Diseño y optimización de los humedales artificiales para el tratamiento de aguas residuales: purines de cerdos

Abstract

[ENG] The last few years, pig farming have seen a great transformation, which is now considered as an agro-industry made up of some major players on the world scale. In several regions within the world, the management of pig manure has become a real environmental problem which needs a solution from the agricultural sector. Many environmental problems concern such as impacts on surface and groundwater, effects on air and soil quality are notably increasing. Most of the environmental problems of the pig production sector is the pig slurry (PS) production and it ́s management. Only Spain generates a volume of pig slurry around 71 million m3 per year (2018) and it’s the first country in Europe with a high number of pig production, this large volume of production needs an adequate treatment and management to minimize the environmental problems. Most common problematics of the pig slurry are: - Excess of N and salts which are transferred to soils and superficial and groundwater when slurry is used as soil amendment. This affects soils and water quality and contributes to water eutrophication and salinization processes. - Lack of control of pollutants in the slurry which is applied to the soil, with transfer of metals (mainly Cu and Zn) to the soil and water, with negative effect on environmental health. - Emissions of ammonia and greenhouse gases (GHG), contributing to climate change. Livestock are responsible for 37% of anthropogenic CH4 and 65% of anthropogenic N2O. -Generation of smells which is the main barriers for the community acceptance of pig farms. Recently the pig slurry concept is changing, and it is not considered as a waste, nevertheless a by-product that can be used as a natural fertilizer that contain the main nutrients a plant needs to thrive. It ́s a source of nutrients that can be valorized in agronomic sector as a valuable economic resource. To reuse this by product, PS should be treated and disposed properly in order to reduce negative impacts caused by agricultural valorization. The importance of the proper management of PS as a by-product is well reflected in the recent Best Available Techniques (BAT). However, most of the existing state-of-the-art solutions are not technologically and economically viable. A proper management such as constructed wetlands present a very efficient and economical solution for the pig slurry management, furthermore, an eco-friendly technology that can generate a by-product promoting circular economy, It can remove a high amount of pollutants from the pig slurry and can greatly reduce the environmental impact of the PS and produce useful resources for agriculture, nevertheless, this treatment process has some inconvenient that can limit its use such as clogging and low efficiency in reducing salts content and heavy metals. The integrated purification system using the constructed wetlands for the pig slurry treatment allows establishing a convergence point for livestock and agricultural farms unlinked by inorganics fertilizers influencing in the sustainability of these sectors. The aim of this thesis consists of designing and optimization of the constructed wetland treatment process in order to increase its efficiency by proposing an effective pre-treatment by coagulation flocculation, and also to find a new layer that can be added to the constructed El bied Oumaima 2021 wetland (CW) to improve its efficiency and to study how the slurry reacts to these natural materials. White and Iberian pigs farm from the southeast of Spain treat their slurry in situ using separation, double filtration, decantation, and constructed wetland treatment. The pretreatment can ́t achieve to reduce solids which provokes clogging in the constructed wetlands (CWs). The main objective of this pretreatment is to reduce the turbidity and chemical oxygen demand (COD) from the effluent to make it appropriate for CW treatment. Optimization of the coagulation-flocculation (CF) process using iron chloride and a cationic flocculent DKFLOCC-1598 was investigated by central composite design method (CCD). The effect of coagulant concentration, pH, and flocculent on the COD and turbidity removal were evaluated. The best results were found using 0.024 mol L-1 of iron chloride, 0.164 ml L-1 of flocculent at pH=7.5, where COD was reduced by 96% and the turbidity removal by 97%. Therefore, the results indicated the high efficiency of the treatment method in removing the COD and suspended solids. This thesis examined the physicochemical properties of micronutrients, macronutrients, and heavy metals (HM) removed after the slow filtration of pig slurry (PS) through multiple media: sands, silt loam soils, fly ash and zeolite. The objective was to find a new layer that can be added to our constructed wetland (CW) to improve its efficiency and to study how the slurry reacts to these natural materials. The filtration achieved an approximate removal rate of 99.99% for total suspended solids (TSS) and nitrogen and 61, 94, 72, and 97%, respectively, for electrical conductivity (EC), turbidity, chemical oxygen demand (COD) and five-day biological oxygen demand (BOD5). The two sands, soil 1, and zeolite, had a macronutrient reduction median of 60%, whereas soil 2, 3, 4 and fly ash released macronutrients such as Na, Ca, and Mg. All the media achieved nearly 99.99% micronutrient removal for Fe and Zn. The Cu removal rate was over 86% except for sand 1 and 2 and soil 1, which reduced it to only 46%; the overall Mn removal rate was more than 80% except for soil 3 and soil 4, where it was only 9%. Zeolite had a 99.99% removal capacity for HM as opposed to sand 2, soil 4 and fly ash, which released some HMs (Ni, Cu). The use of this inexpensive and abundant media filtration process is sound both technically and financially and seems to be an ideal cost-efficient treatment for pig slurry. Both experiment pilot, coagulation flocculation and filtration using other materials proved to be suitable to improve the CW efficiency. With coagulation flocculation pretreatment, more than 90% of total suspended solids (TSS) could be removed which can absolutely minimize the clogging risk of the CWs also increase its lifespan. Zeolite can be perfectly added to the constructed wetland to improve the heavy metals and salts contents absorbance, nevertheless, the nitrogen and phosphorus will also decrease which make the treated effluent not suitable to use as an organic fertilizer, in order to implement a circular economy approach and to minimize environmental impacts associated to pig slurry. Both experiment pilot, coagulation flocculation and filtration using other materials proved to be suitable to improve the CW efficiency. With coagulation flocculation pretreatment, more than 90% of total suspended solids (TSS) could be removed which can absolutely minimize the clogging risk of the CWs also increase its lifespan. Zeolite can be perfectly added to the constructed wetland to improve the heavy metals and salts contents absorbance, nevertheless, the nitrogen and phosphorus will also decrease which make the treated effluent not suitable to use as an organic fertilizer, in order to implement a circular economy approach and to minimize environmental impacts associated to pig slurry. Both experiment pilot, coagulation flocculation and filtration using other materials proved to be suitable to improve the CW efficiency. With coagulation flocculation pretreatment, more than 90% of total suspended solids (TSS) could be removed which can absolutely minimize the clogging risk of the CWs also increase its lifespan. Zeolite can be perfectly added to the constructed wetland to improve the heavy metals and salts contents absorbance, nevertheless, the nitrogen and phosphorus will also decrease which make the treated effluent not suitable to use as an organic fertilizer, in order to implement a circular economy approach and to minimize environmental impacts associated to pig slurry. [SPA] En los últimos años la cría de cerdos ha experimentado una gran transformación, que ahora se considera una agroindustria compuesta por algunos de los principales actores a nivel mundial. En varias regiones del mundo, la gestión del estiércol de cerdo se ha convertido en un problema medioambiental real que necesita una solución del sector agrícola. Muchos de los problemas ambientales que preocupan son los impactos en las aguas superficiales y subterráneas, los efectos en la calidad del aire y el suelo están aumentando notablemente. La mayor parte de los problemas ambientales del sector porcino es la producción de purines (PS) y su gestión. Solo España genera un volumen de purines de alrededor de 71 millones de m3/año (MAPAMA, 2018) y es el primer país de Europa con un elevado número de producción porcina, este gran volumen de producción necesita un tratamiento y gestión adecuados para minimizar los problemas ambientales. Las características del purín de cerdo son: - Exceso de N y sales que se transfieren a suelos y aguas superficiales y subterráneas cuando se utilizan purines como enmienda del suelo. Esto afecta los suelos y la calidad del agua y contribuye a los procesos de eutrofización y salinización del agua. - Falta de control de contaminantes en el purín que se aplica al suelo, con transferencia de metales (principalmente Cu y Zn) al suelo y al agua, con efecto negativo en la salud ambiental. - Emisiones de amoniaco y gases de efecto invernadero (GEI), que contribuyen al cambio climático. El ganado es responsable del 37% del CH4 antropogénico y del 65% del N2O antropogénico. -Generación de olores que son las principales barreras para la aceptación comunitaria de las granjas porcinas. Recientemente, el concepto de purines de cerdo está cambiando y no se considera un residuo, sino un subproducto que puede usarse como fertilizante natural que contiene los principales nutrientes que una planta necesita para prosperar. Es una fuente de nutrientes que se puede valorizar en el sector agronómico como un valioso recurso económico. Para reutilizar este subproducto, el PS debe tratarse y disponerse adecuadamente para reducir los impactos negativos causados por la valorización agrícola. La importancia del manejo adecuado del PS como subproducto se refleja bien en las recientes Mejores Técnicas Disponibles (BAT). Sin embargo, la mayoría de las soluciones de vanguardia existentes no son tecnológica ni económicamente viables. Un manejo adecuado como los humedales artificiales presentan una solución muy eficiente y económica para el manejo del purín porcino, además, una tecnología ecológica que puede generar un subproducto que promueve la economía circular, puede eliminar una gran cantidad de contaminantes del purín porcino y puede reducir en gran medida el impacto ambiental del PS y producir recursos útiles para la agricultura, sin embargo, este proceso de tratamiento tiene algunos inconvenientes que pueden limitar su uso tales como obstrucción y baja eficiencia en la reducción del contenido de sales y metales pesados. El sistema de depuración integrado utilizando los humedales artificiales para el tratamiento de purines porcinos permite establecer un punto de convergencia para las explotaciones ganaderas y agrícolas desvinculadas por los fertilizantes inorgánicos que influyen en la sostenibilidad de estos sectores. El objetivo de esta tesis consiste en diseñar y optimizar el proceso de tratamiento del humedal construido con el fin de incrementar su eficiencia proponiendo un pretratamiento efectivo por coagulación-floculación, y también encontrar una nueva capa de sustrato que se pueda agregar al humedal construido (CWs) para mejorar su eficiencia y estudiar cómo reacciona el purín a estos materiales naturales. Las explotaciones de cerdos blancos e ibéricos del sureste de España tratan sus purines in situ mediante separación, doble filtración, decantación y tratamiento de humedales artificiales. Este pretratamiento no logró reducir los sólidos lo que provoca atascos en los humedales artificiales (AAC). El objetivo principal de este pretratamiento es reducir la turbidez y la demanda química de oxígeno (DQO) del efluente para hacerlo apropiado para el tratamiento de CW. La optimización del proceso de coagulación-floculación (CF) utilizando cloruro de hierro y un floculante catiónico DKFLOCC-1598 se investigó mediante el método de diseño compuesto central (CCD). Se evaluó el efecto de la concentración de coagulante, el pH y el floculante sobre la DQO y la eliminación de la turbidez. Los mejores resultados se obtuvieron utilizando 0.024 mol L-1 de cloruro de hierro, 0.164 ml L-1 de floculante a pH=7.5, donde la DQO se redujo en un 96% y la remoción de turbidez en un 97%. Por tanto, los resultados indicaron la alta eficiencia del método de tratamiento para eliminar la DQO y los sólidos en suspensión. Esta tesis examinó las propiedades fisicoquímicas de micronutrientes, macronutrientes y metales pesados (HM) extraídos después de la filtración lenta del PS a través de múltiples medios: arena, suelos franco-limosos, cenizas volantes y zeolita. El objetivo ha sido encontrar una nueva capa que se pudiera agregar a nuestro humedal artificial (CW) para mejorar su eficiencia y estudiar cómo reacciona el purín a estos materiales naturales. La filtración logró una tasa de eliminación aproximada del 99,99% para el total de sólidos suspendidos (SST) y nitrógeno de 61, 94, 72 y 97%, en la arena, suelos franco-limosos, cenizas volantes y zeolita, respectivamente.