A method for oxidative degradation of lignin and polysaccharide fragments dissolved during polyoxometalate delignification or bleaching of wood pulp, wood fiber or pulp obtained from a non-woody plant. The method comprises the steps of obtaining a spent polyoxometalate bleaching solution containing a polyoxometalate of the formula [V.sub.l Mo.sub.m W.sub.n Nb.sub.o Ta.sub.p (TM).sub.q X.sub.r O.sub.s ].sup.x- where 1 is 0-18, m is 0-40, n is 0-40, o is 0-10, p is 0-10, q is 0-9, r is 0-6, TM is a d-electron-containing transition metal ion, and X is a heteroatom which is p or d block element, provided that l+m+n+o+p.gtoreq.4, l+m+q>0 and s is sufficiently large that x>0, and heating the solution in the presence of an oxidant under conditions wherein the dissolved organic compounds are oxidatively degraded to volatile organic compounds and water.