Energy and exergy analyses of sewage sludge thermochemical treatment

The aim of this research was to provide a methodology for calculating the energy and exergy balances for the thermochemical treatment of sewage sludge. The results of the balances were assessed and compared for three different scenarios (torrefaction, pyrolysis and pyrolysis combined with catalytic post-treatment of the vapors). The balances were calculated based on previously published experimental data and evaluated under different conditions. The results indicated that the endothermicity decreased with the severity of the process. The energy recovery from the products favored the exothermicity of the processes. The three-step process (pyrolysis of torrefied sewage sludge combined with catalytic post-treatment of the hot vapors) was the least exergy efficient scenario

Pyrolysis of cashew nutshells: Characterization of products and energy balance

Cashew cultivation leads to the generation of large amounts of nutshells. In order to determine whether pyrolysis could be a suitable method for the valorization of this agricultural residue, cashew nutshells (CNS) from Burkina Faso were pyrolyzed in the temperature range between 400 and 600 °C in a laboratory-scale fixed bed reactor. The solid, liquid and gaseous fractions were quantified and characterized, with special focus on the solid product. Recovery of the cashew nutshell liquid (CNSL) was accomplished during pyrolysis separately from the pyrolysis liquid. Results suggest that, except for the aqueous fraction, all the products obtained from pyrolysis are suitable for fuel purposes, and that part of the CNSL can be recovered below 200 °C during the heating process. A preliminary energy balance of the process shows that burning the gases can provide the energy necessary for the process at a pyrolysis temperature of 500 °C

Screening of substance use and mental health problems among Spanish medical students: A multicenter study

Background: This study aimed to determine the prevalence of substance consumption and mental health problems among Spanish medical students, and their association with sociodemographic factors. Methods: A multicentre cross-sectional study was conducted. Self-reported data on sociodemographic and clinical characteristics were collected, including BDI-II, PHQ-9, brief STAI, and single-item academic burnout (IUBA). Results: Overall, 1265 students (74.2% female) completed the survey. Of them, 37.4% scored positive for depressive symptoms, as measured by the BDI-II, and more than half (53%) by the PHQ-9. Suicidal ideation was reported by about 12% whilst high levels of state and trait anxiety were informed by 28.8% and 29.4% of the students. The prevalence of burnout was 40.2%. Female and pre-clinical students reported significantly (p < 0.01) higher rates of depressive, anxiety, and burnout symptoms. Alcohol, energy drinks, and tobacco were the most frequently used substances. Total scores of self-reported mental health problems negatively correlated (p < 0.001) with objective academic results and positively correlated (p < 0.02) with the number of substances consumed in the last 30 days. Limitations: Research-based on self-reported data could favour information bias due to the social desirability effect and memory error. Conclusions: A high prevalence of substance consumption and several mental health problems was found among medical students, especially females. The relevant influence of academic-related factors on students' well-being may be a call for medical schools to implement initiatives aimed to improve students' ability to detect, address, and seek help for their mental health issues

Combustion characteristics of hydrochar and pyrochar derived from digested sewage sludge

In this paper, hydrochars and pyrochars were produced at 260 ºC under different residence times (2 and 4 h) using anaerobic digested sewage sludge (SSL) as initial feedstock. The effect of reaction time on the fuel properties of hydrochars and pyrochars was evaluated. Moreover, the combustion kinetics of raw SSL and the derived pyrochars and hydrochars without coal blending were determined at two different air flows (20 and 90 mL/min) and compared. In the same conditions, the yield of hydrochar was significantly lower than that of pyrochar, confirming the different reaction pathways followed in each process. The results showed hydrochars have lower carbon recovery and energy yield than pyrochars, making the latter more suitable for energy purposes. The thermogravimetric combustion study showed that both thermochemical treatments increased the ignition temperature but decreased the burnout temperature, which results in higher stability during handling and storage. However, raw SSL is better for combustion than hydrochar according to the combustibility index. In addition, the kinetic study showed that the activation energy of the combustion of biochars, especially pyrochar, is lower than that of raw SSL, which is advantageous for their combustion

Co-pyrolysis of sewage sludge and manure

The management and valorization of residual organic matter, such as sewage sludge and manure, is gaining interest because of the increasing volume of these residues, their localized generation and the related problems. The anaerobic digestion of mixtures of sewage sludge and manure could be performed due to the similarities between both residues. The purpose of this study is to evaluate the feasibility of the co-pyrolysis of sewage sludge (SS) and digested manure (DM) as a potential management technology for these residues. Pyrolysis of a sewage sludge/manure blend (50:50%) was performed at 525 °C in a stirred batch reactor under N2 atmosphere. The product yields and some characteristics of the product were analyzed and compared to the results obtained in the pyrolysis of pure residues. Potential synergetic and antagonist effects during the co-pyrolysis process were evaluated. Although sewage sludge and manure seem similar in nature, there are differences in their pyrolysis product properties and distribution due to their distinct ash and organic matter composition. For the co-pyrolysis of SS and DM, the product yields did not show noticeable synergistic effects with the exception of the yields of organic compounds, being slightly higher than the predicted average, and the H2 yield, being lower than expected. Co-pyrolysis of SS and DM could be a feasible management alternative for these residues in locations where both residues are generated, since the benefits and the drawbacks of the co-pyrolysis are similar to those of the pyrolysis of each residue

Vibraciones en una sembradora neumática y su incidencia en la dosificación de semillas

En la siembra de precisión uno de los aspectos claves es la distribución controlada de la semilla en el surco, logrando la distancia deseada entre semillas con una baja desviación estándar. El objetivo del estudio fue ensayar una sembradora neumática, recolectar información significativa del proceso de siembra y buscar relaciones entre los datos recolectados y la ubicación final de la semilla en el surco. Se emplazaron dispositivos electrónicos sobre una sembradora para registrar tiempos entre semillas, velocidad tangencial del dosificador y vibraciones. Se realizaron ensayos para distintas rugosidades del suelo y velocidades. La señal de los acelerómetros fue filtrada y se calculó la Transformada de Fourier y densidad de potencia espectral. Se identificaron dos tipos de vibraciones. Los resultados muestran que las que determinan la posición final de la semilla en el surco son las relacionadas a la rugosidad del suelo y velocidad de la sembradora. Se calcularon relaciones numéricas entre parámetros de las vibraciones y distancia entre semillas. Se concluyó que a partir de los tiempos entre semillas, velocidad de la máquina sembradora y energía de vibración, es posible inferir datos estadísticos de la posición final de la semilla en el surco.A key aspect in accurate sowing is to have a controlled distribution of the seed in the furrow, in order to achieve the desired seed spacing with a low standard deviation. The objective was to test a pneumatic planter, to collect significant information about the sowing process and to explore relations between the collected data and the final spot of the seeds in the furrow. Electronic devices were installed in a planter to record the time between seeds, tangential speed of the dispenser disk and its vibrations. Tests have been made with the mentioned sensors for different degrees of soil roughness and different speeds of the planter. Finally, seed spacing in the furrow was measured. Once the accelerometers signal had been analyzed, Fourier transform and spectral power density were calculated. It has been found that the decisive vibrations are the ones related to the roughness of the soil and the speed. As conclusions we found that it is possible to infer statistical data of the final spot of the seed in the furrow from the time intervals between seeds, the speed of the planter, the energy of the vibration, together with the application of the relation factors already found.Sociedad Argentina de Informática e Investigación Operativ

Proceso combinado de tratamiento con ácido y pirólisis para la recuperación de fósforo y la obtención de sólidos adsorbentes a partir de digestato

En el presente trabajo se pretende valorizar digestato de pur&iacute;n de vacuno y otros residuos org&aacute;nicos mediante un proceso combinado de tratamiento con &aacute;cido y pir&oacute;lisis con el fin de recuperar el f&oacute;sforo (P) presente y obtener un s&oacute;lido que pueda emplearse como material adsorbente

Assessment of the Production of Value-Added Chemical Compounds from Sewage Sludge Pyrolysis Liquids

A procedure to analyze sewage sludge (SS) pyrolysis liquids based on solvent fractionation has been developed. Pyrolysis liquids are separated into three different fractions: heptane soluble (Hep-sol), dichloromethane soluble (DCM-sol), and hydrochloric acid soluble (HCl-sol). Diverse techniques (GC-MS, UPLC-TOF-MS) were employed to qualitatively and quantitatively analyze liquid fractions to assess the potential production of value-added chemicals. Aliphatic hydrocarbons, aliphatic nitriles, and steroids were mostly separated in the Hep-sol fraction, phenols and fatty acids in the DCM-sol fraction, and carboxylic acids and amides in the HCl-sol fraction. The largest production was obtained for ammonia (10–14 kg per tonne of SS) and a-olefins (8–9 kg per tonne of SS). The potential production of some of these value-added chemicals from SS pyrolysis liquid was compared with their current European production. In the case of a-olefins, 16 % of their European production could be achieved by SS pyrolysis

Functionalization of sewage sludge char by partial oxidation with molecular oxygen to enhance its adsorptive properties

This study investigates the activation of sewage sludge char through partial oxidation with molecular oxygen with the goal to increase the concentration of oxygen-containing surface functional groups and to enhance its ammonium adsorption capacity. The effects of oxidation temperature (200–350 °C), oxygen concentration (5–21 vol %) and oxidation time (30–120 min) on the degree of char oxidation are analyzed. The results obtained by thermogravimetric and elemental analysis, and Fourier Transform Infrared and X-ray Photoelectron spectroscopy corroborate the incorporation of oxygenated functional groups on the surface of sewage sludge char either at low temperature (200 °C) using air or at higher temperature (350 °C) using 5% O2 for 30 min. The oxidation of sewage sludge char hardly increases its specific surface area. The operating conditions during oxidation must be carefully controlled to avoid runaway reactions that lead to total oxidation of char. The evolution of CO and CO2 during oxidation is a good indicator of the advance of the oxidation/burn-off reactions. The ammonium adsorption capacity of sewage sludge char increases after oxidation under mild operating conditions, providing support to the idea of onsite utilization of sewage sludge as ammonium adsorbent in waste water treatment plants. This would provide a step forward towards the implementation of a circular economy