Comprehensive review of technologies for separate digestate treatment and agricultural valorisation within circular and green economy.

Anaerobic digestion (AD) has the potential to catalyse the shift from a linear to a circular economy. However, effective treatment and management of both solid (DSF) and liquid (DLF) digestate fraction treatment and management require adopting sustainable technologies to recover valuable by-products like energy, biofuels, biochar, and nutrients. This study reviews state-of-the-art advanced technologies for DSF and DLF treatment and valorisation, using life cycle assessment (LCA) and techno-economic analysis (TEA) in integrated digestate management (IDM). Key findings highlight these technologies' potential in mitigating environmental impacts from digestate management, but there's a need to improve process efficiency, especially at larger scales. Future research should prioritize cost-effective and eco-friendly IDM technologies. This review emphasizes how LCA and TEA can guide decision-making and promote sustainable agricultural practices. Ultimately, sustainable IDM technologies can boost resource recovery and advance circular economy principles, enhancing the environmental and economic sustainability of AD processes.

Occurrence and dissipation mechanisms of organic contaminants during sewage sludge anaerobic digestion: A critical review.

Sewage sludge, a complex mixture of contaminants and pathogenic agents, necessitates treatment or stabilization like anaerobic digestion (AD) before safe disposal. AD-derived products (solid digestate and liquid fraction) can be used as fertilizers. During AD, biogas is also produced, and used for energy purposes. All these fractions can be contaminated with various compounds, whose amount depends on the feedstocks used in AD (and their mutual proportions). This paper reviews studies on the distribution of organic contaminants across AD fractions (solid digestate, liquid fraction, and biogas), delving into the mechanisms behind contaminant dissipation and proposing future research directions. AD proves to be a relatively effective method for removing polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pharmaceuticals, antibiotic resistance genes and hydrocarbons. Contaminants are predominantly removed through biodegradation, but many compounds, especially hydrophobic (e.g. per- and polyfluoroalkyl substances), are also sorbed onto digestate particles. The process of sorption is suggested to reduce the bioavailability of contaminants. As a result of sorption, contaminants accumulate in the largest amount in the solid digestate, whereas in smaller amounts in the other AD products. Polar pharmaceuticals (e.g. metformin) are particularly leached, while volatile methylsiloxanes and polycyclic aromatic hydrocarbons, characterized by a high Henry's law constant, are volatilized into the biogas. The removal of compounds can be affected by AD operational parameters, the type of sludge, physicochemical properties of contaminants, and the sludge pretreatment used.

Optimizing hydrothermal treatment for sustainable valorization and fatty acid recovery from food waste.

This study employs response surface methodology and a central composite design (CCD) to optimize hydrothermal treatment (HTT) conditions for the valorization of food waste (FW). Lab-scale pressure reactor-based HTT processes are investigated to detect the effects of temperature (220-340 °C) and resident time (90-260 min) on elemental composition and fatty acid recovery in the hydrothermal liquid. Central to the study is the identification of temperature as the primary factor influencing food waste conversion during the HTT process, showcasing its impact on HTT product yields. The liquid fraction, rich in saturated fatty acids (SFA), demonstrates a temperature-dependent trend, with higher temperatures favoring SFA recovery. Specifically, HTT at 340 °C in 180 min exhibits the highest SFA percentages, reaching up to 52.5 wt%. The study establishes HTT as a promising avenue for nutrient recovery, with the liquid fraction yielding approximately 95% at optimized conditions. Furthermore, statistical analysis using response surface methodology predicts the optimal achievable yields for hydrochar and hydrothermal liquid at 6.15% and 93.85%, respectively, obtained at 320 °C for 200 min.

Postharvest Quality Improvement of Tomato (Solanum lycopersicum L.) Fruit Using a Nanomultilayer Coating Containing Aloe vera.

The effectiveness of an alginate/chitosan nanomultilayer coating without (NM) and with Aloe vera liquid fraction (NM+Av) was evaluated on the postharvest quality of tomato fruit at 20 °C and 85% relative humidity (RH) to simulate direct consumption. Both nanomultilayer coatings had comparable effects on firmness and pH values. However, the NM+Av coating significantly reduced weight loss (4.5 ± 0.2%) and molds and yeasts (3.5-4.0 log CFU g-1) compared to uncoated fruit (16.2 ± 1.2% and 8.0 ± 0.0 log CFU g-1, respectively). It notably lowered O2 consumption by 70% and a 52% decrease in CO2 production, inhibiting ethylene synthesis. Visual evaluation confirmed NM+Av's efficacy in preserving the postharvest quality of tomato. The preservation of color, indicated by the Minolta color (a*/b*) values, demonstrated NM+Av's ability to keep the light red stage compared to uncoated fruit. The favorable effects of NM+Av coating on enhancing postharvest quality indicates it as a potential alternative for large-scale tomato fruit preservation.