Bioremediation of Greenhouse Effluent using Constructed Wetlands

Abstract

Due to problems of water shortages and increased legal constraints concerning effluent content, nursery and greenhouse operations are in need of new methods of cleaning and reusing irrigation water. Using constructed wetlands to improve water quality is a low-cost and rapidly emerging ecotechnology, and is currently used for treating wastewater from cattle operations, catfish ponds, and residential subdivisions. To examine the effectiveness of constructed wetlands, a greenhouse was equipped with five free-standing wetland cells planted with Equisetum hyemale (Horsetail). Cells consisted of 0.9 × 2.4-m metal tanks filled with pea gravel (about 0.7 m deep) with inlet and outlet sampling ports. Each cell collected runoff from individual greenhouse benches stocked with impatiens or marigolds grown in pots containing Sunshine LC1 media and fertigated using trickle irrigation. Runoff flow rates and volume entering each cell were measured. Water samples were taken 1) directly from the irrigation line, 2) as bench crop runoff, 3) after entering the cell, and 4) after exiting the cell, and were analyzed for various N fractions. Preliminary studies indicated that the cell size used in these studies was sufficient to handle runoff volume from each bench and could reduce overall N concentration in the runoff. There was significant variability in effectiveness between the cells, which appears to be due to differences in cell vegetation growth and establishment. Overall evaluation of the system and recommendations will be discussed.