The in situ treatment of Basic Violet 16 synthetic dye in groundwater

Abstract

AbstractSynthetic dyes have been shown to be micropollutants in various aquatic and groundwater systems, often occurring at milligram per liter (mg/L) concentrations. Synthetic dyes are typically introduced into the environment either as a continuous stream from wastewater or as episodic events related to the disposal of residues or spills generated during the manufacturing process. Various studies for the treatment of synthetic dyes have been undertaken for wastewater but studies for the in situ treatment of synthetic dyes in groundwater are limited. A pilot‐scale test was conducted to determine if the use of colloidal activated carbon (CAC) could effectively reduce dissolved concentrations of the synthetic dye Basic Violet (BV16) in groundwater using in situ methods. The pilot test was carried out downgradient of a textile manufacturing facility where historic disposal practices resulted in the release of various chemicals of concern including BV16 to an unconfined silty sand aquifer. A 10‐weight percent CAC solution was injected into a series of temporary direct push injection points to target the synthetic dye that was present at concentrations of up to 1,640 micrograms per liter (μg/L) during the 738‐day study. The results from the pilot test indicated that the CAC was effectively delivered to the target injection zone resulting in a three order of magnitude increase in total organic carbon (TOC) concentrations compared to preinjection TOC concentrations within the aquifer. Distribution of the CAC within the targeted injection zone indicated that heterogeneity affected the distribution with a zone of higher horizontal hydraulic conductivity (KH) having an average TOC concentration approximately 100 percent greater than the mean TOC concentration within the surrounding aquifer targeted by the CAC injection. Analyses of the groundwater chemistry before and postinjection indicated that the CAC had no detrimental impact on the groundwater quality while reducing the concentration of dissolved BV16 within the plume to below the method detection limits within 62 days of injection. The concentration of BV16 remained below the method detection limit of 10 µg/L for the 738‐day duration of the study apart from one detection of 180 µg/L at Day 183 within groundwater sampled from one monitoring well suggesting that the CAC was effective in attenuating the BV16 over the short and moderate term.