Bio-based substances isolated from green compost: application in wastewater treatment

The development of processes to valorize the organic fraction of urban waste is a challenge that is increasingly attracting research groups from all over the world. At this purpose, in recent years is becoming of predominant importance the development of the so-called biorefinery. Here different processes for organic waste treatment are integrated in order to obtain, beside energy and bio-fuels, also added-value chemicals to be released on the market for specific applications or to be used as building blocks in further synthetic processes. In such context, from the compost obtained by aerobic treatment of the green fraction of urban wastes, soluble bio-based products (SBO) have been isolated. In previous studies SBO have shown promising performances in the formulation of detergents and textile dyeing baths, as emulsifiers, auxiliaries for soil/water remediation, flocculants, dispersants and binding agents for ceramics manufacture, in the synthesis of nanostructured materials for catalysis and for application in agriculture and animal husbandry. Investigation of the chemical nature of SBO has shown that they bear chemical similarities with humic substances (HS) naturally present in waters and soil. Particularly interesting at this regard is the fact that HS contain light-absorbing species capable of promoting photochemical transformation of organics of anthropogenic origin present in waters. Based on this similarity, in the present research SBO from green compost have been studied as photosensitizers for the degradation under simulated solar light of phenols, azodyes and aromatic sulphonic acids. Experiments have been designed in order to: i) gain further insight into the main reactive species involved in the SBO assisted photodegradation process; ii) optimize the photodegradation process at laboratory scale under simulated solar light; iii) verify the system detoxification. The abatement of all the studied target molecules was achieved and the photoproduction of singlet oxygen and OH radicals was hypothesized. Additional experiments were performed to verify the photostability of SBO themselves. A progressive decrease of both absorbance and fluorescence of SBO was observed upon irradiation; the obtained data suggested an increased SBO hydrophilicity and solubility. The development of SBO for water detoxification can therefore be attempted as a green process, taking organic urban waste as source of material for environmental application