In this work, a novel up-flow anaerobic sludge blanket solid-state reactor was proposed for the degradation of fruit and vegetable wastes, RAFAELL for its acronym in Spanish (Reactor Anaerobio de Flujo Ascendente Empacado con Lecho de Lodos). The design considers a solid-state section: This is a pre-treatment stage (disintegration) in which organic solid wastes are subjected to shear to increase both the number of particles smaller than 105 μm and the concentration of dissolved solids (particles smaller than 2.5 μm). Hydrolysis and acidogenesis reactions are also presented in the solid-state section. The design also considers a section of sludge blanket to increase the residence time of the cells. The recirculation stream transports the faster biodegradable fraction from the solid-state section to the sludge blanket section, favoring methane productivity. The design includes a buffer section, where the alkalinity leaving the sludge bed consumes the acidity produced in the solid-state section, allowing greater stability of the pH in the reactor. In assessing the behavior of the proposed digester, good volatile solid removal efficiencies (67%) were obtained in 4 days of solids retention time, with an acceptable methane productivity between 0.5 and 3.6 L_CH4/(L · day) for loads between 1 and 10 g VS/(L · day). The productivity expressed in L_CH4/(g SV_consumed · day) was between 0.027 and 0.116 L_CH4/(g SV_consumed · day).

This study examines the anaerobic digestion (AD) of fruit and vegetable waste (FVW) and digestates to assess the effect of particle size on anaerobic biodegradability (AB) and process rate at different stages of digestion progress. Batch assays were conducted with FVW mixtures and digestates from 5, 10, and 15 days of digestion, using four particle size ranges: Ø1 < 1.8 µm, 1.8 < Ø2 < 500 µm, 500 < Ø3 < 1000 µm, and Ø4 > 1000 µm. While AB and specific methanogenic activity (SMA) showed no significant differences among FVW mixtures, particle size significantly influenced these variables. Methane yields were 298.2 and 309.8 $\mathrm{m}\mathrm{L} \mathrm{C}{\mathrm{H}}_4·{\mathrm{g}}^{-1}\mathrm{V}\mathrm{S}$ for Ø4 and Ø3 particles, exceeding the 186.7 and 161.8 $\mathrm{m}\mathrm{L} \mathrm{C}{\mathrm{H}}_4·{\mathrm{g}}^{-1}\mathrm{V}\mathrm{S}$ obtained for Ø2 and Ø1, respectively. These results indicate that particle size reduction enhanced methane production; however, reducing the particle size below 500 µm inhibits methanogenesis due to intermediate accumulation. Compared to FVW, digestates exhibited a 23% reduction in AB, a 73.9% decrease in SMA, and methane yields of 55.8–294 $\mathrm{m}\mathrm{L} \mathrm{C}{\mathrm{H}}_4·{\mathrm{g}}^{-1}\mathrm{V}\mathrm{S}$. Additionally, the surface-based kinetic constant ($K_{SBK}$) decreased from 0.4523 $\mathrm{g}·\mathrm{d}{\mathrm{m}}^{-2}·{\mathrm{d}}^{-1}$for FVW to 0.0437 $\mathrm{g}·\mathrm{d}{\mathrm{m}}^{-2}·{\mathrm{d}}^{-1}$for digestates. These differences are attributed to the rapid consumption of easily biodegradable fractions within the first 5 days of digestion.

Microalgae are used to produce renewable biofuels (biodiesel, bioethanol, biogas, and biohydrogen) and high-value-added products, as well as in bioremediation and CO₂ sequestration tasks. In the case of anaerobic digestion of microalgae, biogas can be produced from mainly proteins and carbohydrates. Anaerobic digestion is a complex process that involves several stages and is susceptible to operational instability due to various factors. Robust controllers with simple structure and design are necessary for practical implementation purposes and to achieve a proper process operation despite process variabilities, uncertainties, and complex interactions. This paper presents the application of a control design based on the modeling error compensation technique for the anaerobic digestion of microalgae. The control design departs from a low-order input–output model by enhancement with uncertainty estimation. The results show that achieving desired organic pollution levels and methanogenic biomass concentrations as well as minimizing the effect of external perturbations on a benchmark case study of the anaerobic digestion of microalgae is possible with the proposed control design.

Waste management in large urban centers is one of the main challenges for public administration. Two of the most abundant wastes in cities are waste solid and municipal wastewater (MWW). Their management can be optimized if they are treated together. This work analyzed an anaerobic–aerobic system for the treatment of fruit and vegetable wastes (FVWs) and MWW. Firstly, FVWs were collected and characterized; once in the laboratory, they were placed in a tank with the MWW, aiming at transferring to the water those solids with a particle size below 105 µm; then, they were separated by sieving. The mixture of MWW and FVWs with a particle size below 105 µm was fed into an up-flow anaerobic sludge reactor (UASB); in the latter, dissolved and suspended organic matter was transformed into methane and carbon dioxide. The water that left the UASB was sent to be post-treated in an activated sludge reactor (ASR). The chemical oxygen demand (COD) was used as an evaluation parameter of the anaerobic–aerobic system; a removal efficiency higher than 80% was achieved, whereas it was 60% in the ASR. Another evaluation parameter was methane (CH₄) productivity, with an average of 3.0 L_CH4 L⁻¹ d⁻¹. VWF leaching achieved an average COD extraction of 7.68 kg∙m⁻³. The UASB efficiency was on average 70% for the assayed loads (2–8 kg COD·L⁻¹·d⁻¹). The energy potential calculated for the anaerobic–aerobic system was 510.2 kW∙h∙d⁻¹

This work presents an autonomous robotic platform aimed at improving indoor air quality and ensuring effective disinfection. The system leverages UVC germicidal radiation and a nebulization module to eliminate pollutants, including ozone and microbial pathogens, aligning with Sustainable Development Goals (SDGs) 3 and 11. The robotic platform incorporates six 253.7 nm UVC lamps arranged to maximize disinfection efficiency, achieving 95% microbial reduction within 14.76 seconds for irradiated areas of 0.98–1.04 m². An integrated olfactory system, using MQ-131 and MQ-135 sensors, monitors ozone and CO2 concentrations, ensuring environmental safety by automatically shutting down disinfection processes when thresholds are exceeded. The nebulization system disperses a hydrogen peroxide (H2O2) solution, reducing ozone levels from 29.22 ppm to 0.05 ppm in enclosed spaces within 3 seconds. The experimental results demonstrate the platform's capability to sanitize surfaces, walls, floors, and ceilings in diverse indoor environments, such as hospitals and classrooms, with minimal human intervention. By combining tele controlled and autonomous functionalities, the system offers a scalable solution for sustainable and inclusive urban environments, addressing key challenges in air quality and health resilience post-COVID-19. This innovation contributes significantly to the goals of creating healthier living spaces and advancing the development of smart, sustainable cities.