ABSTRACTThis article compares the full installation and operational costs of a hydraulic containment (“pump‐and‐treat,” P&T) system with those of a hypothetical contemporary in situ colloidal activated carbon (CAC) barrier. Worked examples are provided using public domain data from the FT‐02 fire‐fighting training site on the former Wurtsmith Air Force Base in Oscoda, MI. The projected CAC costs are approximately a third of the P&T costs over projection periods of 15–100 years ($ 7.2 M vs. $ 19 M at 30 years; 38%). Hydraulic containment and CAC remediation systems prevent the spread of per‐ and polyfluoroalkyl substance (PFAS)‐contaminated groundwater. Hydraulic containment works by extracting contaminated groundwater, removing the contamination using activated carbon or other means, and re‐injecting the cleaned groundwater. The arrangement of extraction and injection wells and the related groundwater pumping rates create a hydraulic barrier that captures and contains the PFAS plume. In situ CAC barriers work as passive underground filters. Micron‐scale particles of activated carbon are injected into contaminated aquifers using drilling equipment or injection wells. Once injected, the carbon particles attach to the soil. An in situ permeable barrier is installed across a contaminant plume through the injection of a number of points at suitable spacings. Groundwater flows through the barrier zone unimpeded while PFAS contamination is captured and contained by the activated carbon. The longevity of the barrier is determined by the quantity of carbon emplaced relative to the contaminant flux. Barriers are typically designed to last for years (decades), after which time, carbon re‐applications can be made, if required. Principal differences between the approaches are the scale of operation and maintenance requirements, and, for P&T, the bringing of PFAS‐impacted water above ground to treat. This generates a filtration medium that is contaminated with PFAS, and which therefore requires handling as a PFAS waste with attendant liability. Hydraulic containment is also an active technology (requiring external energy input) and requires the operation and maintenance of pumping and filtration equipment. In situ CAC barriers are passive (powered by natural groundwater flow) and have no operation and maintenance requirements. They do not bring PFAS‐impacted material above ground and do not generate waste. Performance data of the installed P&T hydraulic containment system were analyzed to estimate the time to remedial completion using the system alone. Data extrapolation supported by statistical analysis indicates clean‐up targets will not be reached within 100 years of pumping. It is not realistic for P&T to be regarded as a means of aquifer clean‐up as the aquifer will remain contaminated for the realistic future. Comparison is made between P&T and CAC on their common basis as containment approaches. The goal is to reduce the exposure of down‐gradient receptors to PFAS.

Abstract Despite addressing the cleanup of petroleum hydrocarbon contamination plumes in groundwater, challenges with site closure persist due to the ongoing long‐term contaminant release from source zones. Thus, source zone monitoring even in the presence of residual light nonaqueous‐phase liquid (LNAPL) is mandated by many countries' regulatory agencies before site closure. In this study, four independent controlled‐release sites, each containing a particular fraction of ethanol in gasoline, that is, 10%, 24%, 25%, and 85% (v/v), were subjected to monitored natural attenuation (MNA) alone (E24 and E85), and with nitrate (E25) and sulfate (E10) biostimulation at the vicinity of the source zone. To the best of the authors' knowledge, this is the longest controlled gasohol release monitoring study performed to date at the source zone for site closure (nearly 18 years of monitoring). Both natural source zone depletion and biostimulation were found to reduce benzene concentrations to acceptable remediation target levels according to environmental regulatory councils. Benzene biodegradation rates (λs) were one order of magnitude higher than those reported in the literature for diluted concentrations in groundwater plumes. The decay rate of benzene varied between 0.45 and 1.75/year and was strongly influenced by the mass of ethanol. Compared to biostimulation with nitrate (half‐life of 1.52 years), MNA alone resulted in faster benzene removal rates (half‐life of 0.96 years). Anaerobic biostimulation with sulfate had negligible effects on benzene, toluene, ethylbenzene, and xylene (o‐, m‐, and p‐xylene [BTEX]) biodegradation compared to natural attenuation alone. The highest ethanol concentration (E85) led to faster benzene removal (with a half‐life of 0.40 years), which was even higher than MNA under lower ethanol concentrations (E24). Benzene half‐life was 2.2‐fold slower in the site with the lowest ethanol (E10) compared to E85, indicating that the negative effects of ethanol on BTEX biodegradation appeared to be short‐lived and may need to be re‐evaluated over the long term. Benzene decay rates were approximately six times slower in the source zone than the rates obtained for groundwater plumes, emphasizing the importance of targeting the LNAPL after plume retreat. The study's findings can assist practitioners in better predicting the lines of evidence for BTEX bioremediation and remediation cleanup times at a lower cost in the presence of ethanol, as well as providing guidance for determining whether biostimulation is necessary to expedite source zone remediation for site closure.

Abstract In this study, activated carbon produced from cassava peel (CP) via carbonization at 400°C was utilized as a biosorbent for the removal of chloride (Cl−) and total hardness (TH) from groundwater. A response surface methodology (RSM) employing a Box–Behnken design (BBD) was implemented to optimize process parameters, including pH (3–10), biosorbent dosage (1–10 g), contact time (10–60 min), initial Cl− concentration (50–2000 mg/L), and initial TH concentration (40–900 mg/L). The biosorbent was applied in a batch reactor setup to evaluate its performance in removing Cl− and TH from groundwater under the optimized conditions. The experimental data showed good agreement with the model predictions, exhibiting R2 of 0.991 and 0.905 for Cl− and TH removal, respectively. The CP biosorbent removed Cl− (245 mg/L) and TH (321 mg/L) by 84% and 90%, respectively, under optimal conditions of 6.9 g CP dose, 19.6 min, and initial pH of 8.1. The sorption kinetics followed a pseudo‐second‐order, and the equilibrium data fit the Freundlich and Langmuir models to Cl− and TH, respectively. The removal of Cl− and TH exhibited maximum adsorption capacities (qm) of 31.25 and 6.57 mg/g for Cl− and TH, respectively. Overall, CP shows potential as an adsorbent for remediating groundwater containing Cl− and TH.

Abstract The accumulation of significant amounts of investigation‐derived waste (IDW) from investigations of per‐ and polyfluoroalkyl substances (PFAS) contamination at active and former military installations has generated the need for viable disposal methods, which are currently limited to incineration or landfilling. Soil washing has been proposed as a more environmentally friendly alternative method to remove PFAS sorbed to IDW media, potentially allowing more cost‐effective disposal of the media as nonhazardous waste. This systematic investigation of IDW washing explored the effect of water‐, methanol‐, and salt‐based solutions, which are typically used for ion exchange (IX) resin regeneration. These solutions were tested for PFAS removal using four different field IDW solids with different pHs, total organic carbon content, and anion exchange capacity. In long washes extending to a week, distilled water was found to be effective in the removal of short‐chain PFASs (perfluorcarboxylic acids with fewer than seven fluorinated carbon atoms and perfluorosulfonic acids with fewer than six fluorinated carbon atoms) and some long‐chain PFASs including perfluorooctanoic acid, but not perfluorooctane sulfonic acid (PFOS). PFOS was only removed using water:methanol solutions with salt. Optimized 30‐min washes containing water:methanol and salt effectively removed precursors, and short‐ and long‐chain PFAS. Kinetic, soil extraction, and leaching experiments revealed that PFAS can be removed within a matter of minutes, with greater than 70% PFAS removal on the first wash; however, longer‐chain PFASs required up to three washes to be removed. Important IDW wash solution relationships influencing PFAS desorption are discussed and PFOS is proposed as an indicator species for IDW washing effectiveness. Results demonstrate that adapting components of IX regeneration solutions to IDW wash solutions facilitates an alternative means to separate PFAS contaminants from IDW, advancing PFAS remediation efforts.

The in situ treatment of PFAS within porewater at the

Remediation JournalVolume 33, Issue 3 p. 185-186 ISSUE INFORMATIONFree Access Issue Information First published: 13 June 2023 https://doi.org/10.1002/rem.21686AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume33, Issue3Summer 2023Pages 185-186 RelatedInformation

Abstract Per‐ and polyfluoroalkyl substances (PFAS) are a group of anthropogenic contaminants that are receiving increasing concern due to their associated negative health effects. The properties of PFAS result in their persistence and stability, which present challenges for remediation. Activated carbon is currently the most widely used method for PFAS treatment since carbon microparticle injection can be used for in‐situ treatment; however, this method does not result in PFAS destruction. Thermal treatment is a promising posttreatment method that can be used with activated carbon as long as sufficient PFAS‐destroying temperatures are achieved (>900°C). A promising in‐situ thermal treatment technology is Self‐Sustaining Treatment for Active Remediation (STAR), which uses smoldering combustion to destroy organic contaminants embedded within a porous matrix. This study investigates carbon injection to support STAR for the treatment of PFAS. Four solutions were used (1) 17% colloidal activated carbon (CAC); (2) 23% CAC; (3) 17% powdered activated carbon (PAC); and, (4) 23% PAC. Smoldering temperatures greater than the required PFAS destruction temperature were reached if 50 g carbon/kg sand was achieved for injection and soil‐mixing delivery methods. Moreover, emulsified vegetable oil (EVO) was a successful secondary surrogate fuel to enhance smoldering temperatures when supplied at a quantity less than or equal to carbon microparticles. These findings present the necessary intermediate laboratory work to evaluate methods that will achieve PFAS treatment through STAR when applied in the field.

Abstract Biochar is a promising engineering material to sequestrate organic pollutants from wastewater. In the current study, several surface‐modified Moringa (M.) oleifera leaf biochars were prepared and utilized for the sorption of methyl orange (MO) dye from an aqueous solution. Raw biochar was produced by the carbonization of M. oleifera leaves at 350°C in a muffle furnace for 2 h. The surface‐modified M. oleifera biochars were prepared at 400°C, 500°C, and 600°C using phosphoric acid (H3PO4) at different combinations to improve the biochar pore structure, surface functional groups, and biochar stability. The highest surface area (267.15 ± 42.40 m2/g) of the modified biochar was achieved at 500°C with H3PO4 to raw biochar ratio of 1.5. Surface morphological results revealed the formation of pores, troughs, and channels with the increasing activation temperature. The carbon (C) content (wt%) was maximum (79.61%) for activated biochar at 500°C. The presence of enhanced functional groups, e.g., hydroxyl, aliphatic carbon‐hydrogen, carbonyl, ester, and phenol structures in surface‐modified biochars was observed from FT‐IR results. The Langmuir isotherm model was fitted to better describe the adsorption phenomenon for both surface‐modified biochars and raw biochar compared to the Freundlich isotherm model. The highest adsorption capacity was 175 mg MO dye/g of activated biochar prepared at 500°C with an H3PO4 impregnation ratio of 1.5. Pseudo‐1st order model fitted the best for raw biochars whereas pseudo‐2nd order and intraparticle diffusion models better describe the sorption of MO onto activated biochar. The results anticipated M. oleifera leaf‐activated biochar as an efficient tool for the treatment of MO contaminated wastewater.