Denitrifying Sulfide Removal Process Research Articles

Nitrogen removal from low C/N wastewater in a novel Sharon&DSR (denitrifying sulfide removal) reactor

Denitrification reactions commonly remove nitrate and other reactive nitrogen (Nr) from wastewater. The C/N ratio indicates the sufficiency of organic carbons to drive heterotrophic denitrification; a low C/N ratio frequently leads to poor denitrification performance in wastewater treatment. This study proposed and tested a novel Sharon&DSR (denitrifying sulfide removal) process, with nitrite generated by the Sharon reactions and sulfide from sulfur-reducing reactions for promoting the following nitrite-based denitrification and denitrifying sulfide removal (DSR) process. The present reactor can remove nitrate at an efficiency of 97.7 %−93.5 % at an influent C/N ratio of 0.646–0.737 over a 96-d continuous-flow test. The microbial community study reveals the functional strains corresponding to individual groups of critical reactions. The stoichiometry analysis reveals the potential to apply the nitrite-based DSR process for Nr removal from ultra-low C/N (<0.64) wastewaters, experimentally demonstrated in the present study with a C/N ratio of 0.16–0.39.

A novel intra- and extracellular distribution pattern of elemental sulfur in Pseudomonas sp. C27-driven denitrifying sulfide removal process

Pseudomonas sp. C27 can achieve the conversion of toxic sulfide to economical elemental sulfur (S0) with various electron acceptors. In this study the distribution pattern of S0 produced by C27 in denitrifying sulfide removal (DSR) process was explored. The SEM observation identified that the particle size of the biogenic S0 was at micron level. Strikingly, a novel distribution pattern of S0 was revealed that the produced S0 was not directly secreted extracellularly, but be stored temporarily in the cell interior. Pyrolysis at 65 °C for 20 min were recommended prior to S0 recovery, which could maximize the separation of extracellular polymeric substances (EPS) from C27. Furthermore, the effects of N/S molar ratio, initial sulfide concentration, and micro-oxygen condition were investigated to improve the production of S0 by C27. The highest S0 production was obtained at S/N of 3 and anaerobic condition seemed to favor the S0 production by C27. This study would provide a theoretical support for highly efficient sulfide removal as well as S0 recovery in sulfide-laden wastewater treatment.

Bio-augmentation of the filler-enhanced denitrifying sulfide removal process in expanded granular sludge bed reactors

Sulfur- and nitrogen-containing organic industrial wastewaters, which primarily result from several processes, including pharmaceutical, slaughter, papermaking, and petrochemical processes, are typical examples of refractory wastewaters. To ensure resource utilization, sulfur compounds at high concentrations in such wastewaters can be converted to elemental sulfur through specific methods. Specifically, the denitrifying sulfide removal (DSR) process can be employed to effectively recover elemental sulfur via biological sulfide oxidation, and reportedly, bio-augmentation presents as an effective strategy by which the challenges that limit the application of the DSR process can be overcome. However, the bacterial loss resulting from microorganism activity inhibition owing to toxic effect of high sulfide concentration as well as the complexity of the organic matter (carbon source) in actual wastewater environments reduce the actual elemental sulfur production rate. In this regard, the bio-augmentation effect of adding fillers under complex carbon source conditions was studied. The structure and function of the microbial community on the surface of the fillers were also analysed to reveal the internal factors that contributed to the increased efficiency of elemental sulfur generation. The results obtained showed that relative to the control, elemental sulfur generation increased 1.5- and 2-fold following the addition of fillers and fillers with microbial inoculants, respectively. Further, in the reactor with the added filler, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Azoarcus, while in reactor with added fillers plus microbial inoculates, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Arcobacter. These findings indicated that bio-augmentation promoted the expression of sulfur oxidation functional genes. Furthermore, adding Pseudomonas sp. gs1 for bio-augmentation improved the impact load resistance of the biofilm on the surface of the filler, leading to the rapid restoration of the elemental sulfur generation rate after the impact.

Recirculation ratio regulates denitrifying sulfide removal and elemental sulfur recovery by altering sludge characteristics and microbial community composition in an EGSB reactor

Expanded granular sludge blanket (EGSB) is regarded as a promising reactor to carry out denitrifying sulfide removal (DSR) and elemental sulfur (S0) 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, S0 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 S0 recovery, but an excessive recirculation ratio (9:1) was likely to cause AGS fragmentation and biomass loss. The S0 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), S0 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 S0 recovery.

Nitrogen and sulfur metabolisms of Pseudomonas sp. C27 under mixotrophic growth condition

Pseudomonas sp. C27 is a facultative autotrophic bacterium that can grow mixotrophically to undergo denitrifying sulfide removal (DSR) reactions with both organic matters and sulfide as electron donors. A detailed understanding of how the C27 strain simultaneously removes nitrogen, sulfur and carbon from water is critical for optimal DSR process design and implementation. This study is the first to reveal the pathways of nitrogen and sulfur metabolisms, identifying a total of 47 proteins that are related to the nitrogen metabolism and seven proteins to the sulfur metabolism of strain C27 using iTRAQ and LC-MS/MS techniques. The proposed pathway of nitrogen metabolism for strain C27 from external nitrate to nitrogen gas and phosphate with a coupled ammonia cycle is based on the identified proteins, and suggests that nitrate was not essential for nitrogen metabolism and could be replaced by nitrite as the sole nitrogen source for C27.

Mitigating adverse impacts of varying sulfide/nitrate ratios on denitrifying sulfide removal process performance

Complete removal of nitrogen, sulfur and carbon in wastewaters by denitrifying sulfide removal (DSR) process can be achieved at stoichiometry sulfide to nitrate ratio (S/N) of 1:1 in expanded granular sludge bed reactor. Wastewaters with varying S/N ratios can adversely impact the DSR performances with deterioration of synergetic cooperation between autotrophic and heterotrophic denitrifiers. DO (dissolved oxygen) serves effectively as supplementary electron receiver for sulfide oxidation, leaving more nitrate for heterotrophic denitrifiers to utilize acetate. The optimal oxygen to sulfide molar ratio (DO/S) is 0.5:1 for complete removal of sulfide, nitrate and acetate at different S/N ratios. The heterotrophic denitrification rate was decreased to 0.03 ± 0.002, 0.24 ± 0.011 and 0.35 ± 0.027 NO3−-N·h−1·gVSS−1 at S/N ratio of 5:2, 5:5 and 5:8, respectively, when DO/S of 3:1 was performed. This optimal condition was proposed as an easy-to-implement control criterion for subsiding the adverse impact by varying S/N ratios in handling real wastewaters.

Interactions of functional bacteria and their contributions to the performance in integrated autotrophic and heterotrophic denitrification

Compared to autotrophic and heterotrophic denitrification process, the Integrated autotrophic and heterotrophic denitrification (IAHD) has wider foreground of applications in the condition where the organic carbon, nitrate and inorganic sulfur compounds usually co-exist in the actual wastewaters. As the most well-known IAHD process, the denitrifying sulfide removal (DSR) could simultaneously convert sulfide, nitrate and organic carbon into sulfur, dinitrogen gas and carbon dioxide, respectively. Thus, systematical metabolic functions and contributions of autotrophic and heterotrophic denitrifiers to the IAHD-DSR performance became an problem demanding to be promptly studied. In this work, three upflow anaerobic sludge bioreactors (UASBs) were individually started up in autotrophic (a-DSR), heterotrophic (h-DSR) and mixotrophic conditions (m-DSR). Then, the operating conditions of each bioreactor were switched to different trophic conditions with low and high sulfide concentrations in the influent (200 and 400 mg/L). The removal efficiencies of sulfide, nitrate and acetate all reached 100% in all three bioreactors throughout the operational stages. However, the sulfur transformation ratio ranged from 34.5% to 39.9% at the low sulfide concentration and from 76.8% to 86.7% at the high sulfide concentration in the mixotrophic conditions. Microbial community structure analyzed by the Illumina sequencing indicated that Thiobacillus, which are autotrophic sulfide-oxidizing, nitrate-reducing bacteria (a-soNRB), was the dominant genus (81.3%) in the a-DSR bioreactor. With respect to the mixotrophic conditions, at low sulfide concentration in the m-DSR bioreactor, Thiobacillus (a-soNRB) and Thauera, which are heterotrophic nitrate-reducing bacteria (hNRB), were the dominant genera, with percentages of 48.8% and 14.9%, respectively. When the sulfide concentration in the influent was doubled, the percentage of Thiobacillus decreased by approximately 9-fold (from 48.8% to 5.4%), and the total percentage of Azoarcus and Pseudomonas, which are heterotrophic sulfide-oxidizing, nitrate-reducing bacteria (h-soNRB), increased by approximately 6-fold (from 10.1% to 59.4%). Therefore, the following interactions between functional groups and their functional mechanisms in the DSR process were proposed: (1) a-soNRB (Thiobacillus) and hNRB (Thauera) worked together to maintain the performance under the low sulfide concentration; (2) h-soNRB (Azoarcus and Pseudomonas) took the place of a-soNRB and worked together with hNRB (Thauera and Allidiomarina) under the high sulfide concentration; and (3) a-soNRB (such as Thiobacillus) were possibly the key bacteria and may have contributed to the low sulfur transformation, and h-soNRB may be responsible for the high sulfur transformation in the DSR process.

Regulation of influent sulfide concentration on anaerobic denitrifying sulfide removal

ABSTRACTThe objective of this study is to find a comprehensive regulation for sulfide removal and elemental sulfur transformation based on the denitrifying sulfide removal process. The experiment was performed based on several influent sulfide concentrations (150–600 mg/L) and nitrate-to-sulfur (N/S) molar ratios (0.5–2.0) at reaction times of 24 and 48 h. Sulfide and nitrate removals were mainly dependent on the influent sulfide concentration at sulfide concentrations of 150–200 and 400–600 mg/L, but on the N/S ratio at sulfide concentrations of 250–350 mg/L. Up to 99.7% and 93.8% of sulfide and nitrate were removed, respectively, with 26.5% of elemental sulfur formed at sulfide concentrations of 250–350 mg/L (N/S of 1.0). Only 4–9.4% of elemental sulfur was formed, with sulfide and nitrate removals of 99.9% and 98.7%, respectively, at sulfide concentrations of 150–200 mg/L. Meanwhile, 46.9–94.7% of sulfate was formed with a nitrogen gas conversion rate of 18.2–57.1%. Fewer microorganisms were detected by fluorescence in situ hybridization (FISH) at high sulfide concentrations of 400–600 mg/L, suggesting that the processes of anaerobic denitrification and desulfurization were inhibited.

Enhanced performance of denitrifying sulfide removal process at high carbon to nitrogen ratios under micro-aerobic condition

The success of denitrifying sulfide removal (DSR) processes, which simultaneously degrade sulfide, nitrate and organic carbon in the same reactor, counts on synergetic growths of autotrophic and heterotrophic denitrifiers. Feeding wastewaters at high C/N ratio would stimulate overgrowth of heterotrophic bacteria in the DSR reactor so deteriorating the growth of autotrophic denitrifiers. The DSR tests at C/N=1.26:1, 2:1 or 3:1 and S/N =5:6 or 5:8 under anaerobic (control) or micro-aerobic conditions were conducted. Anaerobic DSR process has <50% sulfide removal with no elemental sulfur transformation. Under micro-aerobic condition to remove <5% sulfide by chemical oxidation pathway, 100% sulfide removal is achieved by the DSR consortia. Continuous-flow tests under micro-aerobic condition have 70% sulfide removal and 55% elemental sulfur recovery. Trace oxygen enhances activity of sulfide-oxidizing, nitrate-reducing bacteria to accommodate properly the wastewater with high C/N ratios.

Denitrifying sulfide removal process on high-tetracycline wastewater

Antibiotics wastewater from tetracycline (TC) production unit can have high levels of chemical oxygen demand, ammonium and sulfate and up to a few hundreds of milligrams per liter of TC. Denitrifying sulfide removal (DSR) process is set up for simultaneously removal of sulfur, carbon and nitrogen from waters. The DSR process was for the first time studied for treating TC wastewaters. The TC stress has no adverse effects on removal rates of nitrate and acetate; however, it moderately deteriorated sulfide removal rates and S0 accumulation rates when the concentration is higher than 100mgL−1 TC. The Thauera sp., and Pseudomonas sp. present the heterotrophs and Sulfurovum sp. presented the autotroph for the present DSR reactions. The high tolerance of TC stress by the tested consortium was explained by the excess production of extracellular polymeric substances at high TC concentration, which can bind with TC for minimizing its inhibition effects.

Efficient regulation of elemental sulfur recovery through optimizing working height of upflow anaerobic sludge blanket reactor during denitrifying sulfide removal process

In this study, two lab-scale UASB reactors were established to testify S0 recovery efficiency, and one of which (M-UASB) was improved from the previous T-UASB by shortening reactor height once S2− over oxidation was observed. After the height was shortened from 60 to 30cm, S0 recovery rate was improved from 7.4% to 78.8%, and while, complete removal of acetate, nitrate and S2− 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 S0 recovery. The effective control of working height/volume in reactors plays important roles for the efficient regulation of S0 recovery during DSR process.

Microbial community structure and function in response to the shift of sulfide/nitrate loading ratio during the denitrifying sulfide removal process

Influence of acetate-C/NO3−-N/S2− ratio to the functional microbial community during the denitrifying sulfide removal process is poorly understood. Here, phylogenetic and functional bacterial community for elemental sulfur (S0) recovery and nitrate (NO3−) removal were investigated with the switched S2−/NO3− molar ratio ranged from 5/2 to 5/9. Optimized S2−/NO3− ratio was evaluated as 5/6, with the bacterial genera predominated with Thauera, Enterobacter, Thiobacillus and Stappia, and the sqr gene highly expressed. However, insufficient or high loading of acetate and NO3− resulted in the low S0 recovery, and also significantly modified the bacterial community and genetic activity. With S2−/NO3− ratio of 5/2, autotrophic S2− oxidization genera were dominated and NO3− reduction activity was low, confirmed by the low expressed nirK gene. In contrast, S2−/NO3− ratio switched to 5/8 and 5/9 introduced diverse heterotrophic nitrate reduction and S0 over oxidization genera in accompanied with the highly expressed nirK and sox genes.

Denitrifying sulfide removal process on high-salinity wastewaters.

Denitrifying sulfide removal (DSR) process comprising both heterotrophic and autotrophic denitrifiers can simultaneously convert nitrate, sulfide, and acetate into nitrogen gas, elemental sulfur (S(0)), and carbon dioxide, respectively. Sulfide- and nitrate-laden wastewaters at 2-35g/L NaCl were treated by DSR process. A C/N ratio of 3:1 was proposed to maintain high S(0) conversion rate. The granular sludge with a compact structure and smooth outer surface was formed. The microbial communities of DSR consortium via high-throughput sequencing method suggested that salinity shifts the predominating heterotrophic denitrifiers at <10g/L NaCl to autotrophic denitrifiers at >10g/L NaCl.

Simultaneous removal of sulfide, nitrate and acetate under denitrifying sulfide removal condition: Modeling and experimental validation

Simultaneous removal of sulfide (S2−), nitrate (NO3−) and acetate (Ac−) under denitrifying sulfide removal process (DSR) is a novel biological wastewater treatment process. This work developed a mathematical model to describe the kinetic behavior of sulfur–nitrogen–carbon and interactions between autotrophic denitrifiers and heterotrophic denitrifiers. The kinetic parameters of the model were estimated via data fitting considering the effects of initial S2− concentration, S2−/NO3−-N ratio and Ac−-C/NO3−-N ratio. Simulation supported that the heterotrophic denitratation step (NO3− reduction to NO2−) was inhibited by S2− compared with the denitritation step (NO2− reduction to N2). Also, the S2− oxidation by autotrophic denitrifiers was shown two times lower in rate with NO2− as electron acceptor than that with NO3− as electron acceptor. NO3− reduction by autotrophic denitrifiers occurs 3–10 times slower when S0 participates as final electron donor compared to the S2−-driven pathway. Model simulation on continuous-flow DSR reactor suggested that the adjustment of hydraulic retention time is an efficient way to make the reactor tolerating high S2− loadings. The proposed model properly described the kinetic behaviors of DSR processes over wide parametric ranges and which can offer engineers with basis to optimize bioreactor operation to improve the treatment capacity.

Influence of Sulfide to Nitrate Ratios on Denitrifying Sulfide Removal and Elemental Sulfur Reclamation from Wastewater Containing High Organic Carbon Concentration

This study evaluated the effect of sulfide to nitrate (S/N) ratios on elementary sulfur biotransformation in a simultaneous autotrophic and heterotrophic denitrifying sulfide removal (DSR) process, at a carbon to nitrate (C/N) ratio of 3/1. Four groups of batch tests were conducted at S/N ratios of 5/2, 5/5, 5/6 and 5/8, respectively. Results showed a low accumulation of elementary sulfur. Elementary sulfur was first obtained by the oxidizing of sulfide through DSR process and then was reduced back to sulfide with the interaction of surplus acetate. The highest elementary sulfur transformation rates at S/N ratios of 5/2, 5/5, 5/6 and 5/8 were 47.1%, 94.7%, 94.0% and 93.5%, respectively. It can be concluded from analysis of the stoichiometric proportion of the bio-chemical reactions that the proportion of acetate consumed in DSR process to the whole acetate consumption in the first 6 hours were no more than 50%, indicating a low efficiency of DSR process under high concentration of organic carbons, except for the condition under S/N of 5/6, during which period the highest proportion can be as much as 85.6%. Given the elemental sulfur transformation rate and the acetate consumption proportion in DSR process, it can be concluded that adjusting the ratio of sulfide to nitrate at an appropriate level (around 5/6) would be an appropriate strategy for higher elemental sulfur transformation.

Autotrophic and heterotrophic denitrification by a newly isolated strain Pseudomonas sp. C27

The denitrifying sulfide removal (DSR) process applied autotrophic and heterotrophic denitrification pathways to achieve simultaneous conversion of nitrate to N2, sulfide to elementary sulfur, and organic substances to CO2. The current bottlenecks impeding the development of DSR process include the need of balanced growth of both autotrophic denitrifiers and heterotrophic denitrifers in the same reactor and the capability of treating wastewaters at fix compositions. This work isolated a strain, identified as Pseudomonas sp. C27 (GenBank accession number GQ241351), which can grow on heterotrophic and mixotrophic media and can perform both autotrophic and heterotrophic denitrification in mixotrophic medium. The C27 strain can grow well on succinate, acetate, malate, priopionate and ethanol and has the optimal growth temperature at 25-30°C and pH at 9.0. Pathways of DSR reactions by C27 were proposed. Discussion on the potential use of the isolated C27 in novel DSR process was available.

Elementary sulfur in effluent from denitrifying sulfide removal process as adsorbent for zinc(II)

The denitrifying sulfide removal (DSR) process can simultaneously convert sulfide, nitrate and organic compounds into elementary sulfur (S0), di-nitrogen gas and carbon dioxide, respectively. However, the S0 formed in the DSR process are micro-sized colloids with negatively charged surface, making isolation of S0 colloids from other biological cells and metabolites difficult. This study proposed the use of S0 in DSR effluent as a novel adsorbent for zinc removal from wastewaters. Batch and continuous tests were conducted for efficient zinc removal with S0-containing DSR effluent. At pH<7.5, removal rates of zinc(II) were increased with increasing pH. The formed S0 colloids carried negative charge onto which zinc(II) ions could be adsorbed via electrostatic interactions. The zinc(II) adsorbed S0 colloids further enhanced coagulation–sedimentation efficiency of suspended solids in DSR effluents. The DSR effluent presents a promising coagulant for zinc(II) containing wastewaters.

Reduction of produced elementary sulfur in denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.

Enhanced performance of denitrifying sulfide removal process under micro-aerobic condition

The denitrifying sulfide removal (DSR) process with bio-granules comprising both heterotrophic and autotrophic denitrifiers can simultaneously convert nitrate, sulfide and acetate into di-nitrogen gas, elementary sulfur and carbon dioxide, respectively, at high loading rates. This study determines the reaction rate of sulfide oxidized into sulfur, as well as the reduction of nitrate to nitrite, would be enhanced under a micro-aerobic condition. The presence of limited oxygen mitigated the inhibition effects of sulfide on denitrifier activities, and enhanced the performance of DSR granules. The advantages and disadvantages of applying the micro-aerobic condition to the DSR process are discussed.

Functional consortium for denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) process simultaneously converts sulfide, nitrate, and chemical oxygen demand from industrial wastewaters to elemental sulfur, nitrogen gas, and carbon dioxide, respectively. This investigation utilizes a dilution-to-extinction approach at 10(-2) to 10(-6) dilutions to elucidate the correlation between the composition of the microbial community and the DSR performance. In the original suspension and in 10(-2) dilution, the strains Stenotrophomonas sp., Thauera sp., and Azoarcus sp. are the heterotrophic denitrifiers and the strains Paracoccus sp. and Pseudomonas sp. are the sulfide-oxidizing denitrifers. The 10(-4) dilution is identified as the functional consortium for the present DSR system, which comprises two functional strains, Stenotrophomonas sp. strain Paracoccus sp. At 10(-6) dilution, all DSR performance was lost. The functions of the constituent cells in the DSR granules were discussed based on data obtained using the dilution-to-extinction approach.