Removal of benzene in a hybrid bioreactor

A novel hybrid bioreactor was designed to remove volatile organic compounds from wastewater and its performance was investigated. The bioreactor was composed of a biofilter section and a bubble column bioreactor section. Benzene was used as a model compound and the influent benzene was removed by immobilized cells in a bubble column bioreactor. Gas phase benzene stripped by air injection was removed in a biofilter. When the superficial air flow rate was 21.1 m h⁻¹ (0.76 min of residence time in a biofilter), up to 2.2 ppm of benzene in gas phase was removed completely in a biofilter and the maximum removal rate was 4.71 mg day⁻¹ cm⁻³. The concentration profile of benzene along the biofilter column was dependent on the superficial air flow rate and the degree of microbial adaptation. Air flow rate and residence time were found to be the most important operation parameters for the hybrid bioreactor. By manipulating these operational parameters, the removal efficiency and capacity of the hybrid bioreactor could be enhanced. The organic load on the hybrid bioreactor could be shared by the biofilter and bubble column bioreactors and the fluctuation of load on the hybrid bioreactor could be absorbed by changing the distribution of benzene between biofilter and bubble column bioreactors. The maximum removal capacity of the hybrid bioreactor in the experimental range was obtained when the biofilter took 50.3% of influent benzene while 100% of removal efficiency was achieved when the biofilter took 72.3% of influent benzene.     

Batch and fed-batch production of betalains by red beet (Beta vulgaris) hairy roots in a bubble column reactor

Hairy root cultures from red beet (Beta vulgaris L.), which could be used for the commercial production of biologically active betalain pigments, were cultivated in a 3 L bubble column bioreactor in batch mode with various rates of air supply. Both the growth of the roots and betalain volumetric yields were highest (12.7 g accumulated dry biomass/L and 330.5 mg/ L, respectively) with a 10 L/h (0.083 vvm) air supply. The air flow rate also influenced the betacyanins/betaxanthins ratios in the cultures. Growth and betalains production were then examined in two fed-batch regimes (with a 10 L/h air supply), in which nutrient medium was fed just once or on five occasions, designated FBI and FBII, respectively. The root mass accumulation was increased in the FBI feeding regime (to 13.3 g accumulated dry biomass/ L), while in FBII the betalains content was ca. 11% higher (15.1 mg betacyanins/g dry weight and 14.0 mg betaxanthins/g dry weight) than in the most productive batch regime. Data on the time course of the utilization of major components in the medium during both operational modes were also collected. The implications of the information acquired are discussed, and the performance of the hairy roots (in terms of both growth and betalains production) in the bubble column reactor and previously investigated cultivation systems is compared.     

Removal of n-hexane by Fusarium solani with a gas-phase biofilter

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 g m⁻³ and 11 g m⁻³. Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 g m⁻³ _reactor h⁻¹ with a maximum of 130 g m⁻³ _reactor h⁻¹ . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds.

     

Development of laboratory-scale photobioreactor for water purification by use of a biofilter composed of the aerial microalga Trentepohlia aurea (Chlorophyta)

Biofilms formed by the green alga Trentepohlia aurea could be a useful tool in the removal of nitrate and phosphate from water. When a prepared biofilter was dampened with medium and incubated under low light intensity (10 μmol photons m⁻² s⁻¹) between 5 and 50 μmol photons m⁻² s⁻¹, the efficiency of removal of inorganic compounds from water was higher without the decomposition of chlorophylls in the cells. Algal cells immobilized on a glass fiber filter could be kept for 12 weeks under dark conditions at 4°C in the refrigerator. We tried to construct a laboratory-scale photobioreactor for the removal of inorganic nitrogen and phosphate from water by the biofilm. In this study, the synthetic wastewater was prepared by diluting 18-fold Bold’s basal medium with deionized water. The photobioreactor could efficiently remove nitrate and phosphate from the synthetic wastewater under continuous illumination. The removal ability of nitrate and phosphate per sheet of the biofilter in the photobioreactor exhibited about an 8- and 16-fold increase, respectively, in 3 days, compared with the bath experimental results. This study showed that the cycling of wastewater in the reactor by the pump led to a significant improvement in the efficiency of the inorganic ion uptake from water.     

Dynamic bioreactor operation: effects of packing material and mite predation on toluene removal from off-gas

Recent studies have focused on using vapor-phase bioreactors for the treatment of volatile organic compounds from contaminated air streams. Although high removal capacities have been achieved in many studies, long-term operation is often unstable at high pollutant loadings due to biomass accumulation and drying of the packing medium. In this study, three bench-scale bioreactors were operated to determine the effect of packing material and fungal predation on toluene removal efficiency and pressure drop. Toluene elimination capacities (mass toluene removed per unit packing per unit time) above 100 g m(-3) h(-1) were obtained in the fungal bioreactors packed with light-weight, artificial medium, and submersion of the packing in mineral medium once per week was found to provide sufficient moisture and nutrients to the biofilm. The use of mites as fungal predators improved performance by increasing the overall mineralization of toluene to CO(2), and by dislodging biomass along the bioreactor.     

Gas treatment in trickle-bed biofilters: biomass, how much is enough?

The objective of this article is to define and validate a mathematical model that desribes the physical and biological processes occurring in a trickle-bed air biofilter for waste gas treatment. This model considers a two-phase system, quasi-steady-state processes, uniform bacterial population, and one limiting substrate. The variation of the specific surface area with bacterial growth is included in the model, and its effect on the biofilter performance is analyzed. This analysis leads to the conclusion that excessive accumulation of biomass in the reactor has a negative effect on contaminant removal efficiency. To solve this problem, excess biomass is removed via full media fluidization and backwashing of the biofilter. The backwashing technique is also incorporated in the model as a process variable. Experimental data from the biodegradation of toluene in a pilot system with four packed-bed reactors are used to validate the model. Once the model is calibrated with the estimation of the unknown parameters of the system, it is used to simulate the biofilter performance for different operating conditions. Model predictions are found to be in agreement with experimental data. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 583-594, 1997.     

Biofiltration of Butyl Acetate and Xylene Mixtures Using a Trickle‐Bed Air Biofilter

Butyl acetate and xylene mixtures are commonly encountered from the manufacture of semi‐conductor or opto‐electronic apparatuses. The release of these substances into the ambient air may have a negative effect on the air quality. This study attempts to employ a trickle‐bed air biofilter for treating butyl acetate and xylene mixtures under different gas flow rates and influent concentrations. Almost complete VOC removal could be attained with influent carbon loadings of BA (butyl acetate) and X (xylene) below 40 and 15 g/m³h, respectively. As the influent carbon loadings of BA and X were increased up to 150 and 110 g/m³h, removal efficiencies higher than 80 % were achieved. Therefore, the trickle‐bed air biofilter (TBAB) appeared efficient in the control of emissions containing mixtures of butyl acetate and xylene with low to medium carbon loadings. The removal efficiencies of butyl acetate were higher than those of xylene, indicating that butyl acetate was the substrate preferred in the utilization of butyl acetate and xylene mixtures by the microorganisms. Carbon recoveries of 98–101 % were achieved, demonstrating the accuracy of results. The carbon mass rate of the liquid effluent was approximately two to three orders of magnitude less than that of the CO₂ effluent, indicating that the dissolved VOCs and their derivatives in the leachate were present in a negligible amount in the reactor. Applicable operating conditions of the TBAB unit for treating BA and X mixtures were suggested.     

Effects of light intensity and magnesium supplementation in pretreatment cycle on ammonium removal from wastewater of photobioreactor using a biofilter composed of the aerial microalga Trentepohlia aurea

Application of a laboratory-scale photobioreactor containing a biofilter composed of the aerial microalga Trentepohlia aurea to the removal of ammonium from synthetic wastewater was assessed to determine whether the system could be applied to water purification and the treatment of eutrophic water. The removal efficiency of the photobioreactor was tested after ten biofilter sheets (total dry weight cells: 50 mg) were cycled in nitrogen-free Bold’s basal (BB) medium for 72 h (pretreatment cycle). The ammonium removal ability was significantly enhanced when the photobioreactor was operated after performing the pretreatment cycle using nitrogen-free BB medium supplemented with magnesium. Moreover, the illumination conditions during the treatment were shown to affect the nitrogen removal ability, and this ability was strongly dependent on the concentrations of organic compounds (e.g., α-ketoglutarate and pyruvate) for assimilating the nitrogen source in the T. aurea biofilter.     

Removal of benzene and toluene in polyurethane biofilter immobilized with Rhodococcus sp. EH831 under transient loading

The performance of a polyurethane (PU) biofilter inoculated with Rhodococcus sp. EH831 was evaluated under different transient loading conditions, such as shutdown, intermittent and fluctuating loading. A mixture of benzene and toluene vapors was employed as model pollutants. When the biofilter was restarted after a 2 week-shutdown, during which neither clean air nor water was supplied, the benzene and toluene removal capacities were rapidly restored after a re-adaptation period of only 1 day. A comparison of the removal capacity under continuous and intermittent loading revealed that constant and periodic loading (8 h on/16 h off per day) and a 2 day-shutdown did not significantly influence the biofilter performance, although the removals of benzene and toluene were relatively unstable and lower under intermittent loading during the initial week. The result of quantitative real-time PCR showed that Rhodococcus sp. EH831 could be maintained during transient loading periods (10¹⁰–10¹¹ CFU/g-dry PU) irrespective of the different operating conditions.     

Biotrickling air filtration of 2-chlorophenol at high loading rates

The degradation of 2-chlorophenol vapours in air was performed in a trickling biofilter packed with ceramic material seeded with the bacterium Pseudomonas pickettii, strain LD1. The system performance was evaluated under varying operating conditions (inlet 2-chlorophenol air concentrations from 0.10 to 3.50 g m^?3, and superficial air velocities of 30.0, 60.0, and 120.0 m h^?1). For all air velocity the maximum degradation rate was obtained for loading rates of 40 g m^?2 h^?1. Higher loading conditions resulted in strong inhibition of microbial activity, particularly severe at high air velocity. Process analysis, performed using data on pollutant concentration profiles along the filter packing obtained under different conditions of inlet concentration and air velocity, proves that best performance (i.e. maximum degradation efficiency and capacity) can be obtained for a narrow range of operating conditions, which can be ensured by proper design of biofilter size (i.e. diameter and height). Kinetic analysis of experimental data confirms that 2-CP inhibits microbial activity in the biofilter bed. Experimental data are satisfactorily fitted by the Haldane kinetic equation up to a critical value of loading rate, beyond which the experimental degradation rate is overestimated by the kinetic model. The inhibition appears to be affected by the loading rate, and the estimated inhibition constant linearly increases with increasing empty bed residence time.     

Carbohydrates Production and Bio-flocculation Characteristics in Cultures of Arthrospira (Spirulina) platensis: Improvements Through Phosphorus Limitation Process

Carbohydrates are a desirable biomass compound for the generation of several biofuels. Phosphorus nutrient limitation causes a significant increase in the carbohydrate content of the cyanobacterium Arthrospira (Spirulina) platensis. Carbohydrates accumulated up to a content of 63.09?±?3.43?% (±SD) in both batch and semi-continuous cultures. In order the production of carbohydrate-rich biomass through nutrient limitation to be maximized, it is suggested that the limited nutrients have to be supplied in amounts that they on one hand can support the biomass production while on the other hand they alter the composition of the biomass. In this study, phosphorus of 1.82?±?0.16?mg g^?1 of dry biomass was the optimized amount for the maximization of carbohydrates production by A. platensis. Regarding the need to decrease the application amounts of nutrients for biomass production, this study demonstrates that the phosphorus supply could be decreased an order of magnitude with no significant decrease in biomass production. In addition, it was observed that biomass rich in carbohydrates bio-flocculates, during settling without the addition of any flocculation agent or any other intervention. The bio-flocculation efficiency appears to be related with the carbohydrate content of the biomass. In maximum carbohydrate content (60?%), the biomass bio-flocculated at 68.49?±?7.73?% the first 15?min and reached 80.25?±?5.58?% 60?min after settling. The produced carbohydrates might be used as feedstock for biofuel generation, while the bio-flocculation and the overall settling characteristics of the carbohydrate-rich biomass could make its harvesting process much easier.     

The use of pine bark and natural zeolite as biofilter media to remove animal rendering process odours

Studies of odour-control pilot-scale biofilters at a rendering plant were conducted for five years. The biofilters contained different sizes of crushed pine bark or a mixture of zeolite and crushed bark, and treated the exhaust gases from direct-fired meal dryers. The exhaust gases were odorous and contained significant smoke. The odour concentration of the rendering process air ranged between 50,000 and 307,200 OU m(-3). Odour-removal performance measurements of the biofilters were undertaken on five occasions using forced-choice dynamic-dilution olfactometry. Biofilter odour-removal efficiencies of between 80% and 99% were measured at various influent odour concentrations and air loading rates. There was no obvious deterioration in performance of these biofilters between various sampling times in the five year study period. The biofilters also reduced the "offensiveness" of the odour. The fine crushed bark biofilter generally reduced odour concentration more efficiently than the coarse bark biofilter. The additions of zeolite to the bark medium in the biofilter had little effect on the odour-removal performance. An increase in air loading rate produced only a very small decrease in odour-removal performance. The pilot-scale biofilters had smoke removal efficiencies between 71% and 100%. Finely crushed bark removed smoke more effectively than coarsely crushed bark. Drainage from the biofilters contained significant concentrations of pollutants, suggesting that controlled leaching has potential to remove accumulated substances in biofilter media from rendering gas emissions and increase the longevity of a biofilter system.     

Oxygen enriched air supply in Escherichia coli processes: production of biomass and recombinant human growth hormone

In order to investigate the impact of high oxygen and carbon dioxide concentrations, Escherichia coli was grown in batch cultivations where the air supply was enriched with either oxygen or carbon dioxide. The effect of elevated concentrations of oxygen and carbon dioxide on stochiometric and kinetic constants was studied this way. The maximum growth rate was significantly reduced, the production of acetic acid and the biomass yield coefficient on glucose increased in cultures with carbon dioxide enriched air, compared to reference cultivations and cultivations with oxygen enriched air. The application of oxygen enriched air was studied in high cell density cultivations of Escherichia coli. Two production processes were chosen to investigate the impact of oxygen enrichment. Biomass concentration, specific growth rate, yield coefficient, respiration, mixed acid fermentation products and the product yield and quality for the recombinant product were investigated. First, a process for the production of biomass was investigated. Exponential growth could proceed for a longer time and higher growth rates could be maintained with oxygen enriched air supply. However, a higher specific oxygen consumption rate per glucose was measured after the start of the oxygen enrichment, indicating higher maintenance and consequently the growth rate and yield coefficient decreased drastically in the end of the process. Second, a process for the production of recombinant human growth hormone (rhGH) was investigated. Although the glucose feed rate and all medium components were doubled, the amount of produced biomass could only be increased by 77% when oxygen enriched air (40% oxygen) supply was applied. This was due to a decreased yield coefficient of biomass per glucose. The total amount of produced product was decreased by almost 50% compared to the control, although less proteolytically degraded variants were produced.     

Biofiltration of volatile organic compounds

The removal of volatile organic compounds (VOCs) from contaminated airstreams has become a major air pollution concern. Improvement of the biofiltration process commonly used for the removal of odorous compounds has led to a better control of key parameters, enabling the application of biofiltration to be extended also to the removal of VOCs. Moreover, biofiltration, which is based on the ability of micro-organisms to degrade a large variety of compounds, proves to be economical and environmentally viable. In a biofilter, the waste gas is forced to rise through a layer of packed porous material. Thus, pollutants contained in the gaseous effluent are oxidised or converted into biomass by the action of microorganisms previously fixed on the packing material. The biofiltration process is then based on two principal phenomena: (1) transfer of contaminants from the air to the water phase or support medium, (2) bioconversion of pollutants to biomass, metabolic end-products, or carbon dioxide and water. The diversity of biofiltration mechanisms and their interaction with the microflora mean that the biofilter is defined as a complex and structured ecosystem. As a result, in addition to operating conditions, research into the microbial ecology of biofilters is required in order better to optimise the management of such biological treatment systems.     

Dynamic volume-averaged model of heat and mass transport within a compost biofilter: I. Model development

Successful, long-term operation of a biofilter system depends on maintaining a suitable biofilm environment within a porous medium reactor. In this article a mathematical study was conducted of the spatial and temporal changes of biofilter performance due to interphase heat and mass transport. The method of volume averaging was used to spatially smooth the three-phase (solid, liquid, and gas) conservation equations over the biofilter domain. The packing medium was assumed to be inert, removing the solid phase mass continuity equation from the system. The finite element method was used to integrate the resulting nonlinear-coupled partial differential equations, tracking eight state variables: temperature, water vapor, dry air, liquid water, biofilm, gas and liquid phase organic pollutant, and nutrient densities, through time and space. A multiphase, gas and liquid flow model was adapted to the biofilter model from previous studies of unsaturated groundwater flow. Newton's method accelerated by an LU direct solver was used to iterate the model for solutions. Effects of packing media on performance were investigated to illustrate the utility of the model. The moisture dynamics and nutrient cycling are presented in Part II of this article.     

Biomass and photosynthetic productivity of water hyacinth (Eichhornia crassipes) as affected by nutrient supply and mirid (Eccritotarus catarinensis) biocontrol

The biological control of water hyacinth is affected by water nitrogen and phosphorus content and this was investigated experimentally at five levels of nutrient supply by measuring plant photosynthetic and growth responses, and mirid reproduction and herbivory of nutrient treated plants. Low nitrogen (2–0.2 mg L⁻¹) and phosphorus (0.2–0.01 mg L⁻¹) supply decreased hyacinth photosynthesis, growth and biomass accumulation relative to plants supplied 200 mg L⁻¹ N and 20 mg L⁻¹ P. This effect depended more on nitrogen supply than phosphorus supply. Chlorophyll fluorescence showed that the photosynthetic light reactions of low nutrient plants were affected and leaves had decreased chlorophyll content, density of functional photosystems II and dissipated a greater proportion of absorbed energy as heat. Gas exchange parameters showed reduced carboxylation efficiency, rates of RuBP regeneration and light saturated photosynthetic rates, but not quantum yields. Effects on photosynthesis translated into lower plant dry biomass. Mirid herbivory exacerbated the effects of low nutrients noted for chlorophyll fluorescence, gas exchange parameters and biomass accumulation, however, these effects were not always significant and there was no obvious correlation between the level of nutrients supplied and the effect of mirid herbivory. Low nutrient supply did, however, affect mirid performance reducing the number of adult insects, nymphs and herbivory intensity suggesting that in the long-term mirid populations would be significantly affected by water nutrient status.     

Removal of nitrobenzene vapors by a trickling air biofilter

A stable microbial consortium that grew on nitrobenzene (NB) as its sole source of carbon, nitrogen and energy and liberated excess nitrogen as ammonia, was immobilized on a perlite-packed trickling air biofilter. On a sustained basis, the biofilter removed 50 g NB m⁻³ packing h⁻¹ and its operation at pH 8.7 resulted in ammonia stripping, making pH and salinity controls unnecessary. Low maintenance and stable performance during 4 months of continuous operation invite the scale-up of this biofilter for control of NB emissions. Received 12 September 1996/ Accepted in revised form 17 December 1996     

Reduction of ammonia and volatile organic compounds from food waste-composting facilities using a novel anti-clogging biofilter system

The performance of a pilot-scale anti-clogging biofilter system (ABS) was evaluated over a period of 125 days for treating ammonia and volatile organic compounds emitted from a full-scale food waste-composting facility. The pilot-scale ABS was designed to intermittently and automatically remove excess biomass using an agitator. When the pressure drop in the polyurethane filter bed was increased to a set point (50 mm H₂O m⁻¹), due to excess biomass acclimation, the agitator automatically worked by the differential pressure switch, without biofilter shutdown. A high removal efficiency (97-99%) was stably maintained for the 125 days after an acclimation period of 1 week, even thought the inlet gas concentrations fluctuated from 0.16 to 0.55 g m⁻³. Due the intermittent automatic agitation of the filter bed, the biomass concentration and pressure drop in the biofilter were maintained within the ranges of 1.1-2.0 g-DCW g PU⁻¹ and below 50 mm H₂O m⁻¹, respectively.     

Cost-effective IMTA: a comparison of the production efficiencies of mussels and seaweed

This paper compares the biofilter capacity and cost-effectiveness of blue mussels (Mytilus edulis) and seaweed for use in integrated multi-trophic aquaculture (IMTA) based on experiences in Ireland and Denmark. This comparison shows that weight for weight, mussels are a better biofilter than seaweed with regard to the amount of nitrogen assimilated. Furthermore, in optimized systems, areal requirement for mussels is similar to the cultivation of the same tonnage (1,000 t) of seaweed (approximately 8 ha). The cost-effectiveness of a mussel biofilter is €11–30 kg^?1 nitrogen (N) removed based on various examples compared to production costs of €209–672 removed and €1,013 kg^?1 N removed, respectively, for Laminaria digitata and Alaria esculenta from extrapolated laboratory and field trials. However, commercial seaweed (Saccharina latissima) producers claim that production costs are less than €10–38 kg^?1 N removed. These up-scaled and commercial figures make the seaweed cost competitive to mussels for removal of nitrogen. Disadvantages such as predators (e.g. eider ducks) and biofouling should also be taken into account before choice of biofilter is made. These drawbacks can reduce overall biofilter capacity and biomass value as a consequence of biomass spoilage or loss. However, disadvantages may be mitigated by seasonal choice of cultivation and harvest times. Cultivation technologies and harvesting methods may be improved together with breeding to improve the cost-efficiency of the biofilter, especially in the newer European seaweed cultivation. Furthermore, upscaling of IMTA to commercial proportions, other than the Danish example, would allow more real data on production costs and revenues.     

Macrokinetic and quantitative microbial investigation on a bench-scale biofilter treating styrene-polluted gaseous streams

We performed a macrokinetic and quantitative microbial investigation of a continuously operating bench-scale biofilter treating styrene-polluted gases. The device was filled with a mixture of peat and glass beads as packing medium and inoculated with the styrene-oxidizing strain, Rhodococcus rhodochrous AL NCIMB 13259. The experimental data of styrene and microbial concentrations, obtained at different biofilter heights, were used to evaluate the pollutant concentration profiles as well as the influence of styrene loading on biomass distribution along the packing medium. Styrene and biomass concentration profiles permitted detection of a linear relationship between the amount of biomass grown in a given section of the biofilter and that of pollutant removed, regardless of the operating conditions tested. Biomass development in the bed appeared to: depend linearly on pollutant concentration at an inlet styrene concentration of <0.10 g m(-3) in the gaseous stream; achieve a maximum value (7. 10(7) colony forming units per gram of packing material) within a wide styrene concentration range (0.10 to 1.0 g m(-3)); and fall sharply beyond this inhibition threshold. The process followed zeroth-order macrokinetics with respect to styrene concentration, which is consistent with zeroth-order microkinetics with either fully active or not fully active biofilm. The maximal volumetric styrene removal rate was found to be 63 g m(packing material) (-3) h(-1) for an influent pollutant concentration of 0.80 g m(-3) and a superficial gas velocity of 245 m h(-1).