Effects of design parameters on performance and cost analysis of combined ultraviolet-biofilter systems treating gaseous chlorobenzene based on mathematical modeling

Abstract

A conceptual mathematical model was used to evaluate the design parameters of a combined ultraviolet (UV)-biofilter system, and perform a cost analysis. Results showed that the UV light source strength and the gas residence times in the UV system (UVRT) and biofilter (EBRT) had positive effects on the overall chlorobenzene removal efficiency of the system. High ratio of UVRT to EBRT improved the removal efficiency, suggesting that the UV system has a greater effect on the overall performance of the system compared with the biofilter. Analysis of the capital and operating costs showed that the capital costs of the standalone biofilter system were much higher than those of the standalone UV system. However, the biofilter operating costs were lower than those of the UV system. The operating costs of the combined UV-biofilter system increased with increasing UVRT/EBRT ratio, whereas its capital costs decreased.

Keywords

volatile organic compounds / ultraviolet (UV) photodegradation / biofilter / modeling / cost analysis

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Acknowledgements

This project is supported by new teachers’ fund for Doctor Stations, Ministry of Education, China (No. 20110032120035).

Notation

b	light path, 0.04 m
cA	chlorobenzene concentration, mg·m-3
cA0	inlet chlorobenzene concentration, mg·m-3
cA1	outlet chlorobenzene concentration, mg·m-3
E1	energy of one photon, 7.8×10-19 J
ϵA	mole extinction coefficients, 7.4×103 L·mol-1·cm-1
Iave	average light intensity, 38 W·m-3
k	reaction rate constant, s-1
NA	cell number of chlorobenzene molecules converted to products, unit
N	avogadro constant, 6.023×1023 m2·h-1
Q	gas flow rate, m3·h-1
rA	reaction rate, mg·m-3·h-1
t	time, s
τUV	gas empty bed residence time in the UV system, s
VUV	UV system volume, m3
x	number of absorbed photons, unit
Ф	quantum yield, dimensionless
η	removal efficiency, dimensionless
a	specific surface area of filter bed, 820, 860 m2·m-3
cg	chlorobenzene concentration in gas phase, mg·m-3
cf	chlorobenzene concentration in biofilm, mg·m-3
D	diffusion coefficient in water, 8.8×10-6 m2·h-1
Df	diffusion coefficient in biofilm, 6.2×10-6 m2·h-1
Jx	chlorobenzene flux inside biofilm, mg·m-2·h-1
Ks	saturation constant, 1.5 g·m-3
L’	water layer thickness, m
νm	maximum specific substrate degradation rate, 0.85 h-1
Xf	microorganism concentration inside biofilm, 6.7, 7.2×104 g·m-3
u	flow velocity, m·h-1
z	rectangular coordinate, m

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