Environmental Engineering Reference
In-Depth Information
Conclusion
The stormwater runoff analyzed in this study was found to show toxic effects
according to two of the three applied toxicity tests. The stormwater was highly toxic
to the algae, lesser toxic to the crustaceans and non-toxic to the bacteria - revealing
that the bacteria Vibrio fisheri was the least sensitive organism and that the algae
Selenastrum capricornutum was the most sensitive organism. Two stormwater runoff
samples showed a high toxic effect to the algae with EC50-values at 10% dilution
and two samples showed a lower toxic effect with EC50-values at 85% dilution.
To assess the impact of aluminum on the toxic effect of stormwater runoff, alu-
minum was added to two samples in concentrations ranging from 2 to 40 mg Al/L.
The toxicity test using the algae Selenastrum capricornutum showed reduced toxic
effect for aliquots with aluminum concentration from 2 to 10 mg Al/L compared
with the toxic effect for pure stormwater runoff. That is, the aluminum may reduce
the toxic effect in stormwater runoff. At concentration levels above 20 mg Al/L,
aluminum itself becomes toxic and the toxic effect is higher than for the pure run-
off. This limit between beneficial and toxic effects will depend on a number of
water quality parameters, such as the concentration of organic matter, phosphorous,
toxic compound, pH etceteras.
The most effective aluminum concentration to reduce toxic effects was in this
study found to be 7 mg Al/L. However, the most cost effective aluminum concen-
tration is 5 mg Al/L which corresponds to the interval typically applied for cost-
effective phosphorous removal.
Acknowledgements
The work was partly financed by PH-Consult ApS, Denmark, under the
framework of the Urban Water Technology Research School.
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