2017 ASHS Annual Conference

Residual agrichemicals can potentially accumulate in recaptured irrigation water, which can lead to negative effects on crop quality, ecosystems, and human health. Filtration with granular activated carbon (GAC) is one technology for remediating agrichemical residues. The objective was to evaluate the removal of 11 agrichemicals including herbicides (glyphosate and triclopyr), insecticides (acephate, bifenthrin, chlorpyrifos, and imidacloprid), sanitizers (hydrogen peroxide and quaternary ammonium chloride), and plant growth regulators (flurprimidol, paclobutrazol, and uniconazole). Each chemical was mixed to one-tenth of the concentration based on a pesticide label rate for ornamental greenhouse application. The one-tenth dilution was chosen because some dilution would be expected when applied chemical was discharged into collection tanks, ponds, reservoirs, or surface water. Chemical solutions were passed through a small-scale GAC system filled with 0.50 to 4.75 mm particle size (8x30 mesh) bituminous coal GAC at 6L·minute^-1, and fresh carbon was used for each chemical. Solutions were exposed to three contact times (0 (no filtration), 12, or 64 seconds), which corresponded to 0, 1.9, or 10.1L of empty filter housing volume (excluding the carbon). For each chemical tested, the experimental design was a randomized complete block with four blocks (time periods) and one replicate of each GAC treatment per block (12 solutions total). Analysis of all chemicals using gas chromatography-mass spectrometry (GC-MS) or colorimetric testing (hydrogen peroxide only) found that concentrations for acephate, flurprimidol, paclobutrazol, quaternary ammonium, and uniconazole decreased by over 90% with 12 seconds GAC. Chemical concentrations for bifenthrin, chlorpyrifos, and imidacloprid did not decrease by 90% even with the highest treatment level of 64 seconds GAC. Activated carbon filtration was least effective at removing bifenthrin after 64 seconds GAC, with 71% reduction. Chemical concentrations for acephate, flurprimidol, quaternary ammonium, and uniconazole were reduced below the minimum detection limit with 64 seconds GAC. Overall, these series of experiments showed that granular activated carbon filtration has the potential to remediate these 11 commonly applied agrichemicals from water with the short contact times tested.