Interactions of perchlorate and nitrate in biological treatment systems

Perchlorate is often found as a co-contaminant with nitrate in impacted groundwater. This co-contamination is related to the unregulated discharge of ammonium perchlorate wastes from perchlorate manufacturing and use and the application of Atacama fertilizers. Ion-exchange is widely used to remove perchlorate and nitrate from drinking water. During this process, perchlorate and nitrate are concentrated into a brine or resin which must be treated before discharging to the environment. Biological treatment using a salt-tolerant, perchlorate- and nitrate-reducing culture is a very promising technology to treat the brines or resins. This chapter summarizes the literature on the removal of nitrate and perchlorate together and individually in high salt solutions and discusses recent work. A large disparity between nitrate and perchlorate concentrations in pilot plant ion-exchange brine had major effects on the evolution the microbial population in a fluidized bed reactor. In order to further understand the evolution of the culture to enhance stable performance in engineering processes, the interactions of nitrate and perchlorate on the culture were studied. Two mixed cultures: P30 (with perchlorate as the sole electron acceptor) and NP30 (with nitrate and perchlorate as the electron acceptors) were used in this research. The dominant microbial component in P30 was isolated from NP30 as a pure culture P4B1. The effects of the presence of perchlorate and nitrate on culture growth and the degradation rates were also characterized. The results show that when perchlorate and nitrate were both present, P4B1 preferred perchlorate to nitrate as the electron acceptor. When nitrate was used as the sole electron acceptor, P4B1 eventually lost the ability to reduce nitrate. The study suggests that P4B1 might be useful as an inoculum for engineered systems to treat perchlorate and nitrate simultaneously.