Regulatory role of n-propanol in propylene glycol biomethanization under overload

This work examines the transient response of an anaerobic fluidized bed bioreactor to an overload of propylene glycol (PG), the primary component in aircraft de-icing waste. Under favorable operating conditions, PG was converted to n-propanol (nPrOH) and propionate (HPr), and subsequently n-PrOH was completely converted into HPr. HPr was then fully degraded to methane and carbon dioxide via acetate. Under an overload condition, n-PrOH conversion to propionate was completely blocked but propionate degradation continued, contrary to free-energy computations in which n-PrOH should rapidly degrade and HPr should accumulate. When the imposed overload condition was relieved, the accumulated n-PrOH was rapidly converted into propionate. n-PrOH, then, could act as a temporal sink for reducing equivalents (XH2) and could regulate the overall PG methanazation process. n-PrOH should be monitored along with typical VFAs such as HPr to avoid sudden VFA accumulation and thus to optimize process performance for PG methanization.