IMPACT OF INFLUENT MICROORGANISMS UPON POOR SOLIDS SEPARATION IN THE QUIESCENT ZONE OF AN INDUSTRIAL WASTEWATER TREATMENT SYSTEM

Conventional and molecular biology tools were employed to diagnose the biological origin of poor sludge settling in the secondary clarifier of an industrial activated sludge system treating a waste stream from a dairy food processing plant. Gram and acridine orange staining indicated that viable, Gram-positive microorganisms were present in samples removed from the influent waste stream and represented approximately 50% of total cell counts in samples removed from the activated sludge system. Subsequently, the “full-cycle 16S rRNA approach” showed that Paenibacillus spp., a low G+C% DNA content Gram-positive microorganism, represented up to 30% of total DAPI stained cell counts in samples removed from the activated sludge system. Although fluorescence in situ hybridizations with 16S rRNA-targeted oligonucleotide hybridization probes identified Paenibacillus spp. in samples removed from the influent waste stream, their abundance was less than 10% of total DAPI stained cell counts. The results of the study suggest that Paenibacillus spp. were present in low abundance in the influent waste stream, increased in relative abundance within the treatment system, and probably were responsible for the complete failure of liquid-solids separation in the secondary gravity clarifier. However, the lack of information about the role of Paenibacillus spp. in wastewater treatment systems prevented the identification of the specific operating conditions that may have been responsible for its proliferation. This study demonstrated that the “full cycle 16S rRNA approach” could be used to identify problem causing microbial populations in activated sludge systems without the need for previous results from studies employing cultivation or microscopic analyses.