مجله آب و فاضلاب
پیاپی 143 (بهمن و اسفند 1401)

Cyanide ion is highly toxic to human. Cyanide ion is mainly used in processes like electroplating and extraction of silver and gold. Therefore, it can enter the environment and pollute soil and water. In the present work, a colorimetric method based on silver nanoparticle (AgNP) was proposed for detection and determination of cyanide ion. Silver nanoparticle was prepared by carbon dots as reducing agent. Volume of AgNP and concentration of sodium hydroxide were optimized for determination of cyanide ion by AgNP. It was observed that greenly synthesized AgNP can serve as reagent in detection and determination of cyanide ion. In the presence of sodium hydroxide, a method was optimized and a robust model with linear range of 4.0-100.0 μM, limit of detection of 3.8 μM and limit of quantification of 12.7 μM was obtained. In the method presented, the color change of AgNP from yellow to colorless in the presence of cyanide ion was observed. Environmental water samples including spring, well and wastewater were successfully analyzed by this method, which is simple and inexpensive.

Several types of research have been performed to desalinate the water efficiently. Solar energy, as a low-cost, abundant, and clean energy, has a great potential to alleviate water shortages. Solar water desalination has been considered as an efficient method to utilize in the water desalination process. A solar water evaporation and condensation system are implemented to desalinate water. Solar evaporator system has been proposed and used to produce clean water. High solar energy conversion efficiency requires excellent light absorption, thermal conduction, and water supply performance. Several parameters, such as fluid inlet temperature or inlet velocity, were investigated. The results indicate the best performance in the 1 L/min flow rate and 0.6 m of tube length. Computational fluid dynamics using the COMSOL program was used to analyze the process and find the optimum process conditions.

One of the most recent environmental concerns is the emergence of new pollutants, such as antibiotics, and increasing antimicrobial resistance in bacteria. Therefore, achieving effective methods for treating these pollutants is very important and considerable. Extensive studies have been conducted on antibiotic removal from water by carbon-based materials. Engineered biochar-based adsorbents and biochar composites can effectively increase the yield of antibiotics adsorption. Adsorbents based on biochars are made from various raw materials at different conditions. Also, physically and chemically modified biochars and their composites could be used. The structure and physicochemical properties of adsorbents and antibiotics and the environmental conditions affect the absorption of antibiotics by biochars. Research has shown that biochar has many advantages, including a wide variety of available raw materials, and they are cheap. Furthermore, it could be regenerated and reused by efficient management, which is the significant advantage of biochar-based adsorbents. Although biochar usage is a good choice for removing antibiotics from aqueous solutions, it is possible to improve its adsorption capacity with more studies to optimize the main parameters and new methods in its production and thus cause economic benefits.

In this work, the process of biogas production from palm oil factory effluent was simulated and then the produced biosynthetic gas was sweetened. For this purpose, the biogas production process from wastewater treatment was simulated using SuperPro Designer v9.0 software. Then, the resulting biogas entered the chemical absorption and reforming sections for sweetening and conversion to syngas, respectively, and these steps were simulated with Aspen HYSYS v11.0 software. The simulation results of the first stage showed that the effluent feed of this factory with a flow rate of 42000 kg/h and COD of 62000 mg/L leads to the production of 1786 kg/h biogas containing various compounds such as methane, carbon dioxide, hydrogen sulfide and water with the molar fraction of 0.446, 0.245, 0.178 and 0.040, respectively. In the chemical absorption section, MEA solvent 10 %wt. and solvent-to-gas molar ratio of 13.51 were used, which led to the efficient removal of CO2 and H2S up to 1 ppm and 99.99%, respectively. The examination of temperature changes in the absorption tower also showed that the temperature increases along the absorption tower. In the methane steam-reforming unit, two different strategies were used: 1) plug flow reactor (with fluid package of Peng-Robinson-Stryjek–Vera) and 2) conversion and equilibrium reactors (with fluid package of Peng-Robinson). The results showed that the purity of hydrogen in the biogas produced in the second strategy (conversion and equilibrium reactors) was higher than the first one (plug flow reactor), and on the other hand, the purity of CO2 was zero in the second strategy.

Water is the most important material that humans and creatures need, and water contamination caused by chemicals such as dyes has brought many problems. Various methods have been used to remove dyes as organic contaminants. Polymeric nanofibers prepared by electrospinning have a nanostructure with a high adsorption capacity for removing water contaminants. To solve this problem, the adsorption process is used, which is very effective for removing water pollutants. The adsorption process is very important in terms of expense and reuse. The use of natural polymers is being promoted as a suitable alternative to synthetic polymers and to reduce environmental pollution. The results indicate that preparing nanofibers by electrospinning and using them as adsorbents is a suitable method to remove contaminants. The effect of operational parameters on the adsorption removal ability of polymeric nanofibers, the optimal adsorption conditions, and the mechanism of dye adsorption have been investigated in detail. The data indicated that polymeric electrospinning nanofibers can be used as environmentally friendly and effective adsorbents for removing water contaminants. Also, the treated dye wastewater is reused in the dyeing process and is not discharged into the environment to conquer the water shortage.

In the adsorption process of heavy metals, a major challenge is to design and develop adsorbent materials in an abundance of accessible adsorption sites with high affinity to achieve both fast adsorption kinetics and increased adsorption capacity for toxic contaminants. The removal of pollutants by mesoporous silica adsorbents is now in the limelight due to the nontoxicity and biocompatibility of these materials with the environment. In this study, a fibrous core-shell magnetic mesoporous composite (Fe3O4/SiO2/KCC-1) was successfully synthesized and used as a nano-adsorbent to remove Pb(II) from an aqueous solution. The adsorbent was characterized by employing TEM, SEM, FTIR, VSM, XRD, and N2 adsorption–desorption techniques. According to the results, Fe3O4/SiO2/KCC-1 was successfully synthesized with an average pore diameter of 7.94 nm, a surface area of 813.07 m2 g-1, and a pore volume of 1.41 cm3 g-1. The response surface methodology (RSM) was then adopted in the central composite design (CCD) to optimize parameters of the adsorption process. The optimal conditions for Pb(II) adsorption were then determined at a temperature of 80 °C, an adsorption dosage of 0.04 g L-1, a pH 5.6, and the contact time of 38 min. The removal rate of Pb(II) was 90%. Studies of equilibrium and kinetics indicated that the adsorption process followed Langmuir’s isotherm and the pseudo-first-order model with correlation coefficients of 0.98 and 0.99, respectively. The maximum adsorption capacity of Fe3O4/SiO2/KCC-1 was reported 574.4 mg g-1. Moreover, the thermodynamic parameters known as enthalpy (ΔH° = +5.84 kJ mol-1), negative Gibbs free energy (∆G°) values, and entropy (ΔS° = +23.42 kJ mol-1 K-1) indicated that the adsorption was endothermic and spontaneous with the increased disorder at the solid–liquid interphase.