The scientific interest in volatile fatty acids (VFAs) as an energy source and chemical precursor in ruminant diets has been longstanding, as it has significant implications for animal physiology and well-being. The present study explores the substitution of volatile fatty acids (VFAs) derived from agro-food residues via acidogenic fermentation as an alternative energy source in ruminant feed. Utilizing the gas production method, rumen digestibility assays were conducted, wherein the recovered VFA effluent from the acidogenic fermentation of apple pomace and potato protein liquor was substituted for 10%, 20%, and 30% of the total mixed ration (TMR) energy. Various parameters such as gas, VFA yield and composition, VFA peak intervals, changes in pH, and ammonium nitrogen content were investigated. Based on the results obtained, provision of 20% and 30% of the energy with VFAs did not increase methane production or did not cause significant pH alternations. Nevertheless, such supplementation resulted in increased production and accumulation of VFAs in the rumen media. The bioconversion of agro-food side streams into VFAs opens a new path in sustainable nutrient recovery and feed production from low value agro-industrial residues.

The production of date syrup yields a substantial amount of date press cake (DPC), fibrous and moisturising material with great potential for generating value through bioprocessing. However, the recalcitrant structure of DPC affects the yield of products in bioprocesses. To boost the accessibility of the structure as well as increase the soluble fraction of carbohydrates and facilitate further enzymatic hydrolysis, hydrothermal and dilute acid (0.5% (v/v) sulfuric acid) pretreatments as cost-effective and feasible methods were applied on DPC at relatively low temperatures (80, 100, 120 and 140 degrees C) and reaction times (60 and 90 min). The success in pretreatment was then evaluated by a post-enzymatic treatment using an enzyme cocktail of cellulases and hemicelluloses. Based on total accessible sugar with minimum produced inhibitors, an optimal operating condition was considered acid pretreatment at 120 degrees C for 90 min with a 55.02% increase in total sugar yield. To explore the potential use of pretreated DPC, an anaerobic digestion was conducted on untreated and acid-pretreated DPC at 120 degrees C for 90 min. The results showed that pretreatment increased the total bioproduct yield, including hydrogen, ethanol, and volatile fatty acid yields, by 59.75%. This demonstrates the significant impact of pretreatment on product yields in a bioprocess. 

The growing demand for sustainable ruminant feed alternatives has motivated the application of bioconversion approaches for the valorization of agro-food byproducts (AFB) into feed additives and supplements. The present study thoroughly investigated substituting volatile fatty acids (VFAs) obtained from acidogenic fermentation (AF) of AFB as an energy source in ruminant feed. Rumen in vitro digestibility assays were conducted utilizing the gas production method, wherein the VFAs obtained from AF of apple pomace and potato protein liquor was substituted with partial silage and concentrate energy at levels of 10%, 20%, and 30%. The results indicate that substituting 20% of the concentrate’s energy with VFA mixture significantly reduced methane production and had no adverse effect on the production and accumulation of VFAs in the simulated rumen media. Conversely, replacing 10% of the silage energy with VFAs led to a decrease in methane production and further enhanced the production of VFAs. Readily digestible VFAs in ruminant feed have the potential to enhance energy availability and sustainability in ruminant farming practices, aligning with the principles of circular economy and waste valorization. 

Biologically-derived volatile fatty acids (VFAs) are gaining attention as a sustainable alternative to petroleum-based VFAs. The anaerobic digestion (AD) process can effectively recover VFAs from organic-rich waste and wastewater, aligning with the principles of the circular bio-economy and sustainability. However, this approach currently faces several challenges. The AD effluent contains mixed VFAs, in relatively low concentrations, solubilized in water along with other compounds. This necessitates the development of strategies for concentration, separation, and purification. Membrane filtration technologies, particularly nanofiltration (NF), have emerged as advantageous solutions to address these challenges. This study investigates the application of the NF process for concentrating and fractionating solubilized VFAs, exploring the impact of membrane properties and feed pH on permeate flux and VFAs rejection. Two commercial NF membranes (“DK” and “XN45”) were tested under four different pH values of the feed (4, 5.5, 7, and 9). The results indicate that increasing feed pH enhances VFAs concentration but reduces permeate flux. Membrane properties strongly influence permeate flux and VFAs concentration and fractionation. Notably, the application of the XN45 membrane with a feed pH of 9 represents the best alternative among the tested conditions in terms of VFA concentration. 

Waste-derived volatile fatty acids (VFAs) are emerging as a promising sustainable alternative to petroleum-derived VFAs. However, the post-treatment of waste-derived VFAs becomes imperative for the purpose of concentration, purification, and fractionation. This study delves into the application of the nanofiltration process for post-processing of solubilized VFAs, focusing on a comprehensive exploration of the influence of membrane properties and feed pH on process efficiency. Four commercial nanofiltration membranes, with molecular weight cut-off ranging from 150 to 500 Da and substantial differences in zeta potential, were tested under four different feed pH values (4, 5.5, 7, and 9), constant pressure (20 bar) and controlled temperature (20 ± 1 °C). The VFAs' rejection mechanisms were investigated by analyzing membrane behavior at different pH levels. At feed pH 4, all membranes achieved low VFAs rejection (concentration ratios ranging from 1.38 to 1.62) associated with size exclusion. Transitioning from feed pH 4 to 9, electrostatic repulsion became predominant, leading to increased VFAs rejection (from a minimum of 213 % to a maximum of 311 %, with a sharp increase up to 272 % when transitioning from pH 4 to 7, followed by a more gradual increase of up to 114 % from pH 7 to 9) and decreased permeability (with an average reduction of from about 25 % to about 56 %). Notably, the highest VFAs concentration obtained was 40.1 g/L, representing a 4.4-times increase over the VFAs concentration in the feed. These findings underscore the potential of implementing nanofiltration as an efficient process for the VFAs post-processing, emphasizing the importance of membrane selection and operating conditions for optimized performance.

Thermophilic anaerobic digestion (AD) of animal manure offers various environmental benefits but the process requires a microbial community acclimatized to high ammonia. In current study, a lab-scale continuous stirred tank reactor (CSTR) fed with chicken manure was operated under thermophilic condition for 450 days in total. Results showed that the volumetric methane production decreased from 445 to 328 and sharply declined to 153 mL L−1·d−1 with feeding total solid (TS) step increased from 5% to 7.5% and 10%, respectively. While, after a long-term stop feeding for 80 days, highly disturbed reactor was able to recover methane generation to 739 mL L−1·d−1 at feeding TS of 10%. Isotope analysis indicted acetate converted to methane through the syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway increased from 33% to 63% as the concentration of ammonium increased from 2493 to 6258 mg L−1. Significant different in the genome expression of the SAO bacterial from 0.09% to 1.23%, combining with main hydrogenotrophic partners (Methanoculleus spp. and Methanothermobacter spp.) contented of 2.1% and 99.9% during inhibitory and recovery stages, respectively. The highly expressed KEGG pathway in level 3 (enzyme genes) for the Recovery sludge combining with the extraordinary high abundance of genera Halocella sp. suggested that Halocella sp. might be a highly efficient hydrolytic and acidogenic microorganism and enhance the process of SAO during carbon metabolic flow to methane. This report will be a basis for further study of AD studies on high nitrogen content of poultry manure.

Edible filamentous fungi, a source of mycoprotein, are one of the sustainable alternative protein. This study compares protein digestibility (DH%) and amino acid and mineral accessibility in Rhizopus oligosporus cultivated in oat flour (OatRO) or glucose media (GluRO) by using the INFOGEST in vitro digestion protocol. Fungal total amino acids was higher in GluRO (39.0 ± 1.1 % dw) than OatRO (21.8 ± 1.3 % dw) which was also the case for calcium and magnesium content. After completed gastrointestinal digestion, there were no significant differences between GluRO and OatRO regarding DH% (27.21 ± 10.4 % and 29.4 ± 0.5 %), however, GluRO provided significantly higher amino acid accessibility compared to OatRO (64.3 ± 1.6 % and 55.1 ± 3.1 %). Mineral accessibility of GluRO was for Ca: 37.9 ± 1.8 %, Zn: 9.3 ± 0.4 %, Fe: 38.2 ± 1.9 %, Mg: 66.5 ± 1.4 % and Cu: 24.7 ± 1.3 % and for OatRO; Ca: −40.2 ± 2.4 %, Zn: −4.13 ± 0.15 %, Fe:14.6 ± 1.6 %, Mg: 74.5 ± 3.1 %, and Cu: 55.95 ± 0.8 %. Despite the low phytic acid content, OatRO thus showed antinutrient properties with respect to calcium, and zinc, suggesting that oat-derived fungi had antinutrients other than phytic acid. This study hereby revealed that the cultivation substrate affect amino acid and mineral accessibility of filamentous fungi and calls for deeper evaluations of antinutrients in oat-derived fungi.

Purpose of Review

Lignocellulosic biomass, as a green and sustainable resource, can be used in biorefineries to produce bio-based products. The complex and resistant structure of lignocellulose prevents microorganisms access to carbohydrates in the biorefinery’s main processes, necessitating pretreatment. Different conventional pretreatment methods (physical, physico-chemical, chemical, and biological methods) and also novel advanced oxidation processes (AOPs) and their sustainability, environmental impact, economic viability, energy efficiency and, commercialization state are investigated in this review.

Recent Findings

Due to various reviews and studies on conventional pretreatment methods, they are briefly described with proper data. As the mechanisms and principle of operation of AOPs were investigated, during the AOPs pretreatment methods, hydroxyl radicals (·OH) are generated sufficiently to decompose lignocellulosic structure through oxidation. In this paper, we review the different AOPs, i.e., Fenton process, ozonation, photochemical, wet air oxidation, ultrasound, and electrochemical, which are recently used in the pretreatment of lignocellulose. Also, the achievement of different AOPs pretreatment research studies and general trends governing the process operating conditions are presented briefly in tables. Moreover, lignocellulosic biomass pretreatment sustainability assessment approaches such as life cycle assessment (LCA) and economic value and environmental impact (EVEI) are discussed. Although no study compared the sustainability aspects of different AOPs with conventional methods, this review generally addresses them. Further, environmental, energetic, and economic aspects of AOPs methods have been compared as important criteria in selecting a pretreatment method.

Summary

This review provides a thorough insight into the biorefinery’s bottleneck, pretreatment, and comprehensively investigated mechanisms, principle of operation, sustainability, environmental, economic, energy, and commercialization state of AOPs methods.

The resource-intensive nature of the ruminant farming sector, which has been exacerbated by population growth and increasing pressure to reduce feed antibiotics and growth promoters, has sparked interest in looking for sustainable alternative feed sources to enhance ruminant production efficiency. Edible filamentous fungi, rich in macronutrients like proteins, offer promise in reducing the reliance on conventional protein sources and antimicrobials to improve feed quality and animal performance. The inclusion of single-cell proteins, particularly filamentous fungi, in ruminant feed has long been of scientific and industrial interest. This review focuses on the potential application of the extensively studied Aspergillus oryzae and its fermentation extracts in ruminant nutrition. It provides an overview of conventional ruminant feed ingredients, supplements, and efficiency. Additionally, this review analyzes the re-utilization of organic residues for A. oryzae cultivation and examines the effects of adding fungal extracts to ruminant feed on ruminal digestibility and animal performance, all within a circular bioeconomy framework.

Anaerobic digestion is a promising method for organic waste treatment. While the obtained digestate can function as fertilizer, the liquid fraction produced is rather problematic to discharge due to its high nitrogen and chemical oxygen demand contents. Microalgae have great potential in sustainable nutrient removal from wastewater. This study aimed at evaluating native Swedish microalgae cultivation (batch operation mode, 25°C and continuous light of 80 μmol m−2 s−1) on anaerobic digestion effluent of pulp and paper sludge (PPS) or chicken manure (CKM) to remove ammonium and volatile fatty acids (VFAs). While algal strains, Chlorella vulgaris, Chlorococcum sp., Coelastrella sp., Scotiellopsis reticulata and Desmodesmus sp., could assimilate VFAs as carbon source, acetic acid was the most preferred. Higher algal biomass and cell densities were achieved using PPS compared to CKM. In PPS, Coelastrella sp. and Chlorella vulgaris reached the highest cell densities after 15 days, about 79 × 106 and 43 × 106 cells mL−1, respectively. Although in PPS, ammonium was completely assimilated (195 mg L−1), this was only 46% (172 mg L−1) in CKM. Coelastrella sp. produced the highest biomass concentration independently of the medium (1.84 g L−1 in PPS and 1.99 g L−1 in CKM). This strain is a promising candidate for nutrient removal and biomass production in the aforementioned media, followed by Chlorella vulgaris and Chlorococcum sp. They have great potential to reduce the environmental impact of industrial anaerobic digestion effluents in Nordic countries.