Development and Empirical Assessment of a Model Describing N0_3' Removal from RAS Using the Activated Sludge Concept with Intrinsic Organic Matter as the Electron Donor

摘要

The aquaculture industry is a source of large amounts of organic matter and nutrients, which may adversely affect aqueous ecosystems. As a result, the operation of fish farms around the world is becoming limited by environmental regulations, especially in sensitive areas. Recirculating Aquaculture Systems (RAS) are being developed as an alternative to traditional aquaculture technologies. One of the advantages related to RAS operation is low water consumption, allowing a more cost-effective pollutantremoval scheme. Most commercial RAS, however, do not include a nitrate (NO3") removal unit because, in general, nitrate is relatively non-toxic to aquatic species (van Rijn, 1996), and because its removal is rarely obligatory. However, release of largenitrate fluxes to the environment should be avoided. The main goal of the current work was to develop an economic solution to the discharge of nitrate with RAS effluents. The denitrification process, in which nitrate is biologically reduced to innocuousnitrogen gas (N2), was chosen for that purpose, due to its cost effectiveness and reliability. Furthermore, the alkalinity resulting from the process can be used to maintain adequate pH levels in the fish tank, instead of using a costly external base. The electron donor is normally supplied in the form of a soluble organic substance, such as methanol, which results in high reaction rates. Alternatively, the electron donor may be supplied from within the system itself, a method commonly defined as 'single-sludge' denitrification. By implementing this method, the need for the relatively expensive external carbon source is minimized. Additionally, a significant reduction in the mass of solid wastes produced by the fish farm can be achieved. In marine RASapplication, this advantage is of considerable importance because solutions for the disposal of high salinity organic wastes rarely exist.