Addition of Carbon Sorbents to Reduce PCB and PAH Bioavailability in Marine Sediments:  Physicochemical Tests

Abstract

The addition of activated carbon as particulate sorbent to the biologically active layer of contaminated sediment is proposed as an in-situ treatment method to reduce the chemical and biological availability of hydrophobic organic contaminants (HOCs) such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). We report results from physicochemical experiments that assess this concept. PCB- and PAH-contaminated sediment from Hunters Point Naval Shipyard, San Francisco Bay, CA, was contacted with coke and activated carbon for periods of 1 and 6 months. Sediment treated with 3.4 wt % activated carbon showed 92% and 84% reductions in aqueous equilibrium PCB and PAH concentrations, 77% and 83% reductions in PCB and PAH uptake by semipermeable membrane devices (SPMD), respectively, and reductions in PCB flux to overlying water in quiescent systems up to 89%. Adding coke to contaminated sediment did not significantly decrease aqueous equilibrium PCB concentrations nor PCB or PAH availability in SPMD measurements. Coke decreased PAH aqueous equilibrium concentrations by 38-64% depending on coke dose and particle size. The greater effectiveness of activated carbon as compared to coke is attributed to its much greater specific surface area and a pore structure favorable for binding contaminants. The results from the physicochemical tests suggest that adding activated carbon to contaminated field sediment reduces HOC availability to the aqueous phase. The benefit is manifested relatively quickly under optimum contact conditions and improves in effectiveness with contact time from 1 to 6 months. Activated carbon application is a potentially attractive method for in-situ, nonremoval treatment of marine sediment contaminated with HOCs.

Biochar‐mediated reductive transformation of nitro herbicides and explosives

“…Similar to GAC [34,35], biochar has been proposed as an adsorbent to decrease the concentrations and bioavailability of organic and metallic pollutants [17,36,37]. The present study further suggests that biochar may also be applied to promote the degradation of organic compounds including agrochemicals, explosives, and potentially other nitrogenous compounds such as azo dyes [38] and nitrate esters [26,39].…”

Field methods for amending marine sediment with activated carbon and assessing treatment effectiveness

“…Building on this observation, we have tested in the laboratory a new concept for in-situ sediment management in which activated carbon (AC) is mixed into contaminated sediments to repartition hydrophobic organic compounds and reduce their availability to water and biota. The physicochemical (Zimmerman, Ghosh, Millward, Bridges, & Luthy, 2004;Zimmerman et al, 2005) Francisco Bay, CA, USA, was contacted with 3.4% (dry weight) AC on a roller for one month, we observed 87% reductions in aqueous equilibrium PCB concentrations and up to 84% reductions (McLeod et al, 2007) in the bioaccumulation of PCBs by the clam, Macoma balthica. Six months contact with AC reduced aqueous equilibrium concentrations by over 90% (Zimmerman et al, 2004).…”

Bioturbation effects on heavy metals fluxes from sediment treated with activated carbon

“…Adsorbents most frequently used for this purpose include activated carbon (AC) Ghosh 2011, 2013;Kupryianchyk et al 2012;Tomaszewski et al 2007). Adding activated carbon (AC) to sediment has been proposed as a remediation technique to reduce HOC release to the overlying water (Cho et al 2007;Oen et al 2011;Sun and Ghosh 2008;Zimmerman et al 2004). In fact, with high surface areas, the sorption capabilities of activated carbon are very high not only for organic contaminants, but also for metals (Kongsuwan et al 2009;Weber and Van Vliet 1981).…”