Combined aluminium sulfate/hydroxide process for fluoride removal from drinking water

In this study, aluminium hydro(oxide), AO was prepared from locally available aluminium sulfate, and used for fluoride removal from water by combining with Nalgonda Technique. The fluoride removal performance of the combined process was investigated as a function of contact time, proportion of alum-lime/AO dose, initial fluoride concentration and solution pH in series of batch experiments. The rate of fluoride removal was investigated using conventional kinetic models. The fluoride removal efficiency of the combined process was also tested for real water sample from selected community water supply system in the Rift Valley Region of Ethiopia. The removal of fluoride was rapid in the first 15 min. The combined process efficiency was about 93% with an optimum combined alum/AO dose (80 mg alum/mg F, 5 mg AO/mg F and lime = 35% of alum) using initial fluoride concentration of 15 mg/L. The optimum solution pH for fluoride removal was in the range of 5-9, which is suitable for practical application in the Ethiopia Rift Valley Region. Kinetic studies showed that the rate of fluoride removal by alum/AO can be well described by a pseudo-second-order rate equation with an average rate constant of 0.096 g/min.mg. The optimum dose required to attain 85-93% fluoride removal efficiency from real water sample was 90 mg alum/mg F, 5 mg AO/mg F, and 15% lime. Hence, the combined defluoridation process has higher fluoride removal efficiency than the Nalgonda Technique with an additional advantage of minimizing chemical dose. The reported removal efficiency of Nalgonda Technique is 70% at alum dose of 150-170 mg alum/mg F. Besides, sludge production is also minimized. Therefore, this process is highly efficient and could be applied in areas where the fluoride concentration is higher than 10 mg/L, both at household and community level. KEY WORDS: Nalgonda Technique, Aluminium sulfate, Aluminium hydroxide, Fluoride, Drinking water Bull. Chem. Soc. Ethiop. 2016, 30(3), 391-401DOI: http://dx.doi.org/10.4314/bcse.v30i3.

STEP COMPLIANT APPROACH FOR TURN-MILL OPERATIONS

Current machine tools have incurred challenges on limitation such as part programming complexity of G and M code, weak integration of digital machine tools and coverage of universal data modeling for product and manufacturing resources. In response to this manufacturing system requirement, Standard for Exchange of Product data (STEP) and its implementation on developing an interface for the next generation of machine tool controllers (STEP-NC) has become a concern of research interest and performed on basic manufacturing technology limited to a unit domain such as turning, milling or Wire EDM. Therefore; extending this STEP implementation on multipurpose machine tools such as turn-mill machines is mandatory since the machines are the main component in these industries. The research work offers a STEP-NC compliant interface supporting turn-mill machining environment identified as SCSTMO

Levels of selenium in selected river, well and bottled waters in Ethiopia by microwave plasma-atomic emission spectrometry

Selenium is an essential trace element for many organisms, including humans, but it is toxic at higher level than homeostatic levels. Both selenium deficiency and toxicity are problems around the world (specially in China, India, USA). The level of selenium in selected waters of Ethiopia (including Akaki Kality river and some of its tributaries such as Kebena, Saris Abo, and Estifanos areas; bottled waters like Yes, Aqua Safe and Gift; well waters like Ziqualla Wogem, Akaki Kality and Ferensay Legasion; and tap water at Arat Kilo) were determined by microwave plasma-atomic emission spectroscopy after wet digestion and acidification. The levels selenium determined (µg/L) were 7.0, 3.1, 6.4, 3.9, 6.3, 5.0, 5.4, 0.66, 4.2, 6.3, and 2.0, respectively.  The percentage recovery of Se was found to be 95.2% which is in the acceptable range. The ANOVA result showed that there is a significant difference between the mean levels of selenium in the river, well and bottles waters. The results obtained in this study were compared with the permissible limit (10 µg/L) set by Ethiopian Standards Agency and the tolerable level set by WHO (< 40 µg/L). Thus the levels of selenium detected in this study are within the recommended limit.                     KEY WORDS: Selenium, Trace metal, Water samples, Microwave plasma-atomic emission spectroscopy, Ethiopia   Bull. Chem. Soc. Ethiop. 2020, 34(2), 215-226. DOI: https://dx.doi.org/10.4314/bcse.v34i2.

Fluoride levels in commercially available rice in Ethiopia

Rice (Oryza sativa, Asian; Oryza glaberrima, African) is an important staple food crop in many Sub-Saharan African and Asian countries, so the consumer’s daily bowl of rice needs to be safe and of good quality. The objective of this study was to determine level of fluoride in raw and cooked rice by ion selective electrode. Alkaline fusion was used for sample preparation of six varieties for both the raw rice and rice cooked with tap water and fluoridated water. Fluoride levels ranged from 0.1-5.5 mg/kg in raw rice sample. Rice which was cooked with different fluoride levels of water showed increment depending on the method of cooking. In absorption method of cooking fluoride level was higher than that cooked by excess method and it may be due to the fact that all the fluoride in the water used for cooking by absorption method goes in to the grain while in excess method the remaining water was removed. The employed alkaline fusion procedure was evaluated using spiking method and an acceptable percentage recovery was obtained. A statistical analysis of variance at 95% confidence level for fluoride determination indicated significant difference between the mean of each variety of rice samples. KEY WORDS: Fluoride, Ethiopian rice, Imported rice, Staple food, Cooking methods Bull. Chem. Soc. Ethiop. 2013, 27(2), 179-189.DOI: http://dx.doi.org/10.4314/bcse.v27i2.

Assessment of the quality of bottled water marketed in Addis Ababa, Ethiopia

The consumption of bottled drinking water has been increasing in the world. But, the quality of bottled water used for human consumption is not subjected to any stringent quality control measure in Ethiopia. The present study was carried out to determine the physicochemical quality parameters of twenty brands of bottled drinking water available in Addis Ababa and to compare with drinking water guidelines set by World Health Organization (WHO) and Compulsory Ethiopia Standards (CES). The samples were collected by random sampling technique. The physicochemical parameters such as pH; TDS and EC; total alkalinity, total hardness, HCO3-, Cl-; SO42-, NO3-, NO2-, F-) and common cations (Ca2+, Mg2+, Na+, and K+) were determined by pH meter, conductivity meter, titration, UV-Visible spectrometry, fluoride ion selective electrode and microwave plasma-atomic emission spectrometry, respectively. The mean physicochemical concentration of TDS, total alkalinity, total hardness, HCO3-, SO42-, NO3-, NO2-, F-, Cl-, Ca2+, Mg2+, Na+, K+,  pH and EC in bottled water samples were found in the range (4.67-139), (12-165), (4-97), (16.3-202 ), (0.05-3.84), (0.02-0.84), (0.08-0.28), (0.03-1.26), (4.28-20.8), (0.19‑8.9), (0.02‑2.5), (1.8‑24.5), (0.14‑8.08 mg/L), (6.43-7.69) and (9.8-289 µs/cm), respectively. The drinking water quality index (WQI) was calculated based on 15 important quality parameters and the results were found in the range 3.85-49.2. The mean concentrations of physicochemical parameters in almost all the bottled drinking water were below the permissible limit set by WHO and CES. Hence, all the tested bottled water samples are safe for drinking purpose.               KEY WORDS: Bottled water, Common cations, Common anions, Physicochemical parameters, Water quality index Bull. Chem. Soc. Ethiop. 2019, 33(1), 21-41DOI: https://dx.doi.org/10.4314/bcse.v33i1.

Potential of Water Hyacinth (Eichhornia crassipes (Mart.) Solms) for the Removal of Chromium from Tannery Effluent in Constructed Pond System

The objective of the present study was to evaluate the potential use of water hyacinth for the removal of chromium (Cr) from tannery wastewater. This experiment was performed using healthy, young and acclimatized water hyacinth collected from unpolluted Awash River. Cr concentrations of 3, 5, 7, 10 and 20 mg/L were added to five different polyethylene tanks, containing 40 litre tap water cultured with Hoagland’s solution. A sixth tank containing Cr-free water was used as a control group. Six plants of equal wet mass (each 12.5 ± 2 g), shoot length (11 ± 2 cm) and root length (6 ± 2 cm) were transferred into each tank and allowed to grow in a greenhouse for 42 days. From each tank plants were harvested randomly every week. Bioaccumulation factor, translocation factor, shoot and root length; wet biomass and dry weight of the shoot and root were measured, and relative growth rate, tolerance index of the root and tolerance index of wet mass were analyzed. The maximum accumulation of 2.52 X 103 µg/g of water hyacinth was achieved in the plants exposed to 20 mg/L Cr solution. The root part of the plant accumulated 2.42 to 3.82 times higher than the shoot part. An overall Cr removal efficiency of up to 91% was achieved in this study, but the efficiency decreased as the concentration of Cr in water increased. The growth of the plant was inhibited at high concentration due to Cr toxicity. Therefore, the application of water hyacinth for Cr removal will be sustainable, if the concentration of Cr in wastewater does not exceed about 10 mg/L. The relative growth rate (RGR) of the plant decreased with increasing Cr concentration and the growth was inhibited above 15.3 mg/L Cr in water. Based on the above data, it could be concluded that water hyacinth can potentially be used for the removal of Cr from tannery effluents which is a major environmental problem in Ethiopia. However, further investigation is needed to ascertain the optimum conditions for maximum removal

Levels of fluoride in staple cereals and legumes produced in selected areas of Ethiopia

The main objective of this study was to determine the levels of fluoride in cereals (tef, wheat, corn and barley) and legumes (pea, lentil and chickpea) produced in selected areas of Ethiopia. The samples were collected from the rift valley and outside rift valley areas of Ethiopia: Arsi Negele, Adola, Wonji, Ada, Gonder, Bure (Gojam) and Dessie towns. The samples were collected from local markets in the areas where they are cultivated in large amount. Levels of total fluoride in cereal and legume grain samples were determined by fluoride ion selective electrode. Fluoride levels in cereals were found between 0.98 mg/kg in corn from Adola and 10.98 mg/kg in tef from Wonji. Fluoride levels in legumes ranged from 1.52–11.07 mg/kg both in the pea with the lowest and highest levels from Bure and Ada, respectively. Fluoride levels in cereals from rift valley areas were higher than those from outside the rift valley areas. Generally, cereal samples from Arsi Negele and Wonji were found to contain higher levels of fluoride, ranging from 3.70 mg/kg in corn from Wonji to 10.98 mg/kg in tef from Wonji. The highest level of fluoride was found in pea (11.07 mg/kg) from Ada, and the lowest level in chickpea (1.52 mg/kg) from Dessie and in pea (1.52 mg/kg) from Bure. Fluoride contents of legume samples from Ada were found to be higher than those from Gonder, Bure and Dessie. In general, the levels of fluoride in Ethiopian cereals and legumes from non-rift valley areas are comparable to those from other countries