The mechanisms involved in immobilization of soil Cu and the role of extracellular polymeric substances (EPS) in Cu(II) adsorption by Bacillus subtilis DBM were investigated in this study. Adsorption and desorption experiments with intact DBM cells revealed that complexation with surface functional groups and intracellular accumulation were involved in the immobilization of soil Cu. The removal of EPS using cation exchange resin resulted in a 26.6% decrease in the Cu(II) adsorption capacity relative to untreated cells. Compared to intact cells, EPS-free cells showed a 9.9% decrease in the proportion of complexed Cu(II), while the intracellular fraction increased by 8.0%. Surface complexation modeling indicated that the total concentration of complexation sites on the intact DBM cell surface was 1.11 mmol/g dry biomass, which was decreased by 17% to 0.92 mmol/g after EPS removal. Infrared analysis revealed that the pKa values of the carboxyl and phosphate groups in the DBM cell wall differed from those in the EPS. Carboxyl, carbonyl, hydroxyl, amino, and phosphate groups were involved in binding Cu(II) by both intact and EPS-free cells, and Cu(II) was more likely to combine with organic rather than inorganic phosphates. The presence of the EPS increased the binding potential of surface functional groups and may help to prevent heavy metals from entering the cells.

Nanoparticles (NPs) have been reported to cause physiological effects on plant cells and tissue. This study traced the uptake and distribution of magnetic iron oxide nanoparticles (γ-Fe₂O₃ NPs) in citrus (Citrus reticulata) plants under hydroponic condition by fluorescent dye labeled γ-Fe₂O₃ NPs, and described a detailed evidence of physiological effects of 0–100 mg/L γ-Fe₂O₃ NPs on citrus plants by measuring the physiological parameters such as content of chlorophyll, malondialdehyde (MDA), soluble sugar, soluble protein, activity of antioxidant enzyme, and ferric reductase after 21 days exposure. Fluorescence images of citrus stem and root showed that citrus roots could absorb γ-Fe₂O₃ NPs but no translocation from roots to shoots was observed, since NPs aggregated or even clogged the vascular system. Physiological results showed that 20 mg/L γ-Fe₂O₃ NPs could significantly enhance chlorophyll content by 126.4%, while 50 and 100 mg/L of γ-Fe₂O₃ NPs decreased chlorophyll content by 27.8 and 35.4%, respectively. MDA contents in citrus leaves under 20–100 mg/L γ-Fe₂O₃ NPs exposure were increased by 37.8, 107.2, and 61.5%, respectively, while that in roots were decreased by 27.0,11.9, and 7.4%, respectively, with elevated SOD and CAT activity, suggesting that oxidative stress occurred in citrus leaves, but oxidative stress in roots was eliminated by antioxidant defense. It is noteworthy that although Fe(II)-EDTA treatment had a high level of chlorophyll content, it induced strong oxidative stress in citrus plants as well. Collectively, the various physiological responses of citrus plants to γ-Fe₂O₃ NPs exposure were closely correlated with the concentrations of NPs. γ-Fe₂O₃ NPs at proper concentrations, such as 20 mg/L, have the potential to ameliorate chlorosis of plants and be effective nanofertilizers for increasing agronomic productivity.

The adsorption of some benzene derivatives—o-xylene, toluene, phenol, and benzyl alcohol onto dissolved humic acids (HA) was analyzed by equilibrium dialyses experiments. HA were extracted from compost and from leonardite. The humification index (E₄/E₆ ratio) and the distribution coefficient between ammonium sulfate/polyethylene glycol solutions show that HA from compost have a higher hydrophobicity. Assuming that the binding sites onto HA molecules are energetically equivalent, the binding curves were analyzed, and the amount of ligands bound per unit weight of HA and the association constants were derived. The binding capacity was higher for the HA from compost and for more hydrophobic ligands.

The photo-Fenton oxidation treatment combined with a coagulation/flocculation process was investigated for removal of chemical oxygen demand (COD) from a refractory petroleum refinery wastewater. Scrap iron shavings were used as the catalyst source. A response surface methodology (RSM) with a cubic IV optimal design was employed for optimizing the treatment process. Kinetic studies showed that the proposed process could be described by a two-stage, second-order reaction model. Experiments showed that precipitation of iron ions can be utilized as a post-oxidation coagulation stage to improve the overall treatment efficiency. More than 96.9% of the COD removal was achieved under optimal conditions, with a post-oxidation coagulation stage accounting for about 30% of the removal, thus confirming the collaborative role of oxidation and coagulation in the overall treatment. A low-velocity gradient of 8.0 s⁻¹ for a short mixing time of 10 min resulted in optimum post-oxidation coagulation. Comparison of photo-Fenton oxidation to a standard Fenton reaction in the same wastewater showed more rapid COD removal for photo-Fenton, with an initial second-order rate constant of 4.0 × 10⁻⁴ L mg⁻¹ min⁻¹ compared to the Fenton reaction’s overall second-order rate constant of 7.0 × 10⁻⁵ L mg⁻¹ min⁻¹.

Flexible and self-standing membrane composed of ultrafine alumina-silica nanofibers (NFs) has been successfully fabricated by the electrospinning method, and further used as an adsorbent for the adsorptive decolorization of Reactive Red-120 (RR-120) dye from an aqueous system. Effects of pH, adsorbent dosage, and contact time on adsorption have been studied. The adsorption of RR-120 on the NFs was found to be highly pH dependent and the optimum pH was found to be 3. The adsorption equilibrium data was explained well with the Langmuir isotherm model, and the maximum sorption capacity was found to be 884.95 mg/g, which was several folds higher than the adsorption capacity of a number of recently studied potential adsorbents. After adsorption, the NF mat could be separated from the liquid phase conveniently and reused. The sorption kinetics was found to follow an intraparticle diffusion model. The high adsorption performance, excellent flexibility, easy recovery, and reuse characteristic of the alumina-silica NF membrane all favor its practical application in environmental remediation.

This study investigated causes of persistent fecal indicator bacteria (FIB) in beach sand under the pier in Santa Monica, CA. FIB levels were up to 1000 times higher in sand underneath the pier than that collected from adjacent to the pier, with the highest concentrations under the pier in spring and fall. Escherichia coli (EC) and enterococci (ENT) under the pier were significantly positively correlated with moisture (ρ = 0.61, p < 0.001, n = 59; ρ = 0.43, p < 0.001, n = 59, respectively), and ENT levels measured by qPCR (qENT) were much higher than those measured by membrane filtration (cENT). Microcosm experiments tested the ability of EC, qENT, cENT, and general Bacteroidales (GenBac) to persist under in situ moisture conditions (10 and 0.1%). Decay rates of qENT, cENT, and GenBac were not significantly different from zero at either moisture level, while decay rates for EC were relatively rapid during the microcosm at 10% moisture (k = 0.7 days⁻¹). Gull/pelican marker was detected at 8 of 12 sites and no human-associated markers (TaqHF183 and HumM2) were detected at any site during a 1-day site survey. Results from this study indicate that the high levels of FIB observed likely stem from environmental sources combined with high persistence of FIB under the pier.

Little is known about the environmental behavior of fenhexamid (FEN) in aquatic ecosystems such as degradation and bioaccumulation, in spite of the fact that it is critical for a comprehensive assessment of its ecological risks. This study investigated for the first time the degradation of FEN in water-sediment systems under both aerobic and anaerobic conditions and also bioaccumulation by zebrafish (Danio rerio). Water and sediments from different natural waters including river HR and lake HL were applied to build up water-sediment microcosms in the laboratory. When FEN was introduced into the aqueous phase, it would partition from water to sediment gradually and be decomposed in sediment compartment. The dissipation half-lives of FEN in water were 43.8, 75.9, 31.3, and 37.2 days for HR-aerobic, HR-anaerobic, HL-aerobic, and HL-anaerobic microcosms, respectively. Moreover, FEN degradation rate constants of whole systems varied from 0.0045 to 0.0088 per day and the half-lives were from 78.4 to 155 days. The aerobic circumstances were demonstrated to be favor of FEN degradation. The bioconcentration factor (BCF) was 2.6–3.1 obtained from zebrafish exposure experiments at environmentally relevant concentrations. Clearly, our results indicated that FEN could be accumulated in the deeper layer of sediment owing to the anaerobic condition against FEN degradation, but FEN showed a low potential for bioaccumulation. These may aid in comprehensive understanding the fate and risk of FEN in aquatic environment.

The promotive effect of constructed wetlands (CWs) with polyculture on treatment efficiency is still a controversial problem. Additionally, there is limited information regarding the influence of temperature on CWs. In this study, the influence of vegetation type, different NH₄ ⁺-N loading rates, and environmental temperatures on performance of CWs were investigated. Results of different vegetation type indicated that removal of NH₄ ⁺-N and total phosphorus (TP) in polyculture was higher than other CWs. In polyculture, tested nutrients had removal percentages greater than 94.5%. Results of different NH₄ ⁺-N loading rates demonstrated that NH₄ ⁺-N was almost completely removed (around 99.5%) in polyculture under both NH₄ ⁺-N loading rates. Temperature could substantially influenced the performance of CWs and the removal percentages of NH₄ ⁺-N, NO₃ ⁺-N, total nitrogen (TN), and TP in all CWs tended to decrease with a decline of temperature. Especially, a sharp decline in the removal percentage of NO₃ ⁻-N of all CWs (greater than 39%) was observed at low temperature (average temperature of 8.9 °C). Overall, the polyculture also showed the best performance with the decline of temperature as compared to other CWs. This study clearly documented that polyculture was an attractive solution for the treatment of domestic sewage and polyculture systems were effective for domestic sewage treatment in CWs even at low temperature (8.9 °C).

The widespread use of unconventional drilling involving hydraulic fracturing (“fracking”) has allowed for increased oil-and-gas extraction, produced water generation, and subsequent spills of produced water in Colorado and elsewhere. Produced water contains BTEX (benzene, toluene, ethylbenzene, xylene) and naphthalene, all of which are known to induce varying levels of toxicity upon exposure. When spilled, these contaminants can migrate through the soil and contaminant groundwater. This research modeled the solute transport of BTEX and naphthalene for a range of spill sizes on contrasting soils overlying groundwater at different depths. The results showed that benzene and toluene were expected to reach human health relevant concentration in groundwater because of their high concentrations in produced water, relatively low solid/liquid partition coefficient and low EPA drinking water limits for these contaminants. Peak groundwater concentrations were higher and were reached more rapidly in coarser textured soil. Risk categories of “low,” “medium,” and “high” were established by dividing the EPA drinking water limit for each contaminant into sequential thirds and modeled scenarios were classified into such categories. A quick reference guide was created that allows the user to input specific variables about an area of interest to evaluate that site’s risk of groundwater contamination in the event of a produced water spill. A large fraction of produced water spills occur at hydraulic-fracturing well pads; thus, the results of this research suggest that the surface area selected for a hydraulic-fracturing site should exclude or require extra precaution when considering areas with shallow aquifers and coarsely textured soils.

Different from direct application of free nanoparticles (NPs) in water treatment, a composite material is used to reduce the release and potential toxic effects of NPs with maintained adsorption capacity and kinetics. Novel monolithic composites with TiO₂ NPs incorporated into the walls of macroporous cryogels were synthesized and evaluated for material characteristics and their efficiency for removal of Pb(II) from aqueous solution in batch test and continuous mode. The uniformly distributed 6% TiO₂-cryogel is shown to be optimal for minimizing TiO₂ NP losses while maximizing Pb(II) removal. Under (25.0 ± 0.1) °C with the initial Pb(II) concentration of 10 mg/l, TiO₂-cryogels exhibit excellent adsorption characteristic for Pb(II) removal with adsorption capacity up to 23.27 mg/g TiO₂, which is even a little higher than that of TiO₂ NPs (21.58 mg/g TiO₂), and the results fit well with Langmuir–Freundlich isotherm. Both adsorbents work well in higher pH range with the highest removal rate at pH 6 for TiO₂-cryogel, and the adsorption mechanism might be strong chemical interaction. Pseudo-second-order process can better describe the adsorption process rather than pseudo-first-order for both adsorbents. The external mass transfer process of Pb(II) on TiO₂ NPs is much faster than that on TiO₂-cryogel, and the ultimate equilibrium time is about the same (3 h) on both adsorbents. The synthesized composites could also withstand a continuous treatment, and the effect of competing and co-existing constituents such as Cd²⁺, SO₄²⁻ and dissolved organic matter (DOM) is almost negligible. The composite design with small particles embedded into cryogels is proved to successfully keep the adsorption activity of TiO₂ NPs and prevent them from releasing into the environment in engineering practice.