Implementation of In Situ Activated Carbon
Remedies at Contaminated Sediment Sites

SCIENCE OF CARBON SEQUESTRATION

BACKGROUND

Activated (AC) carbon filtration is a well-established treatment practice for removing organic contaminants from water. Produced from coal or biomass feedstock and treated at high temperature to produce a highly porous structure with great sorption capacity, AC filtration of water is a part of our everyday lives. AC filters are used to purify municipal drinking water, pre-discharge polishing at sewage treatment plants, cleaning recycled water at golf courses, filtering waste build up in aquariums and home fish tanks, and at our homes with in-line or counter-top filtration systems. AC is also used in air filtration systems and as a treatment for humans who have consumed certain poisons. AC filtration is especially effective at removing at hydrophobic-organic contaminants (HOCs). HOCs include pesticides (e.g., DDT, atrazine), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls PCBs), dioxins, and phthalates.

The role of natural organic carbon in sequestering and limiting the biological availability of HOCs in sediments and soils is well-established in the scientific, regulatory, and remedial community. The Equilibrium Partitioning Theorem (EqP) (EPA 2003) was developed based on a preponderance of data that suggested that the amount of natural organic carbon (NOC) controlled HOC bioavailability. With subsequent work it became evident in addition to NOC anthropogenic carbon had a stronger influence on HOC sequestration (Luthy et al 1997; Ghosh et al, 2000; Accardi-Day 2002; EPA 2013, and others). EPA defines black carbon (BC) as "A form of carbon produced by the burning of biomass and fossil fuels that can accumulate in sediments. This form of carbon has a large affinity for hydrophobic contaminants of concern (COC) and can substantially reduce bioaccessibility and bioavailability." Examples of BC include diesel soot, coal fly ash, charcoal, and activated carbon. An excellent review of the role of black carbon in reducing HOC bioavailability by Koelmans et al (2006) is available online.

The observations that BC in sediments were active in the sequestration of HOC, coupled with the knowledge of the use of GAC in water treatment, led to research funding by SERDP and ESTCP to determine whether addition of GAC to contaminated sediments could further bind those contaminants, acting as a in-situ remedy for contaminated sediments. Luthy, Ghosh, and collaborator in SERDP project ER-1207 demonstrated that PCB and PAH in the sediment tended to preferentially accumulate in coal-derived and char particles where the compounds were strongly bound. In that same SERP project, they then were able to demonstrate that that the addition of activated carbon sorbent to sediments reduced PCB and PAH bioavailability to benthic organisms. Based on those pioneering demonstrations, ESTCP (ER-200510) funded Luthy and colleagues to conduct the first demonstration of field application of monitoring of an application of AC to PCB-contaminated sediments at Hunters Point. Additional information on that highly successful project may be found at the Hunters Point 2005 Pilot Project case study page.