A new method to treat fumigant pesticides-spent granular activated carbon utilizing alkaline hydrolysis

Abstract

Groundwater treatment of recalcitrant fumigant pesticides (1,2-dibromo-3-chloropropane (DBCP), 1,2-dibromoethane (EDB), 1,2-dichloropropane (DCP), and 1,2,3-trichloropropane (TCP)) often involves a pump and treat system with granular activated carbon (GAC). A novel and promising method of treating the pesticide-spent GAC is based on alkaline hydrolysis, a well-understood abiotic transformation mechanism, that offers a potentially greener approach to conventional thermal regeneration. Here, alkaline hydrolysis of these pesticide chemicals was evaluated under homogeneous (aqueous), and heterogeneous (pesticide spent-GAC) conditions involving bituminous- and coconut-based GAC. Aqueous treatment occurred at elevated pH (pH 12.0–12.4) and the pesticide rate of hydrolysis transformation was first-order (DBCP ≫ TCP ≫ EDB ≫ DCP). Significant pesticide loss (94.95–99.98%) was achieved in both types of GAC (pH 12.0–12.4; 30 d). GAC suspensions held (5 d) at pH 11.0, 12.0, and 12.6, resulted in the DBCP loss of 74%, 89%, and 99%, respectively. The pH dependency of DBCP hydrolysis underscores the correlation between alkaline conditions, aggressive hydrolysis treatment, and reaction time for engineered systems. The estimated time (4–8 min) for full OH- intraparticle diffusion into the GAC from bulk solution was much less than the pesticide hydrolysis half-lives indicating that alkaline hydrolysis treatment of pesticides in GAC was reaction rate limited. Rapid small scale column tests demonstrated that the post-treatment (i.e., base hydrolysis) impact on adsorptive characteristics of the GAC was limited.