THE CHLORINE ALTERNATIVES
Greenpeace on their Christmas Greetings cards, December 1995.
When wood is used to make paper, several methods exists to process the wood. The simplest method is by mechanical treatment: the wood is heated, then grinded, the resulting pulp is bleached with air or oxygen and the filtered and dryed product is paper. This is called TMP or thermo-mechanical paper.
There is one advantage and two drawbacks on this process: The advantage is that all the wood - except the bark - is used. The disadvantages: poor mechanical and recycling quality, because of much short fibers are formed. About one quarter of the wood is lignine, the glue that makes the strength of near all plants. This remains in TMP paper. Although it is bleached, the lignine will rapidely turn yellow when it comes in direct sunlight. That is what you see when your daily newspaper, made from TMP, is lying in the sun.
For newspapers that is not a problem. If it can survive one day, that will do the job. But if you want magazines and books, with a higher quality and which have to withstand longer times, or you need a better strength like as for cardboard, you have to use other procedures.
The process which combines good quality with an affordable price, is the Kraft process. In that process, wood is cut in parts, called chips and these are cooked in caustic soda, which removes most of the lignine, without attacking the remaining cellulose too much.
When the remaining pulp of the Kraft process is not further bleached, it is used as cardboard: the rather dark colour is from the remaining lignine after the cooking process. If you want to have more or less white paper, there are different methods for bleaching: that can be done with chlorine, chlorine dioxyde, oxygen, ozone or hydrogen peroxyde.
Chlorine gives the best result: all remaining lignine is dissolved, without attacking the cellulose and the remaining cellulose is bright white and remains white for tens of years...
The drawback of this method is that some minor amounts of dioxins are formed and released, about 1 microgram per ton of pulp. That meand a few years ago for Sweden about 10 grams per year for 10 million tons of pulp. Not the biggest dioxin problem of that time: the steel industry was discharging much more. The main problem was in fact not the dioxins, it was the dissolved chlorinated lignine, which was rather persistent, wat means quite difficult to break down by bacteria. The amount of dissolved chlorinated organics in the effluent can be measured as AOX (absorbable organic halogens), that is the amount of organochlorines which can be absorbed by active carbon. For this type of process the AOX was 3-5 kg/ton pulp on about 50 kg total discharged organics per ton. That did give an enormous amount of organics per year per paperwork!
The AOX does not mean anything to the toxicity of what is released. But that the total effluent was toxic was clear: the effluent had an unpleasant effect: fish swimming offstream changed external sexual behaviour! That was quite alarming and the use of chlorine with the released dioxins and other chlorinated stuff was accused to be the origin of all evil. Also in chlorine bleached paper there were found small amounts of dioxins, which did give a lot of commotion in the media in Sweden and later in other countries. Strange enough there was no commotion about the amounts of dioxins found in recycled paper and cardboard, although the levels were about ten times higher than of fresh chlorine bleached paper.
With a lot of cooperation from universities and paper works, alternatives were found for chlorine bleaching: with prolonged cooking times, prebleaching with oxygen and the main bleaching with chlorine dioxyde, about the same quality of paper was reached, without the drawbacks of elementary chlorine: No measurable levels of dioxin were found in the pulp, neither in the effluent and the AOX was reduced to 400-800 g/ton. The paper made by this process is called ECF, or Elementary Chlorine Free paper. The remaining effluent was reduced in load to 5 kg/ton of organics by using waste water treatment systems. Although the effluent was more biodegradable and one can find about the same AOX in rivers far away from any paper works as in the river Rhine (with many paper works), it remained toxic for fish...
Another process was introduced and heavely promoted by Greenpeace. Instead of chlorine and chlorine dioxyde, hydrogen peroxyde is used in the bleaching process. That process is called TCF or Totally Chlorine Free. That has some drawbacks: to make more or less the same quality of paper, about 10% more wood has to be used, but even then the fibers remain shorter, what has as consequence that the recyclability will be reduced. Each time paper or cardboard is recycled, the remaining fibers become shorter, with as effect that more new pulp must be added and more too short fibers have to be discarded. In average, recycling gives 11% of waste, to some extend polluted with heavy metals, from the kaolin (clay) used to absorb inks in paper and sometimes from the inks themselves.
But at the other side, no measurable dioxins were found in the effluent and the AOX was virtually zero. Although the effluent is dioxin and AOX-free, fresh TCF paper contains at least 35 times more dioxins than ECF paper! And more... the effluent was readably biodegradable but it remained toxic for fish...
There must be another origin of the strange response of fish to the paper mill effluents. That was found in natural remainders of the wood: phytosteroles (natural plant hormones), phenols, fatty acids and resins are the possible culprits. So the beginning of the anti-chlorine-bleaching story was in fact wrong.
That doesn't mean that the new processes are not better for the environment: less organic effluent and better biodegradability and less dioxins is in fact better in this case. But we don't see why Greenpeace so heavely promotes TCF paper, although it needs more wood and gives a lesser quality and it contains more dioxins, except if they do that because the word chlorinedioxyde, still contains the word 'chlorine', or is it the difference between working for a better environment and anti-chlorine hate (or fundamentalism)...
To give you an impression of the amount of dioxins, found in different pulps and papers:
Dioxin found in different pulp and papers.
All figures as microgram (µg) I-TEQ/ton.
|Dioxin found in different pulp and papers|
|Recycled linerboard (chlorine free):||2.50|
|Totally chlorine free (TCF) Kraftpaper:||0.35|
|Deinked recyclepulp (newsprint):||0.19|
|Bleached Kraft (ECF):||0.01|
The same order of dioxin amounts were found in Swedish investigations. The researchers first thought that the pre-treatment with chlorine of the water used for the cooking could be the origin of the dioxin formation in TCF pulp, but that was not the case: the amount of chlorinated phenols formed by chlorination of the water was not enough to explain the amount of dioxins formed. Probably the oxydation of chloride from salt to elementary chlorine by the peroxyde can be the origin of the higher dioxin content. See also Sources of dioxins.
Pulp and paper researchers are hard at work to find a solution for the still high amount of organic material, chlorinated or not, which is in the effluent of paper works. This can be done by a Totally Effluent Free (TEF) process, where all liquids are recycled internally in the paper works, by destillation of the remaining effluents and incineration of the organic solid waste in well equiped incinerators. This needs further research, because the remaining salts from the process must be reused or discarded too.
It is true that the change from only elementary chlorine use in paper bleaching to alternatives was better for the environment. But it is ecological nonsense to promote TCF paper against ECF paper, only because 'chlorine'dioxyde is used as the bleaching agent. The TCF alternative is clearly not better for the environment than ECF paper.
At this moment ECF paper seems to be the least polluting type of quality paper. But paper making (or recycling) is clearly not 100% environmentally friendly. In short terms a further reduction of the (organic) effluent will be necessary to reduce the overall pollution.
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Created: March 24, 1996.
Last update: May 3, 1998.
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