a pilot plant to process willow-dust for biogas production in a battery of six batch digesters was installed in a textile mill. the depth of loading of a tank during aerobic pretreatment affected the pattern of biogas production with a solid to liquid ratio of 1:6 or 1:1. 5. about 725 m**3 of biogas per 2 tons of willow-dust was obtained in 90 days in all the three levels, 2, 4 and 6 tons of solid loadings during the pretreatment when the solid to liquid ratio was 1:6. there tended to be a gradual decline in gas production during the anaerobic fermentation. when the solid to liquid ratio was changed to 1:1. 5 (dry fermentation), about 500 m**3 of biogas per 2 tons of willow-dust was produced in 30, 60 and 120 days with 2, 4 and 6 tons of initial solid loadings. in this case, there was a more or less constant production rate during the corresponding anaerobic fermentation. the practical significance of the process is discussed. (edited author abstract). 8 refs