Environmental Engineering Science

Hydraulic fracturing has become a well-established and widespread technology for the extraction of oil and natural gas. Hydraulic fracturing fluids (HFFs) are widely varied and contain many chemicals that are toxic to human and ecological health. HFFs are often spilled on surface soils where their fate and transport is uncertain. In this study, six representative mixtures of HFFs were incubated with a surface soil in bench-scale microcosms, and the microbial community was analyzed over 78 days. Chemical oxygen demand decreased over time, although a significant recalcitrant fraction was found for four of the six amended fluids. With Illumina MiSeq sequencing of a 16S ribosomal RNA (rRNA) gene amplification and follow-through quantitative polymerase chain reaction (qPCR) assays, 24 bacterial taxa closely related to known species were identified to be enriched by at least one of the representative HFFs. These taxa are mostly closely related to well-known xenobiotic degraders, however, the composition of the enrichment was highly unique for each representative HFF. Results indicate that the complex mixtures of biocides and other components elicit unique bacterial community responses in the same soil, thus suggesting that the bioremediation pathways of HFF constituents in soils may differ based on exact HFF composition.

Chromium pollution has grave consequences and can cause serious damage to biological systems. Recently, polyamines have received significant attention due to their biotechnological interests. This study is aiming to test the effect of putrescine on hexavalent chromium [Cr(VI)] removal by Wickerhamomyces anomalus and cell surface physicochemical properties of this strain. The experiment was conducted in modified yeast extract, peptone, and glucose medium contaminated with 50 mg/L Cr(VI) and treated with putrescine at 0 (control), 1, and 10 mM. Results showed that putrescine enhanced Cr(VI) removal potential, accompanied by an increased hydrophobicity and electron acceptor character and a decreased electron donor character of surface cells. This putrescine action was dependent on its concentration with a higher effect at 10 mM. At this concentration, scanning electron microscope/energy dispersive X-ray analysis showed a modification of the chemical composition and a high concentration of nitrogen on yeast cell wall. Sorption data were modeled using the pseudofirst-order and pseudosecond-order equations. Results indicated that a pseudosecond-order kinetic model could better describe the metal sorption kinetics by W. anomalus cells at different putrescine concentrations. This work highlights the possibility of enhancement of wastewater treatment, especially heavy metal uptake, by modifying cell surface characteristics.

A scale-up methodology was developed and verified that utilizes bench-scale biofilter results to simulate field-scale (pilot or full scale), flow-through biofilter performance. This methodology builds on recirculating batch reactor methods combined with single-pass flow-through methods at empty bed contact times (EBCTs) equivalent to the field scale. This method allows for control of variables that are often not controllable at the field-scale level, that is, influent primary and secondary substrate concentrations, temperature, and replication. The robustness of the method was verified using dissolved organic carbon (DOC) removal in one drinking water (DW) and two wastewater (WW) effluents and the removal of 12 trace organic contaminants in one WW effluent. The average absolute difference (delta) between bench- and pilot-scale results for 14 comparisons was 2% for DOC removal. Experimental DOC results were not impacted by the range of biofilter hydraulic loading rates (HLRs) with a WW effluent and a DW effluent, confirming that at Damköhler number II values less than 0.1, the biofilters were reaction rate limited with little contribution from mass transfer. This allows for the use of lower HLRs and shorter filter media depths at the bench scale to yield equivalent EBCTs of field scale. Utilizing bioacclimated media, this bench-scale methodology could expedite biofilter implementation in DW and water reuse treatment plants.

Mercury (Hg) intake through rice has been proved as the main pathway for Hg exposure to inland Chinese residents. To evaluate the risk of Hg exposure through rice consumption, 49 rice samples were collected in three provinces of China. Total mercury (THg) concentration in rice samples ranged from 1.9 to 15.3 μg/kg (mean 4.4 ± 2.3 μg/kg), which was lower than the Chinese national standard. In vitro experiments were applied to obtain bioaccessibility of THg in rice and results showed that the range of bioaccessibility was 1.0–11.4%, which was much lower than the data reported in fish studies. Estimated daily intake (EDI) was calculated to assess the potential health risk. When considering bioaccessibility, the EDI_bio was far below the reference dose. Overall, our results suggest that consuming rice planted in non-Hg contaminated sites might not cause severe Hg poisoning for inhabitants in their daily diet.

Direct contact membrane distillation (DCMD) is a promising desalination technology for locations where low-cost energy (e.g., waste heat or geothermal energy) is readily available. Modeling of the DCMD process facilitates the optimization of membrane properties and module design for system performance. Since DCMD is a purely thermal process, membrane thermal conductivity, which greatly influences the conductive heat loss through membranes, plays an important role for DCMD modeling. Most researchers adopted the isostrain model when estimating the thermal conductivity of polyvinylidene fluoride (PVDF)-based membranes during modeling and very few actual measurements have been reported in literature to confirm the validity of these estimations. In this study, the transient plane source (TPS) method was used to measure the thermal conductivities of PVDF-based DCMD membranes and the observed values were compared to commonly used models, such as isostress and isostrain. Measurements showed the membrane thermal conductivity decreased with the increase of porosity at 23.5°C. Contrary to the practices reported in literature, the isostrain model showed a discrepancy of more than 200% from the TPS measurements whereas the isostress model provided the closest predictions. Overestimation of 49–80% from the isostress model was attributed to the Knudsen effect. Once the effect was incorporated, the Knudsen-corrected isostress model predicted the membrane thermal conductivity at 23.5°C accurately. Increasing temperature led to the departure between the Knudsen-corrected isostress model and the TPS measurements. Contribution of radiation conduction, which increases with temperature cubed and is not included in the isostress model, might have resulted in the deviation.

Anaerobic oxidation of methane (AOM) coupled to sulfate reduction is a biological process regulating the methane cycle with potential application in desulfurization of industrial wastewater using methane as an electron donor. However, it has been difficult to control and fully understand this process, mainly due to the slow-growing nature of the AOM-mediating microorganisms. A biotrickling filter (BTF) operating at ambient pressure and temperature was used to enrich microorganisms from a deep-sea anaerobic methane-oxidizing sediment (Alpha Mound, Gulf of Cadiz). Different sulfur compounds namely, sulfate, elemental sulfur, and thiosulfate were used as electron acceptors to understand their effects on the AOM, sulfate reduction rates, and the microbial community distribution. The highest AOM and sulfate reduction rates were obtained in the BTF fed with thiosulfate as the electron acceptor (∼0.4 mmol/[L·day]). Use of thiosulfate triggered the enrichment of sulfate-reducing bacteria (SRB) in the BTF, whereas the highest number of anaerobic methanotrophs (ANME) was visualized in the sulfate-fed BTF (ANME-2 43% of the total visualized archaea), where sulfate was reduced at a maximum rate of 0.3 mmol/[L·day]. This study shows that ANME and SRB obtained from deep-sea conditions (528 m below sea level) can be enriched in a BTF at ambient pressure and temperature with a relatively short start-up time (42 days).

Simultaneous removal of sulfur dioxide (SO₂) and nitrogen oxides (NO_X) is an important research field in air pollution control. The combination application of red mud (RM) with coal mine drainage as absorbent in simultaneous desulfurization and denitrification is an innovative attempt. In this study, a series of bubbling and spray tower tests were conducted to improve desulfurization and denitration abilities. Effects of RM concentration, gas flow, liquid–gas ratio, and SO₂ concentration were investigated in the test. Our results indicated that SO₂ removal efficiency depends primarily on RM concentration, gas flow, and the liquid–gas ratio. In the denitration test, the denitration characteristics of the absorbent were not consistent with industrial requirements, but denitration ability could be improved by the addition of an oxidant. In addition, influence of interactions between SO₂ and NO_X was observed, and low concentrations of SO₂ could enhance NO_X absorption, whereas high SO₂ concentrations inhibit NO_X absorption. Meanwhile, NO_X concentration has a negligible effect on SO₂ removal. Under optimized conditions, such as with RM concentration of 12%, gas flow of 40 L/min, liquid–gas ratio of 20 L/m³, absorbent renewal rate of 15%, and a sodium chlorite concentration of 1.9%, desulfurization efficiency is >99.0%, and denitration efficiency ranges from 45.0% to 47.0%. RM and mine water slurry show strong potential as a novel absorbent for the simultaneous removal of SO₂ and NO_X. This study provides a potential feasible technology for reusing RM and coal mine drainage with low cost instead of conventional method.

Activated carbon is a versatile sorbent and effective contaminant removal media due to its complex porous structure and high surface area. The main purpose of this research is to increase the uptake of perfluoroalkyl and polyfluoroalkyl substances (PFAS) through modifications of granular activated carbon (GAC) by chemical treatment. To increase the adsorption of perfluorooctanoic acid (PFOA) and perfluorohexanesulfonic acid (PFHxS) onto GAC, the surface characteristics of two types of GAC from Calgon Carbon Corporation (charcoal-based Filtrasorb-F400 and coconut-based OLC 12 × 30—CBC) were chemically modified. Two GAC were treated with acid (hydrochloric acid [HCl]), base (sodium hydroxide [NaOH]), heat activated persulfate (PS), and hydrogen peroxide catalyzed with iron (H₂O₂/Fe). The extent of adsorption after 2-, 5-, and 10-day reaction time and the changes in carbon surface physical and chemical characteristics of treated GAC were compared with untreated GAC. Several characterization techniques, including Brunauer–Emmett–Teller surface area, pH of point zero charge, scanning electron microscopy with elemental analysis, and Fourier transform infrared spectroscopy, were used to analyze treated and untreated GAC. The extent of adsorption of both PFHxS and PFOA increased (7–8% in F400 and 6–9% in CBC) with HCl treatment likely due to increase in positive charge density, had no significant change with NaOH treatment, and decreased with PS (22–25% in F400 and 27–35% in CBC) and H₂O₂/Fe (4–8% in F400 and 12–13% in CBC) treatment. All the treated GAC had lower BET surface area compared to untreated GAC which is the main physical property deemed responsible for decreased adsorption. It was found that surface oxygen functional groups increased with treatments and decreased the hydrophobicity of the GAC surface, which resulted in lower PFAS adsorption.

Recyclable magnetic Fe₃O₄/BiOBr microspheres (m-Fe₃O₄/BiOBr MSs) were synthesized by a simple solvethermal method. The crystals' optical, morphology, and magnetic properties of m-Fe₃O₄/BiOBr MSs were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis of X-rays, UV–vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller, and vibrating sample magnetometry techniques. An anionic dye, Congo red (CR), was selected as a model pollutant to evaluate the photocatalytic activity of m-Fe₃O₄/BiOBr MSs under simulated solar light irradiation. By calculation, the pseudo-first-order rate constant for photocatalytic degradation of CR was 0.0011 and 0.0046 min⁻¹ using pure BiOBr MSs and m-Fe₃O₄/BiOBr MSs, respectively. Enhanced photocatalytic activity of m-Fe₃O₄/BiOBr MSs can result from superior adsorption and transfer performance to organic contaminants in aqueous system. Both the h⁺ radicals and O₂^•− radicals were main active species that drive the photocatalytic decolorization of CR solution by m-Fe₃O₄/BiOBr MSs. Furthermore, the m-Fe₃O₄/BiOBr MSs can be easily recovered and recycled after the treatment process because of the presence of magnetic Fe₃O₄. This work suggests that m-Fe₃O₄/BiOBr MSs may be a promising photocatalyst for photocatalytic treatment of organic wastewater and other environmental remediation.

Immobilization of bacterial cells on carriers ensures the stability and intensity of biochemical transformations. The choice of the right carrier is often decisive to the success of the biotechnological process. So far, a relatively small group of materials has been tested in the anaerobic digestion (AD) process and the experiments produced different results. In this study, lignin grafted with polyvinylpyrrolidone (PVP) was used for the first time as an innovative microbial carrier in the AD process due to its particularly positive properties such as porosity, thermal stability, and availability. PVP improved cell adhesion to the carrier surface. Waste wafers (WAF) and sewage sludge (SS) were tested as separate samples. The process was carried out in the batch mode under mesophilic conditions. Monitoring of key process parameters such as pH, the volatile fatty acids (VFA), and the VFA-to-total alkalinity (VFA/TA) ratio proved the stability of digestion both in variants with and without the carrier. Results of microbiological and biochemical analyses proved that the addition of lignin-PVP material considerably increased the proliferation of eubacteria in the wafer sample (by 77%) and increased the enzymatic activity, especially in the SS sample (by 30%). Scanning electron microscope observations revealed the presence of microbial colonies on the lignin surface. Improvement of microbiological and biochemical parameters resulted in a natural increase in the amount of biogas/methane produced, that is, an increase of 33.9% in the WAF sample (1,201.45 m³/Mg volatile solids [VS] of biogas, including 685.53 m³/Mg VS of methane) and an increase of 46.8% in the SS sample (746.82 m³/Mg VS of biogas, including 379.60 m³ Mg/VS of methane). As lignin grafted with PVP was proven to have positive effect on the condition of bacterial flora and AD efficiency, the material can be used as a microbial carrier.

A simple precipitation-calcination method was used to successfully prepare palygorskite (PAL)/CuO composite catalyst. As-prepared PAL/CuO composites were characterized by X-ray diffractions, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffused reflectance spectra. Photocatalytic activities of PAL/CuO composites were evaluated by the Cr(VI) reduction efficiency in the presence of tartaric acid under the illumination of visible light. Compared with a single component of PAL or CuO, the PAL/CuO composite catalyst showed outstanding photocatalytic performance, and Cr(VI) was completely reduced within 30 min. Effects of test parameters, such as initial pH, catalyst loading, and concentrations of tartaric acid, on the reduction efficiency of Cr(VI) have also been investigated. It is worth mentioning that the as-synthesized PAL/5.9CuO catalyst shows good reusability and can be effective in a wide range of pH (3–9) with quite high catalytic performance.

An activated sludge aeration tank and a sieve-plate column with six sieve plates were utilized to remove gas-borne volatile organic compounds (VOCs) in air streams. The tank was used for the biodegradation of absorbed VOCs from the column that utilized the activated mixed liquor drawn from the tank as scrubbing liquor. This research proposed a model for VOC absorption to a down-flow activated sludge liquor in a sieve-plate column. Experiments were conducted and the model was verified based on results of tests on removal efficiencies of isopropyl alcohol, toluene, and p-xylene in the system operated at a range of influent VOC concentrations, air application rates, and liquid/gas flow ratios (L/G). Analysis of the model for effects of affecting parameters on VOC removal effectiveness indicates that L/G, plate number N, biodegradation rate constant k, Henry's law constant of VOC H are important.