APPLICATION OF MICROAUTORADIOGRAPHY TO THE STUDY OF SUBSTRATE UPTAKE BY FILAMENTOUS MICROORGANISMS IN ACTIVATED-SLUDGE

Excessive growth of filamentous microorganisms in activated-sludge tre atment plants is a major operational problem which causes poor settlem ent of activated sludge. An enhanced understanding of the factors cont rolling growth of different filamentous microorganisms is necessary in order to establish more successful control strategies. In the present study, the in situ substrate uptake was investigated by means of micr oautoradiography. It was demonstrated that the uptake of labeled organ ic substrates by the filamentous microorganisms, during short-term inc ubation, could be detected by microautoradiography. Viability and resp iratory activity of the filaments were also detected by reduction of C TC (5-cyano-2,3 ditolyl tetrazolium chloride) and by incorporation of [H-3]thymidine. Gram, Neisser, and fluorescence staining techniques we re used for the localization and identification of the filaments. Acti vated-sludge samples from five wastewater treatment plants with bulkin g problems due to filamentous microorganisms were investigated. Microt hrix parvicella, Nostocoida limicola, and Eikelboom's type 0041 and ty pe 021N were investigated for their ability to take up organic substra tes. A. panel of six substrates, i.e., [C-14]acetate, [H-3]glucose, [C -14]ethanol, [H-3]glycine, [H-3]leucine, and [H-3]oleic acid, was test ed. The uptake response was found to be very specific not only between the different filamentous types but also among filaments of the same type from different treatment plants. Interestingly, M. parvicella con sistently took up only oleic acid among the tested substrates. It is c oncluded that microautoradiography is a useful method for investigatio n of in situ substrate uptake by filamentous microorganisms in activat ed sludge.