Soluble Bio-based Substances Isolated From Urban Wastes

The organic fraction of urban wastes can be considered a cost effective source of added value products for a wide number of uses. The present chapter describes different possible strategies for the treatment of organic wastes, used at the present time in many waste treatment plants. Subsequently the chapter deals with the isolation process of soluble bio-based substances (SBO) from urban biowastes at both laboratory and pilot plant scale. A detailed description of SBO composition and physical-chemical characterization is given.

Soluble bio-based substances (SBO) extracted from urban bio-wastes have similar chemical properties to humic substances (HS) present in natural waters and soils. Therefore, SBO are also expected to have photochemical properties similar to HS. In this chapter, a summary of the photochemistry of HS is presented along with the recent advances related to the photogeneration of reactive species upon irradiation of aqueous solutions of SBO and some examples of pollutant degradation photo-induced by SBO.

The implementation of a photo-Fenton process at mild acidic conditions is a potential environmental application for SBOs. The Fenton reagent (sacrificial amounts of hydrogen peroxide and catalytic iron salts) has been demonstrated as an efficient method for the removal of toxic xenobiotics that is enhanced upon irradiation; sunlight can be used for this purpose. In order to avoid precipitation of iron at pH above 3, several strategies have been tested. One of them involves formation of photoactive iron complexes. Humic substances have been employed for this purpose, due to their ability to complex iron. Because of its similar chemical properties, SBO are candidates for this purpose. Experiments carried out with different pollutants have shown that SBO are not good photocatalysts because of the strong screen effect associated to their color, while they are useful to drive a photo-Fenton at milder pH, as they are good complexing agents for iron. Döehlert matrixes have been employed to determine that the pH range for efficient photo-Fenton can be extended to values of ca. 5 and that optimal SBO concentration is approximately 20 mg/L. Finally, SBO have demonstrated to be non toxic, scarcely biodegradable and relatively resistant to oxidizing conditions.

Humic substances were widely studied for preparing materials to be used for adsorption, photocatalysis and so on. Their parent soluble bio-organic materials (SBO) have potentially similar applications which have to be evaluated. The main advantage of the use of SBO substances concerns their low cost, but they are appealing also for the development of a strategy of recycle and reuse of wastes which needs to be followed worldwide. The application of SBO in materials synthesis is promizing, since they can be used as synthesis intermediates but also as active phases for developing adsorbing and/or photoactive materials usable for environmental applications.

Modeling and simulation are recognized as extremely valuable tools for developing new materials by increasing efficiently the knowledge on systems. The mathematical tools and methods necessary to build a wide range of models are presented here. Two case studies illustrate the different mathematical approaches introduced: the SDZ photodegradation in SBO and the adsorption in SBO-magnetite particles.