Polymerization and depolymerization of lignosulfonate by Phanerochaete chrysosporium immobilized on foam

Abstract Large quantities of lignosulfonate are produced as a byproduct of sulfite pulping, being a reservoir of technical lignin for the production of valuable polymeric or low molecular weight chemicals. Polymerization or depolymerization of the lignosulfonates is necessary as a pretreatment for the production of chemicals. The ligninolytic enzyme system of white-rot fungi could be an alternative to energy-consuming pretreatment processes. Phanerochaete chrysosporium is capable of degrading lignin as well as chemically altered lignin. The object of this study was to polymerize or decompose lignosulfonates by P. chrysosporium . The fungus was cultivated on foam cubes according to the MYCOPOR process. When spent sulfite liquor was treated with the fungus the medium turned dark brown after a week as a result of the polymerization of lignosulfonate and did not clarify afterwards. With commercial sodium lignosulfonate polymerisation started immediately, but a short time later depolymerization of the macromolecular lignosulfonate complex started and reached 70–80% in diluted solutions. A dilution of the spent sulfite liquor produced the same effect, but the lignosulfonate was only degraded by 30%. The reason for the inhibition of the degradation process with undiluted lignosulfonates was the high content of sulfur dioxide. After removing a part of sulfur dioxide by steam stripping the extent of lignosulfonate degradation increased.