Full-scale application of heterogeneous photocatalysis for industrial wastewater treatment remains a challenge because of the complex nature of these matrices and the potential to form toxic by-products during treatment. A recent unsuccessful attempt to find adequate conditions for TiO₂/UV treatment of a cotton dyeing textile mill led to this study on the treatability of mixtures of the dyes used in the greatest amounts at the mill and therefore most likely to be present in mill effluent. Four reactive and three vat dyes were mixed in different combinations and treated (10 mg/L of each dye, 0.5 mg/L TiO₂, pH 4) to evaluate the influence of the different dyes on ADMI color, chemical oxygen demand (COD), and acute toxicity. While ADMI color removal was similar in all dye mixtures, COD removal was higher when vat dyes were absent. When treated individually, vat dyes exhibited greater recalcitrance, with no ADMI color removal and COD removals of less than 30%. Toxicity to Daphnia similis was decreased or eliminated from dye mixtures that exhibited the highest COD removals and corresponded to those in which reactive dyes were partially degraded. For raw textile mill effluent, photocatalysis reduced but did not eliminate treated effluent toxicity (EC50 = 26.8%).

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.

A consortium of highly degrading microorganisms was used in an integrated bioaugmentation/electrocoagulation process for treating olive mill wastewater. The system was investigated for treating 1 m³ day⁻¹, at a pilot scale, for 2 years; hydraulic loading rate and organic loading rate were 2880 l m⁻² day⁻¹ and 37,930 g COD m⁻² day⁻¹, respectively. Average removal efficiency for COD, oils, and total phenols was 63.9%, 85.2%, and 43.6%, respectively. The olive mill consortium, OMC, consisted of seven actinomycete strains. The strains were confirmed, by 16S rDNA analysis, to belong to five Streptomyces, one Kitasatospora, and one Micromonospora strains, at 100–99.06% similarities. Hydrolytic enzyme activities of OMC strains were remarkably higher for degrading cellulosic and lipid constituents (enzyme-cumulative indices, 14–16.1), than the phenolic constituents (indices, 4.1–6.5). The establishment of actinomycetes in the treatment system was indicated by their increased counts in the biofilm at the end of the biofilter, reaching 13-fold higher than that in the control bed. The treated effluent was toxic to the seedlings of Jatropha curcas (Jatropha) and Simmondsia chinensis (Jojoba). Though its application in irrigation of 3-year-old Jatropha shrubs, significantly, enhanced the fruit yield up to 1.85-fold higher than the control, without affecting the seed oil content, after 3-month application, the irrigated soil showed insignificant changes in its biochemical properties. This developed bioaugmentation/electrocoagulation process can treat wastewater with extremely high organic strength, while its approximate construction and operational costs are limited to 0.03 and 0.51 US$ m⁻³, respectively. It produces a treated effluent that can be reused in irrigation of specific plants. Graphical abstract

This study aimed to explore the nitrogen and phosphorus removal performance of the horizontal submerged constructed wetland (HSCW) with Ti-bearing blast furnace slag (T). Another two HSCWs, with the converter steelmaking slag (G) and the stone (S) as wetland substrates, respectively, were simultaneously running as control. The results showed that the nitrogen and phosphorus removal capacities of the T-HSCW were generally better than those of another two HSCWs. When the hydraulic retention time (HRT) was 6 days, the effluent concentrations of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) were 6.66 mg L⁻¹ and 14.02 mg L⁻¹, respectively, and the removal rates of NH₄⁺-N and TN reached 77.54% and 71.07%, respectively. The T-HSCW had better removal efficiency of phosphorus. The effluent concentration of total phosphorus (TP) was lower than 0.3 mg L⁻¹, and the maximum removal rate could reach 98%. Through the characterization of the three substrates before and after experiments, it was found that the removal of nitrogen and phosphorus by T and G mainly relied on chemical adsorption, while S mainly relied on physical adsorption. Ti could also promote the absorption of nitrogen by plants and increase the nitrogen removal capacity of T-HSCWs.

Poultry houses emit large amounts of pollutants, e.g., ammonia and particulate matter (PM), that can affect public health, environment, and quality-of-life, due to odor. Poultry producers need low-cost and low-pressure treatments that can be compatible with existing ventilation systems. The porous windbreak wall coupled with a vegetative strip seems promising as it dissipates exhaust gases and traps PM (as well as adsorbed gases) on the screen, soil surface, as well as in the vegetation. Different windbreak wall-vegetative strip system designs were evaluated to treat the exhaust from 0.9-m fans in two types of layer house, for their abilities to reduce pollutant and odor emissions. The porous chamfered-shape windbreak wall with a footprint length of 3 fan diameters proved the most effective in reducing emissions. Even with a low system pressure of ~ 5 Pa, it greatly reduced odor, by 79% at 10 m and 59% at 5 m. It reduced TSP emissions moderately, by an average of 41%, while ammonia emissions were reduced slightly (by 21%). The chamfered screen was more readily cleaned by rainfall given the sticky nature of poultry house exhaust than the vertical screen. Overall, this low-cost, retrofittable, and modular system with a small footprint could be used by layer producers and, probably, by other poultry producers to reduce their emissions, alone or in combination with other mitigation methods to obtain greater reduction in emissions.

CO₂, SO₂, and NO are the main components of flue gas and can cause serious environmental issues. Utilization of these compounds in oleaginous microalgae cultivation not only could reduce air pollution but could also produce feedstock for biodiesel production. However, the continuous input of SO₂ and NO inhibits microalgal growth. In this study, the toxicity of simulated flue gas (15% CO₂, 0.03% SO₂, and 0.03% NO, balanced with N₂) was reduced through automatic pH feedback control. Integrated lipid production and CO₂ fixation with the removal of SO₂ and NO was achieved. Using this technique, a lipid content of 38.0% DW was achieved in Chlorella pyrenoidosa XQ-20044. The lipid composition and fatty acid profile indicated that lipid production by C. pyrenoidosa XQ-20044 cultured with flue gas is suitable as a biodiesel feedstock; 81.2% of the total lipids were neutral lipids and 99.5% of the total fatty acids were C16 and C18. The ratio of saturated fatty acids to monounsaturated fatty acids in the microalgal lipid content was 74.5%. In addition, CO₂, SO₂, and NO from the simulated flue gas were fixed and converted to biomass and lipids with a removal efficiency of 95.9%, 100%, and 84.2%, respectively. Furthermore, the utilization efficiencies of CO₂, SO₂, and NO were equal to or very close to their removal efficiencies. These results provide a novel strategy for combining biodiesel production with biofixation of flue gas.

Aerosol samples of PM₂.₅ and PM₁₀ were collected every 6 days from March 2012 to February 2013 in Huangshi, a typical industrial city in central China, to investigate the characteristics, relationships, and sources of carbonaceous species. The PM₂.₅ and PM₁₀ samples were analyzed for organic carbon (OC), elemental carbon (EC), char, and soot using the thermal/optical reflectance (TOR) method following the IMPROVE_A protocol. PM₂.₅ and PM₁₀ concentrations ranged from 29.37 to 501.43 μg m⁻³ and from 50.42 to 330.07 μg m⁻³, with average levels of 104.90 and 151.23 μg m⁻³, respectively. The 24-h average level of PM₂.₅ was about three times the US EPA standard of 35 μg m⁻³, and significantly exceeds the Class II National Air Quality Standard of China of 75 μg m⁻³. The seasonal cycles of PM mass and OC concentrations were higher during winter than in summer. EC and char concentrations were generally highest during winter but lowest in spring, while higher soot concentrations occurred in summer. This seasonal variation could be attributed to different seasonal meteorological conditions and changes in source contributions. Strong correlations between OC and EC were found for both PM₂.₅ and PM₁₀ in winter and fall, while char and soot showed a moderate correlation in summer and winter. The average OC/EC ratios were 5.11 and 4.46 for PM₂.₅ and PM₁₀, respectively, with individual OC/EC ratios nearly always exceeding 2.0. Higher char/soot ratios during the four seasons indicated that coal combustion and biomass burning were the major sources for carbonaceous aerosol in Huangshi. Contrary to expectations, secondary organic carbon (SOC) which is estimated using the EC tracer method exhibited spring maximum and summer minimum, suggesting that photochemical activity is not a leading factor in the formation of secondary organic aerosols in the study area. The contribution of SOC to OC concentration for PM₂.₅ and PM₁₀ were 47.33 and 45.38%, respectively, implying that SOC was an important component of OC mass. The serious air pollution in haze-fog episode was strongly correlated with the emissions of pollutants from biomass burning and the meteorological conditions.

Pursuing innovation effect or efficiency is an important trade-off that Chinese local governments need to face in the process of developing economy and protecting the environment. From the perspective of the policy portfolio, we employ the industrial panel data of 30 provinces in China during 2000–2015 to analyze the impacts of effectiveness-based innovation and efficiency-based innovation on ecological total-factor energy efficiency (ETFEE), and further analyze the effects of command-and-control, market-based and voluntary environmental regulations on innovation. The findings reveal that (1) both effectiveness-based innovation and efficiency-based innovation have significant promoting effects on ETFEE. (2) Three types of environmental regulations have significantly inhibitory effects on effectiveness-based innovation and efficiency-based innovation. (3) The interaction term of command-and-control and market-based regulations plays a significant role in promoting effectiveness-based innovation and efficiency-based innovation, whereas the interaction term of market-based and voluntary regulations merely promotes efficiency-based innovation. The interaction term of three types of regulation only has a synergetic and positive effect on the efficiency-based innovation. Finally, this paper gives specific policy recommendations.

The biosphere is polluted with metals due to burning of fossil fuels, pesticides, fertilizers, and mining. The metals interfere with soil conservations such as contaminating aqueous waste streams and groundwater, and the evidence of this has been recorded since 1900. Heavy metals also impact human health; therefore, the emancipation of the environment from these environmental pollutants is critical. Traditionally, techniques to remove these metals include soil washing, removal, and excavation. Metal-accumulating plants could be utilized to remove these metal pollutants which would be an alternative option that would simultaneously benefit commercially and at the same time clean the environment from these pollutants. Commercial application of pollutant metals includes biofortification, phytomining, phytoremediation, and intercropping. This review discusses about the metal-accumulating plants, mechanism of metal accumulation, enhancement of metal accumulation, potential commercial applications, research trends, and research progress to enhance the metal accumulation, benefits, and limitations of metal accumulators. The review identified that the metal accumulator plants only survive in low or medium polluted environments with heavy metals. Also, more research is required about metal accumulators in terms of genetics, breeding potential, agronomics, and the disease spectrum. Moreover, metal accumulators’ ability to uptake metals need to be optimized by enhancing metal transportation, transformation, tolerance to toxicity, and volatilization in the plant. This review would benefit the industries and environment management authorities as it provides up-to-date research information about the metal accumulators, limitation of the technology, and what could be done to improve the metal enhancement in the future.

This study employed a data envelopment analysis (DEA) by using slacks-based measure (SBM) with undesirable outputs to assess the industrial environmental efficiency of western China during the period of 2001–2015. The Malmquist index was further used to examine the changes in the industrial environmental efficiency of the analyzed region. The result showed that western China presented a low industrial environmental efficiency throughout the period of 2001–2015. Chongqing City was the only province that exhibited strong economic and environmental coordination. The level of technical development was identified as a key determinant of industrial environmental efficiency. This study provided policy implications on emissions reduction and the improvement of industrial efficiency. Limitations of the approach were provided to lay foundation for future studies.