Exploiting the Nutrient Potential of Anaerobically Digested Sewage Sludge: A Review

The world is currently witnessing a rapid increase in sewage sludge (SS) production, due to the increased demand for wastewater treatment. Therefore, SS management is crucial for the economic and environmental sustainability of wastewater treatment plants. The recovery of nutrients from SS has been identified as a fundamental step to enable the transition from a linear to a circular economy, turning SS into an economic and sustainable source of materials. SS is often treated via anaerobic digestion, to pursue energy recovery via biogas generation. Anaerobically digested sewage sludge (ADS) is a valuable source of organic matter and nutrients, and significant advances have been made in recent years in methods and technologies for nutrient recovery from ADS. The purpose of this study is to provide a comprehensive overview, describing the advantages and drawbacks of the available and emerging technologies for recovery of nitrogen (N), phosphorus (P), and potassium (K) from ADS. This work critically reviews the established and novel technologies, which are classified by their ability to recover a specific nutrient (ammonia stripping) or to allow the simultaneous recovery of multiple elements (struvite precipitation, ion exchange, membrane technologies, and thermal treatments). This study compares the described technologies in terms of nutrient recovery efficiency, capital, and operational costs, as well as their feasibility for full-scale application, revealing the current state of the art and future perspectives on this topic

Experimental analysis of aluminium/carbon epoxy hybrid laminates under flexural load

Industry needs new materials that present very high structural characteristic, such as high strength, low weight and high damage tolerance. To obtain these characteristics a new class of materials has been introduced: Fibre Metal Laminate (FML); they consist in metal sheets alternated to composite material layers: in such manner, the good characteristics of each constituent material confer the utmost properties to the FMLs. However, the mechanical properties depend, among other factors, on the thickness and the numerousness of the layers constituting the FML, as well as the interface between metal and composite. Therefore, in this paper, the influence of the abovementioned factors on the material answer to flexural load was investigated. In particular, different kinds of laminates were produced varying the layers adhesion and the layers thickness, but maintaining unaltered the metal/composite volume ratio and the total laminate thickness. Then their structural behaviour was investigated through three-point bending test, and it was found that the flexural behaviour was affected by both the investigated factors; in fact, the maximum flexural load diminished incrementing the number of layers and inserting an adhesive layer at the metal/composite interface

analysis of cfrp al hybrid laminates flexural strength

Abstract Very high mechanical properties, such as high strength, high damage tolerance and low weight, can be reached by coupling composite laminae and metal sheets: in such a manner a new material is obtained: the Fibre Metal Laminate (FML). The diversification of the thickness and the number of layers is suitable to change the structural properties. In order to analyse the influence of these factors on flexural strength, some types of CFRP/aluminium sheet FMLs were manufactured and their structural properties were investigated by means of three-point bending tests. It was discovered that both the studied elements affected the flexural strength of FML; in particular, this mechanical characteristic decreased with the existence of an adhesive film between the metal sheet and the composite plies, whereas it augmented if only one metal sheet was used instead of two ones

An integrated model to predict the microstructure evolution and the mechanical behaviour of a two-phases pseudo-elastic SMA

Abstract Shape memory alloys (SMAs) are more and more used in many fields of mechanics and medicine. The reason for the success is the ability to recover the initial shape also after high values of deformation. During the deformation, the SMAs are able to change the structure from an initial one, often named as austenite, to a final one, named martensite. This transformation takes place at low temperature, and no recrystallization occurs, but the bulk of grains is interested by a structure changing. For that, this phenomenon cannot be qualified as a traditional structure transformation, but it is much more correct to talk about the transition of phase. The austenite-martensite transition is reversible, allowing a perfect recovery of the shape shown in the austenite phase. In this work, a model able to describe the microstructure evolution related to the mechanical behaviour of a SMA has been proposed. Results of FEM simulations have been compared with experimental ones both in terms of microstructure modifications and mechanical behaviour

Influence of structural characteristics on the interlaminar shear strength of CFRP/Al fibre metal laminates

Abstract High mechanical characteristics, such as impact and fatigue resistance, coupled with low weight can be obtained combining metal sheets and composite laminates; in this way a new hybrid material is obtained: the FML (Fibre Metal Laminate). In the present paper, an analysis of the influence of both composite/metal interface and layer thickness on ILSS (InterLaminar Shear Strength) of a carbon fibre composite and aluminium FML is presented. In particular, two different interfaces were studied: one obtained with a structural adhesive and the other with the prepreg resin; as concerns the layer thickness, both one and two aluminium sheets were considered in laminate stacking, maintaining constant the metal/composite volume ratio. The produced laminates were tested following the short beam three-point bending standard, in such a manner the ILSS properties can be highlighted. From the test carried out for this work it can be concluded that the most influencing factor was the presence of the structural adhesive, while the number of metal sheets was unaffecting

hydrogen embrittlement in a 2101 lean duplex stainless steel

Abstract Duplex Stainless Steels (DSSs) are an attractive class of materials characterized by a strong corrosion resistance in many aggressive environments. Thanks to the high mechanical performances, DSSs are widely used for many applications in petrochemical industry, chemical and nuclear plants, marine environment, desalination etc. Among the DSSs critical aspects concerning the embrittlement process, it is possible to remember the steel sensitization and the hydrogen embrittlement. The sensitization of the DSSs is due to the peculiar chemical composition of these grades which, at high temperature, are susceptible to carbide, nitrides and second phases precipitation processes mainly at grains boundary and in the ferritic grains. The hydrogen embrittlement process is strongly influenced by the duplex (austenitic-ferritic) microstructure and by the loading conditions. In this work a rolled lean ferritic-austenitic DSS (2101) has been investigated in order to analyze the hydrogen embrittlement mechanisms by means of slow strain rate tensile tests, considering the steel after different heat treatments. The damaging micromechanisms have been investigated by means of the scanning electron microscope observations on the fracture surfaces

Comparison between long and short beam flexure of a carbon fibre based FML

Abstract A Fibre metal laminate (FML) consists of a stack of metal sheets alternating to composite material layers: in such a manner, the best characteristics of both constituents are combined together. In this work, the flexural behaviour of different kinds of FMLs was investigated. In particular, both long beam and short beam specimens were produced and tested, since the length-to-thickness ratio influences the stress type arising in the material and, consequently, the failure mode. Moreover, the influence of both the composite/metal interface and the thickness of the layers was analysed. It was found that the structural adhesive was deleterious for the flexural strength of the long beam, while it improved the behaviour of the short one. As concerns the thickness and the distribution of the layers, this factor was unaffecting for the short beam specimen, while it was decisive for the long beam one. A micrographic analysis was carried out on the tested specimens, in order to characterize the failure mode. It was found a preponderance of fibre breakage in the long beam, while in the short one the failure of the metal/composite interface was prevailing

Fracture micrographic analysis of a carbon FML under three-point bending load

The core of the present work concerns the analysis of the failure mode and the fracture process induced by the flexural load in Fibre Metal Laminates (FMLs). The influence of the connection layer placed between the composite ones and the metal sheets on the fracture mode was analysed. The considered FML was made of aluminium sheets interposed with carbon fibre reinforced polymer (CFRP) layers, joined with two different types of interface: by using a structural adhesive, or by relying on the bonding capacity of the prepreg resin. Then, the mechanical performances of the produced laminates were determined through the three-point bending test procedure, and the support span was varied to investigate different loading conditions. Finally, the fracture surface morphology was analysed by using both optical and scanning electron microscopes. The type of interface was found to influence the strength of the studied FML, and different fracture modes were observed, depending on the loading condition

Assessment of fatigue damage in a fully pearlitic ductile cast iron by evaluation of Acoustic Emission Entropy

Abstract The paper presents the preliminary results of Acoustic Emission (AE) tests on a peralitic ductile cast iron (DCI) subjected to fatigue tensile loading. The focus is on the evaluation of the information Entropy of the AE data, as an innovative tool for a reliable assessment of fatigue damage in DCIs. Two damage indexes are proposed for the identification of the damage evolution and for the prediction of the fracture failure

Epidemiological study on vocal disorders in paediatric age

Few studies analyzed the diffusion of vocal alterations especially in childhood. Aim of our study was to quantify the numbers of subjects, in paediatric age, in which dysphonia was diagnosed in our department of Phoniatrics, during a period of 5 years, (January 2002-December 2006), and also to evaluate the influence of some potential risk factors. In the considered period it emerged that the diagnosis of dysphonia was made in 312 children (17.2% of the patients affected from dysphonia), aged between 2 and 16 years old, with a major prevalence amongst males (57%) than females (43%). On the contrary in the adult population the prevalence was: 23% in males and 77% in females. In paediatric population, the most affected range of age is the one between 8 and 14, in both male and female gender (59.6%). In 82.4% of the cases there were vocal fold lesions. The 90.3% of children with vocal fold alterations presented lesions secondary to vocal abuse and misuse and classifiable as functional dysphonia. The proportion of functional dysphonia in our sample was 92%. The 65% of children belonged to large families with more than two children, and the 30% had a family history of dysphonia (brothers, parents). The study of the behavioural characteristics has shown aggressive and hyperactive attitudes in 83% of the cases. Since in the ethiopathogenesis of the childhood dysphonia the tendency to vocal abuse has a predominant role, it would be useful to encourage the diffusion of programmes of information to show the risks linked to this abuse in children, in order to prevent the development of dysphonia in paediatric age