Sulfide removal by simultaneous autotrophic and heterotrophic desulfurization-denitrification process

Potential electron acceptors for ammonium oxidation in wastewater treatment system under anoxic condition: A review

Anaerobic ammonium oxidation has been considered as an environmental-friendly and energy-efficient biological nitrogen removal (BNR) technology. Recently, new reaction pathway for ammonium oxidation under anaerobic condition had been discovered. In addition to nitrite, iron trivalent, sulfate, manganese and electrons from electrode might be potential electron acceptors for ammonium oxidation, which can be coupled to traditional BNR process for wastewater treatment. In this paper, the pathway and mechanism for ammonium oxidation with various electron acceptors under anaerobic condition is studied comprehensively, and the research progress of potentially functional microbes is summarized. The potential application of various electron acceptors for ammonium oxidation in wastewater is addressed, and the N2O emission during nitrogen removal is also discussed, which was important greenhouse gas for global climate change. The problems remained unclear for ammonium oxidation by multi-electron acceptors and potential interactions are also discussed in this review.

Mapping the knowledge domain of microbial desulfurization application in fuels and ores for sustainable industry

Direct application of high-sulfur fuels and ores can cause environmental pollution (such as air pollution and acid rain) and, in serious cases, endanger human health and contribute to property damage. In the background of preserving the environment, microbial desulfurization technologies for high-sulfur fuels and ores are rapidly developed. This paper aims to reveal the progress of microbial desulfurization research on fuels and ores using bibliometric analysis. 910 publications on microbial desulfurization of fuels and ores from web core databases were collected in this work, spanning 39 years. Through 910 retrieved documents, collaborative networks of authors, institutions and countries were mapped by this work, the sources of highly cited articles and cited documents were statistically analyzed, and keyword development from different perspectives was discussed. The results of the study provide a reference for microbial desulfurization research and benefit environmental protection and energy green applications.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

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.

A comprehensive review on mixotrophic denitrification processes for biological nitrogen removal

Biological denitrification is the most widely used method for nitrogen removal in water treatment. Compared with heterotrophic and autotrophic denitrification, mixotrophic denitrification is later studied and used. Because mixotrophic denitrification can overcome some shortcomings of heterotrophic and autotrophic denitrification, such as a high carbon source demand for heterotrophic denitrification and a long start-up time for autotrophic denitrification. It has attracted extensive attention of researchers and is increasingly used in biological nitrogen removal processes. However, so far, a comprehensive review is lacking. This paper aims to review the current research status of mixotrophic denitrification and provide guidance for future research in this field. It is shown that mixotrophic denitrification processes can be divided into three main kinds based on different kinds of electron donors, mainly including sulfur-, hydrogen-, and iron-based reducing substances. Among them, sulfur-based mixotrophic denitrification is the most widely studied. The most concerned influencing factors of mixotrophic denitrification processes are hydraulic retention times (HRT) and ratio of chemical oxygen demand (COD) to total inorganic nitrogen (C/N). The dominant functional bacteria of sulfur-based mixotrophic denitrification system are Thiobacillus, Azoarcus, Pseudomonas, and Thauera. At present, mixotrophic denitrification processes are mainly applied for nitrogen removal in drinking water, groundwater, and wastewater treatment. Finally, challenges and future research directions are discussed.

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.

Sulfur-based mixotrophic denitrification with the stoichiometric S0/N ratio and methanol supplementation: effect of the C/N ratio on the process

The impact of the organic carbon to nitrate ratio (C/N ratio) on mixotrophic denitrification rate has been scarcely studied. Thus, this work aims to investigate the effect of the C/N ratio on the mixotrophic denitrification when methanol is used as a source of organic matter and elemental sulfur as an electron donor for autotrophic denitrification. For this, two initial concentrations of NO₃^--N (50 and 25 mg/L) at a stoichiometric ratio of S⁰/N, and four initial C/N ratios (0, 0.6, 1.2, and 1.9 mg CH₃OH/mg NO₃^- -N) were used at 25 (±2) °C. The results showed that when using a C/N ratio of 0.6, the highest total nitrogen removal was obtained and the accumulation of nitrites was reduced, compared to an autotrophic system. The most significant contribution to nitrate consumption was through autotrophic denitrification (AuDeN) for a C/N ratio of 0.6 and 1.2, while for C/N = 1.9 the most significant contribution of nitrate consumption was through heterotrophic denitrification (HD). Finally, organic supplementation (methanol) served to increase the specific nitrate removal rate at high and low initial concentrations of substrate. Therefore, the best C/N ratio was 0.6 since it allowed for increasing the removal efficiency and the denitrification rate.

Microscopic analysis towards rhamnolipid-mediated adhesion of Thiobacillus denitrificans: A QCM-D study

Rhamnolipid was proved to increase the abundance of Thiobacillus denitrificans in the mixotrophic denitrification biofilm while its microscopic mechanism remains to be explored. Effect of rhamnolipids on deposition of macromolecular substances and adhesion of Thiobacillus denitrificans at room (20 °C) and low temperature (10 °C) were systematically investigated by the quartz crystal microbalance with dissipation monitoring (QCM-D) for the first time. Results showed that low concentration of rhamnolipids (20-80 mg/L) could promote the deposition of macromolecular substances by reducing hydraulic repulsion force, with the maximum deposition amount increased by 4.28 times than that of the control at room temperature. Deposition amount of microorganisms could be improved by increasing its concentration at room temperature while it didn't work at low temperature. Meanwhile, low temperature could significantly inhibit adhesion of Thiobacillus denitrificans (p < 0.05) and deposited layers under low concentration of rhamnolipids were generally rigid, resulting in the negative feedback effect on the microorganisms' adhesion. While high concentration of rhamnolipids (120-200 mg/L) could regulate the biofilm from rigid to viscoelastic and significantly promote the initial adhesion of Thiobacillus denitrificans on SiO₂ surface (p < 0.05). This study demonstrated the microscopic mechanism of rhamnolipids on the initial biofilm formation, that is, the reduction of hydration repulsion force was responsible for the enhanced deposition of macromolecules while the regulation of biofilm properties was account for the promoted adhesion of Thiobacillus denitrificans.

Sulfate dependent ammonium oxidation: A microbial process linked nitrogen with sulfur cycle and potential application

Sulfate dependent ammonium oxidation (Sulfammox) is a potential microbial process coupling ammonium oxidation with sulfate reduction under anaerobic conditions, which provides a novel link between nitrogen and sulfur cycle. Recently, Sulfammox was detected in wastewater treatments and was confirmed to occur in natural environments, especially in marine sediments. However, knowledge gaps in the mechanism of Sulfammox, functional bacteria, and their metabolic pathway, make it challenging to estimate its environmental significance and potential applications. This review provides an overview of recent advances in Sulfammox, including possible mechanisms, functional bacteria, and main influential factors, and discusses future challenges and opportunities. Future perspectives are outlined and discussed, such as exploration of microbial community structure and metabolic pathways, possible interactions with other microbes, environmental significance, and potential applications for nitrogen and sulfate removal, to inspire more researches on the Sulfammox process.

Auxiliary voltage enhanced microbial methane oxidation co-driven by nitrite and sulfate reduction

In this study, single-chamber bioelectrochemical reactors (EMNS) were used to investigate the methane oxidation driven by sulfate and nitrite reduction with the auxiliary voltage. Results showed that the methane oxidation was simultaneously driven by sulfate and nitrite reduction, with more methane being converted using the auxiliary voltage. When the voltage was 1.6 V, the maximum removal rate was achieved at 8.05 mg L^-1 d^-1. Carbon dioxide and methanol were the main products of methane oxidation. Simultaneously, nitrogen, nitrous oxide, sulfur ions, and hydrogen sulfide were detected as products of sulfate and nitrite reduction. Microbial populations were analyzed by qPCR and high-throughput sequencing. The detected methanotrophs included Methylocaldum sp., Methylocystis sp., Methylobacter sp. and M. oxyfera. The highest abundance of M. oxyfera was (3.97 ± 0.32) × 10⁶ copies L^-1 in the EMNS-1.6. The dominant nitrite-reducing bacteria were Ignavibacterium sp., Hyphomicrobium sp., Alicycliphilus sp., and Anammox bacteria. Desulfovibrio sp., Desulfosporosinus sp. and Thiobacillus sp. were related to the sulfur cycle. Ignavibacterium sp., Thiobacillus sp. and Desulfovibrio sp. may transfer electrons with electrodes using humic acids as the electronic shuttle. The possible pathways included (1) Methane was mainly oxidized to carbon dioxide and dissolved organic matters by methanotrophs utilizing the oxygen produced by the disproportionation in the cells of M. oxyfera. (2) Nitrite was reduced to nitrogen by heterotrophic denitrifying bacteria with dissolved organic compounds. (3) Desulfovibrio sp. and Desulfosporosinus sp. reduced sulfate to sulfur ions. Thiobacillus sp. oxidized sulfur ions to sulfur or sulfate using nitrite as the electron acceptor.

Simultaneous biological nitrification and desulfurization treatment of ammonium and sulfide-rich wastewater: Effectiveness of a sequential batch operation

Sulfide inhibition to nitrifying bacteria has prevented the integration of digestate nitrification and biogas desulfurization to simplify anaerobic digestion systems. In this study, liquid digestate with NaHS solution was treated using nitrifying sludge in a sequential-batch reactor with a long fill period, with an ammonium loading rate of 293 mg-N L^-1 d^-1 and a stepwise increase in the sulfide loading rate from 0 to 32, 64, 128, and 256 mg-S L^-1 d^-1. Batch bioassays and microbial community analysis were also conducted with reactor sludge under each sulfide loading rate to quantify the microbial acclimatization to sulfide. In the reactor, sulfide was completely removed. Complete nitrification was maintained up to a sulfide load of 128 mg-S L^-1 d^-1, which is higher than that in previous reports and sufficient for biogas treatment. In the batch bioassays, the sulfide tolerance of NH₄⁺ oxidizing activity (the 50% inhibitory sulfide concentration) increased fourfold over time with the compositional shift of nitrifying bacteria to Nitrosomonas nitrosa and Nitrobacter spp. However, the sulfur removal rate of the sludge slightly decreased, although the abundance of the sulfur-oxidizing bacteria Hyphomicrobium increased by 30%. Therefore, nitrifying sludge was probably acclimatized to sulfide not by the increasing sulfide removal rate but rather by the increasing nitrifying bacteria, which have high sulfide tolerance. Successful simultaneous nitrification and desulfurization were achieved using a sequential-batch reactor with a long fill period, which was effective in facilitating the present acclimatization.

Merely inoculating anammox sludge to achieve the start-up of anammox and autotrophic desulfurization-denitrification process

Anammox and autotrophic desulfurization-denitrification (AADD) process is feasible for the nitrogen and sulfide removal in the same reactor, and the influence of excess nitrate produced by anammox could also be alleviated simultaneously. This study firstly proposed a novel strategy with inoculating single anammox sludge to start up the AADD process. Results demonstrated that the 90% nitrogen removal efficiency (NRE), 2.55kgm^-3 d^-1 nitrogen removal rate (NRR), and 95% sulfide removal efficiency (SRE) were obtained at the influent total nitrogen of 280mgL^-1 and sulfide of 221.5mgL^-1, and the final effluent nitrate concentration was as low as 8mgL^-1 under the appropriate operation conditions. Tryptophan-like and protein-like substances were characterized as the main components in bound EPS. Thiobacillus (35.68%) and Pseudoxanthomonas (11.61%) were identified as the predominant genera. This study will pave a potential avenue to promote the treatment of high concentration nitrogen and sulfide in wastewater in the future.

Metabolic divergence in simultaneous biological removal of nitrate and sulfide for elemental sulfur production under temperature stress

The simultaneous removal of NO₃^- and HS^- at temperature stress (25-10°C) is evaluated here. An expanded granular sludge bed (EGSB) reactor was run over 120days at N/S molar ratio of 0.35 (for S⁰ production) under constant sulfur loading rate of 0.4kgS/m³d. The simultaneous removal of NO₃^- and HS^-, was achieved at applied conditions. Average HS^--S removal varied from 98 (25°C) to 89.2% at 10°C, with almost complete NO₃^- removal. Average S⁰ yield ranged from 83.7 at 25°C to 67% at 10°C. The temperature drop caused a decrease in granular sludge accumulated S⁰ fraction by nearly 2.5 times. Decreased temperature caused metabolic pathway change observed as higher SO₄^2- production, apparently allowing the biomass to obtain more energy per HS^- consumed. It is hypothesized that the metabolic shift is a natural response to compensate for temperature-induced changes in energy requirements.

Indirect sulfur reduction via polysulfide contributes to serious odor problem in a sewer receiving nitrate dosage

Nitrate dosing is commonly used to control hydrogen sulfide production in sewer systems. However, quick rebound of the sulfide concentration after nitrate depletion has been observed and results in more serious odor and corrosion problem. To investigate the mechanism of sulfide regeneration in the nitrate-free period, a laboratory-scale sewer reactor was run for 30 days to simulate sulfide production and oxidation with intermittent nitrate addition. The results show that nitrate addition substantially reduced the sulfide concentration, but the produced elemental sulfur was then quickly reduced back to sulfide in nitrate-free periods. This induced more and more sulfide production in the sewer reactor. Elemental sulfur and polysulfide reductions were found in the sewage in nitrate-free periods, showing their contributions to the sulfide regeneration. Through batch tests, polysulfide was confirmed as the key intermediate for accelerating sulfur reduction during the nitrate-free period in the sewer. Sulfide production rates significantly increased by 65% and 59% in the presences of tetrasulfide and sulfur with sulfide, respectively, at the beginning of the test. While polysulfide formation was prevented by the ferrous chloride addition, the sulfur reduction rate remarkably decreased from 12.8 mgS/L-h to 1.8 mgS/L-h. This indicates that direct sulfur reduction was significantly slower than the indirect sulfur reduction via polysulfide; the latter process could be the cause for the quick rebound of the sulfide concentration in the sewer with intermittent nitrate dosing. Thus, the pathways of sulfur transformations in a sewer, both in the presence and absence of nitrate, were proposed. Microbial community analysis results reveal that some common sulfate-reducing bacteria (SRB) genera in sewer sediment were possible sulfur reducers. According to this finding, the effect and strategy of nitrate dosing for hydrogen sulfide control in sewers should be re-evaluated and re-considered.

ANAMMOX-like performances for nitrogen removal from ammonium-sulfate-rich wastewater in an anaerobic sequencing batch reactor

Ammonium removal by the ANaerobic AMonium OXidation (ANAMMOX) process was observed through the Sulfate-Reducing Ammonium Oxidation (SRAO) process. The same concentration of ammonium (100 mg N L(-1)) was applied to two anaerobic sequencing batch reactors (AnSBRs) that were inoculated with the same activated sludge from the Vermicelli wastewater treatment process, while nitrite was fed in ANAMMOX and sulfate in SRAO reactors. In SRAO-AnSBR, in substrates that were fed with a ratio of NH4(+)/SO4(2-) at 1:0.4 ± 0.03, a hydraulic retention time (HRT) of 48 h and without sludge draining, the Ammonium Removal Rate (ARR) was 0.02 ± 0.01 kg N m(-3).d(-1). Adding specific ANAMMOX substrates to SRAO-AnSBR sludge in batch tests results in specific ammonium and nitrite removal rates of 0.198 and 0.139 g N g(-1) VSS.d, respectively, indicating that the ANAMMOX activity contributes to the removal of ammonium in the SRAO process using the nitrite that is produced from SRAO. Nevertheless, the inability of ANAMMOX to utilize sulfate to oxidize ammonium was also investigated in batch tests by augmenting enriched ANAMMOX culture in SRAO-AnSBR sludge and without nitrite supply. The time course of sulfate in a 24-hour cycle of SRAO-AnSBR showed an increase in sulfate after 6 h. For enriched SRAO culture, the uptake molar ratio of NH4(+)/SO4(2-) at 8 hours in a batch test was 1:0.82 lower than the value of 1:0.20 ± 0.09 as obtained in an SRAO-AnSBR effluent, while the stoichiometric ratio of 1:0.5 that includes the ANAMMOX reaction was in this range. After a longer operation of more than 2 years without sludge draining, the accumulation of sulfate and the reduction of ammonium removal were observed, probably due to the gradual increase in the sulfur denitrification rate and the competitive use of nitrite with ANAMMOX. The 16S rRNA gene PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) and PCR cloning analyses resulted in the detection of the ANAMMOX bacterium (Candidatus Brocadia sinica JPN1) Desulfacinum subterraneum belonging to the genus Desulfacinum and bacteria that are involved in sulfur metabolism (Pseudomonas aeruginosa strain SBTPe-001 and Paracoccus denitrificans strain IAM12479) in SRAO-AnSBR.

Interaction of organic carbon, reduced sulphur and nitrate in anaerobic baffled reactor for fresh leachate treatment

Interaction of organic carbon, reduced sulphur and nitrate was examined using anaerobic baffled reactor for fresh leachate treatment by supplementing nitrate and/or sulphide to compartment 3. Nitrate was removed completely throughout the study mostly via denitrification (>80%) without nitrite accumulation. Besides carbon source, various reduced sulphur (e.g. sulphide, elemental sulphur and organic sulphur) could be involved in the nitrate reduction process via sulphur-based autotrophic denitrification when dissolved organic carbon/nitrate ratio decreased below 1.6. High sulphide concentration not only stimulated autotrophic denitrification, but it also inhibited heterotrophic denitrification, resulting in a shift (11-20%) from heterotrophic denitrification to dissimilatory nitrate reduction to ammonia. High-throughput 16S rRNA gene sequencing analysis further confirmed that sulphur-oxidizing nitrate-reducing bacteria were stimulated with increase in the proportion of bacterial population from 18.6% to 27.2% by high sulphide concentration, meanwhile, heterotrophic nitrate-reducing bacteria and fermentative bacteria were inhibited with 25.5% and 66.6% decrease in the bacterial population.

Denitrifying sulfide removal process on high-salinity wastewaters in the presence of Halomonas sp

Biological conversion of sulfide, acetate, and nitrate to, respectively, elemental sulfur (S(0)), carbon dioxide, and nitrogen-containing gas (such as N2) at NaCl concentration of 35-70 g/L was achieved in an expanded granular sludge bed (EGSB) reactor. A C/N ratio of 1:1 was noted to achieve high sulfide removal and S(0) conversion rate at high salinity. The extracellular polymeric substance (EPS) quantities were increased with NaCl concentration, being 11.4-mg/g volatile-suspended solids at 70 mg/L NaCl. The denitrifying sulfide removal (DSR) consortium incorporated Thauera sp. and Halomonas sp. as the heterotrophs and Azoarcus sp. being the autotrophs at high salinity condition. Halomonas sp. correlates with the enhanced DSR performance at high salinity.

Elemental sulfur formation and nitrogen removal from wastewaters by autotrophic denitrifiers and anammox bacteria

Elemental sulfur (S(0)) formation from and nitrogen removal on sulfide, nitrate and ammonium-laden wastewaters were achieved by denitrifying ammonium oxidation (DEAMOX) reactor with autotrophic denitrifiers and anaerobic ammonium oxidation (anammox) bacteria. The sulfide to nitrate ratio is a key process parameter for excess accumulation of S(0) and a ratio of 1.31:1 is a proposed optimum. The Alishewanella, Thauera and Candidatus Anammoximicrobium present respectively the autotrophic denitrifiers and anammox bacteria for the reactor. DEAMOX is demonstrated promising biological process for treating organics-deficient (S+N) wastewaters with excess S(0) production.

Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode

This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., −0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.

Regeneration of elemental sulfur in a simultaneous sulfide and nitrate removal reactor under different dissolved oxygen conditions

A continuous reactor in microaerobic conditions was adopted for sulfide-oxidizing, nitrate-reducing and elemental sulfur (S(0)) regenerating, simultaneously. The results showed that appropriate dissolved oxygen (DO) enhanced S(0) regeneration efficiency, sulfide oxidation efficiency, and nitrate reduction efficiency. When the DO concentration was 0.1-0.3 mg L(-1), the microaerobic bioreactor simultaneously converted 8.16 kg-Sm(-3)d(-1) of sulfide to S(0) and 2.48 kg-Nm(-3)d(-1) of nitrate to nitrogen with the sulfide and nitrate removal efficiency of 100% and 90% respectively. Compared with anaerobic sulfide and nitrate removal process previously reported, the loading sulfide was higher and more S(0) was generated during the operation in microaerobic reactor. Analysis using the 16S rDNA gene clone library revealed that Azoarcus, Thauera, Paracoccus, Sulfurospirillum, Arcobacter and Clostridium were the dominant microorganisms in the sulfide and nitrate removal system.

A novel approach to realize SANI process in freshwater sewage treatment--Use of wet flue gas desulfurization waste streams as sulfur source

SANI (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated) process has been approved to be a sludge-minimized sewage treatment process in warm and coastal cities with seawater supply. In order to apply this sulfur-based process in inland cold areas, wet flue gas desulfurization (FGD) can be simplified and integrated with SANI process, to provide sulfite as electron carrier for sulfur cycle in sewage treatment. In this study, a lab-scale system of the proposed novel process was developed and run for over 200 days while temperature varied between 30 and 5 °C, fed with synthetic FGD wastewaters and sewage. The sulfite-reducing upflow anaerobic sludge bed (SrUASB) reactor, as the major bioreactor of the system, removed 86.9% of organics while the whole system removed 94% of organics even when water temperature decreased to around 10 °C. The bactericidal effect of sulfite was not observed in the SrUASB reactor, while thiosulfate was found accumulated under psychrophilic conditions. The sludge yield of the SrUASB reactor was determined to be 0.095 kg VSS/kg COD, higher than of sulfate reduction process but still much lower than of conventional activated sludge processes. The dominant microbes in the SrUASB reactor were determined as Lactococcus spp. rather than sulfate-reducing bacteria, but sulfite reduction still contributed 85.5% to the organic carbon mineralization in this reactor. Ammonia and nitrate were effectively removed in the aerobic and anoxic filters, respectively. This study confirms the proposed process was promising to achieve sludge-minimized sewage treatment integrating with flue gas desulfurization in inland and cold areas.

Simultaneous biological removal of nitrogen-sulfur-carbon: recent advances and challenges

Biological removal of carbon, nitrogen and sulfur is drawing increasing research interest in search for an efficient and cost-effective wastewater treatment. While extensive work on separate removal of nitrogen and sulfur is well documented, investigation on simultaneous denitrifying sulfide removal has only been reported recently. Most of the work on denitrifying sulfide removal has been focusing on bioreactor performance, loading and operating conditions. Nonetheless, underlying principles elucidating the biochemical reactions and the mechanisms of the microbial degradation are yet to be established. In addition, unstable denitrifying sulfide removal which is a major operating problem that hinders practical application of the process, is yet to be resolved. This paper provides a review on the state-of-the-art development of simultaneous biological removal of sulfur, nitrogen and carbon. Research on bioreactor operation and performance, reactor configurations, mechanisms and modeling work including the use of mass balance analysis and artificial neural networks is delineated. An in-depth discussion on the microbial community and functional consortium is also provided. Challenges and future work on simultaneous biological removal of nitrogen-sulfur-carbon are also outlined.

Performance evaluation of oxygen, air and nitrate for the microaerobic removal of hydrogen sulphide in biogas from sludge digestion

The removal performance of hydrogen sulphide in severely polluted biogas produced during the anaerobic digestion of sludge was studied by employing pure oxygen, air and nitrate as oxidant reactives supplied to the biodigester. Research was performed in a 200-L digester with an hydraulic retention time (HRT) of ∼20 days under mesophilic conditions. The oxygen supply (0.25 N m³/m³ feed) to the bioreactor successfully reduced the hydrogen sulphide content from 15,811 mg/N m³ to less than 400 mg/N m³. The introduction of air (1.27 N m³/m³ feed) removed more than 99% of the hydrogen sulphide content, with a final concentration of ∼55 mg/N m³. COD removal, VS reduction and methane yield were not affected under microaerobic conditions; however, methane concentration in the biogas decreased when air was employed as a result of nitrogen dilution. The nitrate addition was not effective for hydrogen sulphide removal in the biogas.

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.

Biological denitrification of high-nitrate wastewater in a modified anoxic/oxic-membrane bioreactor (A/O-MBR)

A modified anoxic/oxic-membrane bioreactor has been applied to the denitrification of a high strength nitrate waste (about 3600 mg/L nitrate-N) generated from an initiating explosive factory. Nitrate removal efficiency and nitrite accumulation in the treated water were investigated under various conditions set by several factors including the type of carbon source used, ratios of carbon to nitrogen, pH and hydraulic retention times (HRTs). The results of the preliminary experiments, which were carried out in parallel CSTR systems, demonstrated that sodium acetate had shown the best performance as the external carbon source. The optimal reaction parameters in the anoxic/oxic-membrane bioreactor were pH 7.5-8.5, C/N 1.56 and HRT 30 h, with over 99.9% of nitrate removed and without accumulation of nitrite. Explicitly high average-specific denitrification rate of 324 mg NO(3)(-)-N/g VSS/h could be attained under these conditions. The aerobic process and membrane module used subsequently could remove the residual COD, excessive biomass and soluble microbial products generated during the denitrification process.