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Water and Wastewater Post-Treatment Process

The post-treatment process is a method that includes steps such as maintaining the stability of the wastewater or stabilization, disinfection, and corrosion control in the water supply system, and can include processes such as degasification or air stripping. The biggest primary issues concerning power and treatment plants in the post-treatment process include the composition of the effluent or water blending, minerals that may have been added to the effluent during the various stages of treatment or remineralization, disinfection, and materials used to store the final effluent. Various processes and methods are used to perform the post-treatment process, including the Electrodeionization method (EDI for short), Mixed Bed, and Ion Exchange methods.

Zirsakht Tadbir Arian (ZETA) Company will choose the most suitable method using indexes such as regulatory requirements, the design of the system, expected water quality criteria and water chemistry. ZETA, with the help of the most up-to-date technologies and equipments will perfrom the chosen process. In the following, explanations will be given to introduce the various processes that are carried out in order to perform the post-wastewater treatment stage and it’s interesting to note that Zirsakht Tadbir Arian (ZETA) Company performs all of those processes with the best equipment and the most suitable methods.

Post-Treatment Methods

Electrodeionization method (EDI)

The Electrodeionization method is actually a membrane process that is performed in order to undertake the post-purification step. In this process, the goal is to separate the ions dissolved in the wastewater from the aqueous feed and will be done with the help of a membrane. This method has provided significant assistance to the chemical and semiconductor industry by producing ultra-pure water from the wastewater received as feed. The process of electrodeionization is usually used to polish reverse osmosis (RO) process and the intensity of the penetration of undesirable factors into the membrane. Due to the fact that this method does not require storage and handling the toxic and hazardous chemicals, which are used for resin reproduction and waste neutralization, it can be considered a good alternative to ion exchange method in mixed beds.

In summary, in this method, several layers of selective membranes are placed between the cathode (negative electrode) and the anode (positive electrode). The chamber between these layers is either alternatively containing a mixed bed ion exchanger or used as a concentrate chamber. Water or sewage flows between the anode and the cathode; This selective membrane sends positive ions to the negative electrode and negative ions to the positive electrode, thereby separating. The result will be the production of high purity deionized water. The main difference between electrodeionization and other purification methods is that this method does not use chemical methods or packages to remove the undesirable contents.

Ion-Exchange method

The Ion Exchange method is actually one of the most common practices used in the post-treatment stage. In this method, usually one or more undesirable ionic contaminants from the effluent are replaced by one or more other ionic compounds that are less undesirable and thus are separated from the effluent. For this process to work well, it is necessary that both the ionic pollutant and the substituted ionic compound have the same structure so that they can be dissolved in the effluent.

In addition to being soluble, these two ionic compounds need to have the same electrical charge; That is, both have a negative electric charge or a positive electric charge. One of the most common examples of the ion exchange process is a process known as “water softening” in which the goal is to reduce the calcium and magnesium compounds in the effluent. However, ion exchange methods can also be very effective in separating toxic metals from the wastewater. In this process, polymeric ion exchange resins are usually used to separate undesirable compounds. One of the most common resins used in this process is zeolites. The advantages of this process include the following:

There is a possibility to regenerate resins
Relatively low initial capital investment cost
One of the most appropriate technologies for separating dissolved inorganic ionic compounds from the wastewater effectively

On the other hand, the most important disadvantages of this method, which depending on the type of ion contaminants can lead to method change, are as follows:

Operation costs over long-term are high
This method is not able to remove bacteria effectively
The process of regeneration of ion exchange beds could possibly dump saltwater into the environment

Zirsakht Tadbir Arian (ZETA) Company, by examining the type of wastewater and considering the undesirable ionic contaminants in it, performs the post-treatment ion exchange process using the best equipment to treat your wastewater or effluent.

Mixed Bed method

Mixed bed resins or ion exchange resins are mainly used in the wastewater treatment industry for demineralization. These models of resins are usually applied to polish the reverse osmosis process and increase the deionization efficiency of the wastewater. The mixed bed, as its name implies, consists of a strong acid cation exchange and a strong base anion exchange resin. Mixed bed resins are usually used at the end of the wastewater treatment process and are normally positioned downstream of either individual two-bed working ion exchange units or reverse osmosis systems and their goal is to improve the deionization efficiency. Typical applications include:

Polishing the Reverse Osmosis process
Improving the quality of distilled water from seawater
Production of ultra-pure water for semi-conductor industries
Treatment of water pre-demineralized with ion exchange resins
Treatment of the turbine condensate in various power plants and industries

In addition to using ion-exchange bed technology for post-treatment processes, Zirsakht Tadbir Arian (ZETA) Company also uses mixed bed resins in order to increase the efficiency of water and wastewater post-treatment.

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