Sulfate Production Research Articles

Biodesulfurization of landfill biogas by a pilot-scale bioscrubber: Operational limits and microbial analysis.

Biogas serves as a crucial renewable energy vector to ensure a more sustainable energy future. However, the presence of hydrogen sulfide (H2S) limits its application in various sectors, emphasizing the importance of effective H2S removal techniques for maximizing its potential. In the present study, the limits of a pilot-scale bioscrubber for biogas desulfurization was study in a real scenario. An increase in the superficial liquid velocity resulted in significant improvements in the H2S removal efficiency, increasing from 76 ± 8% (elimination capacity of 6.2 ± 0.5 gS-H2S m−3 h−1) to 97.7 ± 0.5% (elimination capacity of 8 ± 1 gS-H2S m−3 h−1) as the superficial liquid velocity increased from 50 ± 3 m h−1 to 200 ± 8 m h−1. A USL of 161.4 ± 0.5 m h−1 was able to achieve outlet H2S concentrations as low as 3 ± 1 ppmv (H2S removal efficiency of 97 ± 1%) for 7 days. High superficial liquid velocity favoured the aerobic H2S oxidation reducing the nitrate demand. The maximum EC reached throughout the operation was 50.8 ± 0.6 gS-H2S m−3 h−1 (H2S removal efficiency of 96 ± 1%) and a sulfur production of 60%. Studies in batch flocculation experiments showed sulfur removal rates up to 97.6 ± 0.9% with a cationic flocculant dose of 75 mg L−1. Microbial analysis revealed that the predominant genus with sulfo-oxidant capacity during periods of low H2S inlet load was Thioalkalispira-sulfurivermis (61–69%), while in periods of higher H2S inlet load, family Arcobacteraceae was the most prevalent (11%).

Photoactivation of Chlorine and Its Catalytic Role in the Formation of Sulfate Aerosols.

We present a novel mechanism for the formation of photocatalytic oxidants in deliquescent NaCl particles, which can greatly promote the multiphase photo-oxidation of SO2 to produce sulfate. The photoexcitation of the [Cl--H3O+-O2] complex leads to the generation of Cl and OH radicals, which is the key reason for enhancing aqueous-phase oxidation and accelerating SO2 oxidation. The mass normalization rate of sulfate production from the multiphase photoreaction of SO2 on NaCl droplets could be estimated to be 0.80 × 10-4 μg·h-1 at 72% RH and 1.33 × 10-4 μg·h-1 at 81% RH, which is equivalent to the known O3 liquid-phase oxidation mechanism. Our findings highlight the significance of multiphase photo-oxidation of SO2 on NaCl particles as a non-negligible source of sulfate in coastal areas. Furthermore, this study underscores the importance of Cl- photochemistry in the atmosphere.

New insights into the effect of EDTA on pyrite oxidation and N2O emission during pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) is crucial for removing nitrate in groundwater and advanced wastewater treatment. While disulfide is typically seen as the electron donor, the role of iron in pyrite oxidation is often ignored. In this study, Ethylene Diamine Tetraacetic Acid (EDTA) had been proven to have the potential to facilitate pyrite oxidation by promoting the solubility of iron in solution, thereby enhancing the kinetics of pyrite autotrophic denitrification. Firstly, EDTA could improve PAD performance, i.e. the nitrate removal rate at EDTA addition of 5 mM was 0.69 mg N/L•h and twice that of the control. However, high concentrations of EDTA inhibited the activity of the nitrous oxide reductase, resulting in the maximum accumulation of N2O reaching 13.26 mg N/L with an EDTA concentration of 15 mM. Furthermore, the X-ray Photoelectron Spectroscopy (XPS) result indicated that the EDTA addition promoted the production of bioavailable sulfur, with the concentration of S0 at 15 mM EDTA being more than twice higher than that of the control. Transmission electron microscopy (TEM) analysis indicated that EDTA could relieve the damage of iron encrustation on cell activity because it was difficult for EDTA-chelated ferrous iron to penetrate the cell membrane. Microbial community analyses showed an increase abundance of iron oxidizing bacteria, suggesting that EDTA addition promoted the bioavailability of iron for Fe(II) autotrophic denitrification. Overall, this study will provide insights into the understanding of oxidation mechanism of PAD process and the practical application for efficient nitrogen removal and N2O mitigation.

Molecular biomarkers in Electrohypersensitivity and Multiple Chemical Sensitivity: How They Can Help Diagnosis, Follow-Up, and in Etiopathologic Understanding.

Electrohypersensitivty (EHS) and multiple chemical sensitivity (MCS) are new worldwide emerging neurologic disorders in the framework of sensitivity-related environmental pathology. We have recently extended and confirmed our previous observation showing that EHS and MCS share clinically identical symptoms and may co-exist as a unique, common, sensitivity-related neurologic syndrome in 25% of the cases. There is presently no published biological study of these disorders, except the one we have previously published as preliminary. In the present study, we show that EHS and MCS and the combined syndrome share identical biochemical changes. More precisely, by measuring levels of peripheral blood and urine molecular biomarkers in a cohort of 2,018 consecutive cases, we show that both disorders and the combined syndrome can be objectively characterized, in about 90% of the cases, by a decrease in the production of 6-hydroxymelatonin sulfate in urine, while in 30-50% they are characterized by increased levels of histamine and of heat shock proteins (HSP) 27 and/or 70, and of protein S100B and nitrotyrosine in the peripheral blood. Increased levels of histamine and HSP are indicators of low grade inflammation while increased levels of protein S100B and nitrotyrosine are indicators of blood-brain barrier disruption/opening. In addition, we show that in about 15% of the cases anti-myelin autoantibodies can be detected in the peripheral blood, accounting for the occurrence of an autoimmune response. Sensitivity, specificity and reproducibility of the biochemical tests are discussed, as well as the role of these indicators used as biomarkers for the diagnosis and follow-up of patients. We also discuss cases with undetectable biological change for which they can be nevertheless diagnosed by cerebral neurotransmitters analysis in urine and brain imaging. On the basis of these biological data it is suggested that EHS and/or MCS are new brain disorders, generated via a common etiopathogenic mechanism.

INFLUENCE OF HIGH-MOLECULARS COMPOUNDS OF DIFFERENT NATURE ON THE EFFICIENCY OF PURIFICATION THE MOTHER LIQUOR OF MAGNESIUM SULFATE PRODUCTION FROM IMPURITIES Fe3+, Al3+ AND Cr3+ BY ELECTROFLOTATION

The effect of flocculants and surfactants of different nature on the process of purification of the MgSO4 mother liquor from Fe3+, Al3+ and Cr3+ impurities by electroflotation was investigated. The study is aimed at increasing the yield of magnesium sulfate by returning the purified mother liquor to the head of the process at the stage of acid decomposition of serpentinitomagnesite. In the experiments, model solutions with a concentration of MgSO4 – 100 g/l, the content ions of Fe3+ – 50 mg/l, Al3+ – 10 mg/l and Cr3+ – 10 mg/l were used. It was determined that all impurities during pH adjustment turn into slightly soluble compounds at values 6 – 7. For the MgSO4 purification process by electroflotation, the optimal current density was established, which is 0.4 A/l. The duration of the process of purification by electroflotation is 30 min. When studying the effect of surfactants of cationic, anionic, nonionic and amphoteric types on the MgSO4 purification process by electroflotation, it was found that the degree of extraction of Fe3+, Al3+ and Cr3+ impurities does not exceed 10-30%, the exception is the presence of an amphoteric surfactant, in which the degree of extraction of Fe3+ is 77 – 78%. It was found that the greatest efficiency of extraction of Fe3+, Al3+ and Cr3+ impurities from MgSO4 solution is achieved in the presence of anionic flocculant Praestol 2540. The degree of extraction for all components reaches 98-99% already at the tenth minute of the process. Thus, the purification of MgSO4 from Fe3+, Al3+ and Cr3+ impurities by electroflotation in the presence of anionic flocculant Praestol 2540 will allow the purified mother liquor to be returned to the beginning of the process at the stage of sulfuric acid decomposition of serpentinitomagnesite during the production of magnesium sulfate, which will increase the yield of the product.

The inhibitory effect of sunflower oil amide sulfate product on the corrosion aggressiveness of Karabakh clay water

The inhibitory effect of sunflower oil amide sulfate product on the corrosion aggressiveness of Karabakh clay water

Biological Sulfur Production Potential of Local Sulfur Oxidizing Bacteria Culture and Thioalkalivibrio versutus AL2 in Haloalkaliphilic Conditions

Biological Sulfur Production Potential of Local Sulfur Oxidizing Bacteria Culture and Thioalkalivibrio versutus AL2 in Haloalkaliphilic Conditions

A steady-state pH-control model for the biological production of elemental sulfur from sulfate in mining-influenced water

We developed a model to predict pH, alkalinity, and the Langelier Saturation Index (LSI) in coupled systems of hydrogen-based autotrophic sulfate reduction and aerobic oxidation of sulfide to elemental sulfur. To neutralize the biologically generated base, the model allows for the addition of CO2 as part of the gas mixture, the independent addition of HCl or CO2, or a combination of the alternatives. The model was evaluated against the results from a laboratory system for the production of elemental sulfur from sulfate present in mine-tailings water, which is characterized by the presence of elevated sulfate and calcium concentrations. Model results were consistent with measurements of pH, alkalinity, and LSI. The model showed how the acid demands of the coupled reactors vary with pH, being approximately equivalent at pH over 8, when ionized sulfide predominates. Also, while the sulfidogenic reactor was well buffered due to the production of ionized sulfide, the sulfidotrophic reactor in the absence of sulfide and carbonate alkalinity was prone to pH declines. Considering that both reactors operated in the positive range of LSI, the model also indicated that addition of CO2 should be minimized due to increase in the bicarbonate concentration and its effect on increasing the LSI. Furthermore, the model also showed that exclusive reliance on HCl for pH control can be incompatible with Cl− effluent standards, which means that a compromise must be reached between CO2 and HCl additions.

INCREASING THE EXTRACTION OF VACUUM GAS OIL AT THE ELOU-AVT UNIT

The ELOU-AVT unit is part of a large oil refining complex. This unit is designed for primary processing of oils from various fields, as well as their mixtures. Refining is carried out in order to separate oil into separate fractions (gasoline, kerosene, diesel fuel, fuel oil), which are used as raw materials for secondary oil refining at other units. On the territory of modern refineries, in order to increase the depth of processing of petroleum feedstock, in most cases the following technological units are used: – The isomerization unit is designed for the production of low-boiling high-octane isomerizate used as a component of unleaded motor gasolines. For the production of a low-boiling high-octane component, the plant uses the process of low-temperature isomerization of C5-C6 normal paraffins. – The distillate hydrotreating unit is designed to produce high-quality diesel fuel with low sulfur and nitrogen content, high cetane number, and improved low-temperature properties. – The sulfur production unit is designed to produce solid commercial sulfur by the oxidative conversion of hydrogen sulfide into elemental sulfur. The delayed coking unit is designed to process heavy oil residues (straight-run tar) into lighter gaseous, liquid products and petroleum coke. The process of thermal cracking is the basis for the processing of tar. – The catalytic reformer with preliminary hydrotreatment is designed for the processing of gasoline fractions of oil in order to obtain high-quality gasolines and aromatic hydrocarbons, as well as hydrogen-containing gas (HCG), which is widely used both in petrochemistry and in such oil refining processes as: hydrotreating, hydrocracking, isomerization, etc. Oil refining is a multi-stage process of physical and chemical processing of crude oil, which results in the production of a complex of petroleum products. Industrial primary distillation units are divided into atmospheric (AT), vacuum (VT) and combined (for example, AVT, CDU-AVT, etc.). It is impossible to obtain a single marketable oil product from crude oil directly by one process (with the exception of gases), all of them are obtained by sequential processing at several installations. Keywords: ELOU-AVT machine, distillate hydrotreating unit, Oil refining, multi-stage process, primary distillation units

ANALYSIS OF WASTE GAS CLEANING METHODS FROM SULFUR DIOXIDE

It is shown that sulfur dioxide is one of the most common components of harmful emissions into the atmosphere.
 It is presented that a large amount of SO2 is emitted into the atmosphere in the production of sulfuric acid, during the combustion of fuel in thermal power plants, in modern production of surfactants.
 Sulfur dioxide has been shown to be responsible for the formation of acid rain, which is one of the most common forms of pollution worldwide.
 The transport of sulfur compounds over long distances leads to the deposition of sulfur dioxide in soils and waterways.
 It is known that all known methods of waste gas purification are divided into three main groups: ammonia methods, SO2 neutralization methods, catalytic methods.
 In the general case, absorption methods are divided into open and circulating cleaning schemes.
 It is shown that ammonia-acid methods are economical, but require the cost of a scarce product – ammonia.
 The ammonia-sulfuric acid method consists in the treatment of ammonium bisulfite with sulfuric acid.
 When using the ammonia-phosphorus-acid method, phosphorus methods and sulfuric acid are formed.
 The soda method is based on the absorption of sulfur dioxide by a suspension of CaO.
 The lime method is based on the absorption of sulfur dioxide by a suspension of CaO.
 It is shown that when using a sodium hydroxide solution as an absorbent, both open-loop and circulating cleaning schemes are used.
 Open circuits are characterized by simple hardware design, as well as low energy for cleaning.
 It has been shown that catalytic methods for cleaning exhaust gases do not require the use of an absorbent. However, it is necessary to use an expensive catalyst. More often, this method is used at the first stage of cleaning, and at the second – the above methods of cleaning.
 A table with comparative technical and economic indicators is given.
 It is shown that for the production of surfactants it is better to use open-loop purification schemes.
 It is suggested that sodium hydroxide solution can be chosen as the absorbent. With the content of small amounts of sodium sulfite in a solution of sodium hydroxide, it can be used as a neutralizing agent in the neutralization of sulfation products.

ANALYSIS OF WASTE GASES CLEANING METHODS FROM SULFUR DIOXIDE

It is shown that sulfur dioxide is one of the most common components of harmful emissions into the atmosphere. It is stated that a large amount of SO2 is emitted into the atmosphere in the production of sulfuric acid, during fuel combustion in thermal power plants, and in modern production of surface-active substances.
 It has been shown that sulfur dioxide is responsible for the formation of acid rain, which is one of the most common forms of pollution around the world.
 It is stated that all known methods of waste gas purification are divided into three main groups: ammonia methods, SO2 neutralization methods, catalytic methods.
 In general, absorption methods are divided into open and circulation cleaning schemes.
 It is shown that ammonia-acid methods are economical, but require consumption of a scarce product - ammonia.
 The ammonia-sulfuric-acid method consists in treating ammonium bisulfite with sulfuric acid.
 When using the ammonia-phosphoric-acid cleaning method, phosphoric fertilizers and SO2 are formed, which can be further processed into sulfuric acid.
 The sodium method is based on the absorption of sulfur dioxide by a CaO suspension.
 It is indicated that when using a solution of sodium hydroxide as an absorbent, both open and circulating cleaning schemes are used.
 It is shown that catalytic methods of waste gas purification do not require the use of an absorbent. However, it is necessary to use an expensive catalyst. Most often, this method is used at the first stage of cleaning, and at the second - the cleaning methods listed above.
 The table with comparative technical and economic indicators is presented, the choice of one or another cleaning method depends on specific production conditions.
 It is shown that for the production of surface-active substances it is better to use open cleaning schemes, which are distinguished by the simplicity of the equipment design, as well as the low consumption of energy for cleaning.
 It is stated that sodium hydroxide solution can be chosen as an absorbent. If the sodium hydroxide solution contains small amounts of sodium sulfite, it can be used as a neutralizing agent in the neutralization of sulfation products.

Technology for the production of potassium sulphate from mirabilite and potassium chloride of the Tyubegatan deposit

Technology for the production of potassium sulphate from mirabilite and potassium chloride of the Tyubegatan deposit

Photoelectrochemical degradation of organic compounds via formed reactive chlorine and sulfate species by WO3-based photoanodes

Contamination of aquatic environment and drinking water with various organic compounds and microorganisms has negative effect on human and animal health. Conventional cleaning systems consume a lot of energy and are not fully effective, so new cleaning systems are being sought. Photoelectrochemical (PEC) oxidation systems are based on the light-assisted degradation of organic materials on semiconductor electrodes. In this work tungsten oxide (WO3) photoanodes were formed using hydrothermal synthesis. Synthesis was optimized via adjustment of temperature and addition of polyethylene glycol as a structure-directing agent. X-ray diffraction and scanning electron microscopy analysis were performed to evaluate the phase composition, crystallite size and morphology of the layers. PEC activity of the coatings was evaluated using cyclic voltammetry and chronoamperometry. Faradaic efficiencies of light-induced production of reactive sulfate and reactive chlorine species in 0.1 M Na2SO4 and 0.1 M NaCl electrolytes were in the range of 62–93% and 91–96%, respectively. All coatings demonstrated excellent stability during 4 h lasting photoelectrolysis performed in both electrolytes, however photocurrents in chloride medium were found to be almost twice higher compared to sulfate electrolyte. The efficiency of rhodamine B photoelectrochemical degradation in 0.1 M Na2SO4 was significantly lower than in 0.1 M NaCl, however diclofenac was more efficiently decomposed in sodium sulfate electrolyte. Based on a comparative study of PEC and chemical oxidizing treatments, it has been proposed that highly reactive chlorine, sulfate and hydroxyl radicals are the key promoters of photoelectrochemical degradation of organic molecules, however efficiency of degradation is strongly dependent on the nature of organic molecule.

Techno-Economic-Environmental Analysis of Sustainable Anionic Biosurfactant Production from Palm Fatty Acid Distillate.

Currently, there is increased interest in biosurfactants as a substitute for surfactants synthesized from petroleum due to their superior properties and biodegradability. Palm oil derivatives, which can be converted to various products, were selected for biosurfactant synthesis. This paper simulated the biosurfactant production process from palm fatty acid distillate, that is, methyl ester sulfonate (MES), alkyl sulfate, alkyl phosphate, and alkyl carboxylate. Aspen Plus software was used to estimate the thermodynamic properties of intermediate aliphatic organic acids, e.g., methyl ester sulfonic acid, fatty alcohol sulfuric acid, and fatty alcohol phosphoric acid. The chemical process equipment was designed and evaluated to be used in techno-economic analysis, with comparison to petroleum source surfactant production, that is, sodium dodecylbenzenesulfonate (SDBS). The total production cost of each biosurfactant was expressed in terms of minimum selling price. The profitability of each project was determined and compared using three economic indicators: net present value (NPV), payback period, and internal rate of return (IRR). The life cycle assessment methodology was then used to evaluate the environmental impact of surfactant production. The results showed that all surfactant production processes, except for alkyl phosphate, were attractive alternatives as the project yielded a positive value of NPV. The highest NPV of 13.1 million USD was obtained from the MES production process, while the maximum IRR of 79.81% and payback period of 1.49 years were obtained from the alkyl carboxylate production process at a capacity of 1 ton/h. However, the sulfate production process caused more environmental impact than the other two surfactants (MES and carboxylate) due to more CO2 emission per product unit at the level of 2.88 tons CO2/ton surfactant, which is also more than the SDBS surfactant production process that released 2.46 tons CO2/ton surfactant.

Engineering sulfonate group donor regeneration systems to boost biosynthesis of sulfated compounds

Sulfonation as one of the most important modification reactions in nature is essential for many biological macromolecules to function. Development of green sulfonate group donor regeneration systems to efficiently sulfonate compounds of interest is always attractive. Here, we design and engineer two different sulfonate group donor regeneration systems to boost the biosynthesis of sulfated compounds. First, we assemble three modules to construct a 3'-phosphoadenosine-5'-phosphosulfate (PAPS) regeneration system and demonstrate its applicability for living cells. After discovering adenosine 5’-phosphosulfate (APS) as another active sulfonate group donor, we engineer a more simplified APS regeneration system that couples specific sulfotransferase. Next, we develop a rapid indicating system for characterizing the activity of APS-mediated sulfotransferase to rapidly screen sulfotransferase variants with increased activity towards APS. Eventually, the active sulfonate group equivalent values of the APS regeneration systems towards trehalose and p-coumaric acid reach 3.26 and 4.03, respectively. The present PAPS and APS regeneration systems are environmentally friendly and applicable for scaling up the biomanufacturing of sulfated products.

Durability study and mechanism analysis of red mud-coal metakaolin geopolymer concrete under a sulfate environment

The durability of construction materials in sulfate environments is extremely important for their service life. Geopolymer concrete, as a new type of construction material, has been subjected to very little research in sulfate environments and lacks real-time nondestructive testing methods. For this reason, in this study, the physical and mechanical properties of geopolymer concrete synthesized from red mud and coal metakaolin were tested and compared with ordinary silicate cement concrete. The physical phase composition, micro-morphology, porosity and functional group composition of the red mud-coal metakaolin geopolymer concrete were further analyzed using XRD, SEM-EDS, FT-IR and NMR. In addition, the electrochemical properties of the geopolymer were tested by electrochemical impedance spectroscopy and correlated with the diffusion coefficient of the material. The results show that the stability and compressive strength of geopolymer concrete is significantly better than that of ordinary silicate cement concrete in sulfate environment. Ettringite and gypsum type expansion damage were present in ordinary silicate cement concrete. In contrast, only sodium sulfate crystals were found in geopolymer concrete and no expansion products were found. This nearly indicates that the inert interaction between sulfate and hydration products is the main reason for its superior sulfate resistance. There is a significant correlation between the diffusion coefficient of red mud-coal metakaolin polymer concrete and the electrochemical parameter RCP/t and RDCP/t. Therefore, electrochemical impedance spectroscopy testing can be used as a real-time, non-destructive means of monitoring the performance of geopolymer concrete in sulfate environments.

Groundwater situation before production and after production stoppage in Al-Mishraq Sulfur field-1, northern Iraq

This study dealt with the reality of groundwater before Sulfur production in the Al-Mishraq field-1 and after production stopped in the field, by measuring the groundwater table for (44) wells in 2021, and comparing it to the groundwater table measured by the Polish company Centrozap in 1971, the groundwater table was a range between (187.71-205.8)m in 1971, but in 2021 it ranged was between (188.51-196.55)m.Maps of the groundwater movement and water table were created using these data. It turned out that there was little change in the direction of groundwater flow; in both cases, the flow is from the west and northwest towards the east with a slight slope toward the southeast and the Tigris River. As for hydraulic properties, it was analyzed in (29) wells, depending on pumping test data from the reports of Al-Mishraq, It was noted that the values of Transmissivity ranged between (1557.5-24.4) m2/day before production and (5020.6-39.4) m2/day after production, As for hydraulic conductivity, it ranged between (0.26-14.68) m/day before production, and after production, it was between (0.4-48.9) m/day.

Aerosol high water contents favor sulfate and secondary organic aerosol formation from fossil fuel combustion emissions

Fine-particle pollution associated with high sulfate and secondary organic aerosol (SOA) contents still occurs in winter, despite considerable reductions in precursor emissions in China. The chemical mechanisms involved are consistently acknowledged to be linked with aerosol water but remain poorly understood. Here, we present findings demonstrating that the synergistic effect of elevated aerosol water content and particles originating from fossil fuel combustion significantly enhanced the rapid formation of sulfate and SOAs under high humidity conditions during winter in northern China. The presence of high aerosol water content promoted the aging process of particles containing elemental carbon (EC) and facilitated the formation of SOAs. Evidence from single particles reveals an increased potential for SOA formation from primary organic aerosols (POAs) originating from fossil fuel combustion, in the presence of increasing aerosol water. Under conditions of relative humidity exceeding 85%, the multiphase oxidation of SO2 by in-particle nitrite/nitrous acid, generated through reactions involving aged EC-containing and iron-rich particles, as well as aqueous-phase formation of hydroxymethanesulfonate (HMS), led to a substantial increase in sulfate production. This study emphasizes the critical role of aerosol water in the aerosol chemistry concerning sulfate and SOAs, highlighting the urgent necessity to mitigate primary emissions from fossil fuel combustion.

Adapting to seasonal temperature variations: A dynamic multi-subunit strategy for sulfur autotrophic denitrification bioreactors

Elemental sulfur autotrophic denitrification (S0AD) processes are temperature-sensitive, presenting a substantial challenge for the practical implementation of S0AD bioreactors. In this study, a comprehensive methodology for designing and operating S0AD bioreactors was developed, effectively managing fluctuations in nitrogen removal efficiency caused by seasonal temperature variations. Initially, the nitrate removal rate was correlated with simulated on-site temperature and nitrate loading, revealing correlation coefficients of k1, k2, k3, and A as 5.42×10−4, −0.41, 0.04, and 0.13, respectively, to establish a mathematical model for predicting S0AD efficiency. Subsequently, by considering influence factors such as dissolved oxygen and dynamic sulfur consumption, the model was employed to accurately design a pilot-scale S0AD bioreactor for a case study. By utilizing an alternative multi-subunit operation, a stable effluent nitrate concentration of less than 8 mg-N/L was maintained throughout the year. Importantly, this approach resulted in a substantial reduction of 76.8% in excessive nitrate removal, sulfur consumption, and sulfate production. This study aims to provide an optimal design and operation strategy for the practical application of S0AD bioreactors, thereby enhancing reliability and cost-effectiveness in the face of seasonal temperature changes.

Influence of natural cellulose on hydroxyl radical generation by abiotic oxidation of pyrite under acidic conditions

Natural cellulose is one of the most important substances coexisting on the surface of pyrite. Oxidation of pyrite produces hydroxyl radicals (•OH). In this study, a pyrite-cellulose binary system was constructed with natural cellulose to investigate the effect of cellulose on the mechanism of •OH generation via oxidation of pyrite, and the mechanism for abiotic oxidative •OH production by pyrite under the influence of cellulose was investigated with oxidation and quenching experiments and characterization techniques. It was demonstrated that cellulose was chemisorbed onto the pyrite surface and some of the Fe(II) on the pyrite surface was masked, thus inhibiting the reaction between pyrite and O2 and decreasing the •OH production level from 33.54 to 22.48 μM under oxic conditions. In addition, the cellulose caused SS bond breakage, resulting in defects on the pyrite surface, which oxidized H2O to produce •OH in anoxic conditions. Therefore, under anoxic conditions, cellulose promoted the production of •OH and increased the •OH content from 11.85 to 14.78 μM. In addition to •OH, pyrite oxidation also produced SO42−. The amount of SO42− produced by a single pyrite crystal was less than that produced in the pyrite-cellulose system in all cases, and the amount produced under oxic conditions was approximately 10 times greater than that produced under anoxic conditions. More sulfate production indicated more sulfur intermediates during the reaction, such as S2O32−, which may decompose to produce S0 or Sn2− adsorbed on pyrite and decrease the amount of •OH produced. During the oxidation of pyrite by H2O2, cellulose competed with pyrite to react with H2O2, which inhibited the reaction between pyrite and H2O2 and decreased •OH production. Therefore, natural cellulose influenced the abiotic oxidation of pyrite to produce •OH.