Browsing by Author "Mambrini, Raquel Vieira"
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- Application of carbon-based catalysts derived from compost on catalytic wet peroxide oxidation of leachate waters from mechanical and biological treatment plant units for municipal solid wastePublication . Batista, Gabriel de Freitas; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Mambrini, Raquel Vieira; Gomes, HelderThis work aims at the valorization of compost from mechanical and biological treatment (MBT) units of municipal solid waste by their transformation into carbon-based catalysts for further application in the treatment of MBT leachate waters (chemical oxygen demand (COD) = 60.0 g L-1, total organic carbon (TOC) = 26.7 g L-1, five-day biochemical oxygen demand (BOD5) = 23.3 g L-1 and aromaticity = 10.2 g L-1). The catalyst was prepared in this work by hydrothermal carbonization at 230 ºC from compost obtained in a MBT unit. The treatment of the leachate waters was conducted by combining a pre-treatment with a cationic ion exchange resin followed by catalytic wet peroxide oxidation (CWPO). The CWPO step was operated for 24 h using 7.2 g L-1 of catalyst, 85.7 g L-1 of H2O2 poured inside the reactor in 5 stepwise additions, at 80 ºC and pH = 3. The combined treatment by cationic resin and CWPO led to obtain removals of 68.2, 65.4, 96.8 and 93.1 % for COD, TOC, BOD5 and aromaticity, respectively, after 24 h of reaction. In conclusion, it was found that compost is a suitable precursor to produce active catalysts for the CWPO of leachate waters.
- Assessment of pretreatments for highly concentrated leachate waters to enhance the performance of catalytic wet peroxide oxidation with sustainable low-cost catalystsPublication . Batista, Gabriel de Freitas; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Mambrini, Raquel Vieira; Praça, Paulo; Gomes, HelderMatured compost, derived from a mechanical and biological treatment (MBT) plant, was used as a precursor to produce catalysts through hydrothermal and thermal carbonization, HC and PC, respectively. HC and PC displayed suitable properties to act as catalysts in the catalytic wet peroxide oxidation (CWPO) treatment of the highly polluted leachate waters generated in the same MBT plant (TOC0 = 27 g L-1; COD0 = 60 g L-1; BOD5,0 = 23 g L-1). The influence of catalyst loading and pH were studied, considering multiple additions of H2O2. The best experimental conditions found were T = 80º C, pH0 = 3.0, 7.2 g L-1 of HC catalyst, 85.7 g L-1 of H2O2, added in five batches in one-hour intervals between each addition. Under these experimental conditions, removals of 43%, 52%, 93%, 82%, 35%, 95% and 93% for the COD, TOC, BOD5, aromaticity, chlorides, turbidity and color number (CN) were, respectively, observed. Ion exchange resins and coagulation–flocculation were studied as pretreatment options to reduce the complexity of the leachate waters and enhance the CWPO results. Both strategies resulted in higher mineralization and enhanced the consumption efficiency of H2O2 (H2O2 ). The sequential treatment using coagulation–flocculation and CWPO with PC catalyst showed the best results, achieving abatement of 94%, 70%, 98%, 93%, 31%, 96% and 95% for COD, TOC, BOD5, aromaticity, chlorides, turbidity and CN, respectively.
- Catalytic wet peroxide oxidation of leachate waters using low-cost carbon-based materials as catalystsPublication . Freitas, Gabriel; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Faria, Joaquim; Silva, Adrián; Mambrini, Raquel Vieira; Praça, Paulo; Gomes, HelderThe Directive 2008/98/EC established a hierarchy for management of Municipal Solid Waste (MSW), according to which landfilling should be avoided. In this direction, Mechanical and Biological Treatment (MBT) plants play an important role, since it allows the conversion of the organic fraction of MSW into biogas and compost, with applications as fuel and fertilizer, respectively. However, MBTs generate a wastewater, referred as leachate, with high load of organic matter, that is not properly treated by conventional systems. In addition, the production of compost in MBTs tends to be higher than its demand, resulting in accumulation on landfilling sites. This works aims to address the Catalytic Wet Peroxide Oxidation (CWPO) of a real leachate effluent obtained from a MBT, whose properties are summarized in Table 1. The compost obtained from the MBT was considered to produce the catalyst for the CWPO process. The lowcost catalytic materials were prepared by hydrothermal carbonization at previously optimized operating conditions (230 ºC, 4 h and 130 gcompost/L). Figure 1 shows the profile of H2O2 decomposition, COD and TOC upon time of reaction at 50 °C (solid line) and at 80 °C (dashed lines). At 80 °C, a removal of 40% and 55% for COD and BOD5, respectively, was achieved, increasing BOD5/COD ratio from 0.33 to 0.45, along with a reduction on turbidity (to 12 NTU) and color of the effluent, as observed in Figure 1.
- Treatment of leachate waters by wet peroxide oxidation with a compost-based catalyst: effect of pHPublication . Batista, Gabriel de Freitas; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Mambrini, Raquel Vieira; Gomes, HelderA compost-based catalyst was synthesized by hydrothermal carbonization following the procedure described elsewhere1 (3 g of compost in 30 mL of water, 230 °C for 2 h). The material was assessed in the catalytic wet peroxide oxidation (CWPO) of a leachate water, generated during an anaerobic digestion of municipal solid waste. The leachate water is characterized by a high pollutant load (chemical oxygen demand, COD, of 60 g L-1 and total organic carbon, TOC, of 27 g L-1). The CWPO runs were conducted at initial pH (pH0) of 3 and 6, and at the natural pH of the effluent (7.2), Ccatalyst = 1.8 g L-1, 80 °C, and the stoichiometric concentration of H2O2 needed to mineralize the organic content (based on COD). Fig. 1 shows the results obtained along the reaction. An acidic pH (pH0 = 3) resulted in a more controlled, but also incomplete, consumption of H2O2, leading to a low conversion of COD and TOC (20 and 10%, respectively). Contrarily, the natural pH led to a very fast and uncontrolled consumption of the oxidant source, resulting in 100% decomposition of H2O2 in less than 2 h of reaction, but failing to remove COD or TOC (negligible removal, ca. 0%), ascribed to parasitic reactions occurring by the inefficient consumption of H2O2. At pH0 = 6, an intermediate behavior was observed: complete decomposition of H2O2 was possible, at a more controlled rate compared to the natural pH. The result was an increment in COD (41%) and TOC removals (19%), almost two times than that observed at the pH0 3.
- Valorization of compost obtained from the mechanical and biological treatment of municipal solid waste: catalysts for wet peroxide oxidation of landfill leachatesPublication . Freitas, Gabriel; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Mambrini, Raquel Vieira; Gomes, HelderSince humanity started living in communities and towns, the generation of solid waste has largely increased and, in 2017, each European citizen generated 480 kg of municipal solid waste (MSW). The main concern with MSW is its management and final destination since in many cases MSW is just thrown in landfills. In mechanical and biological plants, MSW is first sorted into discarded, recyclable, and organic waste streams. This organic fraction goes to the biological treatment stage, generating biogas, and as by-products, leachate, and compost are obtained, the compost being mainly used as an agriculture fertilizer. However, the amount of compost produced is higher than its demand, resulting in an excess that is currently accumulated in landfills. This work deals with the valorization of compost to produce hydrochairs, and pyrochars, through hydrothermal carbonization (HTC) and pyrolysis, respectively, with suitable properties as catalysts for the catalytic wet peroxide oxidation of the landfill leachate. Up to seven catalysts were synthesized under several conditions, 2 from HTC and 5 from pyrolysis. The catalysts were characterized to determine the ash content and elemental analysis. All materials were assessed in the degradation of H 2 O 2 , leading to its complete degradation after 2 h of reaction time. Some selected catalysts were further tested in the CWPO of the landfill leachate (TOC = 27 g L -1 , COD = 60 g L -1 , 38.8 mS/cm, and 5 g L -1 of chloride ions) under the following operating conditions: C Catalyst = 1.8 g L -1 ; T = 80 ºC; C H2O2 = 85.7 g L -1 and pH from 3.0 to 7.3.