Contaminated Air Streams Research Articles

Methanol removal efficiency and bacterial diversity of an activated carbon biofilter

Motivated by the need to establish an economical and environmentally friendly methanol control technology for the pulp and paper industry, a bench-scale activated carbon biofiltration system was developed. This system was evaluated for its performance in removing methanol from an artificially contaminated air stream and characterized for its bacterial diversity over time, under varied methanol loading rates, and in different spatial regions of the filter. The biofilter system, composed of a novel packing mixture, provided an excellent support for growth and activity of methanol-degrading bacteria, resulting in approximately 100% methanol removal efficiency for loading rates of 1–17 g/m 3 packing/h, when operated both with and without inoculum containing enriched methanol-degrading bacteria. Although bacterial diversity and abundance varied over the length of the biofilter, the populations present rapidly formed a stable community that was maintained over the entire 138-day operation of the system and through variable operating conditions, as observed by PCR–DGGE methods that targeted all bacteria as well as specific methanol-oxidizing microorganisms. Phylogenetic analysis of bands excised and sequenced from DGGE gels indicated that the biofilter system supported a diverse community of methanol-degrading bacteria, with high similarity to species in the genera Methylophilus (β-proteobacteria), Hyphomicrobium and Methylocella (both α-proteobacteria).

Treatment of benzene vapors from contaminated air stream in a laboratory-scale compost biofilter

Biofiltration of process waste–gas streams using microorganisms attached to porous support matrix, at low concentrations and high gas flow rates, has gained importance as a versatile treatment technology ever since the Clean Air Act Amendments (1990), by the US – EPA came into existence. In this study, we evaluated the potential of a laboratory–scale biofilter, inoculated with mixed culture, to remove gas–phase benzene from a synthetic waste gas stream. Experiments were conducted in three different phases, after the acclimatization step, corresponding to empty bed residence times (EBRT) varying between 0.81–2.45 min and benzene concentrations up to 1.7 g/m3. At high concentrations, significant reduction in removal efficiency was observed, which may be due to insufficient biomass in the filter bed to utilize the substrate, or due to substrate inhibition at high concentrations. Removal efficiencies higher than 90% were achieved for inlet benzene loading rates lesser than 40 g/m3hr.

Simultaneous biofiltration of H2S, NH3 and toluene using cork as a packing material

Simultaneous removal of ternary gases of NH3, H2S and toluene in a contaminated air stream was investigated over 185 days in a biofilter packed with cork as microbial support. Multi-microorganisms including Nitrosomonas and Nitrobactor for nitrogen removal, Thiobacillus thioparus (ATCC 23645) for H2S removal and Pseudomonas aeruginosa (ATCC 15692), Pseudomonas putida (ATCC 17484) and Pseudomonas putida (ATCC 23973) for toluene removal were used simultaneously. The empty bed residence time (EBRT) was 40–120 seconds and the inlet feed concentration was 50-180 ppmv for NH3, 30–160 ppmv for H2S and 40–130 ppmv for toluene, respectively. The observed removal efficiency was 45–100% for NH3, 96–100% for H2S, and 10–99% for toluene, respectively. Maximum elimination capacity was 5.5 g/m3/hr for NH3, >20.4 g/m3/hr for H2S and 4.5 g/m3/hr for toluene, respectively. During long-term operation, the removal efficiency of toluene gradually decreased, mainly due to depositions of elemental sulfur and ammonium sulfate on the cork surface. The results of microbial analysis showed that nearly the same population density was observed on the surfaces of cork chips collected at each sampling point. Kinetic model analyses showed that there were no particular evidences of interactions or inhibitions among the microorganisms.

Solid-liquid two-phase partitioning bioreactors for the treatment of gas-phase volatile organic carbons (VOCs) by a microbial consortium

A two-phase partitioning bioreactor (TPPB), employing styrene-butadiene co-polymer beads as the sequestering/delivery phase, was used to treat high step change loadings of toluene in a contaminated air stream. The polymers, which are biocompatible and non-bioavailable, allowed the use of a microbial consortium and effectively absorbed and released the toluene vapours for biodegradation, while providing a buffering effect against high toluene transients. Toluene loadings were increased from a base steady state rate of 343-6,000 g/m(3) h for 1 h periods, with the polymer-aqueous system substantially outperforming a single phase system on the basis of improving the toluene removal efficiency and reducing the maximum toluene concentrations emitted during the transients.

Simultaneous Biofiltration of H2S, NH3and Toluene using an Inorganic/Polymeric Composite Carrier

Simultaneous removal of ternary gases of NH3, H2S and toluene in a contaminated air stream was investigated over 180 days in a biofilter. A commercially available inorganic/polymeric composite chip with a large void volume (bed porosity > 0.80) was used as a microbial support. Multiple microorganisms including Nitrosomonas and Nitrobactor for nitrogen removal, Thiobacillus thioparus (ATCC 23645) for H2S removal and Pseudomonas aeruginosa (ATCC 15692), Pseudomonas putida (ATCC 17484) and Pseudomonas putida (ATCC 23973) for toluene removal were used simultaneously. The empty bed residence time (EBRT) ranged from 60 - 120 seconds and the inlet feed concentration was 0.0325 g/m 3 - 0.0651 g/m 3 for NH3, 0.0636 g/m 3 - 0.141 g/m 3 for H2S, and 0.0918 g/m 3 - 0.383 g/m 3 for toluene, respectively. The observed removal efficiency was 2% 98% for NH3, 2% - 100% for H2S, and 2% - 80% for toluene, respectively. Maximum elimination capacity was about 2.7 g/m 3 /hr for NH3, > 6.4 g/m 3 /hr for H2S and 4.0 g/m 3 /hr for toluene, respectively. The inorganic/polymeric composite carrier required 40 - 80 days of wetting time for biofilm formation due to the hydrophobic nature of the carrier. Once the surface of the carrier was completely wetted, the microbial activity became stable. During the long-term operation, pressure drop was negligible because the void volume of the carrier was two times higher than the conventional packing materials.

Photoreactor Modeling: Applications to Advanced Oxidation Processes

A general methodology for photoreactor analysis and design based on the fundamentals of chemical reaction engineering and radiative transfer in participating media is presented. Three applications in the field of advanced oxidation processes are considered to illustrate the proposed approach: (i) a photocatalytic reactor for air purification, (ii) a homogeneous photo-Fenton solar reactor, and (iii) a heterogeneous photocatalytic slurry reactor. In the first case, the procedure is exemplified with the modeling of a multiannular photocatalytic reactor for perchloroethylene removal from contaminated air streams. A rigorous physical and mathematical model of the multiannular concentric photoreactor was developed and experimentally verified. The second approach is illustrated with the degradation of a model pollutant by the Fenton and photo-Fenton reactions in a nonconcentrating, flat-plate solar reactor. Formic acid was chosen as the model substrate. The effect of the reaction temperature on the pollutant degradation rate is analyzed. In the case of the slurry photoreactor, the intrinsic kinetics of the photocatalytic decomposition of a toxic organic compound in aqueous solution, using suspended titanium dioxide catalytic particles and ultraviolet polychromatic radiation, is studied. The kinetic parameters are evaluated for different catalyst loadings, irradiation levels and pollutant initial concentrations. By means of these illustrative examples, the need of a systematic and rigorous approach to the analysis and design of photoreactors is emphasized.

Simultaneous Removal of H2S, NH3and Toluene in a Biofilter Packed with Zeocarbon Carrier

Simultaneous removal of <TEX>$NH_3,\;H_2S$</TEX> and toluene in a contaminated air stream was investigated over 185 days in a biofilter packed with Zeocarbon granule as microbial support. In this study, multi-microorganisms including Nitrosomonas and Nitrobacter for nitrogen removal, Thiobacillus thioparus (ATCC 23645) for <TEX>$H_2S$</TEX> removal, and Pseudomonas aeruginosa (ATCC 15692), Pseudomonas putida (ATCC 17484) and Pseudomonas putida (ATCC 23973) for toluene removal were used simultaneously. The empty bed residence time (EBRT) was 40-120 seconds and the feed (inlet) concentrations of <TEX>$NH_3,\;H_2S$</TEX> and toluene were 0.02-0.11, 0.05-0.23 and 0.15-0.21 ppmv, respectively. The observed removal efficiency was 85%-99% for <TEX>$NH_3$</TEX>, 100% for <TEX>$H_2S$</TEX>, and 20-90% for toluene, respectively. The maximum elimination capacities were 9.3, 20.6 and <TEX>$17g/m^3/hr\;for\;NH_3,\;H_2S$</TEX> and toluene, respectively. The results of kinetic model analysis showed that there were no particular evidences of interactions or inhibitions among the microorganisms, and that the three bio degradation reactions took place independently within a finite area of biofilm developed on the surface of the Zeocarbon carrier.

An electrospray-based, ozone-free air purification technology

A zero-pressure-drop, ozone-free air purification technology is reported. Contaminated air was directed into a chamber containing an array of electrospray wick sources. The electrospray sources produce an aerosol of tiny, electrically charged aqueous droplets. Charge was transferred from the droplets onto polar and polarizable species in the contaminated air stream and the charged contaminants were extracted using an electric field and deposited onto a metal surface. Purified air emerged from the other end of the chamber. The very small aqueous electrospray droplets completely evaporate so that the process is essentially dry and no liquid solvent is collected or recirculated. The air purification efficiency was measured as a function of particle size, air flow rate, and specific system design parameters. The results indicate that the electrospray-based air purification system provides high air purification efficiency over a wide range of particle size and, due to the very low power and liquid consumption rate, can be scaled up for the purification of arbitrarily large quantities of air.

UV-A photocatalytic treatment of high flow rate air contaminated with Legionella pneumophila

A new photoreactor geometry has been designed to treat high flow rate air contaminated with airborne Legionella pneumophila bacteria by exclusive UV-A photocatalysis. A specific tangential reactor geometry with periodical illumination allowed high efficiencies for strongly contaminated air streams to be obtained, whereas its self-driven property strongly decreased the charge loss phenomena, crucial for targeting high flow rate air treatment applications. This type of photoreactor has been used as the basis for designing and commercializing photocatalytic decontamination devices for applications in the field of air treatment technology.

Performance of an immobilized cell biofilter for ammonia removal from contaminated air stream

The performance of a lab scale biofilter packed with biomedia, encapsulated by sodium alginate and polyvinyl alcohol was used for treating ammonia (NH(3)) gas at different loading rates. The metabolic end products during NH(3) oxidation were NH(4)(+), NO(3)(-) and NO(2)(-). It is noteworthy to mention that the immobilized cell biofilter required no separate acclimatization period and showed high removal efficiencies during the start of continuous experiments. The removal efficiency was nearly 100% when ammonia loading was 4.5gm(-3)h(-1) and the maximum elimination capacity achieved in this study was 5.5gNH(3)m(-3)h(-1) at a loading rate of 7.5gm(-3)h(-1). Shock loading studies were carried out to ascertain the response of the immobilized cells to fluctuations in inlet concentration and flow rate. The inlet loading rates were varied between 0.05 and 6gNH(3)m(-3)h(-1) during this phase of operation. The biofilter responded effectively to these shock loading conditions and recovered rapidly within 4-8h. Pressure drop values were consistently less and insignificant. The results from this study indicated that this immobilized cell biofilter could be considered as a potential option to treat NH(3) under steady and transient state operation.

Simulation of a multi-annular photocatalytic reactor for degradation of perchloroethylene in air: Parametric analysis of radiative energy efficiencies

A multi-annular photocatalytic reactor was designed, that shows good effectiveness for perchloroethylene (PCE) removal from contaminated air streams. In a previous work, a rigorous physical and mathematical model of the photocatalytic reactor was developed and experimentally verified. In this work, this mathematical model was used to study the radiative energy efficiency of the multi-annular photoreactor. The total quantum efficiency is defined as the ratio of the number of molecules of PCE reacted to the number of photons emitted by the lamp, and it is expressed as the product of the following factors: the reactor radiation incidence efficiency, the catalyst radiation absorption efficiency, and the overall reaction quantum efficiency. For the employed reactor, the numerical values of each one were 83%, 92%, and < 2.5 % , respectively. Particularly, the dependence of the overall reaction quantum efficiency upon operating variables such as the PCE feed concentration, gas flow rate, irradiation level and relative air humidity was analyzed. These results are useful to optimize the operating conditions and design parameters of the photocatalytic reactor.

Two Liquid Phase Biofiltration for Removal of n-Hexane from Polluted Air

Two equal-size biofilters with perlite as the packing material were used to investigate the effect of amending silicone oil to the bed of a biofilter for removal of n-hexane from a contaminated air stream. The bed particles of one of the biofilters were partially coated with silicone oil. An n-hexane degrading bacterial culture was used as a biocatalyst in both biofilters. The biofilters operated in parallel under the same conditions for 70 days. The results showed that the silicone oil amended biofilter performed better than the other consistently during the period of investigation. The maximum elimination capacity for the silicone oil amended biofilter was 167 g · m−3 bed · h−1 compared to 114.9 g · m−3 bed · h−1 for the control biofilter. Sorption capacity of a biofilter plays an important role in damping shock changes at entering concentration. To determine how the amended oil could affect the sorption capacity of the biofilter, the responses of the biofilters to step and pulse changes at the inlet concentrations were investigated. A new steady state was established within several minutes after a change at the inlet concentrations. The outlet concentrations of the biofilters increased almost in parallel after a step increase at the inlet concentrations. For a step decrease at the inlet concentrations, the outlet concentration of the oil-amended biofilter was higher than the other for a short period of time due to the desorption phenomenon. The oil-amended biofilter damped a pulse increase at the inlet concentration much more effective than the control biofilter.

활성탄 함유 폴리우레탄 담체를 사용하는 바이오필터에 의한 가스상 톨루엔의 처리

In recent decades, biofiltration has been widely accepted for the treatment of contaminated air stream containing low concentration of odorous compounds or volatile organic compounds (VOCs). In this study, conventional biofilters packed with flexible synthetic polyurethane (PU) foam carriers were operated to remove toluene from a contaminated air stream. PU foams containing various amounts of pulverized activated carbon (PAC) were synthesized for the biofilter media and tested for toluene removal. Four biofilter columns were operated for 60 days to remove gaseous toluene from a contaminated air stream. During the biofiltration experiment, inlet toluene concentration was in the range of 0-150 ppm and EBRT (i.e., empty bed residence time) was kept at 26-42 seconds. Pressure drop of the biofilter bed was less than 3 mm <TEX>$H_2O/m$</TEX> filter bed. The maximum removal capacity of toluene in the biofilters packed with PU-PAC foam was in the order of column II (PAC=7.08%) > column III (PAC=8.97%) > column I (PAC=4.95%) > column IV (PAC=13.52%), while the complete removal capacity was in the order of column II > column I > column III > column IV. The better biofiltration performance in column II was attributed to higher porosity providing favorable conditions for microbial growth. The results of biodegradation kinetic analysis showed that PU-PAC foam with 7.08% of PAC content had higher maximum removal rate (<TEX>$V_m$</TEX>=14.99 g toluene/kg dry material/day) than the other PU-PAC foams. In overall, the performance of biofiltration might be affected by the structure and physicochemical properties of PU foam induced by PAC content.

Transient performance of two‐phase partitioning bioreactors treating a toluene contaminated gas stream

Two-phase partitioning bioreactors (TPPBs) consist of a cell-containing aqueous phase and an immiscible organic phase that sequesters and delivers toxic substrates to cells based on equilibrium partitioning. The immiscible organic phase, which acts as a buffer for inhibitory substrate loadings, makes it possible for TPPBs to handle high volatile organic compound (VOC) loadings, and in this study the performance of liquid n-hexadecane and solid styrene butadiene (SB) polymer beads used as partitioning phases were compared to a single aqueous phase system while treating transient loadings of a toluene contaminated air stream by Achromobacter xylosoxidans Y234. The TPPBs operated as well-mixed stirred tanks, with total working volumes of 3 L (3 L aqueous for the single-phase system, 2 L aqueous and 1 L n-hexadecane for the solvent system, and 2.518 L aqueous volume and 500 g of SB beads for the polymer system). Two 60-min step changes (7 and 17 times the nominal loading rates, termed "small" and "large" steps, respectively) were imposed on the systems and the performance was characterized by the overall removal efficiencies, instantaneous removal efficiency recovery times (above 95% removal), and dissolved oxygen recovery times. For the small steps, with a nominal loading of 343 g/m3/h increasing to 2,400 g/m3/h, the TPPB system using n-hexadecane as the second phase performed best, removing 97% of the toluene fed to the system compared with 90% for the polymer beads system and only 69% for the single-phase system. The imposed large transient gave similar results, although the impact of the presence of a second sequestering phase was more pronounced, with the n-hexadecane system maintaining much reduced aqueous toluene concentrations leading to significantly improved performance. This investigation also showed that the presence of both n-hexadecane and SB beads improved the oxygen transfer within the systems.

Development of a photoreactive fabric filter for simultaneous removal of VOCs and fine particles

A fabric filter sampling system was manufactured by using a UV lamp and a plate-shape sample fabric coated with titanium dioxide (TiO2) sol to develop a photoreacting fabric filter capable of simultaneously removing dust particles and volatile organic chemicals (VOCs) from contaminated air streams. Variations of pressure drop across the fabric as well as toluene vapor removal efficiency were investigated and examined with respect to various conditions such as the injection duration of dust-laden gas, the photocatalyst particle size, the toluene vapor load, and the photocatalyst load. Again, variations in air permeation and the tensile strength of fabrics with the photocatalyst load were measured and examined to determine the appropriation of nonwoven fabric as a supporter for the photocatalyst. The toluene removal efficiency of this new generation fabric filter was manifestly significant, and a possible deficiency in removal efficiency would be solved through the appropriate design and serial arrangement of a multichannel photoreactor consisting of fabric media coated with the photocatalyst.

BIOFILTRATION OF GASEOUS TOLUENE USING ADSORBENT CONTAINING POLYURETHANE FOAM MEDIA

In this study, conventional biofilters packed with flexible synthetic polyurethane (PU) foam carriers were operated to remove toluene from a contaminated air stream. PU foams containing various adsorbents (e.g., zeolite, sepiolite, dolomite and barite) were synthesized for the biofilter media and their adsorption characteristics of toluene were determined. Adsorption capacity of PU-adsorbent foam was in the order of PU-dolomite PU-zeolite > PU-sepiolite > PU-barite. During the biofiltration experiment, influent toluene concentration was in the range of 0-160 ppm and EBRT (i.e., empty bed residence time) was 45 seconds. Pressure drop of the biofilter bed was 4-5 mm column height. The maximum removal capacity was in the order of PU-dolomite > PU-zeolite > PU-sepiolite > PU-barite, while the complete removal capacity was in the order of PU-dolomite > PU-sepiolite > PU-zeolite > PU-barite. The better biofiltration performance in PU-dolomite foam was because PU-dolomite foam had lower density and higher porosity than the others providing favorable conditions for microbial growth. The results of biodegradation kinetic analysis showed that PU-dolomite foam had higher maximum removal rate ( toluene/kg dry material/day) and saturation constant () than the other PU foams. This supports that PU-dolomite foam was better than the others for biofilteration of toluene.

Oxidation of gas phase trichloroethylene and toluene using composite sol–gel TiO 2 photocatalytic coatings

The previously developed composite sol–gel (CSG) process is proposed for the deposition of thick (10–50 μm) porous films of photocatalytic TiO 2. The CSG titania was developed by binding pre-calcined TiO 2 particles with TiO 2 sol. It had relatively high surface area (15–35 m 2/g) and good resistance against mechanical stress and abrasion. Photocatalytic activity tests were carried out on trichloroethylene (TCE) and toluene, and compared with those of standard Degussa P-25 titania. The CSG photocatalyst provided good photo-efficiency in removing both pollutants from contaminated air streams. When compared with P-25 titania, the CSG photocatalyst showed a similar photo-efficiency with first-order kinetic rate constants not significantly different from that of P-25. For both photocatalysts the rate of photocatalytic oxidation of TCE was significantly greater than that obtained for toluene. Overall, the combination of better mechanical integrity, resistance against abrasion, and comparable photocatalytic efficiency of the CSG titania versus that of P-25 titania, make the composite sol–gel (CSG) photocatalyst a viable alternative for industrial applications where long term stability, superior mechanical properties, and good photo-efficiency are of critical value.

Sequencing batch biofilter operation for treatment of methyl ethyl ketone (MEK) contaminated air

Biofiltration is increasingly used as a method for decontaminating gas streams containing low concentrations of biodegradable volatile organic compounds. In typical biofilter installations, control is quite passive and is often restricted to adjustment of the medium's moisture content or nutrient supply. Although inexpensive, such operation limits implementation of engineering decisions that could improve performance during normal operation or allow effective handling of the short‐term variations in the waste stream typical of industrial operations. This paper describes how sequencing batch operation can be applied to biofilters designed and operated as controlled, unsteady‐state, periodic processes for the destruction of gas‐phase contaminants. In the studies described herein, the impact of sequencing batch operation was assessed in a methyl ethyl ketone degrading biofilter over a 130‐day period. The biofilter was packed with a polyurethane foam medium that contained activated carbon. Methyl ethyl ketone and carbon dioxide concentrations were monitored during both normal steady loading conditions and short‐term, unsteady‐state transient loading conditions (i.e., shock loading). A gas stream containing 106 ppm, methyl ethyl ketone was used for normal loading studies, and several model shock loads consisting of 530 ppm. methyl ethyl ketone for a duration of one hour were used to assess system response to transient loads. Data are presented which clearly demonstrate that sequencing batch operation can be successfully applied to biofilters treating methyl ethyl ketone contaminated air streams. Such operation can increase an operator's ability to minimize contaminant emission during transient periods of elevated contaminant loading

Bioremediation of toluene‐contaminated air using an external loop airlift bioreactor

AbstractAn external loop airlift bioreactor (ELAB) has been used to capture and degrade toluene from a contaminated air stream. Using a spinning sparger, the toluene could be transferred from small, uniform bubbles into the aqueous culture media with an overall mass transfer coefficient as high as 1.1 h−1. Due to the very volatile nature of toluene, Pseudomonas putida (ATCC 23973) was cultured and maintained on benzyl alcohol, the first intermediate compound in the metabolic degradation pathway for toluene. Consequently, before successful continuous operation of the ELAB with toluene‐contaminated air, Pseudomonas putida was acclimatized to toluene by using 30 min intermittent sparging of contaminated air into the bioreactor. Continuous sparging of toluene‐contaminated air could then be successfully carried out with 100% capture and biodegradation efficiency at a contaminated air concentration of 15 mg dm−3 and a loading rate of 35 mg dm−3 h−1. Higher concentrations and loading rates were only partially degraded. Although this capture matches only the low rates reported earlier using biofilters to remediate toluene, the ELAB operates using submerged culture and requires no packing which can plug during biofilter operation. In this study, Pseudomonas putida grew on toluene at a maximum specific growth rate of only 0.05 h−1.© 2003 Society of Chemical Industry

VOCs removal from waste gases: gas-phase bioreactor for the abatement of hexane by Aspergillus niger

In this study, a biofilter reactor was successfully applied to remove hexane (a volatile organic compound) from contaminated air streams. Since hexane is very poorly water soluble and hardly metabolized by most bacteria, because of its short hydrocarbon chain, a gas-phase bioreactor inoculated by Aspergillus niger was adopted. In fact, filamentous fungi include many paraffin-degrading species and develop aerial structures which give a large superficial area and allow for a direct pollutant mass transfer from the gas phase to the biological one without the presence of a liquid phase which is a limiting factor for hydrophobic compounds. Soil near gasoline stations was chosen as an adequate source for isolation of suitable fungi strains which were, then, selected principally on the basis of hexane tolerance. A lab-scale bioreactor of 1.77×10 −3 m 3 was assembled with expanded clay inoculated with the selected strain as the medium. After a first trial to assess the feasibility of the process, many experimental runs were carried out in order to investigate the stability of the system in the long period together with the trend of the elimination capacity and removal efficiency depending on the organic load. The flow rate was always kept constant (4×10 −3 m 3/ h) , while the hexane concentration in the inlet stream varied from 2 to 20 g/m 3/ h . At a certain point of the experimentation a second identical reactor was connected in series to the first one. The system proved to be efficient and stable during a 2-month trial. The average elimination capacity was 150 g/m 3 reactor/h and it increased with the organic load until a maximum level after a load of 300 g/m 3 reactor/h. On the opposite, the removal efficiency was over 70% for the lowest hexane concentrations. Considering the plant as the sum of the two biofiltration columns, the RE was almost always over 80%. The fungal development onto the support was also monitored in terms of weight increase and visual assessment by SEM observations of expanded clay particles from the biofilters. A good aerial mycelial growth was observed together with a large amount of spores over almost all the support surface. A steady-state model was tested to describe the process but many parameters are still lacking since they are very hard to determine. In particular, some preliminary kinetic tests showed the great variability of the fungi growth inside the bioreactor.