Simultaneous biofiltration of BTEX and Hg° from a petrochemical waste stream

Abstract

A biofiltration system was developed to treat benzene, toluene, ethylbenzene, and xylene (BTEX) and Hg° vapour from a petrochemical waste stream during overhaul maintenance. The biofilter compost bed was inoculated with a microbial consortium provided by a petrochemical wastewater treatment plant. The effect of the a BTEX concentration (192.6-973.8 g/m³h) and empty bed residence time (EBRT) of 20-100 s were studied under the conditions of steady state, transient, shock BTEX-loading, and off-restart. The findings revealed that during a biofilter start-up, an increase in the influent BTEX concentration to around 334.3 g/m³h did not notably affect the biofiltration function at an EBRT of 100 s, and the removal efficiency was higher than 98%. Further, the low EBRT of 60 s did not have adverse effects on the BTEX and Hg° biofiltration (the removal efficiency in both was >93%). For the biofiltration system, the BTEX and Hg° critical attenuation capacity were obtained as 663 g_BTEX/m³h and 12.6 g_Hg°/m³h respectively. A maximum attenuation capacity of 774.5 g_BTEX/m³h was achieved in the biofilter when the BTEX loading rate was 973.8 g_BTEX/m³h. The parameters of k_m and r_max of the Michaelis-Menten kinetic model were obtained as 0.099 g/m³ and 0.578 g/m³min respectively. Both BTEX and mercury vapours were completely mass balanced during a continuous biofiltration test. In general, the developed treatment system exhibited a good performance in the treatment of the BTEX stream containing Hg° vapour in the off-gas of a petrochemical company.

Keywords: BTEX; Biofiltration; Compost bed; Empty bed residence time; Mercury vapour; Petrochemical.