Toxicity And Key Toxicants Identification Of Pulp Bleaching Effluents

There are environmental concerns over pulp bleaching effluents, especially chlorine bleaching effluents because of its high COD, BOD load and its formation of toxic chlorinated organic compounds. Based on the characteristic and actuality of our country's pulp industry, bagasse pulp> weed pulp and wood(masson pine) pulp were selected as studied objects. The traditional bleaching process(CEH) and small pollution bleaching process(OHMP) which is researched by National engineering research center of paper making & pollution control, South China University of Technology, were used. With the quickly and exact photobacteria acute toxicity method and chemical analytical method, the toxicity,COD load and key toxicants of pulp bleaching effluents were studied in this paper.The COD load of bagasse pulp CEH bleaching effluent was 94.43kgCOD/ton, its toxicity emission factor(TEF) was 423.92TUm³/ton, be equivalent to 42.93gHgCl2/ton. In bagasse pulp CEH bleaching effluents, the TEF of C bleaching effluent was the largest, which was 67.5% of total TEF, the less one was E bleaching effluent, which was 25.7%, and the TEF of H bleaching effluent was the smallest, with its percentage of 6.8%. The organic compounds analysis results showed that 2,6-dichlorophenol ,4,5-dichloroguaiacol,3,4,6-trichloroguaiacol and tetrachloroguaiacol were key toxicants of C bleaching effluent.3,4,6-trichloroguaiacol , tetrachloroguaiacol , 2,5-dichloro-4-methoxyphenol , 4,5-dichloroguaiacol , 3,5,6-trichloroguaiacol and 2,4-dichlorophenol were key toxicants of E bleaching effluent. Chlorinated organic compounds' toxicity in H bleaching effluent was 22.23% of total toxicity, which were key toxicants of H bleaching effluent of bagasse pulp CEH bleaching process.There were only O bleaching effluent and H bleaching effluent in the OHMP bleaching process of bagasse pulp. The total COD load was 55.738kgCOD/ton, and the total TEF was 54.776 TU ? m³/ton. The TEF of O bleaching effluent was 18.786 TU ? m³/ton, shared 34.3% of total TEF, and the TEF of H bleaching effluent shared 65.7% of the total TEF. The total TEF of bagasse pulp OHMP bleaching effluents was equivalent to 5.477 gHgCl₂/ton, so its toxicity was small. The organic compounds analysis showed that there are 33.63% organic acid,11.14% hydrocarbon of methane series and a small quantity of ester and ketone. Chlorinated organic...