Search

Wastewater from olaquindox-producing factories contains high levels of salts and organics. In this study, we investigated the multiple freeze-thaw technology to recover olaquindox from wastewater and decrease its chemical oxygen demand (COD) and salinity. Results suggested that under lower ice formation rate, the removal efficiencies of COD, electric conductivity, ammonia nitrogen and total nitrogen could reach 99.4%, 98.2%, 98.7% and 98.5% respectively. Higher ice formation rate, however, promoted wastewater concentration and volume reduction. A liter of wastewater concentrate can recover 11.5 g solid through a simple crystallization step at 4 °C for 12 h. This substance contained mostly olaquindox based on Raman infrared spectroscopy, scanning electron microscopy, and energy dispersive spectrometry. An industrial-scale wastewater treatment process, which the theoretical cost is one seventh that of conventional technologies, was then proposed to recover olaquindox and treat wastewater.

Reduction in and recovery of precious metals are research hotspots in the environmental engineering field. In this study, we investigated the transformation and distribution of platinum in microbial fuel cells (MFCs) and demonstrated a feasible approach to recover platinum (Pt) from wastewater with less than 16.88 mg/L platinum through charring biofilms in MFCs and generate Pt/C catalyst. The optimal reaction condition was identified, and charred biofilms were analyzed via SEM-EDS, XRD and XPS. Results showed that less than 10% of Pt was in MFC effluents, and less than 0.5% was in the cathode chamber when the influent concentration was below 16.88 mg/L. Close to 40% of Pt could be recovered. The recovery efficiency could be higher should the reactions run longer. SEM-EDS and XRD results indicated that the metallic form Pt0 is one of the reduction products in MFCs. XPS results induced that Pt (IV) was reduced to Pt (II) and Pt0. Keywords: Microbial fuel cells, Platinum, Bio-reduction, Recovery, Sludge

The long-term effectiveness concern of municipal solid waste incineration (MSWI) fly ash (FA) disposal has been placed more emphatic recently, however, few studies worked on the control of leaching risk of heavy metals under the long-term stability. In this study, the leaching properties and risk assessment of two representative solidified/stabilized (S/S) FA wastes, i.e., sodium dithiocarbamate (DTC) chelator treated and Portland cement + chelator combining treated, were evaluated by a long-term cycles assessment method which coupled multifaceted environmental stresses (e.g., freezing-thawing, drying-wetting, accelerated carbonation). The results showed that the cement/chelator had a better long-term stability and exhibited ~55% lower cumulative overall pollution toxicity index (OPTI) than chelator treatment after the test, which was always rated as “low risk” during the cycles. In addition, the cement/chelator exhibited ~23.3% smaller cumulative mass release rate than the chelator treatment after 6 cycles and restrained the transformation of Pb and Cd from stable states to removable fractions, which attributes to its great erosion resistance and compact pore structure. Under the cumulative external factors and carbon dioxide attacks, the decalcification of hydrate products (e.g., C-S-H, hydrocalumite), as well as deterioration of pore structure are the critical factors increasing the local erosion, cracking and heavy metals release. Thus, the optimization of S/S waste microstructure (e.g., enhancing binder system) and landfill site conditions (e.g., reducing rainfall impact) could be propitious to the S/S waste risk control and management.

A set of experiments was conducted so as to detect the influences of concerned factors including freezing temperature, stirring speed and pH adjustment on combined method of suspension crystallization and freeze-thaw technique for waste cutting fluid treatment and oil recovery. The optimal operating conditions of freezing temperature and stirring speed were confirmed by the experiment result to be −8 °C and 300 rpm respectively, while the chemical oxygen demand (COD) removal efficiency was above 90% without pH adjustment. The concentrates from the suspension crystallization were further treated by freeze-thaw method, and the oil recovery rate could reach to 95%. The micrograms of concentrates from suspension crystallization showed that the size of oil droplets in concentrates was about 148 μm in diameter, which became significantly larger after the suspension crystallization process. As a consequence, higher possibility for oil droplets to gather and separate was provided by their expanded size. The results of infrared spectroscopy studies indicated that the oil recovered from waste cutting fluid precipitates was mainly composed of esters. Up to 2.85 kg fat was recovered from 1 m 3 of waste cutting fluid, while the required power of the combined freezing process is theoretically 42 kW h. Based on the results, a freezing/concentration concept for oil recovery from waste cutting fluid is proposed.

The effective disposal of waste cutting fluid has received increasing attention in recent years. This study focuses on the treatment of waste cutting fluid by freeze-thaw method. The influences of freezing medium, freezing temperature, freezing time, NaCl content and pH on treatment efficiency were studied. The COD removal rate of waste cutting fluid was about 80% and oil recovery reached 3700 mg/L at the freezing temperature of −8 °C for 8 h without NaCl addition or pH adjustment. The micrograms of initial and treated waste cutting fluid showed that the particles of oil droplets in wastewater were significantly larger after freeze-thaw process and easier to gather and separation. Infrared spectroscopy studies indicated that the oil recovered from waste cutting fluid precipitation was mainly composed of esters. Up to 3.7 kg fat extract was recovered from 1 m3 of waste cutting fluid, while the required power of this freezing process is 42.90 kW h by theoretical calculation. Thus, freeze-thaw method appears to be effective and feasible for waste cutting fluid treatment.

Freezing methods, progressive freezing and suspension crystallization, were examined for treating Grignard reagent wastewater containing tetrahydrofuran (THF) used as a solvent. The effect of freezing temperature, addition of seed ice crystals, and stirring speed on performance were investigated. The addition of seed ice with appropriate temperature contributed to enhance the purity. The optimal operating conditions of freezing temperature and stirring speed were −6 °C and 300 rpm respectively while the removal efficiency of COD was above 90%. The suspension crystallization is superior to progressive freezing in terms of performance and energy consumption, with an estimation of about 38.26 kW h per ton of wastewater treated. Based on these results, a freezing/concentration concept for THF recovery from Grignard reagent wastewater is proposed.

Natural magnetite and hematite were explored to decrease sulfide in sewage, compared with iron salts (FeCl3 and FeSO4). A particle size of magnetite and hematite ranging from 45 to 60 μm was used. The results showed that 40 mg L− 1 of powdered magnetite and hematite addition decreased the sulfide in sewage by 79%and 70%, respectively. The achieved decrease of sulfide production capacities were 197.3, 210.6, 317.6 and 283.3 mg S g− 1Fe for magnetite, hematite, FeCl3 and FeSO4 at the optimal dosage of 40 mg L− 1, respectively. Magnetite and hematite provided a higher decrease of sulfide production since more iron ions are capable of being released from the solid phase, not because of adsorption capacity of per gram iron. Besides, the impact on pH and oxidation-reduction potential (ORP) of hematite addition was negligible; while magnetite addition resulted in slight increase of 0.3–0.5 on pH and 10–40 mV on ORP. Powdered magnetite and hematite thus appear to be suitable for sulfide decrease in sewage, for their sparing solubility, sustained-release, long reactive time in sewage as well as cost-effectiveness, compared with iron salts. Further investigation over long time periods under practical conditions are needed to evaluate the possible settlement in sewers and unwanted (toxic) metal elements presenting as impurities. Capsule abstract Powdered magnetite and hematite were more cost-effective at only 30% costs of iron salts, such as FeCl3 and FeSO4 for decreasing sulfide production in sewage.

Attention is drawn to the freezing method for separating organic contaminants from industrial wastewater and simultaneously recovering valuable materials, but the mechanism regarding functional group of organic contaminants how affect ice purity remains unclear. In this work, four types of organics, including hexane, hexanoic acid, N-hexanol and N-hexanal, with various oxygen functional groups were selected as organic contaminants and studied to be separated from aqueous solutions by the suspension freezing method. Experimental results revealed that their separation efficiencies were 67.07%, 87.75%, 94.71% and 95.32%, respectively, after freezing 30 min at 200 rpm and −0.9 °C. The presented theoretical work reveals that hexane, as a non-polar organic contaminant without function group, unable to form hydrogen bonds with water clusters, making it more readily to precipitate and stick on ice surface during freezing, which significantly increased ice impurities with the lowest separation efficiency. Presence of functional group promotes organics to solute in concentrate via forming H-bond with water clusters, and thus improves ice purity by avoiding of precipitation. Hexanoic acid with the largest absorption energy with ice crystal tend to adsorb on ice surface but not stay in concentrate and showed the highest ice impurity corresponding to lowest separation efficiency. This work provides new sight for understanding declination of ice purity and separation efficiency caused by functional group of organic contaminants during freezing.

In search of a cost effective cathode material for microbial fuel cells (MFCs), graphite was chemically treated with H3PO4, HNO3, ZnCl2, urea or melamine, and the effect of chemical activations on the oxygen reduction reaction (ORR) was examined. The performance of MFCs with activated graphite as the catalyst-free cathodes was then compared to those with untreated graphite. Results suggested that H3PO4 and HNO3 activations could improved ORR, showing the highest ORR activity in graphite treated with 14.62 M H3PO4 for 12 h at 30–50 °C. MFCs with H3PO4 and HNO3 activated graphite cathodes generated maximum power densities (7.9 W/m³ and 6.5 W/m³, respectively) 2.4 and 1.8 times higher than that of the untreated control. The chemical activation process involves just a simple immersion step, and it does not require heating, electrochemical process or expensive chemicals. Therefore, it is a highly cost-effective approach to improve the performance of MFCs. We recommend an in-situ modification of graphite cathodes in scale-up MFCs with either H3PO4 or HNO3 to optimize MFCs' various industrial applications.

Although plant-microbial fuel cells (PMFCs) have been considered as an alternative approach to utilize plants as an energy source, the application of a conventional PMFC coupled with rhizodeposits is immensely limited by environmental factors and plant species. In this research, we suggested a new concept for a device that can directly generate continuous bioelectricity from the plant stem associated with microbial fuel cells (MFCs), in which Pachira macrocarpa and Populus alba were employed. Compared with a conventional PMFC, the novel PMFC coupled with the plant stems produced more stable and continuous bioelectricity without oscillatory behaviour as well as a much shorter start-up period. The stem-coupled PMFCs produced bioelectricity that were operated at least 40 days. P. alba coupled PMFC showed higher power output compared to P. macrocarpa counterparts and the maximal power densities were 7.61 mW m−2 and 3.60 mW m−2 anode surface, respectively. Besides, we explored the response of the novel PMFC to different substrate concentrations and observed that the cell voltage effectively increased after the injection of moderate substrate concentrations. Moreover, the anodic bacteria formed a commensal relationship with the plant.

A novel electrochemical micromembrane technology coupling membrane and electric method was developed to demulsify oily wastewater and recover oil. The diameter of the oil droplets increased to 55.0 μm from the initial 7.0 μm after treating the emulsion with the electrochemical micromembrane technology. Chemical oxygen demand removal rate and oil recovery reached 87.89% and 5173 mg/L, respectively, after cycling for 90 min at 10.0 V voltage with a 10.0 mm electrode distance, a 5.0 μm micromembrane pore size and a 0.5 L/min flow rate. Micromembrane pore sizes of 1.0 and 5.0 μm were both effective for decreasing chemical oxygen demand and recovering oil. The recovered oil was the mixture of mineral oil and ester according to the Raman infrared spectroscopy analysis. Surface charge redistribution and electrogenerated destruction for hydrophilic groups of surfactant molecules are responsible for oil coalescence. The electrochemical micromembrane technology used in this study offer an attractive treatment option to demulsify oily wastewater.

Pulsed electrochemical process was explored to remove sulfide in municipal sewage, which successfully achieved higher removal rate of 93.2% compared with 73.2% by direct current (DC) power supply. The sulfur content on the electrode was 0.21% by pulsed electrochemical process compared with that of 1.05% on anode by DC electrochemical process, indicating that pulsed electrochemical process can inhibit anodic passivation resulting from sulfur deposition compared with DC electrochemical process. Besides, the electrode scaling can also be effectively controlled during pulsed electrochemical process. Moreover, the process optimization was investigated for pulsed electrochemical treatment, which obtained the highest removal rate of 97.8% at pH 7–8, cell voltage of 7 V, duty cycle of 60%, pulse frequency at 1000 Hz and electrode spacing of 2.5–3.0 cm. These results indicate that pulsed electrochemical process is a promising method of efficient and sustainable electrochemical sulfide removal from sewage.

Bioelectrochemical systems (BESs) have been focused on by many researchers to treat wastewater and recover energy or valuable chemicals from wastes. In BESs, metal ions play an important role in the conductivity of solution, reactors' internal resistance, power generation, chemical production and activity of microorganisms. Additionally, the metal ions are also involved in anodic or cathodic reaction processes directly or indirectly in BESs. This paper reviews the behavior of metal ions in BESs, including (1) increase of the conductivity of electrolyte and decrease of internal resistance, (2) transfer for desalination, (3) enhancement or inhibition of the biocatalysis in anode, (4) improvement of cathodic performance by metal ions through electron acceptance or catalysis in cathodic process and (5) behavior of metal ions on membranes. Moreover, the perspectives of BESs removing heavy metal ions in wastewater or solid waste are discussed to realize recovery, reduction and detoxification simultaneously.

The abiotic cathodes usually require a catalyst such as Pt to enhance power production, increasing the cost and lowering the operational sustainability. In this paper, the performance of a biocathode microbial fuel cell biocatalyzed by ferro/manganese-oxidizing bacteria was investigated. A scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS) was used to characterize the cathode and analyze the element of cathode. The amount of ferro/manganese-oxidizing bacteria in the biocathode was examined. In batch-fed systems, the maximum open circuit voltage (OCV) was between 700 and 800 mV and the maximum cell potential difference was higher than 600 mV with an external resistance of 100 Ω. The maximum power density was 32 W m −3 MFC for batch-fed systems (20–40% Coulombic yield) and 28 W m −3 MFC for a continuous system with an acetate loading rate of 1.0 kg COD m −3 day −1 . The results of SEM-EDS clearly showed that cathode was impregnated with iron and manganese. The amount of ferro/manganese-oxidizing bacteria was (7.5–20.0) × 10 5 MPN mL −1 in the biocathode. Biocathodes alleviate the need to use noble catalysts for the reduction of oxygen, which step forward towards large-scale application of MFCs.

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10(-3) M 2,6-dithiopurine. The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the pi stacking between the pi electron of the purines and the metal surface. (C) 2008 Elsevier Ltd. All rights reserved.