The Autocatalytic Chemical Reaction of a Soluble Biopolymer Derived from Municipal Biowaste

Abstract

The paper discusses the perspectives of further implementation of the autocatalytic properties of a soluble biopolymer (SBP) derived from municipal biowastes for the realisation of a biorefinery producing value-added bio-products for consumer use. The reaction of an SBP and water is reported to cause the depolymerisation and oxidation of the pristine SBP organic matter with the formation of carboxyl-functionalised polymers having lower molecular weight and CO2. These findings demonstrate the oxidation of the SBP via water, which could only occur through the production of O and OH radicals catalysed by the SBP. According to the adopted experimental plan, the anaerobic digestate supplied by an Italian municipal biowaste treatment plant was hydrolysed in pH 13 water at 60 °C. The dry product was re-dissolved in plain water at pH 10 and used as a control against the same solution with hydrogen peroxide at 0.1–3 H2O2 moles per SBP carbon mole added. 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 pH of the solutions remained constant. Afterwards, the solutions were processed to recover and analyse the crude soluble products. The present work reports the results obtained for the control solution and for the test solutions treated in the presence and absence of H2O2, with and without pH control, in the dark and under irradiation with simulated solar light.

A Low-Cost Ecofriendly Oxidation Process to Manufacture High-Performance Polymeric Biosurfactants Derived from Municipal Biowaste

“…The autocatalysed process allows controlling better the rate of the SBP chemical oxidation, reducing the depolymerization and mineralization degree, and improving the surface activity properties of the oxidized polymer. These findings confirm previous knowledge that, although oxidation of organic carbon to CO 2 is the most thermodynamically favored reaction, the mineralization of organic molecules is markedly slower than their de-aromatization, the latter involving ring opening with the formation of aliphatic carboxylic and hydroxylated C moieties [12][13][14]16,17,33] whose mineralization is the slowest step [36].…”

“…The results reported in Section 3 prove that it is possible to overcome the drawbacks shown in the previous work [12][13][14]16,17] through a process exploiting the autocatalytic properties of SBP. The autocatalysed process allows controlling better the rate of the SBP chemical oxidation, reducing the depolymerization and mineralization degree, and improving the surface activity properties of the oxidized polymer.…”

“…In the above context, several papers have been published [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ] on the properties and performance of new soluble polymeric biosurfactants obtained by hydrolysis and oxidation of collected and fermented municipal biowaste (MBW).…”

“…The new polymeric biosurfactants are a heterogeneous mixture of molecules with a molecular weight in the 5 to >750 kDa range and different chemical compositions, constituted by aliphatic C chains and aromatic lignin-like C moieties, and various functional acidic and basic groups of different strengths bonded to several mineral elements, such as Na, K, Ca, Mg, Al, Fe, and Si in 0.2–9 w/w % and Cu, Ni, and Zn in 20–180 ppm content [ 17 ]. These features are memories of the chemical moieties and macro-molecularity of the pristine MBW polysaccharide, protein, and lignocellulosic approximates from which the polymeric new biosurfactants are derived [ 16 ].…”

“…The product obtained by hydrolysis of the MBW anaerobic digestate was characterized by a surface tension (γ) of 49 mN/m at 1 g/L concentration in water compared to γ 61–63 mN/m at 2–3 g/L for the hydrolysates of three different MBW composts [ 10 , 11 ]. The product obtained by hydrolysis of the MBW anaerobic digestate was further processed by oxidation in plain water in the presence and absence of added hydrogen peroxide at 0.1–3 H 2 O 2 moles per mole of organic C contained in the pristine digestate and in the presence or absence of irradiation with simulated solar light [ 17 ]. The measured surface tension of these products at 2 g/L in water ranged from 69 to 46 mN/m, with the lowest values being 46–49 mN/m measured for the products obtained in the presence of 0.25–0.5 H 2 O 2 /C mol/mol, with or without irradiation [ 17 ].…”