ADVANCED BIOLOGICAL TREATMENT OF PAPER-MILL WASTEWATERS - EFFECTS OF OPERATION CONDITIONS ON COD REMOVAL AND PRODUCTION OF SOLUBLE ORGANIC-COMPOUNDS ACTIVATED-SLUDGE SYSTEMS

Sequencing batch reactor (SBR) experiments have been conducted in the laboratory to study factors affecting the composition and concentratio n of residual organics in the effluent of biological wastewater treatm ent plants. Wastewater discharged by a papermill was used in three SBR s. A fourth reactor was operated with a model synthetic wastewater in order to identify microbially-produced organic compounds in the efflue nt. The highest COD removal and the best sludge settling properties fo r the papermill wastewater were obtained with the greatest sludge age (20 days) and the longest react period (22 hours) investigated. Pyroly sis GC/MS studies showed that the residual COD from the treated paperm ill 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 re sidual COD consisted of microbially altered organics, the rest being o rganics initially present in the wastewater.