Emissions to the Aquatic Environment

The energy demand for oxygen addition is rather high [11], with about

1 kWh kg–1 BOD5 being required for the aeration. About half of the organic material

Is converted into carbon dioxide, while the other half is converted into biomass

And must be separated as sludge. Sludge dewatering and disposal, followed by

Combustion of the sludge, leads to additional costs. Anaerobic fermentation may

be an attractive alternative, as conversion of the organic matter leaves only 5% of

The input carbon as residual for disposal or combustion. The process requires energy,

Predominantly for pumping, but also generates biogas consisting of methane

containing a largeamount of carbon dioxide.The typical process has four steps: (a) the

Fermentation and dissolution of insoluble residuals (fibers); (b) acidic degradation

Into alcohols and aldehydes; (c) conversion of these intermediates into acetic acid and

Acetates by micro-organisms; and (d) conversion into methane. For an effective process,

Acetogenic and methanogenic bacteriamust exist in a close symbiosis.However,

The surplus of energy generated by the conversion of waste sludge from the sustainable

Source wood into biogas does make anaerobic treatment very attractive.

A tertiary treatment is the final precipitation of remaining suspended or dissolved

Compounds by chemical coagulation. Usually, compounds used for such

treatments include aluminum salts, ferric salts (Fe3+), and lime slurries, while

Charged polymers can be used for a further intensification. This process reduces

The residual of recalcitrant compounds such as high molecular-weight degradation

Products of lignin. The resultant sludges may be rather difficult to dewater and

Are rich in inorganic material; thus, their combustion without additional fuel is

Difficult. The tertiary treatment is mainly used to remove excess nutrients such as

phosphorus [2], but it can also reduce higher levels of COD and AOX. In the Tasmanian

guidelines, the tertiary treatment is not considered to be AMT [3].

For the production of kraft pulp, the European Commission describes the BAT

For the discharge of water, with the emission data summarized in Tab. 10.2.

The biological degradation of the organic material – carbon – requires in addition

Trace elements and ammonia, as well as phosphate. These nutrients are typically

Not available in a suitable ratio in pulp mill effluents, and must be added.

Likewise, their levels must be controlled in order to avoid eutropic conditions in

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