No abstract

Activated carbon is used like adsorbent in removing gaseous and liquid pollutants besides purification and chemical recovery. However, its production has a high cost and has sought alternative precursors materials such as coffee grounds. The objective of this study was to determine the removal of caffeine in aqueous solution using activated carbon produced from coffee grounds by adsorption. The coffee grounds was impregnated with ZnCl2 and activated in aluminum capsules where it was used alcohol cotton and put fire to consume the oxygen inside. The adsorption test was performed with concentration of caffeine of 25 mg/L, 0.5 g of activated carbon in 100 mL samples, leaving the suspension under stirring for 120 minutes, in acid, neutral and basic pH. The pH range which obtained better removal was the neutral, removing 99.04% caffeine in 40 minutes. The kinetic test was performed in 20 minutes with the intraparticle model being the best fit.

The electrocoagulation of aqueous matrices has been gaining considerable attention because of the versatility and good results obtained. The treatability of rainwater was evaluated by means of electrocoagulation/flotation in cylindrical reactor with aluminium electrodes. The experimental procedure was conducted in pilot-scale reactor, operated in continuous flow with hydraulic detention time of 100 seconds and 12.3 current density mA/cm2. The reactor was built with acrylic tube on the dimensions of 8 cm in diameter and 60 cm in height, being the electrodes made with aluminum tube with 15 cm high. To assess the degree of treatability of rainwater were carried out analyses of pH, turbidity, color, chlorides, silica, hardness, alkalinity, conductivity, suspended solids and dissolved and chemical oxygen demand. The results were compared ABNT NBR 15527, Portaria 2914 and the ASME standard for boiler water, being that with the exception of the hardness, the other answered. These results showed the cost benefit of electrocoagulation/flotation, which showed spending U$ 1.12 per cubic meter of treated water.

Thymol, a monoterpene phenol, is used as a natural biocide. To circumvent its chemical instability, we propose use of thymol‐loaded biogenic silica nanoparticles (BSiO2#THY NPs); however, the toxicity of this system for aquatic organisms is unknown. Thus, the present study aimed to evaluate the toxicogenetic effects induced by thymol, BSiO2 NP, and BSiO2#THY on Artemia salina and zebrafish (Danio rerio) early life stages. We also investigated the impact of BSiO2 aggregation in different exposure media (saline and freshwater). Based on the median lethal concentration at 48 h (LC5048h), BSiO2#THY (LC5048h = 1.06 mg/L) presented similar toxic potential as thymol (LC5048h = 1.03 mg/L) for A. salina, showing that BSiO2 had no influence on BSiO2#THY toxicity. Because BSiO2 aggregated and sedimented faster in A. salina aqueous medium than in the other medium, this NP had lower interaction with this microcrustacean. Thus, BSiO2#THY toxicity for A. salina is probably due to the intrinsic toxicity of thymol. For zebrafish early life stages, BSiO2#THY (LC5096h = 13.13 mg/L) was more toxic than free thymol (LC5096h = 25.60 mg/L); however, BSiO2 NP has no toxicity for zebrafish early life stages. The lower aggregation of BSiO2 in the freshwater medium compared to the saline medium may have enhanced thymol's availability for this aquatic organism. Also, BSiO2#THY significantly induced sublethal effects as thymol, and both were genotoxic for zebrafish. In conclusion, although BSiO2#THY still needs improvements to ensure its safety for freshwater ecosystems, BSiO2 NP seems to be a safe nanocarrier for agriculture. Environ Toxicol Chem 2021;40:333–341. © 2020 SETAC