Under the current global warming scenario, with temperatures expected to reach 1.5 °C above pre-industrial levels between 2030 and 2052, the role of terrestrial ecosystems’ vegetation in removing carbon (C) from the atmosphere takes on even more importance. In particular, there is a need for researchers to emphasize and further quantify the environmental role of vegetation types such as agro-ecosystems. Woody crops like orchards typically dominate the landscape and the rural economy in producing areas of the Mediterranean region. In this context, the present study aimed to quantify the amount of carbon dioxide (CO₂) sequestered by one of the most important tree crop species widely diffused across the Mediterranean region: Corylus avellana L. (hazelnut). Overall, the results highlighted that the hazelnut orchards under consideration, subjected to routine horticultural care, sequestered a total amount of CO₂ of 58.8 ± 9.1 Mg ha⁻¹ year⁻¹ (mean value), with the highest amount of CO₂ sequestered recorded in May (12.4 ± 2.0 Mg CO₂ ha⁻¹ month⁻¹). Considering also that the area covered by hazelnut cultivation is continuously increasing, we can conclude that this cultivation is important not only for the orchards’ nut production but also for their role as carbon sinks.

Orange and banana peels were dried, chopped, and briquetted under pressures of 2, 3, and 5 tons/cm², and then carbonized at 600 °C for 60 min to investigate some of their physical and thermal properties for use as sustainable carbon and fuel sources. The effects of compaction/briquetting loads on density, durability, and ignition temperature were analyzed for both non-carbonized and carbonized orange and banana peel briquettes. The acceptable compaction load was found to be 2 and 5 tons/cm² for orange and banana peel briquettes, respectively. The acceptable manufacturing condition in order to have less weight reduction in the drop test in terms of durability for solving handling and transportation problems was 2 tons/cm² for both orange and banana peel briquettes. Ignition temperature tests showed that orange peel briquettes produced under 3 tons/cm² and banana peel briquettes produced under 5 tons/cm² had acceptable ignition temperatures. In the case of carbonized briquettes, the acceptable compaction load for orange and banana peel briquettes was 5 and 2 tons/cm², respectively. Based on the analysis of compression strength tests, residual strengths were 2.15, 2.18, and 2.30 MPa for orange peel briquettes and 1.74, 2.03, and 2.45 MPa for banana peel briquettes under 2, 3, and 5 tons/cm², respectively. By increasing the compaction load, residual strengths were increased for both orange and banana peels; however, beyond 5 tons/cm², the quality of the briquettes deteriorated.

Combined application of biochar and organic fertilizer has been widely recommended for improving soil bio-physical properties. However, detailed exploration of combined application on crop eco-physiological performance is limited. In this study, we explored the agronomic and eco-physiological responses of wheat crop grown under different combinations of rice-husk ash (RHA/biochar), farmyard manure (FYM) and chemical fertilizers in a silty loam soil. Aboveground biomass varied significantly across the treatments and was found higher (11–31%) under chemical fertilizer-applied treatments, but lower (6%) under sole RHA-applied treatment as compared to control. Crop eco-physiological parameters varied significantly (at P < 0.01) with the treatment and crop growth stages. Sole chemical fertilizer- and FYM-applied treatments showed better (5–26% higher), whereas sole RHA- and combined RHA + FYM-applied treatments showed poor (2–15% lower) photosynthetic rate as compared to control. Ear length was moderately correlated (r = 0.53) with aboveground biomass and explained 27% of the variability in it. Transpiration rate, intercellular CO₂ concentration and water-use efficiency (WUEp) were identified as the major determinants of photosynthetic rate during vegetative and maturity growth stages. WUEp along with transpiration rate was found to explain 94% of the variability in photosynthetic rate for overall dataset. The findings suggest that combined RHA + FYM amendment may limit crop agronomic and eco-physiological performance due to nutrient immobilization. Therefore, combined application of RHA + FYM with chemical fertilizer application at reduced rate can be suggested for improving crop eco-physiological and agronomic responses under the sustainable agriculture practices in silty loam soils of tropical dryland agro-ecosystems.

Discharging volumes of leather tanneries’ wastewater into the environment without proper treatment is causing severe environmental and public health problems. Therefore, this research aimed to remove chromium ion from tannery wastewater through the adsorption of activated carbon produced from the weed Parthenium hysterophorus. The activated carbon was characterized using proximate analysis, scanning electron microscope, Fourier transforms infrared spectroscopy and an iodine test. Full factorial experimental design of 2⁴ was employed with four factors at two levels pH (2 and 6), contact time (45 and 90 min), initial chromium concentration (40 and 100 mg/L) and adsorbent dosage (9 g/L and 90 g/L), which resulted in 16 experimental runs. The average tannery effluent characteristics were described in terms of Five days biochemical oxygen demand: 1472.00 ± 9.300 mg/L; chemical oxygen demand: 1800.00 ± 50.00 mg/L; total solids: 29,000.00 ± 1000.00; temperature: 21.50 ± 2.01 °C; electrical conductivity (EC): 29.20 ± 1.60 mS/cm and pH: 4.30 ± 0.71. The mechanism of adsorption was tested by the Langmuir and Freundlich isothermal models. Maximum chromium removal of 90% was recorded at the optimum point of pH 2, contact time 90 min and adsorbent dose 90 g/L at initial chromium concentration 100 mg/L. Similarly, the treatment of the real tannery wastewater treatment was performed at the optimum point, which resulted in 89% chromium removal. Experimental data were best fitted with the Freundlich model at the adsorptive capacity 24.8 mg/g. This indicates that the application of this activated carbon for tannery wastewater treatment may be scaled up to mitigate industrial effluent pollution challenges, but detailed investigations of the adsorbent properties remain to be studied.

In this article, we developed a process to design batch algal cultivation systems consisting of outdoor ponds, indoor photobioreactors (PBRs), outdoor PBRs, and indoor ponds for both freshwater and industrial wastes (wastewater and flue gas). We considered pH, temperature, light conditions, carbon, nutrients, inhibitors, mixing, and O₂ degassing as design parameters and sequentially ranked them according to the necessity of cultivation conditions. Although each set of conditions warrants a unique design according to the requirements, some scenarios were common for every system, i.e., microalgae species, temperature, pH, light, size, shape, and material were always ranked before nutrients, and mixing technique and inhibitors were consistently ranked after nutrients. Light and temperature for outdoor conditions, pH for ponds, and nitrogen and phosphorus were deemed noncontrollable. Ponds do not require material for construction; O₂ degassing and the selection of microalgae were always ranked first; and SO _x and NO _x were considered only for industrial flue gas. We constructed cultivation models of Chlorella vulgaris (C. vulgaris) for Bangkok based on the developed designs of algal cultivation systems. Monod’s model (mathematical model) and simulations by SuperPro Designer software using the optimum parameter values predicted a maximum algal productivity of 0.0114–0.0381 and 0.11–0.7 g/l/day (open pond and PBR, respectively), bioremediation of 52–70% and 81–90% (open pond and PBR; only wastewater), and CO₂ biofixation of < 1% (only PBR). A comparison between the results found in this study and the literature on C. vulgaris suggests that both Monod’s model and simulation software can predict algal productivity and bioremediation, but they are not recommended for CO₂ biofixation.

While the concept of environmental Kuznets curve (EKC), which links economic growth to environmental degradation, is well demonstrated, there is disagreement on its shape, extent and determinants. This study investigates the EKC hypothesis in Bahrain and assesses the impact of electricity consumption, foreign direct investment and financial development on CO₂ emissions using time series data over the period 1980–2014. To accomplish this target, the autoregressive distributed lag bounds testing approach is employed, and the results show that the series are cointegrated. Moreover, there is an inverted U-shaped long-run relationship between CO₂ emissions and economic growth, confirming the existence of EKC for Bahrain. In other words, economic growth in Bahrain raises the level of environmental emissions until it reaches a specific threshold of per capita income and then starts to decline. In addition, while more electricity consumption continues to contribute to increasing the level of CO₂ emissions, having more foreign direct investments improves the quality of air in Bahrain. Based on these findings, Bahrain should reduce emissions through expanding CO₂ recovery plants projects and invest more in energy research to achieve efficient electricity generation.