Effect of different plant species in pilot constructed wetlands for wastewater reuse in agriculture

In this paper the first results of an experiment carried out in Southern Italy (Sicily) on the evapotranspiration (ET) and removal in constructed wetlands with five plant species are presented. The pilot plant used for this study is made of twelve horizontal sub-surface flow constructed wetlands (each with a surface area of 4.5 m2) functioning in parallel, and it is used for tertiary treatment of part of the effluents from a conventional municipal wastewater treatment plant (trickling filter). Two beds are unplanted (control) while ten beds are planted with five different macrophyte species: Cyperus papyrus, Vetiveria zizanoides, Miscanthus x giganteus, Arundo donax and Phragmites australis (i.e., every specie is planted in two beds to have a replication). The influent flow rate is measured in continuous by an electronic flow meter. The effluent is evaluated by an automatic system that measure the discharged volume for each bed. Physical, chemical and microbiological analyses were carried out on wastewater samples collected at the inlet of CW plant and at the outlet of the twelve beds. An automatic weather station is installed close to the experimental plant, measuring air temperature, wind speed and direction, rainfall, global radiation, relative humidity. This allows to calculate the reference Evapotranspiration (ET0) with the Penman-Monteith formula, while the ET of different plant species is measured through the water balance of the beds. The first results show no great differences in the mean removal performances of the different plant species for TSS, COD and E.coli, ranged from, respectively, 82% to 88%, 60% to 64% and 2.7 to 3.1 Ulog. The average removal efficiency of nutrient (64% for TN; 61 for NH4-N, 31% for PO4-P) in the P.australis beds was higher than that other beds. From April to November 2012 ET measured for plant species were completely different from ET0 and ETcontrol, underlining the strong effect of vegetation. The cumulative evapotranspiration highest value was measured in the CWs vegetated with P.australis (4,318 mm), followed by A.donax (2,706 mm), V.zizanoides (1,904), M.giganteus (1,804 mm), C.papyrus (1,421 mm).