Valorisation of digestate from biowaste through solid-state fermentation to obtain value added bioproducts: A first approach.

Digestate from biowaste was assessed as a potential source of bioproducts of commercial and industrial interest through solid-state fermentation. The targeted bioproducts were hydrolytic enzymes (cellulases and proteases from autochthonous microbiome), biosurfactants (sophorolipids produced from Starmella bombicola) and biopesticides (produced from Bacillus thuringiensis). Low cellulase production was observed within the range of 0.5-1.5 FPU g-1 DM while protease production showed two discrete peaks of 66 ±â€¯8 and 65 ±â€¯3 U g-1 DM at 3.5 and 48 h, respectively. Low sophorolipids production was also obtained, with a maximum yield of 0.02 g g-1 DM using hygienised digestate supplemented with external sugar and fat sources. Biopesticides produced by B. thuringiensis were successfully at 72 h of operation, reaching a maximum spore production of 8.15 ±â€¯0.04 (107) CFU g-1 DM and 2.85 ±â€¯0.22 (107) CFU g-1 DM using sterile and hygienised digestate, respectively. These biopesticides could contribute to the substitution of chemically produced pesticides, moving towards a sustainable digestate management in a circular economy scheme.

Composting of food wastes: Status and challenges.

This review analyses the main challenges of the process of food waste composting and examines the crucial aspects related to the quality of the produced compost. Although recent advances have been made in crucial aspects of the process, such composting microbiology, improvements are needed in process monitoring. Therefore, specific problems related to food waste composting, such as the presence of impurities, are thoroughly analysed in this study. In addition, environmental impacts related to food waste composting, such as emissions of greenhouse gases and odours, are discussed. Finally, the use of food waste compost in soil bioremediation is discussed in detail.

Cellulase and xylanase production at pilot scale by solid-state fermentation from coffee husk using specialized consortia: The consistency of the process and the microbial communities involved.

Solid state fermentation is a promising technology however rising concerns related to scale up and reproducibility in a productive process. Coffee husk and a specialized inoculum were used in a 4.5L and then in 50L reactors to assess the reproducibility of a cellulase and hemicellulase production system. Fermentations were consistent in terms of cellulase production and microbial communities. The higher temperatures achieved when operating at 50L generated a shift on the microbial communities and a reduction of nearly 50% on cellulase production at pilot scale. In spite, an overall enzymatic production of 3.1±0.5FPUg-1DM and 48±4Ug-1DM for FPase and Xyl activities was obtained, respectively, with low deviation coefficients of 16 and 19% for FPase and Xyl production. Gaseous emissions assessment revealed an emission factor of 2.6·10-3kg volatile organic compounds per Mg of coffee husk and negligible NH3, CH4 and N2O emissions.

Towards a competitive solid state fermentation: Cellulases production from coffee husk by sequential batch operation and role of microbial diversity.

The cost of cellulases is the main bottleneck for bioethanol production at commercial scale. Solid-state fermentation (SSF) is a promising technology that can potentially reduce cellulases cost by using wastes as substrates. In this work, a SSF system of 4.5L bioreactors was operated continuously by sequential batch operation using the fermented solids from one batch to inoculate the following batch. Coffee husk was used as lignocellulosic substrate. Compost was used as starter in the first batch to provide a rich microbiota. Two strategies were applied: using 10% fermented solids as inoculum in 48h batches (SB90) and using 50% solids in 24h batches (SB50). A consistent and robust production process was achieved by sequential batch operation. Similar cellulase activities around 10 Filter Paper Units per gram of dry solids were obtained through both strategies. Microbial diversity in the starting materials and in the final fermented solids was characterized by next generation sequencing. Microbial composition of both fermented solids was similar but the relative abundance of families and species was affected by the operation strategy used. Main bacteria in the final solids came from compost (families Sphingobacteriaceae, Paenibacillaceae and Xanthomonadaceae), while main fungi families came from coffee husk (families Phaffomycetaceae, Dipodascaceae and two unidentified families of the class of Tramellomycetes). There was a high presence of non-identified mycobiota in the fermented solids. Main identified species were the bacteria Pseudoxanthonomas taiwanensis (12.3% in SB50 and 6.1% in SB90) and Sphingobacterium composti (6.1% in SB50 and 2.6% in SB90) and the yeasts Cyberlindnera jardinii and Barnettozyma californica (17.8 and 4.1% respectively in SB50 and 34 and 9.1% in SB90), all four previously described as lignocellulose degraders. The development of these operational strategies and further biological characterization of the end product could eventually benefit the process economics by providing a standard and specialized inoculum for a continuous SSF for cellulases production.

Gaseous emissions during the solid state fermentation of different wastes for enzyme production at pilot scale.

The emissions of volatile organic compounds (VOC), CH4, N2O and NH3 during the solid state fermentation process of some selected wastes to obtain different enzymes have been determined at pilot scale. Orange peel+compost (OP), hair wastes+raw sludge (HW) and winterization residue+raw sludge (WR) have been processed in duplicate in 50 L reactors to provide emission factors and to identify the different VOC families present in exhaust gaseous emissions. Ammonia emission from HW fermentation (3.2±0.5 kg Mg(-1) dry matter) and VOC emission during OP processes (18±6 kg Mg(-1) dry matter) should be considered in an industrial application of these processes. Terpenes have been the most emitted VOC family during all the processes although the emission of sulphide molecules during HW SSF is notable. The most emitted compound was dimethyl disulfide in HW and WR processes, and limonene in the SSF of OP.

The enhancement of antioxidant compounds extracted from Thymus vulgaris using enzymes and the effect of extracting solvent.

We evaluate the total phenolic compounds (TPC) content and the antioxidant activity (AA) of extracts obtained from ground fresh thyme (FT) and depleted thyme (DT), a by-product of the process of essential oil extraction. In addition, enzymatic treatments were evaluated to improve the extraction yields of polyphenolic compounds from thyme. Extractions were performed using several solvents as methanol, ethanol, and water. Enzymes were applied prior to extraction or during the extraction process. The best results were obtained using a mixture of methanol and water, resulting in 2790 and 220 mg Gallic acid equivalent (GAE)/L of TPC for FT and DT, respectively. A similar result was observed for AA. With regard to enzymatic treatment, application of Grindamyl CA 150 enzyme as a pre-treatment resulted in the production of an extract from DT with 614 mg TE (trolox equivalent)/L of AA, 70% more than the control, and an AA of 621 mg TE/L (74% more than the control sample) was obtained using Grindamyl CA 150 during the extraction process. These results suggest that enzymatic treatment is an interesting alternative for producing antioxidant extracts from DT.