In 1990, only about 5% of the world’s bleached pulp was produced using ecf

bleaching sequences, but by 2002 this level had increased to more than 75%, representing

64 Million tons of pulp [14]. The level of pulp still bleached with chlorine

has been affected by a slower than anticipated conversion of pulp mills in

Japan, and its relative high use in the multitude of small non-wood pulp mills in

Asia (mainly China and India). The huge kraft pulp mills in Western Europe, in

the Americas, in Australia and New Zealand, as well as those in South Africa, are

operating in the ECF mode at a level above 90%. These mills reach annual pulp

production rates of between 400 000 and 1 000 000 tons. The mills that still use

chlorine are much smaller, and produce pulp in amounts between 1000 and several

10 000 Tons. These are typically old-fashioned, non-wood mills pending an

upgrade or closure. Some of these mills do not even operate a chemical recovery

unit, and therefore pollution caused by the bleaching process can unfortunately

be labeled as minor compared to the total discharge of waste.

Currently, the extent of TCF bleaching remains static, though the process is

maintaining its niche market position at around 5% of pulp production. TCF

bleaching remains the method of choice for sulfite mills, though the slow

decrease in sulfite operations and the continuing construction of new pulp mills

using ECF bleaching will in time lead to a fall in the share of TCF bleaching.

In developed countries, kraft pulp mills began to use biodegradation plants for

effluent treatment at an early stage. These included the use of large lagoons with

aerators and anaerobic decomposition zones, while activated sludge systems were

less common. The chemical oxygen demand (COD) or total organic carbon (TOC)

are decreased by bacteria which consume the organic material. Today, rather narrow

limits are set for COD and BOD (biochemical oxygen demand). The AOX are

removed in these plants predominantly by adsorption [11], and not by actual biodegradation.

Compared with the pollution levels of the early pulping operations – and also

compared to the situation just 10 to 20 years ago – pulp mills have more recently

developed into very clean operations. Their typical water demand has fallen from

more than 50 m3 t–1 pulp to below 30 m3 t–1, while some mills operate with volumes

below 10 m3 t–1. However, at such low levels of water usage other problems

such as scaling may become a serious threat to the operation. Although water saving

may lead to additional environmental emissions – perhaps via a higher

demand for bleaching chemicals or a higher energy input – sophisticated water

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10 Environmental Aspects of Pulp Production

management and “kidneys” for the separation of nonprocess elements and pollutants

become essential for such an operation.

New mills are typically erected based on the continuing development of technology,

and current terms used to describe the state of the art are “accepted modern

technology” (AMT) or “best available technology” (BAT). As new or “emerging”

technology will develop into “accepted technology” once its applicability is proven,

pulping and bleaching technology cannot be described as established processes.