Effectiveness of different green chemistry approaches during mixed hardwood bamboo pulp bleaching and their impact on environment

摘要

Studies were carried out using conventional bleaching chemicals (chlorine and chlorine dioxide) and green bleaching chemicals (oxygen, enzyme and ozone) to see their effect on the generation of pollutants during bleaching. Results showed that the use of oxygen prior to conventional bleaching reduced the biochemical oxygen demand (BOD), chemical oxygen demand (COD), colour and adsorbable organic halogens (AOX) in the bleaching filtrate by 49-53, 49-56, 70-72 and 48-66, respectively, compared to the use of conventional bleaching chemicals. The use of xylanase enzyme prior to bleaching reduced the colour and AOX in the bleaching filtrate by 5-6 and 9-12% compared to those obtained using conventional bleaching chemicals. The use of oxygen followed by ozone treatment prior to conventional bleaching was able to reduce the BOD, COD, colour and AOX in the bleaching filtrate by 64-68, 73-77, 70-77 and 70-79, respectively, compared to those obtained with the conventional bleaching chemicals. Environmental impact assessment by the index of global pollution methodology suggested that by switching from conventional to green bleaching chemicals the quality of the ecosystem can be improved from class C (discomfort to life forms) to class B (acceptable to life forms). Application of different green chemistry approaches for the bleaching of mixed hardwood pulp substantially reduced the usage of bleaching chemicals and the generation of pollutants during the bleaching of pulp along with the improvement in quality of the pulp.