Characterisation, Treatment and Utilisation of the Effluent from an Intensive Fish Farm

Abstract

This thesis provides control and management information on aspects of water quality in fish farming. The metabolic products produced by intensively farmed rainbow trout have been assessed and the production rates can be used to predict water quality. The water quality requirements of trout have been reviewed and experiments conducted to determine the limiting water quality criteria of intensively farmed fish. The principle factors limiting fish production were carbon dioxide and suspended solids. The oxygen consumption of the fish was also measured. Water treatment by lagooning did not produce a satisfactory effluent and the reasons for the failure of the lagooning system are are discussed. The effluent discharge consent standards imposed by the North West Water Authority were considered stringent and values for the revision of the standards are proposed.  Methods for treatment of the effluent for second reuse or complete water recirculation were considered. these techniques were more expensive than abstracting additional water. The poor disolving efficiency of the oxygenation equipment was demonstrated to be the cause of the high utilisation of liquid oxygen and illustrated that a major redesign of equipment was required.  The nutrients in the solid wastes can be utilised by land disposal and the value of the nutrients can be used to offset the cost of transport and removal of the wastes. Experiments were conducted to utilise  the nutrients dissolved in the n the effluent by a modified form of hydroponic culture. This demonstrated that grass and lettuce crops could be successfully grown in summer.