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The present study reports CO2 capture and conversion to bicarbonate using Escherichia coli expressing carbonic anhydrase (CA) on its cell surface in a novel foam bioreactor. The very large gas-liquid interfacial area in the foam bioreactor promoted rapid CO2 absorption while the CO2 in the aqueous phase was subsequently converted to bicarbonate ions by the CA. CO2 gas removal in air was investigated at various conditions such as gas velocity, cell density and CO2 inlet concentration. Regimes for kinetic and mass transfer limitations were defined. Very high removal rates of CO2 were observed: 9570 g CO2 m(-3) bioreactor h(-1) and a CO2 removal efficiency of 93% at 4% inlet CO2 when the gas retention time was 24 s, and cell concentration was 4 gdw L(-1). These performances are superior to earlier reports of experimental bioreactors using CA for CO2 capture. Overall, this bioreactor system has significant potential as an alternative CO2 capture technology.

The sensitivity of a conceptual model of a foam emulsion bioreactor (FEBR) used for the control of toluene vapors in air was examined. Model parametric sensitivity studies showed which parameters affect the removal of toluene (as model pollutant) in the FEBR the most significantly, and enabled definition of the limits of the process. Detailed examination of the results indicated that the process is highly complex and that both mass transfer and kinetic limitations can coexist in the bioreactor system. These results will help with the optimization of the design and operation of FEBRs.

Recently, a new type of bioreactor for air pollution control referred to as the foamed emulsion bioreactor (FEBR) has been developed. The process relies on the emulsion of an organic phase with a suspension of an actively growing culture of pollutant-degrading microorganisms, made into a foam with the air undergoing treatment. In the current paper, a diffusion and reaction model of the FEBR is presented and discussed. The model considers the fate of the volatile pollutant in the emulsion that constitutes the liquid films of the FEBR. Oxygen limitation as well as substrate inhibition were included in the biokinetic relationships. The removal of toluene vapors served for the validation of the model. All the model parameters were determined by independent experiments or taken from the literature. The model predictions were found to be in good agreement with the experimental data and the model provided useful insights on the phenomena occurring in the FEBR. Model parametric sensitivity studies and further discussion of the factors that limit the performance of the FEBR are presented in Part 2 of this paper.

Effective cometabolic biodegradation of trichloroethylene (TCE) vapors in a novel gas-phase bioreactor called the foamed emulsion bioreactor (FEBR) was demonstrated. Toluene vapors were used as the primary growth substrate for Burkholderia cepacia G4 which cometabolically biodegraded TCE. Batch operation of the reactor with respect to the liquid feed showed a drastic decrease of TCE and toluene removal over time, consistent with a loss of metabolic activity caused by the exposure to TCE metabolites. Sustained TCE removal could be achieved when continuous feeding of mineral medium was implemented, which supported cell growth and compensated for the deactivation of cells. The FEBR exhibited its highest TCE removal efficiencies (82-96%) and elimination capacities (up to 28 gTCE m(-3) h(-1)) when TCE and toluene vapors were fed sequentially to circumvent the competitive inhibition by toluene. The TCE elimination capacity was 2-1000 times higher than reported in other gas-phase biotreatment reports. During the experiments, 85-101% of the degraded TCE chlorine was recovered as chloride. Overall, the results suggestthatthe FEBR can be a very effective system to treat TCE vapors cometabolically.

Continuous operation of a new bioreactor for air pollution control called the foamed emulsion bioreactor (FEBR) has been investigated. The effect of several liquid feeding strategies was explored. The FEBR exhibited high and steady toluene removal performance (removal efficiency of 89%-94%, elimination capacity of 214-226 g/m3h at toluene inlet concentration of 1 g/m3) for up to 360 h, when 20% of the culture was replaced every 24 h by a nutrient solution containing 4 g/L of potassium nitrate as a nitrogen source. This feeding mode supported a high cell activity measured as INT reduction potential and active cell growth without being subject to nitrogen limitation. In comparison, operating the FEBR with the liquid in a closed loop (i.e., batch) resulted in a significant decrease of both the removal efficiency of toluene and INT reduction activity. Operation with feeding active cells resulted in stable and effective treatment, but would require a significant effort for mass culture preparation. Therefore, the continuous process with periodically feeding nutrients was found to be the most practical and effective operating mode. It also allows for stable operation, as was shown during removal of low concentration of toluene or after pollutant starvation. Throughout the study, INT reduction measurements provided insight into the process. INT reduction activity data proved that under normal operating conditions, the FEBR performance was limited by both the kinetics and by mass transfer. Overall, the results illustrate that engineered gas-phase bioreactors can potentially be more effective than conventional biofilters and biotrickling filters for the treatment of air pollutants such as toluene., (Copyright (c) 2005 Wiley Periodicals, Inc.)

A new type of bioreactor for air pollution control has been developed. The new process relies on an organic-phase emulsion and actively growing pollutant-degrading microorganisms, made into a foam with the air being treated. This new reactor is referred to as a foamed emulsion bioreactor (FEBR). As there is no packing in the reactor, the FEBR is not subject to clogging. Mathematical modeling of the process and proof of concept using a laboratory prototype revealed that the foamed emulsion bioreactor greatly surpasses the performance of existing gas-phase bioreactors. Experimental results showed a toluene elimination capacity as high as 285 g(toluene) m(-3) (reactor) h(-1) with a removal efficiency of 95% at a gas residence time of 15 s and a toluene inlet concentration of 1-1.3 g x m(-3). Oxygen limited the reactor performance at toluene concentration above about 0.7-1.0 g x m(-3); consequently, performance was significantly improved when pure oxygen was added to the contaminated air. The elimination capacity increased from 204 to 408 g x m(-3) h(-1) with >77% toluene removal at toluene inlet concentrations of 2-2.2 g x m(-3). Overall, the results show that the performance of the FEBR far exceeds that of currently used bioreactors for air pollution control., (Copyright 2003 Wiley Periodicals, Inc.)

This review analyzes various algal biofilm reactors used for integrated wastewater treatment and biofuel production to overcome the current challenges for algal biofuel production. Various reactor configurations, support materials and operation strategies of algal biofilm reactors are discussed and compared with conventional suspended culture systems in terms of algal biomass productivity, nutrient removal, biomass harvest and biofuel production. The rotating biofilm reactor among various types of biofilm reactors was found to be a promising option to provide high biomass productivity and efficient utilization of nutrients in wastewater. Some materials such as stainless steel, nylon and natural fibers among various materials were found to be highly effective for supporting microalgal biofilm. To date mainly municipal wastewater has been integrated with algal bioreactors while only a few agricultural wastewater have been used for algal bioreactors due to inhibition of algal growth with high ammonium concentrations in animal manure and poor light delivery with high turbidity of animal manure. Overall, the algal biofilm reactors integrated with wastewater would have great potential for high productivity of algal biomass and efficient wastewater treatment if various conditions are optimized. [ABSTRACT FROM AUTHOR]