| Field surveys have found floc formation and deposition of an organic matrix, and suspended sediments, downstream of pulp mills in some rivers. This phenomenon is referred to as pulp mill effluent induced coagulation and flocculation (PMEICF).; PMEICF has created much concern about dissolved oxygen (DO) reduction in rivers and at river bottoms, and about the reliability of the existing models for predicting transport and fate of sediments and contaminants in rivers. If PMEICF causes DO reduction, it may have negative impacts on aquatic habitats, biodiversity and reproductivity of bottom dwellers. If transport models do not include PMEICF effect, they may not be adequate for rivers receiving pulp mill effluent. However, most of the existing transport models could not include this effect, due to a lack of understanding of the mechanisms for its formation. This situation prompted further study. This study includes confirmation of PMEICF occurrence, determination of substances causing and factors affecting PMEICF formation, postulation of mechanisms for PMEICF formation, and evaluation of the impact of PMEICF on DO in rivers or at river bottoms.; In conclusion, PMEICF occurred in the Athabasca River and the Wapiti River. It was more prominent in removal of particles with sizes less than 10 gm. Substances attributed to PMEICF formation were Na+, Ca2+, fibers, hydrolytic lignin, protein, sucrose, cellulose, starch, and extracellular polymeric substances. The major mechanisms for PMEICF formation were sorption, coagulation, flocculation and bioflocculation.; The critical finding from 140-day carbonaceous biochemical oxygen demand (CBOD) tests was that deposited flocs exerted approximately 9 times higher CBOD than a suspension with the same type and concentration of substrate. This may cause DO reduction at river bottoms if the river assimilative ability is low, especially in the winter when the ice cover prevents atmospheric reaeration.; The significance of the study is to develop better understanding of particle formation due to PMEICF. Through this new knowledge it is hoped that improved transport models and effluent treatment technologies or regulations will be developed. This will facilitate efforts for effective management of river water (RW) quality. |
