Microalgae growth using treated domestic effluent added to emerging pollutants: Removal mechanism and generation of by products

Abstract

The objective was to assess the efficiency of microalgae metabolism in removing BOD5, COD, N, P, and emerging pollutants (EPs) from pretreated domestic effluent. Spirulina platensis and Scenedesmus obliquus were cultivated in standard medium with the addition of 5 % and 10 % pretreated domestic effluent every 5 d. The growth parameters, biochemical composition, and removal efficiencies were evaluated. Spirulina was scaled up to 10 L tanks with an open reactor, here using 10 % effluent and 20 μg/L of EPs (caffeine, fluoxetine, and acetylsalicylic acid) every 5 d. EP concentrations and the generation of degradation byproducts were monitored. Microalgae exhibited significant growth in both effluent additions, achieving biomass concentrations exceeding 1 g/L. After 30 days, all the physical-chemical parameters of the effluent were reduced (removals <80 %). The scaled-up experiments demonstrated removal of 39 % caffeine and 80 % fluoxetine after 30 d. EP degradation byproducts (theobromine and norfluoxetine) from caffeine and fluoxetine degradation showed EP biodegradation as a mechanism. Microalgae cultivation proved effective as a posttreatment method for the residual loads remaining after conventional treatment, and it can also target new fractions of pollutants in wastewater, reducing the risk to aquatic organisms. Moreover, the biomass of Spirulina platensis obtained after treatment exhibited high carbohydrate and protein contents (55 % and 29.18 %, respectively), showing potential as a source of bioenergy and biofertilizer products.