Role of Cyanobacteria in Pulp and Paper Waste Treatment Systems, 2002 Environmental Conference Proceedings

A. E. Kirkwood, C. Nalewajko and R. R. Fulthorpe

The pulp and paper industry depends largely on biological waste-treatment systems to treat high-strength organic waste prior to discharge into receiving waters. Aerated Stabilization Basins (ASB) and Activated Sludge (AS) systems house high densities of heterotrophic bacteria for the biodegradation of organic waste, particularly toxic constituents such as organochlorines. Although these systems are highly colored, turbid, and relatively toxic, we have determined that photosynthetic cyanobacteria reside in them as well. Considering that cyanobacteria do not require organic compounds for growth, their function within the microbial community and impact to biological waste-treatment was not known.

Our study investigated the role of cyanobacteria in pulp and paper secondary waste-treatment systems, focusing on their community characterization and ecophysiology. We have found cyanobacteria to be important members of the microbial community in geographically dispersed ASB and AS systems around the world (1). Although heterotrophic bacterial densities tend to be at least one order of magnitude higher than cyanobacterial densities, cyanobacterial biomass levels can exceed bacterial biomass in some cases. The prevalence of cyanobacteria in these waste-treatment systems prompted further monitoring studies to determine what effluent parameters (i.e. nutrients, temperature, pH, etc.) controlled cyanobacterial biomass. Out of all the parameters tested, only effluent toxicity formed a significant (p<0.01) positive="" correlation="" with="" cyanobacterial="" biomass.="" this="" result="" inferred="" that="" effluent="" toxicity="" increased="" as="" cyanobacterial="" biomass="" increased.="" further="" studies="" using="" whole="" effluent="" from="" three="" mills="" confirmed="" that="" toxicity="" removal="" during="" biological="" treatment="" was="" affected="" by="" the="" presence="" of="" cyanobacteria.="" the="" two="" softwood-based="" effluents="" had="" increased="" toxicity="" levels="" with="" increased="" cyanobacterial="" biomass.="" in="" contrast,="" the="" hardwood-based="" effluent="" had="" decreased="" toxicity="" as="" cyanobacterial="" biomass="" increased.="" these="" seemingly="" conflicting="" results="" may="" be="" due="" to="" a="" number="" of="" factors,="" including="" microbial="" community="" and="" effluent="" chemistry="" differences="" among="">