Biofiltration of Air Contaminated by Styrene:  Effect of Nitrogen Supply, Gas Flow Rate, and Inlet Concentration

Abstract

The biofiltration process is a promising technology for the treatment of dilute styrene emissions in air (less than 1 g‚m -3 ). The efficiency of this process is however strongly dependent upon various operational parameters such as the filter bed characteristics, nutrient supplies, input contaminant concentrations, and gas flow rates (gas residence times). The biofiltration of air containing styrene vapors was therefore investigated, employing a novel biomass filter material, in two identical but separate laboratory scale biofiltration units (units 1 and 2), both biofilters being initially inoculated with a microbial consortium. Each biofilter was irrigated with a nutrient solution supplying nitrogen in one of two forms; i.e., mainly as ammonia for unit 1 and exclusively as nitrate for unit 2. The experimental results have revealed that greater styrene elimination rates (up to 141 g‚m -3 ‚h -1 ) are achieved in the biofilter supplied with ammonia as the major nitrogen source in comparison to the lesser elimination performance (up to 50 g‚m -3 ‚h -1 ) obtained with the nitrate provided biofilter. However, in achieving the high styrene removal rates in the ammonia supplied biofilter, the excess of biomass accumulates on the filtering pellets and causes progressive clogging of the filter media. Furthermore, the effectiveness of nitrate supply as the sole nitrogen nutrient form, on reducing or controlling the biomass accumulation in the filter media in comparison to ammonia, could not be satisfactorilly demonstrated because the two biofilters operated with very different styrene elimination capacities. The monitoring of the carbon dioxide concentration profile through both biofilters revealed that the ratio of carbon dioxide produced to the styrene removed was approximately 3/1, which confirms the complete biodegradation of removed styrene, given that some of the organic carbon consumed is also used for the microbial growth. The effects of the most important design parameters, namely styrene input concentrations and gas flow rates, were investigated for each nutrient solution.

Biotrickling Filtration of Air Contaminated with 1-Butanol

“…Here, the corresponding substrate mass loading rates were in the range of 110 to 120 g m −3 h −1 . It is known that exposure to high contaminant loading rates can cause inhibition effects or even kill the microorganisms, and a similar decline in performance was observed in other research [15], where it was attributed to inhibition effects at high contaminant concentration as well. Not until the butanol concentration was reduced to values under 1 g m −3 and after 13 days of operation, was the removal efficiency restored.…”

“…Here, the corresponding substrate mass loading rates were in the range of 110 to 120 g m −3 h −1 . It is known that exposure to high contaminant loading rates can cause inhibition effects or even kill the microorganisms, and a similar decline in performance was observed in other research [15], where After inoculation, the combined effect of butanol inlet concentration and gas flow rate was investigated with respect to removal efficiency and elimination capacities. At start-up, the biotrickling filter (BTF) was run with a butanol inlet concentration of around 0.8 g m −3 and an empty bed residence time (EBRT) of 124 s. From Figure 2, it is clear that the BTF had a rapid development of activity after initial start-up.…”

“…Studies have been reported in literature with laboratory-scale bioreactors to evaluate the performance for a range of hydrocarbons and oxygenated hydrocarbons [9][10][11][12][13][14][15][16]. However, the biological treatment of 1-butanol in air has not been as extensively reported as some other compounds, especially at higher concentrations.…”

Evaluation of Trickle-Bed Air Biofilter Performance under Periodic Stressed Operating Conditions as a Function of Styrene Loading

“…For this reason, some reports have focused on biomass control for longterm operation of biofiltration. Reported biomass control strategies include bed irrigation, 11 stimulation of protozoan predation, 12 mechanical methods employing bed stirring and bed washing 9 and sodium hydroxide washing, 10 and periodic backwashing with full-medium fluidization. 2,5,7,8 Most of these methods have major drawbacks, such as the subsequent reduction in biofilter performance because of the loss of active biomass.…”

“…14 Some studies reported biofilter performance under chemical starvation conditions. 11,13,15,16 Fitch et al studied biofiltration for 1-butanol removal under continuous and diurnal loading conditions and reported that diurnal operation did not contribute to a decrease in biofilter efficiency as compared with continuous operation. 13 Most of these studies were concerned mainly with the reacclimation periods and the duration and mode of starvation.…”