Luigi di Bitonto

The environmental and economic challenges stemming from fossil fuel dependence and climate change highlight the urgent need for sustainable biofuels. Wastewater treatment byproducts, such as sewage sludge (SS), represent a promising, yet underutilized, feedstock for biodiesel production within a circular economy. This research proposes a closed-loop valorization strategy for wastewater treatment byproducts, integrating solventless lipid extraction with the pyrolysis (at 400, 550, and 750 °C) of lipid-free residual biomass to produce the relevant biochars (BC). BCs can be functionalized (sulfonation run at 175 °C, 24 h), characterized (CHNS, FTIR, XRD, SBET, TPD, SEM), and used as catalysts for the esterification reaction of the previously extracted lipids with methanol to produce biodiesel. The extracted lipids were reacted with methanol (1:10 molar ratio, 80 °C, 5 h) using 3 wt.% of sulfonated catalysts per gram of grease, producing fatty acid methyl esters in high yield and conversion (>96%). Catalysts were easily and efficiently recoverable through centrifugation, rendering them stable and reusable for five cycles without losing their catalytic properties. This approach aims to transform SS into a valuable resource, fostering a more sustainable and efficient biofuel production system.

Oleochemicals, which are obtained from vegetable and animal fats and oils, have become indispensable in the food, cosmetics, pharmaceutical and biofuel industries. Traditionally, they are synthesized using chemical catalysts, a process that is often associated with high energy requirements and a considerable environmental impact. Biocatalysis, using enzymes such as lipases, has emerged as a transformative alternative that offers high specificity, environmental friendliness and cost-efficiency. This review comprehensively examines the current state of biocatalysis for oleochemical synthesis, highlighting key reactions such as esterification and transesterification and their integration into industrial processes. A bibliometric analysis uncovers global trends and collaborations, while case studies illustrate cost efficiency and scalability. The article outlines recommendations and future research directions to advance biocatalytic processes. This review is intended to be an important resource for researchers and industries transitioning to sustainable oleochemical production.

The organic fraction of municipal solid waste (OFMSW) is widely recognized as a possible substrate for anaerobic digestion processes. However, the heterogeneity of this matrix and the presence of slowly biodegradable compounds can slow down anaerobic digestion and reduce its performance. This study compares the effectiveness of different thermal pre-treatments in increasing OFMSW anaerobic digestibility. Thermal pre-treatments were compared with OFMSW shredding, considered as the minimum pre-treatment required in order to reduce particles size of the OFMSW. The pre-treatments were performed in autoclave (121 °C and 1.4 bar for 20 min) or in an ad hoc hydrolysis reactor designed for the experimental trial (140 °C and 7 bar for 30 min) with air or nitrogen as gas phase. The thermal pre-treatments affected methane yield (NmLCH₄/gVS), depending on the pre-treatment strategy, with autoclaving allowing for an 80% increase with respect to the control run, and leading to a methane yield of 476 ± 194 NmL_CH4/gVS. The pre-treatments in the hydrolysis reactor caused a loss of organic matter (due to its volatilization) reducing the organic loading rate of the digester. Nevertheless, the digester performance in terms of COD (chemical oxygen demand) and VSS (volatile suspended solid) removal showed limited differences among the pre-treatments applied and ranged on average 79–94%.

In this work, a detailed analysis of the lipid component in primary sludge and sewage scum up-taken from several wastewater treatment plants located in southern Italy was carried out. Lipids in the primary sludge accounted for 200–250 mg/g of the total solids (TS), with calcium soaps as a main component (70–82%), while total lipids made up about 350–500 mg/g_TS in the sewage scum and consisted mainly of FFAs (45–60%) and calcium soaps (27–35%). In addition, estolides and 10-hydroxystearic acid were also quantified. A specific valorization process was then developed and tested for either primary sludge or sewage scum. In detail, lipids were first recovered, chemically activated by the addition of acids (calcium soaps were converted to free fatty acids) and finally reacted with methanol to obtain methyl esters. The lipid recovery from primary sludge and sewage scum was particularly efficient (recoverability of 92–99%). The conversion of the starting acids into FAMEs (yield > 98%) was achieved under very mild conditions (70 °C, 2 h) with AlCl₃·6H₂O as a catalyst. Biodiesel (according to EN14214), methyl 10-hydroxystearate and methyl estolides were efficiently isolated by distillation under vacuum. Finally, a feasibility study of the proposed processes was carried out to evaluate their possible integration into a wastewater treatment plant, critically analyzing both the positive aspects and the relative limitations.

In this work, a closed-loop strategy for the management and valorization of winery waste was proposed. The exhausted pomace and grape stalks that are typically obtained from white wine industries were used as a source of simple sugars, namely, glucose and fructose, and of lignocellulosic feedstock for the preparation of selective catalysts for the 5-hydroxymethylfurfural (5-HMF) production from fructose. A novel synthetic procedure was developed for the synthesis of iron-sulfonated magnetic biochar catalysts (Fe-SMBCs). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), BET surface area, porous structure analysis and determination of total amount of acid sites were performed in order to characterize the physico-chemical properties of the synthesized systems. Then, these heterogeneous catalysts were successfully tested via the dehydration of simple sugars into 5-HMF by using methyl isobutyl ketone (MIBK) and gamma valerolactone (GVL) as co-solvents. The optimum 5-HMF yield of 40.9 ± 1.1%mol with a selectivity of 59.8 ± 2.6%mol was achieved by adopting the following optimized conditions: 0.1 g of catalyst, volume ratio of GVL to H₂O = 2 to 1, 403 K, 6 h. In addition, the catalyst was easily recycled using an external magnetic field and used for at least five reaction cycles without significant loss of catalytic activity.

In this work, a novel sustainable approach was proposed for the integral valorisation of Arctium lappa (burdock) seeds and roots. Firstly, a preliminary recovery of bioactive compounds, including unsaturated fatty acids, was performed. Then, simple sugars (i.e., fructose and sucrose) and phenolic compounds were extracted by using compressed fluids (supercritical CO₂ and propane). Consequently, a complete characterisation of raw biomass and extraction residues was carried out to determine the starting chemical composition in terms of residual lipids, proteins, hemicellulose, cellulose, lignin, and ash content. Subsequently, three alternative ways to utilise extraction residues were proposed and successfully tested: (i) enzymatic hydrolysis operated by Cellulases (Thricoderma resei) of raw and residual biomass to glucose, (ii) direct ethanolysis to produce ethyl levulinate; and (iii) pyrolysis to obtain biochar to be used as supports for the synthesis of sulfonated magnetic iron-carbon catalysts (Fe-SMCC) to be applied in the dehydration of fructose for the synthesis of 5-hydroxymethylfurfural (5-HMF). The development of these advanced approaches enabled the full utilisation of this resource through the production of fine chemicals and value-added compounds in line with the principles of the circular economy.

In this work, the transesterification of methyl estolides (ME) extracted from the lipid component present in the sewage scum was investigated. Methyl 10-(R)-hydroxystearate (Me-10-HSA) and Fatty Acid Methyl Esters (FAMEs) were obtained in a single step. A three-level and four factorial Box–Behnken experimental design were used to study the effects of methanol amounts, catalyst, temperature, and reaction time on the transesterification reaction using aluminum chloride hexahydrate (AlCl₃·6H₂O) or hydrochloric acid (HCl) as catalysts. AlCl₃·6H₂O was found quite active as well as conventional homogeneous acid catalysts as HCl. In both cases, a complete conversion of ME into Me-10-HSA and FAMEs was observed. The products were isolated, quantified, and fully characterized. At the end of the process, Me-10-HSA (32.3%wt) was purified through a chromatographic separation and analyzed by NMR. The high enantiomeric excess (ee > 92%) of the R-enantiomer isomer opens a new scenario for the valorization of sewage scum.