NOVELTY - Complete anaerobic digestion of packaging for biomass comprising polymer mixtures of the composition which comprises: 25-95 wt.% of a polyhydroxyalkanoate comprising poly-4-hydroxybutyrate, poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate); and 5-75 wt.% of an aliphatic polyester, is claimed.    USE - The process is useful for complete anaerobic digestion of packaging for biomass comprising polymer mixtures of the composition.    ADVANTAGE - The process exhibits increased stability and excellent anaerobic digestibility.    DETAILED DESCRIPTION - Complete anaerobic digestion of packaging for biomass comprising polymer mixtures of the composition which comprises: 25-95 wt.% of a polyhydroxyalkanoate comprising poly-4-hydroxybutyrate, poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate); and 5-75 wt.% of an aliphatic polyester comprising (a1) 65-100 mole%, based on components (a1) and (b1), of succinic acid or its derivative; (b1) 0-35 mole%, based on components (a1) and (b1), of an aliphatic 5-35C dicarboxylic acid and/or its corresponding acid derivative; (c1) 98-100 mole%, based on components (a1) and (b1), of a 2-8C alkylenediol or 2-5C oxyalkylenediol; (d1) 0-2 wt.%, based on the polymer obtainable from components (a1) and (c1), of at least one polyfunctional compound comprising at least two isocyanate, isocyanurate, oxazoline or epoxide groups or at least three alcohol or carboxylic acid groups, is claimed. An INDEPENDENT CLAIM is also included for disposing of biomass in a biogas plant comprising collecting or dispensing the biomass in a package comprising polymer mixtures of the composition, collecting the biomass in the package by a waste management company, and sending the biomass in this package to anaerobic fermentation in a biogas plant.