Roberto Braglia

Large-scale production of Limnospira platensis (spirulina) for high-value compounds such as C-phycocyanin generates substantial amounts of underexploited residual biomass. Aligned with circular economy, this study evaluated the agricultural upcycling of industrial L. platensis residual biomass (POST) as a biofertilizer comparing its effects with intact biomass (PRE) and a commercial fertilizer on germination, growth, and physiology of Cichorium intybus under laboratory and greenhouse conditions. Composition analyses showed that POST biomass retained high levels of nitrogen, phosphorus, and proteins despite phycocyanin extraction. Germination assays revealed that POST biomass (5 mg mL⁻ ¹ concentration) did not exert phytotoxic effects and significantly enhanced germination, whereas PRE biomass induced inhibitory effects at higher doses. Germination dynamics showed an initial delay followed by equal or improved final germination, suggesting a priming-like response induced by POST biomass. Growth experiments demonstrated that POST biomass markedly promoted plant development, outperforming both PRE biomass and the commercial fertilizer. Fresh weight increases were dose-dependent and pronounced under greenhouse conditions, indicating robustness under environmentally variable settings. Consistently, POST biomass significantly enhanced chlorophyll and carotenoid contents, supporting improved photosynthetic performance. In contrast, PRE biomass showed weaker and less consistent effects. Phenolic and flavonoid contents revealed no stress-related accumulation in POST-treated plants, confirming the absence of adverse physiological responses. Overall, these findings demonstrate that industrial L. platensis leftovers retain significant bioactivity and can be effectively upcycled into sustainable agricultural product. The integration of agricultural reuse into Spirulina biorefinery chains represents a promising strategy to improve the environmental and economic sustainability of cyanobacterial production systems. Key Points • Limnospira platensis (spirulina) leftover biomass (POST) showed no phytotoxicity on Cichorium intybus seeds. • POST biomass administration (10 mg/mL) increased plant fresh weight up to 170%. • POST biomass administration increased plant pigment both laboratory and greenhouse. • Limnospira platensis downstream leftover showed potential as biofertilizer in agriculture.

The possibility of modifying the surface chemistry of materials and synthetizing inorganic particles in natural aqueous extracts of plants (avoiding calcination), opens the doors to undoubtedly interesting scenarios for innovative functionalization strategies that are increasingly eco-sustainable and rich in interesting chemical–physical and biochemical properties. Among the aerial plants, Satureja montana exhibits interesting antibacterial, antifungal, antimicrobial, and antioxidant activities due to the rich volatile and non-volatile compounds (characterized by gas chromatography–mass spectrometry), contained in the aqueous extracts. For the first time, the latter was applied for the green synthesis of TiO₂ and CaCO₃ particles, characterized by X-ray diffraction, Raman, infrared spectroscopies, and scanning electron microscopy, coupled with microanalysis. Screening through antimicrobial assays under indoor passive sedimentation conditions showed opposite trends for two kinds of particles. TiO₂ anatase spherical particles (400 < φ < 600 nm) increase microbial growth, proportionally to increasing particle concentration. Instead, S. montana-functionalized CaCO₃ prismatic microparticles (1 µm × 1 µm × 1 µm) exhibit strong and dose-dependent antimicrobial activities, achieving near-complete inhibition at 50 mg/mL.

The possibility of modifying the surface chemistry of materials, synthetizing inorganic particles in natural aqueous extracts of plants (at low temperature, avoiding calcination), opens the doors to undoubtedly very interesting scenarios for innovative functionalization strategies that are increasingly eco-sustainable and rich in interesting chemical-physical and biochemical properties. Among the aerial plant, Satureja montana exhibits interesting antibacterial, antifungal, antimicrobial and antioxidant activities due to the rich volatile and non-volatile compounds (as activators/phase controllers characterized by Gas Chromatography-Mass Spectrometry, GC-MS), contained in the aqueous extracts. For the first time, the aqueous extract of Satureja montana plant was applied for the green synthesis of TiO2 and CaCO3 particles, characterized by X-Ray diffraction (XRD), Raman, Infrared/IR spectroscopies, and Scanning Electron Microscopy-SEM/coupled by microanalysis EDX. Screening through antimicrobial assays under indoor passive sedimentation conditions showed opposite trends for both kind of inorganic particles. TiO₂ Anatase spherical particles (400<<600 nm) increase microbial growth, proportionally to increasing particles concentration (dose-dependent response). Probably, the low surface area (1.20 m2/g), low porosity (pore volume 0.0023 cm3/g; pore size of 560 nm) and smooth spherical morphology, don’t provoke chemical or physical damages to microorganisms, and therefore microbial growth is not inhibited. This occurs in the presence of medium/low concentrations of ROS (oxygenated radical species), which are chemically active in generating oxidative stress and cell death. In fact, the chemically reactive defects found in these TiO2/Anatase particles are predominantly carbonyl in nature, less reactive than carboxylic ones in producing ROS. Instead, S. montana-functionalized CaCO₃ prismatic microparticles (1µm x 1µm x 1µm) exhibit strong and dose-dependent antimicrobial activities, achieving near-complete inhibition at 50 mg mL⁻¹. This could be related to the molecular activators/phase controllers that induced defects, edges, dislocations and chemical active surface functionalities on the prismatic calcite particles, making them capable of inhibiting microbial activity. In particular, the presence of carboxyl groups C=(O)-OH, recorded by FTIR on the prismatic surfaces of CaCO3 MPs/SM particles, could be responsible for the production of ROS, the latter known to be dangerous sentinels of oxidative stress and cell death.

The increasing global demand for sustainable food production, coupled with the micronutrient limitations of aquaponic systems, calls for innovative fertilization strategies that enhance crop yield and nutritional quality while preserving environmental integrity. This study evaluates the effectiveness of zinc-functionalized calcium carbonate microparticles (Zn-Alg-CaCO₃ MPs) as a smart foliar fertilizer in aquaponics. Tomato plants (Solanum lycopersicum L. cv. Principe Borghese) were grown in a recirculating aquaponic system and treated with three concentrations of Zn-MPs (10, 50, and 250 ppm) via foliar spray, using a control group treated with water. Each treatment was applied to 15 plants under controlled greenhouse conditions. Yield parameters, antioxidant content, and nutritional quality were assessed. The 250 ppm treatment significantly increased yield per plant (+ 74.9%), number of fruits (+ 44.4%), and average fruit weight (+ 22.1%) compared to control. Antioxidant activity, phenolic, flavonoid, and lycopene content were also enhanced, particularly at the highest dose. Importantly, no increase in zinc was detected in recirculating water, highlighting the environmental safety of foliar application. These findings underscore the potential of Zn-Alg-CaCO₃ MPs as a sustainable solution for precision fertilization in aquaponic agriculture. Further molecular and environmental studies are recommended to optimize and scale this technology.

Aquaponics is an innovative agricultural method combining aquaculture and hydroponics. However, this balance can lead to the gradual depletion of essential micronutrients, particularly iron. Over time, decreasing iron levels can negatively impact plant health and productivity, making the monitoring and management of iron in aquaponic systems vital. This study investigates the use of Fe-Alg-CaCO₃ microparticles (MPs) as foliar fertilizer on lettuce plants in an aquaponic system. The research investigated Lactuca sativa L. cv. Foglia di Quercia Verde plants as the experimental cultivar. Three iron concentrations (10, 50, and 250 ppm) were tested, with 15 plants per treatment group, plus a control group receiving only sterile double-distilled water. The Fe-Alg-CaCO₃ MPs and ultrapure water were applied directly to the leaves using a specialized nebulizer. Foliar nebulization was chosen for its precision and minimal resource use, aligning with the sustainability goals of aquaponic cultivation. The research evaluated rosette diameter, root length, fresh weight, soluble solids concentration, levels of photosynthetic pigments, and phenolic and flavonoid content. The 250 ppm treatment produced the most notable enhancements in both biomass yield and quality, highlighting the potential of precision fertilizers to boost sustainability and efficiency in aquaponic systems. In fact, the most significant increases involved biomass production, particularly in the edible portions, along with photosynthetic pigment levels. Additionally, the analysis of secondary metabolite content, such as phenols and flavonoids, revealed no reduction compared to the control group, meaning that the proposed fertilizer did not negatively impact the biosynthetic pathways of these bioactive compounds. This study opens new possibilities in aquaponics cultivation, highlighting the potential of precision fertilizers to enhance sustainability and productivity in soilless agriculture.

Aquaponics represents an alternative to traditional soil cultivation. To solve the problem of nutrient depletion that occurs in this biotechnological system, the application of a spirulina-based biofertilizer was assessed. The microalgal waste used in this study came from industrial processing. Four different dilutions of the supernatant portion of this waste were sprayed on lettuce plants cultivated in an aquaponics system installed at the Botanical Gardens of the Tor Vergata University of Rome. The biofertilizer was characterized to evaluate its amount of macro- and micronutrients. The analysis conducted on the plants involved both morpho-biometric aspects and qualitative–quantitative measurements. The experiments showed that the spirulina extract had a positive effect on the growth and nutraceutical content of the lettuce plants; the obtained results highlighted that a dilution of 75% was the best for treatment. The use of the proposed organic and recycled fertilizer could increase the sustainability of crop cultivation and promote the functioning of aquaponics systems.

In the framework of regenerative circular economy and Sustainable Development Goals #6, water demand and wastewater production are a crucial environmental issue. To cope with this, a system called Zero Mile has been conceived to reuse/upcycle the dishwasher wastewater in both fertilisation of a vertical garden (for home plant production at zero mile) and the subsequent dishwasher rinsing cycle. The core of the Zero Mile system is a biofilter constituted by an ad hoc engineered microbial consortium, based on the mutualistic relationship between autotrophic and heterotrophic microbial partners, that makes the biodegradative process sustainable over time. Two semi-batch tests were performed to evaluate the capability and the efficiency of the microbial consortium to operate in conditions mimicking the Zero Mile system: consortia were challenged in two dishwasher wastewater volumes (50 and 500 mL), with a replenishing rate of 4 days for ¼ of the dishwasher wastewater volume. The results of these tests showed that the consortium thrives well in dishwasher wastewater over time and can survive with the volume and rates of replenishments. Next Generation Sequencing showed that the microbial consortium maintains a stable taxonomic composition, and chemical analyses demonstrated a very high bioremediation efficiency (total nitrogen and phosphorus removal). Aiming to contribute to the circular economy approach, the consortium ‘treated’ dishwasher wastewater was useful for plant fertilisation, as demonstrated by pigment content and quality indices (total phenols and flavonoids, soluble solids) measured in the lettuce plants grown in the Zero Mile demonstrator and watered with consortium reclaimed dishwasher wastewater.

Our world is facing an environmental crisis that is driving scientists to research green and smart solutions in terms of the use of renewable energy sources and low polluting technologies. In this framework, photovoltaic (PV) technology is one of the most worthy of interest. Dye-sensitized solar cells (DSSCs) are innovative PV devices known for their encouraging features of low cost and easy fabrication, good response to diffuse light and colour tunability. All these features make DSSCs technology suitable for being applied to the so-called agrovoltaic field, taking into account their dual role of filtering light and supporting energy needs. In this project, we used 40 DSSC Z-series connected modules with the aim of combining the devices’ high conversion efficiency, transparency and robustness in order to test them in a greenhouse. A maximum conversion efficiency of 3.9% on a 221 cm² active area was achieved with a transparency in the module’s aperture (312.9 cm²) area of 35%. Moreover, different modules were stressed at two different temperature conditions, 60 °C and 85 °C, and under light soaking at the maximum power point, showing a strong and robust stability for 1000 h. We assembled the fabricated modules to form ten panels to filter the light from the roof of the greenhouse. We carried out panel measurements in outdoor and greenhouse environments in both sunny and cloudy conditions to find clear trends in efficiency behaviour. A maximum panel efficiency in outdoor conditions of 3.83% was obtained in clear and sunny sky conditions.