Abstract
New pulping and bleaching technology, more stringent effluent regulations, environmental pressure groups, and new market demands have had a considerable influence on modern bleaching practices. This chapter focuses on new bleaching processes, which are being used and the consumption of different bleaching chemicals that has been changed. There has been a considerable decrease in the consumption of elemental chlorine in several countries and a steady increase in the consumption of oxygen and hydrogen peroxide. Chlorine dioxide is still an important bleaching agent and is still the only option for bleaching of kraft pulp to full brightness (90% ISO) without affecting the strength properties of the fiber. From biological testing and field studiesconclude that elemental chlorine-free (ECF) bleaching followed by biological effluent treatment would result in a harmless environmental impact. Investigations reveal that ECF/total chlorine-free (TCF) effluents even before treatment show very low acute and subacute toxicity, much lower than that of chlorine bleaching. TCF effluents show slightly lower toxicity than ECF effluents, and natural wood compounds may be responsible for the remaining biological effects.
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