Biodegradation of Alkali-O2 Oxidized Lignins Used as Dispersants

Abstract

Large quantities of lignin are produced as by-streams via chemical pulping and emerging biorefinery processes. These lignins are typically water-insoluble; however, they can be converted into a water-soluble form by chemical modifications. A novel LigniOx technology solubilizes lignin using alkali-O2 oxidation. The product can be used for bio-based dispersants. This study evaluated the biodegradability of alkali-O2 oxidized kraft, organosolv, and hydrolysis lignin. The oxidized lignins exhibited higher biodegradation in soil and in aquatic environments in comparison to a commercial kraft lignin and a commercial lignosulfonate. In soil, the biodegradabilities of oxidized lignins were 19 to 44%, whereas the reference lignins exhibited only 5 to 12% conversion to CO2. Biodegradation of the oxidized lignins and references in the aquatic environment increased in a similar order as in the soil environment, although the degradation in each sample was slightly smaller than in the soil. The improved biodegradability of the oxidized lignins was due to the altered chemical structure of lignin. Compared to the untreated lignin, the oxidized lignin contained structures formed in aromatic ring opening reactions, making the lignin more accessible to microbial degradation. In addition, the oxidized lignin contained carbon originating from small organic compounds, which are easily biodegradable.