Ammonia removal from oil refinery effluent in vertical upflow macrophyte column systems

Constructed vertical macrophyte systems, for nitrogen removal from oil refinery wastewater, were investigated. Detailed studies were carried out in laboratory columns (diameter, 0.06 m; depth, 0.5 m; operating volume, 0.6 L) planted with common reed, Phragmites australis. Through a vertical flow format, collected oil refinery wastewater was supplied directly to the columns. Wastewater quality varied through the experimental period with initial ammonia concentrations ranging from 3 to 20 mg NL^-1. Effective ammonia removal was obtained for the planted columns with a hydraulic detention time of 5 hr. Removal efficiencies above 90% was obtained for high (above 6 mg N L^-1) ammonia inflow concentrations. A satisfactory ammonia removal was obtained at shorter detention times for the low initial concentrations. Longer detention times also provided organic nitrogen removal. Recirculation of the flow, which provides the same total detention time but a higher hydraulic loading, provides the possibility to adjust the flow rate and the inflow ammonia concentration with detention time to achieve a target outflow concentration.