The objective of this study is to investigate the adsorption performance of activated carbon derived from the leaves of Cordia africana for the removal of Cr (III) from an aqueous solution. The plant sample was collected, washed, dried, grounded, and sieved at 125 μm mesh size. Adsorbent activation was done using H3PO4 at concentrations of 25–85% and pyrolysis temperature of 400–500°C. The activated carbon was characterized by proximate, SEM, BET, and FTIR analyses. A batch adsorption study was conducted to determine the effect of contact time, adsorbent dose, initial chromium concentration, and mixing speed on Cr (III) removal. The regeneration of the activated carbon was investigated by using 1 M of HNO3 as a desorbing solution for seven cycles. At optimum acid concentration and pyrolysis temperature, a surface area of 700 m2/g was recorded. The moisture content, volatile matter, ash composition, fixed carbon, and bulk density of the activated carbon were found to be 5.3%, 24.2%, 6.2%, 64.3%, and 0.75 g/mL, respectively. The SEM and FTIR analyses indicated that the surface morphology was full of cracks and different peaks were associated with plenty of functional groups, respectively. The maximum Cr (III) removal was attained at a contact time of 180 min (89%), adsorbent dose of 1.5 g (54%), initial concentration of 0.6 g/L (47%), and mixing speed of 300 rpm (64%). The equilibrium data were better described by Freundlich isotherm at R2 value of 0.88, which implies that the adsorption process is conducted on a heterogeneous surface. The pseudo-first-order kinetics model with R2 value of 0.99 best fits with the equilibrium data, which implies that physisorption controls the adsorption kinetics. Generally, it can be concluded that this locally prepared adsorbent is promising for the removal of chromium from industrial wastewater, but further factorial approach assessment has to be checked.

This study was focused on the synthesis of activated carbon from a waste tire and the enhancement of its specific area by a demineralization technique that can be used for the removal of methylene blue dye (MB). Maximum MB removal (89.41%) was attained at an impregnation ratio value of 0. A maximum yield (42.65%) was found at 48 h. Waste tire-based activated carbon (WTAC)'s ability to remove MB was increased by large values up to an impregnation time of 24 h. WTAC has a maximum MB removal of 90.13% at 4 M of KOH. The sample had a surface area of 53 m2/g. This sample was demineralized by using NaOH and H2SO4 in a 1 : 1 ratio, and the surface area was enhanced to 257 m2/g. In the demineralization process, a massive decrement of metals from the waste was seen; for each metal, namely, Zn2+, Al3+, Ca2+, and Mg2+, 43.79%, 32.45%, 27.95%, and 6.843% reductions were achieved, respectively. After this process, the maximum removal of MB was found at 1.2 g adsorbent dosage, 120 min, pH 8, the temperature of 20°C, and an initial dye concentration of 10 mg/L. The adsorption mechanism revealed that the process of adsorption happens at a specific site of homogeneous adsorption on the surface of the adsorbent. The kinetics study showed that the adsorption process of the dye is mainly affected by the chemical reaction.

This study aimed to investigate the synthesis optimization of activated carbon-driven scrap tires for adsorbent yield and methylene blue removal under response surface methodology. The scrap tire sample was activated by KOH using ethanol as a solvent. The optimized activated carbon was characterized using proximate analysis, scanning electron microscope (SEM), X-ray diffraction (XRD), and Brunauer Emmett Teller (BET) method. The activated carbon was demineralized using 5 M NaOH +  98% H2SO4 (1 : 1) as a solvent to enhance the surface area. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models were used to check the adsorption isotherm. The adsorption kinetics was checked using pseudo-first-order and pseudo-second-order models. Weber-Morris intraparticle diffusion model was used to study the diffusion mechanism. The optimum impregnation ratio, impregnation time, and carbonization temperature for synthesizing the activated carbon were 2 g/g, 12 hr, and 700°C, respectively. The moisture content, volatile matter, ash content, fixed carbon, and bulk density of the activated carbon were 6.13%, 9.42%, 5.34%, 79.11%, and 0.89 mg/L, respectively. The surface area of optimized activated carbon was enhanced by demineralization process and increased from 53 m2/g to 260.26 m2/g. Temkin adsorption isotherm with R2 values of 0.982 and pseudo-second-order adsorption kinetics with R2 values of 0.999 best fits the experimental data respectively. Intraparticle diffusion was not the only rate-controlling step for both optimized and demineralized (NaOH + H2SO4) activated carbon. It can be concluded that the optimized and demineralized activated carbon derived from scrap tires has a promising potential to be used as a low-cost adsorbent in developing countries including Ethiopia. However, further investigation needs to be conducted before scaling up at industrial level.

is one of the ten sub-cities of Addis Ababa, where the biggest market and the biggest bus station in Ethiopia are located. The liquid waste that is generated from this sub-city is not being handled properly. The objective of this study is to assess the liquid waste handling practice of Addis Ketema and its impact on Shankela River. The data is collected by observation, interviewing garage employees, and interviewing residents. In addition, a triplicate water sample was collected from four sampling sites of Shankela River by using grab sampling. The physicochemical characteristics of the river such as temperature, pH, electric conductivity, dissolved oxygen, total suspended solids, total dissolved solids, biological oxygen demand, and chemical oxygen demand were analyzed to determine the impact of the poor liquid waste handling practice of the sub-city on the river. The main reasons that contributed to the poor liquid waste handling practice of Addis Ketema are the discharge of untreated effluents from small and large scale factories, the migration of people from different parts of the country, the poor liquid waste handling practice of residents, the poor solid waste handling practice of Merkato and Autobis Tera, the poor liquid waste handling practice of condominium's and the poor liquid waste handling practice of garages. The interview result shows that out of 81garage employees, only 43 percent have a perception about the health and environmental impacts that come with the poor handling of garage effluent. The questioners that are collected from residents show that compared to other zones, zone 3 has poor liquid waste handling practice. Zone 3 is the third zone with 61 out of 100 residents in having low perception about environmental pollution. It is the first zone in having large number of residents, with 87 out of 100 residents, to be affected with water-borne diseases. It is the third zone with 62 out of 100 residents in dumping their liquid waste improperly. It is the last zone with 12 out of 100 residents in handling the generated liquid waste properly and it is the second zone with 45 out of 100 residents in using bottled water over the water that is supplied by Addis Ababa water and sewerage authority. The physicochemical characteristics of Shankela River indicate that even though the river is polluted by other factors before entering into the sub-city, the poor liquid waste handling practice of the sub-city is affecting the river even more by increasing the pollutant load. Developing sanitary infrastructures, Awareness creation, enforcing environmental laws are some of the methods that can be employed to improve the poor liquid waste handling practice of Addis Ketema.