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.

Energy demand is increasing due to population increment and industrialization. To meet this energy demand, technologies that use renewable energy such as solar energy are being developed. A parabolic solar cooker is one of the main solar cookers, which can cook food and boil water at a high temperature within a short period. This study aimed to design, construct, and evaluate the performance of the constructed parabolic solar cookers. Moreover, this study aimed to compare the constructed cooker with firewood, charcoal, kerosene, and electricity in terms of cooking time and energy cost. The cooker was constructed using different materials such as old satellite dishes, tyres, steel, and aluminum foil. The aperture diameter, aperture area, receiver diameter, receiver area, depth of the parabola, focal length, rim angle, circumference of the circle, surface area, length of the circumference, and concentration of the cooker were 1.8 m, 2.54 m2, 0.16 m, 0.02 m2, 0.3 m, 0.67 m, 67.38°, 5.76 m, 2.81 m2, 5.76 m, and 123.46, respectively. The cooker can track the sun from north to south and from east to west. The performance of the cooker was evaluated by calculating the efficiency and power. The output energy, input energy, and average upcoming solar radiation of the constructed parabolic solar cooker were 0.182 kW/m2, 1.691 kW/m2, and 0.665 kW/m2, respectively. The efficiency and power of the cooker were 10.75% and 0.3 kW/hr, respectively. The constructed parabolic solar cooker relatively showed better performance in cooking different foods. A family, which has five members, was considered to compare the constructed cooker with other fuels in terms of energy cost of cooking. Since the parabolic solar cooker does not have any energy cost, it can save the energy cost of cooking foods. Therefore, parabolic solar cookers have a great advantage for developing countries including Ethiopia.

Tannery industries’ effluent contains a high concentration of Cr (VI) which has the potential to affect the environment and public health. Therefore, this study aimed to investigate the optimization of Cr (VI) adsorption by activated carbon (AC) derived from Eichhornia crassipes from an aqueous solution. The adsorbent was activated with dilute sulfuric acid followed by thermal activation. AC was characterized using proximate analysis, SEM, FTIR, X-ray diffraction, and the BET method. The Cr (VI) removal optimization process was performed using a central composite design under the response surface methodology. The proximate analysis showed that the moisture content, volatile matter, ash content, and fixed carbon of the activated carbon were 5.6%, 18.2%, 14.4%, and 61.8% respectively. The surface areas of the Eichhornia crassipes before activation, after activation, and after adsorption were 60.6 g/m2, 794.2 g/m2, and 412.6 g/m2 respectively. A highly porous structure with heterogeneous and irregular shapes was observed in the SEM micrograph. In the FTIR analysis, different peaks are indicated with various functional groups. The intensity of XRD peaks decreased as 2 theta values increased, which indicates the presence of an amorphous carbon arrangement. The point of zero charge (pHpzc) of the activated carbon was found to be 5.20. A maximum Cr (VI) removal of 98.4% was achieved at pH 5, contact time 90 min, adsorbent dose 2 g, and initial Cr (VI) concentration of 2.25 mg/L. Statistically significant interactions (P < 0.05) were observed between the initial Cr (VI) concentration and adsorbent dose as well as the initial Cr (VI) concentration and contact time. Langmuir adsorption isotherm fitted the experimental data best, with an R2 value of 0.99. The separation constant (RL) indicates that the adsorption process is favorable. The kinetic experimental data were best fitted with the pseudo-second-order model with an R2 value of 0.99 whereas the adsorption rate is controlled by intraparticle and extragranular diffusion processes. Generally, the AC has the potential to be a strong adsorbent candidate for wastewater treatment at the industrial level.

This study aimed to evaluate the treatment potential of gradual hydroponics planted with Duranta erecta in the removal of pathogens from domestic wastewater. Two experimental and control units were configured in series. Each unit contains three bioreactors and was arranged in a cascaded configuration. The two experimental units used both plant and media, but the two control units used only media to treat the wastewater. Gravel and polyester sponge were used as media. Experimental unit 1 and control unit 1 used gravel as media; however, experimental unit 2 and control unit 2 used polyester sponges as media. The experiment was operated at hydraulic retention times of 1, 3, 5, and 7 days in a continuous mode. The performance of the hydroponic system was evaluated by characterizing the influent and effluent quality using standard methods. At optimum hydraulic retention time (7 days), the average removal of experimental units 1 and 2 was 98.7% and 89.8% for heterotrophic bacteria, 96.2% and 86.8% for total coliform, and 92.9% and 84.0% for fecal coliform, respectively. Analysis of variance showed that there was a significant difference P < 0.05 between the two experimental and control units in removing pathogens, but no significant difference P > 0.05 was observed between the two experimental units and between the two control units. Heterotrophic bacteria and coliforms were satisfactorily removed from domestic wastewater via a gradual hydroponic system. Hence, the hydroponic treatment system planted with Duranta erecta has a promising potential in the removal of pathogens from domestic wastewater in developing countries including Ethiopia.

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.