Sludge is produced in sewage treatment plants and is still a problematic waste type after anaerobic digestion. A sustainable sludge management strategy would be to pyrolyze it and obtain biochar suitable for use in biofilters. This article examines the physical and chemical properties of biochar obtained by pyrolyzing sewage sludge at a temperature of 300–600 °C. The pyrolyzed sludge was used in the biofilter as a filler. The results demonstrated biochar packing materials after pyrolysis at 300 °C, 400 °C, 500 °C, and 600 °C, which exhibited porosities of 35%, 42%, 67%, and 75%, respectively. During the research study, it was established that the biofilter showed excellent efficiency (between 55 and 99 percent) when using carbon pyrolyzed at temperatures of 500 °C and 600 °C. In this study, the average growth rates of the number of sulfur-oxidizing microorganisms were 1.55 × 10⁴ CFU/g at the first stage of the biofilter, 2.63 × 10⁴ CFU/g at the second stage, 3.65 × 10⁴ CFU/g at the third stage, 5.73 × 10⁴ CFU/g at the fourth stage, and 2.62 × 10⁴ CFU/g at the fifth stage. The number of sulfur-oxidizing microorganisms in the packing bed of biofilters during the 60-day period of the experiment constantly increased. The experimental results of H₂S purification in biogas were compared with mathematical modeling results. These comparative results revealed a consistent trend: the model-estimated filter efficiency also reached 70–90 percent after 60 days of investigation.

H2S concentrations in biogas are limited by environmental regulations. Because these gases are toxic to human health, cause corrosion, and damage the combined heat and power (CHP) engines and other metallic parts after burning. Hence, the following requirements must be met by a biogas purification method: 1 – high H2S removal efficiency (RE), 2 – stability over a long period of time, 3 – low cost, 4 – minimal biogas dilution, and 5 – straightforward structure. There are various physical, chemical, and biological technologies, which can be undertaken to meet earlier mentioned criteria and efficiently remove H2S from biogas. In this study, electrochemical oxidation, adsorption by zeolite, pressure swing adsorption, adsorption on activated carbon, adsorption on metal oxides, adsorption on nano-particles, metal sulfide precipitation, water scrubbing, membrane separation, organic solvents (amine), microaeration, and purification by sulfur-oxidizing bacteria (anoxic, aerobic, anaerobic), will be introduced, while their pros and cons are compared and discussed in detail.

Background: Following an extensive examination of various biofiltration packing materials within a typical bioreactor (a biofilter) is aiming to remove hydrogen sulfide (H2 S) in the raw biogas. Methods: Both biochar (pre- and post-pyrolysis at 400, 500, and 600 °C) and cellular concrete (CLC) waste, representing organic and inorganic packing materials, respectively, displayed remarkable removal efficiency (RE) performance under dynamic conditions. Nevertheless, the physical and chemical properties of these packing materials play a crucial role in absorbing and trapping H2 S for further filtration from the raw biogas. Key evaluations encompass chemical compositions, porosity, and specific surface area, aligning with contemporary research methodologies (e.g., XRF, Walkley-black, Kjeldahl, BET, T-plot), as analyzed in this study. Results: Subsequently, the modification of these physicochemical properties aimed to demonstrate continued interactions of iron (III) oxide (Fe2 O3 ) with H2 S for chemical modification of CLC waste, and enhance the specific surface area of biochar from 12, 22, and 24 m2 /g to 235, 433, 475 m2 /g, and for porosity from 0.01, 0.42, and 0.025 cm3 /g to 0.096, 4, 0.24 cm3 /g, respectively, for physical modification of biochar samples after pyrolysis at 400, 500, and 600 °C. Conclusion: In the end, improving the possibility of getting better RE from a laboratory-scale biofilter is possible by modification of the most effective physical (adding KOH to biochar and increasing porosity by 9 times, specific surface area by 19 times) and chemical (adding Fe2 O3 to CLC waste) properties of the environment-friendly packing materials.

This study investigated the removal of hydrogen sulfide (H₂S) from biogas using a laboratory-scale biofilter packed with biochar, cellular concrete waste (CLC waste), or polyurethane foam (PUF). The biofilter was tested under varied operational conditions, including H₂S concentrations ranging from 60 to 100 ppm and biogas flow rates of 0.2 to 1.0 L/min, to assess the removal efficiency and elimination capacity (EC). The COMSOL simulation framework was employed to predict biofilter performance and validate the experimental findings. The results revealed that removal efficiencies (REs) varied significantly across the packing materials and operational conditions. The biochar achieved RE values exceeding 92% and an EC of up to 150 g H₂S/m³/h, while the CLC waste demonstrated a moderate RE (~75%) and an EC of 100 g H₂S/m³/h. The PUF exhibited the lowest RE (~48%) but provided structural support for microbial colonization. Notably, the outlet (fourth and fifth) stages of the biofilter consistently outperformed the inlet stages (bottom and first stages), highlighting the influence of the residence time and microbial activity on H₂S removal. These findings provide a foundation for optimizing biofilter design and operational parameters to improve biogas purification efficiency.

This study investigates the removal efficiency of hydrogen sulfide (H₂S) from biogas using a biofilter packed with cellular lightweight concrete (CLC) waste and biochar. A laboratory-scale biofilter was designed and tested under varying operational and environmental conditions, including inlet H₂S concentrations (100–2000 ppm), gas flow rates (0.2–1.0 L/min), temperature (25–35 °C), and humidity (70–90%). The results demonstrated that H₂S removal efficiency reached 95% at low air flow rates and 91% under low H₂S concentrations. In comparison, efficiency declined to 88% at high air flow rates and 87% at high H₂S concentrations. The combination of biochar’s adsorption properties and Fe₂CO₃-modified CLC waste’s catalytic oxidation contributed to the biofilter’s high efficiency and stability. These findings suggest that hybrid biofilters incorporating waste-derived materials provide an environmentally sustainable and cost-effective alternative for biogas purification compared to conventional chemical and physical methods.

This article interrogates the sulfur-oxidation kinetics and spatial biofilm architecture of Acidithiobacillus spp. (DSM 12475, DSM 739) supported on KOH-activated biochar and FeCO₃-modified Cellular Light-weight Concrete (CLC) waste within a 1.0-m controlled biofilter. Pure cultures were anaerobically enriched for 96 h at 30 °C in nitrate-reducing medium, achieving ~10⁷ CFU mL⁻¹ before inoculation. The reactor was operated for 144 h at 30 °C, 45–60% moisture, 0.2–1.0 L min⁻¹ flow, Empty Bed Retention Time (EBRT) 15–60 s, and inlet concentrations of 100–2000 ppm H₂S. Microscopy revealed slower, but highly stable colonization kinetics compared to Pseudomonas spp. Biomass increased from 7.2×10⁵ to 3.1×10⁶ CFU/sample over 72–96 h, with uniform distribution across all six bed layers. Extracellular Polymeric Substance (EPS) visualization confirmed maturation of cohesive biofilms under localized acidification driven by sulfate accumulation. The hierarchical porosity of biochar promoted greater cell loading, while FeCO₃-CLC enhanced catalytic oxidation of thiosulfate and sulfur intermediates, contributing to stable redox cycling. Steady-state operation yielded Removal Efficiencies (RE) of 85–92% and elimination capacities of 14–18 g H₂S m⁻³ h⁻¹ with minimal functional decline across the 144-h cycle. The facultative anaerobic metabolism of Acidithiobacillus spp. enabled sustained oxidation under oxygen-limited and mildly acidic microenvironments – operational regimes in which many conventional SOBs destabilize. Collectively, the results validate the presence of Acidithiobacillus spp. – engineered media systems as robust, acid-tolerant, and long-duration biocatalytic platforms suited for high-sulfur, variable-composition biogas purification. Article in English. Bioplėvelės formavimosi kinetika ir sieros oksidacijos efektyvumas kultivuojant Acidithiobacillus spp. biofiltro įkrovoje iš KOH modifikuotos bioanglies ir FECO₃ impregnuotų CLC atliekų Santrauka Šiame straipsnyje analizuojama Acidithiobacillus spp. (DSM 12475, DSM 739) sieros oksidacijos kinetika ir bioplėvelės erdvinė struktūra, susiformuojanti 1,0 m aukščio biofiltro įkrovoje. Bioplėvelė buvo formuojama ant KOH aktyvuotos bioanglies ir FeCO₃ modifikuoto akytojo lengvojo betono (CLC) atliekų. Prieš mikroorganizmų įterpimą į biofiltrą grynos bakterijų kultūros buvo anaerobiškai papildomos nitratus redukuojančioje terpėje 96 valandas 30 °C temperatūroje, kol pasiekė maždaug 10⁷ CFU mL⁻¹ oncentraciją. Paskui filtras buvo eksploatuojamas 144 valandas palaikant 30 °C temperatūrą, 45–60 % drėgmę ir 0,2–1,0 L min⁻¹ dujų srautą. Biodujų buvimo trukmė biofiltre (EBRT) svyravo nuo 15 iki 60 s, o įeinanti pradinė H₂S koncentracija – nuo 100 iki 2000 ppm. Mikrobiologiniai tyrimai parodė, kad Acidithiobacillus spp. kolonizacijos kinetika buvo lėtesnė nei Pseudomonas spp., tačiau pasižymėjo dideliu stabilumu. Per 72–96 val. biomasės kiekis padidėjo nuo 7,2 × 10⁵ iki 3,1 × 10⁶ CFU mėginyje, o mikroorganizmai tolygiai pasiskirstė visuose šešiuose biofiltro sluoksniuose. Tarpląstelinių polimerinių medžiagų (EPS) struktūros stebėjimas patvirtino vientisos bioplėvelės formavimąsi ir jos brendimą. Šis procesas vyko lokalioje rūgštėjančioje mikroaplinkoje, kuri susidarė dėl elementinės sieros kaupimosi. Daugialygė bioanglies porų struktūra sudarė tinkamas sąlygas gausesniam mikroorganizmų prisitvirtinimui ir jų biomasės kaupimuisi. Su FeCO₃ modifikuotos akytojo lengvojo betono (CLC) atliekos pagerino tiosulfato ir sieros tarpinių junginių katalizinę oksidaciją bei palaikė stabilų oksidacijos–redukcijos procesą. Veikiant pastovios būsenos režimu biofiltras užtikrino 85–92 % sieros vandenilio šalinimo efektyvumą (RE) ir 14–18 g H₂S m⁻³ h⁻¹ šalinimo pajėgumą, o per 144 val. trukmės valymo procesą nenustatyta reikšmingų sistemos veikimo sutrikimų. Fakultatyvinis anaerobinis Acidithiobacillus spp. metabolizmas leido palaikyti nuolatinę sieros oksidaciją net esant ribotam deguonies kiekiui ir šiek tiek rūgščiai mikroaplinkai. Tai sąlygos, kuriomis daugelis kitų sierą oksiduojančių bakterijų tampa nestabilios. Apibendrinant galima teigti, kad Acidithiobacillus spp. pagrindu sukurti inžineriniai biofiltro užpildai yra patikima, rūgštims atspari ir ilgalaikio veikimo biokatalizinė sistema, tinkama biodujoms valyti esant didelėms ir kintančioms sieros vandenilio koncentracijoms. Reikšminiai žodžiai: vandenilio sulfido šalinimas, biofiltras, bioanglis, akytojo lengvojo betono (CLC) atliekos, mikrobiologinis sieros junginių skaidymas, biodujų valymas.