Specific layers in aerobically grown microbial granules

Aims: To determine the optimal size of aerobically grown granules for wastewater treatment by measuring specific layers within the granules. Methods and Results: A variety of biological layers were detected by oligonucleotide probes, specific fluorochromes, and fluorescent microspheres. The channels in the granule matrix penetrated to depths of 900 mum. A layer of obligate anaerobic bacteria was detected at a depth of 800 mum below the granule surface. Dead cells were also observed in the granule interior. Conclusions: Aerobically grown granules contained layers of aerobic and anaerobic microorganisms. Significance and Impact of the Study: The optimal diameter of the aerobic granule is less than 1600 mum. This is twice the distance from the granule surface to the anaerobic layer. This approach can be used to optimize the thickness of other microbial aggregates such as flocs, colonies and biofilms.