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This study evaluated the two-way interaction and main effects of four factors on biomass productivity and phosphorus removal efficiency of a microalgae–bacteria biofilm grown in municipal anaerobic digester centrate, with factor levels and operating conditions selected to mimic a pilot rotating algae biofilm reactor (RABR) at a water resource recovery facility (WRRF) in Utah. The two-way interactions of harvesting period × light intensity (LI), harvesting period × temperature, and LI × hydraulic retention time (HRT) had significant effects on biomass productivity: At high temperature and at low LI, highest biomass productivity was achieved with a 14-day harvesting period (25.5 and 10.9 g AFDW/m2/day, respectively), but at medium temperature and at high LI, highest biomass productivity was achieved with a 7-day harvesting period (16.1 and 16.4 g AFDW/m2/day, respectively). At high HRT, highest biomass productivity occurred at low LI (11.9 g AFDW/m2/day), but at low HRT, highest biomass productivity occurred at high LI (19.3 g AFDW/m2/day). Phosphorus removal was strongly influenced by LI (>70% removal at 1,600 μmol/m2/s) and occurred most rapidly during the first 2 days HRT (e.g. 2,270 TP/m2/day for days 0–2 vs. 217 mg TP/m2/day for days 2–4), which, in combination with chemical equilibrium modeling, suggests precipitation contributed significantly to phosphorus removal in this study.

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  • A native microalgae biofilm was cultivated in anaerobic digester centrate.

  • Two-way interaction and main effects of temperature, light intensity, hydraulic retention time, and harvesting period were studied.

  • Two-way interactions of light intensity × harvesting period, temperature × harvesting period, and light intensity × HRT were significant.

  • Phosphorus removal rates were consistent with mineral precipitation models.

harvesting period, hydraulic retention time, interaction effects, light intensity, rotating algae biofilm reactor, temperature
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