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

Microbiological aspects of sewage odor problems in the urban environment - a review

Growing human population and increasing urbanization call for the need for proper wastewater treatment to reduce environmental pollution and reduce the excess use of natural resources. During the collection of municipal wastewater, the rapid aerobic respiration often causes oxygen depletion and anaerobic conditions in the sewer system resulting in the production of malodorous compounds. The odor problems may lead to public complaints, or in the case of the sewage workers the released volatile compounds even cause serious health hazards. Therefore, microbes have a dual contribution in the urban water cycle, since they have a decisive role in wastewater treatment and the removal of pollutants, but they can also cause problems in the artificial environment. In this review, I would like to summarize the processes underlying the generation of the bad smell associated with sewage and wastewater or with the collection and treatment infrastructure, tracking the way from the households to the plants, including the discussion of processes and possible mitigation related to the released hydrogen sulfide, volatile organics and other compounds.

Dissolved oxygen benefits N-decanoyl-homoserine lactone regulated biological nitrogen removal system to resist acute ZnO nanoparticle exposure

The beneficial effects of N-decanoyl-homoserine lactone (C₁₀-HSL), one of the typical N-acyl-homoserine lactones on biological nitrogen removal (BNR) system to resist the acute exposure of zinc oxide nanoparticles (ZnO NPs) has attracted extensive attentions. Nevertheless, the potential impact of dissolved oxygen (DO) concentration on the regulatory capacity of C₁₀-HSL in the BNR system has yet to be investigated. This study conducted a systematic investigation of the impact of DO concentration on the C₁₀-HSL-regulated BNR system against short-term ZnO NP exposure. Based on the findings, sufficient DO played a crucial role to improve the BNR system's resistance capacity to ZnO NPs. Under the micro-aerobic condition (0.5 mg/L DO), the BNR system was more sensitive to ZnO NPs. The ZnO NPs induced increased intracellular reactive oxygen species (ROS) accumulation, reduced antioxidant enzyme activities, and decreased specific ammonia oxidation rates in the BNR system. Furthermore, the exogenous C₁₀-HSL had a positive effect on the BNR system's resistance to ZnO NP-induced stress, primarily by decreasing ZnO NPs-induced ROS generation and improving ammonia monooxygenase activities, especially under low DO concentrations. The findings contributed to the theoretical foundation for regulation strategy development of wastewater treatment plants under NP shock threat.

The mixed/mixotrophic nitrogen removal for the effective and sustainable treatment of wastewater: From treatment process to microbial mechanism

Biological nitrogen removal (BNR) is one of the most important environmental concerns in the field of wastewater treatment. The conventional BNR process based on heterotrophic nitrogen removal (HeNR) is suffering from several limitations, including external carbon source dependence, excessive sludge production, and greenhouse gas emissions. Through the mediation of autotrophic nitrogen removal (AuNR), mixed/mixotrophic nitrogen removal (MixNR) offers a viable solution to the optimization of the BNR process. Here, the recent advance and characteristics of MixNR process guided by sulfur-driven autotrophic denitrification (SDAD) and anammox are summarized in this review. Additionally, we discuss the functional microorganisms in different MixNR systems, shedding light on metabolic mechanisms and microbial interactions. The significance of MixNR for carbon reduction in the BNR process has also been noted. The knowledge gaps and the future research directions that may facilitate the practical application of the MixNR process are highlighted. Overall, the prospect of the MixNR process is attractive, and this review will provide guidance for the future implementation of MixNR process as well as deciphering the microbially metabolic mechanisms.

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.

The interaction between Pseudomonas C27 and Thiobacillus denitrificans in the integrated autotrophic and heterotrophic denitrification process

Compared to autotrophic and heterotrophic denitrification process, the integrated autotrophic and heterotrophic denitrification (IAHD) shows wider foreground of applications in the actual wastewaters with organic carbon, nitrogen and sulfur co-existing. The efficient co-removal of sulfur, nitrogen, and carbon in the IAHD system is guaranteed by the interaction between heterotrophic and autotrophic denitrificans. In order to further explore the interaction between functional bacteria, Pseudomonas C27 and Thiobacillus denitrifcans were selected as typical heterotrophic and autotrophic bacteria, and their characteristics metabolic responses to different sulfide concentrations were studied. Pseudomonas C27 had higher metabolic activity than T. denitrificans in the IAHD medium with sulfide concentration of 3.12-15.62 mmol/L. Moreover, the fastest sulfide removal rate (0.35 mmol/L·h) was achieved with a single inoculation of Pseudomonas C27. Meanwhile, in mixed inoculant conditions, the interaction between Pseudomonas C27 and T. denitrificans (P:T = 3:1, P:T = 1:1 and P:T = 1:3) yielded the highest sulfide removal efficiency (more than 85%) when sulfide concentration was 6.25-12.5 mmol/L. Additionally, the sulfide removal rate increased with the inoculation proportion of Pseudomonas C27. Thus, this apparent interaction provided a theoretical basis for further understanding and guidance on the efficient operation of IAHD system.

Combined bioaugmentation with electro-biostimulation for improved bioremediation of antimicrobial triclocarban and PAHs complexly contaminated sediments

Haloaromatic antimicrobial triclocarban (TCC) is an emerging refractory contaminant that commonly coexisted with conventional contaminants such as polycyclic aromatic hydrocarbons (PAHs). TCC may negatively affect the metabolic activity of sediment microorganisms and persist in environment; however, remediation methods that relieve the TCC inhibitory effect in sediments remain unknown. Here, a novel electro-biostimulation and bioaugmentation combined remediation system was proposed by the simultaneous introduction of a TCC-degrading Ochrobactrum sp. TCC-2 and electrode into the TCC and PAHs co-contaminated sediments. Results indicated the PAHs and TCC degradation efficiencies of the combined system were 2.9-3.0 and 4.6 times respectively higher than those of the control group (no electro-biostimulation and no bioaugmentation treatments). The introduced strain TCC-2 and the enriched electroactive bacteria and PAHs degraders (e.g. Desulfobulbus, Clostridium, and Paenarthrobacter) synergistically contributed to the accelerated degradation of PAHs and TCC. The preferential elimination of the TCC inhibitory effect through bioaugmentation treatment could restore microbial functions by increasing the functional gene abundances related to various metabolic processes. This study offers new insights into the response of sediment functional communities to TCC stress, electro-biostimulation and bioaugmentation operations and provides a promising system for the enhanced bioremediation of the PAHs and TCC co-contaminated sediments.

Revealing the role of nitrate on sulfide removal coupled with bioenergy production in Chlamydomonas sp. Tai-03: Metabolic pathways and mechanisms

Recently, simultaneous sulfide removal and bioenergy production by microalgal treatment have attracted growing attention. However, the response of nitrogen metabolism to the sulfide-removal process has yet to be explored. Here, variable levels of sulfide could be completely removed by Chlamydomonas sp. Tai-03 under both high and low nitrate conditions in synthetic wastewaters. The highest sulfide removal rate of 5.56 mg-S L^-1 h^-1 was achieved with the addition of 100 mg L^-1 sulfide in the presence of high nitrate. Meanwhile, sulfide was chemically oxidized to sulfate and then ingested by microalgae. Interestingly, sulfide-removal efficiency critically depended on nitrate concentration. Sulfide can also enhance the ability of microalgae to assimilate nitrogen. Based on the analysis of sulfur- and nitrogen-related metabolic profiling, serine as a precursor decreased by 94 % under low levels of nitrate, which induced the significant inhibition of cysteine and methionine biosynthesis. The results indicated that nitrogen source played a critical role in the sulfur cycle because of the positive relationship between the aforementioned metabolic processes and nitrate concentration. Additionally, sulfide can improve lipid and carbohydrate productivity under high levels of nitrate. This study enhances our understanding of the mechanisms underlying the simultaneous removal of sulfide and alternative bioenergy production.

Correlation of extracellular polymeric substances and microbial community structure in denitrification biofilm exposed to adverse conditions

Microbial community may respond to different adverse conditions and result in the variation of extracellular polymeric substances (EPS) in denitrification biofilm; this study discovered the role of EPS in accordance with the analysis of cyclic diguanylate (c-di-GMP) and electron equilibrium (EE) under low organic loading rate, shock organic loading rate and low temperature conditions. Good nitrate removal performance could be achieved under shock organic loading rate and low temperature conditions; however, owing to the low organic loading rate, the carbon source was preferentially utilized for biomass growth. Tightly bound EPS (TB-EPS) contents progressively increased and facilitated cell adhesion and biofilm formation. The stable TB protein (TB-PN) content in TB-EPS built a cross-linked network to maintain internal biofilm structure and led to the rapid biosynthesis of polysaccharides, which could further enhance microbial adhesion and improve nitrate removal. C-di-GMP played an important role in biomass retention and biofilm formation, based on the correlation analysis of c-di-GMP and EPS. TB polysaccharide (TB-PS) contents presented a significant positive correlation with c-di-GMP content, microbial adhesion and biofilm stabilization was further enhanced through c-di-GMP regulation. In addition, a remarkable negative correlation between electron deletion rate (EDR) and TB-PN and TB-PS was discovered, and TB-PS was required to serve as energy source to enhance denitrification according to EE analysis. Surprisingly, dynamic microbial community was observed due to the drastic community succession under low temperature conditions, and the discrepancy between the dominant species for denitrification was found under shock organic loading rate and low temperature conditions. The notable increase in bacterial strains Simlicispira, Pseudomonas and Chryseobacterium was conducive to biofilm formation and denitrification under shock organic loading rate, while Dechloromonas and Zoogloea dramatically enriched for nitrate removal under low temperature conditions. The high abundance of Dechloromonas improved the secretion of EPS through the downstream signal transduction, and the c-di-GMP conserved in Pseudomonas concurrently facilitated to enhance exopolysaccharide production to shock organic loading rate and low temperature conditions.

Heterotrophic sulfide-oxidizing nitrate-reducing bacteria enables the high performance of integrated autotrophic-heterotrophic denitrification (IAHD) process under high sulfide loading

Micro-aerobic enhancement technology has been developed as an effective tool to enhance simultaneous removal of sulfide, nitrate and organic carbon during the integrated autotrophic-heterotrophic denitrification (IAHD) process under high loading; however, its mechanism of enhancement for functional bacteria remains ambiguous. In this study, we discovered that heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) are responsible for enhancing IAHD performance under micro-aerobic conditions with high sulfide loading. In a continuous IAHD bioreactor, aeration rate of 2.6 mL min^-1·L^-1 promoted 2 to 4 times higher removal efficiencies of sulfide, nitrate and acetate with an influent sulfide concentration of 18.75 mmol/L. Metagenomic analysis revealed that trace oxygen stimulated the abundance of genes responsible for sulfide oxidation (sqr, glpE, pdo, sox and cysK), which were upregulated by 15.2%-129.9%, and the genes encoding nitrate reductase were up-regulated by 67.4%. The increased acetate removal efficiency was attributed to upregulation of ack, pta and TCA cycle related genes. The h-NRB Pseudomonas, Azoarcus, Thauera and Halomonas were detected and regarded as h-soNRB in our bioreactor. According to Illumina MiSeq sequencing, these genera were absolutely dominant in the micro-aerobic microbial community at relative abundances ranging from 82.72% to 90.84%. The sulfide, nitrate and acetate removal rates of Pseudomonas C27, a typical h-soNRB, were at least 10 times higher under micro-aerobic conditions than under anaerobic conditions. Besides, the sulfur, nitrogen and carbon metabolic network was constructed based on the Pseudomonas C27 genome. The pdo and cysK genes found in this strain may be the most advantageous for autotrophic sulfide oxidizing nitrate reducing bacteria (a-soNRB), which are closely related to the high-efficiency sulfide, nitrate and acetate removal performance under high sulfide concentrations and a limited oxygen supply. In addition, after micro-aerobic cultivation, the anaerobic sulfide loading tolerance of the IAHD bioreactor increased from 18.75 to 37.5 mmol/L with sulfide, nitrate and acetate removal efficiencies increasing 1.5 to 3 times, which suggests that intermittent micro-aeration might be a more economical and efficient regime for high-sulfide IAHD regulation.

Review on microaeration-based anaerobic digestion: State of the art, challenges, and prospectives

Microaeration (dosing small quantities of air or oxygen) is an effective approach to facilitate anaerobic digestion (AD) process and has gained increased attention in recent years. The underlying mechanisms of the facilitation effect of microaeration on AD process were reviewed in terms of accelerating hydrolysis, scavenging hydrogen sulfide, and affecting microbial diversity. Process parameters and control strategies were summarized to reveal considerable factors in implementing microaeration-based AD process. In addition, current applications, including lab-, pilot- and full-scale level cases, were summarized to provide guidance for further improvement in large-scale applications. The challenges and future perspectives were also highlighted to promote the development of AD process associated with microaeration.

Denitrification with non-organic electron donor for treating low C/N ratio wastewaters

Denitrification with non-organic electron donors for treating low C/N ratio wastewater has attracted growing interests. Hydrogen, reduced sulfur compounds and ferrous ions are mainly used in autotrophic denitrification, holding promise for achieving practical applications. Recently, the development of autotrophic denitrification-based processes, such as bioelectrochemically-supported hydrogenotrophic denitrification and sulfur-/iron-based denitrification assisted multi-contaminant removal, provide opportunities for applying these processes in wastewater treatment. Exploration of the autotrophic denitrification process in terms of contaminant removal mechanism, interaction among functional microorganisms, and potential full-scale applications is thus of great importance. Here, an overview of the commonly used non-organic electron donors, e.g., hydrogen, reduced sulfur compounds and ferrous ions, in denitrification for treating low C/N ratio wastewater is provided. Also, the feasibility of applying the combined processes based on autotrophic denitrification with the compounds is discussed. Furthermore, challenges and future possibilities as well as concerns about the practical applications are envisaged in this review.

Simultaneous removal of sulphur dioxide and nitric oxide at different oxygen concentrations in a thermophilic biotrickling filter (BTF): Evaluation of removal efficiency, intermediates interaction and characterisation of microbial communities

Simultaneous flue gas desulphurisation and denitrification in biotrickling filter was investigated under different O₂ concentrations (0%, 3%, 5%, 8% and 10%) at 45 °C. NO and SO₂ removal efficiency, intermediates (NO₃^-, NO₂^-, NO₂, SO₄^2- and S^2-) interaction and accumulation, S⁰ recovery and microbial community structure were investigated. Results indicated the highest NO removal efficiency was 96.5% at 5% O₂. Maximum SO₂ removal efficiency was 95.6% at 3% O₂. Moreover, N intermediates accumulation increased when O₂ concentration increased from 0% to 10%. The lowest S^2- concentration of 61 mg/L and the maximum S⁰ recovery of 76.9% were achieved at 5% O₂. The bioreactor at 10% O₂ contained less bacterial OTUs richness and evenness compared with other conditions. Illumina analysis indicated Proteobacteria, Firmicutes and Bacteroidetes were the dominant members. Overall, microbial community structure differs significantly under different O₂ concentrations.

The microbial zonation of SRB and soNRB enhanced the performance of SR-DSR process under the micro-aerobic condition

The micro-aerobic condition has proven to effectively enhance the COD removal and elemental sulfur (S⁰) transformation rate in the sulfate reduction-denitrifying sulfide removal (SR-DSR) process. However, the mechanisms of how micro-aerobic condition enhances S⁰ transformation remain largely unknown. Therefore in this work an integrated investigation was performed to document the mechanisms and the effect of different startup modes (micro-aerobic startup (termed as mSR-DSR) and anaerobic startup (termed as aSR-DSR)) on bioreactor performance and microbial community dynamics. The results showed that micro-aerobic startup achieved a shorter period to reach a stable performance for SR-DSR, which could be one of the factors affecting the choice of the bioreactor startup mode considering engineering application. For all the tested conditions, removal of nitrate, sulfate and lactate were 100%, >80% and 100%, respectively. The maximum transformation rate of elemental sulfur in mSR-DSR was 57%, which was higher than that in aSR-DSR. The mechanism explorations revealed that micro-aerobic condition not only particularly enriched the sulfide-oxidizing, nitrate-reducing bacteria (soNRB) but also promoted the microbial zonation of sulfate-reducing bacteria (SRB) and soNRB, thereby achieving more S⁰ transformation in the effluent. Under micro-aerobic condition, SRB were mainly distributed in the bottom and middle part of the reactor, while soNRB were assembled in the top. The relative abundance of soNRB in both aSR-DSR and mSR-DSR notably increased to 41.5% and 23.7% at the top when 5 mL air min^-1 L_reactor^-1 was applied. Furthermore, the degradation of organic carbon was also accelerated under micro-aerobic condition, possibly due to the enrichment of organic compounds degrading bacteria Bacteroidetes_vadin HA17.

Dual purpose microalgae-based biorefinery for treating pharmaceuticals and personal care products (PPCPs) residues and biodiesel production

Microalgal biotechnologies have emerged with high potential for removal of various organic pollutants, such as pharmaceutical and personal care products (PPCPs), from waste streams. In the present study, the removal mechanisms for three typical PPCPs and the lipid performance of Chlamydomonas sp. Tai-03 were thoroughly investigated. Bisphenol A (BPA) and Tetracycline (TCY) achieved complete removal while only ~20% Sulfamethoxazole (SMX) could be removed, even at low concentrations of 1 mg L^-1. The mechanisms of elimination showed variation as only SMX could be removed through biodegradation, while ~68.2% TCY and ~14% BPA were removed by a combination of photolysis and hydrolysis. Analysis revealed three intermediates of SMX biodegradation, two of which exhibited high toxicity. Moreover, the lipid content of Chlamydomonas sp. Tai-03 increased from 5 to 49.5% with the addition of SMX, TCY and BPA, with lipid quality varying according to the type of PPCPs. In particular, the dominant component (C18:1) abundance was increased by 15.2% at 10 mg L^-1 TCY. Overall, these findings provide a baseline for optimization of microalgal biodiesel production coupled with efficient PPCPs treatment biotechnology.

Bioreactor performance and microbial community analysis of autotrophic denitrification under micro-aerobic condition

Autotrophic denitrification process is an effective strategy for treating sulfide and nitrate-enriched wastewater with low organic carbon. This study determined the sulfide oxidation and nitrate reduction rates and characterized the dominant bacteria and microbial community structure stimulated by micro-aerobic conditions in autotrophic denitrification system. With gradually increased sulfide concentration, the sulfide removal rate decreased to 37.8% at S^2- = 600 mg/L, while the peak sulfide and nitrate removal rates (100% and 53.8%) were achieved at S^2- = 800 mg/L with the air aeration rate of 20 mL/min. The Illumina sequencing results indicated that Thiobacillus accounted for 63% of total operational taxonomic units at generic level with sulfide concentration of 200 mg/L under anaerobic condition. However, Azoarcus, Thauera and Aliidiomorina became the dominant genera under micro-aerobic condition and their abundance significantly and positively related to the sulfide concentration and aeration rate (p < 0.05). According to the 16S metaproteomics functional composition prediction, one potential mechanism for autotrophic denitrifying under micro-aerobic condition was deduced that the oxidation of sulfide to thiosulfate further to sulfite was reinforced by trace oxygen, while the sulfite reductase activity was restrained. The decreased sulfide concentration weakened the toxicity inhibition on denitrifiers and accordingly the performance of autotrophic denitrification process was enhanced by micro-aerobic condition.

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.

Mathematical modeling of simultaneous carbon-nitrogen-sulfur removal from industrial wastewater

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 (NO₃^-→NO₂^-→N₂), and that of C-S by SRB (SO₄^2-→S^2-) and SOB (S^2-→S⁰) 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.

Effect of dissolved oxygen on elemental sulfur generation in sulfide and nitrate removal process: characterization, pathway, and microbial community analysis

Microaerobic bioreactor treatment for enriched sulfide and nitrate has been demonstrated as an effective strategy to improve the efficiencies of elemental sulfur (S(0)) generation, sulfide oxidation, and nitrate reduction. However, there is little detailed information for the effect and mechanism of dissolved oxygen (DO) on the variations of microbial community in sulfur generation, sulfide oxidation, and nitrate reduction systems. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) was employed to evaluate the variations of microbial community structures in a sulfide oxidation and nitrate reduction reactor under different DO conditions (DO 0-0.7 mg · L(-1)). Experimental results revealed that the activity of sulfide-oxidizing bacteria (SOB) and nitrate-reducing bacteria (NRB) could be greatly stimulated in 0.1-0.3 mg-DO · L(-1). However, when the DO concentration was further elevated to more than 0.5 mg · L(-1), the abundance of NRB was markedly decreased, while the heterotrophic microorganisms, especially carbon degradation species, were enriched. The reaction pathways for sulfide and nitrate removal under microaerobic conditions were also deduced by combining batch experiments with functional species analysis. It was likely that the oxidation of sulfide to sulfur could be performed by both aerobic heterotrophic SOB and sulfur-based autotrophic denitrification bacteria with oxygen and nitrate as terminal electron acceptor, respectively. The nitrate could be reduced to nitrite by both autotrophic and heterotrophic denitrification, and then the generated nitrite could be completely converted to nitrogen gas via heterotrophic denitrification. This study provides new insights into the impacts of microaerobic conditions on the microbial community functional structures of sulfide-oxidizing, nitrate-reducing, and sulfur-producing bioreactors, which revealing the potential linkage between functional microbial communities and reactor performance.

Accessible mixotrophic growth of denitrifying sulfide removal consortium

Nitrate, sulfide and organic matters in wastewaters can be removed simultaneously by denitrifying sulfide removal (DSR) process. Complicated interactions between different microbial groups in the DSR medium render the process design and control difficult to implement. A consortium with DSR activity was grown mixotrophically at varying concentrations of nitrate, acetate or ammonium. The kinetic diagram previously proposed was adopted to quantitatively represent DSR performance with accessible regimes of the diagram being identified. Example on the use of the so-yielded accessible regime was provided.

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.

Denitrifying sulfide removal by Pseudomonas sp. C27 at excess carbon supply: mechanisms

Pseudomonas sp. C27 can effectively conduct mixotrophic denitrifying sulfide removal (DSR) reactions using both organic matters and sulfide as electron donors. This study conducted DSR tests using C27 and quantitatively analyzed the protein abundances at C/N=1.26, 1.63 and 3.0. At C/N=1.26, C27 principally adopted autotrophic denitrification pathway in DSR reaction. As C/N ratio was increased to 1.63, C27 enhanced heterotrophic denitrification pathway for removing nitrous compounds. As the C/N ratio was further increased to 3.0, C27 accelerated metabolism via coupled-cycles pathway. The C/N ratio for coupled-cycles pathway was estimated ranging 2.0-2.3 in the studied medium. Optimal C/N ratio of traditional DSR processes ranged 1.05-1.26. With the coupled-cycles pathway, the accessible C/N/S regime for C27 on DSR reactions is enlarged. Minor revision of the coupled-cycles pathway considering production of ammonium step was made.

Integrated simultaneous desulfurization and denitrification (ISDD) process at various COD/sulfate ratios

The integrated simultaneous desulfurization and denitrification (ISDD) is a novel treatment process to handle sulfate and nitrate-laden wastewaters of high loadings. This study experimentally explored the effect of COD/SO4(2-) ratio on the performance of ISDD process, particularly considering the complex interactions between sulfate-reducing bacteria (SRB), heterotrophic denitrifiers (hNRB) and autotrophic denitrifiers (aNRB). There existed an optimal COD/SO4(2-) ratio (=1.5:1 in the present study) to reach 100% SO4(2-) and NO3(-) removals and 42.6% S(0) recovery. At COD/SO4(2-)=1.5:1, the functional strains could form granules with high retention in the ISDD reactor. The microbial community analysis identified the SRB, hNRB and aNRB in the studied system, whose shifts correlated well with the noted ISDD performance change at different COD/SO4(2-) ratio. Interactions between different groups of bacteria and the possible strategy to enhance the ISDD performance were discussed.

Proteomic analysis of sulfur-nitrogen-carbon removal by Pseudomonas sp. C27 under micro-aeration condition

Pseudomonas sp. C27 is a facultative autotrophic bacterium (FAB) that can effectively conduct mixotrophic and heterotrophic denitrifying sulfide removal (DSR) reactions under anaerobic condition using organic matters and sulfide as electron donors. Micro-aeration was proposed to enhance DSR reaction by FAB; however, there is no experimental proof on the effects of micro-aeration on capacity of denitrifying sulfide removal of FAB on proteomic levels. The proteome in total C27 cell extracts was observed by two-dimensional gel electrophoresis. Differentially expressed protein spots and specifically expressed protein spots were identified by MALDI TOF/TOF MS. We identified 55 microaerobic-responsive protein spots, representing 55 unique proteins. Hierarchical clustering analysis revealed that 75% of the proteins were up-regulated, and 5% of the proteins were specifically expressed under micro-aerobic conditions. These enzymes were mainly involved in membrane transport, protein folding and metabolism. The noted expression changes of the microaerobic-responsive proteins suggests that C27 strain has a highly efficient enzyme system to conduct DSR reactions under micro-aerobic condition. Additionally, micro-aeration can increase the rates of protein synthesis and cell growth, and enhance cell defensive system of the strain.

Sulfate-reduction, sulfide-oxidation and elemental sulfur bioreduction process: modeling and experimental validation

This study describes the sulfate-reducing (SR) and sulfide-oxidizing (SO) process using Monod-type model with best-fit model parameters both being reported and estimated. The molar ratio of oxygen to sulfide (ROS) significantly affects the kinetics of the SR+SO process. The S(0) is produced by SO step but is later consumed by sulfur-reducing bacteria to lead to "rebound" in sulfide concentration. The model correlated well all experimental data in the present SR+SO tests and the validity of this approach was confirmed by independent sulfur bioreduction tests in four denitrifying sulfide removal (DSR) systems. Modeling results confirm that the ratio of oxygen to sulfide is a key factor for controlling S(0) formation and its bioreduction. Overlooking S(0) bioreduction step would overestimate the yield of S(0).

Facultative autotrophic denitrifiers in denitrifying sulfide removal granules

The denitrifying sulfide removal (DSR) process applied autotrophic and heterotrophic denitrification pathways to achieve simultaneous conversion of nitrate to N, sulfide to elementary sulfur, and organic substances to CO. However, autotrophic denitrifiers and heterotrophic denitrifiers have to grow at comparable rates so the long-term DSR stability can be maintained. This work assessed the autotrophic and heterotrophic denitrification activities by 16 isolates from anaerobic granules collected from a DSR-expanded granular sludge bed reactor. A group of strains with closest relatives as Pseudomonas sp. (89.9-98.3% similarity), Agrobacterium sp. (94.6% similarity) and Acinetobacter sp. (96.6% similarity) were identified with both autotrophic and heterotrophic denitrification capabilities. These facultative autotrophic denitrifiers can be applied as potential strains for lifting the limitation by balanced growth of two distinct bacterial groups in the DSR reactor.

Denitrifying sulfide removal and carbon methanogenesis in a mesophilic, methanogenic culture

The inhibitory effects of 90-189 mg l(-1) of sulfide and 25-75 mg-Nl(-1) of nitrate on methanogenesis were investigated in a mixed methanogenic culture using butyrate as carbon source. In the initial phase of 90 mg l(-1)S(2-) test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg l(-1) of sulfide was dosed alone. When 25-75 mg-Nl(-1) of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NO(x)), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg l(-1) of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.