A COMPARATIVE-STUDY OF EFFLUENT TOXICITY FOR 3 CHLORINE-BLEACHED PULPAND PAPER-MILLS IS SOUTHEAST-ASIA

A study on toxicity discharges from three pulp and paper mills, two in Vietnam and one in Thailand, was conducted using the Microtox method, a rapid toxicity test with the marine bioluminescent bacterium, Photo bacterium phosphoreum, as the test organism. Based on the EC(50) value s after 5 and 15 min of exposure, i.e. 5 min EC(50) and 15 min EC(50), respectively, the hypochlorite bleaching stage (H-H) effluent in the Thai mill was most toxic (EC(50) were about 0.1% of the undiluted effl uent) but still comparable with corresponding data obtained for COGIDO (0.4-0.5%). In BAPACO, toxicity of the effluent from the hypochlorite stages (H1 and H2 was much lower with the EC(50) in the range of 38-8 3%. The chlorination (C) stage effluent in COGIDO with the 15 min EC(5 0) of 18% was less toxic while the 15 min EC(50) of this stage effluen t was almost the same for both BAPACO and the Thai mill. The EC(50) of the alkali-extraction (E) stage effluent were almost in the same rang e in all three mills. The combined effluent from the bleaching process was the most toxic in the Thai mill (EC(50) = 0.4%), second toxic in COGIDO (8-10%) and the least toxic in BAPACO (14-24%). TEF (toxicity e mission factors) values of this effluent show the same ranking: highes t for the Thai mill (15 000) followed by COGIDO with much lower TEF (1 200) and the least was BAPACO (800). A less-than-additive, i.e, antago nistic, mode of toxicity was found for the combined effluent from blea ching plants and for various other combined effluents in the three mil ls. The bleaching plant is the largest toxicity source in terms of TEF in BAPACO, but not in COGIDO where the discharge of black liquor is t he largest contribution of toxicity. For this reason, the total toxici ty discharged from COGIDO with TEF > 6000 was much higher than BAPACO with TEF of 750. For the Thai mill, the TEF of the pond system effluen t alone was already much higher than TEF of the other two mills. Good house-keeping and process control improvement may greatly reduce acute toxicity from the mills. Copyright (C) 1996 Elsevier Science B.V.