Energy cooperation has been emphasized strongly in the Belt and Road (B&R) initiative. Therefore, the energy efficiency of China has attracted much attention from experts. However, relevant studies are still insufficient. This paper analyzes the total factor energy efficiency (TFEE) and its influencing factors of 17 B&R key regions from 2005 to 2015. We use the ratio of target energy input and actual energy input to calculate the regional TFEE under environmental constraints. The Malmquist index and the Tobit model are applied to investigate the internal and external influences of TFEE. Measurement analysis shows that the TFEE of the B&R key regions has not improved in recent years and it is unbalanced during the study period. Regions in the east area have the highest TFEE; regions in the west area have the second high TFEE; and regions in the north area have the lowest TFEE. Regression analysis shows that for the B&R key regions, technical changes, coal consumption, research and development, and environmental pollution have mainly negative effects on TFEE; pure efficiency changes, scale efficiency changes, economic structure, opening up, and government finance have mainly positive effects on TFEE. Finally, precise policy implications are proposed.

To investigate the emission characteristics of the dissolved N₂O in distilled water and activated sludge mixture, the total volume mass transfer coefficients of N₂O in distilled water and activated sludge mixture were determined by batch experiments. The results indicated a difference between emission processes of N₂O in distilled water and activated sludge mixture. At different initial N₂O concentrations, the total volume mass transfer coefficients of N₂O in distilled water were relatively stable, while the total volume mass transfer coefficients of N₂O in activated sludge mixture increased with increasing initial N₂O concentrations, due to endogenous denitrification by microorganisms in the mixture. Since N₂O was reduced and consumed by heterotrophic bacteria in activated sludge, biochemical reactions were involved in the transfer process of N₂O escaping from the mixture to the atmosphere. Therefore, use of distilled water was suggested to determine the total volume mass transfer coefficient in experiments calculating N₂O emission rates for biological nitrogen removal processes.

This article identifies environmental factors that explain most of the dynamic year-to-year changes in mercury concentrations of young-of-year (YOY) yellow perch (Perca flavescens) in study reservoirs. Mercury concentrations in fish, collected each fall, were measured for 9 years in four reservoirs in northeastern Minnesota. Three to 4 years of data were also obtained for two natural lakes and one other reservoir. Average annual concentrations varied considerably from year to year with a mean change of 39% between consecutive years across all lakes. Those averages show a similar time trend for each lake over the years and suggest that important factors influencing mercury bioaccumulation change annually and are also experienced in common over the study region. Three factors satisfying that description are precipitation depth, water level, and average air temperature. This article reveals that all three have statistically significant correlations with observed mercury concentrations. Moreover, multiple regressions indicate that maximum water levels and average air temperatures explain most of the observed variations. Regressions employing precipitation depth and temperature are less significant.

Robust and simple composite films for the removal of methyl orange (MO) and Cr(VI) have been prepared by combining chitosan, saponin, and bentonite at a specific ratio. There are several composite films (chitosan-saponin-bentonite (CSB)) prepared; among them, the composite films CSB₂:₃ and CSB₁:₁ have the highest removal efficiency toward MO and Cr(VI) where the maximum removal is 70.4% (pH 4.80) and 92.3% (pH 5.30), respectively. It was found that different types of adsorbate have different thermodynamic properties of the adsorption process; the adsorption of MO onto CSB₂:₃, chitosan, and acid-activated bentonite (AAB) proceeded endothermically, while the adsorption of Cr(VI) onto CSB₁:₁, chitosan, and AAB proceeded exothermically. The parameters of the adsorption were modeled by using isotherm and kinetic equations. The models of Langmuir, Freundlich, Redlich-Peterson, Sips, and Toth were used for fitting the adsorption isotherm data at a temperature of 30, 45, and 60 °C; all of the isotherm models could represent the data well. The result indicates that CSB₂:₃ has the highest adsorption capacity toward MO with qₘ of 360.90 mg g⁻¹ at 60 °C; meanwhile, CSB₁:₁ has the highest adsorption capacity toward Cr(VI) with qₘ 641.99 mg g⁻¹ at 30 °C. The pseudo-second-order model could represent the adsorption kinetics data better than the pseudo-first-order equation. The adsorption mechanism was proposed, and the thermodynamic properties of the adsorption were also studied.

Sustainable development has by now become an element deeply integrated in the everyday design. It has many shades and may be found under many names. We speak about resiliency in design and procurement of passive, ecologic, plus energy, or nZEB buildings. Nevertheless, if we look closely, we may distinguish certain characteristic ideas. First, sustainable development of societies and urbanization processes should be consistent on a deeper level than presently, and be included within design processes, organization, and planning, as well as modernization and redevelopment procedures of existing urban tissue. Secondly, urbanization should be perceived holistically, as an interaction and harmonious development of both natural and manmade environments, with solutions based on the best technical and technological standards available. Lastly, described ideas are achievable only, if we include continuous cooperation between urban planners, architects, specialist consultants, as well as energy-efficient interdisciplinary solutions to achieve high standard energy measures. One of the thresholds is economic feasibility; the other is health and well-being of the users which should always be discussed as a priority. This paper—outside a brief theoretical approach to initial procedures in design management—will dwell on transformation and modernization of an existing building belonging to the Warsaw University of Technology, one of the oldest universities in Poland, its founding dating back to the beginning of the twentieth century. In 2015, a Nordic Finance Mechanism grant dedicated to the nZEB technology transfer from Norway to Poland was awarded to a group of researchers from Warsaw University of Technology and NTNU Trondheim. The main aim of the project is implementation of nZEB knowledge in Poland, as well as preparation of two integrated concept designs for public (University) buildings as exemplary case studies which could act as the benchmarks for other public buildings.

The aim of this paper is to select feasible agricultural straws as high-quality sustained-release carbon source and examine the effect of determined agricultural organic waste on improving denitrification efficiency. Five kinds of agricultural straws, i.e., the rice straw, the corn straw, the wheat straw, the broomcorn straw, and the reed straw, were evaluated in a self-designed drawer-type biological filter. Results showed that the contents of C, H, and N in the five straws were 34.0~41.0%, 4.9~5.4%, and 1.1~1.5% respectively. The highest TOC release capacity of the rice straw was 12.4 ± 1.3 mg g⁻¹ and the average TOC release of other waste straws ranged from 6.0 to 9.2 mg g⁻¹. The TN release capacities of all the five straws were at a low level, ranging from 0.2 to 1.4 mg g⁻¹. Preliminary denitrification studies showed that the corn and the rice straw could be used as high-quality carbon sources, achieving a COD removal rate of 47.3~50.2% and a TN removal rate of 21.8~24.8% for wastewater with low C/N ratio. The rice straw and the corn straw founctioned both as favorable solid carbon sources and biofilm carriers; the carbon source quality of the corn straw lixivium is more beneficial to microbial utilization. The drawer-type biological filter has showed a good efficiency of denitrification for nitrogen removal when using agricultural straws as biofilm carriers.

The plasma electrolytic oxidation (PEO) technique was used to prepare photocatalytic S-TiO₂ coatings on Ti sheets; the incorporation of the S ions was possible from the electrolyte for modifying the structural and optics characteristics of the material. In this work, substrates of Ti (ASME SB-265 of 20 × 20 × 1 mm) were used in a PEO process in 10 min, using constant voltage pulses of 340 V with frequency of 1 kHz and duty cycles of 10% and of 30%. Solutions with H₂SO₄ (0.1 M) and CH₄N₂S (52 and 79 mM) were used as electrolytes. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (EDS) were utilized to analyze the surface morphology, crystalline phase, and chemical composition of the samples. According to the results, the catalyst coatings had microporous structure and contained anatase-rutile TiO₂ nanocrystalline mixture, until 73.2% rutile and 26.8% anatase in the samples grown with 30% duty cycle and the lowest concentration of CH₄N₂S. From the EDS measurements, the incorporation of sulfur ions to the coatings was 0.08 wt%. 99.5% reduction efficiency of Cr(VI)-EDTA with sunlight was observed after 2 h; it was determined by diphenyl carbazide spectrophotometric method. These coatings have potential for effective sunlight heterogeneous photoreduction of this toxic, cumulative, and non-biodegradable heavy metal that contaminates the soil and water and is a serious risk to sustainability, ecosystems, and human health.

This paper deals with the adsorption of an anionic dye, Eriochrome Black T (EBT), from aqueous solutions onto sawdust, which is a natural, eco-friendly, widespread, and a low-cost bio sorbent. The aim of the work is to append values to the wood industry waste. Thus, sawdust was used as adsorbent in both batch reactor (BR) and fixed bed column (FBC), and various operating parameters influencing the adsorption process were investigated. The kinetic and the equilibrium adsorption results were found to agree with, respectively, the prediction of the pseudo-second-order equation and the Langmuir model. This latter allowed also the determination of the maximum EBT dye adsorbed amount, which was found to be about 40.96 mg EBT per gram of sawdust at pH = 4, corresponding to % dye removal of about 80%. In addition, the influence of various parameters on the dye adsorption, such as the adsorbent dose, the aqueous phase pH, and the initial dye concentration, was also examined. In batch experiments, The EBT adsorbed amount was found to increase either by increasing the amount of sawdust or by decreasing the aqueous phase pH, whereas, in the fixed bed column, the EBT retention was found to increase by decreasing the flow rate of the dye through the column. The overall data indicate that the EBT adsorption is mainly governed by the electrostatic interactions occurring between the adsorbent material and the dye.

The heavy metal Cd(II) in wastewater is highly toxic to organisms and must be removed. In this work, an efficient Cd(II) adsorbent consisting of ground calcium carbonate (GCC) and nano-TiO₂ (GCC/TiO₂) was harvested through a facile two-step strategy. Firstly, GCC was immersed in titanium sol which prepared from titanium butoxide to form the precursor. Secondly, GCC/TiO₂ was obtained via hydrothermal reaction and the optimal hydrothermal condition was determined to be pH of 3, temperature of 200 °C and reaction time of 12 h. The removal of Cd(II) from aqueous solution by adsorbents under different hydrothermal conditions and adsorption experiments was studied by means of SEM, FT-IR, XPS, and ICP. The maximum Cd(II) removal capacity was approximately 124.07 mg/g at 25 °C and the adsorption equilibrium was attained in only 8 min (at 100 mg/g initial Cd(II) concentration, 0.8 g/L adsorbent dosage, and an initial Cd(II) solution pH of 5). Furthermore, the Cd(II) removal capacity of GCC/TiO₂ was significantly higher than that of isolated GCC and TiO₂ and exhibited an excellent self-settlement property, which is beneficial for adsorbent separation in practical applications. The Cd(II) removal mechanisms include ion-exchange reaction between Cd(II) and the Ca²⁺ ions on the GCC/TiO₂ surface and electrostatic attraction. Moreover, the GCC/TiO₂ adsorbent could be regenerated by ethylenediaminetetraacetic acid disodium salt and exhibited a high reusability. The adsorption data could be well fitted by the Langmuir model, and the adsorption kinetic follows the pseudo-second-order model indicating that the removal processes are controlled by the chemisorption mechanism.

Denitrifying bioelectrochemical system provided an alternative technology for nitrogen removal, even power recovery from wastewater, and its nitrogen removal performance and intermediate accumulation were affected by the extracellular electron transfer modes and rate-limiting steps in denitrifying biocathodes. In the current study, the extracellular electron transfer modes and rate-limiting steps for nitrate reduction and nitrite reduction of denitrifying biocathode were investigated through cyclic voltammetry. When the cathode potential swept from 0.003 to − 0.897 V (vs. Ag/AgCl), denitrifiers were indispensable for electrochemical denitrification. Three peak potentials were found in the cyclic voltammogram of denitrifying biocathode, where E₁ (− 0.471 to − 0.465 V) and E₂ (− 0.412 to − 0.428 V) represented respectively nitrate reduction and nitrite oxidation while E₃ (− 0.822 to − 0.826 V) represented nitrite reduction. Nitrate reduction involved the direct electron transfer mode while nitrite reduction involved the mediated electron transfer mode. Intracellular catalytic reaction was the rate-limiting step for nitrate reduction, independent on the electrochemical activity of denitrifying biocathode and the nitrate supply. The nitrate supply posed an effect on the rate-limiting step for nitrite reduction. The mediator transfer was the rate-limiting step for nitrite reduction in the absence of nitrate. But both mediator transfer and intracellular catalytic reaction became the rate-limiting steps for nitrite reduction in the presence of sufficient nitrate.