Biodeterioration of cardboard-based liquid containers collected for fibre reuse.

Liquid packaging board (LPB) collected in Germany is processed in Finland as recycled fibre and as plastic reject for incineration. The chemical, biological and physical changes occurring in recycled LPB bales were monitored during storage of six and 18 months. The moisture content in the core of the bales ranged from 7% to 53%, and pH values varied from 6.0 to 8.5. The average amount of mesophilic bacteria per container was 1.5 x 10(7) - 5 x 10(8), which means that recycled LPB pulp cannot be recommended for sanitary use. The concentration of CO2 inside the bale is an indicator of the activity of aerobic microorganisms and might be suitable for identifying deteriorated bales and removing them from the production line. Insects were found in some bales and the more deteriorated the bale was the more species of insects were found. The results showed the conversion of cellulose into humic acids to be clearly underway in some recycled LPB bales. The bale samples were extracted into hot water and into fulvic acids and humic acid (HA) fractions. The concentration of the humic acid fraction varied in the range 0.3-0.6% of the organic matter in fresh bales and 2.2% in one old bale. During aging nitrogen was enriched in all fractions.