Biological sulfur oxidation in wastewater treatment: A review of emerging opportunities

Simultaneous biofiltration of H2S, NH3, and toluene using compost made of chicken manure and sugarcane bagasse as packing material

Offensive odors from wastewater treatment plants (WWTP) are caused by volatile inorganic compounds such as hydrogen sulfide and ammonia and volatile organic compounds (VOCs), such as toluene. To treat these pollutants, biofiltration is an effective and economical technology used worldwide due to its low investment and environmental impact. In this work, a laboratory-scale prototype biofilter unit for the simultaneous biofiltration of hydrogen sulfide, ammonia, and toluene was evaluated by simulating the emission concentrations of the El Salitre WWTP Bogotá, Colombia, using a compost of chicken manure and sugarcane bagasse as packing material for the biofilter. The prototype biofilter unit was set to an operation flow rate of 0.089 m3/h, an empty bed residence time (EBRT) of 60 s, and a volume of 0.007 m3 (6.6 L). The maximum removal efficiency were 96.9 ± 1.2% for H2S, at a loading rate of 4.7 g/m3 h and a concentration of 79.1 mg/m3, 68 ± 2% for NH3, at a loading rate of 1.2 g/m3 h and a concentration of 2.0 mg/m3, and 71.5 ± 4.0% for toluene, at a loading rate of 1.32 g/m3 h and a concentration of 2.3 mg/m3. The removal efficiency of the three compounds decreased when the toluene concentration was increased above 40 mg/m3. However, a recovery of the system was observed after reducing the toluene concentration and after 7 days of inactivity, indicating an inhibitory effect of toluene. These results demonstrate the potential use of the prototype biofilter unit for odor treatment in a WWTP.

Salt stimulates sulfide-driven autotrophic denitrification: Microbial network and metagenomics analyses

Sulfur autotrophic denitrification (SADN) is a promising biological wastewater treatment technology for nitrogen removal, and its performance highly relies on the collective activities of the microbial community. However, the effect of salt (a prevailing characteristic of some nitrogen-containing industrial wastewaters) on the microbial community of SADN is still unclear. In this study, the response of the sulfide-SADN process to different salinities (i.e., 1.5 % salinity, 0.5 % salinity, and without salinity) as well as the involved microbial mechanisms were investigated by molecular ecological network and metagenomics analyses. Results showed that the satisfactory nitrogen removal efficiency (>97 %) was achieved in the sulfide-SADN process (S/N molar ratio of 0.88) with 1.5 % salinity. In salinity scenarios, the genus Thiobacillus significantly proliferated and was detected as the dominant sulfur-oxidizing bacteria in the sulfide-SADN system, occupying a relative abundance of 29.4 %. Network analysis further elucidated that 1.5 % salinity had enabled the microbial community to form a more densely clustered network, which intensified the interactions between microorganisms and effectively improved the nitrogen removal performance of the sulfide-SADN. Metagenomics sequencing revealed that the abundance of functional genes encoding for key enzymes involved in SADN, dissimilatory nitrate reduction to ammonium, and nitrification was up-regulated in the 1.5 % salinity scenario compared to that without salinity, stimulating the occurrence of multiple nitrogen transformation pathways. These multi-paths contributed to a robust SADN process (i.e., nitrogen removal efficiency >97 %, effluent nitrogen <2.5 mg N/L). This study deepens our understanding of the effect of salt on the SADN system at the community and functional level, and favors to advance the application of this sustainable bioprocess in saline wastewater treatment.

Novel and innovative approaches to partial denitrification coupled with anammox: A critical review

The partial denitrification (PD) coupled with anaerobic ammonium oxidation (Anammox) (PD/A) process is a unique biological denitrification method for sewage that concurrently removes nitrate (NO3--N) and ammonium (NH4+-N) in sewage. Comparing PD/A to conventional nitrification and denitrification technologies, noticeable improvements are shown in energy consumption, carbon source demand, sludge generation and emissions of greenhouse gasses. The PD is vital to obtaining nitrites (NO2--N) in the Anammox process. This paper provided valuable insight by introduced the basic principles and characteristics of the process and then summarized the strengthening strategies. The functional microorganisms and microbial competition have been discussed in details, the S-dependent denitrification-anammox has been analyzed in this review paper. Important factors affecting the PD/A process were examined from different aspects, and finally, the paper pointed out the shortcomings of the coupling process in experimental research and engineering applications. Thus, this research provided insightful information for the PD/A process's optimization technique in later treating many types of real and nitrate-based wastewater. The review paper also provided the prospective economic and environmental position for the actual design implementation of the PD/A process in the years to come.

Development of a flow-cell bioreactor for immobilized sulfidogenic sludge characterization using electrochemical H2S microsensors

The sulfate-reduction process plays a crucial role in the biological valorization of SOx gases. However, a complete understanding of the sulfidogenic process in bioreactors is limited by the lack of technologies for characterizing the sulfate-reducing activity of immobilized biomass. In this work, we propose a flow-cell bioreactor (FCB) for characterizing sulfate-reducing biomass using H2S microsensors to monitor H2S production in real-time within a biofilm. To replace natural immobilization through extracellular polymeric substance production, sulfidogenic sludge was artificially immobilized using polymers. Physical and sulfate-reducing activity studies were performed to select a polymer-biomass matrix that maintained sulfate-reducing activity of biomass while providing strong microbial retention and mechanical strength. Several operational conditions of the sulfidogenic reactor allowed to obtain a H2S profiles under different inlet sulfate loads and, additionally, 3D mapping was assessed in order to perform a hydraulic characterization. Besides, the effects of artificial immobilization on biodiversity were investigated through the characterization of microbial communities. This study demonstrated the appropriateness of immobilized-biomass for characterization of sulfidogenic biomass in FCB using H2S electrochemical microsensors, and beneficial microbiological communities shifts as well as enrichment of sulfate-reducing bacteria have been confirmed.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor

The high-concentration sulfate (SO42-) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42- removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42- removal rate (SRR) of 113.2 ± 5.7 mg SO42--S L-1 d-1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L-1 d-1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42--S L-1 d-1; SPR = 25.5 ± 9.7 mg S0-S L-1 d-1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g-1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42- reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Elemental sulfur biorecovery from phosphogypsum using oxygen-membrane biofilm reactor: Bioreactor parameters optimization, metagenomic analysis and metabolic prediction of the biofilm activity

This work investigated elemental sulfur (S0) biorecovery from Phosphogypsum (PG) using sulfur-oxidizing bacteria in an O2-based membrane biofilm reactor (MBfR). The system was first optimized using synthetic sulfide medium (SSM) as influent, then switched to biogenic sulfide medium (BSM) generated by biological reduction of PG alkaline leachate. The results using SSM had high sulfide-oxidation efficiency (98 %), sulfide to S0 conversion (∼90 %), and S0 production rate up to 2.7 g S0/(m2.d), when the O2/S ratio was ∼0.5 g O2/g S. With the BSM influent, the system maintained high sulfide-to-S0 conversion rate (97 %), and S0-production rate of 1.6 g S0/(m2.d). Metagenomic analysis revealed that Thauera was the dominant genus in SSM and BSM biofilms. Furthermore, influent composition affected the bacterial community structure and abundances of functional microbial sulfur genes, modifying the sulfur-transformation pathways in the biofilms. Overall, this work shows promise for O2-MBfR usage in S0 biorecovery from PG-leachate and other sulfidogenic effluents.

A mixed blessing of influent leachate microbes in downstream biotreatment systems of a full-scale landfill leachate treatment plant

In landfill leachate treatment plants (LLTPs), the microbiome plays a pivotal role in the decomposition of organic compounds, reduction in nutrient levels, and elimination of toxins. However, the effects of microbes in landfill leachate influents on downstream treatment systems remain poorly understood. To address this knowledge gap, we collected 23 metagenomic and 12 metatranscriptomic samples from landfill leachate and activated sludge from various treatment units in a full-scale LLTP. We successfully recovered 1,152 non-redundant metagenome-assembled genomes (MAGs), encompassing a wide taxonomic range, including 48 phyla, 95 classes, 166 orders, 247 families, 238 genera, and 1,152 species. More diverse microbes were observed in the influent leachate than in the downstream biotreatment systems, among which, an unprecedented ∼30 % of microbes with transcriptional expression migrated from the influent to the biological treatment units. Network analysis revealed that 399 shared MAGs across the four units exhibited high node centrality and degree, thus supporting enhanced interactions and increased stability of microbial communities. Functional reconstruction and genome characterization of MAGs indicated that these shared MAGs possessed greater capabilities for carbon, nitrogen, sulfur, and arsenic metabolism compared to non-shared MAGs. We further identified a novel species of Zixibacteria in the leachate influent with discrete lineages from those in other environments that accounted for up to 17 % of the abundance of the shared microbial community and exhibited notable metabolic versatility. Meanwhile, we presented groundbreaking evidence of the involvement of Zixibacteria-encoded genes in the production of harmful gas emissions, such as N2O and H2S, at the transcriptional level, thus suggesting that influent microbes may pose safety risks to downstream treatment systems. In summary, this study revealed the complex impact of the influent microbiome on LLTP and emphasizes the need to consider these microbial characteristics when designing treatment technologies and strategies for landfill leachate management.

Sulfur bacteria-reinforced microbial electrochemical denitrification

Two limiting factors of microbial electrochemical denitrification (MED) are the abundance and efficiency of the functional microorganisms. To supply these microorganisms, MED systems are inoculated with denitrifying sludge, but such method has much room for improvement. This study compared MED inoculated with autotrophic denitrifying inoculum (ADI) versus with heterotrophic denitrifying inoculum (HDI). ADI exhibited electroactivity for 50% less of timethan HDI. The denitrification efficiency of the ADI biocathode was42% higherthan that of the HDI biocathode. The HDI biocathode had high levels of polysaccharides while the ADI biocathode was rich in proteins, suggesting that two biocathodes may achieveMED but via differentpathways. Microbial communities of two biocathodes indicated MED of HDI biocathode may rely on interspecies electron transfer, whereas sulfur bacteria of ADI biocathode take electrons directly from the cathode to achieve MED. Utilizing autotrophic sulfur-oxidizing denitrifiers, this study offers a strategy for enhancing MED.

Bioremediation of acid mine drainage using sulfate-reducing wetland bioreactor: Filling substrates influence, sulfide oxidation and microbial community

Two sulfate-reducing wetland bioreactors (SRB-1 filled with lignocellulosic wastes and SRB-2 with river sand) were applied for synthetic acid mine drainage treatment with bio-waste fermentation liquid as electron donor, and the influence of filling substrates on sulfate reduction, sulfur transformation and microbial community was studied. The presence of lignocellulosic wastes (mixture of cow manure, bark, sawdust, peanut shell and straw) in SRB-1 promoted sulfate reduction efficiency (68.9%), sulfate reduction rate (42.1 ± 11 mg S/(L·d)), dissolved sulfide production rate (27.4 ± 7 mg S/(L·d)), and particularly caused high conversion ratio of sulfate reduction into dissolved sulfide (66.4%). In comparison, the relatively low sulfate reduction efficiency (42.9%), sulfate reduction rate (27.0 ± 10 mg S/(L·d)), dissolved sulfide production rate (5.6 ± 3 mg S/(L·d)) and low dissolved sulfide conversion efficiency (21.2%) occurred in SRB-2. Mixed organic substrates including easily assimilated electron donors (in manure) and lignocellulosic matter were effective to promote quick start and long-term microbial sulfate reduction. More than 98% of produced dissolved sulfide was oxidized dominantly by photoautotrophic green sulfur bacteria (genera Chlorobium and Chlorobaculum), of which 64.6% and 54.5% was converted into elemental sulfur for SRB-1 and SRB-2. The oxidation of sulfide into elemental sulfur for potential recovery rather than sulfate is preferred. Diverse sulfate reducing bacteria and sulfide oxidizing bacteria co-existed in the treatment system, which led to a sustainable sulfur transformation. High metal removal efficiency for Fe (99.6%, 92.5%), Cd (99.9%, 99.9%), Zn (99.4%, 98.5%), Cu (94.5%, 94.6%) except for Mn (9.3%, 3.6%) was achieved, and effluent pH increased to 6.5-7.7 and 6.7-7.7 for SRB-1 and SRB-2, respectively. Microbial community was regulated by filling substrates. Synergism between lignocellulosic decomposing bacteria and sulfate reducing bacteria played a vital role in lignocellulosic bioreactor treating AMD, in addition to fermentation liquid serving as effective electron donor.

Enhancement of sulfide removal and sulfur recovery in piggery wastewater via lighting-anaerobic digestion with bioaugmentation of phototrophic green sulfur bacteria

Anaerobic pig wastewater treatment commonly generates high sulfide concentrations in the treated wastewater. This study aims to apply phototrophic green sulfur bacteria (PGB) to promote sulfide removal in lighting-anaerobic digestion (lighting-AD) treating pig wastewater. Initially, batch AD tests of pig wastewater with/without PGB addition were carried out under dark (D) and light (L) conditions. The results showed that the lighting-AD with PGB gave a higher growth rate of PGB (0.056 h-1) and the highest COD/sulfide removals as compared to the dark-AD with PGB and lighting-AD solely. More experiments under various light intensities were performed in order to find an optimal intensity for PGB growth concurrently with metagenomic changes concerning treatment performance. It appeared that sulfide removal rates had increased as increasing light intensity up to 473 lx by giving the highest rate of 12.5 mg L-1 d-1 with the highest sulfur element content in the biomass. Contrastingly, many PGB species disappeared at 1350 lx exposure subsequently sharply decreasing the rate of sulfide removal. In sum, the application of low light intensities of 400-500 lx with bioaugmented PGB could promote PGB growth and activity in sulfide removal in pig wastewater in the lighting of the AD process.

Towards a new understanding of bioelectrochemical systems from the perspective of microecosystems: A critical review

Bioelectrochemical system (BES) holds promise for sustainable energy generation and wastewater treatment. The microbial communities, as the core of BES, play a crucial role in its performance, thus needing to be systematically studied. However, researches considering microbial communities in BES from an ecological perspective are limited. This review provided a comprehensive summary of the BES with special emphasis on microecological principles, commencing with the dynamic formation and succession of the microbial communities. It also clarified the intricate interspecies relationships and quorum-sensing mechanisms regulated by dominant species. Furthermore, this review addressed the crucial themes in BES-related researches on ecological processes, including growth patterns, ecological structures, and defense strategies against external disturbances. By offering this novel perspective, it would contribute to enhancing the understanding of BES-centered technologies and facilitating future research in this field.

Desulfurization properties, pathways, and potential applications of two novel and efficient chemolithotrophic sulfur-oxidizing strains of Pseudomonas sp. GHWS3 and Sphingobacterium sp. GHWS5

With the accelerated modernization of agriculture and industry, sulfides have been released into the environment as a by-products of various production processes. Elevated levels of sulfide pose a threat to organisms' health and disrupt ecosystem equilibrium. This study successfully isolated two highly efficient sulfur-oxidizing strains, namely Pseudomonas aeruginosa GHWS3 and Sphingobacterium sp. GHWS5. Neither strain exhibited hemolytic activity or pathogenicity. Additionally, GHWS3 inhibited the common aquaculture pathogen Vibrio anguillarum, while GHWS5 exhibited inhibitory effects against Vibrio harveyi. GHWS3 and GHWS5 demonstrated effective removal of sulfide under the following conditions: temperature range of 20-40 °C, pH level of 4.5-8.5, salinity range of 0-50‰, C/N ratio of 5-15, and sulfide concentration of 20-200 mg/L. By amplifying the key functional genes of the sulfur-oxidizing Sox and rDsr systems in both GHWS3 and GHWS5 strains, potential desulfurization pathways were analyzed. Furthermore, both strains displayed high efficiency in removing sulfides from actual aquaculture pond substrate mixtures. The findings of this study provide two promising candidate strains for sulfides removal from farm tailwater, industrial wastewater, and domestic wastewater.

Optimizing Autotrophic Sulfide Oxidation in the Oxygen-Based Membrane Biofilm Reactor to Recover Elemental Sulfur

Biological sulfide oxidation is an efficient means to recover elemental sulfur (S0) as a valuable resource from sulfide-bearing wastewater. This work evaluated the autotrophic sulfide oxidation to S0 in the O2-based membrane biofilm reactor (O2-MBfR). High recovery of S0 (80-90% of influent S) and high sulfide oxidation (∼100%) were simultaneously achieved when the ratio of O2-delivery capacity to sulfide-to S0 surface loading (SL) (O2/S2- → S0 ratio) was around 1.5 (g O2/m2-day/g O2/m2-day). On average, most of the produced S0 was recovered in the MBfR effluent, although the biofilm could be a source or sink for S0. Shallow metagenomic analysis of the biofilm showed that the top sulfide-oxidizing genera present in all stages were Thauera, Thiomonas, Thauera_A, and Pseudomonas. Thiomonas or Pseudomonas was the most important genus in stages that produced almost only S0 (i.e., the O2/S2- → S0 ratio around 1.5 g of the O2/m2-day/g O2/m2-day). With a lower sulfide SL, the S0-producing genes were sqr and fccAB in Thiomonas. With a higher sulfide SL, the S0-producing genes were in the soxABDXYZ system in Pseudomonas. Thus, the biofilm community of the O2-MBfR adapted to different sulfide-to-S0 SLs and corresponding O2-delivery capacities. The results illustrate the potential for S0 recovery using the O2-MBfR.

Efficient nitrite accumulation in partial sulfide autotrophic denitrification (PSAD) system: insights of S/N ratio, pH and temperature

To provide the necessary nitrite for the Anaerobic Ammonium Oxidation (ANAMMOX) process, the effect of nitrite accumulation in the partial sulfide autotrophic denitrification (PSAD) process was investigated using an SBR reactor. The results revealed that the effectiveness of nitrate removal was unsatisfactory when the S/N ratio (mol/mol) fell below 0.6. The optimal conditions for nitrate removal and nitrite accumulation were achieved within the S/N ratio range of 0.7-0.8, resulting in an average Nitrate Removal Efficiency (NRE) of 95.84%±4.89% and a Nitrite Accumulation Rate (NAR) of 75.31%±6.61%, respectively. It was observed that the nitrate reduction rate was three times faster than that of nitrite reduction during a typical cycle test. Furthermore, batch tests were conducted to assess the influence of pH and temperature conditions. In the pH tests, it became evident that the PSAD process performed more effectively in alkaline environment. The highest levels of nitrate removal and nitrite accumulation were achieved at an initial pH of 8.5, resulting in a NRE of 98.30%±1.93% and a NAR of 85.83%±0.47%, respectively. In the temperature tests, the most favourable outcomes for nitrate removal and nitrite accumulation were observed at 22±1 ℃, with a NRE of 100.00% and a NAR of 81.03%±1.64%, respectively. Moreover, a comparative analysis of 16S rRNA sequencing results between the raw sludge and the sulfide-enriched culture sludge sample showed that Proteobacteria (49.51%) remained the dominant phylum, with Thiobacillus (24.72%), Prosthecobacter (2.55%), Brevundimonas (2.31%) and Ignavibacterium (2.04%) emerging as the dominant genera, assuming the good nitrogen performance of the system.

Advance in the sulfur-based electron donor autotrophic denitrification for nitrate nitrogen removal from wastewater

In the field of wastewater treatment, nitrate nitrogen (NO3--N) is one of the significant contaminants of concern. Sulfur autotrophic denitrification technology, which uses a variety of sulfur-based electron donors to reduce NO3--N to nitrogen (N2) through sulfur autotrophic denitrification bacteria, has emerged as a novel nitrogen removal technology to replace heterotrophic denitrification in the field of wastewater treatment due to its low cost, environmental friendliness, and high nitrogen removal efficiency. This paper reviews the advance of reduced sulfur compounds (such as elemental sulfur, sulfide, and thiosulfate) and iron sulfides (such as ferrous sulfide, pyrrhotite, and pyrite) electron donors for treating NO3--N in wastewater by sulfur autotrophic denitrification technology, including the dominant bacteria types and the sulfur autotrophic denitrification process based on various electron donors are introduced in detail, and their operating costs, nitrogen removal performance and impacts on the ecological environment are analyzed and compared. Moreover, the engineering applications of sulfur-based electron donor autotrophic denitrification technology were comprehensively summarized. According to the literature review, the focus of future industry research were discussed from several aspects as well, which would provide ideas for the application and optimization of the sulfur autotrophic denitrification process for deep and efficient removal of NO3--N in wastewater.

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.

Sulfur autotrophic denitrification as an efficient nitrogen removals method for wastewater treatment towards lower organic requirement: A review

The sulfur autotrophic denitrification (SADN) process is an organic-free denitrification process that utilizes reduced inorganic sulfur compounds (RISCs) as the electron donor for nitrate reduction. It has been proven to be a cost-effective and environment-friendly approach to achieving carbon neutrality in wastewater treatment plants. However, there is no consensus on whether SADN can become a dominant denitrification process to treat domestic wastewater or industrial wastewater if organic carbon is desired to be saved. Through a comprehensive summary of the SADN process and extensive discussion of state-of-the-art SADN-based technologies, this review provides a systematic overview of the potential of the SADN process as a sustainable alternative for the heterotrophic denitrification (HD) process (organic carbons as electron donor). First, we introduce the mechanism of the SADN process that is different from the HD process, including its transformation pathways based on different RISCs as well as functional bacteria and key enzymes. The SADN process has unique theoretical advantages (e.g., economy and carbon-free, less greenhouse gas emissions, and a great potential for coupling with novel autotrophic processes), even if there are still some potential issues (e.g., S intermediates undesired production, and relatively slow growth rate of sulfur-oxidizing bacteria [SOB]) for wastewater treatment. Then we present the current representative SADN-based technologies, and propose the outlooks for future research in regards to SADN process, including implement of coupling of SADN with other nitrogen removal processes (e.g., HD, and sulfate-dependent anaerobic ammonium oxidation), and formation of SOB-enriched biofilm. This review will provide guidance for the future applications of the SADN process to ensure a robust-performance and chemical-saving denitrification for wastewater treatment.

Paper-assisted ratiometric fluorescent sensors for on-site sensing of sulfide based on the target-induced inner filter effect

Dissolved sulfide tends to species transformation and loss upon leaving the matrix, thus the development of a practical on-site determination of sulfide is crucial for environmental monitoring and human health. In this work, a novel paper-based ratiometric fluorescence sensor was developed for the field analysis of sulfide, which system was constructed by the inner filter effect (IFE) of CdS quantum dots (QDs) toward carbon dots (C-dots). Instead of an aqueous phase system, the conversion of sulfide to its hydride would induce the in-situ formation of CdS QDs on the paper, which acted as an energy acceptor to quench the emission of C-dots, leading to a variation of ratiometric fluorescence from blue to yellow with the increasing concentration of sulfide. Moreover, we proposed a smartphone-based fluorescence capture device integrated with a programmed Python program, accomplishing both color recognition and accurate detection of sulfide. Under the optimal condition, this ratiometric fluorescence sensor allowed for the on-site analysis of sulfide with a limit of detection of 0.05 μM. The accuracy of the sensor was validated via the successful field analysis of environmental water samples with satisfactory recoveries. Compared to other fluorescence methods used for sulfide analysis, this developed system retains the advantages of label-free, low-cost, ease of operation, and miniaturization, showing great potential for the measurement of sulfide on-site, as well as environmental monitoring.

Research progress of novel bio-denitrification technology in deep wastewater treatment

Excessive nitrogen emissions are a major contributor to water pollution, posing a threat not only to the environment but also to human health. Therefore, achieving deep denitrification of wastewater is of significant importance. Traditional biological denitrification methods have some drawbacks, including long processing times, substantial land requirements, high energy consumption, and high investment and operational costs. In contrast, the novel bio-denitrification technology reduces the traditional processing time and lowers operational and maintenance costs while improving denitrification efficiency. This technology falls within the category of environmentally friendly, low-energy deep denitrification methods. This paper introduces several innovative bio-denitrification technologies and their combinations, conducts a comparative analysis of their denitrification efficiency across various wastewater types, and concludes by outlining the future prospects for the development of these novel bio-denitrification technologies.

Integrating thermodynamics and mathematical modelling to investigate the stoichiometry and kinetics of sulphide oxidation-nitrate reduction with a special focus on partial autotrophic denitrification

In the present study, the stoichiometry of the Sulphur Oxidizing-Nitrate Reducing (SO-NR) process, with a focus on Partial Autotrophic Denitrification (PAD), has been evaluated through a thermodynamic-based study whereas a model-based approach has been adopted to assess process kinetics. Experimental data on process performance and biomass yields were available from a previous work achieving efficient PAD, where a biomass yield of 0.113 gVSS/gS was estimated. First, the free Gibbs energy dissipation method has been implemented, in order to provide a theoretical framework exploring the boundaries for sulphur oxidizing biomass yields. Second, a screening of available mathematical models describing SO-NR process was conducted and five published models were selected, in order to assess the most suitable model structure for describing the observed PAD kinetics. To the best of our knowledge, none of reported biomass yields are estimated in systems operating PAD as the main process and, analogously, none of the proposed models have been applied to case studies aiming at partial denitrification only. The work showed that the very low biomass yield of 0.117 ± 0.007 gVSS/gS, observed in a PAD system in our previous work, suggests that the conditions applied to achieve partial denitrification resulted in a high energy-dissipating metabolism compared to complete denitrification applications. Models' analysis revealed that nitrite accumulation can be described by a classical Monod kinetics if different μmax are adopted for each intermediate reaction, with Theil Inequality Coefficient values lower than 0.21 for both NO3- and NO2-. Nonetheless, adopting Haldane-type kinetics for nitrite uptake inferred higher identifiability to the model structure, resulting in confidence intervals below ±10% for all the parametric estimations. The thermodynamic and modelling outcomes support the experimental results obtained in the reference study and the critical comparison of model suitability to represent PAD process is believed pivotal to pave the way to its real-scale implementation.

Elemental sulfur-driven autotrophic denitrification process for effective removal of nitrate in mariculture wastewater: Performance, kinetics and microbial community

To date, there is a lack of systematic investigation on the elemental sulfur-driven autotrophic denitrification (SDAD) process for removing nitrate (NO3--N) from mariculture wastewater deficient in organic carbon sources. Therefore, a packed-bed reactor was established and continuously operated for 230 days to investigate the operation performance, kinetic characteristics and microbial community of SDAD biofilm process. Results indicate that the NO3--N removal efficiencies and rates varied with the operational conditions including HRT (1-4 h), influent concentrations of NO3--N (25-100 mg L-1) and DO (0.2-7.0 mg L-1), and temperature (10oC-30 °C), in the ranges of 51.4%-98.6% and 0.054-0.546 g L-1 d-1, respectively. Limestone could partially neutralize the produced acidity. Small portions of NO3--N were converted to nitrite (<4.5%) and ammonia (<2.8%) in the reactor. Operational conditions also influenced the production of acidity, nitrite and ammonia as well as sulfate. Shortening HRT and increasing influent NO3--N concentration turned the optimal fitting model depicting the NO3--N removal along the reactor from half-order to zero-order. Furthermore, the NO3--N removal was accelerated by a higher temperature and influent NO3--N concentration and a lower HRT and influent DO concentration. Microbial richness, evenness and diversity gradually decreased during the autotrophic denitrifier enrichment cultivation and the reactor start-up and operation. Sulfurimonas constituted the predominate genus and the primary functional bacteria in the reactor. This study highlights the SDAD as a promising way to control the coastal eutrophication associated with mariculture wastewater discharge.

Physics-informed neural network-based serial hybrid model capturing the hidden kinetics for sulfur-driven autotrophic denitrification process

Sulfur-driven autotrophic denitrification (SdAD) is a biological process that can remove nitrate from low carbon/nitrogen (C/N) ratio wastewater. Although this process has been intensively researched, the mechanism whereby its intermediates (i.e., elemental sulfur and nitrite ions) are generated and accumulated remains elusive. Existing mathematical models developed for SdAD cannot accurately predict the intermediates in SdAD because of the incomplete knowledge of process kinetic resulting from changes in the environmental conditions and electron competition during SdAD. To address this limitation, we proposed a novel serial hybrid model structure based on a physics-informed neural network (PINN) to capture the dynamics of the process kinetics and predict the substrate concentrations in SdAD. In this study, we evaluated the model through numerical experiments and applied it to real case studies involving batch and continuous-flow reactor scenarios. By leveraging the PINN approach, the hybrid model yielded accurate predictions at both the state (i.e. substrate concentration) and kinetic levels in the numerical experiments and performed better than both mechanistic and purely data-driven models in the case studies. Furthermore, we used the trained hybrid model to design control strategies for SdAD and a novel integrated process involving SdAD and anammox for energy-efficient nitrogen removal. Finally, we discuss the advantages and application scope of the PINN-based hybrid model.

Enhancing the Mn-Removal Efficiency of Acid-Mine Bacterial Consortium: Performance Optimization and Mechanism Study

In this study, an acclimated manganese-oxidizing bacteria (MnOB) consortium, QBS-1, was enriched in an acid mine area; then, it was used to eliminate Mn(Ⅱ) in different types of wastewater. QBS-1 presented excellent Mn removal performance between pH 4.0 and 8.0, and the best Mn-removal efficiency was up to 99.86% after response surface methodology optimization. Unlike other MnOB consortia, the core bacteria of QBS-1 were Stenotrophomonas and Achromobacter, which might play vital roles in Mn removal. Besides that, adsorption, co-precipitation and electrostatic binding by biological manganese oxides could further promote Mn elimination. Finally, the performance of the Mn biofilter demonstrated that QBS-1 was an excellent inoculant, which indicates good potential for removing Mn contamination steadily and efficiently.

Development of microbial enrichments for simultaneous removal of sulfur and nitrogenous metabolites in saline water aquaculture

AIM

The aim of the study was to develop microbial enrichments from the nitrifying microbial consortia and the environment for simultaneous removal of ammonia, nitrate, and sulfide in aquaculture systems at varied salinities.

METHODS AND RESULTS

Sulfur and nitrogen metabolites are the major factors affecting the farmed aquatic animal species and deteriorate the receiving environments causing ecological damage. The present study reports the development of microbial enrichments from the nitrifying microbial consortia and the environment. The enrichments used thiosulfate or thiocyanate as an energy source and simultaneously removed sulfur, ammonia, and nitrite in spiked medium (125 mg/l ammonia; 145 mg/l nitrite). Further, the microbes in the enrichments could grow up to 30 g/l salinity. Metagenomic studies revealed limited microbial diversity suggesting the enrichment of highly specialized taxa, and co-occurrence network analysis showed the formation of three micro-niches with multiple interactions at different taxonomic levels.

CONCLUSIONS

The ability of the enrichments to grow in both organic and inorganic medium and simultaneous removal of sulfide, ammonia, and nitrite under varied salinities suggests their potential application in sulfur, nitrogen, and organic matter-rich aquaculture pond environments and other industrial effluents.

Study on the treatment of sulfite wastewater by Desulfovibrio

In the wet flue gas desulfurization (WFGD) process, SO₂ is adsorbed by alkaline liquor to produce alkaline wastewater containing sulfate and sulfite. Although the traditional chemical treatment method can achieve a high removal rate, it consumes a large number of chemicals and yields a large number of low-value by-products. The biological treatment process is a greener and more environmentally friendly treatment method. The current work studies microbial flue gas desulfurization directly using sulfite as the electron acceptor in the reduction process. Desulfovibrio were obtained by isolation and purification, and their growth conditions in sulfite wastewater and desulfurization process conditions were investigated by intermittent and continuous experiments. The results of intermittent experiments indicated that the optimal growth conditions of Desulfovibrio were a temperature of 38 °C, a pH value of 8.0, a COD/SO₃^2- of 2 and that the growth of bacteria would be inhibited at a pH above 9.0 or below 7.3. Furthermore, Desulfovibrio could grow in simulated wastewater with a high SO₃^2- concentration of 8000 mg/L. The results of continuous experiments showed that the removal of sulfite and the recovery of elemental sulfur was realized by a micro-oxygen depletion process, and the removal rate of sulfite of 99%, the yield of elemental sulfur is more than 80% and can reach 90% under the condition of low influent concentration. The bacteria grew well at a temperature of 40 °C and a pH value of the influent water of 7.5. To ensure the treatment effect, the hydraulic retention time (HRT) should be more than doubled for each 1000 mg/L increase in the influent sulfite concentration under the same reflux ratio. When the influent sulfite concentration was 1000 mg/L, 2000 mg/L, 3000 mg/L, and 4000 mg/L, the corresponding HRT was 3.01 h, 6.94 h, 17.4 h, and 31.9 h, respectively. The dominant species in the reactor was Desulfovibrio bacteria at 63.9% abundance. This study demonstrated the feasibility of using sulfite as an electron acceptor for microbial desulfurization, which can optimize the initial process and provide the possibility of treating high-concentration sulfite wastewater.

A novel integrated industrial-scale biological reactor for odor control in a sewage sludge composting facility: Performance, pollutant transformation, and bioaerosol emission mechanism

In order to remove multiple pollutants in the sewage sludge (SS) composting facility, a novel integrated industrial-scale biological reactor based on biological trickling filtration and fungal biological filtration (BTF-FBF) was developed. This study examined bioaerosol emission, odour removal, pollutant transformation mechanism, and project investment. At an inlet flow rate of 7200 m³/h, the average removal efficiencies of hydrogen sulfide (H₂S), ammonia (NH₃), and volatile organic compounds (VOCs) during the steady stage were 97.2 %, 98.9 %, and 92.2 %. The BTF-FBF separates microbial phases (bacteria and fungi) of different modules. BTF removed most hydrophilic compounds, while FBF removed hydrophobic ones. Moreover, the reactor could effectively remove pathogens or opportunistic pathogens bioaerosols, such as Escherichia coli (61.9%), Salmonella sp. (85%), and Aspergillus fumigatus (82.1%). The pollutant transformation mechanism of BTF-FBF was proposed. BTF-FBF annualized costs were 324,783 CNY/year at 15 years. In conclusion, BTF-FBF provides new insights into composting facility bioaerosol, odour, and pathogen emission control.

Response of sulfur-metabolizing biofilm to external sulfide in element sulfur-based dentification packed-bed reactor

Dosing sulfide into the sulfur-packed-bed (S⁰PB) has great potential to enhance the denitrification efficiency by providing compensatory electron donors, however, the response of sulfur-metabolizing biofilm to various sulfide dosages has never been investigated. In this study, the S⁰PB reactor was carried out with increasing sulfide dosages by 3.6 kg/m³/d, presenting a decreasing effluent nitrate from 14.2 to 2.7 mg N/L with accelerated denitrification efficiency (k: 0.04 to 0.27). However, 6.5 mg N/L of nitrite accumulated when the sulfide dosage exceeded 0.9 kg/m³/d (optimum value). The increasing electron export contribution of sulfide as maximum as 85.5% illustrated its competition with the in-situ sulfur. Meanwhile, over-dosing sulfide caused serious biofilm expulsion with significant decreases in the total biomass, live cell population, and ATP by 90.2%, 86.7%, and 54.8%, respectively. This study verified the capacity of dosing sulfide to improve the denitrification efficiency in S⁰PB but alerted the negative effect by exceeded dosing.

Sulfide-driven nitrous oxide recovery during the mixotrophic denitrification process

We propose a novel sulfide-driven process to recover N₂O during the traditional denitrification process. The optimum initial sulfide concentration was 120 mg/L, and the N₂O percentage in the gaseous products (N₂O+N₂) was up to 82.9%. Moreover, sulfide involved in denitrification processes could substitute for organic carbon as an electron donor, e.g., 1 g sulfide was equivalent to 0.5-2 g COD when sulfide was oxidized to sulfur and sulfate. The accumulation of N₂O was mainly due to the inhibiting effect of sulfide on nitrous oxide reductase (N₂OR), which was induced by the supply insufficiency of electrons from cytochrome c (cyt c) to N₂OR. When the initial sulfide concentration was 120 mg/L, the N₂OR activity was only 36.8% of its original level. According to the results of cyclic voltammetry, circular dichroism spectra and fluorescence spectra, significant changes in the conformations and protein structures of cyt c were caused by sulfide, and cyt c completely lost its electron transport capacity. This study provides a new concept for N₂O recovery driven by sulfide in the denitrification process. In addition, the findings regarding the mechanism of the inhibition of N₂OR activity have important implications both for reducing emissions of N₂O and recovering N₂O in the sulfide-driven denitrification process.

Characterization of sulfide oxidation and optimization of sulfate production by a thermophilic Paenibacillus naphthalenovorans LYH-3 isolated from sewage sludge composting

The sulfur-containing odor emitted from sludge composting could be controlled by sulfide oxidizing bacteria, yet mesophilic strains show inactivation during the thermophilic stage of composting. Aimed to investigate and characterize the thermotolerant bacterium that could oxidize sulfide into sulfate, a heterotrophic strain was isolated from sewage sludge composting and identified as Paenibacillus naphthalenovorans LYH-3. The effects of various environmental factors on sulfide oxidation capacities were studied to optimize the sulfate production, and the highest production rate (27.35% ± 0.86%) was obtained at pH 7.34, the rotation speed of 161.14 r/min, and the inoculation amount of 5.83% by employing Box-Behnken design. The results of serial sulfide substrates experiments indicated that strain LYH-3 could survive up to 400 mg/L of sulfide with the highest sulfide removal rate (88.79% ± 0.35%) obtained at 50 mg/L of sulfide. Growth kinetic analysis presented the maximum specific growth rate µ_m (0.5274 hr^-1) after 22 hr cultivation at 50°C. The highest enzyme activities of sulfide quinone oxidoreductase (0.369 ± 0.052 U/mg) and sulfur dioxygenase (0.255 ± 0.014 U/mg) were both obtained at 40°C, and the highest enzyme activity of sulfite acceptor oxidoreductase (1.302 ± 0.035 U/mg) was assessed at 50°C. The results indicated that P. naphthalenovorans possessed a rapid growth rate and efficient sulfide oxidation capacities under thermophilic conditions, promising a potential application in controlling sulfur-containing odors during the thermophilic stage of sludge composting.

Roles, mechanism of action, and potential applications of sulfur-oxidizing bacteria for environmental bioremediation

Sulfur (S) is a crucial component in the environment and living organisms. This work is the first attempt to provide an overview and critical discussion on the roles, mechanisms, and environmental applications of sulfur-oxidizing bacteria (SOB). The findings reveal that key enzymes of SOB embarked on oxidation of sulfide, sulfite, thiosulfate, and elemental S. Conversion of reduced S compounds was oxidatively catalyzed by various enzymes (e.g. sulfide: quinone oxidoreductase, flavocytochrome c-sulfide dehydrogenase, dissimilatory sulfite reductase, heterodisulfide reductase-like proteins). Environmental applications of SOB discussed include detoxifying hydrogen sulfide, soil bioremediation, and wastewater treatment. SOB producing S⁰ engaged in biological S soil amendments (e.g. saline-alkali soil remediation, the oxidation of sulfide-bearing minerals). Biotreatment of H₂S using SOB occurred under both aerobic and anaerobic conditions. Sulfide, nitrate, and sulfamethoxazole were removed through SOB suspension cultures and S⁰-based carriers. Finally, this work presented future perspectives on SOB development, including S⁰ recovery, SOB enrichment, field measurement and identification of sulfur compounds, and the development of mathematical simulation.

Role of iron(II) sulfide in autotrophic denitrification under tetracycline stress: Substrate and detoxification effect

Autotrophic denitrification using inorganic compounds as electron donors has gained increasing attention in the field of wastewater treatment due to its numerous advantages, such as no need for exogenous organic carbon, low energy input, and low sludge production. Tetracycline (TC), a refractory contaminant, is often found coexisting with nutrients (NO₃^- and PO₄^3-) in wastewater, which can negatively affect the biological nutrient removal process because of its biological toxicity. However, the performance of autotrophic denitrification under TC stress has rarely been reported. In this study, the effects of TC on autotrophic denitrification with thiosulfate (Na₂S₂O₃) and iron (II) sulfide (FeS) as the electron donors were investigated. With Na₂S₂O₃ as the electron donor, TC slowed down the nitrate removal rate, which decreased from 1.32 to 0.18 d^-1, when TC concentration increased from 0 mg/L to 50 mg/L. When TC concentration was higher than 2 mg/L, nitrite reduction was seriously inhibited, leading to nitrite accumulation. With FeS as the electron donor, nitrate removal was much more efficient under TC-stressed conditions, and no distinct nitrite accumulation was observed when the initial TC concentration was as high as 10 mg/L, indicating the effective detoxification of FeS. The detoxification effects in the FeS autotrophic denitrification system mainly resulted from the rapid adsorption of TC by FeS and effective degradation of TC, as proven by a relatively higher living biomass area. This study offers new insights into the response of sulfur-based autotrophic denitrifiers to TC stress and demonstrates that the FeS-based autotrophic denitrification process is a promising technology for the treatment of wastewater containing emerging contaminants and nutrients.

Resilience of hollow fibre membrane bioreactors for treating H2S under steady state and transient conditions

H₂S removal performance by hollow fibre membrane bioreactors (HFMBs) was investigated for 271 days at ambient (20 ± 2 °C) temperature employing an inlet H₂S concentrations up to 3600 ppm_v and empty bed residence time (EBRT) of 187, 92 and 62 s. Different operating conditions including pH control (with or without), famine period, shock loads (4-72 h) and different biomass types (presence or absence of suspended biomass) were investigated. The H₂S flux and mass-transfer coefficient were significantly higher for the biotic HFMBs (R₁ and R₂) compared to the abiotic control (R₃) at all employed EBRTs. Significant differences in H₂S removal efficiency (RE) and elimination capacity (EC) were noted for different inlet H₂S concentrations, EBRTs, pH and biomass type. The HFMB achieved >99% RE at steady-state for biotic operation with an EC of 33.8, 30.0 and 30.9 g m^-3 h^-1 at an EBRT of 187, 92 and 62 s, respectively. Sulfate (92-93%) was the main sulfur species in the H₂S bioconversion process. The HFMB showed a good resilience to shock loads and showed quick recovery (<24 h) after withdrawal of the shock loads. The HFMB had a critical loading rate of H₂S about 135 g m^-3 h^-1 under transient-state.

Elemental sulphur recovery from a sulphate-rich aqueous stream in a single hybrid linear flow channel reactor is mediated through microbial community dynamics and adaptation to reactor zones

The coupled application of biological sulphate reduction (BSR) and partial sulphide oxidation to treat sulphate-rich wastewater is an effective strategy to mitigate pollution and recover elemental sulphur for repurposing. The recent development of the hybrid linear flow channel reactor (LFCR) achieves simultaneous BSR and partial sulphide oxidation with biosulphur recovery via a floating sulphur biofilm (FSB). Here, we explore the microbial community zoning and dynamics facilitating the process. A total of three continuous LFCRs were used to evaluate the effect of reactor zones, hydraulic residence time (HRT), carbon source, namely lactate and acetate, as well as reactor geometry and scale on process performance and microbial community dynamics. Community composition of sessile and planktonic microbial consortia were resolved at a 5- and 2-day HRT through 16S rRNA amplicon sequencing. Preferential attachment and prevalence of specific phylotypes within the sessile and planktonic communities revealed clear adaptation of key microorganisms to different microenvironments. Key microbial taxa affiliated with sulphate reduction and sulphide oxidation as well as those implicated in fermentation and syntrophic metabolism, fluctuated in response to changes in HRT and process performance. Through understanding the relationship between microbial community dynamics and process performance, this research will inform better process design and optimization of the hybrid LFCR.

Coupling sulfur-based denitrification with anammox for effective and stable nitrogen removal: A review

Anoxic ammonium oxidation (anammox) is an energy-efficient nitrogen removal process for wastewater treatment. However, the unstable nitrite supply and residual nitrate in the anammox process have limited its wide application. Recent studies have proven coupling of sulfur-based denitrification with anammox (SDA) can achieve an effective nitrogen removal, owing to stable provision of substrate nitrite from the sulfur-based denitrification, thus making its process control more efficient in comparison with that of partial nitrification and anammox process. Meanwhile, the anammox-produced nitrate can be eliminated through sulfur-based denitrification, thereby enhancing SDA's overall nitrogen removal efficiency. Nonetheless, this process is governed by a complex microbial system that involves both complicated sulfur and nitrogen metabolisms as well as multiple interactions among sulfur-oxidising bacteria and anammox bacteria. A comprehensive understanding of the principles of the SDA process is the key to facilitating the development and application of this novel process. Hence, this review is conducted to systematically summarise various findings on the SDA process, including its associated biochemistry, biokinetic reactions, reactor performance, and application. The dominant functional bacteria and microbial interactions in the SDA process are further discussed. Finally, the advantages, challenges, and future research perspectives of SDA are outlined. Overall, this work gives an in-depth insight into the coupling mechanism of SDA and its potential application in biological nitrogen removal.

Extracellular DNA plays a key role in the structural stability of sulfide-based denitrifying biofilms

Sulfide-based biofilm processes are increasingly used for wastewater denitrification, yet little is known about the extracellular polymeric substance (EPS) composition of sulfide-oxidizing biofilms. This can have an important impact on biofilm mechanical strength and stability. In this research, the properties and roles of EPS components in biofilm stability were investigated. Weak biofilm stability characterized by high roughness and numerous "needle" structures was visualized by optical coherence tomography (OCT) and microscopy. A high abundance of extracellular DNA (eDNA) and a low protein to polysaccharide ratio were found in the biofilm. The roles of eDNA, protein and polysaccharide in biofilm cohesion and adhesion were identified through enzyme treatment and atomic force microscopy (AFM). The enzymatic hydrolysis of eDNA increased the elastic modulus of biofilms by 57 times and reduced the adhesion energy by 96%. The hydrolysis of proteins led to an increase of elastic modulus by 27 times and a loss of adhesion energy by 95.5%. The enzymatic hydrolysis of polysaccharides caused minimal changes in elastic modulus and adhesion energy. These results suggest that eDNA was the key EPS component for biofilm cohesion and adhesion, possibly because it provided special binding sites and can form strong cross-linking with magnesium or other multivalent cations. This study provided new insights into the role of eDNA in biofilm stability and shed light on the development of sulfide-based denitrifying biofilms.

Sulfide removal characteristics, pathways and potential application of a novel chemolithotrophic sulfide-oxidizing strain, Marinobacter sp. SDSWS8

Sulfide generally exists in wastewater, black and odor river, as well as aquaculture water, and give rise to adverse effect on ecological stability and biological safety, due to the toxicity, corrosivity and malodor of sulfide. In the present study, a chemolithotrophic sulfide-oxidizing bacteria (SOB) was isolated and identified as Marinobacter maroccanus strain SDSWS8. And it produced no hemolysin and was susceptible to most antibiotics. There were no accumulation of sulfide, sulfate and thiosulfate during the sulfide removal process. The optimum conditions of sulfide removal were temperature 15-40 °C, initial pH value 4.5-9.5, salinity 10-40‰, C/N ratio 0-20 and sulfide concentration 25-150 mg/L. The key genes of sulfide oxidation, Sox system (soxB, soxX, soxA, soxZ, soxY, soxD, soxC), dissimilatory sulfur oxidation (dsrA, aprA and sat) and sqr, were successfully amplified and expressed, indicating the three pathways coordinated to complete the sulfide oxidation. Besides, strain SDSWS8 had inhibitory effect on four pathogen Vibrio (V. harveyi, V. parahaemolyticus, V. anguillarum and V. splendidus). Furthermore, efficient removal of sulfide from real aquaculture water and sludge mixture could be accomplished by strain SDSWS8. This study may provide a promising candidate strain for sulfide-rich water treatment.

A novel sulfur-driven autotrophic denitrification coupled with bio-cathode system for bioelectricity generation and groundwater remediation

This study explored the feasibility of treating wastewater using sulfur-driven autotrophic denitrification (SAD) coupled with the bio-cathode of microbial fuel cell (MFC), focusing on simultaneous bioelectricity generation, denitrification, and desulphurization. A maximum output voltage of 360 mV was obtained with a power generation cycle of 25 h when simulated wastewater with 100.0 mg/L of each NO₃^--N and S^2--S was employed as the influent in the SAD-BMFC. Compared with solo SAD or MFC, SAD-BMFC obtained a higher NO₃^--N removal rate (E_{12 h} = 87.7%, E_{24 h} = 100%), and less NO₂^--N accumulation. S^2--S of the influent was almost completely removed, oxidized to S⁰-S (88.6-90.2 mg/L) and SO₄^2--S (9.8-11.4 mg/L). The reaction system achieved self-balance of acidity-alkalinity (pH 7.05-7.35). The SAD process was the main pathway for NO₃^--N removal (80.2%) and a smaller proportion of electrons came from the bio-cathode. This study effectively combined SAD with a bio-cathode system for simultaneous energy harvest and bio-enhanced remediation of groundwater contaminated by both NO₃^--N and S^2--S.

Assessing Intermediate Formation and Electron Competition during Thiosulfate-Driven Denitrification: An Experimental and Modeling Study

There is increasing interest in thiosulfate-driven denitrification for low C/N wastewater treatment, but the denitrification performance varies with the thiosulfate oxidation pathways. Models have been developed to predict the products of denitrification, but few consider thiosulfate reduction to elemental sulfur (S⁰), an undesirable reaction that can intensify electron competition with denitrifying enzymes. In this study, the model using indirect coupling of electrons (ICE) was developed to predict S⁰ formation and electron competition during thiosulfate-driven denitrification. Kinetic data were obtained from sulfur-oxidizing bacteria (SOB) dominated by the branched pathway and were used to calibrate and validate the model. Electron competition was investigated under different operating conditions. Modeling results reveal that electrons produced in the first step of thiosulfate oxidation typically prioritize thiosulfate reduction, then nitrate reduction, and finally nitrite reduction. However, the electron consumption rate for S⁰ formation decreases sharply with the decline of thiosulfate concentration. Thus, a continuous feeding strategy was effective in alleviating the competition between thiosulfate reduction and denitrifying enzymes. Electron competition leads to nitrite accumulation, which could be a reliable substrate for anammox. The model was further evaluated with anammox integration. Results suggested that the branched pathway and continuous supply of thiosulfate are favorable to create a symbiotic relationship between SOB and anammox.

Low H2S content biogas biodesulfurization from high solid sludge anaerobic digestion using limited external aeration biotrickling filter: Effect of gas-liquid pattern on oxygen utilization performance

An efficient and precise method is needed for low H₂S content biogas biodesulfurization, produced during high solid sludge anaerobic digestion. Continuous experiments were conducted to evaluate the performance of a lab-scale biotrickling filter (BTF) in H₂S removal and oxygen utilization. The results show that the sulfur loading rate decreased by 66% compared to conventional H₂S content, thus achieving a sufficient removal efficiency (>0.9). With a limited external aeration (0.5-2.0 molO₂·molS^-1), the oxygen consumption (O/S_re) to its supplement (O/S_in) ratios increased from 50-71% (conventional H₂S) to 83-92% (low H₂S), indicating that low H₂S flux promotes a sufficient oxygen utilization. Furthermore, the difference in oxygen utilization between co-current and counter-current flow patterns decreased under limited external aeration as the H₂S content sharply decreased. These results indicate that a dynamic oxygen-sulfur (O-S) balanced multistage BTF is expected to achieve a more precise vertical O-S distribution for sulfur resource recovery.

Sustainable vs. Conventional Approach for Olive Oil Wastewater Management: A Review of the State of the Art

The main goal of this review is to collect and analyze the recently published research concerning the conventional and sustainable treatment processes for olive mill wastewater (OMW). In the conventional treatment processes, it is noticed that the main objective is to meet the environmental regulations for remediated wastewater without considering the economical values of its valuable constituents such as polyphenols. These substances have many important environmental values and could be used in many vital applications. Conversely, sustainable treatment processes aim to recover the valuable constituents through different processes and then treat the residual wastewater. Both approaches’ operational and design parameters were analyzed to generalize their advantages and possible applications. A valorization-treatment approach for OMW is expected to make it a sustainable resource for ingredients of high economical value that could lead to a profitable business. In addition, inclusion of a recovery process will detoxify the residual OMW, simplify its management treatment, and allow the possible reuse of the vast amounts of processed water. In a nutshell, the proposed approach led to zero waste with a closed water cycle development.

Metagenomic Insights Into Competition Between Denitrification and Dissimilatory Nitrate Reduction to Ammonia Within One-Stage and Two-Stage Partial-Nitritation Anammox Bioreactor Configurations

Anaerobic ammonia oxidizing bacteria (Anammox) are implemented in high-efficiency wastewater treatment systems operated in two general configurations; one-stage systems combine aerobic ammonia oxidizing bacteria (AOB) and Anammox within a single aerated reactor, whereas two-stage configurations separate these processes into discrete tanks. Within both configurations heterotrophic populations that perform denitrification or dissimilatory nitrate reduction to ammonia (DNRA) compete for carbon and nitrate or nitrite and can impact reactor performance because DNRA retains nitrogen in the system. Therefore, it is important to understand how selective pressures imposed by one-stage and two-stage reactor configurations impact the microbial community structure and associated nitrogen transforming functions. We performed 16S rRNA gene and metagenomic sequencing on different biomass fractions (granules, flocs, and suspended biomass) sampled from two facilities treating sludge dewatering centrate: a one-stage treatment facility (Chambers Creek, Tacoma, WA) and a two-stage system (Rotterdam, Netherlands). Similar microbial populations were identified across the different samples, but relative abundances differed between reactor configurations and biomass sources. Analysis of metagenome assembled genomes (MAGs) indicated different lifestyles for abundant heterotrophic populations. Acidobacteria, Bacteroidetes, and Chloroflexi MAGs had varying capacity for DNRA and denitrification. Acidobacteria MAGs possessed high numbers of glycosyl hydrolases and glycosyl transferases indicating a role in biomass degradation. Ignavibacteria and Phycosphaerae MAGs contributed to the greater relative abundance of DNRA associated nrf genes in the two-stage granules and contained genomic features suggesting a preference for an anoxic or microoxic niche. In the one-stage granules a MAG assigned to Burkholderiales accounted for much of the abundant denitrification genes and had genomic features, including the potential for autotrophic denitrification using reduced sulfur, that indicate an ability to adapt its physiology to varying redox conditions. Overall, the competition for carbon substrates between denitrifying and DNRA performing heterotrophs may be impacted by configuration specific selective pressures. In one-stage systems oxygen availability in the bulk liquid and the oxygen gradient within granules would provide a greater niche space for heterotrophic populations capable of utilizing both oxygen and nitrate or nitrite as terminal electron acceptors, compared to two-stage systems where a homogeneous anoxic environment would favor heterotrophic populations primarily adapted to anaerobic metabolism.

Advances in elemental sulfur-driven bioprocesses for wastewater treatment: From metabolic study to application

Elemental sulfur (S0) is known to be an abundant, non-toxic material with a wide range of redox states (-2 to +6) and may serve as an excellent electron carrier in wastewater treatment. In turn, S0-driven bioprocesses, which employ S0 as electron donor or acceptor, have recently established themselves as cost-effective therefore attractive solutions for wastewater treatment. Numerous related processes have, to date, been developed from laboratory experiments into full-scale applications, including S0-driven autotrophic denitrification for nitrate removal and S0-reducing organic removal. Compared to the conventional activated sludge process, these bioprocesses require only a small amount of organic matter and produce very little sludge. There have been great efforts to characterize chemical and biogenic S0 and related functional microorganisms in order to identify the biochemical pathways, upgrade the bioprocesses, and assess the impact of the operating factors on process performance, ultimately aiming to better understand and to optimize the processes. This paper is therefore a comprehensive overview of emerging S0-driven biotechnologies, including the development of S0-driven autotrophic denitrification and S0-based sulfidogenesis, as well as the associated microbiology and biochemistry. Also reviewed here are the physicochemical characteristics of S0 and the effects that environmental factors such as pH, influent sulfur/nitrate ratio, temperature, S0 particle size and reactor configurations have on the process. Research gaps, challenges of process applications and potential areas for future research are further proposed and discussed.

High-Rate Sulfate Removal Coupled to Elemental Sulfur Production in Mining Process Waters Based on Membrane-Biofilm Technology

It is anticipated that copper mining output will significantly increase over the next 20 years because of the more intensive use of copper in electricity-related technologies such as for transport and clean power generation, leading to a significant increase in the impacts on water resources if stricter regulations and as a result cleaner mining and processing technologies are not implemented. A key concern of discarded copper production process water is sulfate. In this study we aim to transform sulfate into sulfur in real mining process water. For that, we operate a sequential 2-step membrane biofilm reactor (MBfR) system. We coupled a hydrogenotrophic MBfR (H₂-MBfR) for sulfate reduction to an oxidizing MBfR (O₂-MBfR) for oxidation of sulfide to elemental sulfur. A key process improvement of the H₂-MBfR was online pH control, which led to stable high-rate sulfate removal not limited by biomass accumulation and with H₂ supply that was on demand. The H₂-MBfR easily adapted to increasing sulfate loads, but the O₂-MBfR was difficult to adjust to the varying H₂-MBfR outputs, requiring better coupling control. The H₂-MBfR achieved high average volumetric sulfate reduction performances of 1.7-3.74 g S/m³-d at 92-97% efficiencies, comparable to current high-rate technologies, but without requiring gas recycling and recompression and by minimizing the H₂ off-gassing risk. On the other hand, the O₂-MBfR reached average volumetric sulfur production rates of 0.7-2.66 g S/m³-d at efficiencies of 48-78%. The O₂-MBfR needs further optimization by automatizing the gas feed, evaluating the controlled removal of excess biomass and S⁰ particles accumulating in the biofilm, and achieving better coupling control between both reactors. Finally, an economic/sustainability evaluation shows that MBfR technology can benefit from the green production of H₂ and O₂ at operating costs which compare favorably with membrane filtration, without generating residual streams, and with the recovery of valuable elemental sulfur.

Microbial transformations by sulfur bacteria can recover value from phosphogypsum: A global problem and a possible solution

Rising global population and affluence are increasing demands for food production and the phosphorus (P) fertilizers needed to grow that food. Essential are new approaches for managing the growing amount of phosphogypsum (PG) that is a by-product of phosphoric-acid production from phosphate rock. Today, only ~15% of the worldwide production of PG is recycled, mainly for agriculture and road construction. This review addresses microbial valorization of PG through strategies that apply sulfur-transforming bacteria: sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). The focus is on recovering elemental sulfur (S⁰), which can be used to make the sulfuric acid needed to produce phosphoric acid from rock phosphate. Our review provides in-depth understanding of the microbiological, chemical, and technological bases for microbial reclamation of S⁰ from PG. The review presents the principles and practices for sulfate leaching from PG, reduction of sulfate to sulfide by SRB, and oxidation of sulfide to S⁰ by SOB. The choice of electron donor for SRB, control of oxygen delivery to SOB, and nutrient requirements are emphasized. Although microorganism-based technologies for PG reclamation are far from mature, the efficiency of such SRB- and SOB-based processes has been documented at laboratory and industrial scales. This review should spur biotechnological advances toward recovering value from PG.

Enhanced microbial nitrate reduction using natural manganese oxide ore as an electron donor

Nitrate contamination of groundwater is a global problem. Enhanced biological nitrate reduction by liquid organics combined with low-cost natural materials (as electron donors) can cost-effectively remove nitrate from groundwater. Dissolved Mn(II) as an electron donor has been thoroughly investigated to support microbial nitrate reduction. However, most Mn in soil and sediments is in solid form, and the ability of solid-phase natural manganese oxide ore (NMO) as electron donor and for supporting microbial nitrate reduction is unknown. Therefore, a microcosm experiment was conducted to bridge this gap in knowledge. The results demonstrated that microbial nitrate reduction (mainly converted to nitrite) was enhanced by NMO (rich in cryptomelane). The electrochemical and X-ray photoelectron spectroscopy analyses suggested that NMO may be oxidized by microbial metabolism. Illumina Miseq sequencing results indicated that Acidovorax spp. played a crucial role in NMO-supported nitrate reduction. Further Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analyses indicated that bacterial extracellular electron transfer may be one of the mechanisms for the microbial NMO oxidation. The results of our study highlight the potential importance of NMO in nitrate reduction in the natural environment and may pave the way for NMO-assisted technology for nitrate removal from groundwater with less usage of organic electron donors.

Effect of glucose oxidase treatment on the aroma qualities and release of cooked off-odor components from heat-treated Hami melon juice

Melon juice produces strong cooked off-odors during heat processing, leading to serious deterioration of aroma quality. In this work, the aroma quality of melon juice, the changes in GOD reaction products, and the interactions of reaction products and cooked off-odor components were analyzed by sensory evaluation, gas chromatography-mass spectrometry/olfactory, ultraperformance liquid chromatography-triple quadrupole mass spectrometry, and isothermal titration calorimetry to study the effect mechanism of glucose oxidase (GOD) on the release of cooked off-odor components from heat-treated melon juice. The results showed that GOD treatment improved the aroma quality mainly by controlling off-odor attributes and maintaining characteristic odor attributes. This was because the reaction products (hydrogen peroxide and gluconic acid) of GOD treatment inhibited the release of cooked off-odor components from heat-treated melon juice through oxidation and hydrophobic effects. Furthermore, these products reduced the loss of characteristic odor compounds by restraining Maillard, degradation, and oxidation reactions during heat processing.

Sulphur in Jharia and Raniganj coalfields: Chemical fractionation and its environmental implications

In coal, total sulphur content is not the only important factor for the industry, but also the forms of sulphur and their distributions should be considered before utilizing any coal for a particular use. In Jharia and Raniganj coalfields, sulphur is present in the forms of organic sulphur (OS), pyritic sulphur (PS), and sulphate sulphur (SS). In this perspective, the present study aims to know the different forms of sulphur in coking and non-coking coals of Jharia and Raniganj coalfields. Twenty samples were collected from both the mining areas. The total sulphur content in coking coals varied from 0.28% to 0.55% and in non-coking coals it varied from 0.33% to 0.54%. The distribution pattern of sulphur showed that PS and OS are dominating in both the coalfields. The OS in Jharia field varied from 0.13% to 0.47%, and in Raniganj coalfield it varied from 0.19% to 0.41%. This depicts that both the coalfields were formed under freshwater condition. Similarly, PS varied from 0.01% to 0.21% and from 0.06% to 0.29%, and SS varied from 0.0052% to 0.01% and 0.005%-0.02% in the above fields, respectively. It is noticed that the content of sulphate sulphur is less than 0.1 wt%, which is lower than other forms of sulphur. In the past two decades, sulphur emission has increased with the increase of thermal power plants due to more demand for power, which is one of the causes of global warming. During coal combustion, H₂S and SO_x, are produced and that can react with O₂ and H₂O to form H₂SO₃, H₂SO₄ or H₂S. Thus, sulphur release can respond within the ecosystem in the form of acidic precipitation that may acidify and affect lakes and streams, sub-surface water and historical monuments. In India, coal consumption and ecological contaminations are increasing day by day due to the rapid energy consumption. Therefore, special attention should be given to adopt clean coal technologies though the coal contains less sulphur.

Rapid start of high-concentration denitrification and desulfurization reactors by heterotrophic denitrification sulphur-oxidising bacteria

High sulphide concentrations can be toxic to denitrifying and desulphurising microorganisms. In this study, bioaugmentation was used to solve this problem. Pseudomonas sp. gs1 can tolerate 400 mg/L sulphide and converts most of the sulphide into elemental sulphur after 4 h. A solid inoculum of Pseudomonas sp. h1 was prepared. Two reactors, that is, one with and one without inoculum, were simultaneously run for 60 days. Bioreactor II to which bacterial inoculum was added reached a good treatment performance on day 3. The elemental sulphur concentration of the effluent was 342.6 mg/L. It was maintained at 245.3-333.8 mg/L during the subsequent operation. In contrast, reactor I without inoculants achieved the same performance on day 50. High-throughput sequencing shows that Pseudomonas and Azoarcus are the dominant genera. The abundance of the genus Pseudomonas and related denitrifying sulphur-oxidising bacteria in reactor I increases with the operation time. This phenomenon was confirmed by testing the sqr and gltA genes. The quantitative fluorescence PCR test also proves that the addition of bacteria leads to a rapid increase in the sulphur oxidation and carbon metabolism of the activated sludge in the reactor.

Alkalinity regulation in a sulfur autotrophic denitrifying filter substantially reduced total dissolved solids and sulfate in effluent

Sulfur autotrophic denitrification (SAD) filters are considered a promising technology due to their stable and excellent performance in nitrogen removal, affordable costs, and operational advantages. In this work, a novel operational strategy that employed sodium bicarbonate as an alkalinity source in the autotrophic denitrification filter (S-SAD) was established. With the sufficient supply of alkalinity, the S-SAD reached an excellent denitrification performance (98.01%±0.43%) with a nitrate concentration of 10 mg/L in influent and hydraulic retention time of 3 hrs. The total dissolved solids increment and sulfate concentration in effluent were significantly reduced by one-third, compared with that of the traditional SAD process under the same conditions. The analysis of microbial community indicated that Thiobacilhus, typical species with the functions of simultaneous sulfur oxidation and denitrification, was evidently enriched in the S-SAD. Thus, this present work demonstrated a feasible, relatively cost-effective and environmentally friendly approach to operate SAD towards further application.