Issues with reclaimed water reuse

As recycled water, reclaimed water is used for circulating cooling; it is essential to control the corrosion parameters within it, and monitoring must also be carried out throughout this process. There is also an issue related to cumulative effects

As recycled water, reclaimed water is subject to clear specifications for its key parameters; however, no such specifications exist for salts in it. Since the tertiary treatment of reclaimed water often involves coagulation, the concentrations of chloride or sulfate ions in the water are quite high. When reclaimed water is used as make-up water, the ion concentrations increase further due to the concentration of anions, which greatly increases the likelihood of anionic corrosion. Moreover, there are few methods available for removing anions or these methods are costly; as a result, no pretreatment is carried out in this regard, leading to corrosion during actual operation. Additionally, the COD level of reclaimed water should be less than 50; however, it still contains some organic matter that can promote the growth of microorganisms. If insufficient amounts of biocides and algaecides are used, it can lead to an overgrowth of microorganisms, which is also one of the causes of corrosion.

It is recommended that the poster use scale and corrosion inhibitors as well as biocides, with the amounts to be determined through pilot tests; the specific types of chemicals can be chosen by the poster themselves. At the same time, it is advisable to increase the capacity of the bypass filtration system to prevent the accumulation of dirt.

What the brother on the 3rd floor said makes a lot of sense; reusing reclaimed water requires caution, as it is necessary to check the concentrations of certain ions in the water, such as CL ions, as well as CA and Mg ions. These are all ions that can cause corrosion and damage to structures. From a chemical perspective, you need to examine the quality of your chemicals and the concentration at which they are added.

To reuse treated water in circulating cooling systems, it is necessary to comply with the relevant standards for \"Reuse of municipal wastewater – Water quality for industrial use.\" These standards are divided into those applicable to closed-loop cooling systems and those applicable to open-loop circulating cooling systems; they mainly regulate parameters such as pH value, suspended solids, COD, and BOD. There are no specific standards regarding salts. In general, domestic water that has been thoroughly treated through biological methods can meet the requirements for reuse, as the salt content is not very high. It depends on the quality of the original water – if the salt content is already high, it will be difficult to meet the requirements. Currently, there are not many methods for removing salts, and such processes are costly. It is recommended to use the treated water for other purposes. This is just my personal opinion, provided for your reference

For the reuse of reclaimed water, it is necessary to determine the calcium hardness, magnesium hardness, alkalinity of the water, as well as the concentrations of ions such as chloride and sulfate; these values can have a significant impact on the operation of this system. If reusing treated water is necessary for environmental reasons, the simplest approach is to dilute the treated water with tap water to reduce its ion concentration, and then adjust the dosage of chemicals accordingly. Alternatively, additional pre-treatment equipment for water replenishment can be added, such as membrane treatment processes or ion exchange processes, which **increases the costs**. :)

The chlorine ions, COD, BOD, and the number of abnormal bacteria in the reclaimed water should be controlled before it is reused in the cooling water cycle, through methods such as the addition of disinfectants and biological oxidation.

The reuse of reclaimed water in circulating cooling systems will be increasingly adopted in the northern regions. The effects of parameters such as pH, COD, Cl-, SO42-, and hardness on the operation of such systems are well-known, but there are also many unknown factors that play a crucial role and can determine the success or failure of a project. The process technologies used as well as operational management are of utmost importance. Cases of such systems in operation are starting to appear gradually; at present, it is still in the exploration phase, but it is expected that these systems will soon reach maturity

When reclaimed water is used to replenish circulating water, its quality must strictly meet the standards for circulating water quality. For example, requirements such as turbidity, COD, pH, and Cl ions. It’s not clear where your reclaimed water comes from; if it is wastewater from a desalination plant, and seawater is used as the makeup water for the circulating water, it can be reused after pH adjustment.