Browsing by Author "Kiros, Solomon (PhD)"

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    Adsorption of Heavy Metal from Constituent Waste Water by Tea Waste Adsorbent
    (Addis Ababa University, 2016-06) Oljira, Lalise; Kiros, Solomon (PhD)
    Most industries such as electroplating, textile, fertilizer, batteries, leather, and others in less developed countries discharge huge volumes of untreated wastewater into water bodies. The industrial wastewater may contain toxic chemicals in excess of the threshold level when released into the environment, particularly to the aqueous environment and soil; significantly degrade the quality of the water thereby affecting river health substantially and subsequently human health. There are several techniques for removing toxic chemicals such as ion exchange, membrane filtration, adsorption, irradiation and chemical and biological treatments. However, the adsorption method is believed to be the better option because it is cost-effective, efficient, simple and easy to operate, and environmentally friendly according to many studies. Accordingly, this method can be a preferable option for developing countries like Ethiopia, where advanced treatment technologies for high volumes of toxic industrial waste water are unaffordable. The aim of this work was to determine the potential of tea waste (TW) as a useful adsorbent for the removal of copper and zinc ions from aqueous systems. The study was conducted using batch experiments with constituted wastewater having copper and zinc ion concentration of 1000 mg·L-1. The effects of initial concentration, contact time and pH on adsorption efficiency were investigated. Adsorption isotherm was also studied. Generally, the result showed an increase in removal efficiency with increase in contact time, pH and decrease of initial concentration. The adsorption equilibrium data correlate well with Freundlich model and Langmuir model respectively for zinc removal and copper removal with regression coefficient (R2=0.9913, R2=0.981). The results showed that efficiencies of (TW) for the removal of copper and zinc ion were 95.98% and 99.80% respectively at optimum point of 5pH, 10ppm, and 120min. These results clearly indicate the efficiency of tea waste (TW) as a low-cost adsorbent for treatment of wastewater containing copper and zinc ions. Therefore, it is recommended that tea waste can be used, as a low cost and abundant source for the removal of heavy metals as an alternative to more costly materials. KEY WORDS: Copper, zinc, toxicology, adsorption, tea waste, batch study, atomic adsorption spectrometer.
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    Characterization of Indigenous Wild Yeasts and Evaluation of Their Bread Leavening Capacity
    (Addis Ababa University, 2017-08-03) Beyene, Elsa; Muleta, Diriba (PhD); Kiros, Solomon (PhD); Tesfaye, Anteneh (PhD)
    Ethiopia is a developing country with a high baker’s yeast demand for bread making and beverage industries. However, there is no baker’s yeast producing plant in the country. Therefore, the objective of this study was to assess bread leavening potential of wild yeasts from teff and wheat dough, shamita, tej, tella, molasses and honey samples, following standard methods. A total of 180 wild yeast isolates were, out of these isolates 23 isolates with high biomass yield (1.7 to 2.6 of 600 nm OD reading) and the efficient gas (CO2) producers in durum tube within 12 to 24 hours were selected for further analysis. Morphological, biochemical and molecular features were used to identify and characterize the yeasts. Isolates identified by biolog were belongs to genera Saccharomyces, Candida humilis and Kluyveromyces and found to utilize glucose, sucrose, raffinose, trehalose and maltose. Genetically, the sequence analysis of the ITS-5.8S rDNA region showed that the isolates belong to 5 species namely, Saccharomyces cerevisiae, Candida humilis (synonyms Candida milleri), Kazachstania bulderi, Pichia fermentans and Pichia kudriavzevii. All the test isolates were found to produce maximum cell mass at a temperature of 30oC, pH of 5.5 and 48 hours of incubation. Isolate AAUTf1 did not produce hydrogen sulfide. The isolates AAUTf5, AAUTj15 and AAUSh17 including commercial yeast produced light level of hydrogen sulfide, while AAUMl20 and AAUWt21 produced heavy level of hydrogen sulfide. The assessment of leavening performance of the yeasts indicated that, isolates AAUTf1 (Candida humilis) and AAUTf5 (Kazachstania bulderi) had higher leavening activity with raising dough by 131 cm3 and 128 cm3 respectively each within 120 min. Similarly, isolates AAUSh17 (Saccharomyces cerevisiae) and AAUTj15 (Saccharomyces cerevisiae), were found rising the volume of the dough by 127 cm3 and 125 cm3, respectively at 60 min compared to the commercial yeast that increased the volume to 117 cm3 within 90 min. The combined bread dough rising effects of AAUTf1 + AAUTf5 + AAUTj15, AAUTf5 + AAUTj15 and AAUTf1 + AAUTj15 + AAUSh17 caused volume increment to 143 cm3 at 90 min, 141 cm3 at 60 min and 140 cm3 at 60 min, in that order. Generally, mixed cultures showed superior leavening potential than that of single cultures and commercial yeast.
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    Characterization of Indigenous Wild Yeasts and Evaluation of Their Bread Leavening Capacity
    (Addis Ababa University, 2017-08-02) Beyene, Elsa; Muleta, Diriba (PhD); Kiros, Solomon (PhD); Tesfaye, Anteneh (PhD)
    Ethiopia is a developing country with a high baker’s yeast demand for bread making and beverage industries. However, there is no baker’s yeast producing plant in the country. Therefore, the objective of this study was to assess bread leavening potential of wild yeasts from teff and wheat dough, shamita, tej, tella, molasses and honey samples, following standard methods. A total of 180 wild yeast isolates were, out of these isolates 23 isolates with high biomass yield (1.7 to 2.6 of 600 nm OD reading) and the efficient gas (CO2) producers in durum tube within 12 to 24 hours were selected for further analysis. Morphological, biochemical and molecular features were used to identify and characterize the yeasts. Isolates identified by biolog were belongs to genera Saccharomyces, Candida humilis and Kluyveromyces and found to utilize glucose, sucrose, raffinose, trehalose and maltose. Genetically, the sequence analysis of the ITS-5.8S rDNA region showed that the isolates belong to 5 species namely, Saccharomyces cerevisiae, Candida humilis (synonyms Candida milleri), Kazachstania bulderi, Pichia fermentans and Pichia kudriavzevii. All the test isolates were found to produce maximum cell mass at a temperature of 30oC, pH of 5.5 and 48 hours of incubation. Isolate AAUTf1 did not produce hydrogen sulfide. The isolates AAUTf5, AAUTj15 and AAUSh17 including commercial yeast produced light level of hydrogen sulfide, while AAUMl20 and AAUWt21 produced heavy level of hydrogen sulfide. The assessment of leavening performance of the yeasts indicated that, isolates AAUTf1 (Candida humilis) and AAUTf5 (Kazachstania bulderi) had higher leavening activity with raising dough by 131 cm3 and 128 cm3 respectively each within 120 min. Similarly, isolates AAUSh17 (Saccharomyces cerevisiae) and AAUTj15 (Saccharomyces cerevisiae), were found rising the volume of the dough by 127 cm3 and 125 cm3, respectively at 60 min compared to the commercial yeast that increased the volume to 117 cm3 within 90 min. The combined bread dough rising effects of AAUTf1 + AAUTf5 + AAUTj15, AAUTf5 + AAUTj15 and AAUTf1 + AAUTj15 + AAUSh17 caused volume increment to 143 cm3 at 90 min, 141 cm3 at 60 min and 140 cm3 at 60 min, in that order. Generally, mixed cultures showed superior leavening potential than that of single cultures and commercial yeast.