Basic parameters for designing physical separation treatments from an intensive on-shore fish farm.

The pollutant load was monitored in an intensive on-shore plant; evaluation especially concerned one basin, during a period of time in which the water temperature (21-23°C), the stocking density (25 kg/m3), the loading and unloading flow (40 dm3/s) remained steady at the highest values. The results show that the maximum pollution levels are characterized by high concentrations of suspended organic materials, as well as by high BOD5/COD rates; moreover, more than 60% of the suspended solid waste consists of particles with a maximum dimension ranging from 200 μm to more than 500 μm. Tests show that an effluent channel is less efficient in reducing the pollutant load of waste water than sedimentation treatment. The laboratory sedimentation trials showed - for a period of about 3 hours - minimum and maximum solid particle sedimentation speeds of 2.56 mm/s and 46.8 mm/s respectively, which should be considered when deciding the turbid speed and the dimensions of basins for this type of effluent. In any case, the sedimentation process carried out in the laboratory was only just sufficient to bring the farm effluent within the legal limits. Therefore mechanical filtration treatment may suit the specific requirements of the farm waste water used for the experimental trials. A 50 μm mesh would be considered sufficient for any critical situation.