Uso combinado de microalgas e wetlands construídos com fluxo vertical como tratamento terciário descentralizado de efluente sanitário.

Abstract

The present work involved the development of a domestic effluent treatment system combining the use of microalgae turf scrubber with vertical flow constructed wetlands, aiming at their use as a decentralized treatment. The system presents a configuration of three tanks of two hundred liters each, both made of high-density polyethylene with a rectangular shape. The first tank was designed using microalgae turf scrubber (MA), while the second (WC 1) and third (WC 2) were designed using vertical flow constructed wetlands. The affluent for treatment was transferred from the WTP equalization tank to a decanter, followed by 3 anaerobic tanks for the secondary treatment. The microalgae tank was the initial point of feeding. An acrylic support was used as base for the adhesion of spontaneously developed algae. The system had submerged pump recirculation with flow rate of 520 L. h-1, which continuously distributes the effluent over the entire surface with a hydraulic load of 0.27 mm.s-1. The system also had a 600 lumens LED artificial illumination at night. The WCs tanks had the same configuration, having a substrate composed of 150 mm of gravel at the base for drainage, and 400 mm of gravel No. 2. The system was planted with Hymenachne grumosa with a density of 24 shoots per square meter. The system was divided into two phases: Phase I and Phase II. During the Phase I two hydraulic detention times were tested. The first one having a HDT of 21 days, with 7 days in each of the tanks, and the second one with 14 days of HDT, being 7 days, to the microalgae tank and 7 days in the two WCs that were fed simultaneously by the effluent coming from the microalgae tank. For the TDH of 21 days, the microalgae tank was fed with 71 liters, after 7 days the effluent was transferred to WC 1 with a hydraulic rate of 0.14 m3.m-2, and after another 7 days was transferred for WC 2, where it was treated for the last 7 days before being discarded. For the 14-day HDT, the MA tank was fed with 101.2 liters, being transferred 50.6 liters simultaneously for each tank, counting for a hydraulic rate of 0.10 m3.m-2. During the Phase II the hydraulic regime presented HDT of 21 days. The combined use microalgae turf scrubber and constructed wetlands indicated efficient removal of pollutant loads, contributing for the reduction of conductivity (49%), TDS (48%), turbidity (98%), apparent color (82%), ammonia (99%), total nitrogen (70%), soluble phosphorus (44%), TOC (69%), IC (86%), TC (83%) and COD (72%). The microalgae tank contributed with an average of 76 ± 24% of the total efficiency of the system, for ammoniac nitrogen, IC and TC the contribution was 100%, indicating that microalgae turf scrubber was the mean mechanism for the treatment viability. The system also enabled the detoxification of the system, reducing acute ecotoxicity by 100% right after the first tank.