Cyanobacteria and their metabolites are an issue for water authorities; however, little is known as to the fate
of coagulated cyanobacterial-laden sludge during waste management processes in water treatment plants
(WTPs). This paper provides information on the cell integrity of Anabaena circinalis and Cylindrospermopsis
raciborskii during: laboratory-scale coagulation/sedimentation processes; direct filtration and backwashing
procedures; and cyanobacterial-laden sludge management practices. In addition, the metabolites produced
by A. circinalis (geosmin and saxitoxins) and C. raciborskii (cylindrospermopsin) were investigated with respect
to their release (and possible degradation) during each of the studied processes. Where sedimentation
was used, coagulation effectively removed cyanobacteria (and intracellular metabolites) without any considerable
exertion on coagulant demand. During direct filtration experiments, cyanobacteria released intracellular
metabolites through a stagnation period, suggesting that more frequent backwashing of filters may be
required to prevent floc build-up and metabolite release. Cyanobacteria appeared to be protected within
the flocs, with minimal damage during backwashing of the filters. Within coagulant sludge, cyanobacteria released
intracellular metabolites into the supernatant after 3 d, even though cells remained viable up to 7 d.
This work has improved the understanding of cyanobacterial metabolite risks associated with management
of backwash water and sludge and is likely to facilitate improvements at WTPs, including increased monitoring
and the application of treatment strategies and operational practices, with respect to cyanobacterialladen
sludge and/or supernatant recycle management.