Oxygenation for fish farms

This thesis provides a detailed study of methods for dissolving oxygen in water to reduce water requirements for fish farming. The principal sources of oxygen are air or pure oxygen gas. Aeration methods have the distinct advantage of the universal availability of air. However, the effectiveness of such methods is diminished by the presence of nitrogen in the air and, in general, the maintenance of dissolved oxygen levels above 70% saturation is likely to result in excessive power requirements. Pure oxygen has five times the solubility of oxygen in air and it is possible, therefore to achieve much higher transfer rates. However, oxygen is expensive and its economic use is essential: it is important, therefore, to dissolve a high proportion of the oxygen. Four distinct oxygenation systems were evaluated by the author. A detailed analysis of a column oxygenator is given first. The column was designed so that the oxygen bubbles generated are trapped within the column until dissolved. In seawater, much smaller bubbles are formed and this led to the development of a jet oxygenator which disperses gas rubbles within the rearing tank. Both the above systems were designed primarily for oxygenating recycled tank water. For oxygenating a primary water source, a U -tube device was evaluated. Lastly, the possibility of supporting fish stocks without any external power source, other than a pressured supply of oxygen from a liquid oxygen store, was considered. Experience of running commercial-scale oxygenation systems in high-intensity fish farms has made it possible to estimate operating costs of both aeration and oxygenation systems. The significance of these costs is discussed.

Sustainable agricultural production:an investigation in Brazilian semi-arid livestock farms

This paper investigates the environmental sustainability and competitiveness perceptions of small farmers in a region in northern Brazil. The main data collection instruments included a survey questionnaire and an analysis of the region's strategic plan. In total, ninety-nine goat and sheep breeding farmers were surveyed. Data analysis methods included descriptive statistics, cluster analysis, and chi-squared tests. The main results relate to the impact of education, land size, and location on the farmers' perceptions of competitiveness and environmental issues. Farmers with longer periods of education have higher perception scores about business competitiveness and environmental sustainability than those with less formal education. Farmers who are working larger land areas also have higher scores than those with smaller farms. Lastly, location can yield factors that impact on farmers' perceptions. In our study, farmers located in Angicos and Lajes had higher perception scores than Pedro Avelino and Afonso Bezerra, despite the geographical proximity of these municipalities. On the other hand, three other profile variables did not impact on farmers' perceptions, namely: family income, dairy production volume, and associative condition. The authors believe the results and insights can be extended to livestock farming in other developing countries and contribute generally to fostering effective sustainable development policies, mainly in the agribusiness sector. © 2013 Elsevier Ltd. All rights reserved.

Protection schemes for meshed VSC-HVDC transmission systems for large-scale offshore wind farms

This chapter discusses network protection of high-voltage direct current (HVDC) transmission systems for large-scale offshore wind farms where the HVDC system utilizes voltage-source converters. The multi-terminal HVDC network topology and protection allocation and configuration are discussed with DC circuit breaker and protection relay configurations studied for different fault conditions. A detailed protection scheme is designed with a solution that does not require relay communication. Advanced understanding of protection system design and operation is necessary for reliable and safe operation of the meshed HVDC system under fault conditions. Meshed-HVDC systems are important as they will be used to interconnect large-scale offshore wind generation projects. Offshore wind generation is growing rapidly and offers a means of securing energy supply and addressing emissions targets whilst minimising community impacts. There are ambitious plans concerning such projects in Europe and in the Asia-Pacific region which will all require a reliable yet economic system to generate, collect, and transmit electrical power from renewable resources. Collective offshore wind farms are efficient and have potential as a significant low-carbon energy source. However, this requires a reliable collection and transmission system. Offshore wind power generation is a relatively new area and lacks systematic analysis of faults and associated operational experience to enhance further development. Appropriate fault protection schemes are required and this chapter highlights the process of developing and assessing such schemes. The chapter illustrates the basic meshed topology, identifies the need for distance evaluation, and appropriate cable models, then details the design and operation of the protection scheme with simulation results used to illustrate operation. © Springer Science+Business Media Singapore 2014.