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The goal of ENVIRO.wiki is to make scientific and engineering research results more accessible to environmental professionals, facilitating the permitting, design and implementation of environmental projects. Articles are written and edited by invited experts (see Contributors) to summarize current knowledge for the target audience on an array of topics, with cross-linked references to reports and technical literature.

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Featured article: PFAS Ex Situ Water Treatment

Well-developed ex situ treatment technologies applicable to treatment of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in drinking water and non-potable groundwater include membrane filtration (reverse osmosis or RO and nanofiltration or NF), activated carbon adsorption (granular and powdered), and anion exchange. However, these technologies are less demonstrated for removal of PFAS from more complex matrices such as wastewater and leachate. There are also a variety of separation and destructive technologies in various stages of development. Some of these processes may also be applicable to more complex matrices including wastewater and landfill leachate. Site-specific considerations that affect the selection of optimum treatment technologies for a given site include water chemistry, required flow rate, treatment criteria, waste residual generation, residual disposal options, and operational complexity. Treatability studies with site water are highly recommended because every site has different factors that may affect engineering design for these technologies.

Given their ability to remove dissolved contaminants at a molecular size level, RO and some NF membranes can be highly effective for PFAS removal. For RO systems, several studies have demonstrated effective removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from drinking water with removal rates well above 90%.The removal efficiency of individual PFAS compounds using GAC is a function of both the PFAS functional group (carboxylic acid versus sulfonic acid) and also the perfluoro-carbon chain length. Anion exchange has also been demonstrated for the adsorption of PFAS, and published results note higher sorption per pound than GAC. Several newer technologies are being evaluated in the lab and in the field which include electro-oxidation, heat-activated persulfate, sonolysis, electrocoagulation, low temperature plasma, supercritical water oxidation, and foam fractionation. These and other potential treatments for PFAS are still largely in the developmental stage. Several technologies show promise for improved management of PFAS sites. However, it is unlikely that a single technology will be adequate for full remediation at many sites. A multi-technology treatment train approach may be necessary for effective treatment of this complicated group of compounds.

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Enviro Wiki Highlights

Molecular diffusion slowly transports solutes into clay-rich, lower permeability zones

Typical subgrade biogeochemical reactor (SBGR) layout. The SBGR is an in situ remediation technology for treatment of contaminated source areas and groundwater plume hot spots

An Hydraulic Profiling Tool (HPT) log with electrical conductivity (EC) on left, injection pressure in middle, and flow rate on the right

Diagram of mineral surface exchanging hydrogen ions with varying pH. The surface of most aquifer minerals carries an electrical charge that varies with pH

Comparison of the longitudinal redox zonation concept (A) and the plume fringe concept (B). Both concepts describe the spatial distribution of electron acceptors and respiration processes in a hydrocarbon contaminant plume

Schematic of an Hydraulic Profiling Tool (HPT) probe. HPT were developed to better understand formation permeability and the distribution of permeable and low permeability zones in unconsolidated formations

In situ chemical oxidation using (a) direct-push injection probes or (b) well-to-well flushing to delivery oxidants (shown in blue) into a target treatment zone of groundwater contaminated by dense nonaqueous phase liquid compounds (shown in red)

High-resolution 3D cross-borehole electrical imaging of contaminated fractured rock at the former Naval Air Warfare Center in New Jersey. Cross-borehole resistivity tomography imaging is a geophysical technique that can be used for site characterization and monitoring by observing variations in the electrical properties of subsurface materials

Stable isotope probing (SIP) in use: Loading, deployment and recovery of Bio-Trap® passive sampler with 13C-labeled benzene. Stable isotope probing (SIP) is used to conclusively determine whether in situ biodegradation of a contaminant is occurring

Summary of anticipated, primary reaction pathways for degradation of 1,2,3-Trichloropropane (TCP). TCP is a man-made chemical that was used in the past primarily as a solvent and extractive agent, a paint and varnish remover, and as a cleaning and degreasing agent

Distribution of BTEX plume lengths from 604 hydrocarbon sites. Monitored Natural Attenuation (MNA) is one of the most commonly used remediation approaches for groundwater contaminated with petroleum hydrocarbons (PHCs) and certain fuel additives such as fuel oxygenates or lead scavengers

No-purge and passive sampling methods eliminate the pre-purging step for groundwater sample collection and represent alternatives to conventional sampling methods that rely on low-flow purging of a well prior to collection. The Snap SamplerTM is an example of a passive grab sampler

Conceptualization of Vapor Transport-related Natural Source Zone Depletion (NSZD) processes at a Petroleum Release Site

Conceptual diagram of basic Soil Vapor Extraction (SVE) system for vadose zone remediation. (SVE) is a common and typically effective physical treatment process for remediation of volatile contaminants in vadose zone (unsaturated) soils

Emulsified Vegetable Oil (EVO) mixed in field during early pilot test. EVO is commonly added as a slowly fermentable substrate to stimulate the in situ anaerobic bioremediation of chlorinated solvents, explosives, perchlorate, chromate, and other contaminants

Key elements of vapor intrusion pathways

Batch reactor experiments to generate points on a sorption isotherm

Results for metagenomic analysis of a groundwater sample obtained from a site impacted with petroleum hydrocarbons

Perchlorate releases and drinking water detections

Data input screen for ESTCP Mass Flux Toolkit

Amendment addition for biobarrier

Thermal Remediation - Desorption schematic

Key exposure pathways for human health risk from contaminated sediments

The PFAS family of compounds

Table of Contents Attenuation & Transport Processes Biodegradation - 1,4-Dioxane Biodegradation - Cometabolic Biodegradation - Hydrocarbons Biodegradation - Reductive Processes Groundwater Flow and Solute Transport Matrix Diffusion Mobility of Metals and Metalloids pH Buffering in Aquifers Sorption of Organic Contaminants Vapor Intrusion (VI) Vapor Intrusion - Separation Distances from Petroleum Sources Vapor Intrusion – Sewers and Utility Tunnels as Preferential Pathways Characterization, Assessment & Monitoring Characterization Methods – Hydraulic Conductivity Compound Specific Isotope Analysis (CSIA) Direct Push (DP) Technology DP Logging DP Sampling Geophysical Methods Case Studies Groundwater Sampling - No-Purge/Passive Long-Term Monitoring (LTM) LTM Data Analysis LTM Data Variability Molecular Biological Tools (MBTs) Metagenomics Quantitative Polymerase Chain Reaction (qPCR) Stable Isotope Probing (SIP) Natural Attenuation in Source Zone and Groundwater Plume - Bemidji Crude Oil Spill Climate Change Climate Change Primer Coastal and Estuarine Ecology Phytoplankton (Algae) Blooms Contaminated Sediments In Situ Treatment of Contaminated Sediments with Activated Carbon Mercury in Sediments Light Non-Aqueous Phase Liquids (LNAPLs) LNAPL Conceptual Site Models LNAPL Remediation Technologies NAPL Mobility Munitions Constituents Alkaline Degradation Composting Deposition Dissolution Passive Sampling Metal(loid)s - Small Arms Ranges Soil Sampling Sorption Toxicology TREECS™ Monitored Natural Attenuation (MNA) MNA of Chlorinated Solvents MNA of Metals and Metalloids MNA of Petroleum Hydrocarbons Natural Source Zone Depletion (NSZD) Transitioning from Active Remedies Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) PFAS Ex Situ Water Treatment PFAS Soil Remediation Technologies PFAS Sources PFAS Transport and Fate Regulatory Issues and Site Management Alternative Endpoints Mass Flux and Mass Discharge Plume Response Modeling REMChlor-MD Source Zone Modeling Sustainable Remediation Remediation Technologies Amendment Distribution in Low Conductivity Materials Anaerobic Bioremediation Design Considerations Design Tool - Base Addition for ERD Emulsified Vegetable Oil (EVO) for Anaerobic Bioremediation Low pH Inhibition of Reductive Dechlorination Secondary Water Quality Impacts In Situ Chemical Oxidation (ISCO) Design Considerations Oxidant Selection In Situ Chemical Reduction (ISCR) Zero-Valent Iron (ZVI) Zerovalent Iron Permeable Reactive Barriers In Situ Groundwater Treatment with Activated Carbon Injection Techniques for Liquid Amendments Injection Techniques - Viscosity Modification Landfarming Remediation of Metals and Metalloids Remediation Performance Assessment at Chlorinated Solvent Sites Soil Vapor Extraction (SVE) Stream Restoration Subgrade Biogeochemical Reactor (SBGR) Supercritical Water Oxidation (SCWO) Thermal Remediation Combined Remedies Electrical Resistance Heating (ERH) Smoldering Steam Enhanced Extraction (SEE) Thermal Conduction Heating (TCH) Soil & Groundwater Contaminants 1,4-Dioxane Chlorinated Solvents Metals and Metalloids N-nitrosodimethylamine (NDMA) Perchlorate Petroleum Hydrocarbons (PHCs) Polycyclic Aromatic Hydrocarbons (PAHs) Trichloropropane (TCP)