Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) are efficient processes to degrade organic pollutants in water. In this paper, we especially reviewed the WAO and CWAO processes for phenolic compounds degradation. It provides a comprehensive introduction to the CWAO processes that could be beneficial to the scientists entering this field of research. The influence of different reaction parameters, such as temperature, oxygen pressure, pH, stirring speed are analyzed in detail; Homogenous catalysts and heterogeneous catalysts including carbon materials, transitional metal oxides and noble metals are extensively discussed, among which Cu based catalysts and Ru catalysts were shown to be the most active. Three different kinds of the reactor implemented for the CWAO (autoclave, packed bed and membrane reactors) are illustrated and compared. To enhance the degradation efficiency and reduce the cost of the CWAO process, biological degradation can be combined to develop an integrated technology.
This work presents an overall introduction to the Station for Observing Regional Processes of the Earth System–SORPES in Nanjing, East China, and gives an overview about main scientific findings in studies of air pollution-weather/climate interactions obtained since 2011. The main results summarized in this paper include overall characteristics of trace gases and aerosols, chemical transformation mechanisms for secondary pollutants like O3, HONO and secondary inorganic aerosols, and the air pollution–weather/climate interactions and feedbacks in mixed air pollution plumes from sources like fossil fuel combustion, biomass burning and dust storms. The future outlook of the development plan on instrumentation, networking and data-sharing for the SORPES station is also discussed.
Treating water contaminants via heterogeneously catalyzed reduction reaction is a subject of growing interest due to its good activity and superior selectivity compared to conventional technology, yielding products that are non-toxic or substantially less toxic. This article reviews the application of catalytic reduction as a progressive approach to treat different types of contaminants in water, which covers hydrodehalogenation for wastewater treatment and hydrogenation of nitrate/nitrite for groundwater remediation. For hydrodehalogenation, an overview of the existing treatment technologies is provided with an assessment of the advantages of catalytic reduction over the conventional methodologies. Catalyst design for feasible catalytic reactions is considered with a critical analysis of the pertinent literature. For hydrogenation, hydrogenation of nitrate/nitrite contaminants in water is mainly focused. Several important nitrate reduction catalysts are discussed relating to their preparation method and catalytic performance. In addition, novel approach of catalytic reduction using in situ synthesized H2 evolved from water splitting reaction is illustrated. Finally, the challenges and perspective for the extensive application of catalytic reduction technology in water treatment are discussed. This review provides key information to our community to apply catalytic reduction approach for water treatment.
Effect of different carbon sources on purification performance and change of microbial community structure in a novel A2N-MBR process were investigated. The results showed that when fed with acetate, propionate or acetate and propionate mixed (1:1) as carbon sources, the effluent COD, NH4+-N, TN and TP were lower than 30, 5, 15 and 0.5 mg?L–1, respectively. However, taken glucose as carbon source, the TP concentration of effluent reached 2.6 mg?L–1. Process analysis found that the amount of anaerobic phosphorus release would be the key factor to determine the above effectiveness. The acetate was beneficial to the growth of Candidatus Accumulibacter associated with biological phosphorus removal, which was the main cause of high efficiency phosphorus removal in this system. In addition, it could eliminate the Candidatus Competibacter associated with glycogen-accumulating organisms and guarantee high efficiency phosphorus uptake of phosphorus accumulating organisms in the system with acetate as carbon source.
A new type of Au/TiO2/reduced graphene oxide (RGO) nanocomposite was fabricated by the hydrothermal synthesis of TiO2 on graphene oxide followed by the photodeposition of Au nanoparticles. Transmission electron microscopy images showed that Au nanoparticles were loaded onto the surface of both TiO2 and RGO. Au/TiO2/RGO had a better photocatalytic activity than Au/ TiO2 for the degradation of phenol. Electrochemical measurements indicated that Au/TiO2/RGO had an improved charge transfer capability. Meanwhile, chemiluminescent analysis and electron spin resonance spectroscopy revealed that Au/TiO2/RGO displayed high production of hydrogen peroxide and hydroxyl radicals in the photocatalytic process. This high photocatalytic performance was achieved via the addition of RGO in Au/TiO2/RGO, where RGO served not only as a catalyst support to provide more sites for the deposition of Au nanoparticles but also as a collector to accept electrons from TiO2 to effectively reduce photogenerated charge recombination.
Heterogeneous photocatalysis has long been considered to be one of the most promising approaches to tackling the myriad environmental issues. However, there are still many challenges for designing efficient and cost-effective photocatalysts and photocatalytic degradation systems for application in practical environmental remediation. In this review, we first systematically introduced the fundamental principles on the photocatalytic pollutant degradation. Then, the important considerations in the design of photocatalytic degradation systems are carefully addressed, including charge carrier dynamics, catalytic selectivity, photocatalyst stability, pollutant adsorption and photodegradation kinetics. Especially, the underlying mechanisms are thoroughly reviewed, including investigation of oxygen reduction properties and identification of reactive oxygen species and key intermediates. This review in environmental photocatalysis may inspire exciting new directions and methods for designing, fabricating and evaluating photocatalytic degradation systems for better environmental remediation and possibly other relevant fields, such as photocatalytic disinfection, water oxidation, and selective organic transformations.
Mercury enrichment in response to elevated atmospheric mercury concentrations in the organs of rape (Brassica napus) was investigated using an open top chamber fumigation experiment and a soil mercury enriched cultivation experiment. Results indicate that the mercury concentration in leaves and stems showed a significant variation under different concentrations of mercury in atmospheric and soil experiments while the concentration of mercury in roots, seeds and seed coats showed no significant variation under different atmospheric mercury concentrations. Using the function relation established by the experiment, results for atmospheric mercury sources in rape field biomass showed that atmospheric sources accounted for at least 81.81%of mercury in rape leaves and 32.29% of mercury in the stems. Therefore, mercury in the aboveground biomass predominantly derives from the absorption of atmospheric mercury.
Biochar (BC) is a potential material for removal of polycyclic aromatic hydrocarbons from soil and water, and base modification is a promising method for improving its sorption ability. In this study, we synthesized a series of base-modified biochars, and evaluated their sorption of phenanthrene. Original biochars were produced by pyrolysis of three feedstocks (rice straw, wood and bamboo) at five temperatures (300°C, 350°C, 400°C, 500°C and 700°C). Base-modified biochars were further obtained by washing of biochars with base solution. The base soluble carbon (SC) was extracted from the supernatant, which were only obtained from biochars pyrolyzed at low temperatures (<500°C) and the content was decreased with the increase of pyrolysis temperature. The SC content between different feedstocks followed the trend of rice straw>wood>bamboo when same pyrolysis conditions were applied. It was found that base modification improved the sorption of phenanthrene on biochars that SC could be extracted from (extractable-BCs). However, base treatment but had limited effects for biochars that no SC could be extracted from. It suggested that base modification improved the sorption of phenanthrene to extractable-BCs by removing the SC and thus increasing the surface area and hydrophobicity. Therefore, base modification was suggested to be used in modifying extractable-BCs.
Methane production from low-strength wastewater (LSWW) is generally difficult because of the low metabolism rate of methanogens. Here, an up-flow biofilm reactor equipped with conductive granular graphite (GG) as fillers was developed to enhance direct interspecies electron transfer (DIET) between syntrophic electroactive bacteria and methanogens to stimulate methanogenesis process. Compared to quartz sand fillers, using conductive fillers significantly enhanced methane production and accelerated the start-up stage of biofilm reactor. At HRT of 6 h, the average methane production rate and methane yield of reactor with GG were 0.106 m3/(m3·d) and 74.5 L/kg COD, which increased by 34.3 times and 22.4 times respectively compared with the reactor with common quartz sand fillers. The microbial community analysis revealed that methanogens structure was significantly altered and the archaea that are involved in DIET (such as Methanobacterium) were enriched in GG filler. The beneficial effects of conductive fillers on methane production implied a practical strategy for efficient methane recovery from LSWW.
In this research, supercritical carbon dioxide extraction (SFE) showed better extraction effect when compared with Solid- liquid extraction (SLE), Soxhlet extraction (SE) and Ultrasonic extraction (UE), not only in the rate but also the time. The comparison among these three extraction modifiers, including acetone, ethanol and methanol demonstrated that ethanol was preferred to SFE due to its high extraction effect and low toxicology. In addition, parameter of SFE, influence of temperature and pressure were investigated, and the best extraction effect was achieved at the optima conditions, temperature of 40°C and the pressure of 35 MPa. Thus, SFE is a highly effective method for flavonols extraction, requiring minimum energy and producing non-toxic byproduct. SFE-GC system is applied for the evaluation on flavonols that plays a key role in plant resistance to heavy metal, with its content and synthetase gene expression significantly increasing in plant when threatened by heavy metal. Besides, results indicated that flavonols can improve plant resistance to oxidative stress by quenching the redundant ROS in matrix.
The development of cost-effective and highly efficient anode materials for extracellular electron uptake is important to improve the electricity generation of bioelectrochemical systems. An effective approach to mitigate harmful algal bloom (HAB) is mechanical harvesting of algal biomass, thus subsequent processing for the collected algal biomass is desired. In this study, a low-cost biochar derived from algal biomass via pyrolysis was utilized as an anode material for efficient electron uptake. Electrochemical properties of the algal biochar and graphite plate electrodes were characterized in a bioelectrochemical system (BES). Compared with graphite plate electrode, the algal biochar electrode could effectively utilize both indirect and direct electron transfer pathways for current production, and showed stronger electrochemical response and better adsorption of redox mediators. The maximum current density of algal biochar anode was about 4.1 times higher than graphite plate anode in BES. This work provides an application potential for collected HAB to develop a cost-effective anode material for efficient extracellular electron uptake in BES and to achieve waste resource utilization.
Nitrogen (N) and phosphorus (P) released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil (RS) was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N (TN), ammonium (NH4+-N), total P (TP) and soluble reactive P (SRP) of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.
Investigation of demulsification of polybutadiene latex (PBL) wastewater by polyaluminum chloride (PAC) indicated that there was an appropriate dosage range for latex removal. The demulsification mechanism of PAC was adsorption-charge neutralization and its appropriate dosage range was controlled by zeta potential. When the zeta potential of the mixture was between -15 and 15 mV after adding PAC, the demulsification effect was good. Decreasing the latex concentration in chemical oxygen demand (COD) from 8.0 g/L to 0.2 g/L made the appropriate PAC dosage range narrower and caused the maximum latex removal efficiency to decrease from 95% to 37%. Therefore, more accurate PAC dosage control is required. Moreover, adding 50 mg/L sulfate broadened the appropriate PAC dosage range, resulting in an increase in maximum latex removal efficiency from 37% to 91% for wastewater of 0.2 g COD/L. The addition of sulfate will favor more flexible PAC dosage control in demulsification of PBL wastewater.
Bioelectrochemical systems (BES) have been extensively studied for resource recovery from wastewater. By taking advantage of interactions between microorganisms and electrodes, BES can accomplish wastewater treatment while simultaneously recovering various resources including nutrients, energy and water (“NEW”). Despite much progress in laboratory studies, BES have not been advanced to practical applications. This paper aims to provide some subjective opinions and a concise discussion of several key challenges in BES-based resource recovery and help identify the potential application niches that may guide further technological development. In addition to further increasing recovery efficiency, it is also important to have more focus on the applications of the recovered resources such as how to use the harvested electricity and gaseous energy and how to separate the recovered nutrients in an energy-efficient way. A change in mindset for energy performance of BES is necessary to understand overall energy production and consumption. Scaling up BES can go through laboratory scale, transitional scale, and then pilot scale. Using functions as driving forces for BES research and development will better guide the investment of efforts.
Methane fermentation process can be restricted and even destroyed by the accumulation of propionate because it is the most difficult to be anaerobically oxidized among the volatile fatty acids produced by acetogenesis. To enhance anaerobic wastewater treatment process for methane production and COD removal, a syntrophic propionate-oxidizing microflora B83 was obtained from an anaerobic activated sludge by enrichment with propionate. The inoculation of microflora B83, with a 1:9 ratio of bacteria number to that of the activated sludge, could enhance the methane production from glucose by 2.5 times. With the same inoculation dosage of the microflora B83, COD removal in organic wastewater treatment process was improved from 75.6% to 86.6%, while the specific methane production by COD removal was increased by 2.7 times. Hydrogen-producing acetogenesis appeared to be a rate-limiting step in methane fermentation, and the enhancement of hydrogen-producing acetogens in the anaerobic wastewater treatment process had improved not only the hydrogen-producing acetogenesis but also the acidogenesis and methanogenesis.
In the present study, a novel approach was used to control zero valent iron aggregation and separation problems by fixing zero valent iron (ZVI) on bentonite-fly ash pellets. For this purpose, porous low cost bentonite-fly ash (BFA) pellets with size of 2.00 cm in length and 0.35 cm in diameter were prepared and fixed with ZVI to manufacture zero valent iron bentonite-fly ash (ZVI-BFA) pellets. Importantly, unlike powdered adsorbents, ZVI-BFA can easily be separated from final effluents when exhausted without any disintegration. The performance of the developed novel adsorbent was investigated for the removal of Pb2+ and Cd2+ from aqueous media. At 100 mg·L–1 and 1 g adsorbent, a maximum of 89.5% of Cd2+ and 95.6% of Pb2+ was removed by ZVI-BFA as compared to 56% and 95% removal by BFA. At 200 mg·L–1, Cd2+ and Pb2+ removal by ZVI-BFA was 56% and 99.8% respectively as compared to only 28% and 96% by BFA. Further, the removal kinetics was best fitted for pseudo-second order model. The study provides the basis for improving the removal capacity of porous materials by iron fixation while taking separation ability into consideration.
In this paper, we present a three-step methodological framework, including location identification, bias modification, and out-of-sample validation, so as to promote human mobility analysis with social media data. More specifically, we propose ways of identifying personal activity-specific places and commuting patterns in Beijing, China, based on Weibo (China’s Twitter) check-in records, as well as modifying sample bias of check-in data with population synthesis technique. An independent citywide travel logistic survey is used as the benchmark for validating the results. Obvious differences are discerned from Weibo users’ and survey respondents’ activity-mobility patterns, while there is a large variation of population representativeness between data from the two sources. After bias modification, the similarity coefficient between commuting distance distributions of Weibo data and survey observations increases substantially from 23% to 63%. Synthetic data proves to be a satisfactory cost-effective alternative source of mobility information. The proposed framework can inform many applications related to human mobility, ranging from transportation, through urban planning to transport emission modeling.
Polycyclic aromatic hydrocarbons (PAHs) often occur in oil-contaminated soil, coke wastewater and domestic sludge; however, associated PAH degraders in these environments are not clear. Here we evaluated phenanthrene degradation potential in the mixed samples of above environments, and obtained a methanogenic community with different microbial profile compared to those from sediments. Phenanthrene was efficiently degraded (1.26 mg/L/d) and nonstoichiometric amount of methane was produced simultaneously. 16S rRNA gene sequencing demonstrated that bacterial populations were mainly associated with Comamonadaceae Nocardiaceae and Thermodesulfobiaceae, and that methanogenic archaea groups were dominated by Methanobacterium and Methanothermobacter. Substances such as hexane, hexadecane, benzene and glucose showed the most positive effects on phenanthrene degradation. Substrate utilization tests indicated that this culture could not utilize other PAHs. These analyses could offer us some suggestions on the putative phenanthrene-degrading microbes in such environments, and might help us develop strategies for the removal of PAHs from contaminated soil and sludge.
In addition to maximizing economic benefits, reverse supply chains should further seek to maximize social benefits by increasing the quantity of waste electrical and electronic equipment (WEEE). The paper investigates cooperative models with different parties in a three-echelon reverse supply chain for WEEE consisting of a single collector, a single remanufacturer, and two retailers based on complete information. In addition, the optimal decisions of four cooperative models and the effect of the market demand of remanufactured WEEE products and the market share of two retailers on the optimal decisions are discussed. The results indicate that optimal total channel profit and recycle quantity in a reverse supply chain are maximized in a centralized model. The optimal total channel profit and recycle quantity increase with an increase in the market demand of remanufactured WEEE products. The three-echelon reverse supply chain consisting of duopolistic retailers maximizes total channel profit and recycle quantity in a reverse supply chain for WEEE.
The phytotoxicity of added copper (Cu) and nickel (Ni) is influenced by soil properties and field aging. However, the differences in the chemical behavior between Cu and Ni are still unclear. Therefore, this study was conducted to investigate the extractability of added Cu and Ni in 6-year field experiments, as well as the link with their phytotoxicity. The results showed that the extractability of added Cu decreased by 6.63% (5.10%–7.90%), 22.5% (20.6%–23.9%), and 6.87% (0%–17.9%) on average for acidic, neutral, and alkaline soil from 1 to 6 years, although the phytotoxicity of added Cu and Ni did not change significantly from 1 to 6 years in the long term field experiment. Because of dissolution of Cu, when the pH decreased below 7.0, the extractability of Cu in alkaline soil by EDTA at pH 4.0 could not reflect the effects of aging. For Ni, the extractability decreased by 18.1% (10.1%–33.0%), 63.0% (59.2%–68.8%), and 22.0% (12.4%–31.8%) from 1 to 6 years in acidic, neutral, and alkaline soils, respectively, indicating the effects of aging on Ni were greater than on Cu. The sum of ten sequential extractions of Cu and Ni showed that added Cu was more extractable than Ni in neutral and alkaline soil, but similar in acidic soil.
