BTEX removal in a modified free water surface wetland

A pilot scale free water surface (FWS) wetland with provision of additional intermediate berms composed of gravel material was tested for assessing its potential to remediate hydrocarbons present in produced water from a gas field. The average influent BTEX values were as follows: benzene (1.57 mg/L), toluene (0.14 mg/L), ethyl benzene (0.29 mg/L), m and p-xylene (2.01 mg/L) and o-xylene (0.13 mg/L). The FWS wetland removed all monitored hydrocarbons with very good removal efficiencies during the monitoring period: benzene (92.6%), toluene (93.4%), ethyl benzene (98.3%), m and p-xylene (91.3%) and o-xylene (87.4%). Biodegradation was considered to be the main pathway for benzene removal in the studied system. Reaction kinetics were studied and the first-order area based rate coefficient for benzene was 0.13 m/d while for BTEX it was 0.12 m/d. Metagenomic analysis of bacterial community retrieved from the wetland showed majority of sequences were related to phylum proteobacteria.