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.

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The influence of solid retention time, cadmium loading and the effect of the process of acclimation on the activity of activated sludge in the presence of the metal were studied. Activated sludge was cultivated in plug-flow and continuous completely mixed lab-scale bioreactors. Respirometric measurements were applied to evaluate the inhibition effects of cadmium on activated sludge. Monod's equation and the equation of non-competitive inhibition were applied to describe the toxicity and inhibition of cadmium. Maximum inhibition effect of cadmium was observed at different time periods of cadmium acting on both acclimated and non-acclimated sludges. The dependence of the attainment of maximum inhibition effect on the metal loading as well as solid retention time was observed. Therefore, maximum inhibition should be included in the assessment of metal toxicity.