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Article

Biodesulfurization of Consortia Immobilized on Oil Palm Frond Biochar in Biotrickling Filters under Anoxic Conditions

by
Pajongsuk Sutarut
1,2,
Benjamas Cheirsilp
2 and
Piyarat Boonsawang
2,*
1
Faculty of Science and Technology, Songkhla Rajabhat University, Muang, Songkhla 90000, Thailand
2
Center of Excellence in Innovative Biotechnology for Sustainable Utilization of Bioresources, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai 90110, Thailand
*
Author to whom correspondence should be addressed.
Fermentation 2023, 9(7), 664; https://doi.org/10.3390/fermentation9070664
Submission received: 20 June 2023 / Revised: 9 July 2023 / Accepted: 12 July 2023 / Published: 14 July 2023
(This article belongs to the Special Issue The Role of Microbial Fermentation in Sewage Sludge Treatment)
Browse Figures
Review Reports Versions Notes

Abstract

:
Biodesulfurization using biotrickling filters (BTFs) under anoxic conditions is a cost-effective method for biogas clean-up. To improve the performance of BTFs, the microbial consortia from the anaerobic pond of a swine farm (SW), the denitrification pond of a tuna factory (DN), and the UASB of the concentrated latex industry (LW) were immobilized on BTFs. In this study, the efficiency of BTFs immobilized with the microbial consortia for the reduction of H2S gas combined with the reduction of nitrate contained in wastewater was investigated. The results showed that H2S was completely removed at the inlet H2S concentration of 207.8–1476 ppmv with wastewater circulation under anoxic conditions. However, only the DN-BTF achieved H2S removal of 95.2% at an inlet concentration of 2500 ppmv. An increase in the N/S ratio (0.356–2.07 mol/mol) improved the H2S removal of the SW-BTF, LW-BTF, and DN-BTF but not the BTF-C. Moreover, the DN-BTF had the highest nitrate removal rate (71.1%) with an N/S ratio of 2.07 mol/mol. When oxygen was supplied in wastewater at DO = 3.60 ± 0.41 mg/L, sulfate was generated at a higher rate, but nitrite production was lower than at DO~0. After microbial community analysis, Proteobacteria were the main phyla involved in the biodesulfurization process.

1. Introduction

Biotrickling filters (BTFs) are a good-performing form of technology for biogas clean-up, including hydrogen sulfide removal [1,2,3,4]. This technology is generally based on an aerobic process using sulfur-oxidizing bacteria (SOB) to convert H2S into sulfate and elemental sulfur [1,5]. During biological conversion, O2 acts as an electron acceptor under aerobic conditions, whereas NO3− acts as an electron acceptor under anoxic conditions [1,6,7]. The aerobic process is an effective biological treatment due to its low nutritional requirements and high H2S affinity [8]. However, there are several drawbacks to the aerobic process for H2S removal from biogas, such as biogas dilution by air or O2, potential explosions by CH4/O2 mixtures, and frequent clogging by elemental sulfur [2,9,10].
Recently, biodesulfurization has been studied under anoxic conditions without an oxygen requirement [6,9,11,12]. Under these conditions, nitrate-reducing sulfide-oxidizing bacteria (NR-SOB) are the main microorganisms for simultaneous desulfurization and denitrification [13]. BTFs have also been used to combine physical and biological processes [6,9,10,11,12]. Packing materials in BTFs include either natural or synthetic materials such as pall rings, polypropylene pall rings, polyurethane foams, ball rings, and compost [6,9,10,12,14,15]. Zhao et al. [16] reported that biochar produced from sawdust and urea phosphate, maple wood, pig manure, food waste and sludge, and coffee industrial waste was successfully applied for hydrogen sulfide removal with an adsorption capacity of 54.8–281.5 mg/g. In addition, biochar was mostly used for hydrogen sulfide removal under O2 conditions [17,18]. Up to the present, the study of desulfurization under anoxic conditions using biochar as packing media is limited.
Typically, biochar is a cost-effective material for packing media due to its production from agricultural residue, manure, activated sludge, and waste [16,19]. In addition, biochar is an alkali-catalyzed carbon that is highly effective for H2S adsorption without alkaline pre-treatments [20]. There have been reports of biochar production from palm residues, including oil palm fronds (OPF), and its use as a bioabsorbent for pollutant removal [21,22,23]. According to our knowledge, no previous research has been conducted on H2S gas removal integrated with nitrogen removal from wastewater using BTFs packed with OPF biochar.
The purpose of this study is to explore the performance of OPF biochar immobilized with consortia from industrial wastewater for the reduction of H2S gas and nitrogen contained in wastewater. The effects of the initial H2S concentration in the synthetic biogas, the N/S ratio, the dissolved oxygen (DO), and the microbial community on the performance of the BTFs were investigated.

2. Materials and Methods

2.1. Consortia Sources and Immobilization on OPF Biochar

The consortia sludge was obtained from the wastewater treatment systems of the following industries: (1) the up-flow anaerobic sludge blanket (UASB) reactor of the concentrated latex industry; (2) the anaerobic pond of a swine farm; and (3) the denitrification pond of the tuna canning industry, Songkhla province. The characteristics of three sources of seeding sludge are presented in Table 1. For enrichment of NR-SOB, the seeding sludge was acclimated in a modified mineral medium (M3) according to Fernández et al. [9] with 5 g/L NaNO3 and 3.9 g/L Na2S∙xH2O supplements for 6 days. Following that, the consortia were inoculated in the nutrient broth (NB) medium (DifcoTM) with 5 g/L NaNO3 and 3.9 g/L Na2S∙xH2O supplement until the total viable cells were estimated at approximately 107 cfu/mL.
The OPF biochar was prepared from oil palm fronds using a slow pyrolysis process at 438 °C under limited oxygen. For the immobilization of sludge on the OPF biochar, 130 ± 0.5 g of dry OPF biochar (with a particle size of 354–500 µm, a specific surface area of 69.0 m2/g, an average pore diameter of 1.68 nm, and a pore volume of 0.0229 cm3/g) [23] was placed into 1 L Duran bottles. Afterward, the consortia prepared in the NB medium and the M3C medium (the M3 medium with 3.9 g/L Na2S∙xH2O, 1.8 g/L NaHCO3, and 0.68 g/L CH3COONa) at a ratio of 1:1 (v/v) were placed into the Duran bottles. During the cultivation period, the 50% fresh M3C medium was replaced every 3 days until the total immobilized cells were estimated at approximately 107 cfu/g dry OPF biochar.

2.2. Biotrickling Filter (BTF) Setup and Operation

BTFs, with a total height of 100 cm and a diameter of 6 cm, were used in this study. The OPF biochar immobilized with consortia was packed in the BTFs at a height of 82 cm with a working volume of 2.32 L. The schematic of the four BTFs designated as SW, LW, DN, and C-BTFs is shown in Figure 1. SW, LW, and DN-BTFs were immobilized with consortia from different sources, whereas C-BTF was a control set without immobilization. In addition, the 4 L of M3C medium supplemented with NaNO3 was prepared in the 5 L of the circulated tank and fed into the BTFs at the top of the column to provide nutrients for microorganisms. The liquid released from the BTFs at the bottom of the column was collected and recirculated at 7.7 L/h through a diaphragm pump from the recirculation tank to the top of the BTFs. The fresh M3C medium supplemented with NaNO3 was replaced every 5 days. To avoid clogging problems, the pump was operated with the 1 min on and 2 min off cycle mode. During the experiment, the temperature was maintained at room temperature (30 ± 2 °C).
The counter-current mode of gas/liquid flow was the chosen mode of operation. The gas stream, consisting of a mixture of N2 and H2S, was fed to the BTFs in up-flow mode. The desired concentration of H2S was achieved by using HCl (0.5 N) and changing the molarity of Na2S. The diaphragm pump was used to feed Na2S and HCl into the mixing tank, where a constant flow of N2 was also supplied using a gas solenoid valve for the N2 flow controller. After that, the mixing gas was kept in a storage bag before being fed to the BTF. The mixing gas was fed continuously to the BTFs using a gas pump at a flow rate of 60 L/h. The operating conditions are given in Table 2. The biotrickling filter experiment was divided into three phases. For phases I and II, the effects of the inlet H2S concentration and the initial nitrate concentration were investigated under anoxic conditions. For phase III, air was fed to the recirculation tanks to provide oxygen to the BTFs at dissolved oxygen levels of 3.60 ± 0.41 mg/L. To maintain the constant pH of the biofilm, the pH of the recirculating systems was adjusted at 6.5–7.25 by using an aqueous solution of 2N HCl and 2N NaOH.

2.3. Next-Generation Sequencing (NGS) of Microbial Community

Samples of the biochar from each BTF were collected for microbial community analysis on the 51st day prior to the shock load of the system. The DNA from the collected samples was extracted using the E.Z.N.A. soil DNA kit (Omega Bio-Tek Inc., Norcross, GA, USA) following the manufacturer’s protocol. To amplify the genomic DNA, the specific primer was 341F-806R to target the V3–V4 region of the 16S rRNA gene. The PCR products were mixed at equal density ratios. The mixed PCR products were purified using a Qiagen Gel Extraction Kit (Qiagen, Stockach, Germany). After that, the NEBNext® UltraTM DNA Library Prep Kit for Illumina was used and quantified via Qubit and Q-PCR (Illumina, San Diego, CA, USA, Nova Seq 6000) for DNA library construction. Operational taxonomic units (OTUs) clustering was employed, and taxonomic annotation was prepared for the representative sequence of each OTU with the matching taxa information and taxa-based abundance distribution.

2.4. Analytical Methods

The inlet and outlet gas samples were collected in 1 L Tedlar bags for the determination of hydrogen sulfide concentration by gas chromatography (HP 7890) with a flame photometric detector (GC-FPD) and GS-Gaspro (length 30′ × 0.32′ capillary column). The flow rate of the helium carrier gas was set constantly at 30 mL/min. The column temperature program was as follows: initial temperature of 60 °C, hold for 1 min, and ramp up to 120 °C at 15 °C/min. The detector temperature was set at 200 °C.
For SEM analysis, the packing media samples of each BTF were taken from the bottom of the column on the 20th day to monitor the immobilization of consortia on the fresh biochar. The samples were fixed in glutaraldehyde solutions for 2.5 h. After fixation, each sample was washed with phosphate-buffered solution, followed by washing with deionized water. Each sample was dehydrated in an ethanol-series solution and then dried to a critical point [9]. Finally, the samples were coated with gold to enhance their electrical conductivity. The samples were examined with an SEM (Model Quanta 400, FEI Technologies Inc., Hillsboro, OR, USA).
The liquid samples from the recirculation tanks were determined for the concentration of sulfide, sulfate, nitrate, and nitrite by the iodometric method, turbidimetric method, ultraviolet spectrophotometric screening method, and colorimetric method, respectively [24]. The pH and DO values of the recirculating liquid were measured by pH meters (Mettler-Toledo International Inc., Columbus, OH, USA) and DO meters (Model 200, Clean Instrument Co., Ltd., Taipei, Taiwan), respectively.

3. Results

3.1. Effect of Inlet H2S Concentration

During the start-up period (0–20 days), microorganisms that attached to the OPF biochar were investigated. The SEM observation showed that bacterial cells were directly attached to the surface of the OPF biochar packing medium. SW-BTF, LW-BTF, and DN-BTF contained abundant microorganisms, mostly rod-shaped bacteria, on the surface of the OPF biochar. Moreover, there were fewer microorganisms on the surface of the OPF biochar in the C-BTF (Figure 2).
Experiments were carried out for a period of 96 days to evaluate the H2S removal performance of the different BTFs. After the start-up, the removal efficiencies (Res) of H2S rapidly increased to 100% in all BTFs between days 1 and 4, with an inlet H2S concentration of 317–405 ppmv. However, an increase in the inlet H2S concentration from 876 to 4500 ppmv resulted in a reduction in H2S removal for the BTFs without the augmentation of microbial immobilization (C-BTF). The removal efficiencies were 36.9% at the inlet H2S concentration of 4491 ppmv (day 70) (Figure 3). In addition, a continuous increase in the elemental sulfur accumulation was visibly observed in the C-BTF after 20 days.
In contrast, the BTFs with microbial immobilization (SW-BTF, LW-BTF, and DN-BTF) completely removed H2S until the inlet H2S concentration reached 1476 ppmv (day 20). Afterward, it was observed that an increasing H2S concentration (>1500 ppmv) resulted in a decrease in removal efficiency. On days 28–31, the inlet H2S concentration was reduced to 395 ppmv to maintain the stability of the systems. During days 31–37, the inlet H2S concentration gradually increased. It was found that all BTFs maintained the removal efficiency until the inlet H2S concentration reached 1577 ppmv (day 37). However, only the DN-BTF achieved a high removal efficiency (>90%) at an inlet concentration of 2500 ppmv. At day 70, the removal efficiencies were 56.5, 50.9, and 59.9% at the inlet H2S concentration of 4491 ppmv for SW-BTF, LW-BTF, and DN-BTF (Figure 3), respectively. At the end of phase I, the inlet H2S concentration was reduced to 244.6 ± 26.9 ppmv. It was noted that all BTFs maintained good performance with 100% H2S elimination for a long-term period (3 months). In addition, it was discovered that C-BTF recovery would take longer without the consortia augmentation (Figure 3). Moreover, yellow elemental sulfur was found in all BTFs but not in the DN-BTF after 80 days.

3.2. Microbial Community Analysis

Packing media samples of all BTFs at the bottom filter were taken on day 51 to monitor the microbial communities before the shock load of the system was found. DNA extraction from the C-BTF, DN-BTF, LW-BTF, and SW-BTF samples was studied based on 16S rRNA gene amplicons. The Illumina Nova SeqTM 6000 platform was used to generate ~400 bp paired-end raw reads. Total tags of 454 and 570 analyzed reads were obtained from all BTFs. The total number of obtained raw reads were as follows: C-BTF (91,155), DN-BTF (94,846), LW-BTF (109,037), and SW-BTF (159,532). Sequences with ≥97% similarity were assigned to the same OTUs. The number of OTUs observed was as follows: C-BTF (281 OTUs), DN-BTF (291 OTUs), LW-BTF (334 OTUs), and SW-BTF (506 OTUs). The richness of the microbial community in the samples was observed in the SW-BTF, LW-BTF, DN-BTF, and C-BTF. When compared with the performance of the BTF, the richness of the microbial community in the samples did not influence the efficiency of H2S removal. According to the common and unique OTU clustering, a Venn diagram and a flower diagram were generated and are shown in Figure 4. It shows that the DN-BTF, LW-BTF, and SW-BTF shared 235, 229, and 161 OTUS with the C-BTF, respectively (Figure 4A). The relative abundance of the selected top 10 taxa in each sample is illustrated in Figure 4B. It found that the phylum Proteobacteria was the major phylum of all BTFs. According to the abundance information for the top 16 genera of all of the samples collected from the C-BTF, DN-BTF, LW-BTF, and SW-BT, the relative abundance and taxonomic classification are shown in Table 3. Based on the results of the genera, Arenimonas sp. (29.3% and 17.3%) and Castellaniella sp. (26.2% and 32.9%) were the dominant genera in the DN-BTF and the LW-BTF, respectively. Rhodanobacter sp. (20.4%) and Castellaniella sp. (16.1%) were the dominant genera in the SW-BTF. Unexpectantly, the dominant genera in the C-BTF were Acinetobacter sp. (34.8%) and Pseudomonas sp. (20.4%) (Table 3).

3.3. Effect of the N/S Ratio

The N/S ratio was calculated from the initial H2S concentration and the nitrate addition ratio. At the end of phase I, the N/S ratio of 2.07 mol/mol was obtained, and 100% H2S removal was found for all BTFs. Afterward, the BTFs with the exhausted packing materials were operated at an N/S ratio of 0.356–1.23 mol/mol with initial NO3-concentrations of 2.6 g/L (days 97–125) at a constant EBRT of 139 s. The result demonstrated that an increase in the N/S ratio improved the H2S removal (gas phase) for the SW-BTF, LW-BTF, and DN-BTF. In addition, a decrease in the N/S ratio from 2.07 to 1.23 resulted in a drastic decrease in H2S removal due to the saturated adsorption of biochar. An increase in the N/S ratio (0.356–1.23 mol/mol) had no effect on H2S removal for the BTF-C. At the N/S ratio of 1.23 mol/mol, the H2S removal was 91.4%, 88.6%, 83.8%, and 31.3% for the DN-BTF, SW-BTF, LW-BTF, and C-BTF, respectively. In addition, the nitrate removal was not significantly different at an N/S ratio of 0.51–2.07 mol/mol for DN-BTF, SW-BTF, and LW-BTF. The DN-BTF had the highest nitrate removal rate (71.1%) with an N/S ratio of 2.07 mol/mol, while the SW-BTF, LW-BTF, and C-BTF had slightly different nitrate removal rates (59.8–60.8%). Moreover, nitrate removal significantly decreased at an N/S ratio of 0.36 mol/mol (Figure 5).
In addition, this study found that sulfate formation occurred with decreasing nitrate concentrations for all BTFs at an N/S ratio of 0.356–2.07 mol/mol (Figure 6). Moreover, the yellow particles were formed and accumulated in the BTF. The highest elemental sulfur concentration was visibly seen, and the lowest sulfate concentration was produced in the C-BTF. In contrast, the lowest elemental sulfur concentration was visibly seen, and the highest sulfate concentration was produced in the DN-BTF. This indicated that bioaugmentation with microbial immobilization on the BTFs affected the biological process and product selectivity. Moreover, the diversity of the microbial community and the microbial sources played a significant role in the performance of the BTF. In addition, a small amount of nitrite (209–268 mg/L) was produced in all BTFs.

3.4. Elimination Capacity of the BTFs

The highest elimination capacity (EC) was found in the DN-BTF, with a maximum elimination capacity (ECmax) of 117 g/m3-h (Figure 7). This indicated that the DN-BTF has a better ability to remove H2S than the LW-BTF (ECmax = 107 g/m3-h), SW-BTF (ECmax = 106 g/m3-h), and C-BTF (ECmax = 85.6 g/m3-h) under anoxic conditions (phase II). In addition, a linear relationship between the EC and ILR for the DN-BTF was observed until the ILR was 120 gS/m3-h, which was two times greater compared with the C-BTF without microbial immobilization. In comparison with other works, the ECmax from the anoxic DN-BTF with microbial consortia from the denitrification pond of the tuna canning industry in this study was similar to the ECmax from the anoxic BTFs with ammonium-rich water (EC = 119.5 g/m3-h) [14] and the BTFs immobilized with Paracoccus versutus CM1 (EC = 113.7 g/m3-h) [25].

3.5. Effect of DO in the Recirculating Liquid on the Performance of the Anoxic BTF System

For phase III, the BTFs were fed with a difference H2S concentration of 402.8–3112 ppmv (ILR from 12.7–97.9 g S/m3-h) at a constant EBRT of 174 s. Nitrate was added at 2.6 g/L, and air was supplied with a DO of 3.60 ± 0.41 mg/L in recirculating media. It was observed that increasing the DO concentration results in an increase in sulfate production, a reduction in nitrate consumption, and low nitrite formation (Figure 6). In the presence of oxygen, H2S oxidizes to sulfate. We visibly observed that the DO concentrations not only provide enough oxygen for sulfide oxidation but also oxidize the elemental sulfur accumulated in packing media [26]. In this phase, the value of the pH in the recirculating media of all BTF systems drastically changed from 6.5–7.25 to 3.01–3.21. To maintain the system, the pH was adjusted to 6.5–7.25 every day.
The H2S removal efficiencies of the DN-BTF, SW-BTF, LW-BTF, and C-BTF were 88.0%, 80.9%, 69.7%, and 43.0%, respectively, at the inlet H2S concentration of 2119 ± 50 ppmv. A low nitrate removal rate was found at 34.8%, 26.8%, 31.3%, and 19.2% for the DN-BTF, SW-BTF, LW-BTF, and C-BTF, respectively. It could be seen that the oxygen supplied to the BTFs did not improve H2S and nitrate removal. In addition, it affected the operating cost and the stability of the system. The stability and performance of the anoxic BTFs were maintained by using sufficient nitrate as an electron acceptor [9]. Excess amounts of oxygen result in a change in the electron acceptor from nitrate to oxygen and the promotion of sulfate production.

4. Discussion

In this experiment, the BTFs were operated continuously for almost 5 months. With the limitations of the equipment and the long period of operation, the data were from a single run. At the beginning (0–20 days), the biofilm formation was developed. From the SEM analysis, it was shown that the consortia attached to the surface of the biochar for the DN-BTF, SW-BTF, and LW-BTF but not for the C-BTF (Figure 3). This indicated that the H2S removal in the C-BTF was mostly a physical or chemical process. Oliveira et al. [18] reported that biochar is mostly used for H2S removal via chemisorption. The surface of the OPF biochar contained functional groups, including COOH and OH, which were bound to dissociate hydrogen sulfide ions [18,23]. Pudi et al. [3] reported that good H2S adsorption occurred in the presence of water due to the dissolution of H2S gas in the water phase and the interactions between the sorbent and water.
It was evident that H2S removal was improved by consortia immobilized on the OPF biochar. The DN-BTF achieved H2S removal of 95.2% at an inlet concentration of 2500 ppmv. At an inlet H2S concentration of 200 ppmv, H2S removal was 100% in phases I and II. However, the initial H2S concentrations for phase III were twice the initial H2S concentrations for phases I and II. Nevertheless, the SW-BTF and the DN-BTF both achieved 99% and 100% H2S removal effectiveness, respectively. In comparison with the previous investigation, the completed H2S removal at the low inlet H2S concentrations was achieved for all BTFs with consortia augmentation, which was consistent with other works [7,10,12]. This included the C-BTF with fresh biochar. This indicated that the OPF biochar could have the potential to be used as a packing material for BTFs to remove H2S.
In the microbial distribution of this study, Proteobacteria was the dominant phylum (83.3–96.7%), which agreed with other works [27,28]. This indicated that Proteobacteria were dominant in the BTFs and played an important role in the anoxic desulfurization system. At the genus level, Castellaniella sp. and Arenimonas sp. Were found dominant in all BTFs immobilized with the sludge from wastewater, which involved denitrification and desulfurization [29,30]. In the SW-BTF, Rhodanobacter (chemolithotrophic sulfide oxidizers) were dominant, which use either oxygen or nitrate as electron acceptors to oxidize H2S to elemental sulfur and sulfate [31]. This implied that the microbial consortia enhanced H2S removal through the activities of NR-SOBs, which reduced nitrate to nitrite and oxidized H2S to elemental sulfur and sulfate. Bai et al. [32] reported that Castellaniella, Pseudomonas, and Thiobacillus were the dominant genera in an autotrophic denitrification biofilter with thiosulfate as an electron donor. Thauera, Enterobacter, and Thiobacillus were reported to be sulfide oxidization and denitrification bacteria, which convert sulfide to elemental sulfur and nitrate to nitrogen [33]. Unexpectantly, the dominant genera in C-BTF were Acinetobacter sp. and Pseudomonas sp., which are sulfur-oxidizing bacteria [25]. Pseudomonas sp. were facultative sulfur-oxidizing bacteria, which involved denitrifying sulfide removal under mixotrophic conditions [31,34]. It could be seen that the microbial community affected the performance of the BTF.
In addition, it was found that the N/S ratio affected the efficiency of the BTFs. Complete H2S oxidation generated S0 as a by-product with an N/S ratio of 0.4 mol/mol, whereas partial H2S oxidation produced SO42− with an N/S ratio of 1.6 mol/mol [9,35]. However, sulfate and nitrite were formed at N/S = 4, and elemental sulfur and nitrite were generated at N/S = 1 [35]. In this study, it was found that the efficiency of H2S removal for the C-BTF rapidly decreased from 100% (at N/S = 2.06) to 30% (at N/S = 1.23) due to the saturated adsorption of exhausted biochar. Interestingly, the efficiency of H2S removal for BTFs with consortia immobilization slightly decreased from 100% (at N/S = 2.06) to 83.8–91.4% (at N/S = 1.23). In addition, it was found that sulfate and sulfur formation occurred with decreasing nitrate concentrations. This result confirmed that desulfurization and denitrification occurred simultaneously under anoxic conditions due to microbial activity. This finding is consistent with Li et al. [36], who discovered that decreasing the S/N ratios (or increasing the N/S ratios) resulted in an increase in sulfate formation.
In the case of oxygen supplied in the circulation liquid phase, a high sulfate concentration was produced and low nitrite formation was obtained. It was implied that nitrate was mostly converted to sulfate and elemental sulfur via desulfurization rather than denitrification. Zhang et al. [37] reported that sulfide-oxidizing nitrate-reducing bacteria used oxygen as an electron acceptor at the first stage and used nitrate as an electron acceptor at the later stage. It is noted that oxygen was preferred over nitrate [27,37].

5. Conclusions

BTFs with fresh OPF biochar as a packing material demonstrated that the immobilization with microbial consortia from the wastewater treatment system enhanced H2S removal from the gas stream at high efficiency (>95%). The DN-BTF showed better performance than the BTFs for H2S removal from the gas phase (ECmax of 117 g/m3-h) and nitrate removal (64.5%) in the liquid phase using exhausted OPF biochar as a packing material. N/S and DO influence H2S removal and metabolic products. The microbial community analysis indicated that Proteobacteria were the main Phyla involved in the biodesulfurization process of all anoxic BTFs. At the genus level, Arenimonas sp., Castellaniella sp., Rhodanobacter, Acinetobacter sp., and Pseudomonas sp. were the dominant genera in the BTFs. This study could be a promising, cost-effective technology for biodesulfurization simultaneously with wastewater treatment for nitrogen removal. To improve the performance of BTFs, the optimal operation with exhausted OPF biochar should be further studied. The pilot-scale experiment and long operation were required to ensure the stability of the BTFs. In addition, the metabolite products, including elemental sulfur, could be used as fertilizer as an alternative valorization for the zero-waste concept.

Author Contributions

Conceptualization, P.B.; investigation and writing—original draft, P.S.; writing—review and editing, P.B.; supervision, B.C. and P.B.; funding acquisition, P.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Graduate School, Prince of Songkla University, Thailand (ID5811030020). The first author was financially supported by a Royal Thai Government Scholarship (Ministry of Science and Technology). The second and third authors were supported by the Thailand Research Fund under grant No. RTA6280014.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Fermentation 09 00664 g001 550
Figure 1. Schematic of the anoxic biotrickling filter for H2S removal. The dotted and continuous lines represent the gas and liquid flows, respectively.
Figure 1. Schematic of the anoxic biotrickling filter for H2S removal. The dotted and continuous lines represent the gas and liquid flows, respectively.
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Figure 2. Scanning electron microscopy image of consortia in the biofilm of DN-BTF, LW-BTF, SW-BTF, and C-BTF at 20 days of the experiment (magnification = 15,000×).
Figure 2. Scanning electron microscopy image of consortia in the biofilm of DN-BTF, LW-BTF, SW-BTF, and C-BTF at 20 days of the experiment (magnification = 15,000×).
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Figure 3. Effect of the inlet H2S concentration on the H2S removal by the anoxic biotrickling filters.
Figure 3. Effect of the inlet H2S concentration on the H2S removal by the anoxic biotrickling filters.
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Figure 4. Venn diagram on the OTUs (A) and the relative abundance (B) in the phylum of the C-BTF, DN-BTF, LW-BTF, and SW-BTF.
Figure 4. Venn diagram on the OTUs (A) and the relative abundance (B) in the phylum of the C-BTF, DN-BTF, LW-BTF, and SW-BTF.
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Figure 5. Effect of the N/S ratio on H2S removal (gas phase) (A) and nitrate removal (liquid phase) (B).
Figure 5. Effect of the N/S ratio on H2S removal (gas phase) (A) and nitrate removal (liquid phase) (B).
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Figure 6. Nitrate, nitrite, and sulfate profiles in the SW-BTF (A), LW-BTF (B), DN-BTF (C), and C-BTF (D).
Figure 6. Nitrate, nitrite, and sulfate profiles in the SW-BTF (A), LW-BTF (B), DN-BTF (C), and C-BTF (D).
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Figure 7. Elimination capacity (EC) of H2S at the various inlet loading rates (ILRs) in the BTFs under anoxic conditions.
Figure 7. Elimination capacity (EC) of H2S at the various inlet loading rates (ILRs) in the BTFs under anoxic conditions.
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Table
Table 1. The characteristics of the three sources of seeding sludge.
Table 1. The characteristics of the three sources of seeding sludge.
ParameterSWLWDN
pH7.03 ± 0.017.49 ± 0.57.91 ± 0.03
Total solid (mg/L)17,172 ± 34.25348 ± 9.29518.7 ± 8.37
Nitrate (mg/L)0.47 ± 0<0.200.66 ± 0
Sulfide (mg/L)1180 ± 5.01312 ± 2.5230.0 ± 1.53
Sulfate (mg/L)37 ± 1.0280 ± 029 ± 0
Total organic carbon (mg/L)11,320 ± 113791 ± 50.7107 ± 7.35
Total Carbon (mg/L)2870 ± 113824 ± 9.33257 ± 3.07
Total phosphorus (mg/L)80.7 ± 0.68250.4 ± 0.39753.1 ± 0.010
Note: SW = sludge from the anaerobic pond of a swine farm; LW = sludge from the UASB tank of the concentrated latex industry; DN = sludge from the denitrification pond of a seafood factory.
Table
Table 2. Operational conditions and parameters for the BTFs.
Table 2. Operational conditions and parameters for the BTFs.
ParameterPhase
IIIIII
Day1–9697–125126–145
Initial H2S concentration (CI) (ppmv)207.8–4509207.8–4131402.8–3112
Inlet loading rate (ILR)
(gS/m3-h)		8.17–177.38.17–162.512.7–97.9
The gas flow rate (m3/h)0.06 0.060.48
EBRT (s)139139174
DO (mg/L)~0~03.60 ± 0.41
Initial NO3− concentration in the recirculating media (g/L)1.55 ± 2.12.6 ± 1.22.6 ± 1.2
Recirculation flow rate (L/h)7.77.77.7
pH of the initial nutrient solution6.25–7.256.5–7.256.5–7.25
pH in the recirculating systemsNo controlNo control6.5–7.25
Table
Table 3. Predominant functional microbial genera associated with the bioconversion process in the BTFs.
Table 3. Predominant functional microbial genera associated with the bioconversion process in the BTFs.
Microbial GeneraTaxa Relative Abundance %
C-BTFDN-BTFLW-BTFSW-BTF
Proteiniphilum4.371.182.660.23
Acinetobacter34.81.462.950.80
Arenimonas6.1029.317.313.8
Castellaniella5.9226.232.916.1
Pseudomonas20.41.172.081.45
Paracoccus4.420.351.110.14
Enterobacter1.870.600.255.89
Achromobacter1.730.160.150.10
Ottowia0.369.362.534.77
Thauera0.070.520.060.06
Zoogloea0.601.050.360.98
Alicycliphilus1.125.436.337.21
Rhodanobacter1.005.2810.520.4
Thiobacillus0.924.041.241.98
Aquamicrobium1.381.732.571.13
Sphingopyxis1.160.631.980.17
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Sutarut, P.; Cheirsilp, B.; Boonsawang, P. Biodesulfurization of Consortia Immobilized on Oil Palm Frond Biochar in Biotrickling Filters under Anoxic Conditions. Fermentation 2023, 9, 664. https://doi.org/10.3390/fermentation9070664

AMA Style

Sutarut P, Cheirsilp B, Boonsawang P. Biodesulfurization of Consortia Immobilized on Oil Palm Frond Biochar in Biotrickling Filters under Anoxic Conditions. Fermentation. 2023; 9(7):664. https://doi.org/10.3390/fermentation9070664

Chicago/Turabian Style

Sutarut, Pajongsuk, Benjamas Cheirsilp, and Piyarat Boonsawang. 2023. "Biodesulfurization of Consortia Immobilized on Oil Palm Frond Biochar in Biotrickling Filters under Anoxic Conditions" Fermentation 9, no. 7: 664. https://doi.org/10.3390/fermentation9070664

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