Effect of a Non‐Ionic Surfactant on Xylene Removal in a Scoria‐Compost‐Based Biofilter

Abstract

The effect of a non-ionic surfactant, Tween-20, on xylene removal performance of a previously acclimated scoria-compost-based biofilter was evaluated. In the presence of the surfactant, the maximum elimination capacities (EC max ) of 71.0, 84.1, and 93.6 g m À3 h À1 were obtained for xylene inlet loading rates (ILRs) of 114.9, 124.1, and 197.1 g m À3 h À1 at empty bed residence times (EBRTs) of 40, 60, and 90 s, respectively. When the biofilter was fed the nutrient solution with Tween-20, the average removal efficiency (RE avg ) was increased approximately 13 and 14% at EBRTs of 40 s (ILR avg of 43-47 g m À3 h À1 ) and 60 s (ILR avg of 61 g m À3 h À1 ), respectively. This indicates that the surfactant improved the performance of the biofilter at moderate ILRs. However, the removal of xylene was not significantly affected by the surfactant at high ILRs, around which EC max was achieved. This means that the non-ionic surfactant probably had a positive effect on the biofiltration of xylene when the diffusion through the biofilm, rather than biodegradation rates, appears to be the main process governing the performance of biofilter. Overall, this study showed that Tween-20, in terms of xylene removal efficiency, may not have similar effects on the performance of biofilter at various loading conditions.

Mathematical modeling and sensitivity analysis of xylene removal in a scoria‐compost biofilter

“…According to Fan et al, the value of f ( X v ) depends on the biomass concentration in the biofilm ( X v ) as Equation : where D b , i and D w , i are the diffusion coefficients of compound i in biofilm and water (m 2 s −1 ), respectively. There was no accumulation of biomass on the filter bed. Our experiments showed that the pressure drop values were less than 4 mm water and almost no clogging were seen to occur within the biofilter during the entire experiments . Biomass properties (thickness, specific surface area and kinetic coefficients) were uniform and constant along the bed under different operating conditions. There was no oxygen (O 2 ) supply limitation because O 2 was abundantly present and was more readily transferred than xylene. Adsorption of xylene onto the packing material was assumed to be negligible.…”

“…The details of biofilter setup were described elsewhere . Briefly, experiments were performed in a four‐stage biofilter with the diameter and effective length of 0.115 m and 0.8 m, respectively.…”

“…In Equations , the consumption rate of xylene, r b ,xylene , is equal to the elimination capacity (EC xylene ) of the biofilter. In the other hand, some inhibition was observed at high xylene loading rates in experimental work . Therefore, the Haldane‐type kinetic model for the description of xylene consumption rate in a biofilter could be written as Equation : where EC i is the elimination capacity of compound i (g m −3 s −1 ), EC max, i is the maximum elimination capacity of compound i (g m −3 s −1 ), k m , i is the semi‐saturation or affinity constant of compound i (g m −3 ) and K I , i is substrate inhibition constant for compound i (g m −3 ).…”

“…The experiments demonstrated that the mixture of scoria and compost could be considered as a potential biofilter bed with low pressure drop. Moreover, the nonionic surfactant improved the performance of the biofilter at moderate inlet loading rates (ILRs), while no significant improvement was observed at high ILRs, around EC max conditions …”

“…Xylene is a well‐known solvent in printing, painting, and varnishing industries . It is released into the atmosphere mainly from petrochemical industries . According to the US Occupational Safety and Health Administration (OSHA), the permissible exposure limit for xylene is 100 ppm (435 mg m −3 at 298 K and 101.3 kPa) on an 8‐hr time weighted average concentration basis .…”