Effect of transition metals and homogeneous hydrogen producers in the hydrothermal liquefaction of sewage sludge

Hydrothermal liquefaction (HTL) of sewage sludge (SS) was performed in the presence of metallic Zn, Fe and Ni to investigate their effect on the performances of the process in terms of product yields and quality. Experiments were performed in subcritical water at 350 ◦C for 10 min using each metal individually and in the presence of homogenous hydrogen producers like formic acid (FA) and KOH. Interesting results were obtained with Zn that when used alone or in the presence of KOH, increased the cumulative biocrude (BC) yields and resulted in energy recoveries (ER) higher than 100% with respect to initial energy content of the biomass, thus indicating that HTL of SS is globally endothermic. …

Catalytic hydrothermal liquefaction of municipal sludge assisted by formic acid for the production of next-generation fuels

Abstract Hydrothermal liquefaction (HTL) of municipal sludge (MS) was studied at 325 °C and 30 min at 10 and 30% w/w concentration of MS using formic acid (FA) as a green liquid hydrogen donor both in the absence and in the presence of heterogeneous catalysts. Pellets of commercial NiMo/Al2O3, CoMo/Al2O3 and felt of activated carbon ACF 1600 were used as catalysts. The addition of FA at high MS loading allowed to increase the yields in BC from 41 to 62% and its H/C ratio from 1.80 to 2.01 leading to energy recovery (ER) higher than 100%.When heterogeneous catalysts were used together with FA, a marked improvement of BC yields and quality was obtained at 10% MS loading. This behavior was not…

Electrochemical Treatment of Synthetic Wastewaters Contaminated by Organic Pollutants at Ti 4 O 7 Anode. Study of the Role of Operative Parameters by Experimental Results and Theoretical Modelling

In the last years, an increasing attention has been devoted to the utilization of anodic oxidation (AO) technologies for the treatment of wastewater polluted by recalcitrant organics. Recently, Ti4O7 was proposed as a promising anode for AO for the treatment of various organics. Here the potential utilization of commercial Ti4O7 anodes has been evaluated considering the electrochemical treatment of synthetic wastewater contaminated by three very different organic molecules (namely, oxalic acid, phenol and Acid Orange 7), all characterized by a very high resistance to AO. The performances of Ti4O7 were compared with that of two largely investigated anodes: Boron-doped diamond (BDD), which is…

Hydrothermal liquefaction of sewage sludge: towards the effects of transition metals in the presence of homogeneous hydrogen producers

Waste carbonaceous matrices, such as sewage sludge (SS) seem to have a great potential, because they are namely costless matrices compared to the microalgae and hydrothermal liquefaction (HTL) can be considered an interesting route to dispose and valorize them [1-5]. However, SS are characterized by high amount of non-biogenic fractions, such as plastics, salts and metals. In particular SS contains a high amount of inorganics [5], such as Al, Ba, Ca, Cr, Cu, Fe, Ni, K, Mg, Mn, Na, P, S, Ti, Zn, Si which are distributed in the products at the end of the reaction. The presence of heavy metals represent a big challenge for the implementation of HTL on the industrial scale as they can affect pr…

Hydrothermal co-liquefaction of sewage sludge and formic acid

The biocrude produced by non-catalytic hydrothermal liquefaction (HTL) has a too high heteroatom content to be used directly as a fuel [1-3]. Several studies found that different H2 initial pressures during HTL experiments were ineffective in improving the biocrude yield [4-6], nevertheless it was observed that higher initial pressures of H2 brought an improvement of the concentration of light compounds in the biocrude, decreasing the average molecular weight of biocrude oil. To date H2 is mainly generated from fossil sources and realization of a possible hydrogen economy from alternative sources presents many challenges. The use of a liquid hydrogen storage media could represent for the HT…

Electrochemical Treatment of Wastewater by ElectroFenton, Photo-ElectroFenton, Pressurized- ElectroFenton and Pressurized Photo ElectroFenton: A First Comparison of these Innovative Routes

In the last few years increasing attention has been devoted to the utilization of electroFenton (EF) and EF based technologies for the treatment of wastewater polluted by recalcitrant organics. It has been shown that the performances of EF can be strongly improved using ultraviolet (UV) irradiation, e.g., by the photo-electroFenton (PEF) method, or pressurized air or oxygen, e.g., by the pressurized-electroFenton (PrEF) one. Although several studies were carried out on the degradation of many organic pollutants using EF, PEF or PrEF, a systematic comparison between PEF and PrEF was never reported as well as the possibility to couple the irradiation with pressurized air. In this study the pe…

Removal of Phenol from Water in the Presence of NaCl in Undivided Cells Equipped with Carbon Felt or Ni Cathodes: Effect of Air Pressure

Recently, the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides was shown to be significantly improved adopting proper operative conditions such as suitable anodes and cathodes and low current density. In particular, the use of suitable cathodes such as carbon felt or silver could increase the removal of TOC and reduce the formation of chlorinated by-products. In this study, attention was focused on the utilization of carbon felt cathodes with the main aim to evaluate the effect of air pressure on the process using phenol as model organic pollutant. It was shown that, in the presence of carbon felt cathode, the use of pressurized air allows b…

Interesterification of triglycerides with methyl acetate for biodiesel production using a cyclodextrin-derived SnO@γ-Al2O3 composite as heterogeneous catalyst

International audience; Particle morphology and surface properties of metal oxides are topics of great importance in the field of heterogeneous catalysis. Herein, we have developed a molecular-colloidal coassembly approach combined with an ultrasonic-assisted precipitation method to fabricate SnO@γ-Al2O3 composites with tuneable pore size and well-defined octahedral-shape crystal structure. The supramolecular assemblies formed between the randomly methylated β-cyclodextrin (RaMeβCD) and Pluronic F127 were employed as template to tailor the size and shape of γ-Al2O3 nanoparticles and direct their assembly almost exclusively on the surface of micrometer-sized SnO single …

New prototypes for the isolation of the anodic chambers in microbial fuel cells

This work has been focused on the assessment of new prototypes of MFC in which a more strict separation of the anode and cathode compartments is looked for, in order to attain strict anaerobic conditions in the anode chamber and hence, avoid lack of efficiency due to the prevalence of non-electrogenic competing microorganisms and to optimize composition of the anolyte and catholyte. A cylinder reactor with an inner chamber with graphite bars acting as anodes and the outer one with a stainless steel tube acting as cathode was used in three different configurations and results obtained during lifetests are compared in terms of electricity production, cathode oxygen consumption and anode COD d…

Specific separation and recovery of phosphate anions by a novel NiFe-LDH/rGO hybrid film based on electroactivity-variable valence

Phosphorus is a non-renewable resource. Supplies are limited and much phosphorus is currently wasted during the production and utilization process, causing concerns about future supplies and widespread environmental problems. To solve these problems, a new type of NiFe-LDH/rGO electrically switched ion-selective (ESIX) film is designed, based on the dominant mechanism of inner-sphere complexation. An ESIX process allows the NiFe-LDH/rGO hybrid film to achieve a controllably selective uptake and release of the phosphate anions. This route involves tuning potential steps to regulate the redox states of the composite film and the variable metal (e.g., Ni, Fe (II)/(III)) in coordination centers…

Hydrothermal liquefaction of wet biomass in batch reactors: Critical assessment of the role of operating parameters as a function of the nature of the feedstock

A scientometric analysis of articles published from 1986 to 2022 on batch hydrothermal liquefaction of microalgae, macroalgae, lignocellulosic biomass, sewage sludge and organic wastes in water was performed. We found that biocrude yield can be correlated with the kinetic severity factor (KSF) and scattering of experimental data increases in the supercritical region probably for uncertainty in the medium density affecting the kinetics of reactions involved in the process. The level of correlation and the yield increased when fast heating rates of the reactor, higher than 25 ◦C/min, were adopted. Energy recovery of biocrude obtained in fast heating experiments changes linearly with biocrude …

Hydrothermal liquefaction of wet waste biomass: a practical assessment to achieve an integral valorization of municipal sludge

Hydrothermal liquefaction of municipal sludge was conducted to perform a practical assessment to achieve an integral valorization of this wet waste biomass. Experiments were done to investigate the effects of sub- and supercritical water and of the fluid dynamic regime on the energy recovery of the process and on the quality of the products. Experimental runs were performed at two different temperatures (350°C and 400°C) changing reaction time in order to work at the same kinetic severity of the process (LogR0=8.9, calculated as in ref. [3]). An improvement of the C % in the solid residues and of the ration of H/C of the biocrude was obtained when stirred reactor was used both in sub- and s…

Comparative investigation on the value-added products obtained from continuous and batch hydrothermal liquefaction of sewage sludge

Hydrothermal liquefaction (HTL) can be considered a promising route for the energy valorisation of waste sewage sludge (SS). However, not much information is available on continuous flow processing. In this study, the mixed SS was subjected to HTL at 350°C for 8 min in a continuous reactor with loadings of 10 wt% in the feed flow. The results show that the mass recovery reached 88%, with a biocrude yield of 30.8 wt% (3.9 wt% N content). The recovered biocrude yields are highly dependent on the selection of the recovery solvent for extraction, and dichloromethane can contribute an additional 3.1 wt% biocrude from aqueous phase, acetone can extract some pyrrole derivatives into the trapped ph…

Sewage sludge as cheap alternative to microalgae as feedstock of catalytic hydrothermal liquefaction processes

Abstract Production of biocrude through hydrothermal liquefaction (HTL) of sewage sludge (SS) and Chlorella vulgaris was investigated. NiMo/Al2O3 (KF 851), CoMo/Al2O3 (KF 1022) and activated carbon felt, tested as catalysts at 598 K for 30 min, did not change the biocrude yield but significantly improved its quality. Quantitative sulfur removal and lower oxygen content were found in biocrude when KF 851 and KF 1022 were used with C. vulgaris. The same catalysts decreased O/C and S/C ratio of the biocrude from SS. The highest HHV (38.19 MJ/kg) and H/C ratio (1.65) and the lowest O/C (0.11) of the biocrude from SS were obtained with the cheaper activated carbon felt. A new product phase, prob…

HYDROTHERMAL LIQUEFACTION OF WASTE BIOMASS FOR THE PRODUCTION OF FUELS

Liquefazione idrotermica di fanghi di depurazione dalle acque reflue in presenza di acido formico come co-solvente

A causa del progressivo impoverimento delle risorse di combustibili fossili e dell’impatto negativo che il loro utilizzo ha sull'ambiente, la produzione di carburanti da fonti alternative, come le biomasse, ha ricevuto negli ultimi anni una notevole e crescente attenzione. Questo studio è incentrato sulla liquefazione idrotermica (HTL) dei fanghi provenienti dalla depurazione delle acque reflue civili. Tale tipo di biomassa oltre ad avere un alto tasso di umidità, ha un elevato contenuto organico e per essere smaltita è necessario che gli impianti di depurazione investano un ingente capitale [1]. L’HTL tradizionale prevede l’utilizzo dell’acqua, in parte già contenuta nella biomassa, come s…

Hydrothermal liquefaction of waste biomass in stirred reactors: One step forward to the integral valorization of municipal sludge

Abstract Hydrothermal liquefaction (HTL) of municipal sludge (MS) was performed at 350 °C for 30 min (subcritical water) and at 400 °C for 0 min (supercritical water) at fixed kinetic severity (LogR0 = 8.9) in static and stirred batch reactors to study the effect of the flow regime on the energy recovery (ER) of the process and on the quality of the products. With adopted experimental procedures it was possible to reduce to less than 10% the yield of lost organic compounds, termed volatiles (VT), and to collect and quantify a liquid hydrocarbon fraction (HC) separated from the biocrude (BC). The highest value of the HC yield, 25% w/w, was obtained in supercritical conditions. The C content …

Electrochemical treatment of wastewater containing NaCl. Methods to increase the removal of organic pollutants and minimize the formation of toxic by-products

In many cases, wastewater can contain both organic pollutants and NaCl. Electrochemical methods allow to treat very effectively organic pollutants in the presence of NaCl. However, the utilization on an applicative scale of this route is limited by the fact that usually the high removals of organics is coupled with the generation of significant amounts of chlorinated by-products. The role of several operative parameters on the performances of the process was systematically evaluated using phenol as a model organic pollutant. It was shown that the removal of phenol and TOC and the generation of many by-products including chlorophenols, chloroacetic acids, chlorate and perchlorate dramaticall…

Catalytic hydrothermal liquefaction of municipal sludge in subcritical water

In the last decades, the dwindling of the fossil sources of energy coupled with the growth of energy demand and of waste production prompted the research in developing novel industrial technologies for renewable energy production and waste valorization. Hydrothermal liquefaction (HTL) is a good alternative to transform wet biomasses as microalgae, macroalgae, agricultural residues, food waste, and municipal sludge (MS) into value-added products with high efficiency and decreasing the amounts that has to be disposed of. HTL takes place in an aqueous environment, without the energy cost of drying the biomass, at 300-400°C and pressure of 10-40 MPa [1,2]. At these operative conditions, an inte…