Removal of hydrogen sulfide by complete aerobic oxidation in acidic biofiltration

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

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%).

Low cost and renewable H2S-biofilter inoculated with Trichoderma harzianum

The use of biogas to produce hydrogen is currently gaining more attention. One of the drawbacks for the valorization of biogas is the presence of H2S, a hazardous molecule that can cause damage in the metallic internal structures of industries. In this study, the H2S-removal performance of a fungi-based biofilter was investigated. First, an H2S-resistant fungal species was isolated from an industrial digestate and identified as Trichoderma harzianum. The capacity of this microorganism to metabolize H2S in a mineral medium was confirmed. Then, a bioreactor was constructed and put in place to monitor the elimination of gaseous H2S. A mix of cardboard, perlite, woodchips, and wood pellets was used as filling. Microbial development and the outlet gas composition were monitored during a 60-day experimental process during which H2S was completely removed. 97% of the introduced sulphur was detected in the used filling material (fungal species + packing material) by elemental analysis. 24% of the detected sulphur was identified by ion-exchange chromatography as SO42-. Elemental analysis, gas chromatography, and ion-exchange chromatography were used to determine the bioreactor sulphur balance. Metagenomic analysis underlined that H2S elimination was due to the presence of Trichoderma harzianum with a H2S-specific bacterial consortium.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

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.

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

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

The effect of biofilm growth on the sulfur oxidation pathway and the synergy of microorganisms in desulfurization reactors under different pH conditions

Biofilm growth affects the oxygen transfer in biofilm and thus the oxidation pathway of sulfur and the synergy of microorganisms. In this study, the effect of biofilm growth on the oxidation pathway of H₂S and the synergy of microorganisms in desulfurization reactors under different pH conditions was first discussed to enhance the understanding of desulfurization process. A biotrickling filter (BTF) was operated for 168 days under acidic condition (pH<4.7) and 32 days under alkaline condition (7.0 <pH<10.2). In acidic period, the average growth mass (AGM) of biofilm was 0.04 g/L-BTF/d, and most of S-H₂S was converted to S-SO₄^2- (>89.0%). In alkaline period, the AGM raised to 0.97 g/L-BTF/d, and 77.0% of S-H₂S was transferred to elemental sulfur (S⁰) and polysulfanes (R-S_x-R) accumulated in biofilm. The increase of biofilm and sulfur-oxidizing bacteria activity limited the oxygen transfer in alkaline biofilm, leading to the accumulation of S⁰ and the emergence of an obligate anaerobe- Acetoanaerobium (8.1%). The formation of R-S_x-R may be due to the reaction of S⁰ with thiols produced by a thiol-producing bacterium- Pseudomonas (6.7%). The uneven distribution of oxygen in biofilm caused by biofilm growth complicated the transfer pathway of sulfur and the synergy of microorganisms in desulfurization system.

Hemoglobin I from Lucina pectinata on Collagen Scaffold: A Prospective Hydrogen Sulfide Scavenger

Hydrogen sulfide (H2S), independently of being a toxic gas with a characteristic smell of rotten eggs, is a crucial signaling molecule with significant physiological functions. Given the rapid diffusivity of the gas, it is a challenge to develop robust sensors and biomarkers to quantify free or bound H2S. In addition, there is the need to further develop a robust biosystem to efficiently trap or scavenge H2S from different producing environments. The work presented here uses recombinant met-aquo rHbI (rHbI-H2O) immobilization techniques on collagen to determine its ability to bind H2S due to its high affinity ( $1.24\times {10}^8$  M-1). The hemeprotein will function as a scavenger on this scaffold system. UV-Vis absorption and UV-Vis diffuse reflectance (%R) spectroscopy of rHbI-H2O and rHbI-sulfide (rHbI-H2S) complex in solution and collagen scaffold demonstrated that the heme chromophore retains its reactivity and properties. UV-Vis diffuse reflectance measurements, transformed using the Kubelka-Munk function (K-M function), show a linear correlation ( $R_2=0.9987$ and 0.9916) of rHbI-H2O and rHbI-H2S within concentrations from 1 μM to 35 μM for derivatives. The extraordinary affinity of rHbI-H2O for H2S suggests recombinant met-aquo HbI in a collagen scaffold is an excellent scavenger moiety for hydrogen sulfide. These findings give insight into H2S trapping using the rHbI-H2O-collagen scaffold, where the rHbI-H2S concentration can be determined. Future pathways are to work toward the development of a met-aquo rHbI collagen solution capable of being printed as single drops on polymer, cotton or chromatographic paper. Upon exposure of these matrixes to H2S, the rHbI-H2S complex is formed and its concentration determined using UV-Vis diffuse reflectance technique.

Extremely acidic condition (pH<1.0) as a novel strategy to achieve high-efficient hydrogen sulfide removal in biotrickling filter: Biomass accumulation, sulfur oxidation pathway and microbial analysis

Extremely acidic conditions (pH < 1.0) during hydrogen sulfide (H₂S) biotreatment significantly reduce the cost of pH regulation; however, there remain challenges to its applications. The present study investigated the H₂S removal and biomass variations in biotrickling filter (BTF) under long-term highly acidic conditions. A BTF operated for 144 days at pH 0.5-1.0 achieved an H₂S elimination capacity (EC) of 109.9 g/(m³·h) (removal efficiency = 97.0%) at an empty bed retention time of 20 s, with an average biomass concentration at 20.6 g/L-BTF. The biomass concentration at neutral pH increased from 22.3 to 49.5 g/L-BTF within 28 days. In this case, elemental sulfur (S⁰) accumulated due to insufficient oxygen transfer in biofilm, which aggravated the BTF blockage problem. After long-term domestication under extremely acidic conditions, a mixotrophic acidophilic sulfur-oxidizing bacteria (SOB) Alicyclobacillus (abundance 55.4%) were enriched in the extremely acidic biofilm, while non-aciduric bacteria were eliminated, which maintained the balance of biofilm thickness. Biofilm with optimum thickness ensured oxygen transfer and H₂S oxidation, avoiding the accumulation of S⁰. The BTF performance improved due to the enrichment of active mixotrophic SOB with high abundance under extremely acidic conditions. The mixotrophic SOB is expected to be further enriched under extremely acidic conditions by adding carbohydrates to enhance H₂S removal.

Biological elimination of a high concentration of hydrogen sulfide from landfill biogas

Hydrogen sulfide (H₂S) is one of the main contaminants found in biogas, which is one of the end products of the anaerobic biodegradation of proteins and other sulfur-containing compounds in solid waste. The presence of H₂S is one of the factors limiting the valorization of biogas. To valorize biogas, H₂S must be removed. This study evaluated the performance of a pilot-scale biotrickling filter system on H₂S removal from landfill biogas. The biotrickling filter system, which was packed with stainless-steel pall rings and inoculated with an H₂S-oxidizing consortium, was designed to process 1 SCFM of biogas, which corresponds to an empty bed residence time (EBRT) of 3.9 min and was used to determine the removal efficiency of a high concentration of hydrogen sulfide from landfill biogas. The biofiltration system consisted of two biotrickling filters connected in series. Results indicate that the biofiltration system reduced H₂S concentration by 94 to 98% without reducing the methane concentration in the outlet biogas. The inlet concentration of hydrogen sulfide, supplied to the two-phase bioreactor, was in the range of 900 to 1500 ppmv, and the air flow rate was 0.1 CFM. The EBRTs of the two biotrickling filters were 3.9 and 0.9 min, respectively. Approximately 50 ± 15.7 ppmv of H₂S gas was detected in the outlet gas. The maximum elimination capacity of the biotrickling filter system was found to be 24 g H₂S·m^-3·h^-1, and the removal efficiency was 94 ± 4.4%. During the biological process, the performance of the biotrickling filter was not affected when the pH of the recirculated liquid decreased to 2-3. The overall performance of the biotrickling filter system was described using a modified Michaelis-Menten equation, and the K_s and V_m values for the biosystem were 34.7 ppmv and 20 g H₂S·m^-3·h^-1, respectively.

Microbial interaction promotes desulfurization efficiency under high pH condition

The existence of H₂S in biogas may cause equipment corrosion and considerable SO₂ emission. Commonly used biotrickling filters may cause biogas dilution or generation of explosive mixtures. Compared with biotrickling filters, two-step process such as bioscrubber filters can overcome these shortages. However, its removal efficiency was still limited due to low microbial activity under high pH condition. Here, a bioreactor filter was carried out under pH 9.0. Removal efficiency higher than 99% was achieved under sulfide loading rate reaching 4.24 kg S m^-3d^-1. Results of network and high throughput sequencing showed that Thiobacillus acted as both dominant species (accounting for 75%) and unique kinless hub in this bioreactor. Other bacteria (accounting for 25%) contributed 75% to the network, which implied the intensive interaction between Thiobacillus and others. Sulfide removal ability and pH tolerance of pure bacteria and mixed culture were considered to verify how microbial interaction influenced them. Compared with pure bacteria, mixed culture had better performance under high pH condition, which confirmed that microbial interaction promoted desulfurization efficiency under high pH condition. These results showed that intensive microbial interaction might be the key to enhance sulfide removal efficiency under high pH condition.

Simultaneous removal of carbon dioxide, sulfur dioxide and nitric oxide in a biofilter system: Optimization operating conditions, removal efficiency and bacterial community

Anthropogenic NO_x, SO₂ and CO₂ emission from the fossil-fuel-fired power plants has aroused growing attention. This study investigated the removal performance of CO₂, SO₂ and NO_x in flue gas as well as conversion efficiency of nitric- and sulfur-compounds in liquid phase in a biofilter. In order to develop the potential of the biofilter, simulative industry wastewater was employed as the spray solution. The satisfactory flue gas removal performance (75.23% CO₂, 100% SO₂ and 82.81% NO) were achieved under the optimal operating conditions of biofilter: initial solution pH of 9 and liquid-gas ratio (L/G) of 3. The gas film mass transfer coefficients (k_Ga) results showed that the resistance of gas mass transfer was decreased with increasing the pH value and L/G ratio, respectively. The final transformation product of NO was mostly N₂ while about 78% SO₂ was converted to elemental sulfur. The microbial community analysis results showed that the relative abundance of bacteria with denitrification capacity was increased by 3.05% which might have contributed to the conversion of NO intermediates products in present study. Collectively, this biofilter system achieve a better flue gas removal performance via the proper operation system, which provides an economic feasible strategy of flue gas purification and increases potential for industrial application.

Effect of pH on the performance of an acidic biotrickling filter for simultaneous removal of H2S and siloxane from biogas

Acidic biotrickling filters (BTF) can be used for simultaneous removal of hydrogen sulfide (H₂S) and siloxane from biogas. In this study, the performance of a BTF under different acidic pH conditions was investigated. The removal profile of H₂S showed that 90% of H₂S removal was achieved during the first 0.4 m of BTF height with down-flow biogas. Decamethylcyclopentasiloxane (D5) removal decreased from 34.5% to 15.6% when the pH increased from 0.88 to 3.98. Furthermore, the high partition coefficient of D5 obtained in under higher pH condition was attributed to the higher total ionic strength resulting from the addition of sodium hydroxide solution and mineral medium. The linear increase in D5 removal with the mass transfer coefficient (k_L) indicated that the acidic recycling liquid accelerated the mass transfer of D5 in the BTF. Therefore, the lower partition coefficient and higher k_L under acidic pH conditions lead to the efficient removal of D5. However, the highly acidic pH 0.9 blocked mass transfer of H₂S and O₂ gases to the recycling liquid. Low sulfur oxidation activity and low Acidithiobacillus sp. content also deteriorated the biodegradation of H₂S. Operating the BTF at pH 1.2 was optimal for simultaneously removing H₂S and siloxane.

A multifunctional fluorescent probe for visualizing H2S in wastewater with portable smartphone via fluorescent paper strip and sensing GSH in vivo

In this paper, a bifunctional tri-site fluorescent probe was designed for the first time not only for visualization and quantitative analysis of sensing H₂S in wastewater by coupling paper strip and smartphone (Color recognizer, Xiyi Technology) but also for sensitively monitoring GSH in living cells, which relied on different emission channels and the pH of solutions. The recognition properties of GH towards H₂S/GSH were satisfactorily demonstrated through fluorescence, UV-vis, ¹H NMR and DFT calculations. More importantly, integrated with the paper strip, portable smartphone-sensing platform with a color recognizer app would accomplish cost-effective and rapid assays for colorimetric water quality testing, which displayed huge application potential in fields of environmental monitoring.

Modelling of hydrogen sulfide fate and emissions in extended aeration sewage treatment plant using TOXCHEM simulations

Odors due to the emission of hydrogen sulfide (H₂S) have been a concern in the sewage treatment plants over the last decades. H₂S fate and emissions from extended aeration activated sludge (EAAS) system in Muharram Aisha-sewage treatment plant (MA-STP) were studied using TOXCHEM model. Sensitivity analysis at different aeration flowrate, H₂S loading rate, wastewater pH, wastewater temperature and wind speed were studied. The predicted data were validated against actual results, where all the data were validated within the limits, and the statistical evaluation of normalized mean square error (NMSE), geometric variance (VG), and correlation coefficient (R) were close to the ideal fit. The results showed that the major processes occurring in the system were degradation and emission. During summer (27 °C) and winter (12 °C), about 25 and 23%, 1 and 2%, 2 and 2%, and 72 and 73% were fated as emitted to air, discharged with effluent, sorbed to sludge, and biodegraded, respectively. At summer and winter, the total emitted concentrations of H₂S were 6.403 and 5.614 ppm, respectively. The sensitivity results indicated that aeration flowrate, H₂S loading rate and wastewater pH highly influenced the emission and degradation of H₂S processes compared to wastewater temperature and wind speed. To conclude, TOXCHEM model successfully predicted the H₂S fate and emissions in EAAS system.

Simultaneous removal of siloxanes and H2S from biogas using an aerobic biotrickling filter

The feasibility of simultaneous removal of siloxane and H₂S from biogas was investigated using an aerobic biotrickling filter (BTF). The biodegradation of H₂S in the BTF followed a first-order kinetic model and more than 95 % H₂S was eliminated within a residence time of 0.3 min. The removal of decamethylcyclopentasiloxane (D5) increased with longer empty bed residence time (EBRT). The partition test and microbial community analysis further reveals that up to 52 % removal of D5 was reached mainly by the chemical-absorption in acid recycling liquid. Finally, D5 was converted into mixtures of dimethylsilanediol (DMSD) and hexamethyldisiloxane (L2) via ring-opening hydrolysis in acid liquid and ring-shrinking polyreaction using CH₄ derived from biogas. These operational characteristics demonstrate that the abiotic removal of D5, in addition to biological removal of H₂S in an aerobic BTF can significantly decrease the siloxane loading to the downstream siloxane removing units.

The performance and microbial community in a slightly alkaline biotrickling filter for the removal of high concentration H2S from biogas

In this study, high concentration of H₂S (i.e., 5000 ppmv) in biogas was effectively removed by a slightly alkaline biotricking filter (BTF) with Polypropylene rings as packing material and oxygen from air as the electron acceptor. The results showed that when the inlet loading of H₂S increased from 101.7 to 422.0 g/m³/h, the removal efficiency of H₂S decreased from 100.0% to 91.4%, and the maximum elimination capacity (EC) was 386.0 ± 10.5 gH₂S/m³/h when empty bed retention time (EBRT) was 1.0 min. The slightly alkaline condition could increase the mass transfer of H₂S from gas to liquid phase and avoid the toxic effect of high concentration of H₂S, resulting in high removal performance of H₂S in the system. With the increase of H₂S inlet loading, the ratio of SO₄^2- in bio-desulfurization products gradually decreased, while that of S⁰ increased. At 101.7-210.7 gH₂S/m³/h of inlet loading, SO₄^2- was the dominant product with the ratio of above 50.00%, while S⁰ became the dominant product with 62.96% at 422.0 gH₂S/m³/h of inlet loading. The 16S rDNA sequencing results showed that the dominant genus in the BTF was sulfide-oxidizing bacteria (SOB), with the abundance of SOB decreased with the increase of inlet loading. The dominant genus were Pseudomonas, Halothiobacillus and Sulfurimonas in the BTF at 101.7, 139.8 and 210.7 gH₂S/m³/h of inlet loading, respectively. The SOB Sulfurimonas might play an important role for bio-desulfurization of high concentration of H₂S in a slightly alkaline BTF under high inlet loading of H₂S.

H2S removal from sour water in a combination system of trickling biofilter and biofilter

Desulfurization of sour water was investigated in a combination system of trickling biofilter (BTF) and biofilter (BF) filled with ceramic packing materials. A critical elimination capacity (EC) of 251.93 g S m^-3 h^-1 was obtained for the BTF/BF system during a stepwise increase of sulfide concentration from 10 to 60 g S m^-3. This stepwise increment of loading rate also led to critical ECs of 176.21 and 478.88 g S m^-3 h^-1 for BTF and BF, respectively. A dynamic model describing biological H₂S removal from sour water in the BTF/BF was developed and calibrated by a set of experimental data. The model includes the main processes occurring in the BTF/BF such as mass transfer between phases, diffusion and biological reaction inside the biofilm. The model also considers the intermediate (elemental sulfur) production/consumption and sulfate formation through the different oxidation pathways. The model validation was performed under a starvation period and a dynamic H₂S loading period. A sensitivity analysis was carried out to evaluate the relative importance of the key parameters on the performance of the BTF/BF system. Sensitivity analysis showed that the BTF performance is more affected by the parameters related to H₂S mass transfer.

Operational parameters in H2S biofiltration under extreme acid conditions: performance, biomass control, and CO2 consumption

This paper reports the treatment of gaseous hydrogen sulfide, H₂S, in a biotrickling filter (BTF) under extreme acidic pH conditions (≈ 1.2). The effect of adding thiosulfate (Na₂S₂O₃.5H₂O) to promote biomass growth, feeding low concentrations of ozone to control excess biomass, and the carbon dioxide, CO₂, consumption by the chemolithoautotrophic consortium were evaluated. The results showed a global removal efficiency over 98.0% with loads of H₂S > 50 g m^-3 h^-1 (at 639 ppmv) and a linear relation between H₂S elimination capacity with the CO₂ consumption rate of around 0.1 gCO₂/gH₂S. Supplementing sulfur in the medium with 2 g L^-1 thiosulfate resulted in negative effect performance. Respirometry tests proved that the consortium could not utilize this sulfur form at this pH. Additionally, continuous and intermittent O₃ feeding to the BTF in gaseous concentrations of 98 ± 5.4 mg m^-3 caused a slight decreased in the performance but the biomass activity in the BTF was only slightly affected allowing a quick performance recovery once O₃ addition was suspended.

Removal of Hydrogen Sulfide in Septic Tanks for Treating Black Water via an Immobilized Media of Sulfur-Oxidizing Bacteria

In South Korea, the installation of septic tanks for treating black water (STBW) is regulated even in sewage treatment areas to prevent the black water deposition in combined sewers. STBWs in which black water is anaerobically decomposed generate high concentrations of hydrogen sulfide (H₂S). In this study, an immobilized media of sulfur-oxidizing bacteria (SOB) was used to remove the H₂S. SOB media was prepared by using activated sludge collected from a wastewater treatment plant. Prior to field application, an appropriate cultivation period and aeration rate for SOB activation were estimated through a laboratory-scale test. The SOB was activated after a 23-day cultivation period and an aeration rate of 0.25 L-water/L-air/min. Moreover, the maximum H₂S removal efficiency was observed at a cultivation period of 43 days and an aeration rate of 0.38 L-water/L-air/min. Then, the SOB media was installed on STBWs of various capacities. The H₂S removal efficiency was compared between with and without SOB media. The maximum H₂S elimination capacity with SOB media was 12.3 g/m³/h, which was approximately three times higher than without SOB media. Furthermore, the energy efficiency and oxidation rate were also three times higher with SOB, demonstrating the applicability of SOB for H₂S removal in STBW.

Biological removal of H2S gas in a semi-pilot scale biotrickling filter: Optimization of various parameters for efficient removal at high loading rates and low pH conditions

In this study, a semi-pilot scale biotrickling filter (BTF) was operated in a continuous co-current mode to remove high concentration of hydrogen sulfide (H₂S) at optimum operational conditions. The early startup period of 6 days was needed, and then stable removal of H₂S gas at inlet concentrations up to about 2000 ppm was successfully obtained at gas retention time (GRT) of 15 min and liquid recirculation rate (LRR) of 120 ml/min. The elimination capacities (ECs) increased linearly with increase in H₂S loading rates (HLRs up to 38.5 g/m³ h), but a gradual decrease in removal efficiency was observed from a volumetric HLR of 18.1 g/m³ h. The LRR was further decreased from 120 to 30 ml/min, and the minimum liquid-gas ratio of 0.24 was found without decrease in removal efficiency. The MiSeq analysis revealed the presence of sulphur oxidizing bacteria (SOB) dominated by Acidithiobacillus caldus (>97%) at all portions of BTF.

Technologies for deodorization of malodorous gases

There is an increasing number of citizens' complaints about odor nuisance due to production or service activity. High social awareness imposes pressure on entrepreneurs and service providers forcing them to undertake effective steps aimed at minimization of the effects of their activity, also with respect to emission of malodorous substances. The article presents information about various technologies used for gas deodorization. Known solutions can be included into two groups: technologies offering prevention of emissions, and methodological solutions that enable removal of malodorous substances from the stream of emitted gases. It is obvious that the selection of deodorization technologies is conditioned by many factors, and it should be preceded by an in-depth analysis of possibilities and limitations offered by various solutions. The aim of the article is presentation of the available gas deodorization technologies as to facilitate the potential investors with selection of the method of malodorous gases emission limitation, suitable for particular conditions.

Performance of a compost and biochar packed biofilter for gas-phase hydrogen sulfide removal

The main aim of this study was to evaluate the performance of an aerobic biofilter packed with compost for the removal of gas-phase hydrogen sulfide (H₂S). After 52 d of operation, the biofilter was re-packed by replacing a certain portion (25%, v/v) of the existing compost with biochar and its performance was tested. The steady and transient performance of the biofilter was evaluated by varying the H₂S concentrations from 0.1 to 2.9 g m^-3 at an empty bed residence time (EBRT) of 119 and 80 s, respectively. The maximum elimination capacity (EC_max) of the compost and compost + biochar biofilter were ∼19 and 33 g m^-3 h^-1, respectively, with >99% removal efficiency at an EBRT of 119 s. The compost biofilter showed a quick response to shock loads and the critical load to the biofilter during the shock loading step was ∼81 g m^-3 h^-1.

Performance of a monolith biotrickling filter treating high concentrations of H2S from mimic biogas and elemental sulfur plugging control using pigging

A novel biotrickling filter using a 3D-printed honeycomb-monolith as its filter bed has been proposed and studied in this work and a solution to bed-clogging problems using pigging was demonstrated. The inlet H₂S concentration in the mimic biogas was controlled around 1000 ppm_v and the empty bed gas residence time (EBRT) was 41 s corresponding to a loading rate of 127 g S-H₂S m^-3 h^-1. The influence of different H₂S/O₂ ratios on the removal performance and fate of sulfur end-products was investigated. The results indicated that at a H₂S/O₂ molar ratio of 1:2, an average removal efficiency of 95% and an elimination capacity of 122 g H₂S m^-3 h^-1 was obtained. Under all conditions investigated, elemental sulfur (rather than sulfate) was the dominant end-product which mostly accumulated in the bed. However, the monolith bed design reduced the risk of clogging by elemental sulfur, while bed pigging was shown to be an effective means to remove excess biomass and elemental sulfur accumulated inside the bed and extend the life of the system indefinitely. Altogether, these findings could lead to significant process improvement for biological sweetening of biogas or for removing biomass in biotrickling filters at risk of plugging.

Removal of hydrogen sulfide generated during anaerobic treatment of sulfate-laden wastewater using biochar: Evaluation of efficiency and mechanisms

Removal of hydrogen sulfide (H₂S) from biogas was investigated in a biochar column integrated with a bench-scale continuous-stirred tank reactor (CSTR) treating sulfate-laden wastewater. Synthetic wastewater containing sulfate concentrations of 200-2000mg SO₄^2-/L was used as substrate, and the CSTR was operated at an organic loading rate of 1.5g chemical oxygen demand (COD)/L·day and a hydraulic retention time (HRT) of 20days. The biochar was able to remove about 98.0 (±1.2)% of H₂S for the ranges of concentrations from 105-1020ppmv, especially at high moisture content (80-85%). Very high H₂S adsorption capacity (up to 273.2±1.9mg H₂S/g) of biochar is expected to enhance the H₂S oxidation into S⁰ and sulfate. These findings bring a potentially novel application of sulfur-rich biochar as a source of sulfur, an essential but often deficient micro-nutrient in soils.

Biofilter for generation of concentrated sulphuric acid from H2S

Biofilters are used for the conversion of odorous hydrogen sulphide to odourless sulphate in wastewater treatment plants under the right conditions of moisture and pH. One of the consequences of maintaining the suitable pH and moisture content is the production of large volumes of weakly acidic leachate. This paper presents a biofilter with a maximum H2S elimination capacity of 16.3 g m(-3) h(-1) and removal efficiency greater than 95 % which produces small volumes (1 mL of solution L(-1) of reactor day(-1)) of sulphuric acid with a concentration greater than 5.5 M after 150 days of continuous operation. The concentrated sulphuric acid was produced by intermittently trickling a minimum amount of nutrient solution down the upflow biofilter which created a moisture and pH gradient within the biofilter resulting in an environment at the top for the bacterial conversion of H2S, while sulphuric acid was accumulated at the base. Genetic diversity profiling of samples taken from different sections of the biofilter confirms that the upper sections of the biofilter had the best environment for the bacteria to convert H2S to sulphate. The formation of concentrated sulphuric acid presents an opportunity for the recovery of sulphur from the waste stream as a usable product.

Methane production from a field-scale biofilter designed for desulfurization of biogas stream

The development of a simple and low maintenance field-scale biotrickling filter (BTF) for desulfurization of swine wastewater-derived biogas stream that was also capable of increasing biomethane concentrations was investigated. BTF was continuously fed with wastewater effluent from an air sparged nitrification-denitrification bioreactor installed downgradient from an UASB-type digester. BTF maximum removal efficiency (RE) of 99.8% was achieved with a maximum elimination capacity (EC) of 1,509 g H2S m(-3) h(-1). Average EC obtained with inlet biogas flow rates of 0.024, 0.036 and 0.048 m(3) h(-1) was 718, 1,013 and 438 g H2S m(-3) h(-1), respectively. SO4(-2) and S(0) were the major metabolites produced from biological conversion of H2S. Additionally to the satisfactory biodesulfurization capacity, an average increase in methane concentration of ≅ 3.8 ± 1.68 g m(-3) was measured in the filtered gas stream throughout 200 days of BTF operation. RT-PCR analyses of archaea communities in the biofilm confirmed dominance of hydrogenotrophic methanogens thus corroborating with the observed strong correlation between CO2 removal and CH4 production. Among the three major archaea orders investigated (i.e., Methanosarcinales, Methanobacteriales, and Methanomicrobiales), Methanobacteriales were encountered at highest concentrations (1.9 × 10(11) gene copies mL(-1)). The proposed BTF was robust efficiently removing H2S from biogas stream while concomitantly enhancing the concentration of valuable methane as source of renewable fuel.

Comparison of Removal Behavior of Two Biotrickling Filters under Transient Condition and Effect of pH on the Bacterial Communities

Although biotrickling filters (BTFs) applied under acidic condition to remove H₂S from waste gases have been reported, the removal behavior of the acidic BTF under transient condition which was normal in most industry processes, and corresponding bacterial community have not been thoroughly studied. In the present study, two BTFs were run under neutral (BTFn) and acidic (BTFa) conditions, respectively. The results revealed that the removal performance of BTFa under transient condition was superior to that of BTFn; the maximum H₂S eliminating capacities (ECs) achieved by BTFa and BTFn were 489.9 g/m³ h and 443.6 g/m³ h, respectively. High-throughput sequencing suggested that pH was the critical factor and several other factors including nutrient and the inlet loadings also had roles in shaping bacterial community structure. Acidithiobacillus was the most abundant bacterial group. The results indicated that BTF acclimation under acidic condition may facilitate generating microbial community with high H₂S-degrading capability.

Concentration of field and skim latex by microfiltration - membrane fouling and biochemical methane potential of serum

Cross-flow microfiltration was used to concentrate field and skim latex suspensions and recover the smallest compounds (proteins, sugars, etc.) in permeate (serum solutions). The experiments were performed in a lab-scale microfiltration unit equipped with ceramic membranes. In continuous mode, the operations were performed at constant trans-membrane pressure (0.5 bars), constant cross-flow velocity (3 m/s) and constant temperature (28 ± 2°C). In retentate, the volumetric concentration factor was only close to 2 (about 54% of total solid content, TSC) when concentrating the field latex suspensions, and it reached 10 (close to 40% TSC) when concentrating skim latex suspensions. The quality of retentate suspensions let envisage a significant potential of industrial valorization. The membrane fouling rates appeared as an increasing function of dry rubber content suspension, and the main fouling origin (94%) was linked to a reversible accumulation of suspended compounds on the membrane surface. Permeate appeared as a clear yellow solution containing the smallest soluble organic fractions that show a high degree of biodegradability when using biochemical methane potential tests. The chemical oxygen demand (COD) removal was then higher than 92% and the methane production yield was close to 0.29 NLCH4/gCODremoved. The association of a membrane separation step and anaerobic digestion appeared, then, as a relevant solution to recover rubber content from skim latex suspensions and energy from the anaerobic digestion of serum.

Bio-desulfurization of biogas using acidic biotrickling filter with dissolved oxygen in step feed recirculation

Triple stage and single stage biotrickling filters (T-BTF and S-BTF) were operated with oxygenated liquid recirculation to enhance bio-desulfurization of biogas. Empty bed retention time (EBRT 100-180 s) and liquid recirculation velocity (q 2.4-7.1 m/h) were applied. H2S removal and sulfuric acid recovery increased with higher EBRT and q. But the highest q at 7.1 m/h induced large amount of liquid through the media, causing a reduction in bed porosity in S-BTF and H2S removal. Equivalent performance of S-BTF and T-BTF was obtained under the lowest loading of 165 gH2S/m(3)/h. In the subsequent continuous operation test, it was found that T-BTF could maintain higher H2S elimination capacity and removal efficiency at 175.6±41.6 gH2S/m(3)/h and 89.0±6.8% versus S-BTF at 159.9±42.8 gH2S/m(3)/h and 80.1±10.2%, respectively. Finally, the relationship between outlet concentration and bed height was modeled. Step feeding of oxygenated liquid recirculation in multiple stages clearly demonstrated an advantage for sulfide oxidation.

The effect of oxygen supply on the dual growth kinetics of Acidithiobacillus thiooxidans under acidic conditions for biogas desulfurization

In this study, to simulate a biogas desulfurization process, a modified Monod-Gompertz kinetic model incorporating a dissolved oxygen (DO) effect was proposed for a sulfur-oxidizing bacterial (SOB) strain, Acidithiobacillus thiooxidans, under extremely acidic conditions of pH 2. The kinetic model was calibrated and validated using experimental data obtained from a bubble-column bioreactor. The SOB strain was effective for H₂S degradation, but the H₂S removal efficiency dropped rapidly at DO concentrations less than 2.0 mg/L. A low H₂S loading was effectively treated with oxygen supplied in a range of 2%–6%, but a H₂S guideline of 10 ppm could not be met, even with an oxygen supply greater than 6%, when the H₂S loading was high at a short gas retention time of 1 min and a H₂S inlet concentration of 5000 ppm. The oxygen supply should be increased in the aerobic desulfurization to meet the H₂S guideline; however, the excess oxygen above the optimum was not effective because of the decline in oxygen efficiency. The model estimation indicated that the maximum H₂S removal rate was approximately 400 ppm/%-O₂ at the influent oxygen concentration of 4.9% under the given condition. The kinetic model with a low DO threshold for the interacting substrates was a useful tool to simulate the effect of the oxygen supply on the H₂S removal and to determine the optimal oxygen concentration.

Aerobic desulfurization of biogas by acidic biotrickling filtration in a randomly packed reactor

Biotrickling filters for biogas desulfurization still must prove their stability and robustness in the long run under extreme conditions. Long-term desulfurization of high loads of H2S under acidic pH was studied in a lab-scale aerobic biotrickling filter packed with metallic Pall rings. Reference operating conditions at steady-state corresponded to an empty bed residence time (EBRT) of 130s, H2S loading rate of 52gS-H2Sm(-3)h(-1) and pH 2.50-2.75. The EBRT reduction showed that the critical EBRT was 75s and the maximum EC 100gS-H2Sm(-3)h(-1). Stepwise increases of the inlet H2S concentration up to 10,000 ppmv lead to a maximum EC of 220gS-H2Sm(-3)h(-1). The H2S removal profile along the filter bed indicated that the first third of the filter bed was responsible for 70-80% of the total H2S removal. The oxidation rate of solid sulfur accumulated inside the bioreactor during periodical H2S starvation episodes was verified under acidic operating conditions. The performance under acidic pH was comparable to that under neutral pH in terms of H2S removal capacity. However, bioleaching of the metallic packing used as support and chemical precipitation of sulfide/sulfur salts occurred.

Biogas biodesulfurization in an anoxic biotrickling filter packed with open-pore polyurethane foam

Biogas biodesulfurization by an anoxic biotrickling filter packed with open pore polyurethane foam at the laboratory scale (packed volume 2.4L) has been studied. The biotrickling system was operated for 620 days with biogas supplied continuously and two nitrate feeding regimes were tested (manual and programmed). Biomass immobilization was carried out under the manual nitrate feeding regime and a study was then carried out on the effects on removal efficiency of the following parameters: nitrate source, H2S inlet load, nitrate concentration, sulfate accumulation, temperature, pH and trickling liquid velocity. The effect of increased H2S inlet load was studied under the programmed nitrate feeding regime. The results show that a removal efficiency of 99% can be obtained when working under the following conditions: inlet loads below 130gSm(-3)h(-1), a programmed nitrate feeding system, temperature of 30°C, sulfate concentration below 33gL(-1), a pH between 7.3 and 7.5, and a trickling liquid velocity higher than 4.6mh(-1).

Operational aspects, pH transition and microbial shifts of a H2S desulfurizing biotrickling filter with random packing material

Pall rings, a common random packing material, were used in the biotrickling filtration of biogas with high H2S. Assessment of 600d of operation covered the reactor start-up, the operation at neutral pH and the transition from neutral to acid pH. During the start-up period, operational parameters such as the aeration rate and the trickling liquid velocity were optimized. During the steady-state operation at neutral pH, the performance of the random packing material was investigated by reducing the gas contact time at both constant and increasing H2S loads. The random packing material showed similar elimination capacities and removal efficiencies in comparison with previous studies with a structured packing material, indicating that Pall rings are suitable for biogas desulfurization in biotrickling filters. The diversity of Eubacteria and the structure of the community were investigated before and after the pH transition using the bacterial tag-encoded FLX amplicon pyrosequencing. The pH transition to acid pH drastically reduced the microbial diversity and produced a progressive specialization of the sulfur-oxidizing bacteria community without any detrimental effect on the overall desulfurizing capacity of the reactor. During acidic pH operation, a persistent accumulation of elemental sulfur was found.

Oxidation of hydrogen sulfide in biogas using dissolved oxygen in the extreme acidic biofiltration operation

This work aimed to investigate the interactive effects of empty bed retention time (EBRT), specific hydraulic loading rate (q) and initial pH (pHi) of the aerated recirculating liquid to remove H2S in extreme acidic biofiltration. Biogas containing H2S 6395±2309ppm and CH4 79.8±2.5% was fed to the biofilter as pH of the high dissolved oxygen recirculating liquid swung between pHi to 0.5. Response surface methodology was employed that gave the H2S removal relationship model with R(2) 0.882. The predicted highest H2S removal within the studied parameter ranges was 94.7% at EBRT 180.0s, q 4.0m(3)/m(2)/h and pHi 3.99. Results from separate runs at a random condition were not statistically different from the model prediction, signifying a validity of the model. Additionally, CH4 content in the exit biogas increased by 4.7±0.4%. Acidithiobacullus sp. predominance in the consortia of this extreme acidic condition was confirmed by DGGE.

Performance study of biofilter developed to treat H2S from wastewater odour

Biofiltration is an efficient biotechnological process used for waste gas abatement in various industrial processes. It offers low operating and capital costs and produces minimal secondary waste streams. The objective of this study was to evaluate the performance of a pilot scale biofilter in terms of pollutants' removal efficiencies and the bacterial dynamics under different inlet concentrations of H2S. The treatment of odourous pollutants by biofiltration was investigated at a municipal wastewater treatment plant (WWTP) (Charguia, Tunis, Tunisia). Sampling and analyses were conducted for 150 days. Inlet H2S concentration recorded was between 200 and 1300 mg H2S.m(-3). Removal efficiencies reached 99% for the majority of the running time at an empty bed retention time (EBRT) of 60 s. Heterotrophic bacteria were found to be the dominant microorganisms in the biofilter. The bacteria were identified as the members of the genus Bacillus, Pseudomonas and xanthomonadacea bacterium. The polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) method showed that bacterial community profiles changed with the H2S inlet concentration. Our results indicated that the biofilter system, containing peat as the packing material, was proved able to remove H2S from the WWTP odourous pollutants.