TOXICITY TO MICROTOX, MICROALGAE AND DUCKWEED OF EFFLUENTS FROM THE BAI-BANG-PAPER-COMPANY (BAPACO), A VIETNAMESE BLEACHED KRAFT PULP AND PAPER-MILL

Toxicity of the combined effluent as well as effluents from different production units of BAPACO, a Vietnamese bleached kraft integrated pul p and paper mill, was studied using three ecotoxicological tests. Micr otox, the micro-alga, Selenastrum capricornutum, and the duckweed, Lem na aequinoctialis. Physico-chemical characteristics of the effluents w ere also analyzed. Due to unstable operating conditions of the mill, a number of samples taken at different monitoring periods from each eff luent were tested in order to get statistically reliable ranges and av erages of toxicity characteristics. For the mill combined effluent, it was found that the micro-algae were the most sensitive followed by Mi crotox bacteria, while duckweed was not sensitive. Microtox tests show ed that the bleaching filtrate from the chlorination stage (C-stage) w as the most toxic among all effluents in the mill. The combined efflue nt from the bleaching plant contributed the largest TEF (Toxicity Emis sion Factor) to the toxicity balance of the whole BAPACO combined effl uent. A less-than-additive mode of toxicity was obtained. In spite of high pollution loads, e.g. BOD, GOD, SS, to the Red River, the toxicit y of the effluent was considered to be low. However, during periods of low river water sublethal toxic effects on the biota may be expected.