The biological removal of hydrogen sulfide in biogas is an increasingly adopted alternative to conventional physicochemical processes because of its economic and environmental benefits. In this study, a real-scale biotrickling filtration (BTF) process packed with polypropylene carrier was used to investigate the removal of high concentrations of H2S in biogas from an anaerobic digester. The results show that H2S in biogas was entirely removed under different inlet concentrations of H2S from 2,923 to 4,400 ppmv, and the elimination capacity of H2S in the filter achieved about 52.71 g H2S/m3/h). In addition, the process efficiency was found to be independent of the inlet H2S concentration. The removal of high concentrations of H2S in biogas was accomplished by the BTF process with SOB (Acidithiobacillus thiooxidans), which is active in the acidic environment (pH 1.5–3.5). In addition, the process efficiency was found to be independent of the inlet H2S concentration. Consequently, a real-scale BTF process allowed the potential use of biogas and the recovery of elemental sulfur resources simultaneously.

  • H2S in biogas produced from WWT sludge was removed by a real-scale BTF plant.

  • The process efficiency was found to be independent of inlet H2S concentration.

  • The elimination capacity of the system reached a maximum of value.

  • The real-scale BTF unit was found to provide sufficient removal efficiency for H2S in the biogas.

Graphical Abstract

Graphical Abstract
Graphical Abstract

Anaerobic digestion (AD) is commonly used in the treatment of organic waste, such as agricultural waste, sewage sludge and organic forms of municipal solid waste. During this process, approximately 95% of the organic matter and 95% of the energy present in the substrate are contained in the biogas (Guerrero et al. 2015). The most important ingredients in the biogas produced by the digestion of treatment sludges through anaerobic processes are: 60–70% methane (CH4), 30–35% carbon dioxide (CO2), 1–2% hydrogen sulfide (H2S) and 0.3–3% other gases (Al Mamun & Shuichi Torii 2015). The components of biogas can vary depending on the used substrate for their production (Rasi et al. 2007). If the substrate used for biogas production contains sulfur, the formation of H2S is inevitable (Chaiprapat et al. 2015; Dumont 2015).

The concentration of H2S in biogas varies from a few hundred to ten thousand ppm depending on the amount of bioavailable sulfur compounds in the feedstock and the outcome of the competition among sulfate-reducing bacteria, acetogens and methanogens for the organic substrates (Stams et al. 2005). A presence of a high concentration of H2S causes corrosion on equipment and increases the maintenance costs. In particular, due to the corrosive effect on the gas engines, engine life is shortened, the service/maintenance costs increase, and the conversion of biogas to electricity decreases (Rasi et al. 2011). For this reason, H2S must be removed from the produced biogas.

Actually, H2S is produced under anaerobic conditions because sulfate (SO42−) acts as an electron acceptor while organic compounds are decomposed biologically (Yan et al. 2018). H2S is produced by anaerobic degradation of sulfur-containing compounds (mainly proteins) and reduction of anionic species (especially SO42−) in the feedstock of the digester (Ramos et al. 2013). Kuenen (1975) proposed the mechanism of H2S removal that occurs through a series of physico-chemical processes and biological reactions, summarized by Equations (1)–(4) below.

  • (a)
    H2S(g) dissolution in water
    (1)
  • (b)
    H2S biological oxidation to SO42−
    (2)
  • (c)
    H2S biological oxidation to S(s)
    (3)
  • (d)
    S(s) biological oxidation to SO42−
    (4)

For the removal of H2S in biogas, solid phase adsorption, liquid phase absorption, membrane seperation, chemical, biological, and thermal methods are used (Rasi et al. 2011; Lin et al. 2013; Angelidaki et al. 2018; Peluso et al. 2019). The biological desulfurization of biogas can be performed in additional units mainly using biofilters and biotrickling filters during digestion process and by applying microaerobic conditions directly in anaerobic digestors (Ramos et al. 2013). This biological desulfurization treatment method for the cleaning of contaminated biogas is a relatively new trend and is of great interest. On the other hand other gas desulfurization methods have high operation costs and produce wastes that must be disposed of. The biological desulfurization method is economically more advantageous and more environment friendly than the other methods. In addition, this treatment method is also more useful because the gas stream contains biodegradable or biconvertable compounds (Tomas et al. 2009).

In bioreactor systems, the H2S is dissolved into the film, followed by the oxidization of H2S by sulfur-oxidizing bacteria (SOB) with oxygen in the liquid phase (Duan et al. 2006; Kobayashi et al. 2012; Nhut et al. 2020). High elimination capacity (EC) and stability in the presence of severe operating conditions are required for bioreactor systems to apply biological methods for the removal of hydrogen sulfide in a biogas stream. A large number of biodesulfurization processes are present, such as the biofilter processes (Montebelloa et al. 2014; Ramos & Fdz-Polanco 2014; Rodriguez et al. 2014), the bioscrubber processes (Valeroa et al. 2019), and the process using headspace of the digesters (headspace process) (Ramos & Fdz-Polanco 2012). The differences between these systems are the phase of the biomass (suspended or fixed), the state of the liquid phase (flowing or stationary) and the state of having or not having a carrier material (Ramirez et al. 2009). In real-scale biotrickling filtration (BTF), the waste airstream passes through a bed that is packed and has pollutant-degrading organisms immobilized in the form of biofilms. The contaminant either moves from the gas phase to the liquid phase and then to the biofilm, or it moves directly from the gas phase to the biofilm, where it is biologically degraded to harmless compounds (Gabriel & Deshusses 2003). Its major advantages are having low operation cost, requiring low-energy and chemicals and having high removal efficiencies (REs), mostly above 99% (Aita et al. 2016). Recently, BTFs have been widely applied to the treatment of H2S on both laboratory and industrial scales (Nhut et al. 2020; Khoshnevisan et al. 2018; Khanongnuch et al. 2019). However, limited studies are available regarding the removal of H2S in bıogas from wastewater treatment (WWT) sludge by real-scale BTF process at acidic pH for highly loaded H2S gas streams in a real scale BTF. Thus, in this study, a real-scale BTF was used to investigate the removal of high concentrations of H2S contained in biogas from an anaerobic digester.

Real-scale BTF process

This study was performed at Konya advanced biological urban wastewater treatment plant (WWTP) with an equivalent population of 1,000,000 and 200,000 m3/day flow rate. Real-scale BTF was used for the purification of H2S in the biogas collected at the AD output used for sludge stabilization. In this process, the H2S is removed from biogas, the biogas is cooled to condense the moisture in it and the condensate is discarded. Biogas collected from anaerobic sludge digesters are transferred to the feeding chamber at the bottom of the closed tower where the BTF unit is located. The biogas moves from the bottom to the top and in the tower that contains layers of polypropylene media filling circles (Table 1) where desulfurization occurs. A complexed culture of SOB dominated by Acidithiobacillus thiooxidans acclimated from activated sludge was used as the bacterial strain and a biofilm was formed. To supply the substrate (nutrients) for the SOB, treated wastewater was fed to the feeding chamber at the bottom of the tower. The feeding water was heated in heat exchangers before adjusting the temperature to 35–36 °C, and it was sprayed onto the media material from the top of the tower. Some authors reported that for similar sulfide-oxidizing microorganisms, an optimum growth temperature at around 30 °C (Ravichandra et al. 2006; Sanchez et al. 2014). Yang & Allen (1994) reported 100% removal efficiency at 30–50 degrees Celsius but only 20% at temperatures below 10 °C. At the entrance point of the desulfurization unit 1.5–3.5% air was added to the biogas. In this process, O2/H2S ratio was 2/1. The end product of oxidation, sulfate (high O2/H2S ratio in biofilm) or elemental sulfur (low O2/H2S ratio), should vary depending on the availability of oxygen for microorganisms in the bioreactor. If the oxygen is more than the stoichiometric requirement, the formation of elemental sulfur decreases (Buisman et al. 1991). The treated biogas was passed through cooling units to decrease the temperature and moisture before it was fed into the gas conversion engines. The filtrate collected at the bottom of the unit was discharged into the sulphur fertiliser tank. The sludge layer accumulated on the polypropylene material was removed from the system by back-washing. The flow diagram of the BTF process is given in Figure 1.

Table 1

BTP media material characteristics

Material Polypropylene (PP) 
Shape Perforated rings 
Size (D1-D2/L) (mm) 100–90/50–35 
Colour Black 
Porosity 92% 
Specific surface area (m2 m−3140 
Weight (g) 39 
Pieces per unit volume (pieces m−32,080 
Density (kg m−380 
Material Polypropylene (PP) 
Shape Perforated rings 
Size (D1-D2/L) (mm) 100–90/50–35 
Colour Black 
Porosity 92% 
Specific surface area (m2 m−3140 
Weight (g) 39 
Pieces per unit volume (pieces m−32,080 
Density (kg m−380 
Figure 1

Real-scale BTF process.

Figure 1

Real-scale BTF process.

Close modal

Real-scale BTF operational conditions

Real-scale BTF design criteria are given in Table 2. The biogas contains 65% methane (CH4), 34% carbon dioxide (CO2), 1% H2S, and other gases. The process was designed for the average biogas to be 30 °C and the dilution water average temperature to be 15 °C. The H2S content in the BTF system is approximately 3,600 pmv.Air was supplied to the BTF process by blowers at 1% of the biogas flow rate. The inlet biogas temperature is 35–37 °C, and 15–20 of mbar pressure is given to the system. Treated wastewater was used as feedwater, and its flow rate is 6–8 tons/day. The feed water was sprayed into the tower at 14–16 m3/h flow rates, continuously circulating. The temperature of this water is 35–36 °C. Hot water was supplied with heat exchangers. The pH value in the BTF system was 1–2. The process discharged 6–8 m3/day of sulfurous water after treatment.

Table 2

Biological desulfurization process design criteria

ParameterUnitValue
Flow rate Nm3/hour 1,500 
Inlet H2S concentration ppmv 5,000 
Outlet H2S concentration ppmv 200 
Inlet biogas temperature °C 30 
Outlet biogas temperature °C 
Biogas pressure mbar 15 
Methane (CH462 
Carbon dioxide (CO231 
Nitrogen (N2
Oxygen (O2
ParameterUnitValue
Flow rate Nm3/hour 1,500 
Inlet H2S concentration ppmv 5,000 
Outlet H2S concentration ppmv 200 
Inlet biogas temperature °C 30 
Outlet biogas temperature °C 
Biogas pressure mbar 15 
Methane (CH462 
Carbon dioxide (CO231 
Nitrogen (N2
Oxygen (O2

Monitoring and analytical methods

The pH is an important parameter affecting the process efficiency and the system was operated in the pH range of 1.5–3.5. The optimum pH should be in the range of 2–3.5 for activities of sulfide-oxidizing A. thiooxidans bacteria (Syed et al. 2006; Montebello 2013; Rodriguez et al. 2014). Kim & Deshusses (2005) reported that the biological activity of microorganisms was inhibited due to the low pH and high sulfate content (at pH 2 the sulfate content in the water was 1,900 ppm). To monitor and control the environment conditions of sulfur bacteria taking active role in the system, a full automation (SCADA) system was used. In this biological desulfurization process, biogas flow meters, air flow meter, circulation liquid flow meter, pH and temperature measurement devices, dilution (addition) liquid indicators, biogas oxygen analysis system, sulfur removal tower, tank level indicator, gas detector, pressure indicator, and other instruments were used. To compare the ability of biofilters on the same basis, the EC was used. It represents the ability in remove pollutants in gaseous form compared to the incoming pollutant mass, expressed as the mass of pollutant removed per unit time per bed volume. The parameters used in this study to describe the operating conditions and determine of the removal performances are given in Table 3.

Table 3

Process control parameters used in this study

FormulaNomenclature
Loading rate (gH2S m−3 h−1 Cin = concentration of H2S in gas entering biofilter (ppmv) 
EC (gH2S m−3 h−1 Cout = concentration of H2S in gas exiting biofilter (ppmv) 
Removal efficiency (%)  Q: Flow rate of mixed gas entering biofilter (m3 h−1
Empty bed residence time (min)  V: Empty packed bed volume (m3
FormulaNomenclature
Loading rate (gH2S m−3 h−1 Cin = concentration of H2S in gas entering biofilter (ppmv) 
EC (gH2S m−3 h−1 Cout = concentration of H2S in gas exiting biofilter (ppmv) 
Removal efficiency (%)  Q: Flow rate of mixed gas entering biofilter (m3 h−1
Empty bed residence time (min)  V: Empty packed bed volume (m3

H2S removal efficiency on a real scale in the BTF system was monitored for 12 months between January 2017 and December 2017 and the performance of the process was evaluated. During this period, the flow rate of biogas produced in the anaerobic sludge digesters, minimum, maximum, and average values of H2S levels in the biogas and at the process outlet were monitored on a monthly basis to determine the H2S removal efficiency of the process. During this study, biogas flow was measured by a flow meter (Drager) and H2S concentration was measured by H2S measurement tubes (Rea), and analyzed by colorimetric method (TS EN 1231: 2000).

Microorganisms are an important factor in evaluating the effectiveness of the BTF system because the other elements, such as biofilm and pH, depend on the development condition of microorganisms. Like this study, most studies, mainly in an SOB community, used wastewater for H2S removal. This study carried out subsequent denaturing gradient gel electrophoresis (DGGE) analyses to identify SOB.

Total solids (TS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), volatile fatty acid (VFA), protein, and alkalinity parameters were monitored in the anaerobic sludge digester, which affects the BTF process. These parameters were determined following the procedures described in Standard Methods (APHA, AWWA, WEF 1998). TS, COD, TKN, VFA, protein, and alkalinity were analyzed using the following methods: Gravimetric method SM 2540 D, COD; Closed Reflux Method SM 5520 C, Macro Kjeldahl method SM 4500 B, Capillary titrimetric method, Combustion, and Distillation method SM 4500 N B and titration method SM2320 B.

Production of anaerobic digester and biogas

The biogas flow rate and the H2S concentration in the biogas were measured for the efficient process operation. The operational parameters of the mesophilic anaerobic sludge digester (pH, organic loading rate, sludge feeding rate, ambient temperature, volatile organic acid concentration, sludge retention time) during the operation of the biological desulfurization process, were given in Table 4. The characteristics of sludge at the inlet and outlet of sludge digester (total solid material, COD, protein concentration, alkalinity) were given in Table 5. The most important indicator showing the efficient operation of the anaerobic sludge digesters is the biogas production. During the working period, the flow rate of biogas produced in anaerobic sludge digesters varied between 18,123 and 21,383 m3/day and an average of 19,519 m3/day (Table 6; Figure 2). However, the range of percentage composition of the biogas produced from AD processes is dependent upon several factors including the digestibility of organic matter, digestion kinetics, digester retention time, and the digestion temperature (Dobre et al. 2014).

Table 4

Anaerobic sludge digester operation parameters

ParametersValueAverage value
pH 7.3–8.1 7.9 ± 0.1 
Organic loading ratio (OLR) (kg day−1 m−31.2–1.5 1.3 ± 0.1 
Sludge feed flow (m3 h−116–17 16.9 ± 0.1 
Temperature (°C) 36–41 38 ± 1 
Volatile fatty acid (VFA)/alkalinity 0.02–0.08 0.05 ± 0.02 
Sludge retention time (days) 17 17 ± 0.01 
ParametersValueAverage value
pH 7.3–8.1 7.9 ± 0.1 
Organic loading ratio (OLR) (kg day−1 m−31.2–1.5 1.3 ± 0.1 
Sludge feed flow (m3 h−116–17 16.9 ± 0.1 
Temperature (°C) 36–41 38 ± 1 
Volatile fatty acid (VFA)/alkalinity 0.02–0.08 0.05 ± 0.02 
Sludge retention time (days) 17 17 ± 0.01 
Table 5

Sludge characteristics in anaerobic sludge digester

ParametersFeed sludgeAnaerobic sludge digester outlet
TS (mg L−1Min: 25,100 Min: 21,000 
Max: 37,500 Max: 30,100 
Mean: 33,568 Mean: 25,306 
SD: 3,480 SD: 3,873 
COD (mg L−1Min: 19,100 Min: 9,400 
Max: 32,000 Max: 9,000 
Mean: 26,243 Mean: 8,762 
SD: 4,336 SD: 1,523 
TKN (mg L−1Min: 1,500 Min: 1,300 
Max: 4,150 Max: 4,700 
Mean: 3,189 Mean: 2,460 
SD: 502 SD: 571 
Protein (mg L−1Min: 11,000 Min: 7,400 
Max: 23,100 Max: 22,000 
Mean: 17,992 Mean: 17,820 
SD: 2,854 SD: 3,381 
Alkalinity (mg L−1Min: 720 Min: 2,450 
Max:1,300 Max:3,900 
Mean: 1,218 Mean: 3,100 
SD: 144 SD: 279 
VFA (mg L−1Min: 450 Min: 60 
Max: 1,450 Max:230 
Mean: 1,094 Mean: 128 
SD: 308 SD: 42 
ParametersFeed sludgeAnaerobic sludge digester outlet
TS (mg L−1Min: 25,100 Min: 21,000 
Max: 37,500 Max: 30,100 
Mean: 33,568 Mean: 25,306 
SD: 3,480 SD: 3,873 
COD (mg L−1Min: 19,100 Min: 9,400 
Max: 32,000 Max: 9,000 
Mean: 26,243 Mean: 8,762 
SD: 4,336 SD: 1,523 
TKN (mg L−1Min: 1,500 Min: 1,300 
Max: 4,150 Max: 4,700 
Mean: 3,189 Mean: 2,460 
SD: 502 SD: 571 
Protein (mg L−1Min: 11,000 Min: 7,400 
Max: 23,100 Max: 22,000 
Mean: 17,992 Mean: 17,820 
SD: 2,854 SD: 3,381 
Alkalinity (mg L−1Min: 720 Min: 2,450 
Max:1,300 Max:3,900 
Mean: 1,218 Mean: 3,100 
SD: 144 SD: 279 
VFA (mg L−1Min: 450 Min: 60 
Max: 1,450 Max:230 
Mean: 1,094 Mean: 128 
SD: 308 SD: 42 
Table 6

Operation parameters for BTF

TimeBiogas (m3/d)Inlet [H2S]biogas (ppmv)Outlet [H2S]biogas (ppmv)H2S LR (gH2S m−3 h−1)EBRT (min)EC (gH2S m−3 h−1)H2S removal efficiency (%)
January 19,627 2,923 63 33.47 7.34 32.74 97.84 
February 19,581 3,233 14 36.93 7.35 36.77 99.57 
March 19,673 3,200 23 36.72 7.32 36.46 99.28 
April 19,714 2,900 12 33.35 7.30 33.21 99.59 
May 19,526 3,253 17 37.05 7.37 36.86 99.48 
June 18,233 4,103 43.64 7.90 43.58 99.85 
July 18,123 4,000 20 42.29 7.95 42.08 99.50 
August 18,683 3,900 42.50 7.71 42.46 99.90 
September 20,583 4,400 10 52.83 7.00 52.71 99.77 
October 21,383 4,133 51.55 6.73 51.50 99.90 
November 18,617 3,433 11 37.28 7.73 37.16 99.68 
December 20,483 4,100 12 48.99 7.03 48.85 99.71 
SDa 945.53  504.69 15.16 6.48 0.36 6.57 0.53 
Average 19,519 3,632 16 41.38 7.39 41.20 99.55 
TimeBiogas (m3/d)Inlet [H2S]biogas (ppmv)Outlet [H2S]biogas (ppmv)H2S LR (gH2S m−3 h−1)EBRT (min)EC (gH2S m−3 h−1)H2S removal efficiency (%)
January 19,627 2,923 63 33.47 7.34 32.74 97.84 
February 19,581 3,233 14 36.93 7.35 36.77 99.57 
March 19,673 3,200 23 36.72 7.32 36.46 99.28 
April 19,714 2,900 12 33.35 7.30 33.21 99.59 
May 19,526 3,253 17 37.05 7.37 36.86 99.48 
June 18,233 4,103 43.64 7.90 43.58 99.85 
July 18,123 4,000 20 42.29 7.95 42.08 99.50 
August 18,683 3,900 42.50 7.71 42.46 99.90 
September 20,583 4,400 10 52.83 7.00 52.71 99.77 
October 21,383 4,133 51.55 6.73 51.50 99.90 
November 18,617 3,433 11 37.28 7.73 37.16 99.68 
December 20,483 4,100 12 48.99 7.03 48.85 99.71 
SDa 945.53  504.69 15.16 6.48 0.36 6.57 0.53 
Average 19,519 3,632 16 41.38 7.39 41.20 99.55 

aStandard Devation: SD.

Figure 2

Variation of biogas production.

Figure 2

Variation of biogas production.

Close modal

Hydrogen sulfide removal from biogas

The inlet H2S concentration was routinely measured per day to assess the variation of the inlet H2S load. The H2S concentration of biogas at the inlet of the BTF unit varied between 2,900 and 4,400 ppmv and an average of 3,632 ppmv (Table 6). The H2S concentration in biogas is consistent with the literature (Jenicek et al. 2008; Charnnok et al. 2013; Reddy et al. 2019). The biogas generated in AD facilities in WWTPs contains average concentrations of H2S in the range from 0.1 to 0.5 vol. % (1,000–5,000 ppmv) (Walsh et al. 1989). At the outlet of the BTF process, H2S concentration varied between 4 and 63 ppm and an average of 16 ppm (Figure 3). No relation was determined between the biogas flow rate produced in the anaerobic sludge digester and the H2S concentration in the biogas. It is thought that H2S is produced depending on the other factors (protein and sulfate concentrations in wastewater, etc.) completely independent from the produced biogas quantity.

Figure 3

Variation of H2S concentration at BTF inlet and outlet.

Figure 3

Variation of H2S concentration at BTF inlet and outlet.

Close modal

Since the produced biogas is used in the production of electrical energy, H2S needs to be removed due to the corrosive effect of H2S on gas engines and other auxiliary equipment. As a result, before using biogas in gas engines, the H2S concentration schuld be reduced below the limit value For this reason, the H2S concentration should be reduced below the limit value (≤260 ppm).The recommended level of H2S in the produced biogas is in the range of 0.02–0.05% (w/w) (200–500 ppm) while H2S-free biogas is more desirable (Rodriguez et al. 2014). During the working period, the H2S removal efficiency ranged between 97.84 and 99.90% and an average of 99.55% (Table 6). In January 2017, when the performance of the process started to be monitored, H2S removal efficiency was observed to be 97.8% and increased during operation to 99% (Figure 4). It was determined that the H2S concentration at the outlet of the BTF process was well below the determined limit value.

Figure 4

Variation of H2S removal efficiency and EC.

Figure 4

Variation of H2S removal efficiency and EC.

Close modal

The EC and RE as functions of the load supplied to the system were analyzed for the BTF reactor. Figure 4 shows the removal efficiency and elimination capacity of H2S monthly. EC changes as a function of empty bed residence time (EBRT) and loading rate (LR) values. In the BTF process, EBRT values were between 6.3 and 7.95 min, LR values were between 33.35 and 52.83 g H2S m−3 h−1, EC values were between 33.21 and 51.71 g H2S m−3 h−1 (Figure 4). The average H2S removal was 99.9% at EBRT of 7.39 min (i.e., a LR of 41.38 g H2S m−3 h−1). Also, this study shows that BTF process performance according to EC and H2S RE is better than in previous studies (Table 7).

Table 7

Comparison of the performance of BTF reported in the literature on the treatment of biogas polluted by H2S

ScaleType bedPacked bed volumeInlet [H2S] (ppmv)Empty bed residence time (EBRT)Elimination capacity (EC) g H2S m−3 h−1H2S RE (%)Reference
Laboratory-scale Polypropylene pall rings 1 L 170 36 s 20 100 Cox & Deshusses (2001)  
Laboratory-scale HD-QPAC 2 L 2,000 3 min 55 99 Maestre et al. (2010)  
Laboratory-scale Polypropylene rings 1 L 5,415 5.5 min 89.4 100 Zhou et al. (2015)  
Laboratory-scale (bench) Calgon AP460 6.4 L 20–100 4–16 min 22.1 90 Duan et al. (2005)  
Laboratory-scale (pilot) Plastic pall rings 5.15 m3 1,954± 454 180 s 50 ± 11 94 Rodriguez et al. (2014)  
Laboratory-scale HD Q-PAC 2.15 L 2,000–8,000 180 s 50 100 Montebello et al. (2010)  
Laboratory-scale (pilot) Metallic Pall rings (AISI 316) 2 L 2,000 180 s 100–140 95–100 Montebello et al. (2012)  
Laboratory-scale Polypropylene Pall rings 2 L 2,000 131 s 50–100 35–100 Montebello et al. (2013)  
Laboratory-scale Metallic Pall rings 2.4 L 2,000–10,000 130 s 100–140 70–80 Montebelloa et al. (2014)  
Laboratory-scale HS- Q-PAC 2.15 L 900 – 10,000 180 s 200 84 Fortuny et al. (2008)  
Laboratory-scale HD-Q-PAC 2 L 2,000 167–180 s 84 97 ±0.3 Fortuny et al. (2011)  
Laboratory-scale Polypropylene pall rings 2.4 L 850–8,500 2.4–3.5 min 99.8–130 99 Fernandez et al. (2014)  
Laboratory-scale (pilot) Polyurethane foam 600 m2 m−3 surface area and 35 kg m−3 5–25 15–40 s 15–95 99 Gabriel & Deshusses (2003)  
Laboratory-scale (pilot) Ceramic granules Volcanic rocks 1,177 L 2.84± 1.76 mg m−3 5–20 s 2.82–2.85 60–100 Li et al. (2012)  
Full-scale Polypropylene pall rings – 3,000 180 s 170 90 Tomas et al. (2009)  
Laboratory-scale (pilot) BioSulfidEx 2.21 m3 500–600 84 32.3 98 Naegele et al. (2013)  
Laboratory-scale Polyethylene (HDPE) 1 L 0–2,040 120 78.57 100 Vikromvarasiri et al. (2017)  
Laboratory-scale (pilot) Commercial polyester fibers 12 L 1,000–4,000 10.29–72 min 14.58 100 Soreanu et al. (2008)  
Laboratory-scale Schist 7.85 L 1,100 300 s 30.3 100 Jabera et al. (2017)  
Laboratory-scale 3D-printed honeycomb monolith 0.2 L 2,000 41 s 122 95 Qiu et al. (2017)  
Laboratory-scale K1 packing material 0.5 L 200 40–100 s 92.27 ± 10.30 Zhuoa et al. (2019)  
Laboratory-scale HDPE Plastics 1 L 2,000 120 s 82.98 99.5 Juntranapaporn et al. (2019)  
Laboratory-scale (Semi-pilot) Polypropylene Pall rings 4,000 L 2,000 15 min 29.5 94.6–99.6 Reddy et al. (2019)  
Laboratory-scale Bamboo charcoal 643 L 5–20 10.9–28.9 s 6.58 99.8 Chen et al. (2019)  
Laboratory-scale Polyurethane foam 3 L 1,246–305 1.6 min 98 95–99 Tayar et al. (2019)  
Laboratory-scale Polypropylene pall rings 2.8 L 2,000 118 s 120 100 Lopez et al. (2019)  
Pilot scale Polypropylene spheres 440 L 1.2 g m−3 40 s 122 100 Xia et al. (2019)  
Real-scale (WWT) Polypropylene pall rings 100,000 L 2,900–4,400 6–8 min 33–53 98–100 This study 
ScaleType bedPacked bed volumeInlet [H2S] (ppmv)Empty bed residence time (EBRT)Elimination capacity (EC) g H2S m−3 h−1H2S RE (%)Reference
Laboratory-scale Polypropylene pall rings 1 L 170 36 s 20 100 Cox & Deshusses (2001)  
Laboratory-scale HD-QPAC 2 L 2,000 3 min 55 99 Maestre et al. (2010)  
Laboratory-scale Polypropylene rings 1 L 5,415 5.5 min 89.4 100 Zhou et al. (2015)  
Laboratory-scale (bench) Calgon AP460 6.4 L 20–100 4–16 min 22.1 90 Duan et al. (2005)  
Laboratory-scale (pilot) Plastic pall rings 5.15 m3 1,954± 454 180 s 50 ± 11 94 Rodriguez et al. (2014)  
Laboratory-scale HD Q-PAC 2.15 L 2,000–8,000 180 s 50 100 Montebello et al. (2010)  
Laboratory-scale (pilot) Metallic Pall rings (AISI 316) 2 L 2,000 180 s 100–140 95–100 Montebello et al. (2012)  
Laboratory-scale Polypropylene Pall rings 2 L 2,000 131 s 50–100 35–100 Montebello et al. (2013)  
Laboratory-scale Metallic Pall rings 2.4 L 2,000–10,000 130 s 100–140 70–80 Montebelloa et al. (2014)  
Laboratory-scale HS- Q-PAC 2.15 L 900 – 10,000 180 s 200 84 Fortuny et al. (2008)  
Laboratory-scale HD-Q-PAC 2 L 2,000 167–180 s 84 97 ±0.3 Fortuny et al. (2011)  
Laboratory-scale Polypropylene pall rings 2.4 L 850–8,500 2.4–3.5 min 99.8–130 99 Fernandez et al. (2014)  
Laboratory-scale (pilot) Polyurethane foam 600 m2 m−3 surface area and 35 kg m−3 5–25 15–40 s 15–95 99 Gabriel & Deshusses (2003)  
Laboratory-scale (pilot) Ceramic granules Volcanic rocks 1,177 L 2.84± 1.76 mg m−3 5–20 s 2.82–2.85 60–100 Li et al. (2012)  
Full-scale Polypropylene pall rings – 3,000 180 s 170 90 Tomas et al. (2009)  
Laboratory-scale (pilot) BioSulfidEx 2.21 m3 500–600 84 32.3 98 Naegele et al. (2013)  
Laboratory-scale Polyethylene (HDPE) 1 L 0–2,040 120 78.57 100 Vikromvarasiri et al. (2017)  
Laboratory-scale (pilot) Commercial polyester fibers 12 L 1,000–4,000 10.29–72 min 14.58 100 Soreanu et al. (2008)  
Laboratory-scale Schist 7.85 L 1,100 300 s 30.3 100 Jabera et al. (2017)  
Laboratory-scale 3D-printed honeycomb monolith 0.2 L 2,000 41 s 122 95 Qiu et al. (2017)  
Laboratory-scale K1 packing material 0.5 L 200 40–100 s 92.27 ± 10.30 Zhuoa et al. (2019)  
Laboratory-scale HDPE Plastics 1 L 2,000 120 s 82.98 99.5 Juntranapaporn et al. (2019)  
Laboratory-scale (Semi-pilot) Polypropylene Pall rings 4,000 L 2,000 15 min 29.5 94.6–99.6 Reddy et al. (2019)  
Laboratory-scale Bamboo charcoal 643 L 5–20 10.9–28.9 s 6.58 99.8 Chen et al. (2019)  
Laboratory-scale Polyurethane foam 3 L 1,246–305 1.6 min 98 95–99 Tayar et al. (2019)  
Laboratory-scale Polypropylene pall rings 2.8 L 2,000 118 s 120 100 Lopez et al. (2019)  
Pilot scale Polypropylene spheres 440 L 1.2 g m−3 40 s 122 100 Xia et al. (2019)  
Real-scale (WWT) Polypropylene pall rings 100,000 L 2,900–4,400 6–8 min 33–53 98–100 This study 

Microbial community

In the effective removal of H2S, microorganisms have an important role. SOB are gram negatives that can use sulfide and thiosulfate as an energy source. Analysis of sequenced bands using DGGE in samples drawn from the BTF tower showed different SOB in the HS samples with a similarity of at least 94% of the closely related cultures, all belonging to the Proteobacteria division. Members found it belonged to A. thiooxidans (99% similarity), employed for the aerobic treatment of H2S in BTFs found in anaerobic enriched cultures for the anaerobic bio-oxidation of sulfide (Tang et al. 2009). This bacterium is thought to be an ideal inoculum for the biofiltration of H2S in biogas and it is the most acidophilic SOB (Aita et al. 2016; Caicedo-Ramirez et al. 2016). It has a pH range between 0.5 and 5.5 and an optimum at pH 2–3 for growth (Wang et al. 2019). This result is similar to the results of Lee et al. (2006), which showed that in degradation of H2S, Thiobacillus thiooxidans proliferating between pH 2 to 0.5 and A. thiooxidans AZ11 could grow at pH as low as 0.2. It was reported that it was still possible to reach high removal efficiencies of 99.9%, 98.0%, and 94.0%, respectively. In their study, Rodriguez et al. (2014) predicted that the dominant SOB species in wastewater might be A. thiooxidans and T. thiooxidans, thus requiring an acidic pH to promote bacterial growth. In acidic conditions, Acidithiobacillus sp. was reported to reach an H2S EC of 113 (Aita et al. 2016), 150.3 (Charnnok et al. 2013) and 113.5 gH2S m−3 h−1 (Chaiprapat et al. 2011). Our EC 35 gH2S m−3 h−1 at the condition for H2S removal is similar to those reported in the mentioned Acidithiobacillus sp. predominant experiments. pH of the recirculating fluid was found to decrease rapidly and vary between 1.5 and 3.5. Aroca et al. (2007) proposed that RE was 100% when utilizing A. thiooxidans for H2S oxidation at pH 1.8–2.5. It can be seen from the results that the SOB culture in the BTF reactor has already adapted to the condition of inlet H2S concentration and removed H2S from biogas.

In this study, the removal of H2S from biogas produced at a real-scale anaerobic sludge digester by the BTF process was investigated. The average biogas flow rate produced in the mesophilic anaerobic sludge digester varied between 18,123 and 21,383 m3day−1 and H2S concentrations varied between 2,923 and 4,400 ppmv. The H2S concentration in the produced biogas is completely in independent of the biogas flow rate. The removal of high concentrations of H2S in biogas was accomplished by a real-scale BTF process with SOB (A. thiooxidans)m which are active in an acidic environment (pH 1.5–3.5.). The BTF process was operated at pH:1.5–3.5, O2/H2S:1/2, EBRT:6.3–7.95 minutes, LR:33.35–52.83 g H2S m−3 h−1. The H2S RE varied in the range of %97.84–99.90 and the H2S EC varied in the range of 33.21–52.71 gH2S m−3 h−1. The process efficiency was found to be independent of the inlet H2S concentration. The average H2S values in biogas desulphurized by the BTF process ranged between 4 and 63 ppm. As a result, the BTF process regardless of the biogas flow and the inlet H2S concentration was found to be an effective and efficient process for the removal of H2S from biogas produced in the real-scale anaerobic sludge digester.

We sincerely thank General Directorate of Water and Sewerage Administration (KOSKİ) of Konya Metropolitan Municipality for providing technical and financial support to this study.

Not applicable

Not applicable

Not applicable

We declare that they have no conflict of interest.

No funding was received for conducting this study.

Not applicable

Not applicable

All authors contributed to the study conception and design. Material preparation and data collection were done by SK. The study of analysis was performed by SA. The first draft of the manuscript was written by SA and SK commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Data cannot be made publicly available; readers should contact the corresponding author for details.

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