Ozonation of Activated Sludge of Pulp and Paper Industry for Reduction in Quantity and Contamination

Abstract

Aerobic biological treatment with activated sludge process is predominantly applied for the treatment of wastewater in integrated pulp and paper mill around the world. 50-70% of the biodegradable organic material is mineralized with generation of additional biological cells, typically termed as excess sludge or waste activated sludge (WAS). Handling and disposal of WAS is confronted with several difficulties; regulatory stringency due to contamination of organochlorine compounds is the greatest hurdle. The objectives of the present research are to reduce the net disposable biomass and organochlorine compounds in the integrated pulp and paper industry. The research was carried out on the ozonation of filamentous biosludge of both laboratory reactor and integrated pulp and paper mill, and flocculating biosludge in the batch mode in the laboratory set-up. Ozonated biosludge was post treated in laboratory scale activated sludge process. In the initial phase of the research, biosludge was characterized for different parameters and sludge yield was determined in the laboratory reactors. The concentration of adsorbable organic halogens (AOX) and extractable organic halogens (EOX) compounds in dewatered biosludge from integrated pulp and paper mill was 2119 and 641 mg/kg respectively. Ten chlorophenolic compounds out of 12 compounds identified for regulation by USEPA were detected in the biosludge and the combined concentration was 2043 µg/kg. Toxicity equivalency (TEQ) due to chlorophenolic compounds in the biosludge was 717 µg/kg. The concentration of 2,3,7,8-TCDD and 2,3,7,8-TCDF was 16 and 210 pg/g of dry sludge respectively; the upper bound I-TEQ from PCDD/Fs was 54 pg/g DS. The concentration of organochlorine compounds in sludge was dependent on the concentration of the same in influent wastewater. The application of ozone on biosludge altered its physical, chemical and biological characteristics.