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Abstract
A cost-effective optical sensor for continuous in-situ monitoring of turbidity and suspended particulate matter concentration (SPM), with a production cost in raw materials less than 20 (sic), is presented for marine or fluvial applications. The sensor uses an infrared LED and three photodetectors with three different positions related to the light source-135 degrees, 90 degrees and 0 degrees-resulting in three different types of light detection: backscattering, nephelometry and transmitted light, respectively. This design allows monitoring in any type of environment, offering a wide dynamic range and accuracy for low and high turbidity or SPM values. An ultraviolet emitter-receiver pair is also used to differentiate organic and inorganic matter through the differences in absorption at different wavelengths. The optical transducers are built in a watertight structure with a radial configuration where a printed circuit board with the electronic signal coupling is assembled. An in-lab calibration of the sensor was made to establish a relation between suspended particulate matter (SPM) or the turbidity (NTU) to the photodetectors' electrical output value in Volts. Two di fferent sizes of seashore sand were used (180 mu m and 350 mu m) to evaluate the particle size susceptibility. The sensor was tested in a fluvial environment to evaluate SPM change during sediment transport caused by rain, and a real test of 22 days continuous in-situ monitoring was realized to evaluate its performance in a tidal area. The monitoring results were analysed, showing the SPM change during tidal cycles as well as the influence of the external light and biofouling problems.

Abstract
Raw materials are very important for the development of economies and also to assure quality of life. Due to our production and consumption patterns new challenges emerged. The consumption of raw materials is very high, what raises important issues such as the depletion of resources, instability of prices and markets, risk of rupture of supply and other environmental, economic and social impacts. The European Union as many other regions of the world are implementing some strategies to overcome this problem, being the most recent the circular economy package, which intends to maintain materials as long as possible in the economic cycle, avoiding the use of new resources. There is a list of critical raw materials for EU and in this work the methodology of pairwise comparison was applied to a set of those raw materials for determining the importance of each taking in consideration several factors, such import reliance, end of life, economic importance, etc. The main goal was to develop a method based on pairwise comparison in a case of European Union to define priorities for acting, enhancing the achievement of sustainable solutions. It was also performed a sensitivity analysis. It was possible to conclude that the top position for the majority of the several raw materials does not change with the weights. Tantalum, Tungsten, Baryte and Antimony are always in the top positions. (C) 2019 The Authors. Published by Elsevier B.V.

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