Three coagulants were initially studied—
ferric chloride, aluminum chlorohydrate
(ACH), and aluminum sulfate (alum)—at
ambient pH and pH controlled to 6. 3.
The emphasis of the study then shifted
to alum coagulation at pH 6. 3 as this was
considered the most cost-effective coagulant ( Table 1) and it was shown that a pH
drop to below 6 may result in damage to
cells and release of metabolites.
Two source waters were the main focus,
Myponga Reservoir water and River
Murray water, in Australia. These waters
were chosen because they provided
contrasting water quality. Several other
waters and environmental samples were
also tested where possible to strengthen
the operational applicability of the
The application of pre-chlorination at
low and moderate doses was also investigated, as it may be used to improve coagulation, or to destroy cyanobacteria and
toxins prior to conventional treatment.
In addition, limited experiments were
undertaken using potassium permanganate to oxidize manganese or iron prior to
coagulation. Release of the dissolved metals from the sediment often occurs under
the same conditions that are favorable for
cyanobacteria proliferation, namely warm
weather and minimal water column mixing leading to stratification.
Finally, the behavior of the cyanobacteria bound in the floc was studied. This
is an important but often overlooked
aspect of conventional treatment, which
essentially concentrates intact cells containing metabolites such as taste and odor
compounds and cyanobacterial toxins
The experimental work undertaken
by the Australian Water Quality Centre,
a business unit of the South Australian
Water Corporation (SA Water), and the
Metropolitan Water District of Southern
California (MWDSC), helped identify key
best practices when addressing cyano-
toxin events . These best practices include:
º Understanding at what point chlori-
nation does/does not have beneficial
effects on coagulation.
º Knowing what oxidant alternatives
can be used in the treatment process.
Potassium permanganate dosing
may be applied for the control of
manganese and iron in the presence
of A. circinalis and M. aeruginosa.
º Understanding the effectiveness of
specific coagulants on cell and natu-
ral organic material removal. Based
on this analysis, alum is considered
the most cost-effective coagulant.
º Knowing what role turbidity can play
in the treatment process. While tur-
bidity cannot be used as an indicator
of the presence of cyanobacteria or
cell concentration, use the decrease
in settled water turbidity with coagu-
lant dose as a surrogate for, or indica-
tor of, cell removal if the initial
turbidity is ≈ 10 NTU or above
(Figures 1 and 2).
º Understanding the removal rate of
specific toxin strains, such as
C. raciborskii. In most conditions
C. raciborskii was least readily
removed by coagulation. For species
other than C. raciborskii, the presence
of mineral turbidity, for example in R.
Murray water, improved coagulation
and settling due to the added weight
of the flocs provided by the mineral
particles, suggesting that a settling
aid may be an option to improve
settled water quality in low turbidity
waters affected by cyanobacteria.
Although cell removals of up to 99%
were observed, in general 90–95%
removal was the optimum. This percentage removal appeared to apply to a wide
range of cell concentrations. While this
indicates effective coagulation, in the
presence of high inlet cell numbers this
could rapidly lead to an accumulation of
cyanobacteria in clarifiers and filters.
Guidance for Water Utility
IN PREPARATION FOR the warmer summer
months when algal blooms are more likely
to occur, WRF and AWWA published project #4548, A Water Utility Manager’s Guide
to Cyanotoxins (Sklenar et al.), in April 2015.
This report is presented in a simple Q&A
format to address cyanotoxin occurrence,
source water management, and treatment
strategies. Answers to the following questions are presented in this report:
1. What are cyanotoxins and where do
they come from? What does a cyanotoxin-producing bloom look like?
2. Why are cyanotoxins a human
3. Are cyanobacteria blooms a new
4. Are cyanotoxins regulated in drinking water, and what levels of toxins
are of concern?
5. What are the most important conditions leading to cyanobacteria
6. If the surface water supply has cyanobacteria blooms, does that mean
my utility has a cyanotoxin
Table 1. Cost of each dose of coagulant for a 1L jar test
Cost of coagu-
Cost of coagulant (USD)
Cost of coagulant (USD)
40 0.017 20 0.026 10 0.020
60 0.025 40 0.052 20 0.039
80 0.034 60 0.078 30 0.059
100 0.042 80 0.104 40 0.078
120 0.050 100 0.130 50 0.100
Source: Newcombe et al. 2015