Water
samples were analysed according to standard methods
(APHA, 1998), and the analyses of biomass were performed at
the end of the assays, according to AOAC (1997). Biomass
composition was expressed on a dry weight basis. To evaluate
the specific growth rate Azolla’s fresh weight was measured
three times a week. The plants were harvested and gently
blotted between absorbent papers, to remove adhering liquid,
and let to dry during half an hour on filter paper (Whatman no
1). Specific growth rate (admitting an exponential growth as
reported by Vermaat and Hanif (1998) and Rai et al. (2006)) and
maximum plant density (considering biomass at the end of
the assays and the area of PVC boxes) were evaluated.
Productivities were calculated based on Azolla’s densities and
specific growth rates for each time interval. Phosphorus and
nitrogen removal rates coefficients were calculated using firstorder
kinetics equations, as referred by Ko¨ rner and Vermaat
(1998) and Sooknah and Wilkie (2004). The phosphorus and
nitrogen uptake rates by A. filiculoides’s biomass were determined
based on productivity values and biomass phosphorus
and nitrogen contents.