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Study on the Application of Floating Beds of Macrophites (Vetiveria zizanioides and Phragmites australis), in Pilot Scale, for the Removal of Heavy Metals from Água Forte Stream (Alentejo-Portugal)

Borralho Teresa, Gago David, Almeida Adelaide

Journal of Ecological Engineering

2020

Vol. 21, nr 3

153--163

The surrounding area of the Roxo stream sub-basin (basin of the Sado River, Portugal) has completely sterile sections, jeopardizing the productivity of the agricultural activities practiced there. This may be due to the inflow of the Água Forte stream, which has characteristics of Acid Mining Drainage (AMD). The objective of this study was to test the efficiency of heavy metal removal from the Água Forte stream using the macrophyte floating bed technology (Vetiveria zizanioides and Phragmites australis) in a pilot plant, monitoring and evaluating the water quality and performance of macrophytes. Two experiments were carried out in 2019 over 6 months (January to June). Both experiments were performed in polyvinyl chloride (PVC) tanks with the nominal capacity of 1 m3 each. The tanks were filled with about 0.8 m3 of water coming from the Água Forte stream, which was renewed monthly. The floating beds consisted in a high-density polyethylene floating system and an organic plant support mat filled with a plant density of 285 plants m-2. The heavy metal removal rates obtained from the Vetiveria zizanioides and Phragmites australis floating bed were Fe = 40%; Zn = 33%; Cu = 23%; Mn = 14% and Fe = 27%; Zn = 19%; Mn = 17%; Cu = 14%; respectively. The order of heavy metals accumulation in Vetiveria zizanioides and Phragmites australis in plant biomass was Fe > Zn > Cu > Mn and Fe > Zn > Mn > Cu, respectively. The growth of Vetiveria zizanioides and Phragmites australis in leaf biomass was 7.1 ± 0.3 cm/month and 2.5 ± 0.0 cm/month and in root biomass 3.8 ± 0.1 cm/month and 4.1 ± 0.1 cm/month, respectively. The growth of macrophytes showed the ability to survive in the AMD-containing waters without severe damage in their external and anatomical morphology, although their growth suffered inhibition. The results suggest that the floating bed technology may be an environmentally sustainable alternative, allowing long-term heavy metal removal.

Study of catalytic processes for biodiesel production wastewater treatment

Borralho Teresa, Coelho Solange, Estrelo Andreia

Archives of Environmental Protection

2019

Vol. 45, no. 2

66--72

The study of the possibility of removing organic compounds from wastewater originating from the biodiesel purification stage by two catalytic processes, HSO5-/transition metal and Fenton method has been presented. The source of the ion HSO5-is potassium monopersulphate (2KHSO5∙KHSO4∙K5SO4) (Oxone) that may be decomposed into radicals (OH., SO4-., SO5-.) by means of transition metal as Co(II). Different concentrations were used for both compounds and the combination ([Co2+] = 1.00μM/[HSO5-] = 5.00·10-2 M) achieved the highest COD removal (60%) and complete decomposition of the oxidant was verified for contact times of 45 min. This process has some advantages comparing to the conventional Fenton method such as the absence of the costly pH adjustment and the Fe(III) hydroxide sludge which characterize this treatment process. The Fenton process showed that the combination of [H2O2] = 2.00M/[Fe2+] = 0.70 M was the best and archived COD removal of 80%. The treatments studied in this research have achieved high COD removal, but the wastewater from the biodiesel purification stage presents very high parametric values of Chemical Oxygen Demand (667,000 mgO2/L), so the final COD concentration reached is still above the emission limit of discharge in surface water, according the Portuguese Law (Decree-Law 236/98). However, both treatments have proved to be feasible techniques for the pre-oxidation of the wastewater under study and can be considered as a suitable pre-treatment for this type of wastewaters. A rough economic analysis of both processes was, also, made.