FuturEnviro | Junio June 2019 www.futurenviro.es 29 Desarenador-desengrasador con aireación Existían dos unidades de funcionamiento combinado, tipo “canal” con preaireación, separación de grasa y extracción de arenas, con capacidad suficiente para tratar el caudal máximo admisible. En esencia, cada desarenador tiene 2 canales paralelos de 12,5 m de longitud, uno de 1,35 m de anchura que actúa como desarenador y otro lateral de 2,40 m de anchura, separado del anterior por tabique, que funciona como desengrasador. Para los volúmenes establecidos, la carga superficial a caudal máximo, punta y medio son de 28,00, 14,93 y 9,33 m3/m2/h, respectivamente. El tiempo de retención para dichos caudales es de 5,69 10,67 y 17,08 minutos, respectivamente La alimentación de agua se realiza por la parte frontal, siendo aislables mediante sus correspondientes compuertas. La cantidad de aire necesaria para conseguir la desemulsión de las grasas depende, fundamentalmente, de la relación de superficies efectivas de agitación-tranquilización. Para ello existían tres soplantes, una de ellas en reserva y caudal unitario máximo 240 Nm3/h. La inyección de aire se realiza mediante 24 difusores de burbuja gruesa por línea. Extracción y separación de arenas Sobre cada unidad de desarenado desengrasado se disponía un puente móvil, soporte del bombeo de arenas y del sistema de rasquetas de superficie, dotado de movimiento longitudinal mediante motorreductor, y dirigido en su sentido de desplazamiento por unos inversores de marcha. Un mecanismo de control dirige la posición de las rasquetas superficiales de forma que permanezcan levantadas cuando el puente avanza en sentido contrario al del flujo de agua, y quedan abatidas cuando la dirección de su movimiento sea el mismo que el de la corriente de agua. La bomba viajante sobre el puente de cada aparato va aspirando a su vez las arenas depositadas en la canaleta central del desarenador. Cada puente viajante cuenta con una bomba vertical de 40 m3/h de capacidad. Antes del almacenamiento final, con la finalidad de obtener unas arenas limpias y con la menor humedad posible es necesario un elemento de separación, para ello la planta cuenta con un clasificador de arenas del tipo tornillo de 100 m3/h con capacidad para tratar el volumen de agua y arena a extraer. particles, mainly grit and grease, which could have an adverse effect on subsequent treatment operations. In this way, both the formulation of flakes or floccules in the activated sludge and the abrasive action of the grit are prevented. Degritter-degreaser with aeration Two “channel type” combined degritter-degreaser units were in operation at the plant. These units featured pre-aeration, grease separation and grit extraction and they had sufficient capacity to treat the maximum flow. In essence, each degritter has 2 parallel channels of 12.5 m in length. One has a width of 1.35 m and acts as a degritter, while the other has a width 2.40 m and acts as a degreaser. The two channels are separated by a partition. For the established volumes, the surface loading at maximum, peak and average flow is 28,00, 14.93 and 9.33 m3/m2/h, respectively. The retention times for these flows is 5.69, 10.67 and 17.08 minutes, respectively. The water is fed through the front section of the channels and the channels can be isolated by means of their corresponding sluice gates. The quantity of air required for grease de-emulsion depends basically on the ratio of the effective surface areas of the agitation and calming sections. Three blowers, one of which is a standby unit, are installed to supply the necessary air. These blowers have a maximum unitary capacity of 240 Nm3/h. The air is injected by means of 24 coarse bubble diffusers per line. Grit extraction and separation A travelling bridge is arranged over each degritting-degreasing unit. This bridge holds the grit pumps and the surface scraper system and it moves longitudinally by means of a gear motor. The direction of movement of the bridge is controlled by means of an inverter drive. A control mechanism guides the position of the surface scrapers so that they are in the raised position when the bridge moves in the opposite direction to the flow of water and folded when the bridge moves in the same direction as the flow. The pump on each travelling bridge suctions the grit deposited in the central duct of the degritter. Each travelling bridge is equipped with a vertical pump with a capacity of 40 m3/h. Prior to final storage, a separation element is required to obtain clean grit with the least possible moisture content. For this purpose, the plant is equipped with a screw-type grit classifier with a capacity of 100 m3/h, which is sufficient to treat the volume of water and the extracted grit. Extraction and separation of grease and supernatants The grease, once in the lateral calming section of the degritterdegreaser, i.e., in the degreasing channel, is dragged by the surface scrapers of the travelling bridge towards a submerged container and sent to the pumping chambers. Although the surface sweeping device can be adjusted to regulate the depth of the surface layer to be scraped, experience EDAR de Aranjuez (Madrid) | AranjuezWWTP (Madrid)
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