Effluents of pulp and paper mills are relatively simple to treat by activated sludge process - in theory. Some severe problems have arisen in practice, however.
Temperatures of incoming waste waters have risen during last years. The most obvious reason for this phenomenon is the increased recirculation of process waters inside the mills. Poor sedimentation of flogs, caused by the heavy growth of filamentous bacteria, has also become to be more and more hard problem for purification plants. There may be some kind of correlation between temperature and bulking of sludge?
Another problem, potentially very hazardous, is the growth and recirculation of Legionella pneumophila inside activated sludge process. The role of Protozoa has now been established: they act as carrirs of bacteria backwards in returned sludge.
Dosing of nutrients into biological treatment steps isn't any hard task anymore because the need of phosphorus and nitrogen has been studied very deeply, and simpe AT LINE testing for the optimization of them is easy to perform in the mill labs.
Two problems, mentioned before, still exist and need R&D activities to be solved: bulking of the sludge (by filamentous organisms) and L.pneumophila.
Thursday, February 26, 2009
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