Microbiological treatment of chemically decolorized pulp mill wastewaters

Kornprabha Kruawal

Abstract

Samples from a kraft pulp mill wastewater system (equalization basin, activated sludge, and secondary clarifier) were analyzed for heterotrophic bacteria. Isolates were identified using the Biolog system and confirmed by cell morphology, the oxidase/catalase reaction and other biochemical tests. Studies revealed the most variation in bacterial isolates from the equalization basin. There was more bacterial variation in the activated sludge than in the secondary clarifier. The caustic sewer (E1) was chemically treated to produce the liquid by product (TE1) (U.S. patent no. 5,529,697), then this water was mixed with other mill effluents to produce the refined effluent (RE). The appropriate sample volumes for BOD experiment were 0.5 and 1.0 ml of E1 and TE1, and 1.0 and 5.0 for RE. The study demonstrated that RE was deficient in nutrient. The treatment processes examined were a suspension culture (SC), a suspension culture plus trickling filter (SCT) and a biofilm column (BC). Microbial consortia were established by enrichment culture using ATCC cultures, Arthohacter sp., oil contaminated soil, and wastewater samples from the paper mills. Pseudomonas sp. was dominant among the culturable isolates from the treatment of RE. The biological treatment systems of RE performed extremely well for reduction of BOD and COD. The highest levels of treatment for RE were suspension culture and suspension culture plus trickling filter. The poorest results were obtained using the biofilm column. The established consortia could also be used to treat the original mill effluent (ME). The stored seeds were found to possess suitable characteristics for future development in the biological treatment. The kraft mill effluent decolorization (KMED) process followed by biological treatment of pulp and paper mill effluents offers many advantages. Not only is color removed but also the BOD and COD are removed.