This different behavior was further confirmed as the SAD filter had a better hydraulic flow pattern. Analysis according to high-throughput 16S rRNA gene-based Illumina MiSeq sequencing clearly showed the microbial community evolution and differentiation among the samples of seed sludge, SAD and HD filters. Finally, the economic assessment was carried out, showing the operation cost of SAD filter was over 50% lower than that of HD filter. • Startup time of SAD filter (14 days) was 3-fold longer than that of HD filter by using same inoculum. • SAD filter had similar denitrification performance compared to HD filter with dosing 90 mg/L COD. • SAD filter showed better hydrodynamic characteristics even without backwash for 15 days. • The operating cost of SAD filter was 56.6% of that of HD filter. [ABSTRACT FROM AUTHOR]