This research was conducted to evaluate the feasibility of using the bioenergy crop Saccharum officinarum (sugarcane) as vegetation and mineral wastes for filling in constructed wetlands (CWs) designed for the removal of nutrients from wastewater. Four horizontal subsurface flow pilot-scale CWs were monitored during one year: two filled with fragmented limestone and two with clay brick fragments, two planted and two unplanted controls. Sugarcane stalk height, diameter and foliar area were evaluated during the plant-cane cycle along with total phosphorus (TP) and total nitrogen (TN) removal efficiencies from the wastewater. Sugarcane biomass production was 107 ton/ha for the brick fragments filled CW and 67 ton/ha for the fragmented limestone filled CW. Planted CWs show better nutrient removal efficiencies than the unplanted. Planted CW filled with brick fragments show average efficiencies of 77%˘4% for TP and 60%˘12% for TN, and planted CW filled with fragmented limestone 68%˘3% for TP and 58%˘7% for TN. Results showed that the use of sugarcane as CW vegetation is a viable alternative to produce a bioethanol raw-material without the use of arable land and irrigation water, while it maintains the wastewater treatment capabilities of CWs.
Constructed wetlands (CW) are a clean and environmentally friendly alternative to conventional wastewater treatment methods, namely in the removal of the nutrients responsible for the eutrophication of receiving water bodies, as is the case of phosphorus compounds. The materials used as CW filling can directly contribute to the removal of phosphorus compounds from wastewater, but with the operating time they tend to become saturated and treatment efficiency decreases. In order to evaluate the viability of producing an energy crop in phosphorus-saturated CW, sugarcane growth was monitored in two pilot-scale CW filled with two different expanded clay aggregates used for 10 years in wastewater treatment. This paper presents the results obtained during the first year of plant development in the plant-cane cycle. Morphologic aspects of sugarcane growth, such as height and average diameter of stems, average leaf area and number of new sprouts, have been monitored. The results obtained are comparable with those cited in the literature for traditional cultivation. Dry biomass productivity of 26.6 ton per hectare per year can be achieved. Estimated sucrose productivity can reach 13.5 ton per hectare per year, and related bioethanol production potential can be between 2.4 and 7.6 cubic meters per hectare per year, depending on the CW filter media used. It is concluded that the cultivation of sugarcane in CW allows to extend the life of these systems by reusing fillers, and simultaneously is an alternative to produce bioethanol raw-material without the use of scarce resources such as arable land, fresh water and plant nutrients.
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