Optimal conditions for chlorothalonil and dissolved organic carbon in horizontal subsurface flow constructed wetlands

ABSTRACT

The most efficient system of horizontal subsurface flow constructed wetlands (HSSFCW) for removing dissolved organic carbon (DOC) in the presence of chlorothalonil pesticide (CLT) present in synthetic domestic wastewater was determined using the macrophyte Phragmites australis. Two concentrations of CLT (85 and 385 μg L⁻¹) and one concentration of glucose (20 mg L⁻¹) were evaluated in four pilot scale horizontal surface flow constructed wetlands coupled with two sizes of silica gravel, igneous gravel, fine chalky gravel (3.18–6.35 mm), coarse gravel (12.70–25.40 mm) and two water surface heights (20 and 40 cm). For a month, wetlands were acclimated with domestic wastewater. Some groups of bacteria were also identified in the biofilm attached to the gravel. In each treatment periodic samplings were conducted in the influent and effluent. Chlorothalonil was quantified by gas chromatography (GC-ECD m), DOC by an organic carbon analyzer and bacterial groups using conventional microbiology in accordance with Standard Methods. The largest removals of DOC (85.82%–85.31%) were found when using fine gravel (3.18–6.35 mm) and the lower layer of water (20 cm). The bacterial groups quantified in the biofilm were total heterotrophic, revivable heterotrophic, Pseudomonas and total coliforms. The results of this study indicate that fine grain gravel (3.18–6.35 mm) and both water levels (20 to 40 cm) can be used in the removal of organic matter and for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT in HSSFCW.

KEYWORDS:

• Chlorothalonil
• dissolved organic carbon
• Phragmites australis
• biofilm
• constructed wetlands

Acknowledgments

The Pollution Control and Diagnosis Research Group (University of Antioquia) and the Environmental Engineering Department, Civil Engineering Faculty (University of Cauca) are thanked for their technical support; and Isabel Cristina Carmona Quintero, Deisy Mabel Cardona Chalarca and Edwin Rengifo gratefully acknowledge the assistance generous for their support in statistical analysis; The author Juan C. Casas-Zapata dedicates this paper to the memory of his father Hugo de Jesus Casas Upegui (1933–2008) and his brother Julian David Casas Zapata (1980–1997)

Funding

The authors acknowledge the financial support of Colciencias (Colombia) and Alfa TECSPAR Network (European Community), as well as the 2011–2012 sustainability grant of the Research Vice-Rectory of the University of Antioquia.