Showing papers by "Maurizio Volpe published in 2021"

Process Water Recirculation during Hydrothermal Carbonization of Waste Biomass: Current Knowledge and Challenges

Abstract: Hydrothermal carbonization (HTC) is considered as an efficient and constantly expanding eco-friendly methodology for thermochemical processing of high moisture waste biomass into solid biofuels and valuable carbonaceous materials. However, during HTC, a considerable amount of organics, initially present in the feedstock, are found in the process water (PW). PW recirculation is attracting an increasing interest in the hydrothermal process field as it offers the potential to increase the carbon recovery yield while increasing hydrochar energy density. PW recirculation can be considered as a viable method for the valorization and reuse of the HTC aqueous phase, both by reducing the amount of additional water used for the process and maximizing energy recovery from the HTC liquid residual fraction. In this work, the effects of PW recirculation, for different starting waste biomasses, on the properties of hydrochars and liquid phase products are reviewed. The mechanism of production and evolution of hydrochar during recirculation steps are discussed, highlighting the possible pathways which could enhance energy and carbon recovery. Challenges of PW recirculation are presented and research opportunities proposed, showing how PW recirculation could increase the economic viability of the process while contributing in mitigating environmental impacts.

Industrial-Scale Hydrothermal Carbonization of Agro-Industrial Digested Sludge: Filterability Enhancement and Phosphorus Recovery

Abstract: Hydrothermal carbonization (HTC) provides an attractive alternative method for the treatment of high-moisture waste and, in particular, digested sludge. HTC could reduce the costs and environmental risks associated with sludge handling and management. Although it is recognized that the dewaterability of hydrochars produced from digested sludge, even at mild temperatures (180–190 °C), is highly improved with respect to the starting material, the filterability of HTC slurries for the recovery of the solid material (hydrochar) still represents a challenge. This study presents the results of an investigation into the filterability of agro-industrial digested sludge HTC slurries produced by a C-700 CarboremTM HTC industrial-scale plant. The filterability of HTC slurries, produced at 190 °C for 1 h, with the use of acid solutions of hydrochloric acid, sulfuric acid or citric acids, was investigated by using a semi-industrial filter press. The use of sulfuric acid or citric acid solutions, in particular, significantly improved the filterability of HTC slurries, reducing the time of filtration and residual moisture content. The acid treatment also promoted the migration of heavy metals and phosphorus (P) in the HTC filtrate solution. This study demonstrates that P can be recovered via the precipitation of struvite in high yields, recovering up to 85 wt% by mass of its initial P content.

Enhancement of energy and combustion properties of hydrochar via citric acid catalysed secondary char production

Abstract: The present study investigates the use of hydrothermal carbonization (HTC) to upgrade agro-waste into solid biofuels and the use of citric acid (CA) as a catalyst capable of enhancing energy properties of hydrochars. HTC of pineapple waste (PA) was carried out at 180, 220, and 250 °C at a fixed 1-h residence time with and without the addition of CA. Contrarily to the current understanding with regard to the use of an acid catalyst during HTC, CA addition shows to appreciably increase hydrochar mass yields with HTC temperature, while increasing their degree of coalification and carbon retention. PA hydrochars produced with the addition of CA exhibit higher heating values (HHV) up to 29.7 MJ/kg dry basis (db), low residual ash (between 0.53 and 0.75 wt% db), and better combustion properties when compared to those of hydrochars obtained without CA addition. We show that the increase in mass yields and energy properties observed for hydrochars is due to CA catalytic effect toward back-polymerization of organics in the liquid phase to form secondary char. Secondary char formation and its role in influencing the hydrochar properties as solid biofuels are demonstrated by scanning electron microscopy, proximate, elemental analysis, and combustion reactivity.

Hydrothermal Carbonization of Lemon Peel Waste: Preliminary Results on the Effects of Temperature during Process Water Recirculation

Abstract: Hydrothermal carbonization (HTC) is a promising thermochemical pre-treatment to convert waste biomass into solid biofuels. However, the process yields large amounts of organic process water (PW), which must be properly disposed of or reused. In this study, the PW produced from the hydrothermal carbonization of lemon peel waste (LP) was recycled into HTC process of LP with the aim of maximize energy recovery from the aqueous phase while saving water resources and mitigating the overall environmental impact of the process. The effects of HTC temperature on the properties of solid and liquid products were investigated during PW recirculation. Experiments were carried out at three different operating temperatures (180, 220, 250 °C), fixed residence times of 60 min, and solid to liquid load of 20 wt%, on a dry basis. Hydrochars were characterized in terms of proximate analysis and higher heating values while liquid phases were analyzed in terms of pH and total organic carbon content (TOC). PW recirculation led to a solid mass yield increase and the effect was more pronounced at lower HTC temperature. The increase of solid mass yield, after recirculation steps (maximum increase of about 6% at 180 °C), also led to a significant energy yield enhancement. Results showed that PW recirculation is a viable strategy for a reduction of water consumption and further carbon recovery; moreover preliminary results encourage for an in-depth analysis of the effects of the PW recirculation for different biomasses and at various operating conditions.

Slow pyrolysis for energy valorization of pistachio shells

Abstract: Pistachio shell waste was treated via slow pyrolysis using a fixed bed horizontal lab scale pyrolyzer to evaluate the possibility to product high energy dense solid biofuel and/or a valuable carbonaceous material for advanced applications Pistachio shells, obtained from a fruit processing industry located in Catania, Sicily, were pyrolyzed with flowing nitrogen (150 ml/min) at 200, 250, 315 400 and 500 °C for 05 hours Pyrolysis products, solid, liquid and gas fractions were characterized in terms of mass yields, while raw material and biochars were characterized via thermogravimetric and calorimetric analysis to evaluate proximate analysis and high heating values (HHV) respectively Results showed that, on a dry basis, solid mass yields, on a dry basis, varied between 98 and 25% at 200 and 500 °C respectively, while liquid yields increased up to 48% at 500 °C HHV of solid residues increased with temperature up to 313 MJ/kg at 500 °C but with a sharp increase between 250 and 315 °C showing values of 214 and 269 MJ/kg respectively

Characterization of Italian food waste bio-methane potential evaluation via anaerobic digestion

Abstract: In Italy more than 7 Mtons of organic solid waste are generated each year, on average 117.29 kg/hab.year The eating habits of the Italian population was studied to identify the most consumed foods. The most consumed foods were used to prepare a representative sample of food waste. Two methods were used to estimate the bio-methane production potential. The first method, calculate the bio-methane production potential based on the concentrations of lipids, carbohydrates and proteins, the second method use the results of the elemental analysis. The characterization results showed a potential for generating bio-methane of 219 ml.CH4/g for method 1 and 534 ml.CH4/gSV for method 2. Considering the generation of food waste in Italy and the potential for bio-methane production results show that it would be possible to produce 1,543.x 106 and 3,092 x 106 m3CH4 for method 1 and 2 respectively and thus For the method 1, it is possible to recovery equivalent energy 50,942 TJ/year and 102,044 TJ/year for method 2.