A hybrid biological process of indoor air treatment for toluene removal.

Bioprocesses, such as biofiltration, are commonly used to treat industrial effluents containing volatile organic compounds (VOCs) at low concentrations. Nevertheless, the use of biofiltration for indoor air pollution (IAP) treatment requires adjustments depending on specific indoor environments. Therefore, this study focuses on the convenience of a hybrid biological process for IAP treatment. A biofiltration reactor using a green waste compost was combined with an adsorption column filled with activated carbon (AC). This system treated a toluene-micropolluted effluent (concentration between 17 and 52 µg/m3), exhibiting concentration peaks close to 733 µg/m3 for a few hours per day. High removal efficiency was obtained despite changes in toluene inlet load (from 4.2 x 10(-3) to 0.20 g/m3/hr), which proves the hybrid system's effectiveness. In fact, during unexpected concentration changes, the efficiency of the biofilter is greatly decreased, but the adsorption column maintains the high efficiency of the entire process (removal efficiency [RE] close to 100%). Moreover, the adsorption column after biofiltration is able to deal with the problem of the emission of particles and/or microorganisms from the biofilter. Implications: Indoor air pollution is nowadays recognized as major environmental and health issue. This original study investigates the performance of a hybrid biological process combining a biofilter and an adsorption column for removal of indoor VOCs, specifically toluene.

Evaluation of compost and a mixture of compost and activated carbon as biofilter media for the treatment of indoor air pollution.

Indoor air pollution (IAP), defined by a lot of pollutants at low concentrations (microg m(-3)), is recognized as a major environmental health issue. In order to remove this pollution, biofiltration was investigated in this study. Two biofilters packed with compost and a mixture of compost and activated carbon (AC) were compared during the treatment of an influent with characteristics close to those of IAP. Very high removal efficiencies (RE) were achieved for the two biofilters (RE more than 90% for butyl acetate, butanol, formaldehyde, limonene, toluene and undecane at mass loading from 6-24mg m(-3) h(-1) and 19s empty bed retention time). The fact that high RE of hydrophobic compounds (undecane and limonene) were achieved, along with the results of an abiotic sorption study, lead us to suggest a mechanism including adsorption followed by biodegradation at the interface of the biofilm where microorganisms tend to concentrate near the available substrate. Both chemical reactions with the packing materials and biological degradation led to average RE greater than 91.4% for nitrogen dioxide. It was observed that adding AC to compost had significant effects. First, its buffering capacity led to shorter acclimation duration and more stable operation efficiencies than for the compost biofilter. Secondly, the only compound which was not removed by the compost biofilter, trichloroethylene, was strongly adsorbed by the compost/AC biofilter. Finally, the concentration profile along the two biofilters demonstrated that adding of AC could lead to a reduction of the retention time required to reach the maximal RE.

Modelling of free radicals production in a collapsing gas-vapour bubble.

This paper deals with a model linking bubble dynamics under an acoustic pressure field and production of free radicals in the resulting collapses of this bubble. The bubble dynamics model includes interdiffusion of gas and vapour in the bubble as well as evaporation or condensation at the interface, and it assumes uniformity of the internal pressure and perfect gas law for the gas vapour mixture. At the maximum compression of the bubble, all the reactions of dissociation which can occur are assumed at thermodynamic equilibrium. The local composition (especially in free radicals) in the bubble is then calculated by an algorithm based on free energy minimization using the information concerning the maximum compression provided by the bubble dynamics model resolution. Using this model a comparison of free radicals production has been made for two different driving frequencies (20 kHz and 500 kHz), and at given bubble radius and acoustic pressure, an optimum of liquid bulk temperature has been derived for the production of free radicals very similar to the experimental one concerning oxidation reactions in aqueous phase.