Formaldehyde and methanol biodegradation with the methylotrophic yeast Hansenula polymorpha in a model wastewater system

In search of the optimal way to reduce the hazards of environmental contamination by formaldehyde (FD) and methanol the use of unconventional yeasts is proposed as exemplified by the methylotrophic yeast Hansenula polymorpha. In a very simplified environment of a model wastewater solution, H. polymorpha cells were able to grow on, and metabolize formaldehyde and methanol, applied as sole carbon sources, at concentrations typical for wastewaters of the chemical industry. Several experimental conditions were tested for cell growth and biodegradation kinetics. It was found that the yeast culture inoculated at low cell density was able to grow on initial FD levels up to 400 mg/l and the biomass yield was dependent on both, the amount of total carbon added and the physiological state of the cells. When high density of preadapted cell culture was used, the methylotrophs were fully viable and able to degrade formaldehyde present at initial concentrations up to 700 mg/l. The maximum limiting FD consumption rate was determined as approx. 400 mg/l per hour. Methanol, at concentrations up to 2%, was easily utilized and did not have a negative effect on cell growth and respiration. It is suggested that in real wastewaters the eukaryotic microorganisms — in contrast to bacteria — might reveal greater adaptation potential to toxic levels of formaldehyde as well as to other wastewater constituents.