Field Application of Activated Carbon Amendment for In-Situ Stabilization of Polychlorinated Biphenyls in Marine Sediment

Abstract

We report results on the first field-scale application of activated carbon (AC) amendment to contaminated sediment for in-situ stabilization of polychlorinated biphenyls (PCBs). The test was performed on a tidal mud flat at South Basin, adjacent to the former Hunters Point Naval Shipyard, San Francisco Bay, CA. The major goals of the field study were to (1) assess scale up of the AC mixing technology using two available, large-scale devices, (2) validate the effectiveness of the AC amendment at the field scale, and (3) identify possible adverse effects of the remediation technology. Also, the test allowed comparison among monitoring tools, evaluation of longer-term effectiveness of AC amendment, and identification of field-related factors that confound the performance of in-situ biological assessments. Following background pretreatment measurements, we successfully incorporated AC into sediment to a nominal 30 cm depth during a single mixing event, as confirmed by total organic carbon and black carbon contents in the designated test plots. The measured AC dose averaged 2.0-3.2 wt% and varied depending on sampling locations and mixing equipment. AC amendment did not impact sediment resuspension or PCB release into the water column over the treatment plots, nor adversely impactthe existing macro benthic community composition, richness, or diversity. The PCB bioaccumulation in marine clams was reduced when exposed to sediment treated with 2% AC in comparison to the control plot Field-deployed semi permeable membrane devices and polyethylene devices showed about 50% reduction in PCB uptake in AC-treated sediment and similar reduction in estimated pore-water PCB concentration. This reduction was evident even after 13-month post-treatment with then 7 months of continuous exposure, indicating AC treatment efficacy was retained for an extended period. Aqueous equilibrium PCB concentrations and PCB desorption showed an AC-dose response. Field-exposed AC after 18 months retained a strong stabilization capability to reduce aqueous equilibrium PCB concentrations by about 90%, which also supports the long-term effectiveness of AC in the field. Additional mixing during or after AC deployment, increasing AC dose, reducing AC-particle size, and sequential deployment of AC dose will likely improve AC-sediment contact and overall effectiveness. The reductions in PCB availability observed with slow mass transfer under field conditions calls for predictive models to assess the long-term trends in pore-water PCB concentrations and the benefits of alternative in-situ AC application and mixing strategies.

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].…”

Extraction of sediment‐associated polycyclic aromatic hydrocarbons with granular activated carbon

“…Apparent sorption to GAC in the presence of sediment was quantified by subtracting the amount of PAH sorbed to sediment without GAC treatment from the amount of PAH sorbed to the GAC-sediment mixtures (Eqns. [2][3][4]. This assumes that PAH partitioning to pH sediment can be quantified by concentrationindependent linear partitioning, as was discussed previously, and is not affected by the presence of GAC.…”

“…Over the last decade, in situ addition of activated carbon (AC) to polluted sediments has been proposed as an effective remediation strategy to reduce risks of sediment-bound HOCs and to improve the ecological quality of surface waters [1,2]. Sediment remediation with AC has been shown to result in reduced freely dissolved HOC concentrations in sediment porewater in laboratory and field settings [3][4][5][6][7] and in reduced bioaccumulation and toxicity of HOCs in benthic invertebrates [5,6,8].…”

“…Small particles have cumulatively large external surface area and, therefore, large accessible numbers of sorption sites per unit of weight [9]. Recently, risk reduction of sediment-bound HOCs in pilot field studies has been accomplished through addition of AC to the sediment biologically active layer (upper 30 cm) using commercial mixing units, by capping with a thin layer of AC or by mixing AC in a layer of clay [3,4,10,11].…”

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

“…Therefore, ACs are hypothesized to be effective to enhance heavy metals binding to sediments, and thus to reduce the bioavailability of heavy metals. However, most earlier studies addressed the effectiveness of AC on remediation of HOCs contaminated sediment (Cho et al 2009;Kupryianchyk et al 2013), whereas the effectiveness on heavy metals has been studied less frequently. Bioturbation can influence the fate, transport, and bioavailability of sediment-bound heavy metals (Ciutat and Boudou 2003;Schaller 2014), it may be responsible for a major fraction of the pollutants released from sediments to the water column (Cardoso et al 2008;Josefsson et al 2010;Thibodeaux and Bierman 2003).…”