Effects of oil refining steps (degumming, neutralizing, bleaching, and deodorizing) on rheological properties of catfish oil were investigated. Four rheological models (Newtonian, Bingham, Herschel-Bulkley, and Casson) were used to fit the experimental data. Refined catfish oil behaves like a Newtonian fluid. Based on the Casson model, the yield stress values of oils gradually decreased after each refining step. The highest shear rate index (0.904) was observed in the deodorized oil. The Casson model was used to predict rheological properties because it works well at both lower and higher shear rates.
The thermal degradation (weight loss) of individual FA and of catfish and menhaden oils collected from different refining steps was investigated by thermogravimetric analysis. The heat resistance of FA was partially dependent on chain length and degree of unsaturation. The weight loss of catfish and menhaden oils increased with increased heating temperatures, regardless of the oil refining process. All oil samples (except crude catfish oil) were decomposed after the heating temperature reached 550°C. Based on the thermogravimetric curves, the following thermal stability sequence at different refining steps for both catfish and menhaden oils was proposed: crude > degummed > neutralized > bleached > deodorized oils. FIG. 1. Thermogravimetric curves indicating remaining weight (%) of catfish oils at 100-600°C.FIG. 2. Thermogravimetric curves indicating remaining weight (%) of menhaden oils at 100-600°C.
This study focuses on the effects of socioeconomic and political factors in solid waste generation and water pollution in the catchments of Pinga Oya, a tributary of the Mahaweli river. The direct solid waste disposal into water bodies and the untreated dumping sites are supposed to be some of the major causes of water pollution in Sri Lanka. The main objectives of this paper were to determine and evaluate the causal link between consumption pattern and solid waste generation and to understand the underlining socioeconomic stories of waste disposal and their link with water pollution. Semi-structured household questionnaires (200) and in-depth interviews with key informants were used to collect quantitative and qualitative data from Pinga Oya watershed areas. The samples were selected on stratified basis and purposively and data were analysed quantitatively and qualitatively. The secondary information was mostly collected from the sociological literature. The consumption patterns of people often determine the nature and amount of solid waste generation based on their livelihood, class and culture. Here, the symbolic consumption which has become the life style of urban middle and upper class people, promotes a "consumer society" with the influence of monthly household income and cultural ritual. As a result of higher social value given for mass consumption in this global economic order, people frequently consume unwanted goods to achieve symbolic value and cultural satisfaction rather than limiting their consumption to actual necessities. This study revealed that there was a positive relationship between the monthly household income and consumption pattern and people with the higher monthly household income (>Rs.25,000) generate more solid waste daily (1.5-2 kg) than low income groups. The domestic solid waste generation was mainly influenced by weekly food consumption (R 2 = 0.61). The family size and gender relationship of consumer behaviour were also found significant in determining solid waste generation. This consumption culture that generates more and more solid waste especially in urban social environment influences the quality of water and aggravates the crisis of water pollution. Therefore, water pollution created by solid waste disposal is not only a problem limited to natural scientists to solve but also a social problem caused by many socioeconomic and cultural practices of people.
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