Proper sample storage before RNA isolation is crucial for a reliable assessment of microbial activity in activated sludge. In our studies, different amounts of activated sludge expressed in mg of total suspended solids (TSS) were fixed with a constant volume of RNA later RNA Stabilization Reagent (QIAGEN, Germantown, MD, USA) and stored for 3 or 6 months. The results obtained point out that for the best RNA recovery, 1 mg of activated sludge TSS should be fixed with 33 ?l of the RNAlater. It was also observed that a longer storage period (6 vs. 3 months) of the activated sludge in RNA later lowered RNA recovery by, on average, 25 ? 15% although bacterial diversity in all samples remained unaltered.
The effect of bioaugmentation with nitrifying bacteria on activated sludge granulation in column SBR was determined. Two reactors (R1, R2), operating at hydraulic retention time of 0.62 d, wastewater exchange ratio of 80%, and settling time of 5 minutes, were employed for the removal of organic, nitrogen and phosphorus compounds from the mixture of synthetic wastewater and wastewater from sludge dewatering (COD/N = 2.4). After 50 days of cultivation, mature granules appeared. In the last stage of the experiment COD, nitrogen and phosphorus load was about 0.3 g CODg TSS-1cycle-1, 0.08 g Ng TSS-1cycle-1, and 0.02 g Pg TSS-1cycle-1. COD and phosphorus removal rates were at the level of 60 and 50%, respectively. Bioaugmentation positively influenced nitrification efficiency in the reactor.
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