Effect of Temperature on Anaerobic Digestion of Pulp and Paper Industry Wastewater Sludges Available to Purchase

Mesophilic and thermophilic digestion of wastewater sludges from the forest industry were studied in semicontinuous flow reactors. Laboratory scale reactors were used for anaerobic treatment studies of a mixture of primary and secondary sludges from a CTMP mill. The VSS reductions in mesophilic and thermophilic digestion of combined CTMP sludge were 41 and 36%, respectively. Specific gas production in the mesophilic process was 0.09 m³/kgVSS added or 0.38 m³/kgVSSreduced. In thermophilic digestion the respective numbers were 0.05 and 0.13. The mesophilic digestion process was stable at an organic loading rate of 2.5 kgVSS/m³d, which represents a 15 days retention time. The supernatant quality of thermophilic digestion was poor (CODsol usually between 3000 and 4000 mg/l) compared with the supernatant of mesophilic digestion (CODsol 1000-2000 mg/l.