The Wastewater is normal after treatment, but after a period of time it will turn yellow, which does not meet the Wastewater discharge standards. In Wastewater treatment, we will add many different coagulants. The water quality appears much clearer to the naked eye, but it will change color over time. This is a situation that many people encounter. First of all, we need to understand what substances are contained in our water quality. The situation of different types of wastewater is also different, but most of them are due to the addition of ferrous coagulants in the pre-treatment. Although most of them are precipitated by adding lime, in general, ferrous is still excessive. After a period of time in the water control sedimentation tank, it reacts with oxygen in the air to generate trivalent iron ions, which are orange yellow at low concentrations. So we must control the amount of ferrous in the early stage to prevent the water from turning yellow.
Some people may also say that using iron to replace copper in water, how do you understand it as using ferrous salts for flocculation? Is it impossible for it to be a direct displacement reaction between metal ions? If we understand it according to the function of coagulants, since copper ions have coagulated into sludge and settled down, there is no need to add lime precipitation.
