Anaerobic treatment of biodiesel by-products in a pilot scale reactor

Abstract

In this work, long-term operation of a pilot scale mixed anaerobic reactor processing crude glycerol and rapeseed meal is discussed. These materials are generated as by-products of biodiesel production. Mixed reactor was operated under mesophilic conditions for the period of 654 days. Total cumulative production of biogas reached 379 m³ (at atmospheric pressure and ambient temperature). Maximum volumetric loading achieved during the operation was 2.17 kg m⁻³ d⁻¹ for the crude glycerol dose of 2 L. When dosing crude glycerol as a single substrate, average specific production of biogas of 0.76 m³ per L of the g-phase was achieved. The lack of nutrients in the g-phase had to be compensated by an addition of ammonium nitrogen in the form of urea into the reactor. Long term processing of crude glycerol demonstrated that accumulation of dissolved inorganic salts in the reactor can lead to inhibition of the methanogenic activity of microorganisms, causing breakdown of the system. Co-fermentation of crude glycerol with rapeseed meal provided stable biogas production and it was shown to be a feasible way of anaerobic degradation of these substrates. At the maximum volumetric load of 1.33 kg m⁻³ d⁻¹ (500 mL of g-phase and 500 g of rapeseed meal), the average biogas production reached 0.58 m³ d⁻¹.