RESUMO
The present study aimed to develop a pilot-scale integrated system composed of anaerobic biofilter (AF), a floating treatment wetland (FTW) unit, and a vertical flow constructed wetland coupled with a microbial fuel cell (CW-MFC) and a reactive bed filter (RBF) for simultaneously decentralized urban wastewater treatment and bioelectricity generation. The first treatment stage (AF) had 1450 L and two compartments: a settler and a second one filled with plastic conduits. The two CWs (1000 L each) were vegetated with mixed plant species, the first supported in a buoyant expanded polyethylene foam and the second (CW-MFC) filled with pebbles and gravel, whereas the RBF unit was filled with P adsorbent material (light expanded clay aggregate, or LECA) and sand. In the CW-MFC units, 4 pairs of electrode chambers were placed in different spacing. First, both cathode and anode electrodes were composed of graphite sticks and monitored as open circuit. Later, the cathode electrodes were replaced by granular activated carbon (GAC) and monitored as open and closed circuits. The combined system efficiently reduced COD (> 64.65%), BOD5 (81.95%), N-NH3 (93.17%), TP (86.93%), turbidity (94.3%), and total coliforms (removal of three log units). Concerning bioenergy, highest voltage values were obtained with GAC electrodes, reaching up to 557 mV (open circuit) and considerably lower voltage outputs with closed circuit (23.1 mV). Maximum power densities were obtained with 20 cm (0.325 mW/m2) and 30 cm (0.251 mW/m2). Besides the electrode superficial areas, the HRT and the water level may have influenced the voltage values, impacting DO and COD concentrations in the wastewater.
Assuntos
Fontes de Energia Bioelétrica , Purificação da Água , Eletricidade , Eletrodos , Águas Residuárias , Áreas AlagadasRESUMO
This study evaluated the performance of urban wastewater treatment in pilot-plant by an integrated system consisting of anaerobic reactor, microalgae cultivation, Venturi tube ozone recirculation, coagulation/flocculation with tannin-based agent natural coagulant, and dissolved air flotation (DAF). Ozone concentrations (without ozone, 0.13 and 0.25â mg O3/mg of biomass) and tannin dosages (65, 85 and 105â mg/L) were evaluated regarding microalgae separation and their influences on wastewater treatment performance. During the experiments, it was verified that the treatment efficiency increased when ozone was applied and with higher tannin dosages. The best results were found with 0.13â mg O3/mg of biomass and 105â mg/L of tannin, obtaining excellent removal of turbidity removal (99.4%), apparent colour at 420â nm (94.5%), TN (83.2%), N-NH3 (100%), TOC (86.8%), BOD5 (86.5%) and COD (100%), 47.6% reduction in electric conductivity, 46.1% in TDS, 66.4% TP removal for the integrated system and 84% microalgae biomass recovery were obtained. Our results showed that the system proved to be a viable alternative for the treatment of urban wastewater and the recovery of microalgae through the insertion of ozone via Venturi tube combined with tannin-based agent.
Assuntos
Microalgas , Biomassa , Floculação , Taninos , Águas ResiduáriasRESUMO
Floating treatment wetlands (FTWs) have attained tremendous popularity for water purification purposes. Through this phyto-technology, naturally occurring macrophytes are allowed to grow on the water surface on a buoyant raft or a rigid support, keeping the plant roots permanently in contact with the water and removing pollutants via several processes. The objective of this study was to review studies that have developed FTWs and to perform a bibliometric analysis using three keywords: "Floating", "Treatment" and "Wetlands". From bibliometric analysis using VOSviewer software and the Web of Science database, it was possible to verify the number of publications over the years and the countries and authors with the most published articles on these systems and other related terms. Subsequently, a review was performed on the main mechanisms of pollutant removal by FTWs as well as experiences and recommendations for major design and operating aspects for their application, such as water depth, hydraulic retention time (HRT), floating mat, water surface coverage, artificial aeration, plant selection and pruning or harvesting. It was verified that FTWs are a potential technology for treating several wastewater types and water remediation under different conditions. Even with the increasing number of publications in recent years, many design and operation aspects related to system performance still demand more research in order to better understand the relations between macrophytes and other pollutant removal mechanisms and to thereby improve the treatment efficiency of FTW systems.