Performance of three pilot-scale immobilized-cell biotrickling filters for removal of hydrogen sulfide from a contaminated air steam

Hydrogen sulfide (H₂S) is a major malodorous compound emitted from wastewater treatment plants. In this study, the performance of three pilot-scale immobilized-cell biotrickling filters (BTFs) spacked with combinations of bamboo charcoal and ceramsite in different ratios was investigated in terms of H₂S removal. Extensive tests were performed to determine the removal characteristics, pressure drops, metabolic products, and removal kinetics of the BTFs. The BTFs were operated in continuous mode at low loading rates varying from 0.59 to 5.00 g H₂S m⁻³ h⁻¹ with an empty bed retention time (EBRT) of 25 s. The removal efficiency (RE) for each BTF was >99% in the steady-state period, and high standards were met for the exhaust gas. It was found that a multilayer BTF had a slight advantage over a perfectly mixed BTF for the removal of H₂S. Furthermore, an impressive amount >97% of the H₂S was eliminated by 10% of packing materials near the inlet of the BTF. The modified Michaelis–Menten equation was adopted to describe the characteristics of the BTF, and K_s and V_m values for the BTF with pure bamboo charcoal packing material were 3.68 ppmv and 4.26 g H₂S m⁻³ h⁻¹, respectively. Both bamboo charcoal and ceramsite demonstrated good performance as packing materials in BTFs for the removal of H₂S, and the results of this study could serve as a guide for further design and operation of industrial-scale systems.     

Abatement of odorant compounds in one- and two-phase biotrickling filters under steady and transient conditions

The removal of hydrophobic volatile organic compounds (VOCs) still remains the main restriction in the biological treatment of odorous emissions due to mass transfer limitations. The addition of a non-aqueous phase to conventional biotrickling filters (BTF) may overcome this limitation by enhancing VOCs transport from the gas to the microorganisms. This study compared the long-term and transient performance of a one- (1P) and two-liquid phase (2P; with silicone oil as non-aqueous phase) BTFs for the removal of four VOCs (butanone, toluene, alpha-pinene, and hexane) at empty bed residence times (EBRT) ranging from 47 to 6 s. Removal efficiencies (RE) >96 % were obtained for butanone, toluene, and alpha-pinene in both bioreactors regardless of the EBRT, while higher hexane REs were recorded in the 2P-BTF (81–92 %) compared to the 1P-BTF (60–97 %). The two-phase system always showed a more consistent performance, being able to better withstand step VOC concentration increases and starvation periods, although it was more affected by liquid recycling shutdowns due to a reduced VOC mass transfer. The analysis of the microbial communities showed a high biodiversity and richness despite the low C source spectrum and high community evenness and richness. In this context, the presence of silicone oil mediated the development of a highly different phylogenetic composition of the communities.     

Performance of a biotrickling filter in the removal of waste gases containing low concentrations of mixed VOCs from a paint and coating plant

The performance of a field-scale biotrickling filter (BTF) in the removal of waste gases containing low concentrations of mixed volatile organic compounds was evaluated. Results showed that acetone and methyl ethyl ketone (MEK) were more easily removed than toluene and styrene. The removal efficiency for acetone and MEK reached over 99% on days 28 and 25 of the operation, whereas those for toluene and styrene were 80 and 63% on day 38. The maximum individual elimination capacities for styrene, toluene, acetone, and MEK were 10.2, 2.7, 4.7, and 8.4 g/m³ h, respectively. These values were achieved at inlet loading rates of 13.9, 3.3, 4.8, and 8.5 g/m³ h, respectively, at an empty bed retention time of 14 s. the removal efficiency for styrene and toluene rapidly increased from 67% and 83% to 86% and over 99%, respectively, when the concentration of ammonia nitrogen (N–NH₄ ⁺) and phosphates (P) in the nutrients increased from 350 to 840 mg/l and 76 to 186 mg/l. When the BTF was restarted after a four-day shutdown, the removal efficiency for toluene was restored to over 99% within a week. However, that for styrene was not restored to its previous level before the shutdown. No noticeable adverse effect on acetone and MEK removal was observed. Denaturing gradient gel electrophoresis results for the bacterial community in the BTF during VOC removal showed that proteobacterial phylum was dominant, and the changes of nutrient concentration and shutdown periods may have played a role in the community structure differences.     

Biodegradation of gas-phase styrene in a high-performance biotrickling filter using porous polyurethane foam as a packing medium

A biotrickling filter (BTF) packed with porous polyurethane (PU) foam sheets was developed and operated for removal of gas-phase styrene. The specific surface area and void fraction of the PU foam sheet were determined to be 497 m²/m³ and 0.92, respectively, by using mathematical modeling and experimental measurement. The effects of gas flow direction (co-current and counter-current), styrene loading rate and empty bed residence time on the efficiency of the BTF were analyzed. The BTF achieved a high elimination capacity of 4.0 ∼ 5.0 kg styrene/m³ day due to the high specific surface area of the PU foam. The BTF could be operated repeatedly when excessively-grown biomass was periodically removed, using circulating NaOH solution for 2 h every four days.     

Biotrickling filtration of isopropanol under intermittent loading conditions

This paper investigates the removal of isopropanol by gas-phase biotrickling filtration. Two plastic packing materials, one structured and one random, have been evaluated in terms of oxygen mass transfer and isopropanol removal efficiency. Oxygen mass transfer experiments were performed at gas velocities of 104 and 312 m h^?1 and liquid velocities between 3 and 33 m h^?1. Both materials showed similar mass transfer coefficients up to liquid velocities of 15 m h^?1. At greater liquid velocities, the structured packing exhibited greater oxygen mass transfer coefficients. Biotrickling filtration experiments were carried out at inlet loads (IL) from 20 to 65 g C m^?3 h^?1 and empty bed residence times (EBRT) from 14 to 160 s. To simulate typical industrial emissions, intermittent isopropanol loading (16 h/day, 5 day/week) and intermittent spraying frequency (15 min/1.5 h) were applied. Maximum elimination capacity of 51 g C m^?3 h^?1 has been obtained for the random packing (IL of 65 g C m^?3 h^?1, EBRT of 50 s). The decrease in irrigation frequency to 15 min every 3 h caused a decrease in the outlet emissions from 86 to 59 mg C Nm^?3 (inlet of 500 mg C Nm^?3). The expansion of spraying to night and weekend periods promoted the degradation of the isopropanol accumulated in the water tank during the day, reaching effluent concentrations as low as 44 mg C Nm^?3. After a 7-week starvation period, the performance was recovered in less than 10 days, proving the robustness of the process.     

The operating performance of a biotrickling filter with Lysinibacillus fusiformis for the removal of high-loading gaseous chlorobenzene

Removal of gaseous chlorobenzene (CB) by a biotrickling filter (BTF) filled with modified ceramics and multi-surface hollow balls during gas–liquid mass transfer at the steady state was by microbial degradation rather than dissolution in the spray liquid or emission into the atmosphere. The BTF was flexible and resistant to the acid environment of the spray liquid, with the caveat that the spray liquid should be replaced once every 6–7 days. The BTF, loaded with Lysinibacillus fusiformis, performed well for purification of high-loading CB gas. The maximum CB gas inlet loading rate, 103 g m^?3 h^?1, CB elimination capacity, 97 g m^?3 h^?1, and CB removal efficiency, 97.7 %, were reached at a spray liquid flow rate of 27.6 ml min^?1, an initial CB concentration of up to 1,300 mg m^?3, and an empty bed retention time of more than 45 s.     

Biofiltration of reduced sulphur compounds and community analysis of sulphur-oxidizing bacteria

The present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H₂S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS > DMS > MM. The EC values were 9.8 g_MM-S/m³/h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g_DMDS-S/m³/h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g_H2S-S/m³/h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H₂S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H₂S concentration from 75 to 432 ppmv.     

Laboratory-scale biofiltration of acrylonitrile by <Emphasis Type="Italic">Rhodococcus rhodochrous</Emphasis> DAP 96622 in a trickling bed bioreactor

Acrylonitrile (ACN), a volatile component of the waste generated during the production of acrylamide, also is often associated with aromatic contaminants such as toluene and styrene. Biofiltration, considered an effective technique for the treatment of volatile hydrocarbons, has not been used to treat volatile nitriles. An experimental laboratory-scale trickling bed bioreactor using cells of Rhodococcus rhodochrous DAP 96622 supported on granular activated carbon (GAC) was developed and evaluated to assess the ability of biofiltration to treat ACN. In addition to following the course of treatability of ACN, kinetics of ACN biodegradation during both recycle batch and open modes of operation by immobilized and free cells were evaluated. For fed-batch mode bioreactor with immobilized cells, almost complete ACN removal (>95%) was achieved at a flow rate of 0.1 μl/min ACN and 0.8 μl/min toluene (TOL) (for comparative purposes this is equivalent to 6.9 mg l^?1 h^?1 ACN and 83.52 mg l^?1 h^?1 TOL). In a single-pass mode bioreactor with immobilized cells, at ACN inlet loads of 100–200 mg l^?1 h^?1 and TOL inlet load of ~400 mg l^?1 h^?1, with empty bed retention time (EBRT) of 8 min, ACN removal efficiency was ~90%. The three-dimensional structure and characteristics of the biofilm were investigated using confocal scanning laser microscopy (CSLM). CLSM images revealed a robust and heterogeneous biofilm, with microcolonies interspersed with voids and channels. Analysis of the precise measurement of biofilm characteristics using COMSTAT^® agreed with the assumption that both biomass and biofilm thickness increased along the carbon column depth.     

Ammonia removal from a waste air stream using a biotrickling filter packed with polyurethane foam through the SND process

This paper presents the results of a bench-scale biotrickling filter (BTF) on the removal of ammonia gas from a waste stream using a simultaneous nitrification/denitrification (SND) process. It was found that the developed BTF could completely remove 100 ppm ammonia from a waste stream, with an empty bed retention time of 60 s and 98.4% nitrogen removal through the SND process under the tested conditions. It was elucidated that both autotrophic and heterotrophic bacteria were involved in the nitrogen removal trough the SND process in the BTF. Additionally, the elimination capacity of total nitrogen by the BTF increased from 3.5 to 18.4 g N/m³ h with an inlet load of 20.6 g N/m³ h (73.6%). The findings of this study suggest that the BTF can be operated to attain complete ammonia removal through the SND process, thereby making the treatment of ammonia-laden gas streams both short and cost-effective.     

Hydrogen sulfide removal performance of a bio-trickling filter employing Thiobacillus thiparus immobilized on polyurethane foam under various starvation regimes

In the present study a biotrickling filter (BTF) with countercurrent gas/liquid flow packed with open-pore polyurethane foam — as a carrier of Thiobacillus thioparus (DSMZ5368) — was subjected to various starvation regimes such as non-contaminant loading, idleness, and complete shutdown. During the starvation periods specific oxygen uptake rates of microorganisms (SOUR) on packing were monitored. The BTF was subjected to non-contaminant loading (up to 16 h), cyclic non-contaminant loading (for 4 days) and gas shut-off (up to 24 h), and it recovered to its pre-starvation removal efficiency within a 2 ～ 3 h period after resuming normal operating conditions. The recovery time values obtained during the runs in which these starvation regimes were imposed could be indirectly correlated with the corresponding SOUR values suggesting that the recovery time after such starvation regimes are dependent on the degree to which the aerobic biological activity has been reduced as a result of the imposed starvation regime. In the case of the complete shutdown of the BTF, the recovery time increased substantially after 1 and 2 days of complete shutdown, and after 5 days of complete shutdown the pre-starvation removal efficiency was not achieved even after 12 days of normal operation.     

Effects of nitrogen source and empty bed residence time on the removal of styrene gaseous emissions by biotrickling filtration

The removal of styrene-polluted air emissions by biotrickling filtration was performed to evaluate the influence of using nitrate and urea as a nitrogen source in the nutrient solution supplied to two bioreactors run in parallel under the same operational conditions for 3 months. The use of urea resulted in less biomass content along the packed bed and better performance of the process, with a maximum elimination capacity (EC) of 57.6 g C m⁻³ h⁻¹ (removal efficiency (RE) of 88.3% and empty bed residence time (EBRT) of 60 s), which was around 54% higher than when using nitrate. EBRTs of 60, 30 and 15 s were evaluated with a urea-based nutrient supply. By decreasing the EBRT from 60 to 30 s the styrene concentration that could be treated with REs above 80% was almost the half, from 1,100 to 600 mg C m⁻³, resulting in ECs of 52.8 g C m⁻³ h⁻¹. Working at 15 s was not possible to obtain REs higher than 40% with a maximum EC of 28.5 g C m⁻³ h⁻¹.     

Reverse-flow strategy in biofilters treating CS2 emissions

The bacteriostatic properties of carbon disulphide (CS₂) hamper its biodegradation in conventional biofilters. The response of four biofilters operating in downflow mode and reverse-flow mode was compared in a laboratory-scale plant treating CS₂ under sudden short-term changes in operating conditions. A process shutdown for 24 h, an inlet concentration increase and an interruption of the inlet air humidification for 48 h at an empty bed residence time (EBRT) of 240 s did not impact significantly on biodegradation performance, regardless of flow mode. Nevertheless, a reduction in the EBRT to 60 s resulted in a significant decrease in removal efficiency in all the biofilters. The CS₂ degradation profile showed that the reverse-flow mode strategy rendered a more homogenous distribution of biomass along the bed height. The benefits of the reverse-flow mode were demonstrated even when the unidirectional flow mode was re-established.     

Styrene removal from polluted air in one and two-liquid phase biotrickling filter: steady and transient-state performance and pressure drop control

A Sporothrix variecibatus-inoculated biotrickling filter (BTF) was examined for styrene removal, without and with the addition of silicone oil, at different empty bed residence times. The highest elimination capacities (ECs) were 172.8 (without silicone oil) and 670 g m⁻³ h⁻¹ (with silicone oil), respectively, corresponding to a 4-fold improvement in presence of oil. The addition of silicone oil formed a well-coalesced emulsion of fungi and silicone oil, resulting in filter-bed clogging. Clogging prevention strategies adopted were; (i) lowering the volume ratio of silicone oil from 10% to 2% (v/v), and (ii) periodic increase in trickling rate of the medium from 50 to 190 mL min⁻¹. During shock-load experiments, the BTF with silicone oil (2% v/v) could withstand high styrene loads, of up to 1900 g m⁻³ h⁻¹, when compared to the BTF without silicone oil (400 g m⁻³ h⁻¹).     

Purification of waste gas containing high concentration trimethylamine in biotrickling filter inoculated with B350 mixed microorganisms

A biotrickling filter packed with ceramic particles and seeded with B350 microorganisms was applied to remove trimethylamine (TMA) from gaseous waste. A 100% removal efficiency (RE) was obtained when the empty bed residence time (EBRT) was larger than 110 s at an inlet concentration of 0.30 mg/L. Maximum elimination capacity (EC) was 13.13 g m⁻³ h⁻¹ (RE = 64.7%) at 55 s of EBRT. TMA concentrations <0.20 mg/L at 83 s of EBRT did not affect the REs (100%). Maximum EC was 13.95 g m⁻³ h⁻¹ (RE = 78.1%) at a TMA concentration of 0.42 mg/L. Approximately 53.1% of the carbon in TMA was completely mineralized. Bacterial community analysis in the bioreactor revealed more than 21 species in a stable state. Based on all these results, biotrickling filter inoculated with B350 microorganisms is deemed highly capable of ridding waste gas of TMA.     

Steady-state and transient-state performance of a biotrickling filter treating chlorobenzene-containing waste gas

Biotrickling filter (BTF) technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. An adapted microbial community was immobilised on a structured packing material. The strategy followed was to reach high removal efficiencies at initially low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only 2 weeks. A 3-month operation under steady-state conditions showed good performance, with >95% removal efficiency at a mass loading rate of 1,800 g m^–3 day^–1. Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l^–1 and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralisation of the pollutant. Transient-state experiments with five times higher mass loading rates caused a decrease in the removal efficiency that recovered rapidly once the mass loading rate returned to its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads of up to 5,200 g m^–3 day^–1 over several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a BTF system with excellent performance and stability that efficiently removes a mixture of cholorobenzene vapours from air can be obtained.     

Control of methanol vapours in a biotrickling filter: performance analysis and experimental determination of partition coefficient

Methanol vapours were treated in a biotrickling filter (BTF) packed with inert polypropylene spheres. The effects of the nitrogen concentration in the nutrient solution, the empty bed residence time (EBRT) and the methanol inlet concentration, on the BTF performance, were all examined. The elimination capacity (EC), the biomass and the carbon dioxide production rates were all increased with the rising of the nitrogen concentration and the EBRT. The EC also rose with increasing methanol inlet load (IL) when the methanol inlet concentration and the EBRT were varied, from 0.3 to 37.0 g m(-3), and from 20 to 65 s, respectively. The BTF reached its maximum EC level of 2160 g m(-3) h(-1) when it was operated at an IL level of 3700 g m(-3) h(-1). The input methanol was removed through two mechanisms: biodegradation and absorption in the liquid phase. The partition coefficient for the methanol in the BTF was determined at five EBRTs and along the packed bed. It generally followed the Henry model, having an average value of 2.64 x 10(-4)[mol L(-1)](gas)/[mol L(-1)](liquid).     

Styrene degradation by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. SR-5 in biofilters with organic and inorganic packing materials

Pseudomonas sp. SR-5 was isolated as a styrene-degrading bacterium. In liquid culture containing 1% (v/v) styrene, more than 90% styrene was degraded in 53 h and the doubling time of SR-5 was 2 h. The removal of styrene gas was investigated in biofilters for 31 days using an organic packing material of peat and an inorganic packing material of ceramic inoculated with SR-5. The maximum-styrene-elimination capacities for peat and ceramic packing materials were 236 and 81 g m^–3 h^–1, respectively. The percentage of styrene converted to low molecular weight compounds including CO₂ in the peat and ceramic biofilters during a 10-day operation were estimated to be 90.4 and 36.7%, respectively. As the pressure drop in the peat bioflter at the end of experiment was significantly higher than that in ceramic biofilter, a biofilter using a mixture of peat and ceramic was tested. We determined that the maximum elimination capacity was 170 g m^–3 h^–1 and the production of low molecular weight compounds was 95% at a low pressure drop for this mixed packing material filter.     

Sexual reproduction and seed dispersal pattern of annual and perennial Zostera marina in a heterogeneous habitat

The sexual reproduction of annual and perennial Zostera marina was investigated in Moon Lake, Shandong, China. Based on the disturbance and stress regimes, the Z. marina beds were classified into five types: intertidal annual (IA) and perennial (IP) eelgrass patches, subtidal patch area (PA), meadow margin (MM) and meadow center (MC). Seed dispersal was investigated using artificial seagrass units in the five areas and another two areas [adjacent bare area and Zostera japonica meadow (Zj)]. Total and flowering shoot density and aboveground biomass of flowering shoots per unit area were higher in PA and MM, and lower in IA and IP, whereas the total biomass per unit area in MC showed the highest value. Reproductive effort (RE) in IA showed negative response to intertidal stress, while in perennial IP, PA and MM it showed significantly positive response to anthropogenic or natural disturbances. The density-based RE in perennial IP, PA and MM was 1.1-, 5.1- and 5.1-fold higher than that in MC, while in annual IA it was 0.46-fold lower. Additionally, the biomass-based RE in IP, PA and MM was 1.8-, 3.5- and 3.8-fold higher than that in MC, while the RE in IA was 0.84-fold lower. The estimated seed production per unit area was much greater in PA (60,793 ± 9,843 seeds m^?2) and MM (43,414 ± 8,718 seeds m^?2) than in IA (416 ± 83 seeds m^?2), IP (3,820 ± 1,470 seeds m^?2) and MC (9,779 ± 631 seeds m^?2), while the seed density ranged from 24 ± 6 to 584 ± 56 seeds m^?2. Results suggested that in response to disturbances and stress, Z. marina in subtidal areas increased their RE and seed production and thus seeds were available to be dispersed into areas where seed production was limited.     

Performance evaluation and microbial community analysis of the composite filler micro-embedded with Pseudomonas putida for the biodegradation of toluene

The composite filler micro-embedded with Pseudomonas putida (P. putida) was prepared and the biodegradation performance of the filler was evaluated in a biofilter. Five phases were set up to evaluate the performance of the biofilter under different toluene inlet loadings and transient shock loadings. In particular, the microbial community structure in the biofilms and fillers was measured by sequence analysis of the 16S rRNA gene. The results show that the biofilter packed with the composite fillers was suitable for the biodegradation of toluene. The biofilter could start up quickly with high removal efficiency (RE), and remain above 90 % RE when the empty bed residence time (EBRT) was 18 s and the inlet loading rates were not higher than 41.4 g/(m³·h). Moreover, the biofilter could tolerate substantial transient shock loadings. The high removal efficiency and elimination capacity contributed to rich bacterial communities for the efficient degradation of toluene. The dominant microbial communities at the phylum level were mainly Firmicutes, Actinobacteria and Proteobacteria. It is noteworthy that the abundance of Bacteroidetes at phylum level and Chungangia and Stenotrophomonas at genus level increased significantly during the re-start period.     

Optimization of Influencing Parameters on Phenanthrene Removal Efficiency in Soil Washing Process by Using Response Surface Methodology

Response surface methodology (RSM) under Box–Behnken design (BBD) was applied to evaluate the effect of the influencing parameters including surfactant concentration, liquid/soil ratio, Humic Acid concentration, and washing time on phenanthrene removal efficiency in soil washing process by using the nonionic surfactant Tween 80 and find an optimal operational conditions to achieve the highest removal efficiency. A polynomial quadratic model was used to correlate phenanthrene removal efficiency and four independent variables (R² = 0.9719). Based on the obtained results the most influential parameter on phenanthrene removal efficiency was surfactant concentration with an impact value of 69.519%. Liquid/soil ratio was also another factor that significantly influenced on removal efficiency with an impact value of 25.014%. The interaction between surfactant concentration and liquid/soil ratio was also shown to have a positive significant effect on removal efficiency (p_value = 0.0027). However, the other independent variables Humic Acid concentration and time were not significant in the ranges selected in this study. Based on the optimization results maximum removal efficiency of 70.692 ± 3.647% was achieved under the conditions of surfactant concentration 5000 mg L^?1, liquid/soil ratio 30 v/w, HA concentration 9.88 mg L^?1, and washing time 2 h, which was in good agreement with predicted value (66.643%).