Fate and transport of DBPs in a deep confined aquifer during artificial recharge process

Abstract

Although the behavior of disinfection by-products (DBPs) in groundwater artificial recharge projects is considered as one of the crucial factors affecting potable water, surprisingly, its mechanism remains unclear. Our in situ study on transport and fate of DBPs (especially chloroform) was carried out in a test site located in Southeast China. In this study, four types of DBPs: dichloromethane, chloroform, bromodichloromethane (BDCM), and dibromochloromethane (DBCM), were detected, among which the occurrence rate and concentration of chloroform were found the highest. The DBPs concentration within the observation well (J4) situated 10 m away is higher than that in the source water, especially during the first 10 days since the beginning of recharge. And the difference between peak concentration in J4 and the other observation well (J5) located 17 m away was approximately 13 μg/L for chloroform, 0.1 μg/L for dichloromethane, 0.7 μg/L for DBCM, and insignificant for BDCM. The breakthrough took 16 days for chloroform from J4 to J5. According to attenuation analysis, the chemical hydrolysis, adsorption, and other processes were insignificant. Therefore, biodegradation was most likely dominating the attenuation process, and half-lives of chloroform ranged from 11.2 to 40.5 days, which was mainly a contribution of ammonia-oxidizing bacteria Nitrosomonas europaea via aerobic co-metabolism. In consistence with the transformation of groundwater redox conditions, the biodegradation rate of chloroform was changing as well. As the recharge time got longer, half-lives of chloroform had a tendency to stabilize at roughly 14 days.