ABSTRACT
95This study aimed at evaluating the possible impact of substrate accumulation (Sulphate and PHB) in microorganisms on bioprocess control of an inversed fluidized bed (IFB) bioreactor. To investigate the impact of substrate accumulation, step feed changes were induced to an IFB bioreactor performing biological sulphate reduction (SR). A first step feed change load set the COD and sulphate influent concentration to zero. Surprisingly, sulphide was still being produced after 15 days of operation without electron donor and sulphate supply. This suggests that accumulated and/or sorbed COD and sulphate supported the continued biological sulphide production. Polyhydroxybutyrate (PHB) was indeed found present in the sludge and could support the sulphate reduction. A second step feed change of adding solely COD (and no sulfate) resulted in the production of sulphide, suggesting that sulphate had accumulated in the IFB sludge. A mathematical model that includes microbial growth, storage products and metabolism of lactate oxidizing SRB was developed, calibrated and validated. This model was able to simulate the accumulation of both PHB and sulphate in the IFB bioreactor.
