Sulfide Removal Rates Research Articles

Manganese oxide-based porous electrodes for rapid and selective (electro)catalytic removal and recovery of sulfide from wastewater

Sulfide and its removal is a major concern in wastewater treatment as it represents a threat to human health and the structural integrity of the water distribution system. In this study, we demonstrated for the first time an exceptional performance of manganese oxide-coated graphite felt (GF-MnxOy) electrodes for selective sulfide oxidation to sulfur. Oxidation state, loading, morphology and crystallinity of MnxOy coating was tuned using electrodeposition synthesis method to enable an efficient and selective sulfide oxidation to sulfur. Excellent (electro)catalytic activity of GF-MnxOy yielded up to 25-fold increase in sulfide removal rates compared to pristine GF, both in the open circuit (OC, no applied potential) and under anodic polarization at 0.4 V vs Standard Hydrogen Electrode (SHE). Although anodic polarization did not further enhance sulfide oxidation rate compared to OC, it enabled a continuous re-oxidation of the reduced MnxOy coating after its reaction with sulfide. Thus, restoring of the catalytic properties of MnxOy coating enabled higher sulfide removal rates compared with the OC experiment. The formed elemental sulfur remained at the surface of GF-MnxOy leading to a gradual electrode passivation. The deposited sulfur was successfully dissolved by reversing the polarity of the GF-MnxOy electrode to -0.8 V vs SHE. However, full electrode recovery and restoring of the initial sulfide removal rates could not be achieved as cathodic polarization at -0.8 V vs SHE during longer time (>3 hours) required to remove S0 also caused a partial dissolution of the MnxOy coating. (Electro)catalytic sulfide removal was somewhat decreased in real sewage (2.42 ± 0.02 h-1 vs 0.93 ± 0.15 h-1 in NaNO3 supporting electrolyte and real sewage, respectively). The selectivity of the process towards deposition of elemental sulfur was decreased in real sewage due to partial production of colloidal sulfur, which was presumably caused by diffusion limitation imposed by presence of other ions. Due to lesser extend of GF-Mn2O3 electrode passivation in real sewage, sulfide removal rates remained stable over six subsequent application cycles. In summary, MnxOy-based electrodes demonstrated exceptional (electro)catalytic activity and selectivity for sulfide oxidation to sulfur and thus its complete separation from water. Upscaling of the proposed electrochemical system and its application for the treatment of complex wastewater streams requires further efforts to maintain the selectivity towards deposited sulfur as a final product and allow its complete recovery.

Deep and high-efficiency removal of sulfate through a coupling system with sulfate-reducing and sulfur-oxidizing capacity under haloalkaliphilic condition.

Sulfide from anaerobic treatment of high-sulfate wastewater would always have some adverse effects on downstream processes. In this study, a coupling anaerobic/aerobic system was developed and operated under haloalkaliphilic condition to realize deep and high-efficiency removal of sulfate without production of sulfide. A haloalkaliphilic sulfur-oxidizing strain, Thioalkalivibrio versutus SOB306, was responsible for oxidation of sulfide. The anaerobic part was first operated at optimum condition based on a previous study. Then, its effluent with an average sulfide concentration of 674 ± 33mg·l-1 was further directly treated by a set of 1 l biofilter with SOB306 strain under aerobic condition. Finally, 100% removal rate of sulfide was achieved at aeration rate of 0.75l·l-1·min-1, ORP of -392mV and HRT of 4h. The average yield of elemental sulfur reached 79.1 ± 1.3% in the filter, and the CROS achieved a conversion rate of sulfate to sulfur beyond 54%. This study for the first time revealed the characteristics and performance of the haloalkaliphilic CROS in deep treatment of high-sulfate wastewater, whichpavedthewayforthedevelopmentandapplicationofthis method in the real world.

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

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

Electron Equilibrium Analysis of Integrated Autotrophic and Heterotrophic Denitrification Process Under Micro-aerobic Conditions

The integrated autotrophic and heterotrophic denitrification (IAHD) process, which can simultaneously degrade sulfide, nitrate, and organic carbon with nitrate as a solo electron acceptor, has gained increasing attention as a key unit in industrial wastewater treatment. Micro-aerobic technology, which introduces trace oxygen as an additional electron acceptor, has been demonstrated as an effective strategy for enhancing the IAHD performance. This study focus on the electronic balance calculation of the IAHD process and reveals for the first time that the IAHD process can efficient proceed with an insufficient supply of electron acceptors (nitrate) under micro-aerobic conditions. In the IAHD batch tests, the highest sulfide, nitrate, and acetate removal efficiencies and rates were obtained with an electronic deletion rate peak at 55.1%. Further sulfide oxidizing batch tests demonstrated that the electronic deletion rates were 18.7% and 38.2% under oxygen contents of 5 mL and 10 mL, respectively, in the biological sulfide oxidizing process. Illumina sequencing was used to analyze the microbial community structure in the sulfide oxidation process and indicated Thiobacillus, Thauera, Mangroviflexus, and Erysipelothrix dominated in all community compositions, in which the relative abundance of Thiobacillus increased with an increase in the electronic deletion rate. This study reveals a potential linkage between the electronic gap and the enhanced IAHD performance, which proves new insights into the simultaneous sulfur, nitrogen, and organic carbon removal process.

In-situ remediation of sediment by calcium nitrate combined with composite microorganisms under low-DO regulation

In this work, in-situ remediation of sediment was carried out by combining various methods. The results showed that the treatment effect of Calcium nitrate + composite functional microorganisms + Low-DO (dissolved oxygen) aeration (CN/CFM/LDA) was the best, in which 2.5 g calcium nitrate, 1 g functional bacteria and intermittent aeration (0.1 m3/h, 3 h per day) were utilized for the remediation of 500 g sediments within 40-day experimental period. The DO and oxidation reduction potential (ORP) in overlying water have been improved from 3.23 mg/L to 4.4 mg/L and 25.8 mV to 112.4 mV, respectively. The release fluxes of ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2−-N) and nitrate nitrogen (NO3−-N) were respectively reduced by 30.51%, 13.11% and 77.45% compared with the control and the removal rate of the acid volatile sulfide (AVS) in sediments was 94.14% compared with the original sample. The results of high-throughput sequencing show that the dominant bacterial community in CN/CFM/LDA was transformed into Proteobacteria (relative abundance of 74.17%) at the phylum level and Thiobacillus (relative abundance of 38.52%) at the genus level. The results of 16S functional prediction indicated that the remediation method can enhance the numbers of microbial key enzymes (92360) in the nitrification and denitrification process, where Low-DO aeration can mediate the growth of denitrifying bacteria and promote the performance of key enzymes. In conclusion, the experimental results show that the use of calcium nitrate and composite functional microorganisms under low-DO regulation has a promising remediation effect on sediments of black-malodorous water.

Remediation of simulated malodorous surface water by columnar air-cathode microbial fuel cells

Malodorous surface water is an important worldwide environmental concern. Current remediation methods, such as aeration or the addition of chemicals, are not eco-friendly due to their high energy consumption or secondary pollution. This study proposed a modified columnar air-cathode microbial fuel cell as a sustainable and effective remediation module to improve water quality. The excellent and economic sheet air-cathode (activated carbon and carbon black as the catalyst layer) and a carbon brush anode were applied in the columnar air-cathode microbial fuel cell (MFC). The results after 48 h showed that by providing the anode as an electron acceptor and enriching electrochemically-active bacteria, MFCs with different external resistances (5 k Ω, 30 Ω, and 2 Ω) exhibited the much better capacity to improve water quality than the Blank group. The maximum COD and sulfide removal rates in the MFCs were approximately 86.3% and 100%, respectively, which were higher than those of the Blank group by 30% and 35%, respectively. The MFCs also showed maximum sulfate increments from 28 mg L−1 to 98 mg L−1 compared with the sulfate reduction to 10 mg L−1 in the Blank group. The oxidation reduction potential (ORP) of the MFCs dramatically increased from −281.2 mV to −135.7 mV after 24 h, whereas the ORP of the Blank group decreased to −287.7 mV. The enrichment of the aerobic bacteria Acinetobacter on the anodes and chemolithoautotrophic sulfide oxidation bacteria Sulfuricurvum, Thiovirga and Thiobacillus in the MFCs could also contribute to COD and sulfide removal. Cathode reduction, which could produce small amounts of hydroxyl radicals, might assist with the ORP elevation and the complete oxidation of dissolved sulfide to sulfate.

Anammox granule as new inoculum for start-up of anaerobic sulfide oxidation (ASO) process and its reverse start-up

The feasibility of implementing anaerobic ammonium oxidation (anammox) granules to start up high-loading anaerobic sulfide oxidation (ASO) in an upflow anaerobic sludge bed (UASB) reactor was investigated. An innovation method of the reverse start-up of anammox was also validated. Firstly, the reactor was operated to treat sulfide-rich wastewaters into which nitrite was introduced as an electron acceptor. An high-rate performance with sulfide and nitrate removal rates of 105.5 ± 0.11 kg S m−3 d−1 and 28.45 ± 3.40 kg N m−3 d−1, respectively, was accomplished. Sulfurovum were enriched with the increase of the substrate load and then conquered Candidatus Kuenenia to be the predominant bacteria. Excitation-emission matrix (EEM) spectroscopy showed that the intensities of fluorescence decreased and protein-like substrates were the main components associated with the process of start-up. FT-IR analysis found that the main functional groups indicator were O-H groups. Secondly, the reverse start-up of anammox (achieving 90% TN removal) was achieved immediately when the substrate changed. 16S rRNA analysis indicated the successfully enrichment of anammox bacteria (Candidatus Kuenenia). These results suggest that anammox granules can act as inoculum of high-loading ASO process and the reverse start-up provides a new perspective for the fast initiation of anammox process.

Electrochemical removal of hydrogen sulfide from swine manure

Hydrogen sulfide (H2S) produced in swine manure storage is a safety hazard to both humans and animals. An electrochemical treatment method based on low carbon steel electrodes was developed to reduce aqueous sulfide and emitted H2S concentration from manure storage. At the selected condition (applied voltage of 0.7 V, immersed electrode surface area of 19 cm2/L, initial sulfide concentration around 6 mM, and operating temperature of 19 °C), the process achieved an average sulfide removal rate of 0.97 mg S2−/(cm2·day) for the zero order kinetics model, and a rate coefficient of 0.267/day for the first order kinetics model. The electrical charge consumption was 5.26 C/mg S2−. With the removal of over 90% (95% maximum) of sulfide and H2S, the risk of massive release of H2S can be significantly reduced. The installation of this treatment technology may reduce the risk of manure pump-out in terms of H2S over-exposure and may be applied in similar circumstances where H2S poses threats to health and life.

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 S2− = 600 mg/L, while the peak sulfide and nitrate removal rates (100% and 53.8%) were achieved at S2− = 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.

Removal of hydrogen sulfide with granulated coal ash under aerobic and anaerobic conditions

Annual emissions of fly ash from the burning of coal have increased to approximately 750 million tons. It is hoped that new applications utilizing by-products from coal-fired power plants will contribute to further waste reduction and set the standard for industrial-scale recycling. The purpose of this study was to evaluate the removal rate of hydrogen sulfide by a new recycled material called granulated coal ash, which is produced from coal fly ash from coal thermal electric power stations and blast furnace cement. A batch experiment was carried out to evaluate the removal rate of hydrogen sulfide by granulated coal ash under both anaerobic and aerobic conditions. The granulated coal ash could remove hydrogen sulfide under both anaerobic and aerobic conditions. However, the maximum removal of hydrogen sulfide by granulated coal ash was only 5.1 mg-S g−1 under anaerobic conditions because the manganese oxide which oxidizes hydrogen sulfide to sulfur could not be regenerated under anaerobic conditions. In contrast, the rate constant for hydrogen sulfide under aerobic conditions was high due to the multiplier effect attributed to both increasing Eh and the regeneration of manganese oxide by dissolved oxygen.

Interactive effect of electrode potential on pollutants conversion in denitrifying sulfide removal microbial fuel cells

The denitrifying sulfide removal microbial fuel cell (MFC) provided an approach for treatment of wastewater containing both sulfide and nitrogenous compounds, but the production of sulfate and nitrite need to be prevented. The interactive effect of electrode potential on sulfide and nitrate conversion was investigated using potentiostatic three-chamber MFC. Both abiotic and biotic processes involved in anodic sulfate formation. Rising anode potential led to an increase of sulfide removal rate and a decrease of sulfur formation percent. The suitable anode potential favoring both sulfide removal and sulfur recovery ranged from −188 mV to −146 mV. The nitrate removal rate and gaseous nitrogen formation percent showed an increase followed by a decrease along with the rise of cathode potential. The suitable cathode potential favoring both nitrate removal and gaseous nitrogen formation ranged from −181 mV to −125 mV. Regulating cathode potential through varying the external resistance was feasible, achieving the optimal sulfur formation percent (32.4 ± 1.9%) and gaseous nitrogen formation percent (92.5 ± 0.3%) at a cathode potential of −139 ± 37 mV. The potentiostatic three-chamber MFC is a suitable configuration for investigating the effect of electrode potential on pollutant conversion because its uncontrolled electrode could simulate the electron driving force situation occurring in a MFC.

Simultaneous sulfide removal, nitrification, denitrification and electricity generation in three-chamber microbial fuel cells

Abstract Sulfide and ammonium in some industrial wastewaters need abolishing. The three-chamber microbial fuel cell (MFC), consisting of an oxic-cathode and an anoxic-cathode sharing same anode, was explored to accomplish simultaneous sulfide removal, nitrification, denitrification and electricity generation. It provided a promise of recovering electricity from wastewater containing sulfide and ammonium. The three-chamber MFC run with separate sulfide feeding and ammonium feeding showed preferable nitrogen removal and electricity generation performance as compared to that with a mixed sulfide/ammonium feeding. The desirable feeding sulfide concentration for this MFC was deemed as 193.6 ± 0.8 mg S L−1 considering both pollutant removal and electricity generation performance. Temperature rise favored both pollutants removal and electricity generation but hampered elemental sulfur recovery. The suitable temperature for this MFC was found to be 30 °C, achieving a total nitrogen removal rate of 10.0 ± 1.3 g N m−3 d−1, a sulfide removal rate of 206.5 ± 1.9 g S m−3 d−1, a sulfur recovery efficiency of 28.9%, and an electricity generation of 428.0 ± 26.2 C/batch cycle. The distribution of coulombs to both cathodes affected the performance of nitrogen removal and electricity generation.

Optimum reaction ratio of coal fly ash to blast furnace cement for effective removal of hydrogen sulfide

Reducing hydrogen sulfide concentration in eutrophic marine sediments is crucial to maintaining healthy aquatic ecosystems. Managing fly ash, 750 million tons of which is generated annually throughout the world, is another serious environmental problem. In this study, we develop an approach that addresses both these issues by mixing coal fly ash from coal-fired power plants with blast furnace cement to remediate eutrophic sediments. The purpose of this study is to optimize the mixing ratio of coal fly ash and blast furnace cement to improve the rate of hydrogen sulfide removal based on scientific evidence obtained by removal experiments and XAFS, XRD, BET, and SEM images.In the case of 10 mg-S L−1 of hydrogen sulfide, the highest removal rate of hydrogen sulfide was observed for 87 wt% of coal fly ash due to decreased competition of adsorption between sulfide and hydroxyl ions. Whereas regarding 100 mg-S L−1, the hydrogen sulfide removal rate was the highest for 95 wt% of coal fly ash. However, for both concentrations, the removal rate obtained by 87 wt% and 95 wt% were statistically insignificant. The crushing strength of the mixture was over 1.2 N mm−2 when the coal fly ash mixing ratio was less than 95 wt%. Consequently, the mixing ratio of coal fly ash was optimized at 87 wt% in terms of achieving both high hydrogen sulfide removal rate and sufficient crushing strength.

Preparation of CoWO4/g-C3N4 and its Ultra-Deep Desulfurization Property

The ultra-deep desulfurization of fuel oil has become inevitable for environmental protection. Here, CoWO4/g-C3N4 was used as a catalyst, H2O2 as an oxidant, and 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO4], IL) as an extractant for the oxidative desulfurization of model oil. Scanning electron microscopy, FT-IR spectroscopy, N2 adsorption isotherms, and X-ray diffraction were used to confirm the morphology, structure, and properties of the catalysts. The influence of calcination temperature, loading dose of cobalt, amount of H2O2, reaction temperature, and other parameters were investigated. The removal rate of sulfide in model oil could reach 92.9 % at 80°C in 180 min under the optimal operation conditions (V(oil) = 5 mL, T = 80°C, m(catalyst) = 0.03 g, V(H2O2) = 0.4 mL, t = 180 min, V(IL) = 1.0 mL). In addition, the catalyst was reused five times with no significant reduction in the catalytic activity.

Towards simultaneously removing nitrogen and sulfur by a novel process: Anammox and autotrophic desulfurization–denitrification (AADD)

The combined anammox (anaerobic ammonium oxidation) and autotrophic desulfurization–denitrification (AADD) process represents a promising innovative technology for biological nitrogen and sulfur removal. In this study, an up-flow anaerobic sludge blanket reactor, which was started with anammox and methanogenic granules, was operated for 245days to evaluate the co-treatment of wastewater containing nitrogen and sulfur. The reactor demonstrated good performance in terms of nitrogen and sulfide removal and exhibited excellent behavior for removal of NH4+-N, NO2−-N and S2−-S exceeding 252, 333 and 330mgL−1, respectively. The highest nitrogen removal rate and sulfide removal rate attained were 4.00kgNm−3d−1 and 2.39kgSm−3d−1, respectively, which were also the highest reported values for a coupling-system. The influent NH4+-N:S2−-S and NO2−-N:S2−-S ratios set at 1.74 and 2.20–2.27 are suitable for maintaining system stability. The specific activities of anammox and autotrophic desulfurization–denitrification (SAA and SADD), extracellular polymeric substance (EPS), heme c (an important cofactor of some anammox bacterial enzymes) and the diversity of anammox and autotrophic desulfurization–denitrification (ADD) bacteria were investigated during the operation. The SAA and SADD are regarded as key factors for high efficiency. The granules contained many EPS (128.4–204.5mgg−1VSS) and minor heme c content (1.17μmolg−1VSS). The dominant bacteria belonged to members of Brocadiaceae and Hydrogenophilaceae, a majority of which were anammox bacteria and ADD bacteria, respectively. These observations suggest a new removal process for ammonia, nitrite and sulfide utilizing an uncommon mechanism involving simultaneous anammox and ADD.

Denitrifying sulfide removal process on high-tetracycline wastewater

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

Removal of aqueous hydrogen sulfide by granular ferric hydroxide—Kinetics, capacity and reuse

Aqueous hydrogen sulfide causes a number of sulfide-related problems in sediment/aqueous environments. This paper investigates the use, regeneration and reuse of granular ferric hydroxide (GFH) for removal of aqueous hydrogen sulfide in batch experiments simulating water environments. The sulfide removal by GFH can be described by pseudo-first-order reaction kinetics with respect to dissolved sulfide concentrations and the removal rate was proportional to the GFH dosage. The sulfide removal rate almost tripled as pH decreased from 9.0 to 7.2. An increasing ionic strength (in NaCl solution) and the presence of SO42− in simulated seawater decreased the removal rate while Ca2+ and Mg2+ in seawater hardly had any influence. The aqueous sulfide was mainly oxidized to elemental sulfur with the concurrent reduction of solid Fe(III) to Fe(II). The accumulation of the products (elemental sulfur, iron sulfide and surface-associated Fe(II)) on the surface of GFH eventually led to the latter’s exhaustion. By mixing with water containing dissolved oxygen, the exhausted GFH was able to recover with the simultaneous oxidation of Fe(II) to ferric (hydr)oxides and of solid sulfide to elemental sulfur and sulfur of higher valence states. The recovery in removal capacity could be attributed to the formation of amorphous or less ordered ferric (hydr)oxides on the GFH surface and the reduction in GFH granule size. This study suggests that GFH is a promising renewable material for removal of aqueous hydrogen sulfide in sediment/aqueous systems.

Removal of Sulfide and Production of Methane from Carbon Dioxide in Microbial Fuel Cells–Microbial Electrolysis Cell (MFCs–MEC) Coupled System

Removal of sulfide and production of methane from carbon dioxide in microbial electrolysis cells (MECs) at the applied voltage of 0.7 V was achieved using sulfide and organic compound as electron donors. The removal rate of sulfide was 72% and the Faraday efficiency of methane formation was 57% within 70 h of operation. Microbial fuel cell (MFCs) can be connected in series to supply power and drive the reaction in MECs. Removal of sulfide and production of methane from carbon dioxide in MFCs-MEC coupled system was achieved. The sulfide removal rates were 62.5, 60.4, and 57.7%, respectively, in the three anode compartments. Methane accumulated at a rate of 0.354 mL h(-1) L(-1) and the Faraday efficiency was 51%. Microbial characterization revealed that the biocathode of MEC was dominated by relatives of Methanobacterium palustre, Methanobrevibacter arboriphilus, and Methanocorpusculum parvum. This technology has a potential for wastewater treatments and biofuel production from carbon dioxide.

Kinetic characteristics of biological simultaneous anaerobic sulfide and nitrite removal

The kinetic characteristics of biological simultaneous anaerobic sulfide and nitrite removal were studied in UASB reactor. The results showed that the process was capable of tolerating high influent sulfide and nitrite concentrations of 880 mg S/L and 252.78 mg N/L, respectively. It could hold a high sulfide and nitrite removal loading rates of 13.45 kg S/m3/d and 2.26 kg N/m3/d, respectively. Half-order model, first-order model, and second-order model were applied to predict the performance of the process, which indicated that second-order substrate removal model was best to predict the substrate removal in the bioreactor. Monod model, Michaelis–Menten model and Stover–Kincannon model were used to calculate the kinetic constants, which showed that modified Stover–Kincannon model and modified Michaelis–Menten model were ideal for determining maximum sulfide and nitrite removal rates, respectively.

Release and Transformation of Nitrogen from Sediments during &lt;i&gt;In Situ&lt;/i&gt; Treatment with Calcium Nitrate Injection for Odor Control

Sediments sampled from the Pearl River tributary inlet, with seriously black and odor problem, was treated with calcium nitrate injection in the river simulator. During the course, release and transformation of nitrogen from sediments was investigated. The results showed that calcium nitrate injection is one kind of feasible approaches for sediments odor control. Removal rate of sulfide in sediments reached up to 99% in a month, the color of sediments turned to light brown from black, and the odor disappeared. However, release of NH4+-N and NO3--N was accelerated with calcium nitrate injection, the maximum release concentration of NH4-N and NO3-N was close to 48 mg/L and 417.4 mg/L with injecting dosing of 8%(W/W, dry-weight). Furthermore, continued aeration to overlying water seemed not to be a good way for NO3-N removal. Contrastively, under low DO condition, both concentration of NH4-N and NO3-N took increasing-decrease trends. In this work, TN concentration decreased from 97.7 mg/L to 27.4 mg/L. That is, by maintaining low DO concentration in sediment-water interface, the extra release of nitrogen caused by calcium nitrate injection could be well controlled.