Bioelectricity Generation and Production of Ornamental Plants in Vertical Partially Saturated Constructed Wetlands

Humberto Raymundo González-Moreno,Eddy Sánchez-Dela-Cruz,Noemí Nava-Valente,Luis Carlos Sandoval-Herazo,David Reyes-Gonzalez,Oscar Andrés Del Ángel-Coronel,Carlos Nakase,José Luis Marín-Muníz

doi:10.3390/w13020143

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).

Highlights

Vertical partially saturated constructed wetlands (VPS-CWs) are an emerging technology for domestic and industrial wastewater treatment, the operation of which is not clearly known [1]
Considering that Canna hybrids are adapted to wetlands, as reported by some authors [29], and their typical growth is higher (2.5 m) than that of Zantedeshia aethiopica (1 m) [30], which could favor more radial oxygen release and more aerobic conditions [31], we developed the following two hypotheses: (1) Zantedeshia aethiopica adapts to constructed wetland conditions; its growth is lower than that of Canna hybrids, (2) pollutant removal and bioelectricity production is higher in systems with Canna hybrids compared with systems planted with Zantedeshia aethiopica
Our study demonstrated that VPS-CWs are an efficient technology for the treatment of domestic wastewater, since removal of organic matter was observed

Summary

Introduction

Vertical partially saturated constructed wetlands (VPS-CWs) are an emerging technology for domestic and industrial wastewater treatment, the operation of which is not clearly known [1]. Recent studies have aimed at evaluating the performance of CWs such as microbial fuel cell (MFCs) in producing bioelectricity through biochemical reactions that occur in these systems [12,13,14,15] The operation of these systems evokes a cell, where the zone with absence of oxygen (anaerobia) acts as an anode (zones far from roots of CW plants) and zones with presence of oxygen (aerobic) as a cathode (regions close to the root zone of CW plants). Research aimed at the use of CW-MFCs is recent, with limitations such as the cost of materials used to favor the generation of bioenergy and make the systems more efficient in terms of energy production Elements of these novel systems that promote energy production include the anode and the cathode that treat contaminated water, which generates bioelectricity. Operating mechanisms require hybrid aerobic and anaerobic operating conditions with the aim of improving the processes of

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