This is the first study to systematically investigate the microbial community structure in cyanobacteria-laden
drinking water sludge generated by different types of
coagulants (including
AlCl3, FeCl3, and polymeric
aluminum ferric chloride (
PAFC)) using Illumina
16S rRNA gene MiSeq sequencing. Results show that Cyanobacteria, Proteobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia, and Planctomycetes were the most dominant phyla in sludge, and because of the toxicity of high Al and Fe level in
AlCl3 and FeCl3 sludges, respectively, the
PAFC sludge exhibited greater microbial richness than that in
AlCl3 and FeCl3 sludges. Due to lack of light and
oxygen in sludge, relative abundance of the dominant genera Microcystis, Rhodobacter, Phenylobacterium, and Hydrogenophaga clearly decreased, especially after 4 days storage, and the amounts of extracellular
microcystin and organic matter rose. As a result, the relative abundance of
microcystin and organic degradation bacteria increased significantly, including pathogens such as Bacillus cereus, in particular after 4 days storage. Hence, sludge should be disposed of within 4 days to prevent massive growth of pathogens. In addition, because the increase of extracellular
microcystins, organic matter, and pathogens in
AlCl3 sludge was higher than that in FeCl3 and
PAFC sludges, FeCl3 and
PAFC may be ideal
coagulants in
drinking water treatment plants.