Evaluación de los parámetros operacionales de un vermifiltro, para eliminar materia orgánica, nutrientes y cuantificar las emisiones de gases de efecto invernadero.
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Date
2025
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Universidad de Concepción
Abstract
Chile, es uno de los países más vulnerables a la escasez hídrica, y se estima que al menos el 25% de la sequía experimentada por el país desde el 2009, estaría relacionada con el cambio climático. Estos eventos de escasez hídrica afectan por, sobre todo, el suministro y el tratamiento de las aguas servidas que provienen de zonas rurales y que actualmente son administradas por Comités y Cooperativas. Aunque el 2018, la cobertura de agua potable llegó a un 99% en las zonas rurales concentradas, aún existen más de 300 mil viviendas que no cuentan con un sistema apropiado de abastecimiento y saneamiento de aguas residuales.
En regiones, las zonas rurales que presentan mayores problemas y que no cuentan con un abastecimiento formal de agua potable, se encuentran en el Biobío (68%), La Araucanía (71%), los ríos (62%) y Los lagos (64%). Por lo general, las viviendas que se encuentran en estas zonas no cuentan con la infraestructura suficiente para instalar un sistema de saneamiento adecuado y solo cuentan con pozos negros y fosas sépticas. Por lo tanto, los vermifiltros se han planteado como una solución viable para estas localidades.
La vermifiltración es un proceso bio-oxidativo en el que las lombrices detritívoras interactúan intensamente con microorganismos para eliminar los contaminantes que se encuentran presentes en el agua. Este sistema consta de un estanque relleno por diferentes capas filtrantes, con lombrices en la capa superficial que pueden bioacumular, biodegradar y/o biotransformar diferentes tipos de contaminantes. Aun cuando estos sistemas han sido presentados como una solución plausible para los sectores rurales, el 48% de los vermifiltros implementados presentan fallas por parámetros de operación que aún siguen siendo estudiados y que guardan relación con la tasa de carga de nutrientes, la tasa de carga hidráulica, el medio filtrante, la cantidad de lombrices y las emisiones de gases que pueden generar estos procesos de degradación. Sobre estas materias, aun no existe un consenso científico que indique cuales son los parámetros de funcionamiento óptimo de los vermifiltros y como las lombrices impactan el balance de los gases de efecto invernadero (GEI). Es por esta razón que el presente proyecto de investigación tiene como objetivo general “Evaluar los parámetros de diseño y operación de un vermifiltro a escala real, para optimizar el diseño y la operación de un vermifiltro para eliminar la materia orgánica, nutrientes y controlar las emisiones de gases de efecto invernadero”. En primer lugar, se evaluaron las condiciones de operación de un vermifiltro a escala real, para eliminar materia orgánica y nutrientes (Capitulo III, IV). Luego, se analizó el efecto de las lombrices y la estacionalidad sobre la capa activa de un vermifiltro a escala real (Capitulo V) y finalmente se determinaron las emisiones de gases de efecto invernadero de un vermifiltro a escala real (Capitulo VI). Para cumplir con este objetivo, se generó una revisión bibliográfica para evaluar la influencia de los parametros de diseño y operación en los vermifiltro, posteriormente se evaluó el desempeño de un vermifiltro en la zona rural para eliminar materia orgánica y nutrientes. Los estudios realizados en el VF consideraron la caracterización fisicoquímica y biológica del influente, efluente secundario y efluente final. Luego se caracterizó la capa activa del medio filtrante utilizando técnicas de respirometria. Para esto se consideró la estacionalidad (Otoño-invierno y Primavera-Verano) y la densidad de lombrices por zonas de la capa activa (Zona A: 1105 ± 982 lombrices/m3; Zona B: 7221 ± 1699 lombrices/m3). Para evaluar la cinética heterotrófica se determinó la tasa de consumo de oxígeno (OURend), la tasa especifica de consumo de oxígeno (SOURend), la biomasa generada (YH) y la tasa de crecimiento de microrganismos (μmax). Finalmente se utilizó el método de la cámara estática para medir las emisiones de CO2, CH4 y N2O en la capa activa considerando la estacionalidad.
Los principales resultados de esta tesis doctoral demostraron que los parametros óptimos de un VF están entre 3000-6000 lombrices/m3, tasa de carga hidráulica (HLR) bajo 2.5 m3/dm2, tasas de carga orgánica (OLR) entre 0.2-0.4 kgDQO/m2d, tiempos de operación de la capa activa (TO) que no superen los 24 meses y temperaturas entre 15°C y 30°C. En cuanto al desempeño del VF a escala real, este registró una eficiencia de eliminación de un 77% para la DQO, un 53% para el nitrógeno total (NT), un 36% para el fosforo total (PT) con incrementos en primavera verano de un 9% para la DQO y una disminución de NT en un 20%. Respecto a los coliformes fecales (CF), VF eliminó de 8,9 a 6,9 log10(MPN/100mL). Por lo tanto, la estacionalidad es un factor que afecta significativamente la eliminación de la DQO, NT y el VF no es capaz de eliminar coliformes en niveles seguros.
En cuanto a la capa activa (viruta de madera), los resultados mostraron YH de 0.39 en otoño-invierno y 0.54 en primavera-verano, mientras que μmax fue de 0.07 d-1 en otoño invierno y 0.02 d-1 en primavera-verano. OURend y SOURend incrementaron un 95% más en primavera Verano que en otoño-invierno y un 64% más en la zona B que en la zona A. Estos resultados indican que la estacionalidad y la densidad de lombrices, afectan los parametros cinéticos del VF que determinan la eliminación de la materia orgánica.
Finalmente, las emisiones generadas por una persona al año en un VF (kgCO2eq/per·año) presentan los siguientes rangos, CO2: 0.8 – 7.5 kg/per·año, CH4: 0.1 – 0.5 kgCO2eq/ per·año, y N2O: 5.7 – 9.5 kgCO2eq/per·año, respectivamente. Respecto al efecto de la estacionalidad, el CO2 incrementa un 139% in primavera – verano comparado con el otoño-invierno. N2O incrementa un 139% en otoño-invierno comparado con primavera-verano. Por otro lado, existe una correlación positiva entre la concentración de DQO del influente y las emisiones de CO2 (r2 = 0,7) y una correlación negativa entre la relación carbono/nitrógeno (C/N) y las emisiones de N2O (r2 = -0,6). Estos resultados muestran que la estacionalidad y las características del influente respecto a la carga orgánica y la relación C/N, tienen un efecto en las emisiones de gases de efecto invernadero en un Vermifiltro a gran escala.
Chile is one of the countries most vulnerable to water scarcity, and it is estimated that at least 25% of the droughts experienced in the country since 2009 are associated with climate change. These water scarcity events primarily affect the supply and treatment of wastewater originating from rural areas, which are currently managed by Committees and Cooperatives. Although by 2018 potable water coverage had reached 99% in concentrated rural areas, more than 300,000 households still lack an appropriate system for water supply and wastewater sanitation. At the regional level, the rural areas facing the greatest difficulties and lacking a formal potable water supply are located in Biobío (68%), La Araucanía (71%), Los Ríos (62%), and Los Lagos (64%). Generally, households in these areas do not have sufficient infrastructure to install adequate sanitation systems and only have cesspools and septic tanks. Consequently, vermifilters have been proposed as a viable solution for these communities. Vermifiltration is a bio-oxidative process in which detritivorous earthworms interact intensively with microorganisms to remove contaminants present in water. This system consists of a tank filled with different filtering layers, with earthworms in the surface layer that can bioaccumulate, biodegrade, and/or biotransform various types of contaminants. Although these systems have been presented as a plausible solution for rural areas, 48% of the vermifilters implemented show operational failures associated with parameters that are still under investigation, including nutrient loading rate, hydraulic loading rate, filter medium, earthworm density, and the greenhouse gas emissions generated during degradation processes. At present, there is no scientific consensus identifying the optimal operational parameters of vermifilters, nor is there clarity on how earthworms impact the balance of greenhouse gases (GHGs). For this reason, the general objective of this research project was to “Evaluate the design and operational parameters of a full-scale vermifilter, in order to optimize its design and operation for the removal of organic matter, nutrients, and the control of greenhouse gas emissions.” First, the operational conditions of a full-scale vermifilter were evaluated for the removal of organic matter and nutrients (Chapters III and IV). Subsequently, the effect of earthworms and seasonality on the active layer of a full-scale vermifilter was analyzed (Chapter V), and finally, the greenhouse gas emissions of a full-scale vermifilter were quantified (Chapter VI). To achieve this objective, a literature review was conducted to evaluate the influence of design and operational parameters on vermifilters. Thereafter, the performance of a vermifilter in a rural area was assessed in terms of organic matter and nutrient removal. The studies conducted on the vermifilter included the physicochemical and biological characterization of influent, secondary effluent, and final effluent. The active layer was then characterized using respirometric techniques, considering seasonality (autumn–winter and spring–summer) and earthworm density in different zones of the active layer (Zone A: 1105 ± 982 earthworms/m³; Zone B: 7221 ± 1699 earthworms/m³). To evaluate heterotrophic kinetics, the oxygen uptake rate (OURend), biomass yield (YH), and maximum microbial growth rate (μmax) were determined. Finally, the static chamber method was applied to measure CO₂, CH₄, and N₂O emissions from the active layer, also accounting for seasonal variation. The main results of this doctoral thesis demonstrated that the optimal parameters for a vermifilter are a worm density of 3,000–6,000 earthworms/m³, a hydraulic loading rate (HLR) below 2.5 m³/d·m², organic loading rates (OLR) between 0.2–0.4 kg COD/m²·d, active layer operating times (TO) not exceeding 24 months, and temperatures between 15 °C and 30 °C. Regarding its performance, the full-scale vermifilter achieved removal efficiencies of 77% for COD, 53% for total nitrogen (NT), and 36% for total phosphorus (PT), with seasonal increases of 9% in COD removal during spring–summer and a 20% reduction in NT removal. For fecal coliforms (CF), the vermifilter reduced concentrations from 8.9 to 6.9 log₁₀ (MPN/100 mL). Therefore, seasonality significantly affects COD and TN removal, and vermifilters are not capable of reducing coliform concentrations to safe levels. Regarding the active layer (wood shavings), the results showed YH values of 0.39 in autumn–winter and 0.54 in spring–summer, while μmax was 0.07 d⁻¹ in autumn–winter and 0.02 d⁻¹ in spring–summer. OURend and SOURend were 95% higher in spring–summer than in autumn–winter, and 64% higher in Zone B compared to Zone A. These findings indicate that seasonality and earthworm density affect the kinetic parameters of vermifilters, which in turn determine organic matter removal efficiency. Finally, the annual emissions generated per person in a vermifilter (kg CO₂eq/person·year) fell within the following ranges: CO₂: 0.8–7.5, CH₄: 0.1–0.5, and N₂O: 5.7–9.5. With respect to seasonal effects, CO₂ emissions increased by 139% in spring–summer compared to autumn–winter, while N₂O emissions increased by 139% in autumn–winter compared to spring–summer. In addition, a positive correlation was identified between influent COD concentration and CO₂ emissions (r² = 0.7), and a negative correlation between the carbon-to-nitrogen ratio (C/N) and N₂O emissions (r² = –0.6). These results demonstrate that both seasonality and influent characteristics—particularly organic load and C/N ratio—significantly influence greenhouse gas emissions in large-scale vermifilters.
Chile is one of the countries most vulnerable to water scarcity, and it is estimated that at least 25% of the droughts experienced in the country since 2009 are associated with climate change. These water scarcity events primarily affect the supply and treatment of wastewater originating from rural areas, which are currently managed by Committees and Cooperatives. Although by 2018 potable water coverage had reached 99% in concentrated rural areas, more than 300,000 households still lack an appropriate system for water supply and wastewater sanitation. At the regional level, the rural areas facing the greatest difficulties and lacking a formal potable water supply are located in Biobío (68%), La Araucanía (71%), Los Ríos (62%), and Los Lagos (64%). Generally, households in these areas do not have sufficient infrastructure to install adequate sanitation systems and only have cesspools and septic tanks. Consequently, vermifilters have been proposed as a viable solution for these communities. Vermifiltration is a bio-oxidative process in which detritivorous earthworms interact intensively with microorganisms to remove contaminants present in water. This system consists of a tank filled with different filtering layers, with earthworms in the surface layer that can bioaccumulate, biodegrade, and/or biotransform various types of contaminants. Although these systems have been presented as a plausible solution for rural areas, 48% of the vermifilters implemented show operational failures associated with parameters that are still under investigation, including nutrient loading rate, hydraulic loading rate, filter medium, earthworm density, and the greenhouse gas emissions generated during degradation processes. At present, there is no scientific consensus identifying the optimal operational parameters of vermifilters, nor is there clarity on how earthworms impact the balance of greenhouse gases (GHGs). For this reason, the general objective of this research project was to “Evaluate the design and operational parameters of a full-scale vermifilter, in order to optimize its design and operation for the removal of organic matter, nutrients, and the control of greenhouse gas emissions.” First, the operational conditions of a full-scale vermifilter were evaluated for the removal of organic matter and nutrients (Chapters III and IV). Subsequently, the effect of earthworms and seasonality on the active layer of a full-scale vermifilter was analyzed (Chapter V), and finally, the greenhouse gas emissions of a full-scale vermifilter were quantified (Chapter VI). To achieve this objective, a literature review was conducted to evaluate the influence of design and operational parameters on vermifilters. Thereafter, the performance of a vermifilter in a rural area was assessed in terms of organic matter and nutrient removal. The studies conducted on the vermifilter included the physicochemical and biological characterization of influent, secondary effluent, and final effluent. The active layer was then characterized using respirometric techniques, considering seasonality (autumn–winter and spring–summer) and earthworm density in different zones of the active layer (Zone A: 1105 ± 982 earthworms/m³; Zone B: 7221 ± 1699 earthworms/m³). To evaluate heterotrophic kinetics, the oxygen uptake rate (OURend), biomass yield (YH), and maximum microbial growth rate (μmax) were determined. Finally, the static chamber method was applied to measure CO₂, CH₄, and N₂O emissions from the active layer, also accounting for seasonal variation. The main results of this doctoral thesis demonstrated that the optimal parameters for a vermifilter are a worm density of 3,000–6,000 earthworms/m³, a hydraulic loading rate (HLR) below 2.5 m³/d·m², organic loading rates (OLR) between 0.2–0.4 kg COD/m²·d, active layer operating times (TO) not exceeding 24 months, and temperatures between 15 °C and 30 °C. Regarding its performance, the full-scale vermifilter achieved removal efficiencies of 77% for COD, 53% for total nitrogen (NT), and 36% for total phosphorus (PT), with seasonal increases of 9% in COD removal during spring–summer and a 20% reduction in NT removal. For fecal coliforms (CF), the vermifilter reduced concentrations from 8.9 to 6.9 log₁₀ (MPN/100 mL). Therefore, seasonality significantly affects COD and TN removal, and vermifilters are not capable of reducing coliform concentrations to safe levels. Regarding the active layer (wood shavings), the results showed YH values of 0.39 in autumn–winter and 0.54 in spring–summer, while μmax was 0.07 d⁻¹ in autumn–winter and 0.02 d⁻¹ in spring–summer. OURend and SOURend were 95% higher in spring–summer than in autumn–winter, and 64% higher in Zone B compared to Zone A. These findings indicate that seasonality and earthworm density affect the kinetic parameters of vermifilters, which in turn determine organic matter removal efficiency. Finally, the annual emissions generated per person in a vermifilter (kg CO₂eq/person·year) fell within the following ranges: CO₂: 0.8–7.5, CH₄: 0.1–0.5, and N₂O: 5.7–9.5. With respect to seasonal effects, CO₂ emissions increased by 139% in spring–summer compared to autumn–winter, while N₂O emissions increased by 139% in autumn–winter compared to spring–summer. In addition, a positive correlation was identified between influent COD concentration and CO₂ emissions (r² = 0.7), and a negative correlation between the carbon-to-nitrogen ratio (C/N) and N₂O emissions (r² = –0.6). These results demonstrate that both seasonality and influent characteristics—particularly organic load and C/N ratio—significantly influence greenhouse gas emissions in large-scale vermifilters.
Description
Tesis presentada para optar al grado de Doctor en Ciencias Ambientales con Mención en Sistemas Acuáticos Continentales.
Keywords
Sequías, Aguas servidas Purificación, Materia orgánica, Cambios climáticos, Gases efecto invernadero