Reducing the potential environmental impact of tank aquaculture effluents through intensification and recirculation

Abstract

Aquaculture effluents may contain a variety of constituents that could cause negative impacts when released into the environment. The constituents include dissolved or particulate organics, nutrients, and specific organic or inorganic compounds. Their impact on the environment depends on the total amount or concentration released and the assimilative capacity of the environment for the particular constituent. In this paper, the different types of constituents will be reviewed as they relate to a current trend in the aquaculture industry: intensification of production and recirculation systems. Although most water treatment methods used in intensive or recirculating aquaculture systems result in a relocation of nutrients and organic matter and not in an overall reduction in discharges, this relocation makes it possible to reduce potential environmental impacts by facilitating effluent treatment. For example, solids removal operations produce a stream with high concentration of solids (the sludge removed from the flow) that is also rich in nutrients and organic matter, while reducing the concentrations of these parameters in the culture water. The stream with a high concentration of solids could be treated prior to disposal using techniques appropriate for high strength wastes and sludge. The fate of constituents will be examined for a variety of water treatment operations. The impacts of a number of treatment methods on these constituents will be discussed from the standpoint of overall mass discharges and concentration of the constituents in the discharge flow.