This study aimed to model the flow of streams and identify the sub-basins responsible for the high flow in the Didessa watershed, southwest Ethiopia, considering the regional soils types. Soil and Water Assessment Tool (SWAT) model was used to simulate stream flow and quantify surface runoff. The input data used were Digital Elevation Model (DEM), land use/land cover map, soil map and metrological data. The data were obtained from Ministry of Water, Irrigation and Electricity and National Meteorology Agency of Ethiopia. Simulation of SWAT was used to identify the most vulnerable sub-basins to the hydrological process. The model was calibrated and validated using the stream flow data. The simulated stream flow was calibrated by the SWAT-CUP2012 calibration sub-model of SWAT-CUP SUFI2. Sensitivity analysis showed that curve numbers (CN2), ALPHA-BNK and CH-K2 are the most sensitive top three parameters. The R2 and Nash-Sutcliffe Efficiency (NSE) values were used to examine the model performance. The results indicate 0.84 and 0.80 for R2 and 0.65 and 0.54 for NSE during calibration and validation, respectively. The average annual surface runoff in the delineated catchment was 774.13 mm. Changes in precipitation explained 89% of the variation in surface runoff, as more than 89% of precipitation from the catchment converted to surface runoff. The most three annual surface runoffs contributing were the 11, 23 and 5 sub-basins. INFLUÊNCIA DO TIPO DE SOLO NO FLUXO DE CÓRREGOS PARA A BACIA SUPERIOR DO RIO DIDESSA, SUDOESTE DA ETIÓPIA UTILIZANDO O MODELO SWATResumoEste estudo teve como objetivo modelar o fluxo de córregos e identificar as sub-bacias responsáveis pelo alto fluxo na bacia hidrográfica do Rio Didessa, sudoeste da Etiópia, considerando os tipos de solos regionais. O modelo SWAT (Solo and Water Assessment Tool) foi utilizado para simular o fluxo da corrente e quantificar o escoamento superficial. Os dados de entrada utilizados foram o Modelo Digital de Elevação (DEM), mapa de uso / cobertura do solo, mapa do solo e dados metrológicos. Os dados foram obtidos no Ministério da Água, Irrigação e Eletricidade e Agência Nacional de Meteorologia da Etiópia. A simulação do SWAT foi utilizada para identificar as sub-bacias mais vulneráveis ao processo hidrológico. O modelo foi calibrado e validado usando os dados de fluxo dos córregos. O fluxo de corrente simulado foi calibrado pelo submodelo de calibração SWAT-CUP2012, do SWAT-CUP SUFI2. A análise de sensibilidade mostrou que os números da curva (CN2), ALPHA-BNK e CH-K2 são os três principais parâmetros mais sensíveis. Os valores de R2 e Nash-Sutcliffe Efficiency (NSE) foram usados para examinar o desempenho do modelo. Os resultados indicam 0,84 e 0,80 para R2 e 0,65 e 0,54 para NSE durante a calibração e validação, respectivamente. O escoamento superficial médio anual na bacia hidrográfica foi de 774,13 mm. Mudanças na precipitação explicaram 89% da variação no escoamento superficial, pois mais de 89% da precipitação da bacia foi convertida em escoamento superficial. As sub-bacias 11, 23 e 5 foram as que mais contribuíram para os fluxos superficiais anuais da Bacia do Rio Didessa. Palavras-chave: Tipo de solo. Análise sensitiva. Fluxo de córregos. Swat-Cup. Bacia Superior do Rio.

The contamination of surface and groundwater with phosphate originating from industrial, agricultural and household wastewater remains a serious environmental issue in low-income countries. Currently, demolished concrete is mainly recycled as aggregate for reconstruction and conventional wastewater treatment systems for removing phosphate are expensive and complex. In this study, we were aiming at testing crushed concrete as an efficient adsorbent for the removal of phosphate from aqueous solutions, obtained from the demolition of construction site. It can reduce pollution and landfill disposal by converting construction waste into valuable products and an alternative solution for phosphate removal. Batch adsorption experiments were conducted using phosphate solutions to examine the adsorption kinetic as well as equilibrium conditions. Results show that the phosphate adsorption of all absorbents follows the adsorption isotherms with a varying phosphate concentration from 3 mg/L to 18 mg/L, and the adsorption isotherms data are fitted well by Langmuir equation as compared with the Freundlich isotherm. The maximum phosphate adsorption (97.67 %) was obtained at a contact time of 120 min, an initial phosphate concentration of 10 mg/L, and a solution pH of 4. The pseudo second-order equation describes the experimental data has good agreement, with a correlation value of R2 = 0.99. The results obtained indicate that the environmentally available crushed concrete have a good adsorptive capacity for phosphate and shall be considered in future studies as test materials for phosphate removal from water in technical-scale experiment.

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Pollution of surface water with harmful chemicals and eutrophication with excess nutrients are recent serious environmental concerns. This lends the need of knowing the nutrient loading and transport mechanism that will occur with different spatial and temporal extent. Thus, effective information regarding the nutrients load and transport mechanisms are important to hydrologists, water use planners, watershed managers and decision makers for water resource projects and planet ecosystem. Our study aimed for modeling of phosphorous loading and its transport pathways and to identify the most vulnerable sub basin responsible for a significant phosphorus load in Dhidhessa catchment using Soil and Water Assessment Tool (SWAT) model. The pathways of phosphorus were identified and found that the organic phosphorus was dominant exporting mechanism accounted for 58.89% of the total path in the study area. For all forms of phosphorus, surface run off was the most dominant means of transport agent. The average annual loading of total phosphorus was identified as 20 kg ha -1 . The sub basins 17, 23, and 3 were identified as the highest loading area of total phosphorous in the study catchment. Best management plan which is simple, economical and adaptable over the study catchment for managing severe impact of surface run off on water resources should be adopted. It is better to undergo detail re-examination over the physical and chemical properties of P in fertilizers and manures to propose the minimizing, neutralizing, replacing strategies to reduce at the source.

In order to lower the high prices of individual feedstock, extend the life of a more limited feedstock and to improve the fuel properties of biodiesel it imperative to optimize process parameters for biodiesel derived from mixed feedstocks. Samples of castor seeds were collected from Jimma zone, southwest Ethiopia while sample of wet microalgal biomass was obtained from wastewater stabilization ponds using a 60µm filter screen. The castor seeds and algal biomass were sun-dried before further dried at 800C in an oven and ground to pastes. Oils were extracted from dried and milled castor seeds and micro-algae pastes with a Soxhlet apparatus using methanol. The extracted oil was purified and characterized before converted to biodiesel. A transesterification process designed using Response Surface Methodology (RSM) based on central composite design (CCD) experimental design was used to optimize the biodiesel production process parameters from mixed oil using alkaline catalyst. The Design Expert® 12 software was used to analysis experimental results. The effects of catalyst concentration, ethanol to mixed oil molar ratio and reaction temperature on the biodiesel yield were investigated using the experimental results. Accordingly, the optimum conditions for biodiesel production from mixed oil were a catalyst concentration of 1.23 % w.t of the oil, alcohol to mixed oil molar ratio of 5.94:1 (v/v) and reaction temperature of 51.300C. The yield of biodiesel under these conditions was 93.88%. Experiment was conducted under the specified optimum conditions to validate the result predicted by the software. The yield of biodiesel from the experiment was 93.36% which is very close to the value predicted by the software. The fatty acid composition of the biodiesel from mixed oil was analyzed using Gas chromatograph. The various fuel properties of biodiesel were determined using standard methods and results were compared with ASTM D6751 and EN 14214 standards. The physicochemical properties fulfill both standards.