What is the best way to treat wastewater from circulating water that uses liquid chlorine as a disinfectant?
Thread Content
Our company uses liquid chlorine as a disinfectant for the circulating water in its ongoing projects. Let’s discuss what characteristics such water has and what the best way is to treat the wastewater generated.
The water quality of circulating water that uses liquid chlorine as a disinfectant has no special characteristics; it simply has a high level of chloride ions. There are no requirements regarding chloride ions in wastewater discharge, and if treatment is necessary, it is for other parameters such as SS and total P. For circulating water, liquid chlorine is used as a disinfectant; it is required that the residual chlorine level remain above 0.5PPM. At the same time, 1427 or isothiazolinone, which are also disinfectants, are added intermittently, usually once every half month (once a month in winter).
The use of liquid chlorine as a disinfectant is prohibited in our area (Zhongshan, Guangdong), as leaks of liquid chlorine are difficult to handle, spread rapidly, and affect a wide area. When used as a disinfectant, a certain amount of liquid chlorine is added, and the amount added is controlled by monitoring the residual chlorine in the water. Therefore, normally, the wastewater from circulating water contains little residual chlorine, so there is no major issue with discharging it directly without any treatment needed. However, if the wastewater from circulating water is intended to be reused, that’s a different matter
Thank you to those who commented above. Since we haven’t started operations yet, we’re not sure how to control residual chlorine or what the standards are. At present, the design firm has provided only a chlorination plan; we hope to get more suggestions. Thank you
I have a question: Using liquid chlorine as a disinfectant will increase the levels of HCl and HClO in the water, which wouldn’t it accelerate the corrosion of the heat exchangers? ?
Of course, corrosion occurs; that’s why corrosion inhibitors are added to all large-scale circulating water systems!
Is the circulating water system in your company made of stainless steel? If so, do not use chlorine, otherwise it will cause severe corrosion! ! ! I don’t need to go into detail about galvanic corrosion, right? Other options can be used, such as isothiophos.
The heat exchangers involved are all made of stainless steel, but why did the design institute choose to use liquid chlorine for sterilization? ?
This is a misconception; it is necessary to distinguish between liquid chlorine and chloride ions. Stainless steel can generally tolerate 300 mg/l of chloride ions, while liquid chlorine decomposes in water into hydrochloric acid and hypochlorous acid – so how much do the chloride ions increase?
Can HCLO exist for a long time? Corrosion and scale inhibition agents must be added to circulating water; however, prolonged use of high levels of chloride ions can lead to electrocorrosion in heat exchangers. Therefore, regular drainage is carried out to keep these levels within safe limits
My company is considering using wastewater that has been filtered through a sand filter as makeup water for the circulating water system. Is this feasible? I have my doubts.
Wastewater treatment aims to reduce dissolved salts, while filtration is used to remove suspended solids – they are two different concepts! ! I guess there’s a misunderstanding on your part; it’s possible that your company is adding a side filter to remove suspended solids, and it’s not necessary to discharge wastewater as you think
The design includes a side filter; indeed, the wastewater is meant to pass through a sand filter before being reintroduced into the cooling tower’s water tank. However, this was not part of the original design by the design firm – it was added by us. We claim to have consulted the design firm, but I think it’s not feasible. I’d like to hear everyone’s opinions.
As you said, that’s a huge joke! Just wait and see the scaling and corrosion in the circulating water piping (especially inside the heat exchangers)!
It is sufficient to measure residual chlorine; the manufacturer that supplies chemicals for circulating water can provide this information to you – they have it available. Also, be mindful of the precautions associated with using liquid chlorine for disinfection. What they should provide
Wastewater treatment reduces the concentrations of calcium, magnesium, chloride ions, sulfate ions, etc., lessens the load on the chemicals used in circulating water, and enhances the safety of such water. The circulating water is required to have a salt content (usually expressed as conductivity) of less than 2500 us/cm, and the sum of chloride ions and sulfate ions to be less than 1500 mg/l
I recommend avoiding the use of liquid chlorine as a disinfectant; although its cost might be lower. Chloride ions can cause pitting on stainless steel. You can consult manufacturers that specialize in chemicals for circulating water treatment – they will have disinfectants that are more suitable for your system