In a hollander, and effluent from the bleach plant was discharged without

Further treatment. Sulfite pulp responds much better to bleaching than do kraft

Pulps, and by the end of the nineteenth century the demand for bright paper was

Satisfied by the wide use of sulfite pulp. The intensity of the exposure to hypochlorite

Cannot be enforced without damaging the fiber properties, however. A multistage

Treatment with intermediate washing reduced the demand for hypochlorite

in a HEH treatment and permitted higher brightness at about 80% ISO (using

Current scales for better comparison).

Bleaching in towers with elemental chlorine was first introduced during the

Mid-1920s, whereupon the standard bleaching sequence became a CEH configuration.

Because chlorination causes less fiber damage at low temperature, and

The solubility of chlorine gas in water is higher at low temperature, chlorine was

Applied using and discharging large amounts of water. Indeed, for the very bleachable

Sulfite pulp this sequence remained standard until the early 1970s.

During the 1950s, chlorine dioxide became the standard chemical for the production

Of brighter kraft pulp. Initially, chlorine dioxide was applied simply as an

Additional final stage (CEHD). This procedure rapidly gained acceptance, due

Mainly to its high effectiveness in brightening without causing fiber damage.

Consequently, bleaching sequences such as CEHDED became commonplace.

Increasing pulp production resulted in increasing effluent volumes and loads.

The discharge without any treatment became a significant problem, especially for

Mills located on streams with poor water flow. The need to reduce the amount of

Organic material was most pronounced in highly populated countries, where filtered

River water was used as source for drinking water. In other countries, a low

Availability of water did not allow high pollution levels. Already in the late 1960s,

Sappi in South Africa began to develop oxygen delignification with the target of

Cutting the demand for bleaching chemical and decreasing the remaining discharge

of organic compounds [5]. In Germany, the effluent of the extraction stage

Was evaporated together with the calcium sulfite pulping liquor at Schwabische

Zellstoff [6]. The aim of another project was to adsorb all higher molecular-weight

compounds in the effluent on aluminum oxide [7], and then to reactivate the

Adsorbent by thermal treatment in a rotating kiln. However, serious corrosion

Problems as a result of high levels of chloride ions and hydrochloric acid stopped

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