The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940 NmL CH4 per g TOC) among the effluents. For the KP-mills, methane yields above 50 % were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10-15 % of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60 % of the theoretical potential.
The TMP mill (A) gave the best average yield with all six effluents ranging 40-65 % of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40 % while three of the six effluents at mill G (CTMP) yielded 45-50 % .