Growth of Microthrix parvicella in nutrient removal activated sludge plants: Studies of in situ physiology

The in situ physiological activity of Microthrix parvicella in nutrient rem oval activated sludge systems was investigated by uptake of labeled substra tes and subsequent determination by microautoradiography. M. parvicella had a considerable capacity to take up oleic acid under oxic, anoxic and anaer obic conditions. For the lipid trioleic acid, the: most pronounced uptake w as found under anaerobic conditions, indicating that M. parvicella benefits from the degradation of lipids under these conditions. Starvation experime nts with different electron accepters available showed that M. parvicella w as able to maintain its high uptake capacity for 4, > 7 and 1-2 days under oxic, anoxic (with nitrate or nitrite present) and anaerobic conditions, re spectively. This indicates that besides oxygen, also nitrate and nitrite co uld be used as electron acceptors. The limited tolerance to starvation unde r oxic condition indicates that highly oxic conditions were toxic for the o rganism. No autotrophic or mixotrophic growth on [C-14]hydrogencarbonate wa s detected, and the organism was not found to store [P-33]-labeled orthopho sphate under alternating anaerobic and anoxic/oxic conditions applied for e nhanced biological phosphate removal. Based on the information available on the physiology of A. parvicella, a hypothesis for the growth in nutrient r emoval plants was presented together with possible control measures. (C) 20 00 Elsevier Science Ltd. All rights reserved.