Bioelectricity generation and production of ornamental plants in vertical partially saturated constructed wetlands

Abstract

Energy production in constructed wetlands is a little-known field, as is the operation of vertical partially saturated constructed wetlands (VPS-CWs) that promote both aerobic and anaerobic microbial interactions. By doing so, bacterial degradation is increased, becoming the main mechanism of pollutant removal in constructed wetlands (CWs). For the first time, the generation of bioelectricity, together with the production of ornamental plants in vertical partially saturated constructed wetlands during the treatment of domestic wastewater, was evaluated. Six VPS-CW systems functioned as bioelectricity generators, where the systems were filled with red volcanic gravel and activated carbon as anode and cathode. Three systems were planted with Zantedeschia aethiopica and three with Canna hybrids plants. The development was measured through mother plants and shoots produced every 60 days. The input and output of each VPS-CW was monitored using control parameters such as BOD5, phosphates (P-PO4), and total Kjeldahl nitrogen (TKN). Bioelectricity, power, voltage, and current measurements were performed every 15 days for a period of 7 months. It was found that the VPS-CWs used as biobatteries in combination with the use of domestic wastewater as a substrate improved the development of the two evaluated plant species and stimulated growth and germination of new shoots. No significant differences were found between the different treatments (p ≤ 0.05). Likewise, an average efficient removal of BOD5 (98%) for both systems without statistical differences was observed (p ≤ 0.05), but for TKN and P-PO4, significant differences (p ≤ 0.05) were found between systems planted with Z. aethiopica (TKN: 65%; P-PO4: 20%) and Canna hybrids (TKN: 69%; P-PO4: 27%). This method of water treatment and bioelectricity production with Canna hybrids was an efficient system that generated a great electric current (140 mA/m2 ), voltage (750 mV), and electric power (15 mW/m2 ), compared with those observed in systems with Z. aethiopica (60 mA/m2, 500 mV, 9 mA/m2 ).