Phosphorus and nitrogen removal from tertiary treated urban wastewaters by a vertical flow constructed wetland

Autores UPV
Revista Ecological Engineering


Lake L¿Albufera is a hypertrophic lake exposed to anthropic pressures. To reduce nutrient loads, a set ofhorizontal and vertical sub-surface flow constructed wetlands (CWs) were built to treat wastewater froma tertiary wastewater treatment plant (WWTP) before its discharge into the lake.These CWs were designed to remove nutrients, primarily total phosphorus (TP). This paper is focused ona vertical flow constructed wetland (VFCW), the primary objective of which was to remove TP by adsorp-tion and biological uptake. Prior to construction, laboratory experiments were conducted to determinewhich materials and in what proportions are best suited to achieve that goal. Two different sands (types 0and 1), as filling material, two types of clays (types 1 and 2) and two types of iron oxides (types a and b), assorption agents, were used. The primary parameters studied were the phosphate adsorption isotherm, thefilter medium hydraulic conductivity and the depletion of adsorption capacity in experimental columns.Laboratory results showed that the best mixture was formed by sand type 0 (Qmax= 2.94 mg P kg−1)and 10% of iron oxide type b (Qmax= 1666.67 mg P kg−1). Operation was established in a daily cycle witha hydraulic loading of 0.068 m d−1.Following this procedure, a VFCW planted with reeds and with 157.9 m3water capacity per cyclewas constructed. The inflow contained 0.635 mg TP l−1, 1.906 mg NH4+-N l−1, 8.9 mg TN l−1and 20.9 mgCOD l−1. During the first year of operation, total phosphorus removal was 77.0%, ammonium 95.0%, totalnitrogen 24.4% and organic matter (COD) 49.3%.