Biodegradation of N-methylmorpholine-N-oxide.

N-Methylmorpholine-N-oxide (NMMO) is capable of dissolving cellulose without any further addition of chemicals. The solution can be used to produce cellulosic staple fibres by pressing it through spinning jets into an aqueous spinning bath. Because of results from conventional biodegradation tests using non-adapted activated sludge, the solvent is generally considered being persistent. The object of the described work was to show, whether and how activated sludge can be adapted to N-methylmorpholine-N-oxide and whether it is possible to purify NMMO-containing wastewaters in conventional wastewater treatment plants. The experiments showed that the sludge can be adapted within about 15-20 days. Adapted sludge can degrade the substance itself and its most important metabolites to concentrations below their detection levels and retain this ability even during limited periods without solvent being present in the wastewater. The main requirement for a successful adaptation is a high sludge age. The degradation takes place in several steps. First, NMMO is reduced to N-methylmorpholine. The next step is a demethylation of N-methylmorpholine to morpholine. This step is crucial for the adaptation process. Once morpholine has been formed, the adaptation proceeds very quickly until none of the substances in question can be detected any longer. So the next step must be the cleavage of the morpholine ring structure.