Emergy assessment to assess the ecological sustainability of smolt production and innovative options for the reuse and valorisation of aquaculture discards

Abstract

Two Emergy Assessments (EMA) were conducted to evaluate the ecological performances of novel eco-intensification innovations for the treatment and valorisation of sludge and fish mortalities from finfish aquaculture, including upstream directly and indirectly used resources such as energy, materials, and labour. One innovation consists in a novel process to filter and dry particles from the reject water out of a Recirculating Aquaculture System (RAS), with dried nutrients and biomass being reused as organic fertiliser or as an energy source. The other process concerns the disposal of fish mortalities, which are mixed with by-product from the brewery industry and dried. The resulting product can be used in the pet food industry or as an energy source. Both innovative solutions were tested on a RAS for smolt production in Norway. A set of standard Unit Emergy Values and emergy indicators was selected and calculated, including specific emergy (sej/kg), environmental loading ratio, and emergy sustainability index, among others. The results are compared with Life-Cycle Assessment values derived from the same innovations and with other emergy values obtained for other aquaculture processes. All in all, the novel solutions imply higher impacts related to water and technological inputs, yielding savings in the other indicators, thus confirming overall positive performances, yet requiring either some trade-off to be addressed and assessed more widely, or more efforts to possibly abate the factors that are responsible for increased impacts.