Search

Six elemental chlorine-free bleaching sequences were studied to see their effect on quality of pulp produced and quantity of pollutants generated during bleaching of wheat straw soda pulp. Impact of parameters like adsorbable organic halogens (AOX), chemical oxygen demand (COD), biochemical oxygen demand (BOD) and sodium adsorption ratio, pH and total dissolved solids generated during bleaching on environment as index of global pollution (I GP ) was also studied. The purpose of the study was to investigate six elemental chlorine-free bleaching sequences to compare the pulp quality, effluent properties and their impact on environment. An oxygen delignification stage before D 0 E OP D bleaching sequence reduced the AOX, COD, colour and BOD by 44%, 42%, 36% and 33%, respectively, whereas an ozonation stage before bleaching reduced the same by 70%, 66%, 73% and 60%, respectively, as compared to those of control. The generation of pollutants as AOX, COD, colour and BOD was reduced further by 88%, 80%, 90% and 77%, respectively, with the use of short bleaching sequences (DD, DP and PD) as compared to those of control. The environmental impact as I GP with D 0 E OP D bleaching sequence was 2.65 which got reduced to 1.44 with bleaching sequence OZPD. Bleaching sequence OZD 0 E OP D was found the most effective for improving brightness and whiteness of the pulp, whereas short bleaching sequence OZPD found the most effective for reducing generation of pollutants during bleaching among different bleaching sequences studied. Graphical abstract.

Aqueous solution of diclofenac sodium (DCFNa) from commercial analgesic pill was electro-oxidized on platinum and stainless steel (SS) anodes. On platinum anode, 66% degradation of the parent drug was achieved at pH 4.5 with a corresponding COD reduction of 49% for a specific charge of 4200 Coulombs/L. Degradation and COD reduction were less at higher pHs of 8.5 and 10.9. A number of intermediates were detected with some of them persisting at the end of the treatment. On SS anode, 84% drug removal and 80% COD decline were achieved for a specific charge of 4200 Coulombs/L at pH 10.9, owing to combined electro-oxidation and electrocoagulation. Contrary to platinum anode, here the drug removal and COD reduction were lesser at lower pHs of 8.5 and 4.5. Electrocoagulation was found to proceed with the organics directly forming complex with iron in the matrix of the SS anode with the iron oxidizing to Fe(III) at pH 10.9 and Fe(II) at pHs 8.5 and 4.5. Intermediates detected in residual liquid were much less in number and abundance.