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

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%).

Effect of commutation on pressure drop and microbial diversity in a horizontal biotrickling filter for toluene removal

A horizontal biotrickling filter (HBTF) was designed to understand the toluene removal process and microbial community structures. The start-up time of the HBTF, immobilized by the dominant fungi was only about 6 days and the toluene removal efficiency was found to be more than 95% when the inlet toluene concentration remained at around 1560.0 mg/m3. In the stable operation stage of the HBTF, based on not greatly reducing the removal efficiency, a simple and convenient periodic commutation was adopted to reduce the pressure drop (△P) and regulate the distribution of microorganisms in the packing area of the HBTF. The △P decreased from about 90 Pa to 10 Pa after the commutation, which indicated its feasibility. The performance of the HBTF was improved by changing the inlet direction of waste gas flow. When the inlet concentration of toluene was about 640 mg/m3, the removal efficiency was nearly 70.0% before commutation and it remained 95.0-98.0% after commutation. Microbial abundance and diversity analysis showed that the corresponding Shannon-Weiner index was 2.73 and 1.84, respectively. The front section of the HBTF, which was exposed to toluene earlier, consistently exhibited higher microbial diversity than that in the back section. Following commutation, microbial diversity decreased in both the front and back sections, with a maximum decline of around 50%. The main fungi treating toluene were Aplanochytrium, Boletellus, and Exophiala.

Recent advances in biological technologies for anoxic biogas desulfurization

Recovery of the energy contained in biogas will be essential in coming years to reduce greenhouse gas emissions and our current dependence on fossil fuels. The elimination of H₂S is a priority to avoid equipment corrosion, poisoning of catalytic systems and SO₂ emissions in combustion engines. This review describes the advances made in this technology using fixed biomass bioreactors (FBB) and suspended growth bioreactors (SGB) since the first studies in this field in 2008. Anoxic desulfurization has been studied mainly in biotrickling filters (BTF). Elimination capacities (EC) up to 287 gS m^-3 h^-1 have been achieved, with a removal efficiency (RE) of 99%. Both nitrate and nitrite have been successfully used as electron acceptor. SGBs can solve some operational problems present in FBBs, such as clogging or nutrient distribution issues. However, they present greater difficulties in gas-liquid mass transfer, although ECs of up to 194 gS m^-3 h^-1 have been reported in both gas-lift and stirred tank reactors. One of the major disadvantages of using anoxic biodesulfurization compared to aerobic biodesulfurization is the need to provide reagents (nitrates and/or nitrites), with the consequent increase in operating costs. A solution proposed in this respect is the use of nitrified effluents, some ammonium-rich effluents nitrified include landfill leachate and digested effluent from the anaerobic digester have been tested successfully. Among the microbial diversity found in the bioreactors, the genera Thiobacillus, Sulfurimonas and Sedimenticola play a key role in anoxic removal of H₂S. Finally, a summary of future trends in technology is provided.

Characteristics of biotrickling filter system for hydrogen sulfide removal with seasonal temperature variations: A strategy for low temperature conditions

The impact of temperature on the biological removal of hydrogen sulfide (H₂S) from air is critical to its effective application in cold regions or seasons. This study investigated the effect of seasonal temperature variations (7-30 °C) on the H₂S removal performance of a biotrickling filter system, with an effective H₂S elimination capacity of 98.1 g/m³/h (removal efficiency = 83.1 %) achieved at temperatures of 10-12 °C. Biofilm growth was found to be accelerated by increased secretion of extracellular polymeric substances, enhanced biofilm adhesion capacity and relatively high levels of elemental sulfur accumulation, which help to retain heat within the filter bed under cold conditions. High-throughput sequencing showed that the psychrotolerant sulfur-oxidizing bacterium (SOB) Metallibacterium was gradually enriched (54.8 %) at temperatures below 15 °C. The major pathways of sulfur metabolism under low temperature conditions were determined based on the detection of enzymes related to sulfur metabolism. Finally, a strategy to enrich Metallibacterium was proposed to promote the application of biodesulfurization under low temperature conditions.

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.

Biogas purification and ammonia load reduction in sewage treatment by two-stage down-flow hanging sponge reactor

In this study, a two-stage down-flow hanging sponge (TSDHS) reactor was used as biotrickling filter for biogas desulfurization by utilizing the anaerobic digester supernatant (ADS) of sewage sludge of an activated sludge process (ASP). The reactor comprises a closed-type first-stage down-flow hanging sponge (1st DHS) and an open-type second-stage down-flow hanging sponge (2nd DHS) reactors. In the 1st DHS, hydrogen sulfide in biogas was dissolved into the ADS, and then it was oxidized into elemental sulfur and sulfate by microbe using dissolved oxygen and nitrite in the ADS. More than 99.9 % of hydrogen sulfide was removed within 400 s of empty bed residence time, and >50 % of removed hydrogen sulfide was oxidized into elemental sulfur and accumulated at the surface of the sponge carrier in the 1st DHS. The 1st DHS effluent was fed into the 2nd DHS for nitrogen removal via nitrification and sulfur-based denitrification with the recirculation of the 2nd DHS effluent under nonaeration condition. In the 2nd DHS, 36.8 % of ammonia and 5.3 % of total inorganic nitrogen were removed. Sulfurimonas and Halothiobacillus were increased and contributed to the sulfur-based denitrification as well as the accumulation of elemental sulfur in the 1st DHS, respectively. In the 2nd DHS, Nitrosococcus, Nitrobacter, and Sulfuritalea were considered as the contributors of nitrogen removal via nitrification and sulfur-based denitrification. Further, this study shows that a TSDHS reactor can achieve not only desulfurization of biogas in the 1st DHS but also a 3.5 %-15 % reduction of the ammonia load in the 2nd DHS by effective utilization of the ADS during sewage treatment, assuming that the ADS is returned to the ASP.

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.

Simultaneous biodegradation of dimethyl sulfide and 1-propanethiol by Pseudomonas putida S-1 and Alcaligenes sp. SY1: "Lag" cause, reduction, and kinetics exploration

Simultaneous biodegradation of malodorous 1-propanethiol (PT) and dimethyl sulfide (DMS) by Pseudomonas putida S-1 and Alcaligenes sp. SY1 was investigated and the interactions implicated were explored. Results showed that PT was completely degraded in 33 h, while a lag of 10 h was observed for DMS degradation alone, and the lag was even extended to 81 h in the binary mixture. Mechanism analysis found that the lag was mainly attributed to the exposure of DMS degrader (Alcaligenes sp. SY1), rather than PT metabolites and PT degrader. The exposure time and PT concentration also influenced the lag duration much. Citric acid could effectively reduce the lag. Pseudo-first-order model was proved suitable for the description of PT degradation, revealing that PT degradation could be enhanced in presence of DMS with a concentration of < 50 mg L-1. A modified Gompertz model, incorporated the lag phase, was developed for the description of DMS degradation in the mixture, revealing that DMS degradation depended on the initial PT concentration, and when the lag was not considered, PT with low-concentration could promote DMS biodegradation, while a higher concentration (> 20 mg L-1) cast negative effect.

A Two-Stage Biogas Desulfurization Process Using Cellular Concrete Filtration and an Anoxic Biotrickling Filter

A two-stage desulfurization process including an abiotic filtration using cellular concrete waste (first stage) and an anoxic biotrickling filter filling with an inoculated expanded schist material (second stage) was investigated to remove H2S in mimic biogas with limited O2 amount (ranged from 0.5 to 0.8%). The two-stage process was able to satisfactorily remove H2S for all experimental conditions (RE > 97%; H2S concentration = 1500 mg m−3; total Empty Bed Residence Time (EBRT) = 200 s; removal capacity (RC) = 26 g m−3 h−1). Moreover, at a total EBRT = 360 s (i.e., 180 s for each stage), the H2S loading rate (LR) was almost treated by the bed of cellular concrete alone, indicating that abiotic filtration could be applied to satisfactorily remove H2S contained in the gas. According to the H2S concentration entering the biotrickling filter, the majority end-product was either elemental sulfur (S0) or sulfate (SO42−). Thus, the ability of the abiotic filter to remove a significant part of H2S would avoid the clogging of the biotrickling filter due to the deposit of S0. Consequently, this two-stage desulfurization process is a promising technology for efficient and economical biogas cleaning adapted to biogas containing limited O2 amounts, such as landfill biogas.

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 biogas purification: Recent developments, challenges and future prospects

Raw biogas generated in the anaerobic digestion (AD) process contains several undesired constituents such as H₂S, CO₂, NH₃, siloxanes and VOCs. These gases affect the direct application of biogas, and are a prime concern in biogas utilization processes. Conventional physico-chemical biogas purification methods are energy-intensive and expensive. To promote sustainable development and environmental friendly technologies, biological biogas purification technologies can be applied. This review describes biological technologies for both upstream and downstream processing in terms of pollutant removal mechanisms and efficiency, bioreactor configurations and different operating conditions. Limitations of the biological approaches and their future scope are also highlighted. A conceptual framework Driver-Pressure-Stress-Impact-Response (DPSIR) and Strengths-Weaknesses-Opportunities-Threats (SWOT) analysis have been applied to analyse the present situation and future scope of biological biogas clean-up technologies.

Effects of filler voidage on pressure drop and microbial community evolution in fungal bio-trickling filters

Bio-trickling filters (BTFs) can be used to remediate pollution by volatile organic compounds such as toluene. To investigate the effect of filler voidage on pressure drop (△P), two parallel BTFs were constructed using ceramsite with different voidages (47.5% for BTF1 and 55% for BTF2) and inoculated with Fusarium fungus to purify toluene. Commutation and stagnation operations were explored as ways to relieve △P. In BTF1, commutation temporarily relieved △P and maintained it for 7 days. Implementing stagnation on the 178th day for 69 days effectively reduced the △P from 720 Pa/m to below 20 Pa/m, which was maintained for 36 days. Compared with BTF1, the filler in BTF2 effectively delayed the increase in △P for 70 days or more and ensured stable operation for as long as 174 days. High-throughput sequencing revealed that Fusarium was mainly replaced by Protoctista, Fronsecaea and other fungi in both BTFs, although there were significant differences in their microbial communities. The influences of commutation and stagnation operations on fungal evolution were more obvious in BTF2, in relation to both time and space. The results provide guidance for designing better BTFs to treat hazardous pollutants.

Anoxic biogas biodesulfurization promoting elemental sulfur production in a Continuous Stirred Tank Bioreactor

Biological desulfurization of biogas has been extensively studied using biotrickling filters (BTFs). However, the accumulation of elemental sulfur (S°) on the packing material limits the use of this technology. To overcome this issue, the use of a continuous stirred tank bioreactor (CSTBR) under anoxic conditions for biogas desulfurization and S° production is proposed in the present study. The effect of the main parameters (stirring speed, N/S molar ratio, hydraulic residence time (HRT) and gas residence time (GRT)) on the bioreactor performance was studied. Under an inlet load (IL) of 100 g S-H₂S m^-3 h^-1 and a GRT of 119 s, the CSTBR optimal operating conditions were 60 rpm, N/S molar ratio of 1.1 and a HRT of 42 h, in which a removal efficiency (RE) and S° production of 98.6 ± 0.4 % and 88 % were obtained, respectively. Under a GRT of 41 s and an IL of 232 g S-H₂S m^-3 h^-1 the maximum elimination capacity (EC) of 166.0 ± 7.2 g S-H₂S m^-3 h^-1 (RE = 71.7 ± 3.1 %) was obtained. A proportional-integral feedback control strategy was successfully applied to the bioreactor operated under a stepped variable IL.

Simultaneous removal of ammonium from landfill leachate and hydrogen sulfide from biogas using a novel two-stage oxic-anoxic system

Anoxic biodesulfurization has been achieved in several bioreactor systems that have shown robustness and high elimination capacities (ECs). However, the high operating costs of this technology, which are mainly caused by the high requirements of nitrite or nitrate, make its full-scale application difficult. In the present study, the use of biologically produced nitrate/nitrite by nitrification of two different ammonium substrates, namely synthetic medium and landfill leachate, is proposed as a novel alternative. The results demonstrate the feasibility of using both ammonium substrates as nutrient solutions. A maximum elemental sulfur production of 95 ± 1% and a maximum H₂S EC of 141.18 g S-H₂S m^-3 h^-1 (RE = 95.0%) was obtained using landfill leachate as the ammonium source. Next Generation Sequencing (NGS) analysis of the microbial community revealed that the most common genera present in the desulfurizing bioreactor were Sulfurimonas (91.8-50.9%) followed by Thauera (1.1-24.2%) and Lentimicrobium (2.0-9.7%).

Simultaneous removal of bioaerosols, odors and volatile organic compounds from a wastewater treatment plant by a full-scale integrated reactor

Biological control of odors and bioaerosols in wastewater treatment plants (WWTPs) have gained more attention in recent years. The simultaneous removal of odors, volatile organic compounds (VOCs) and bioaerosols in each unit of a full-scale integrated-reactor (FIR) in a sludge dewatering room was investigated. The average removal efficiencies (REs) of odors, VOCs and bioaerosols were recorded as 98.5 %, 94.7 % and 86.4 %, respectively, at an inlet flow rate of 5760 m3/h. The RE of each unit decreased, and the activated carbon adsorption zone (AZ) played a more important role as the inlet flow rate increased. The REs of hydrophilic compounds were higher than those of hydrophobic compounds. For bioaerosols, roughly 35 % of airborne heterotrophic bacteria (HB) was removed in the low-pH zone (LPZ) while over 30 % of total fungi (TF) was removed in the neutral-pH zone (NPZ). Most bioaerosols removed by the biofilter (BF) had a particle size larger than 4.7 μm while bioaerosols with small particle size were apt to be adsorbed by AZ. The microbial community in the BF changed significantly at different units. Health risks were found to be associated with H2S rather than with bioaerosols at the FIR outlet.

Interactions and microbial variations in a biotrickling filter treating low concentrations of hydrogen sulfide and ammonia

A lab-scale biotrickling filter (BTF) packed with porcelain Rasching ring and ceramsite was applied for co-treating of low concentrations of hydrogen sulfide (H₂S) and ammonia (NH₃), as major pollutants typically found in e.g., intensive livestock production facilities. In this study, the outlet gas concentrations of H₂S and NH₃ were used for indicators if the treated gas reached odor-free condition. Overall, excellent removal efficiencies were obtained for both H₂S and NH₃ in the BTF during Stage I (H₂S alone) and Stage II (H₂S and NH₃). Specifically, the H₂S outlet concentration was below the detection limit (∼3.6 ppbv) and the NH₃ outlet concentration was less than 0.4 ppmv when the inlet concentrations of H₂S and NH₃ were around 1.8 ppmv and 35.3 ppmv, respectively. In this case, the running empty bed residence time was 10.2 s. During Stage II, the outlet H₂S concentration was decreased significantly when the inlet NH₃ concentration was increased, likely due to the influence by pH. Meanwhile, the outlet nitrous oxide (N₂O) concentration was kept low (<2% NH₃) during the experiment, suggesting a proper operation of the BTF. After the inlet gas shifted from H₂S alone at Stage I to H₂S and NH₃ at Stage II, the main sulfur-oxidizing bacteria (SOB) species in the BTF switched from Acidithiobacillus to Thiobacillus.

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.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H₂S, but it's difficult to remove high concentration of H₂S in biogas efficiently due to the mass transfer limitation of H₂S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H₂S (about 5000 ppmv) from biogas. The removal efficiency of H₂S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H₂S loading was 143.1 ± 4.5 g/(m³·h). Moreover, the removal capacity of H₂S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m³·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O₂ and H₂S from gas to liquid through gas reflux.

Single-/triple-stage biotrickling filter treating a H2S-rich biogas stream: Statistical analysis of the effect of empty bed retention time and liquid recirculation velocity

Biogas containing H₂S has limited use in electricity and heat production as H₂S can be corrosive to metal equipment. Bio-filtration has proved to be a suitable technology for biogas desulfurization because of economical and environmental benefits over physicochemical techniques. In the present study, a response surface methodology using 3² full factorial design was employed to determine the effects of two operating parameters, namely empty bed retention time (EBRT: 100-180 sec) and liquid recirculation velocity (LRV: 2.4-7.1 m³ m^-2 h^-1) on H₂S removal efficiency (%) in single-stage and triple-stage bio-trickling filters (SBTF and TBTF) treating an H₂S-rich biogas. Quadratic model was found to be the best predictive model for H₂S removal efficiency. The results indicated that H₂S removal efficiency was significantly influenced by the synergistic effect of linear terms of EBRT and LRV with a greater effect associated with EBRT. However, the quadratic term of LRV had an antagonistic effect. The quadratic term of EBRT and cross-product term between EBRT and LRV did not exhibit a significant effect on H₂S removal efficiency. The predicted values from the established models showed a close agreement with the experimental data with the coefficient of determination (R²) of 0.99 for H₂S removal efficiency in both SBTF and TBTF. Response analysis demonstrated that the performance of TBTF was superior compared to SBTF.Implications: Bio-trickling filter technology has gained a lot of attention for biogas desulfurization because it is economically and environmentally superior over chemical methods. Empty bed retention time (EBRT) and liquid recirculation velocity (LRV) are crucial variables influencing the performance of bio-trickling filters. In this work, the authors established a model that can properly predict H₂S removal efficiency in a single/triple bio-trickling filter (SBTF and TBTF) treating H₂S-rich biogas with regard to the individual and interaction effects between EBRT and LRV. Analysis with the help of response surface methodology indicated that TBTF was more efficient compared to SBTF for H₂S removal.

Simultaneous removal of nitric oxide and sulfur dioxide in a biofilter under micro-oxygen thermophilic conditions: Removal performance, competitive relationship and bacterial community structure

The efficiency of a biofilter to simultaneously remove nitric oxide (NO) and sulfur dioxide (SO₂) was investigated under thermophilic (48 ± 2 °C) micro-oxygen (3 vol%) conditions. After the start-up stage (Days 0-14), the stable operation period was divided into three stages. SO₂ inlet concentration remained 500 mg/m³, NO inlet concentrations were 300 mg/m³ (Days 15-40), 500 mg/m³ (Days 41-70) and 700 mg/m³ (Days 71-100). In each stable stage, the removal efficiency of NO and SO₂ exceeded 90%, the maximum removal rates of NO and SO₂ were 98.08% and 99.61%, respectively. The final products of SO₂ were mostly sulphur. Nitrate-reducing bacteria inhibited sulphate-reducing bacteria. Illumina high-throughput sequencing confirmed that the relative abundance of nitrate-reducing bacteria was positively correlated with NO removal efficiency, the relative abundance of sulphate-reducing bacteria was related to the conversion rate of sulphur.

Desulphurisation of Biogas: A Systematic Qualitative and Economic-Based Quantitative Review of Alternative Strategies

The desulphurisation of biogas for hydrogen sulphide (H2S) removal constitutes a significant challenge in the area of biogas research. This is because the retention of H2S in biogas presents negative consequences on human health and equipment durability. The negative impacts are reflective of the potentially fatal and corrosive consequences reported when biogas containing H2S is inhaled and employed as a boiler biofuel, respectively. Recognising the importance of producing H2S-free biogas, this paper explores the current state of research in the area of desulphurisation of biogas. In the present paper, physical–chemical, biological, in-situ, and post-biogas desulphurisation strategies were extensively reviewed as the basis for providing a qualitative comparison of the strategies. Additionally, a review of the costing data combined with an analysis of the inherent data uncertainties due underlying estimation assumptions have also been undertaken to provide a basis for quantitative comparison of the desulphurisation strategies. It is anticipated that the combination of the qualitative and quantitative comparison approaches employed in assessing the desulphurisation strategies reviewed in the present paper will aid in future decisions involving the selection of the preferred biogas desulphurisation strategy to satisfy specific economic and performance-related targets.

Technical and economic investigation of chemical scrubber and bio-filtration in removal of H2S and NH3 from wastewater treatment plant

A detailed techno-economic comparison of a chemical scrubber (CS) and a bio-filter (BF) was conducted over a 45-day time period at a municipal wastewater treatment plant (WWTP), Yazd city. The assessment of emissions quantity indicated that odor emissions from the Yazd WWPT mainly consist of hydrogen sulfide (H₂S) and ammonia (NH₃). It was also found that odor gaseous loading changes corresponding to water consumption pattern in society (R² = 0.922) for H₂S and (R² = 0.978) for NH₃. The highest level of 25 and 3 ppm for H₂S and NH₃, respectively were detected at specific times during the day. The BF system was continuously supplied with Yazd WWPT's off-gas treatment while the CS was only examined at the times during the day when the gas emissions are at the highest level. The removal efficiency of NH₃ and H₂S were found to be affected by their respective loading rate. Additionally, among the various oxidants examined in the CS, the NaOCl solution showed the best results in terms of removal efficiency and compatibility. The experiment revealed almost complete removal of NH₃ while the H₂S removal efficiency remained above 95% for both systems regardless of the operating conditions. This study clearly demonstrates the effectiveness of both systems in treating actual waste gases containing H₂S and NH₃. By comparing the gas loading rate of both systems and considering limitations of the BF system, the CS seems to be more efficient applicable odor control technology from a technical viewpoint. From the economic viewpoint, comparisons revealed that chemical usage and operating expenses were costly parts of the CS and the BF, respectively. The economic indexes of 1.58 €.m^-3. h^-1 and 2.57 €.m^-3. h^-1 were obtained for the BF and CS, respectively, reflecting cost-effectiveness of the BF system.

Characteristics of low H2S concentration biogas desulfurization using a biotrickling filter: Performance and modeling analysis

This study investigated the characteristics of low H₂S concentration biogas biodesulfurization using a lab-scale biotrickling filter (BTF). The influence of operational parameters on H₂S removal efficiency and H₂S distributions in packed bed was evaluated by establishing a counter-current one-dimensional multi-layer BTF model and statistical analysis of the simulation results. The overall biodesulfurization efficiency of counter-current BTF on treating low H₂S concentration was 92.27 ± 10.30%. The H₂S distribution of the BTF packed bed could be predicted by the calibrated BTF model. The influence of the operational parameters on the H₂S distribution of the packed bed was following the sequence of pH > empty bed retention time (EBRT) > gas-to-liquid flow ratio (G/L). The biogas biodesulfurization process was strongly related to the sulphide affinity constant. Moreover, a high substrate concentration of the SOB could further accelerate the biodesulfurization process of the biogas with low H₂S concentration.

Evaluation of Biogas Biodesulfurization Using Different Packing Materials

The packing material selection for a bioreactor is an important factor to consider, since the characteristics of this material can directly affect the performance of the bioprocess, as well as the investment costs. Different types of low cost packing materials were studied in columns to reduce the initial and operational costs of biogas biodesulfurization. The most prominent (PVC pieces from construction pipes) was applied in a bench-scale biotrickling filter to remove the H2S of the biogas from a real sewage treatment plant in Brazil, responsible for 90 thousand inhabitants. At the optimal experimental condition, the reactor presented a Removal Efficiency (RE) of up to 95.72% and Elimination Capacity (EC) of 98 gS·m−3·h−1, similar to open pore polyurethane foam, the traditional material widely used for H2S removal. These results demonstrated the high potential of application of this packing material in a full scale considering the robustness of the system filled with this support, even when submitted to high sulfide concentration, fluctuations in H2S content in biogas, and temperature variations.

Miniaturized Biotrickling Filters and Capillary Microbioreactors for Process Intensification of VOC Treatment with Intended Application to Indoor Air

Typical biofilters and biotrickling filters used for volatile organic compounds (VOCs) control have treatment rates limited to 30-200 g m^-3 h^-1, mostly because they are exposed to dilute VOC streams, have moderate biomass density and activity, and moderate mass transfer coefficients. For these reasons and the concern over releasing bioaerosols and humidity, traditional biofilters and biotrickling filters are not ideal for the treatment of indoor air. Here we report on the development and evaluation of microbioreactors for the intensive treatment of VOCs that could be used for indoor air quality control, when coupled with a VOC microconcentrator (developed separately). The microconcentrator will function to adsorb VOCs from indoor air and release them to the microbioreactor at a higher concentration. The miniaturized bioreactors, with maximized surface area-to-volume ratios, allow for increased mixing and mass transfer of pollutants to the biofilm, resulting in a greater degradation rate of the VOCs. Three different microbioreactors were designed, constructed and their performance for removing vapors of toluene and methanol was assessed. Results showed that they were able to achieve maximum elimination capacities (ECs) for methanol around 1000 g m^-3 h^-1, 780 g m^-3 h^-1, and 12 600 g m^-3 h^-1 for the glass beads packed bed, polyurethane (PU) foam biotrickling filters and capillary microbioreactor, respectively, and around 120 g m^-3 h^-1, 250 g m^-3 h^-1 and 3050 g m^-3 h^-1, respectively, when treating toluene vapors. These values, especially for the capillary microbioreactor, are 40-80 times greater than the rates generally obtained in conventional biofilters and biotrickling filters. The interphase mass transfer coefficient (K_La) was determined. The capillary microbioreactor had values 13-17 times greater than the other two bioreactors, suggesting that improved mass transfer could have contributed to the very high performance observed in the capillary microbioreactor. The results demonstrate that microbioreactors are promising novel technologies for controlling small amounts of organic pollutants.