Large amounts may be generated in the primary and secondary treatment stages.

Outlook

The amounts of sludge become smaller with anaerobic treatment conditions.

Because aerobic sludge can be difficult to dewater, primary sludge (with fibers) or

Bark is frequently added to improve results. The amount of inorganic material in

Sludge may be rather high; a few ppm of transition metals in the wood and bark

will translate, together with the lime mud and other waste, into over 40 kg adt–1 of

solid waste [2]. It should be noted that this value is the sum of all waste, consisting

Of dewatered wastewater treatment sludge, wood and other ash and wood waste.

Lime mud and green liquor clarification dregs can be disposed of in landfills.

However, they must be washed very well to avoid the emission of H2S during

Mud drying, and to avoid the leaching of caustic soda residual. Sludge with a high

Content of combustible material may be dried and incinerated.

10.6

Outlook

Hopefully, this short summary on the environmental impact of pulp production

Has highlighted the point that there is no simple solution to all negative impacts.

The close interrelation of the different process steps makes it almost impossible to

Avoid one problem without raising or increasing the size of another one. To name

a few examples: An effluent-free mill will need to dispose of more solid waste and

Consequently may require more fossil fuel or more energy in general. Very tight

Water loops might require more chemical for more frequent cleaning steps, or the

Application of poorly biodegradable chelants. They might at the same time

Increase pollution by causing a higher demand for a chemical to achieve identical

Results. Pulping to very low kappa number for less bleaching chemical demand

And effluent load might result in a lower yield, and so require more wood. It can

In addition negatively affect fiber strength, which in turn triggers a higher

demand for strong reinforcement fiber. Taken together, all of these “pros” and

“cons” can result in a negative ecobalance for the positive intention.

Slogans such as effluent-free, chlorine-free or closed loop must be placed into

Perspective and analyzed very carefully for their total impact. Unfortunately, the

Tendency to simplify a complicated matter, and the desire to impress with achievements,

Have caused misleading impressions about the feasibility and impact of

Loop closure. On occasion, frequent loop opening is described as the use of kidneys,

And the yield on wood as a parameter to be neglected. One study which aims

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