H2S Removal Research Articles

Simulation of acid gas removal unit using DIPA+TEA amine solvent

Due to the inexpensive cost of amine solvent, more than 95 % of natural gas (NG) processing plants use an acid gas removal unit that utilizes an aqueous amine solvent to remove sour gas components such as carbon dioxide (CO2) and hydrogen sulfide (H2S). Different technologies are available to capture CO2 from NG. However, chemical absorption is the most reliable and used technology all over the world. However, it is challenging to determine the amine blend’s optimal composition for the effective removal of CO2 and H2S and solvent regeneration. This is mainly due to the difference in reservoir gas compositions, affecting gas removal efficiency and solvent regeneration energies. The present investigation addresses the performance of using a novel solvent blend of diisopropanolamine (DIPA) and Triethanolamine (TEA) to determine the absorption capacity of CO2 & H2S using Aspen HYSYS software. A study on the effects of solubility on CO2 absorption was performed at varying pressure (10-80 bar) and temperature (25°C to 50°C). The percentage of CO2 removal increased from 80% to 98% as the temperature increased from 25°C to 50°C. The results revealed that the concentration of CO2 and H2S in sweet gas decrease with the increase in pressure while the concentration of CO2 and H2S increases with the increase in temperature.

In-situ removal of odorous NH3 and H2S by loess modified with biologically stabilized leachate

The loess regions distribute widely in Northwestern China, North America and Eastern Europe. For these regions, landfill is a suitable technology for solid waste treatment. However, as a landfill cover material, loess is not very effective in controlling the emission of malodorous gases. The present study modified loess with biologically stabilized leachate, and investigated the capacities and mechanisms of the modified loess to remove odorous NH3 and H2S. The removal rates of NH3 and H2S at different acclimation time, targeted gas concentrations and temperatures were measured. It was found that the NH3 removal rate of the modified loess was up to 0.08 μmol/(g·hr), which was 1.8 times that of the virgin loess. The H2S removal rate of the modified loess was up to 1.74 μmol/(g·hr), which was 1.25 times that of the virgin loess. The half-meter loess layer modified by biologically stabilized leachate achieved nearly 100% removal of H2S. The improvement of NH3 and H2S removal ability was mainly due to the enrichment of relevant microorganisms. This work proposed a novel method for in-situ control of malodorous pollutants in landfills in the loess regions, and proved that the in-situ removal of NH3 and H2S using the loess modified with biologically stabilized leachate is feasible and cost-effective.

Ternary metal oxide nanocomposite for room temperature H2S and SO2 gas removal in wet conditions

A ternary Mn–Zn–Fe oxide nanocomposite was fabricated by a one-step coprecipitation method for the remotion of H2S and SO2 gases at room temperature. The nanocomposite has ZnO, MnO2, and ferrites with a surface area of 21.03 m2 g−1. The adsorbent was effective in mineralizing acidic sulfurous gases better in wet conditions. The material exhibited a maximum H2S and SO2 removal capacity of 1.31 and 0.49 mmol g−1, respectively, in the optimized experimental conditions. The spectroscopic analyses confirmed the formation of sulfide, sulfur, and sulfite as the mineralized products of H2S. Additionally, the nanocomposite could convert SO2 to sulfate as the sole oxidation by-product. The oxidation of these toxic gases was driven by the dissolution and dissociation of gas molecules in surface adsorbed water, followed by the redox behaviour of transition metal ions in the presence of molecular oxygen and water. Thus, the study presented a potential nanocomposite adsorbent for deep desulfurization applications.

Adding organics to enrich mixotrophic sulfur-oxidizing bacteria under extremely acidic conditions—A novel strategy to enhance hydrogen sulfide removal

Biotreatment of high load hydrogen sulfide (H2S) can lead to rapid acidification of a bioreactor, which greatly challenges the application of bio-desulfurization technology. In this study, the bio-desulfurization performance was improved by enriching acidophilic mixotrophic sulfur-oxidizing bacteria (SOB) by adding organics under extremely acidic conditions (pH < 1.0). A biotrickling filter (BTF) for the removal of H2S was established and operated under pH < 1.0 for 420 days. In the autotrophic period, the maximum H2S elimination capacity (ECmax-H2S) was 135.8 g/m3/h with biofilm mass remaining within 11.1 g/L-BTF. The autotrophic SOB bacterium Acidithiobacillus was dominant (62.1 %). When glucose was added to the BTF system, ECmax-H2S increased by 272 % to 464.3 g/m3/h as biofilm mass increased to 22.3 g/L-BTF. The acidophilic mixotrophic SOB bacteria Mycobacterium (78.4 %) and Alicyclobacillus (20.7 %) were enriched while Acidithiobacillus was gradually eliminated (<0.1 %). Furthermore, the major sulfur metabolism pathways were identified to explore the desulfurization mechanism under extremely acidic conditions. To maintain optimal desulfurization performance and avoid biofilm overgrowth in the BTF system, biofilm mass should be maintained within 20–22 g/L-BTF. This can be achieved by adding 1.0 g/L-BTF glucose every 20 days under a load rate of H2S in 50–90 g/m3/h and a trickling liquid velocity of 1.8 m/h. Extremely acidic conditions eliminated non-aciduric microorganisms so that the addition of organics can increase the abundance of acidophilic mixotrophic SOB (>99 %), thus offering a novel strategy for enhancing H2S removal.

A novel process of low-temperature fractionation combined with extractive distillation for H2S removal from natural gas

H2S is a common component of natural gas. In order to meet the quality standards for U.S. commodity natural gas that contains less than 5.7 mg/m3 of H2S, it is necessary to process the natural gas to remove H2S. Since H2S will form azeotropes with ethane and propane in natural gas, it is impossible to achieve complete separation of H2S by ordinary distillation columns. Therefore, a novel low-temperature fractionation combined with extractive distillation process is proposed and designed, which can achieve the removal of H2S from sulfur-containing natural gas and obtain sweet gas(almost pure methane), ethane product and H2S gas. The process consists of three steps: demethanization with low temperature, deethanization with extractive distillation and H2S recovery. Extensive simulation and analysis have confirmed that extractive distillation using high molecular weight, high boiling point benzene homologs (toluene, o-Xylene, p-Xylene, m-Xylene) as extractant is a good method to separate ethane-H2S azeotrope. Furthermore, the effects of parameters such as the number of column stages, the reflux ratio, the location of feed stream inlet stage, the type of extractants, the inlet stage location of extractant, the molar flow rate of extractant on the product purity and the column duty have been studied, and the optimal applicable ranges of different parameters are finally determined. The simulation results show that o-Xylene is the best extractant for the separation of ethane and H2S. Under the economic optimization, the minimum total annual cost for the demethanizer is $952,611 per year and the minimum total annual cost for the deethanizer is $2,026,364 per year.

Electrochemically enhanced liquid-phase catalysis for simultaneous purification of phosphine, hydrogen sulfide and hydrogen cyanide: Interactions and synergistic mechanisms

The growth of modern industry has resulted in the unregulated release of an increasing number of industrial tail gases (especially toxic and hazardous gases), putting significant strain on the environment and human health. In this paper, a simple and effective electrochemically enhanced liquid-phase catalysis approach was proposed for simultaneous removal of PH3, H2S, and HCN from industrial tail gases. Pd(II) and Cu(II) were used as the liquid-phase catalyst. Under the synergistic effect of electrochemical reactions and liquid-phase catalysis, PH3, H2S, and HCN were finally oxidized to PO43-, elemental sulfur, SO42-, CO2, and N2. HO·, H2O2, and HO2·generated in the electrochemical process had a strong oxidative ability. Influencing parameters such as the catalyst types, electrochemical conditions (electrode voltage, electrode current, etc.), access sequence and mono/bi-component catalyst were investigated. The law of interaction among PH3, H2S and HCN components in the purification process was analyzed in detail. At a constant voltage of 3 V, the optimal purification effect was achieved when Pd/Cu catalyst was used, PH3, H2S and HCN purification rates were approximately 84 %, 100 % and 95 %. Furthermore, the system is more stable when mimicking the removal of PH3, H2S, and HCN from tail gas. This study proposes a practical strategy for removing poisonous and hazardous industrial waste gases at the same time. It significantly reduces hazardous exhaust emissions and enables cleaner industrial processes.

Research and Performance Evaluation on Selective Absorption of H2S from Gas Mixtures by Using Secondary Alkanolamines

Exploring new solvents for efficient acid gas removal is one of the most attractive topics in industrial gas purification. Herein, using 2-tertiarybutylamino-2-ethoxyethanol as an absorbent in a packed column at atmospheric pressure was examined for selective absorption of H2S from mixed gas streams. In the present work, the acid gas load, H2S absorption selectivity, acid gas removal ratio, amine solution regeneration performance, and corrosion performance were investigated through evaluating experiments absorbing H2S and CO2 by using methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol. The experimental results illustrate that the H2S absorption selective factors were 3.88 and 15.81 by using 40% methyldiethanolamine and 40% 2-tertiarybutylamino-2-ethoxyethanol at 40 °C, respectively, showing that 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, even better than methyldiethanolamine. Based on the consideration of cost, we added 5% TBEE to 35% MDEA to form a blended aqueous solvent. To our satisfaction, the blended amine solvent obtained a 99.79% H2S removal rate and a 22.68% CO2 co-absorption rate, while using the methyldiethanolamine alone achieved a 98.33% H2S removal rate and a 23.52% CO2 co-absorption rate; the blended solvent showed better H2S absorption efficiency and selectivity. Taken together, this work provides valuable information for a promising alkanolamine for acid gas removal, and the preliminary study has found that the aqueous blend of methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, which not only extends the application field for sterically hindered amines, but also opens up new opportunities in blended solvent design.

Fabrication and application of novel core–shell MIL-101(Cr)@UiO-66(Zr) nanocrystals for highly selective separation of H2S and CO2

Removal of H2S and CO2 is essential in diverse industrial applications such as natural gas treatment for avoiding their corrosion, toxicity, and environmental damages. To improve selective separation of H2S and CO2 at ambient temperature, we designed novel core–shell-structure MOFs based on a porous MIL-101(Cr) as seeds and a less porous UiO-66(Zr) shell. MU-4 and MU-8 nanocrystals, with different shell growth times, were synthesized and characterized by different techniques. The adsorption isotherms of H2S, CO2, CH4, and N2 on individual and hybrid samples were measured, using a volumetric method in a wide pressure region and at different temperatures. MU nanocrystals exhibited high adsorption capacity for both H2S (20.62 mmol g−1 at 15 bar) and CO2 (17.21 mmol g−1 at 35 bar), elevated up to 84.4 % and 121.8 % compared to pristine UiO-66(Zr). Most importantly, ideal adsorbed solution theory (IAST) showed that adsorption selectivity of H2S/CH4, H2S/N2, CO2/CH4, and CO2/N2 was significantly improved up to 7.8 %, 47.0 %, 32.1 % and 59.9 % at highest pressure compared to pristine MIL-101(Cr). Besides additional open metal sites, this high separation efficiency was ascribed to the size exclusion separation due to optimized pores diameter of MU nanocrystals. According to impressive preferential gas adsorption along with excellent cyclic adsorption–desorption performance and thermal stability, MU nanocrystals can broaden the horizon of H2S and CO2 capture and separation.

Removal of H2S in an extremely acidic-biotrickling filter: Evaluation of removal performance and characterization of microbial communities

A cost-efficient, environmentally friendly, and extremely acidic biotrickling filter is essential for desulfurization to recover elemental sulfur and sulfate for extensively remediating H2S. The present study investigated the H2S removal capacity, accumulation of desulfurization products, sulfur balance, microbial community, and the H2S biodegradation kinetics. The results showed that when the empty bed retention time (EBRT) decreased from 180 s to 60 s, the removal efficiency of H2S decreased from 100% to 95.4%, and the elimination capacity increased from 18.0 ± 1.3–51.5 ± 3.2 gH2S m–3 h–1. Furthermore, with the increase of EBRT, the proportion of SO42–-S in the biodesulfurization products gradually decreased from 74.83% to 38.71%, whereas that of S0-S increased from 16.04% to 53.30%. The content of polysaccharide (PS), protein (PN), and the change of PN/PS values during the H2S removal process were studied. Moreover, 16 S rRNA high-throughput sequencing analysis showed that Acidithiobacillus, Thiobacillus, Sulfuricurvum, and Sulfobacillus were the main genera in the removal of H2S, and their total abundance was higher than 68.00%. In addition, the system viability and robustness were proved by shock loads and starvation regimes.

Urea-modified Cu-based materials: Highly efficient and support-free adsorbents for removal of H2S in an anaerobic and dry environment

In this work, we report a novel urea-modified copper-based material (XUrea@Cu) obtained by directly calcinating a mixture of urea and copper nitrate. This material enables the efficient purification of H2S under dry and anaerobic conditions. The performance test results showed that the H2S capacity of the optimal adsorbent (2Urea@Cu) could reach 364.2 mg(H2S)∙gsorbent-1, which is much superior to those of other adsorbents in the literature. Further study demonstrates that the ultra-desulfurization performance of 2Urea@Cu is mainly attributed to the extensive alkaline site, the high concentrations of active oxygen, and the abundance of oxygen vacancy; which are quite effective for capturing H2S (acidic and strong reducibility). Interestingly, the deactivation adsorbent (De-2Urea@Cu) is mainly composed of high-purity CuS, which means that the Urea@Cu adsorbent can simultaneously achieve efficient purification of H2S and recovery of sulfur resources since CuS is a valuable product. In addition, in-situ FT-IR and theoretical calculation results indicate that H2S molecules dissociate on the CuO(111) surface by stepwise dehydrogenation, while S combines with adjacent Cu to form CuS. The consumption of active components (CuO) and the accumulation of reaction products (CuS) are the primary reasons for the deactivation of adsorbents. Considering the simple preparation process, low cost, and excellent H2S adsorption activity, these urea-modified copper-based materials are very promising H2S adsorbents.

Review of Hydrogen Sulfide Removal from Various Industrial Gases by Zeolites

Hydrogen sulfide (H2S) removal from various industrial gases is crucial because it can cause huge damage to humans, the environment, and industrial production. Zeolite possesses huge specific surface area and well-developed pore structure, making it a promising adsorbent for H2S removal. This review attempts to comprehensively compile the current studies in the literature on H2S removal in gas purification processes using zeolites, including experimental and simulation studies, mechanism theory, and practical applications. Si/Al ratio, cations of zeolite, industrial gas composition and operating conditions, and H2S diffusion in zeolites affect desulfurization performance. However, further efforts are still needed to figure out the influence rules of the factors above and H2S removal mechanisms. Based on an extensive compilation of literature, we attempt to shed light on new perspectives for further research in the future.

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 ppmv 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.

Degradation of mixed typical odour gases via non-thermal plasma catalysis

The simultaneous treatment of H2S and NH3 typical odours by plasma was investigated and the co-treatment of both was found to have a facilitating effect the conversion. The degradation efficiency and by-product emissions of single plasma technology and plasma co-catalytic two-stage technology were compared and the degradation mechanism was further analyzed. The results show that in the single plasma technology conversion experiment, the conversion rate of the treated odours mixture is higher than that of the treated single odours, and the by-product emissions of SO2 and NOx are also reduced due to the reaction of intermediate products and by-products during the reaction process. The absolute removal of the odours mixture is optimal when treating at a gas flow rate of 6 L/min, a voltage of 16 kV and a frequency of 200 Hz. The M(Ce,Cu)-Mn/13X loaded catalyst was synthesized by co-precipitation method. Under the conditions of gas flow rate of 3–7 L/min, the efficiency of H2S and NH3 removal and the reduction of by-product emission were ranked as: uncatalyzed > Cu-Mn/13X > Ce-Mn/13X, which proved that Ce-Mn/13X showed better catalytic activity and application value.

Carbon-Rich carbon nitride nanocatalysts for H2S selective oxidation

Selective catalytic oxidation (SCO) of hydrogen sulfide (H2S) to sulfur exhibits significant advantages for H2S removal, including high efficiency, mild operating conditions and thermodynamic unlimitation for H2S removal. Recently, polymeric carbon nitride (PCN) has emerged as a candidate for H2S selective oxidation reactions, benefiting from its aromatic C-N hybridized π-conjugated system for H2S adsorption/dissociation and good sulfur tolerance. However, its performance is greatly hampered by the lack of sufficient surface active sites for O2 adsorption and activation. Herein, we demonstrate that the incorporation of carbon atoms in PCN matrix to constructure carbon-rich carbon nitride nanosheets is a facile strategy to advance the desulfurization performance. The carbon atoms uniformly incorporated in PCN backbones can effectively extend the aromatic π-conjugated electronic system and create abundant oxygen-containing functional groups on the surface. The improved electronic configurations and surface properties are beneficial for the adsorption and activation of H2S and O2. In addition, the nanosheet morphology favors for increasing the surface area of the material, thereby promoting the mass transfer of H2S and O2 during the desulfurization process. The optimized carbon-rich carbon nitride nanosheets exhibit a H2S conversion of 99% and a S selectivity up to 95% for H2S selective oxidation at 200 °C, and the reaction is not restricted by mass transportation and heat transfer at such a high conversion rate. This synthetic strategy allows ample choice of low-cost and easy-available organic precursors for the large-scale production of the desulfurization catalysts.

Effect of Bimetallic-Activated Carbon Impregnation on Adsorption–Desorption Performance for Hydrogen Sulfide (H2S) Capture

This study reports on the impregnation of bi-metallic adsorbents based on commercial coconut activated carbon (CAC), surface-modified with metal acetate (ZnAc2), metal oxide (ZnO and TiO2), and the basic compound potassium hydroxide (KOH). The morphology of the adsorbents was then characterized with SEM-EDX, the microporosity was determined using Brunauer–Emmett–Teller (BET) analysis, the thermal stability was investigated via thermogravity analysis (TGA), and functional group analysis was undertaken with Fourier-transform infrared (FTIR) spectroscopy. These modified adsorbents were subjected to a real adsorption test for H2S capture using a 1 L adsorber with 5000 ppm H2S balanced for N2, with temperature and pressure maintained at an ambient condition. Adsorption–desorption was carried out in three cycles with the blower temperature varied from 50 °C to 150 °C as the desorption condition. Characterization results revealed that the impregnated solution homogeneously covered the adsorbent surface, effecting the morphology and properties. Based on this study, it was found that ZnAc2/TiO2/CAC_DCM showed a significant increase in adsorption capacity with the different temperatures applied for the desorption in the second cycle: 1.67 mg H2S/g at 50 °C, 1.84 mg H2S/g at 100 °C, and 1.96 mg H2S/g at 150 °C. ZnAc2/ZnO/CAC_DCM seemed to produce the lowest percentage of degradation in the three cycles for all the temperatures used in the adsorption–desorption process. Therefore, ZnAc2/ZnO/CAC_DCM has the potential to be used and commercialized for biogas purification for H2S removal.

Tuning the redox activity of polyoxometalate by central atom for high-efficient desulfurization

The efficient removal of hydrogen sulfide (H2S) is of great importance for various industrial processes such as the sewage stream depollution and syngas upgrade. Oxidative desulfurization with polyoxometalates (POMs) has been proved one of the most attractive ways to remove H2S from the systems, while the role of the central atom in POMs has not been well evaluated. Herein, we demonstrate the desulfurization activity of POMs could be well internally switched by the central atoms. In particular, the SVI-centered POM of [Himi]SMo, exhibited greatly enhanced desulfurization performance compared to its structural analogs with GeIV or PV as central atoms, with a breakthrough H2S capacity of 627.0 mg g−1 compared to 39.5 and 54.9 mg g−1 respectively, well surpassing state-of-the-art H2S desulfurizes. In addition, its activity was well maintained at a wide range of temperature (0–50 °C) and pH (4−9). More interestingly, electrochemical re-oxidation of the H2S laden [Himi]SMo was found much more active than the fresh one, achieving H2S capacity up to 2174 mg g−1. Air involved in-situ re-oxidation and S-O metathesis mechanisms were proposed and experimentally evidenced to explain the high capacity. This work opens a new concept for the rational design of POMs in terms of H2S removal.

Evaluation of H2S gas removal by a biotrickling filter: Effect of oxygen dose on the performance and microbial communities

A cost-efficient and environmentally friendly biofiltration system is essential for desulfurization to recover elemental sulfur and sulfate for extensively remediating H2S. This work investigated the H2S removal capacity, accumulation of desulfurization products, sulfur balance, microbial community, and the pathway for sulfide oxidation under different O2 doses (1%, 3%, 5%, and 10%). The results showed that the removal efficiency of H2S increased from 94.1% to 100.0% with the increase of O2 dose. At 1% O2, the elimination capacity (EC) was 5.72 ± 0.33 gH2S m–3 h–1, and about 78.13% of S0-S was generated. However, with stepwise increase of O2 concentration to 10%, the EC became 6.00 ± 0.35 gH2S m–3 h–1, and SO42–-S was the dominant product at 80.39%. Furthermore, the sulfur balance was verified by calculating the proportion of sulfur compounds (S0-S, SO42−-S, and SO32−-S) and comparing the microstructure of packing material in the biotrickling filter. Moreover, 16 S rRNA high-throughput sequencing analysis showed that the cooperation of sulfur-oxidizing bacteria in the biofiltration system was the key to the stable and efficient removal of H2S. In addition, possible reaction pathways in which H2S was transformed to S0 and SO42− were proposed.

Recent Attempts on the Removal of H2S from Various Gas Mixtures Using Zeolites and Waste-Based Adsorbents

Natural gas, biogas, and refinery gas all include H2S, which has adverse effects not only on the environment and human health but also on the equipment and catalysts that are employed in the relevant processes. H2S is removed from the aforementioned gases using a variety of techniques in order to fulfill the necessary sales criteria and for reasons of safety. The adsorption method stands out among various other approaches due to its straightforward operation, high level of efficiency, and low overall cost. This technique makes use of a variety of adsorbents, such as metal-organic frameworks (MOFs), activated carbon, and zeolites. The use of zeolite-based adsorbents is by far the most common of these various types. This is due to the specific properties of zeolite-based adsorbents, which include a high adsorption capacity, the ability to be regenerated, a high temperature stability, a diversity of types, the possibility of modification, high efficiency, and low cost. In addition, research is being done on adsorbents that are made from inexpensive raw materials in order to remove H2S. This article focuses on zeolites, zeolite modifications, and wastes as an adsorbent for the removal of H2S, all of which have been investigated fruitfully in recent years, as well as the promising applications of zeolites.

Biogas desulfurization and calorific value enhancement in compact H2S/CO2 absorption units coupled to a photobioreactor

Biogas desulfurization is in many cases the main purification step required for energy generation. This is the case of wastewater treatment plants, waste management facilities or intensive livestock farms where the produced biogas is burned in situ to generate thermal and electrical power. The potential of compact H2S/CO2 absorption units coupled to a photobioreactor for biogas desulfurization was investigated in the present study. Two absorption unit configurations, bubble column and airlift, were evaluated in terms of H2S and CO2 removal at biogas retention times of 10 and 30 min, and liquid-to-biogas flowrate ratios of 1/1 and 4/1. Complete H2S removal was achieved in both absorption unit configurations regardless of the biogas retention time or liquid-to-biogas flowrate ratio applied. These results confirmed the feasibility of setting biogas retention times as short as 10 min, resulting in absorption units up to 49-fold smaller than that required for biogas upgrading up to biomethane. Biogas calorific value increases from 14.7 ± 4.0–19.3 ± 7.2 % were observed in the airlift configuration, while increases from 5.5 ± 2.2–25.2 ± 4.0 % were recorded in the bubble column. N-NO3- removal rates ranging from 16 ± 4–25 ± 5 g m−3 d−1 were recorded under the experimental conditions tested, no significant differences in nitrogen removal being observed between the airlift and bubble column configurations. The significant removal of CO2 that can be achieved at short biogas retention times certainly constitutes a motivation for implementing photobioreactors for biogas desulfurization, broadening the application niches of microalgae-bacteria systems in the context of renewable energy production.

Efficacy of H2O2 on the removal kinetics of H2S in saltwater aquaculture systems, and the role of O2 and NO3−

The occurrence of hydrogen sulfide (H2S) represents a challenge for recirculating aquaculture systems (RAS) under saline conditions. Even low concentrations of the toxic gas can result in sudden mass mortalities of fish, leading to large economic losses. There is an urgent need for efficient strategies to remove H2S, which can be applied effectively with a short response time, to prevent the risk of H2S-induced casualties. This study examines the kinetics of the two common oxidants applied to rearing water in a RAS facility; oxygen (O2) and hydrogen peroxide (H2O2) and evaluates their efficiency and applicability for the removal of H2S in an industrial RAS. Furthermore, we tested whether nitrate (NO3−) can be an oxygen donor in the chemical oxidation of H2S. The baseline oxidation rates of H2S by O2 were determined in air-equilibrated seawater (SW) and RAS water (RASW). The feasibility of using H2O2 as a practical treatment was evaluated by testing increasing H2O2 to H2S ratios in SW. In addition, RASW dilutions that yielded different concentrations of NO3− and total chemical oxygen demand (TCOD) were tested to identify their effects on H2S removal. The half-lives (t½) of H2S, derived from O2 oxidation rates, were considerably shorter in SW (118.5 ± 28.6 min) compared to RASW (168.0 ± 18.7 min). The addition of a 1:1 mole ratio of H2O2 to H2S, significantly increased the removal rate and decreased the half-life (t½) of H2S in SW to 29.5 ± 6.6 min. Further increasing H2O2:H2S ratios to 2:1 and 4:1, reduced t½ to 21.7 ± 5.2 and 17.4 ± 6.1 min, respectively. Similarly, a dosage of H2O2 at a ratio of 1:1 in RAS water resulted in a considerably shorter t½ of 86.1 ± 10.1 min. The influence of organic matter on the required H2O2 dose was demonstrated by the t½, which were reduced by 49% in RAS water and 75% in SW. NO3− was not found to be involved in the chemical removal of H2S. The results provide an improved understanding of the influence of RAS water chemistry and quality on H2S kinetics and the direct applicability of the kinetics for treating acute H2S levels in RAS to avoid mass mortalities. In conclusion, the addition of H2O2 is an efficient water treatment technology for H2S removal, and by adjusting H2O2 dosages accordingly to the concentrations of H2S and specific systems water parameters, a t½ <30 min can be achieved. Thus the technology is applicable in an industrial RAS, as a treatment process for acute levels of the hazardous gas H2S that is easily implemented, and safe for the fish.