The power of power: electrokinetic control of PAH interactions with exfoliated graphite

Mechanisms of heating-electrokinetic co-driven perfluorooctanoic acid (PFOA) adsorption on zeolite

Slow release of emerging contaminants limits their accessibility from soil to pore water, constraining the treatment efficiency of physio-chemical treatment sites. DC fields mobilize organic contaminants and influence their interactions with geo-matrices such as zeolites. Poor knowledge, however, exists on the joint application of heating and electrokinetic approaches on perfluorooctanoic acid (PFOA) transport in porous media. Here, we investigated electrokinetic PFOA transport in zeolite-filled percolation columns at varying temperatures. Variations of pseudo-second-order kinetic constants (kPSO) were correlated to the liquid viscosity variations (η) and elctroosmotic flow velocities (vEOF). Applying DC fields and elevated temperature significantly (>37%) decreased PFOA sorption to zeolite. A good correlation between η, vEOF, and kPSO was found and used to develop an approach interlinking the three parameters to predict the joint effects of DC fields and temperature on PFOA sorption kinetics. These findings may give rise to future applications for better tailoring PFOA transport in environmental biotechnology.

Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon

Sorption to activated carbon is a common approach to reducing environmental risks of waterborne perfluorooctanoic acid (PFOA), while effective and flexible approaches to PFOA sorption are needed. Variations in temperature or the use of electrokinetic phenomena (electroosmosis and electromigration) in the presence of external DC electric fields have been shown to alter the contaminant sorption of contaminants. Their role in PFOA sorption, however, remains unclear. Here, we investigated the joint effects of DC electric fields and the temperature on the sorption of PFOA on activated carbon. Temperature-dependent batch and column sorption experiments were performed in the presence and absence of DC fields, and the results were evaluated by using different kinetic sorption models. We found an emerging interplay of DC and temperature on PFOA sorption, which was linked via the liquid viscosity (η) of the electrolyte. For instance, the combined presence of a DC field and low temperature increased the PFOA loading up to 38% in 48 h relative to DC-free controls. We further developed a model that allowed us to predict temperature- and DC field strength-dependent electrokinetic benefits on the drivers of PFOA sorption kinetics (i.e., intraparticle diffusivity and the film mass transfer coefficient). Our insights may give rise to future DC- and temperature-driven applications for PFOA sorption, for instance, in response to fluctuating PFOA concentrations in contaminated water streams.

Removal of biological effects of organic pollutants in municipal wastewater by a novel advanced oxidation system

The Advanced Oxidation System (AOS) is a novel electrochemical advanced oxidation process that effectively removes bacterial and organic contaminants from wastewater. However, potential formation of secondary oxidative species may pose additional hazards to aquatic organisms living in the receiving water affected by the post-treatment effluent. The effect of exposure to AOS treated water, especially the potential long-term effects on aquatic organisms, requires further investigation to demonstrate both efficacy and safety of this process. To examine the potential adverse effects of AOS treated water, three aquatic species, including daphnia, zebrafish, and rainbow trout, were exposed to treated and untreated municipal wastewater effluent (MWE) spiked with one of two model organic contaminants, benzo[a]pyrene (BaP) and 17β-estradiol (E2). The results indicated AOS treatment significantly reduced the adverse effects caused by exposure to MWE and model organic contaminants to baseline levels in daphnia (reduced fecundity), zebrafish embryo (elevated EROD activity), and rainbow trout (elevated plasma vitellogenin). The Ames test was also conducted to confirm the removal efficacy of carcinogenicity of BaP spiked in MWE. Overall, this study demonstrated that AOS treatment is a promising and environmentally friendly technology for wastewater treatment, remediation, and management.

Effects of Electrokinetic Phenomena on Bacterial Deposition Monitored by Quartz Crystal Microbalance with Dissipation Monitoring

Bacterial deposition is the first step in the formation of microbial biofilms in environmental technology, and there is high interest in controlling such deposition. Earlier work indicated that direct current (DC) electric fields could influence bacterial deposition in percolation columns. Here, a time-resolved quartz crystal microbalance with dissipation monitoring (QCM-D) and microscopy-based cell counting were used to quantify DC field effects on the deposition of bacterial strains Pseudomonas putida KT2440 and Pseudomonas fluorescens LP6a at varying electrolyte concentrations and weak electric field strengths (0-2 V cm^-1). DC-induced frequency shifts (Δf), dissipation energy (ΔD), and ratios thereof (Δf/ΔD) proved as good indicators of the rigidity of cell attachment. We interpreted QCM-D signals using a theoretical approach by calculating the attractive DLVO-force and the shear and drag forces acting on a bacterium near collector surfaces in a DC electric field. We found that changes in DC-induced deposition of bacteria depended on the relative strengths of electrophoretic drag and electro-osmotic shear forces. This could enable the prediction and electrokinetic control of microbial deposition on surfaces in natural and manmade ecosystems.

Electrokinetic effects on the interaction of phenanthrene with geo-sorbents

Interactions with solid matrices control the persistence and (bio-)degradability of hydrophobic organic chemicals (HOC). Approaches influencing the rate or extent of HOC interactions with matrices are thus longed for. When a direct current (DC) electric field is applied to a matrix immersed in an ionic solution, it invokes transport processes including electromigration, electrophoresis, and electroosmotic flow (EOF). EOF is the surface charge-induced movement of pore fluids. It has the potential to mobilize uncharged organic contaminants and, hence, to influence their interactions with sorbing geo-matrices (i.e. geo-sorbents). Here, we assessed the effects of weak DC electric fields on sorption and desorption of phenanthrene (PHE) in various mineral and carbonaceous geo-sorbents. We found that DC fields significantly changed the rates and extent of PHE sorption and desorption as compared to DC-free controls. A distinct correlation between the Gibbs free energy change (ΔG°) and electrokinetic effects such as the EOF velocity was observed; in case of mineral sorbents EOF limited (or even inhibited) PHE sorption and increased its desorption. In strongly sorbing carbonaceous geo-sorbents, however, EOF significantly increased the rates of PHE sorption and reduced PHE desorption by > 99% for both activated charcoal and exfoliated graphite. Based on our findings, an approach linking ΔG° and EOF velocity was developed to estimate DC-induced PHE sorption and desorption benefits on mineral and carbonaceous sorbents. We conclude that such kinetic regulation gives rise to future technical applications that may allow modulating sorption processes e.g. in response to fluctuating sorbate concentrations in contaminated water streams.

Fungal biocatalyst activated by an electric field: Improved mass transfer and non-specificity for hydrocarbon degradation in an airlift bioreactor

The combination of biological and electrochemical techniques enhances the bioremediation efficiency of treating oil-contaminated water. In this study a non-growing fungal whole cell biocatalyst (BC; Aspergillus brasiliensis attached to perlite) pretreated with an electric field (EF), was used to degrade a hydrocarbon blend (hexadecane-phenanthrene-pyrene; 100:1:1w/w) in an airlift bioreactor (ALB). During hydrocarbon degradation, all mass transfer resistances (internal and external) and sorption capacity were experimentally quantified. Internal mass transfer resistances were evaluated through BC effectiveness factor analysis as a function of the Thiele modulus (using first order reaction kinetics, assuming a spherical BC, five particle diameters). External (interfacial) mass transfer resistances were evaluated by k_La determination. EF pretreatment during BC production promoted surface changes in BC and production of an emulsifier protein in the ALB. The BC surface modifications enhanced the affinity for hydrocarbons, improving hydrocarbon uptake by direct contact. The resulting emulsion was associated with decreased internal and external mass transfer resistances. EF pretreatment effects can be summarized as: a combined uptake mechanism (direct contact dominant followed by emulsified form dominant) diminishing mass transfer limitations, resulting in a non-specific hydrocarbon degradation in blend. The pretreated BC is a good applicant for oil-contaminated water remediation.