Thermophilic High-Rate Biological Treatment of Kraft Mill Effluent in a Biofilm-Chip MBBR Process, 2005 Engineering, Pulping & Environmental Conference

A high-rate, thermophilic biological treatment process was found to be a very effective, economical alternative to reduce the discharge of organic matter from the Munksjö Aspa kraft mill in Sweden.

Based on the results from a successful laboratory scale trial, a full-scale bioprocess was installed in an existing bleaching tower at the mill. Treatment of the filtrate from the chlorine dioxide bleaching step at a hydraulic retention time of 0.5-0.7 hours and a process temperature of 57°C is expected to decrease the discharge of organic matter enough to meet new stricter effluent demands.

The full-scale treatment process was initially started in April 2005. During the first months of operation the bioprocess has shown a significant degradation of organic matter and high process stability. Optimisation of the process parameters such as nutrient dosage is expected to increase the efficiency further. The first re-start after a four weeks shut down showed that the biological process was fully operational again after only 2-3 days.