Abiotic and Biotic Perchlorate removal in an activated carbon filter

Abstract

Granular activated carbon (GAC) filtration experiments demonstrated that perchlorate was removed by ion exchange rather than by chemical reduction. A column ion‐exchange capacity of 0.172 mg perchlorate per g GAC was calculated. Batch tests confirmed that ion exchange was the dominant mechanism of perchlorate removal by GAC. When influent dissolved oxygen (DO) was 2.5 mg/L and an electron donor solution was supplied, efficient reduction of 50 μg/L perchlorate was achieved using biologically active carbon (BAC) filtration. Perchlorate reduction decreased as the concentration of nitrate in the filter increased. With low influent DO and nitrate concentrations and excess electron donor added, the BAC filter removed 50 μg/L perchlorate to below detection for 103 days of flow at a 25‐min empty bed contact time. Batch biological experiments verified the occurrence of biological reduction and demonstrated that microorganisms in the BAC filter converted perchlorate completely to chloride.

Microbial Degradation of Perchlorate: Principles and Applications

“…Nitrate has been found to have different effects on perchlorate removal rates. Nitrate has inhibited the perchlorate reduction rate in some studies (Herman and Frankenberger, 1999;Brown et al, 2002) but not in others (Burns et al, 2001;Logan and LaPoint, 2002). A PRB isolate, perc1ace, was able to completely remove perchlorate (130 mg/L) and to simultaneously remove more than 95% of the nitrate (20 mg/L) in a sand-packed bioreactor (Herman and Frankenberger, 1999).…”

Chemisorption of oxygen onto activated carbon can enhance the stability of biological perchlorate reduction in fixed bed biofilm reactors

“…This corresponds to an empty bed contact time of 23.5 min. The BAC reactor was seeded using biomass collected from two other BAC reactors: one had been fed Urbana (IL) tap water amended with acetate at a concentration of 2 mg/L as C and 50 μg/L perchlorate (Brown et al, 2002), the other had been fed Urbana groundwater amended with 50 μg/L perchlorate (Lin, 2004). Sorption capacities of the GAC for perchlorate and oxygen were exhausted before initial start-up by recirculating water containing 50 μg/L of perchlorate and saturated by oxygen through the reactor.…”

“…Biological removal of perchlorate has been evaluated in biofilm reactors using different carrier media including plastic (Min et al, 2004), sand (Min et al, 2004), Celite (Losi et al, 2002), and granular activated carbon (GAC) (Brown et al, 2002) for fixed bed reactors, and sand and GAC for fluidized bed reactors (McCarty and Meyer, 2005;Sutton, 2006). Other reactor configurations include membrane diffuser biofilm reactors (Nerenberg et al, 2002) and ion exchange membrane bioreactor (Matos et al, 2006).…”

Effect of backwashing on perchlorate removal in fixed bed biofilm reactors

“…Several studies have shown that biological treatment is an effective technology to remove perchlorate from drinking water (Brown et al, 2002;Giblin et al, 2000;Herman and Frankenberger, 1999;Min et al, 2004). For example, for a typical groundwater concentration of 50 μg/L, biologically active carbon (BAC) fixed bed reactors consistently removed perchlorate to below 2 μg/L (Brown et al, 2002(Brown et al, , 2005. Despite these encouraging studies, the reliability of biological drinking water treatment is sometimes questioned, in particular under dynamic loading conditions and during changes in reactor operation, such as after backwashing (Kim and Logan, 2001).…”

“…Regular backwashing is a key process for fixed bed biofilm reactors that is necessary to prevent clogging, to reduce excessive head loss across the filter, to maintain an active biofilm, to prevent the proliferation of filamentous bacteria and eukaryotic organisms, such as fungi and protozoa, and to enhance the mass transfer of contaminants to the biofilm (Brown et al, 2002;Hozalski and Bouwer, 1998;Laurent et al, 2003). However, backwashing also reduces the amount of active biomass in the reactor, which could potentially lead to unstable reactor performance (Lahav et al, 2001;Nakhla and Farooq, 2003).…”