TRATAMIENTO DE AGUAS RESIDUALES Los diferentes procesos incluidos en la línea de proceso principal tienen flujos secundarios. Algunos de ellos se envían directamente a la torre de vertido, ya que sus características son similares a las del agua de mar y no tienen ningún impacto ambiental. Otros, sin embargo, requieren de un tratamiento específico para reducir la concentración de sólidos antes de ser devueltos al mar. El tratamiento de los lodos se compone de espesadores por gravedad y centrifugadoras de deshidratación. Los lodos deshidratados y almacenados en los silos se envían a un vertedero certificado por los organismos locales de Emiratos i para su eliminación. La normativa medioambiental aplicable se cumple en todos los puntos del tratamiento y el objetivo del diseño es conseguir una deshidratación de los lodos superior al 20%. El lodo espesado en el fondo del espesador se purga periódicamente al tanque de lodo espesado. El agua de rebose del espesador se recoge en la fosa de drenaje junto con el agua de deshidratación. El lodo seco se bombea a los silos por una bomba de tornillo para cada centrífuga de 11 m³/h a 12 bar de presión. Dos silos de servicio y dos de reserva de 150 m3 de capacidad unitaria proporcionan 15 días de capacidad de almacenamiento. SISTEMA DE DOSIFICACIÓN DE PRODUCTOS QUÍMICOS El sistema de dosificación de productos químicos para el funcionamiento fiable de la planta de desalación incluye, entre otras cosas a: • Electrocloración: Hipoclorito de sodio • Sistema de dosificación de cloruro férrico (coagulante) • Sistema de dosificación de ácido sulfúrico • Sistema de dosificación de polielectrolito Permeate Pumps The permeate is sent to post-treatment from the service water tank. Three pumps of 4.121 m3/h at 3.50 bar are installed to send the permeate to the potable water tanks subsequent to remineralisation. All the permeate pumps are equipped with VFDs. POST-TREATMENT Potabilisation of the RO permeate water is carried out by means of a re-carbonation system. This system treats the permeate water from the reverse osmosis process to achieve compliance with the potable water specification. The potabilisation process consists of a re-hardening stage followed by a disinfection stage. CO2 gas is injected into a carrier water stream from the permeate to dissolve the gas in the water and convert it into carbonic acid. The carbonic acid solution is then injected into the permeate mainstream by means of a diffuser device and a static mixer. Subsequently, the permeate goes through the limestone filters. Disinfection is carried out by means of chlorine dioxide dosing. The dosing point is located just prior to the RO potable water tank. Dosing can also take place at the outlet of the tank in the event of potable water remaining stagnant in the tank, with a consequent high probability of chlorine decay. The RO permeate flow is divided into two streams. The first stream, approximately 40% of the total flow, is treated in the post-treatment system. The remaining 60% of the RO permeate flow is by-passed. The two streams are mixed subsequent to post- treatment. The combined flows require sodium hydroxide dosing to adjust the pH of the water. WASTEWATER TREATMENT The different processes in the main treatment line produce secondary flows. Some of These are sent directly into the outfall, as their characteristics are similar to those of seawater and they do not have any environmental impact. Others, however, will require specific treatment in order to reduce the concentration of solids before being returned to the sea. Sludge treatment is composed of gravity thickeners and dewatering centrifuges The dewatered sludge is sent for disposal at a landfill certified by the Municipal Council of Dubai. All applicable statutory environmental regulations are complied with at all treatment points. The design objective is to achieve a sludge dryness rate of over 20%. Thickened sludge at the bottom of the thickener is periodically removed and sent to the thickened sludge tank. The overflow from the thickener overflow is collected in the drainage pit together with the water from the dewatering process. The dry sludge is pumped into the silos by one screw pump of 11 m³/h for each centrifuge at a pressure of 12 bar. Two duty and two standby silos, each with a capacity of 150 m3 provide 15 days’ storage capacity (one day in the red tide worst case scenario). www.futurenviro.es | Junio-Julio June-July 2021 Desaladora de Jebel Ali en Dubái (Emiratos Árabes Unidos) | Jebel Ali desalination plant in Dubai (United Arab Emirates)
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