The aim of the present study was to evaluate the efficiency of removal of microcystin-LR from drinking water using a three-stage bench-scale treatment comprising Fenton oxidation/coagulation/flocculation/sedimentation, filtration through a sand column (15 cm bed), and adsorption onto a granular activated carbon (GAC) column with 15-cm (GAC1) or 20-cm bed (GAC2). Optimal first-stage conditions were determined to be FeSO₄∙7H₂O 0.054 mM, H₂O₂ 0.162 mM, coagulation pH 8.4, sedimentation time 15 min, and flow rate 2 L h⁻¹. Under these conditions, water turbidity was reduced from 5.8 to 3.0 uT, apparent color from 115 to 81 uH, and the concentration of microcystin-LR from 18.52 to 9.59 μg L⁻¹. Column GAC2 was more efficient than GAC1, as shown by the higher adsorption capacity (4.15 μg g⁻¹) and lower carbon usage rate (1.70 g L⁻¹). Microcystin breakthrough occurred after 2 h of operation with GAC1 column and after 6 h with GAC2 column, and the greater efficiency of the latter column was confirmed by the high qe (4.15 μg g⁻¹) and low CUR (1.70 g L⁻¹) values attained. The results demonstrate that adsorption on a GAC column plays an essential role in reducing the concentration of microcystin-LR to levels compatible with current legislation. By-products of the Fenton oxidation of microcystin-LR were analyzed by mass spectrometry, and the ADDA amino acid present in the analyte was identified from its characteristic fragment at m/z 135. It is concluded that the combination of Fenton oxidation and adsorption on a GAC column represents a viable option for purifying eutrophic water containing high concentrations of microcystin-LR.

PLFA analysis was conducted to profile microorganisms and trace sulfate-reducing bacteria (SRB) in water samples from an offshore oil reservoir. From the results of spiked phospholipid standards, more than 90% of the phospholipids were recovered before the treatment of fatty acid methyl ester (FAME) derivatization while the relative standard deviations (RSD) were below 8.0%. The water samples from the injection well and four producing wells exhibited various reducing conditions and were further subjected to PLFA analysis. Fourteen kinds of phospholipid fatty acids were detected in the five wellbores and the concentrations of total fatty acids ranged from 368.4 to 3468.9 ng/L. Possible SRB biomarkers and significant phospholipid fatty acids associated with SRB including C14:0, i-C15:0, a-C15:0, C15:0, C16:1 (cis-9), C17:0, C18:1 (cis-9), C18:1 (cis-11) and C18:0 were selected for determining the presence of SRB species and evaluating the sulfate-related microbial biomass. The possible existence of SRB genera Desulfobacter, Desulfotomaculum, Desulfovibrio, and sulfur-oxidizing bacteria (SOB) in the reservoir were proposed based on PLFA profiles. The highest biomass was found in the most reducing well where very limited SOB biomarkers were found. Results indicated that the presence of SRB and SOB species was closely associated with the redox environment of the reservoir wellbores. The species distribution patterns were interpreted to elucidate the biological souring process.

Water contamination has reached an alarming state due to industrialization and urbanization and has become a worldwide issue. Dyes contaminate water and are addressed extensively by researchers. Various technologies and materials have been developed for the treatment of contaminated water. Among them, adsorption has attracted great attention due to its ease and cost-effective nature. In recent years, graphene-based composites have shown great potential for the removal of contaminants from water. The literature reveals the usefulness of composites of graphene with metal oxides, carbon derivatives, metal hybrids and polymers for the removal of organic dyes from contaminated water. In this review, efforts have been made to compile the studies on the removal of cationic and anionic dyes from water using graphene-based composites.

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.