Tratamiento de lixiviados de vertedero maduros y sus concentrados de ósmosis inversa: aumento de la biodegradabilidad y análisis de costes

La gestión de los residuos es uno de los retos actuales de la Sociedad a consecuencia del crecimiento de la población mundial, de la mejora en la calidad de vida, del aumento del tamaño de las ciudades y de los cambios en el consumo y el estilo de vida de los ciudadanos. De este modo, cada vez se genera una mayor cantidad de residuos, se estima un crecimiento del 70% para el año 2050, alcanzando los 3,4billones de toneladas de residuos sólidos urbanos (RSU) (1). Una buena gestión de residuos es fundamental para proteger el medio ambiente, la salud y la calidad de vida en el futuro. Por tanto, es importante minimizar el impacto que tienen los residuos sobre el medio ambiente. Las políticas y la legislación europea actual (Directiva Marco 2008/98/CE; Ley 22/2011) se basan en promover la reducción, reutilización, reciclado y valorización de los residuos, pasando de una economía lineal a una circular. Sin embargo, a pesar de los esfuerzos realizados más del 50% de los residuos generados en España, acaban todavía en vertederos controlados (2). En los vertederos se producen una serie de degradaciones tanto químicas como biológicas que, junto con la percolación del agua de lluvia, generan la aparición de un efluente residual con una elevada carga contaminante llamado lixiviado de vertedero (LV)..

Combining coagulation and electrocoagulation with UVA-LED photo-fenton to improve the efficiency and reduce the cost of mature landfill leachate treatment

Producción CientíficaThis study focused on the reduction of the treatment cost of mature landfill leachate (LL) by enhancing the coagulation pre-treatment before a UVA-LED photo-Fenton process. A more efficient advanced coagulation pretreatment was designed by combining conventional coagulation (CC) and electro-coagulation (EC). Regardless of the order in which the two coagulations were applied, the combination achieved more than 73% color removal, 80% COD removal, and 27% SUVA removal. However, the coagulation order had a great influence on both final pH and total dissolved iron, which were key parameters for the UVA-LED photo-Fenton post-treatment. CC (pH = 5; 2 g L−1 of FeCl36H2O) followed by EC (pH = 5; 10 mA cm−2) resulted in a pH of 6.4 and 100 mg L−1 of dissolved iron, whereas EC (pH = 4; 10 mA cm−2) followed by CC (pH = 6; 1 g L−1 FeCl36H2O) led to a final pH of 3.4 and 210 mg L−1 dissolved iron. This last combination was therefore considered better for the posterior photo-Fenton treatment. Results at the best cost-efficient [H2O2]:COD ratio of 1.063 showed a high treatment efficiency, namely the removal of 99% of the color, 89% of the COD, and 60% of the SUVA. Conductivity was reduced by 17%, and biodegradability increased to BOD5:COD = 0.40. With this proposed treatment, a final COD of only 453 mg O2 L−1 was obtained at a treatment cost of EUR 3.42 kg COD−1.Ministerio de Economía, Industria y Competitividad (CTM2016-77948-R)Comunidad de Madrid - Project RETOPROSOST-2 (S2018/EMT-4459

UVA-LED technology’s treatment efficiency and cost in a competitive trial applied to the photo-fenton treatment of landfill leachate

Producción CientíficaThe objective of this trial was to assess the application of UVA-LED technology as an alternative source of irradiation for photo-Fenton processes, aiming to reduce treatment costs and provide a feasible treatment for landfill leachate. An optimized combination of coagulation with ferric chloride followed by photo-Fenton treatment of landfill leachate was optimized. Three different radiation sources were tested, namely, two conventional high-pressure mercury-vapor immersion lamps (100 W and 450 W) and a custom-designed 8 W 365 nm UVA-LED lamp. The proposed treatment combination resulted in very efficient degradation of landfill leachate (COD removal = 90%). The coagulation pre-treatment removed about 70% of the COD and provided the necessary amount of iron for the subsequent photo-Fenton treatment, and it further favored this process by acidifying the solution to an optimum initial pH of 2.8. The 90% removal of color improved the penetration of radiation into the medium and by extension improved treatment efficiency. The faster the Fenton reactions were, as determined by the stoichiometric optimum set-up reaction condition of [H2O2]0/COD0 = 2.125, the better were the treatment results in terms of COD removal and biodegradability enhancement because the chances to scavenge oxidant agents were limited. The 100 W lamp was the least efficient one in terms of final effluent quality and operational cost figures. UVA-LED technology, assessed as the application of an 8 W 365 nm lamp, provided competitive results in terms of COD removal, biodegradability enhancement, and operational costs (35–55%) when compared to the performance of the 450 W conventional lamp.Ministerio de Economía, Industria y Competitividad - (project CTM2016- 77948-R)Comunidad Autónoma de Madrid - (project S2018/EMT-4459

Assessing an integral treatment for landfill leachate reverse osmosis concentrate

Producción CientíficaAn integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation treatment, which best results were obtained using a dosage of 5 g L−1 of ferric chloride at an initial pH = 6 (removal of the 76% chemical oxygen demand (COD), 57% specific ultraviolet absorption (SUVA), and 92% color). The second step is a photo-Fenton process, which resulted in an enhanced biodegradability (i.e., the ratio between the biochemical oxygen demand (BOD5) and the COD increased from 0.06 to 0.4), and an extra 43% of the COD was removed at the best trialed reaction conditions of [H2O2]/COD = 1.06, pH = 4 and [H2O2]/[Fe]mol = 45. An ultra violet-A light emitting diode (UVA-LED) lamp was tested and compared to conventional high-pressure mercury vapor lamps, achieving a 16% power consumption reduction. Finally, an optimized 30 g L−1 lime treatment was implemented, which reduced conductivity by a 43%, and the contents of sulfate, total nitrogen, chloride, and metals by 90%. Overall, the integral treatment of LLROC achieved the removal of 99.9% color, 90% COD, 90% sulfate, 90% nitrogen, 86% Al, 77% Zn, 84% Mn, 99% Mg, and 98% Si; and significantly increased biodegradability up to BOD5/COD = 0.4.Ministerio de Economía, Industria y Competitividad (Proyecto CTM2016-77948-R)Comunidad Autónoma de Madrid - (Proyecto (S2018/EMT-4459

Treatment of a Mature Landfill Leachate: Comparison between Homogeneous and Heterogeneous Photo-Fenton with Different Pretreatments

This study focuses on the treatment of a mature landfill leachate by coagulation and photo-Fenton at different conditions. Optimal coagulation is carried out with ferric chloride in acid conditions; and with alum in near-neutral conditions, to minimize the use of sulphuric acid for pH adjustment (1 g/L vs. 7.2 g/L), the generation of sludge and the increase of conductivity in the final effluent. In both cases, a similar chemical oxygen demand (COD) removal is obtained, higher than 65%, which is high enough for a subsequent photo-Fenton treatment. However, the removal of absorbance at 254 nm (UV-254) was significantly higher with ferric chloride (83% vs. 55%), due to the important removal of humic acids at acid pH. The best results for coagulation are 2 g/L ferric chloride at initial pH = 5 and 5 g/L alum at initial pH = 7. After coagulation with ferric chloride, the final pH (2.8) is adequate for a homogeneous photo-Fenton using the remaining dissolved iron (250 mg/L). At these conditions, using a ratio H2O2/COD = 2.125 and 30 min contact time, the biodegradability increased from 0.03 to 0.51. On the other hand, the neutral pH after alum coagulation (6.7) allows the use of zero valent iron (ZVI) heterogeneous photo-Fenton. In this case, a final biodegradability of 0.32 was obtained, after 150 min, using the same H2O2/COD ratio. Both treatments achieved similar results, with a final COD, UV-254 and color removal greater than 90%. However, the economic assessment shows that the approach of ferric chloride + homogeneous photo-Fenton is much cheaper (6.4 €/m3 vs. 28.4 €/m3). Although the discharge limits are not achieved with the proposed combination of treatments, the significant increase of the pre-treated leachate biodegradability allows achieving the discharge limits after a conventional biological treatment such as sequencing batch reactor, which would slightly increase the total treatment cost

Modelling the Mineralization of Formaldehyde by Treatment with Nitric Acid

Formaldehyde is a recalcitrant pollutant, which is difficult to remove from wastewater using conventional and advanced treatments. The objective of this research was to remove the organic matter from formaldehyde from an industrial wastewater, achieving its total mineralization and allowing the reuse of the water. The treatment was based on the reaction of formaldehyde with nitric acid, which was first studied and modelled with synthetic waters. Results show that it was possible to almost completely mineralize the formaldehyde (>95% TOC removal) at the best conditions studied (1.72 M of nitric acid and 85 °C of temperature). The addition of NaNO2 accelerated this reaction; however, after 2 h of reaction time, its effect was negligible at the maximum concentration of HNO3 studied. The results obtained with industrial wastewater fit well with the model. It is concluded that formaldehyde in actual wastewaters can be successfully removed through direct mineralization with nitric acid, under selected conditions

Treatment of mature landfill leachate by electrocoagulation followed by Fenton or UVA-LED photo-Fenton processes

The main objective of this study is to optimize a two-step treatment for mature landfill leachate consisting of electrocoagulation (EC) followed by Fenton or UVA-LED photo-Fenton processes aiming to provide a more efficient and feasible alternative treatment strategy that also increases biodegradability and decreases conductivity. Although 5 mA cm−2 EC is cheaper than 10 mA cm−2 EC per kg of removed COD (0.63 vs. 0.89 € kgCOD−1), it achieved the half total COD removal (13% compared to 26%), and the low residual iron concentration (100 mg L−1) that remained at the end of the process made necessary a long treatment time to perform the posterior Fenton (48 h) or UVA-LED photo-Fenton (6 h) process. When EC was performed at 10 mA cm−2, the residual iron concentration (220 mg L−1) was high enough to reduce treatment time by one half for both Fenton processes. Consequently, treatment cost decreases from 5.91 to 3.48 € kgCOD−1 for the EC + UVA-LED photo-Fenton ([H2O2]/COD = 1.063) treatment combination; whereas it slightly decreases from 1.68 to 1.61 € kgCOD−1 for the alternative EC + conventional Fenton combination. In both cases, total COD removal was around 87%. In addition, SUVA removal was >40%, conductivity was reduced about 20–30%, and biodegradability (BOD5/COD) increased over 0.3

Transformación de prácticas de laboratorio a modalidad no presencial: desarrollo de una metodología más allá de la simulación

Desarrollo de una metodología para trasformar las prácticas de laboratorio presenciales en prácticas virtuales para mejorar la docencia presencial, complementando las prácticas presenciales, y resolver el problema actual de la pandemia