Phytoremediation and On-Site Treatment of Septic Effluents in Sub-Surface Flow Constructed Wetlands

Abstract

Phytoremediation may be one of the mechanisms leading to improvement of water quality in sub-surface flow constructed wetlands. Experiments were undertaken in a glasshouse by growing plants in microcosms, and at a sub-surface flow constructed wetland to evaluate the importance of phytoremediation in improving water quality and the adaptability of different aquatic plants to grow in domestic wastewater from septic tanks. Wastewater was provided every two days to microcosms to simulate detention time in a constructed wetland. An initial screening of 20 plant species resulted in selection of Cyperus alternifolius, C. isocladus, Sagittaria lancifolia, Canna flacccida, Iris sp., Typha latifolia and T. angustifolia, based on their ability to grow well in the wastewater, for experimentation on phytoremediation. Phytoremediation generally reduced biological oxygen demand, NH4 +-N, P, turbidity, and volatile suspended solids. Populations of fecal coliforms were consistently reduced by 90 to 99% by 2-d detention in microcosms with and without plants. Overall it appears that for improvement of water quality, largest water loss by evapotranspiration, vigor of plant growth and ease of maintenance, Typha and Cyperus were the best performers. Cyperus alternifolius seemed highly desirable because of its high water requirement, resistance to insects, ability to grow throughout the year, winter hardiness, absence of a period of dormancy and rapid recovery from frost damage. Phytoremediation in sub-surface flow constructed wetlands has potential for improvement of water quality and reducing the quantity of water to be disposed.