New Insights on Protein Recovery from Olive Oil Mill Wastewater through Bioconversion with Edible Filamentous Fungi

Abstract

Olive oil mills represent an important sector in the Mediterranean Sea Basin but also an environmental hazard due to untreated wastewater. Recovery of nutrients from olive oil mill wastewater (OMWW) as protein-rich microbial biomass can produce novel feed and reduce its chemical oxygen demand; however, low-protein containing products have been reported. New strategies leading to higher protein-containing fungal biomass could renew the research interest on bioconversion for pollution mitigation of OMWW. In this work, through cultivation of edible filamentous fungi (Aspergillus oryzae, Neurospora intermedia, and Rhizopus delemar), a link between the protein content in the originated fungal biomass, and the addition of nitrogen and medium dilution was established. Addition of nitrogen in the form of NaNO3 reduced the cultivation time from 96 h to 48 h while achieving a similar biomass mass concentration of 8.43 g/L and increased biomass protein content, from w = 15.9% to w = 29.5%. Nitrogen addition and dilution of OMWW, and consequent reduction of suspended solids, led to an increase in the protein content to up to w = 44.9%. To the best of our knowledge, the protein contents achieved are the highest reported to date and can open new research avenues towards bioconversion of OMWW using edible filamentous fungi.

Evaluation of the Cultivation of Aspergillus oryzae on Organic Waste-Derived VFA Effluents and Its Potential Application as Alternative Sustainable Nutrient Source for Animal Feed

“…The highest amount of biomass (2.16 g/L, Figure 1) was obtained in the medium of VFA effluents from the CKM containing the highest total VFAs (Table 1). High carbon content might have a positive effect on biomass production, and the initial pH and nitrogen content of the medium also have a critical role in fungal growth and sporulation and cultivation yield [17,[27][28][29].…”

“…In addition, it was found that the VFAs obtained from the mixture of CM with FW, whose C/N ratio was much higher than the others (except for FW), was preferable for the growth of A. oryzae, achieving a higher biomass production yield of 0.37-0.47 g dry biomass/gCOD eq.consumed (Table 2), whereas the amount of fungal biomass produced in this mixture medium was relatively lower than in the other media. Similarly, the biomass production efficiency was increased by adding nitrogen such as ammonia, ammonium sulfate or sodium nitrate to balance the C/N ratio [17,32,33].…”

“…Souza Filha et al [36] reported that the produced A. oryzae biomass in 2% pea-processing byproduct yielded between 0.11 and 0.14 (g/g substrate) protein content. In another research study by Sar et al [17], A. oryzae fungal biomass produced in olive oil mill wastewater was generally characterized by varied protein contents (between 15 and 45% of dry weight). Interestingly, A. oryzae was found to grow in the mixture of VFA effluents performed in shake flasks and resulted in a fungal biomass with 37-41% protein content in a recent study by Uwineza et al [10].…”

“…Among the filamentous fungi strains studied, A. oryzae has proven to be able to grow on different waste-derived effluents yielding a fungal biomass with 20% to 62% protein content [11,16,17]. In addition to the high protein content, A. oryzae has potential application in animal feed supplementation, especially in ruminant feeding [18,19].…”

Impact of Emerging Technologies on Virgin Olive Oil Processing, Consumer Acceptance, and the Valorization of Olive Mill Wastes

“…Alternatively, OMWW can serve as a substrate for edible filamentous fungi, which can be used as a protein source. However, the process still needs to be optimized to increase the production of fungal proteins above the 15% yields currently achieved [ 92 ].…”