Toxicity effects of formaldehyde on methanol degrading sludge and its anaerobic conversion in Biobed((R)) expanded granular sludge bed (EGSB) reactors

Methanogenesis from formaldehyde mainly occurred via intermediates as confi rmed by the increased concentrations of methanol and H-2 in the liquid and gas phases respectively during formaldehyde conversion. While formaldehyde was readily transformed, the methane production rate was immediately and st rongly inhibited. Formaldehyde toxicity was in part reversible since the me thane production rate recovered after formaldehyde depletion. This recovery can not be explained by biomass growth. The toxicity of formaldehyde was a lso in part irreversible, since the degree of recovery was not complete. Th is loss in the methane production rate likely can be attributed to biomass decay as suggested by its linens relation with the amount of formaldehyde d osed, as well as by scan-ng electron microscopy observations. The addition of the same amount of formaldehyde either in a slug or in a continuous mode caused the same loss in the methane production rate. Thus for the treatmen t of formaldehyde-containing streams,a balance between loss in the rate (fo rmaldehyde-related decay) and bacterial growth should be attained .By combi ning good biomass retention and internal dilution of the wastewater, indust rial streams containing formaldehyde can still be treated anaerobically. (C ) 1999 Published by Elsevier Science Ltd on bahalf of the IAWQ. All rights reserved.