ADVANCED BIOLOGICAL TREATMENT OF PAPERMILL WASTEWATERS; EFFECTS OF OPERATION CONDITIONS ON COD REMOVAL AND PRODUCTION OF SOLUBLE ORGANIC COMPOUNDS IN ACTIVATED SLUDGE SYSTEMS

Sequencing batch reactor (SBR) experiments have been conducted in the laboratory to study factors affecting the composition and concentration of residual organics in the effluent of biological wastewater treatment plants. Wastewater discharged by a papermill was used in three SBRs. A fourth reactor was operated with a model synthetic wastewater in order to identify microbially-produced organic compounds in the effluent. The highest COD removal and the best sludge settling properties for the papermill wastewater were obtained with the greatest sludge age (20 days) and the longest react period (22 hours) investigated. Pyrolysis GC/MS studies showed that the residual COD from the treated papermill wastewater consisted of refractory organic compounds (i.e. lignins). These compounds bad a molecular size between 10,000 - 1,000 dalton and were responsible for the brown colour. Approximately 10% of the residual COD consisted of microbially-altered organics, the rest being organics initially present in the wastewater.