Hydrogen sulphide removal from air by biotrickling filter using open-pore polyurethane foam as a carrier

A study was conducted on H₂S removal in a biotrickling filter packed with open-pore polyurethane foam. Thiobacillus denitrificans was used as inoculum and a mixed culture population was developed during the process. The inhibitory effect of sulphate concentration (1.8–16.8 g L⁻¹), pH (6.9–8.6), trickling liquid velocity (TLV, 9.1–22.8 m h⁻¹), H₂S inlet concentration (20–157 ppmv) and the empty bed residence time (EBRT, 9–57 s) on the H₂S removal efficiency (RE) were thoroughly investigated. An increase in pH from 6.9 to 8.5 led to a corresponding increase in H₂S removal. In addition, an inhibitory effect of sulphate concentration was observed from 16.8 g L⁻¹ and the maximum elimination capacity was found to be 22 gS m⁻³ h⁻¹ (RE 98%). The RE was constant (98.8 ± 0.30%) for EBRT ≥ 16 s, but a decrease in the EBRT from 16 to 9 s led to a corresponding decrease in RE from 98.2 to 89.6% for a TLV of 9.1 m h⁻¹ and from 97.9 to 94.9% for a TLV of 22.8 m h⁻¹ (inlet load of 11.0 ± 0.2 gS m⁻³ h⁻¹). The sulphur oxidation capacity in the biotrickling filter was not diminished by the presence of other bacteria.     

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.     

Removal of hydrogen sulfide by immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam

In the work described here, a biotrickling filter with Thiobacillus thioparus (ATCC 23645) immobilized on polyurethane foam is proposed for the removal of hydrogen sulfide contained in air. The effect of surface velocity of the recirculation medium (5.9–1.2 m/h), sulfate concentration inhibition (3.0–10.7 g/L), pH (6.0–8.2), empty bed residence time (EBRT) (150–11 s) for constant loads of 11.5 and 2.9 g S/m³/h, and pressure drop of the system were investigated.     

Biodegradation of gaseous styrene by <Emphasis Type="Italic">Brevibacillus</Emphasis> sp. using a novel agitating biotrickling filter

A novel biofilter with an agitator to control excessive biomass accumulation, the agitating biotrickling filter (ABTF) system, was developed for treatment of gaseous styrene using Brevibacillus sp. as the sole microorganism the ABTF exhibited an elimination capacity of 3 kg styrene m(-3) day(-1). After 110 days, the biodegradation efficiency decreased because of the clogging. The excess biomass was effectively removed by agitation. After the first agitation step, 42.4 g biomass was eliminated, and the removal efficiency increased from 60% to 95%. Stable operation of the ABTF was achieved by controlling the biomass accumulation via the agitation of the filter bed.     

Potential of silver nanoparticle-coated polyurethane foam as an antibacterial water filter

Silver nanoparticles can be coated on common polyurethane (PU) foams by overnight exposure of the foams to nanoparticle solutions. Repeated washing and air-drying yields uniformly coated PU foam, which can be used as a drinking water filter where bacterial contamination of the surface water is a health risk. Nanoparticles are stable on the foam and are not washed away by water. Morphology of the foam was retained after coating. The nanoparticle binding is due to its interaction with the nitrogen atom of the PU. Online tests were conducted with a prototypical water filter. At a flow rate of 0.5 L/min, in which contact time was of the order of a second, the output count of Escherichia coli was nil when the input water had a bacterial load of 10(5) colony-forming units (CFU) per mL. Combined with the low cost and effectiveness in its applications, the technology may have large implications to developing countries.     

Toluene-styrene secondary acclimation improved the styrene removal ability of biotrickling filter

In this work, ceramic pellets were used as packing material to establish a biotrickling filter (BTF) with acclimated sludge being inoculated on the surface of the packing to purify waste gas containing styrene. A method of toluene-styrene secondary acclimation was applied to achieve rapid formation of biological films. Results showed that the total time of start-up was 48 days and the removal efficiency (RE) of styrene reached up to 95%. The suitable empty bed residence time (EBRT) was obtained that is 57 s for higher RE of styrene with the inlet loading rates of 6.7–271.6 g/m³/h. The pH and moisture content showed small effect on styrene removal indicating that the operation of BTF was stable. Biomass accumulation was normal and its rising velocity under the condition of short EBRT was faster than that of long EBRT.     

Biodegradation of automotive waste polyester polyurethane foam using Pseudomonas chlororaphis ATCC55729

Automotive waste polyester polyurethane (PUR) foams represent a major solid waste management problem. In the present investigation, we examined the capacity of Pseudomonas chlororaphis ATCC 55729 to biodegrade waste polyester PUR foam obtained from an automotive industry in shake cultures. Ammonia nitrogen, pH and diethylene glycol (DEG) concentrations were found to increase steadily over a period of 12 days. Furthermore, scanning electron photomicrographs of foam pieces also showed evidence of biodegradation. This shows that waste PUR foams can be successfully biodegraded under controlled laboratory environment.     

Treatment of odorous volatile fatty acids using a biotrickling filter

In this study, a novel fibrous bioreactor was developed for treating odorous compounds present in contaminated air. The first stage of this work was a preliminary study which aimed at investigating the feasibility of using the fibrous bioreactor for the removal of malodorous volatile fatty acids (VFA) that is a common odorous contaminant generated from anaerobic degradation of organic compounds. The kinetics of microbial growth and VFA degradation in the selected culture, and the performance of the submerged bioreactor at different VFA mass loadings were studied. Above 95% of VFA removal efficiencies were achieved at mass loadings up to 22.4 g/m(3)/h. In the second stage, the odour treatment process was scaled up with system design and operational considerations. A trickling biofilter with synthetic fibrous packing medium was employed. The effects of inlet VFA concentration and empty bed retention time (EBRT) on the process performance were investigated. The bioreactor was effective in removing VFA at mass loadings up to 32 g/m(3)/h, beyond which VFA started to accumulate in the recirculation liquid, indicating the biofilm was unable to degrade all of the VFA introduced. Although VFA accumulated in the liquid phase, the removal efficiency remained above 99%. This suggested that the biochemical reaction rather than gas-liquid mass transfer was the limiting step of the treatment process. In addition, the biotrickling filter was stable for long-term operation with relatively low and steady pressure drop, no clogging and degeneration of the packing material occurred during the four-month study.     

A novel solid-state fermentation system using polyurethane foam as inert carrier

Summary A novel solid-state fermentation method using polyurethane foam as inert carrier impregnated with a synthetic liquid medium was developed simulating the nutritional composition and culture conditions of solid-state fermentation on wheat bran. With this system, biomass, the important parameter involved in solid-state fermentation processes, can be measured directly. Some other superiorities of this system over conventional solid-state fermentation systems are discussed.     

Anchorage-dependent mammalian cell culture using polyurethane foam as a new substratum for cell attachment

Summary Anchorage-dependent mammalian cells were cultivated at high cell density in a novel culture system using polyurethane foam (PUF) as a substratum for cell attachment. PUF has a macroporous structure giving a high surface area to volume ratio. Monkey kidney cells (Vero) and Chinese hamster ovary cells (CHO-K1) attached to the internal surface of PUF and grew to a high cell density (1.04 × 10⁸ cells/ cm³ PUF and 3.5 × 10⁷ cells/ cm³ PUF, respectively) in PUF stationary cultures. In addition, we have designed a PUF-particle packed-bed culture system for high density mass cell culture. A maximum cell density of 2.4 × 10⁷ cells/cm³ culture vessel volume was obtained in a packed-bed culture of Vero cells. Offprint requests to: K. Funatsu     

Biodegradation of polyurethane: a review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. Increasingly, raw materials such as crude oil are in short supply for the synthesis of plastics, and the recycling of waste plastics is becoming more important. As the importance of recycling increases, so do studies on elucidation of the biodegradability of polyurethanes. Polyurethanes are an important and versatile class of man-made polymers used in a wide variety of products in the medical, automotive and industrial fields. Polyurethane is a general term used for a class of polymers derived from the condensation of polyisocyanates and polyalcohols. Despite its xenobiotic origins, polyurethane has been found to be susceptible to biodegradation by naturally occurring microorganisms. Microbial degradation of polyurethanes is dependent on the many properties of the polymer such as molecular orientation, crystallinity, cross-linking and chemical groups present in the molecular chains which determine the accessibility to degrading-enzyme systems. Esterase activity (both membrane-bound and extracellular) has been noted in microbes which allow them to utilize polyurethane. Microbial degradation of polyester polyurethane is hypothosized to be mainly due to the hydrolysis of ester bonds by these esterase enzymes.     

Incomplete protein packing as a selectivity filter in drug design

The conservation of structure across paralog proteins promotes alternative protein-ligand associations often leading to side effects in drug-based inhibition. However, sticky packing defects are typically not conserved across paralogs, making them suitable targets to reduce drug toxicity. This observation enables a strategy for the design of highly specific inhibitors involving ligands that wrap nonconserved packing defects. The selectivity of these inhibitors is evidenced in affinity assays on a cancer-related pharmacokinome: a powerful inhibitor is redesigned by using the wrapping technology to enhance its selectivity and affinity for a target kinase. In this way, the packing defects of a soluble protein may be used as selectivity filters for drug design.     

Bacterial degradation of styrene in waste gases using a peat filter

A biofiltration process was developed for styrene-containing off-gases using peat as filter material. The average styrene reduction ratio after 190 days of operation was 70% (max. 98%) and the mean styrene elimination capacity was 12 g m⁻³ h⁻¹ (max. 30 g m⁻³ h⁻¹). Efficient styrene degradation required addition of nutrients to the peat, adjustment of the pH to a neutral level and efficient control of the humidity. Maintenance of the water balance was easier in a down-flow than in an up-flow process, the former consequently resulting in much better filtration efficiency. The optimum operation temperature was around 23 °C, but the styrene removal was still satisfactory at 12 °C. Seven different bacterial isolates belonging to the genera Tsukamurella, Pseudomonas, Sphingomonas, Xanthomonas and an unidentified genus in the γ group of the Proteobacteria isolated from the microflora of active peat filter material were capable of styrene degradation. The isolates differed in their capacity to decompose styrene to carbon dioxide and assimilate it to biomass. No toxic intermediate degradation products of styrene were detected in the filter outlet gas or in growing cultures of isolated bacteria. The use of these isolates in industrial biofilters is beneficial at low styrene concentrations and is safe from both the environmental and public health points of view. Received: 30 May 1997 / Received revision: 22 August 1997 / Accepted: 25 August 1997     

Continuous semi-solid cultivation for the production of cellulase by Trichoderma reesei mutants using a polyurethane foam carrier and a liquid medium

The production of cellulase was investigated in semi-solid state culture using the immobilized mycelium of Trichoderma reesei mutants on polyurethane foam impregnated with lactose medium. An extremely high value of about 2.6 FPU/ml was reached after the cultivation of T. reesei D-78085 on a 0.5% lactose medium in continuous culture at a pH medium of 4.0 when a bioreactor with vertical polyurethane foam plates was used. The enzyme yield on lactose was 520 FPU/g of lactose metabolized in comparison with 160 FPU/g using a stirred tank bioreactor.     

Biodegradation of toluene in a trickling filter

A trickling filter packed with PVC 16?mm Raschig rings was used to study the degradation of toluene in a polluted air stream, by means of a bacterial biofilm of Pseudomonas putida ATCC 17484. A polluted stream was simulated by blending air with a controlled amount of toluene. The mixing was accomplished in a special mixing chamber designed for that purpose. Induction of the enzymes of the toluene degradative pathway and adaptation of the inoculum were done in batch cultures with minimum mineral media and phenol. The continuous experiments were monitored by mass spectrometry for the quantification of the various gases and of toluene removal. A 94% toluene removal was achieved with contacting times above one minute and toluene concentrations up to 400?ppm.     

Evaluation of a pilot-scale biotrickling filter as a VOC control technology for the plastic coating sector

The performance and feasibility of a biotrickling filter (BTF) pilot unit for the treatment of exhaust gases from two robotic spray paint booths at a plastic coating facility were investigated. The volatile organic compound (VOC) concentrations in the emissions of the exhaust gases from the paint booths were relatively stable, although the VOC composition depended on the applied solvent-paint formulation in the booths. The pilot plant was operated for one year at empty bed residence times (EBRTs) ranging from 30 to 93 s. The performance of the system was affected by the solvent-paint formulations. An EBRT between 30 and 40 s was enough to meet legal requirements for products containing more than 60% biodegradable compounds, whereas a minimum EBRT of 80 s was required for emissions mainly composed of hydrophobic VOCs. The dynamics of the microbial population was carried out by fluorescence in situ hybridisation (FISH), indicating a high microbial diversity with composition changes associated with the solvent-paint used. The feasibility of the BTF was evaluated, showing that this technology is economically and environmentally competitive in comparison with thermal treatment technology.     

Prolonged lidocaine metabolizing activity of primary hepatocytes with spheroid culture using polyurethane foam as a culture substratum

Primary rat hepatocytes formed spheroids in the pores of polyurethane foam (PUF) used as a culture substratum. The hepatocytes in monolayer and spheroid stationary culture converted lidocaine to monoethylglycinexylidide (MEGX) which was N-deethylation of lidocaine. The metabolic activity of the hepatocytes/spheroid stationary culture system was 1.5∼2.0-fold higher than that of monolayer culture for 10 days. The activity of albumin production and cell survival of hepatocytes in monolayer and spheroid cultures decrease due to lidocaine treatment dependend on the lidocaine concentration, but the activity and cell survival in PUF/spheroid stationary culture were maintained at a higher level than that in monolayer culture under the lidocaine treatment. We developed a device for an in vitro liver model, drug metabolism simulator (DMS), using a PUF/spheroid packed-bed module including 4.00 ± 0.68 × 10⁷ hepatocytes and analyzed pharmacokinetics of lidocaine in a one-compartment model. Lidocaine clearance and extraction ratio of hepatocytes in the DMS corresponded to 1.354 ± 0.318 ml/min/g-liver and 0.677 ± 0.0159/g-liver, respectively (N=4). These values were comparable with in vivo values, 1.930 ml/min g-liver and 0.965/g-liver reported by Nyberg (1977). Consequently, PUF/spheroid culture maintained high lidocaine metabolizing activity over a long term and seems to provide a promising culture system as a drug metabolism simulator which will be used for drug screening, cytotoxicity tests and prediction of pharmacokinetics. This revised version was published online in July 2006 with corrections to the Cover Date.     

7-Amino-2,4,6-trimethylquinoline as a mutagenic pyrolysate compound of polyurethane foam

Commercial polyurethane foam was pyrolyzed by gas burners at 600-700 degrees C for 2 h with introduction of air (200 ml/min). Gaseous pyrolysate was trapped in water and 10% hydrochloric acid. Basic and neutral pyrolysates have a mutagenic activity (447 revertants/10 micrograms) in Salmonella typhimurium TA98 in the presence of a mammalian metabolic activation system. These pyrolysates contained 12.32 mg of amino compounds as diaminotoluene per g polyurethane foam, amounts which are 120 times higher than those in unpyrolysed polyurethane foam. Basic and neutral pyrolysates were subjected to silica gel column chromatography, and 6 fractions having mutagenic potency were obtained. The colorless needles (m.p. 200.5-202 degrees C) were separated from fraction 4. These needles have the most potent mutagenicity (678 revertants/2 micrograms) in basic and neutral pyrolysates in Salmonella typhimurium TA98 with 10% S9 mix. From the physicochemical data, the structure of the compound was estimated to be an aminoquinoline derivative, and was identified using synthesized 7-amino-2,4,6-trimethylquinoline by mixed melting point, thin-layer co-chromatography and gas chromatography-mass spectrometry.     

Odorous composting gas abatement and microbial community diversity in a biotrickling filter

This study aimed to remove complex odorous gas produced from composting using a biotrickling filter and to observe the temporal and special distributions of bacteria, fungi, and actinomycetes. The removal efficiencies of the total volatile organic compounds (TVOC) were 26.1% and 81.5% before and after inoculation of volatile organic compounds (VOC)-degrading microbes, respectively. Especially trimethylamine was 100% degraded. In the first and second composting period, the odor reduction efficiencies showed average values of 86.2% and 94.5%, respectively. The total average of the bacteria in the biofilm was 2.06 × 10⁹ CFU/g TS, which was 22.2% higher than that of the control (the culture of microbes prior to the inoculation of VOC-degrading microbes). The bacteria may have played a predominant role in odor removal. The total average of the fungi in the biofilm was 9.64 × 10⁶ CFU/g TS, which was only 6.40% of the control. The total average of the actinomycetes in the biofilm was 5.10 × 10⁵ CFU/g TS, which was 5.63 times higher than that of the control. Findings from this study showed that usage of a biotrickling filter is a promising process for the treatment of complex odorous gas.