In this study, several biowaste materials are screened for adsorptive removal of methylene blue (MB) from synthetic water. Among the tested adsorbents, barley (Hordeum vulgare) bran (BB) and enset (Ensete ventricosum midrib leaf, EVML) were selected for further evaluation of MB (a model cationic dye) adsorption. Batch MB adsorption performance of BB and EVML adsorbents was significantly high in a wide pH range (4-9). The well fitting of experimental data with pseudosecond-order kinetic model suggests a monolayer adsorption of MB. The MB adsorption onto both adsorbents was fit well with the Langmuir isotherm model with maximum MB adsorption capacities of 63.2mg/g (BB) and 35.5mg/g (EVML). The biowaste materials exhibit considerable adsorption capacity for cationic dye (MB), perform well under acidic and basic conditions, and are reusable. Therefore, the use of these materials as adsorbents may have an environmental benefit in terms of the conversion of wastes into valuable materials. Further studies are suggested to investigate the performance of these adsorbents in a continuous mode using real wastewater.

The wide use of chromium (Cr) in different industries led to the release of a considerable amount of Cr(VI) into water bodies. Exposure to Cr(VI) can cause diseases in humans and animals. Therefore, low-cost technology for Cr(VI) removal is required. In this study, the biowastes, Tella residue (TR) and Pea (Pisum sativum) seed shell (PSS), were evaluated for their Cr(VI) removal efficiency from aqueous solutions. The physicochemical properties of adsorbents were studied, and the adsorbents were further characterized using FTIR and XRD. Batch adsorption experiments have shown that the Cr(VI) uptake was pH-dependent and found to be effective in a wide range of pH values (pH 1 to 10) for PSS. The kinetics of Cr(VI) removal by the adsorbents was well expressed by the pseudo-second-order model. The experimental equilibrium adsorption data fitted well with Freundlich isotherm indicating multilayers adsorption. The estimated Cr(VI) adsorption capacities of TR and PSS were 15.6mg/g and 8.5mg/g, respectively. On top of this, the possibility of reusing adsorbents indicates the potential applicability of TR and PSS for the treatment of Cr(VI) contaminated water. Further study on the evaluation of the efficiency of the adsorbents using real chromium-contaminated wastewater is recommended.

Freeze desalination, i.e., desalination of water by freezing it, may be an option to treat polluted water at individual household level. Taking into account the widespread fluoride contamination of Ethiopian water resources and with the reason that most households in semi-urban and urban areas do have easier accessibility of refrigerators, this study aimed to investigate the defluoridation capacity of freeze desalination and its energy consumption for different water sources. For this purpose, synthetic solutions that emulate the major ion compositions of natural waters (hereafter called simulated water), tap water, and double-distilled water to which variable concentrations of fluoride ions were added were evaluated using home-use insulated refrigerator (BEKO, RRN 2650). The effects of conditions such as initial fluoride concentration, multi-ion existence, fraction of ice frozen, volume of the container, and freezing duration were evaluated in relation to the produced ice quality. It was found that nearly 48% and 62% removal of fluoride were achieved from tap water spiked with 10 mg/L F⁻ and 10 mg/L F⁻ aqueous solutions, respectively, with a total water recovery of 85 to 90%. The energy consumption predicted to produce the ice from tap water spiked with 10 mg/L F⁻ and double-distilled water alone was found to be 93.9 and 91.8 kJ/L, respectively. The results showed that freeze desalination can be a potential technique for fluoride removal from water to be used as drinking water at household level in semi-urban and urban areas as well as in colder regions.

Polyaniline-based materials have been widely used for supercapacitors due to their outstanding properties, such as high specific capacitance, excellent electrochemical properties, and ease of synthesis methods; however, the short-cycle stability of PANI-based supercapacitors and swelling and shrinking of polymeric structures limit their commercialization. Herein, we synthesized polyaniline (PANI) nanomaterials, which meet high specific capacitance through the chemical oxidative polymerization of aniline with ammonium persulfate (APS) in aqueous salicylic acid. The electrode materials were characterized using UV–vis, TGA, SEM, XRD, BAS-50 W potentiostat, and FTIR instrumentations. The electrical conductivity of the prepared materials was analyzed and found to be relatively high. The electrochemical supercapacitance performance of PANI nanomaterials was characterized using cyclic voltammetry. The polyaniline nanomaterials with a [salicylic acid]/[aniline] molar ratio of 0.8 showed a maximum specific capacitance of 688.5 Fg-1 at a scan rate of 50 mV s⁻¹. Polyaniline nanomaterials were found to exhibit better specific capacitance when compared to bulk polyanilines. Thus, PANI nanomaterials have been found to be a promising alternative for supercapacitor applications.