Evaluation of primary and secondary production using wastewater as a culture medium

Abstract

The ability of rotifers and cladocerans to convert primary to secondary production in wastewaters was tested. Scenedesmus acutus was cultured on Bold's (defined) medium, wastewater from the tertiary phase of water treatment and a mixture of both. The algal growth rates (µ) ranged from 0.4 to 0.7 day⁻¹, being highest in defined medium. The demographic characteristics of Brachionus rubens and Moina macrocopa were tested using algae at a density of 1.0 x 10⁶ cells mL⁻¹. Into each test jar, we introduced 20 neonates (< 12-h-old) of either B. rubens or M. macrocopa. Daily (for M. macrocopa) or twice a day (for B. rubens), dead adults and the neonates were enumerated and removed. Average life-span and generation time of B. rubens were not significantly influenced by the algal treatment type. Gross and net reproductive rates were significantly influenced by the medium on which the algae was cultured; in the case of B. rubens, they ranged from 20-36 and 10-22 offspring female⁻¹; the corresponding values for M. macrocopa were higher (38-110 and 13-31 offspring female⁻¹, respectively). The rate of population increase was higher for Brachionus (0.41-0.65 day⁻¹)) compared to Moina (0.28-0.57 day⁻¹). Brachionus had significantly higher growth rates on algae cultured on Bold medium than on treated wastewater while Moina grew significantly better on Scenedesmus cultured on Bold medium or a mixture of treated wastewater and Bold medium than on treated wastewater alone.