Reduction in chlorophenolic compounds during bleaching of rice straw pulp by replacing elemental chlorine with chlorine dioxide

Speedy running down of forest cover has put great stress on paper industry for finding new fibrous raw materials. Rice straw is an abundantly available lignocellulosic material especially in wood-short countries and can be utilized as an alternate fibre resource by paper mills. Bleaching is a crucial step in papermaking that involves the chemical reactions to reduce the colour of the pulp and makes it brighter for manufacturing writing and printing grade paper. Contrary to this, bleaching results into the formation of toxic, biorefractory and carcinogenic chlorolignin compounds that pose serious health hazards to aquatic life and human beings. A study was carried out using rice straw soda-AQ pulp for bleaching with sequence based on elemental chlorine (CEOPHH). Further, to reduce the wastewater pollution load, emphasis was given on replacement of elemental chlorine with chlorine dioxide at the first bleaching stage (CD10EOPHH CD30EOPHH and CD50EOPHH) and elemental chlorine-free (ECF) bleaching (DEOPD). The study revealed that generation of chlorophenolic compounds was the highest in CEOPHH sequence followed by CD10EOPHH CD30EOPHH and CD50EOPHH, i.e. 6047, 4765, 4247 and 3864 mg/t, respectively. In DEOPD bleaching sequence, the generation of chlorophenolic compounds in wastewater was reduced to 421 mg/t. ECF bleaching had major impacts on reduction in chloroguaiacols (97%) and chlorophenols (92%) that were in the highest quantity in effluents of CEOPHH bleaching sequence. DEOPD bleaching was found to be a promising option for pulp and paper industry for cutting down the generation of chlorophenolic compounds in bleaching effluents.