Biowaste management is in the center of attention in recent years, due to the increased focus on Circular Economy practices. Recent management solutions promote exploration for small and medium scale processing and monitoring practices. In this context, two pathways of biowaste valorization are analyzed: composting and anaerobic digestion. This study focuses on energy production with the hydrothermal carbonization (HTC) of anaerobic residues from biogas production. Lesvos has numerous processing facilities and olive mills, and therefore Olive Mill Wastewater (OMWW) are the main biowaste streams in the island, along with olive tree pruning, the organic fraction of municipal solid waste and sludge from wastewater treatment facilities. Most studies present applications on specific types of biowaste, while this study aims to co-treat several biowaste streams. A holistic experimental set-up that combines aerobic and anaerobic treatment strategies was developed taking into consideration the hydrothermal treatment of AD digestate along with locally available biowaste, like OMWW, sludge etc. A main target objective is to investigate if solid fraction could have a high heating potential In addition, HTC was able significantly to reduce the COD of OMWW while resulting in hydrochars with increased heating values.

A soluble biopolymer (SBP) was obtained by hydrolysis in pH 13 water at 60 °C. The dry product was re-dissolved in plain water at pH 10 and used as control against the same solution added with hydrogen peroxide at 0.1-3 H2O2 moles per SBP carbon mole. The control and test solutions were kept at room temperature, in the dark or in a climatic chamber under irradiation with simulated solar light, until the solutions pH remained constant. Afterwards, the solutions were processed to recover and analyze the crude soluble products. For the control solution, the results indicated significant production of CO2, production of organic carboxyl functional groups and de-polymerization of the pristine SBP organic matter. These findings demonstrate the oxidation of SBP by water, which could only occur through the production of O and OH radicals catalyzed by SBP. The present work reports the results obtained from the control solution and for the test solution treated in the presence and absence of H2O2, with and without pH control, in the dark and under irradiation with simulated solar light. The paper discusses the perspectives of further implementation of the autocatalytic properties of SBP for the realization of a municipal biowaste-based biorefinery producing value added bio-products for consumer’s use.