Eficiência da remoção e recuperação de nutrientes utilizando microalgas em diferentes ciclos de fotoperíodos, para seu uso combinado com Wetland construído no tratamento terciário de uma estação de tratamento de esgotos (ETE).

Abstract

This research aimed at evaluating the nutrients removal and recovery using microalgae in different photoperiod cycles, for their combined use with Constructed Wetland (CW) in the Sewage Tertiary Treatment Station of University of Santa Cruz do Sul, RS, Brazil. Three light cycles were considered: 12 /12h, 24h light and 18h/06h, and the experiments were carried out between July and December 2018. The effluent treatment procedure used was defined by the next steps: conventional preliminary treatment (racking, desander and equalizer tank), secondary treatment by anaerobic reactor (AR), microalgae tank (MT), sand filter (SF) and Constructed Wetland system (CW). The macrophyte used was Chrysopogon zizanioides, with a density of 16 shoots per square meter. The artificial ilumination in the microalgae system was powered by a 9 Watt and 6000 Kelvin white light LED tubular lamp, and regulated by a light controller. To reduce the influence of sunlight from external environment, the system was covered with a vinyl tarp and aluminum foil. In addition to physical-chemical analyzes, quantitative analyzes of organic matter were carried out to determine the best performance in nutrient removal and recovery. The results indicated the predominance of three microalgae species in the three light cycles; two diatoms (Nitzschia and Gomphonema sp.) and one Chlorophyta (Chlorella sp). Under the experimental conditions established, there was no significant differences (p<0,05) between the values of the following variables at the microalgae system: soluble phosphorus, ammoniacal nitrogen (NH3), chemical oxygen demand (COD) and biochemical oxygen demand (BOD), comparing the three photoperiod cycles (12h/12h, 24h light and 18h/06h). However, it was observed that the system as a whole (Raw, AR, MA, FA and WC) showed high nutrients removal efficiency. In the photoperiod of 12h/12h, there was a removal of 99.4% turbidity, 95.0% apparent color, 89.1% total carbon, 85.7% total nitrogen, 69.5% inorganic carbon, 50.6% conductivity and 44.2% STD at the end of the treatment process. In the 24-hour light photoperiod, a 99.7% removal of turbidity, 87.5% apparent color, 77.2% STD and 75.0% conductivity were observed at the end of the treatment. In the photoperiod of 18h/06h, 100.0% of apparent color, 99.6% of turbidity, 71.0% of STD and 69.7% of conductivity were removed. As for the total suspended solids, total coliforms and Escherichia coli, a 100% removal was observed at the end of the treatment process in the three light cycles. For the removal of nutrients and organic matter, the photoperiod of 24h presented better performance, being more efficient to remove soluble phosphorus (67.6%), NH3 (94.0%), COD (63.7%) and BOD (42.7%). removal of these parameters was positively related to the cycle of longer duration of light.