Abstract
Fish processing towards production of fillet gives rise to wastewater streams that are ultimately directed to biogas production and/or wastewater treatment. However, these wastewater streams are rich in minerals, fat, and proteins that can be converted to protein-rich feed ingredients through submerged cultivation of edible filamentous fungi. In this study, the origin of wastewater stream, initial pH, cultivation time, and extent of washing during sieving, were found to influence the amount of recovered material from the wastewater streams and its protein content, following cultivation with Aspergillus oryzae. Through cultivation of the filamentous fungus in sludge, 330 kg of material per ton of COD were recovered by sieving, corresponding to 121 kg protein per ton of COD, while through its cultivation in salt brine, 210 kg of material were recovered per ton of COD, corresponding to 128 kg protein per ton of COD. Removal ranges of 12–43%, 39–92%, and 32–66% for COD, total solids, and nitrogen, respectively, were obtained after A. oryzae growth and harvesting in the wastewater streams. Therefore, the present study shows the versatility that the integration of fungal cultivation provides to fish processing industries, and should be complemented by economic, environmental, and feeding studies, in order to reveal the most promising valorization strategy.Graphic abstract
Highlights
Filamentous fungi contribute to the global economy through production of valuable products such as antibiotics, enzymes, and organic acids [1]
Some filamentous fungal strains have been used for production of fermented foods for human consumption, being considered as Generally Regarded As Safe (GRAS) microorganisms
The medium before and after fungal treatment was characterized regarding content of total solids and dissolved solids according to Sluiter et al [17], ash according to Sluiter et al [18], and chemical oxygen demand (COD) using a COD kit (Nanocolor COD 1500, Düren, Germany)
Summary
Filamentous fungi contribute to the global economy through production of valuable products such as antibiotics, enzymes, and organic acids [1]. Filamentous fungi are taxonomically wide and enzymatically versatile biocatalysts, able to grow on a wide range of substrates and produce various products. Their investigation in the context of circular bioeconomy, converting nutrients containing low-value substrates into value-added products, has gained momentum over the years. Potential substrates and derived products are wide. The former include lignocellulosic materials, starch- and fat-containing streams, while the latter can include enzymes, alcohols, and fungal biomass [3, 4]
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