THE FATE OF NOCARDIA IN ANAEROBIC-DIGESTION

Laboratory-scale completely-mixed and batch experiments investigated the fate and foaming potential of Nocardia during mesophilic anaerobic sludge digestion. Nocardia filament concentration was measured by an immunofluorescent technique (Hernandez et al., 1993); filament viability was by dehydrogenase activity staining (Awong et at, 1986). Continuous flow digesters, fed with waste activated sludge (WAS) containing high Nocardia levels were operated at solids retention times (SRT's) of 10, 14, and 28 days to determine SRT effects on Nocaudia survival. in two-phase digestion experiments, the digestion was divided into an initial acid phase (4-day SRT; pH 5.4 to 6.4) and a second methanogenic phase (11- and 24-day SRT's; pH 7.2). Batch digestion experiments determined effects of pH, TS concentrations, and Nocardia filament mass on digesting sludge foaming potential. None of the digestion systems completely removed or rendered non-viable all influent Nocardia filaments. In single-phase digesters Nocaudia filament viable fraction decayed with a first order rate coefficient of approximately 0.02 day(-1), so that with an SRT of 14 days, the viability decreased by approximately 37%. In two-phase digestion viability decreased more rapidly; for a 14-day total SRT, reductions were approximately 54%. In batch foaming tests on digested sludge, foam production levels increased in proportion to Nocardia filament concentration over the range of 0.01 to 0.2 g Nocardia/g TS.