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Orange peels (OPs) were valorized in a lab-scale biorefinery loop for the recovery of limonene and the subsequent production of volatile fatty acids (VFAs) and activated carbon (AC). Solid/liquid extraction of limonene was optimized using n-hexane at 85 °C with an OPs-to-solvent ratio of 2:1, allowing for a limonene recovery yield of 1.20% w/w. Then, post-extraction OPs were used for the production of both VFAs and AC. For VFA production, a hydraulic retention time (HRT) of 5 days and a total solid (TS) inlet content of 10% w/w were adopted leading to a VFA yield of about 43% gVFAs/gTS. Adsorption tests revealed that, among all the solid matrixes tested, only powdered activated carbon (PAC) was able to discriminate no-VFA compounds and allowed for VFA purification. For AC production, post-extraction OPs were firstly converted into biochar through slow pyrolysis at 550 °C for 1 h and then physically activated with CO2 at 880 °C for 1 h. Extraction did not appreciably affect OP properties, while pyrolysis increased the carbon content (from 43 to 83%) and the heating value (from 17 to 29 MJ/kg) of the material. Physical activation of OP biochar increased its surface area by almost ten times, from 40 to 326 m2/g, proving the effectiveness of the treatment. [ABSTRACT FROM AUTHOR]

This work investigates an innovative process to valorise agricultural digestate by the exploitation of solar energy. Digestate has been located in a lab-scale greenhouse to evaporate the liquid phase. Digestate vapours, rich in ammonia, are sent in a Drechsler trap, filled with 38% w/w sulfuric acid solution, through three solar air fans. A concentration of about 2 M of ammonium sulphate solution was recovered. The remaining dried solid phase, rich in phosphorous compounds, was evaluated as alternative to the commercial fertilizers (46% P2O5) in the growth of maize plants. Equal amount of P was applied to each pot (25 mg/kg soil). The plants were evaluated along the 8 weeks in a greenhouse monitoring the growth parameters and leaf SPAD index, micro-, macronutrients and non-essential heavy metals. The results evidenced that the dried solid phase of digestate can be used as an alternative source of P. [ABSTRACT FROM AUTHOR]

A pilot scale biorefinery platform for the treatment of agro-waste and the production of hydrogen, methane and volatile fatty acids was studied in real environment. The system adopted was a two stage anaerobic process where hydrogen and volatile fatty acids were produced in the first phase (fermentation) and methane in the second one (digestion). The study demonstrated the possibility to produce a biogas composed by hydrogen and methane (10% and 55%, respectively) while recovering volatile fatty acids. The yield for acids production was equivalent to 0.13 gVFA/gTVS (as COD) with acetate and butyrate as dominant observed species. [ABSTRACT FROM AUTHOR]

This study investigated the advantages of the anaerobic codigestion process of two urban organic waste: the organic fraction of municipal solid wastes and the waste activated sludge produced during biological wastewater treatment. In particular, a comparison between mono and double stage anaerobic digestion for biogas and biohythane (hydrogen and methane) production, respectively, was conducted at thermophilic conditions in a pilot scale rig with a hydraulic retention time of 20 days. Considering yields, the specific gas productions for the single stage process was 490 l biogas per kg TVS fed to the system while in the two stage process hydrogen and methane productions reached average values of 24 LH2 and 570 LCH4 per kg VS fed to the system, respectively. Obtained biohythane, after upgrading, is particularly valuable for the automotive sector contributing to improve the combustion engine performance and to reduce the contaminants emissions in the atmosphere. [ABSTRACT FROM AUTHOR]

Digestate represents the semi-liquid byproduct of the anaerobic digestion process. It was estimated that 56 Mtonnes of digestate are annually produced only in Europe. Digestate composition depends on the initial total solids (TS) mixture fed to the digester and by its origin (manure, food wastes, agricultural residues, wastewater sludge). Typical values for the different components include a stabilized organic matter content between 20 and 50 g/L, a good content of nitrogen compounds (2–8 g/kg) and of phosphorous compounds (up to 3 g/kg). In particular, ammonia presence in digestate is interesting for ammonium sulfate production, a fertilizer which favors plants' growth. Traditional ammonium sulfate synthesis is conducted by stripping followed by sulfuric acid absorption, a process which requires high energy and chemicals consumptions. This work investigates the exploitation of solar energy to evaporate the liquid phase of digestate in a lab-scale greenhouse. Digestate vapors, rich in ammonia, are sent in a Drechsler trap, filled with 38% w/w sulfuric acid solution, through three solar air fans. The process has been tested on digestates differing for TS content and origin. It emerged that the process is favored by digestates with high ammonia content, as those originated from manure, and a TS content of about 10% w/w, which allowed to obtain an ammonium sulfate concentration of about 2 M in the final solution. [ABSTRACT FROM AUTHOR]

The hydrolytic effect of a commercial enzymes mixture, containing mainly cellulose-degrading and hemicellulose-degrading enzymes, was studied during the mesophilic anaerobic digestion of two different mixtures of maize (Zea mays L.) and triticale (× Triticosecale Wittm. ex A. camus). Laboratory-scale trials demonstrated that, for the crop mixtures studied, the enzymatic pretreatment had limited practical value as enhancement agent in terms of both, specific gas production and viscosity reduction. Then, a complete set of biomethane potential essays was conducted aiming to build a more robust base of knowledge regarding hydrolytic powerfulness of enzyme supplementation. Two commercial enzymatic products were applied in different supply modes to several lignocellulosic substrates which are typically employed in real biogas plants. Results confirmed that neither enzymatic pretreatment nor direct application of enzymes in the reactor contribute meaningfully during mesophilic digestion of substrates with original high degradability such as maize and triticale. Nevertheless, significant enhancements of the degradation and conversion into biogas were observed when enzymes were supplied to digestion of agricultural biomasses with complex lignocellulosic structure: both enzymes tested improved the degradation performance of sorghum (Sorghum bicolor L. Moench) silage, straw or corn cob flour leading to increases over 30% of biogas production. [ABSTRACT FROM AUTHOR]

Stable operation of high-rate thermophilic sludge anaerobic reactors is sometime hard to achieve because of the nature of the anaerobic digestion (AD) process itself and the combination of biological and chemical reactions. An interesting and innovative way to handle AD data resides in multivariate statistical approaches since a more accurate analysis can be performed and fault or abnormal schemes detections can be enhanced. In this paper, principal component analysis (PCA) was the basic multivariate tool used to compare single and two stage AD process performances when treating waste activated sludge (WAS), in order to improve their monitoring and control. Two experiments were carried out to perform single and two-stage AD using WAS and fermented WAS as substrates, respectively. Findings from the PCA model agreed with results from the univariate data analysis but additionally showed a higher variability and changes on the stability trend in the AD of WAS. Besides, multivariate statistical process control using Hotelling T2 and Shewhart control charts combined with PCA displayed an out-of-control scheme revealing a transition period, in which the stability pattern of this experiment changed strongly, towards an accumulation of volatile fatty acids. [ABSTRACT FROM AUTHOR]