Biodegradation of gasoline compounds (BTEX) in a water works sand filter

Various chemical compounds including aromatic gasoline compounds frequently contaminate drinking water wells in urban areas. Because ground water treatment is simple, usually consisting of aeration/stripping and sand-filtration, it is of significant interest to know the ability of the conventional treatment to remove the chemical contaminants. The removal of gasoline compounds was investigated in a two-stage pilot scale sand filter, each with a filter depth of 0.8–1 m and with a filtration rate of 7.6 m/h. The concentrations of aromatic compounds were in the range 7–15 μg/L, which are realistically low concentrations. The experiments demonstrated a surprisingly high removal efficiency of the filter system. Most of the hydrocarbons were removed already in the primary filter (3 mm sand grains) and the concentrations were in the range 0.05–0.1 μg/L at the outlet from the secondary filter (1 mm sand grains). Influent iron concentrations in the range 0–4 mg/L and backwashing did not adversely affect the biodegradation of hydrocarbons. This study has shown that a conventional biological active sand filter can act as an efficient barrier against gasoline compounds, thereby saving the consumer capital costs and operational costs from installation of supplementary treatment.