How to adjust the pH value of acidic wastewater

Lime is the cheapest and easiest to obtain, making it the best choice, but it is necessary to consider whether there are components in the wastewater that facilitate the precipitation of calcium. Caustic soda and soda ash yield good results, but the cost is high.

This post was last edited by CoCo070563 on 2015-7-6 21:30. Actually, the most straightforward method is to conduct pilot tests. Lime is cheap, indeed. However, if a large amount needs to be added, the resulting solid waste also poses a problem. Although liquid caustic is expensive, the amount used is small, so the amount of solid waste generated is also low. But here’s the problem: the amount of solid waste is too small, which makes coagulation and sedimentation ineffective. So, can liquid alkali be used in combination with lime? As for sodium carbonate. I really haven’t used it to adjust the pH of concrete (I’ve only used it to adjust the pH of biological treatment tanks). So, here’s my speculation: bubbles will form, and that should have more or less an impact on coagulation and sedimentation. In summary, the three can be used, either individually or in pairs, for small-scale tests. Looking forward to the results. . . I hope there are pictures to prove it, O(∩_∩)O Thank you. . .

What are the main pollutants in wastewater? If dephosphatization is required, quicklime is a better choice. For other cases, it is necessary to compare the solid waste generated and the costs associated with caustic soda and lime before making a decision. Sodium carbonate has not been used; it is generally added in caustic soda pre-treatment processes to remove calcium ions from water, as the bubbles it produces can affect the coagulation process.

Lime can be used to adjust the pH; more sediment may form； Sodium hydroxide can be used; although it is more expensive than lime, it saves hassle. I have never used sodium percarbonate. This is my personal opinion for reference only.

The common chemicals used to adjust acidic water are lime and liquid alkali: 1. Lime includes quicklime (calcium oxide) and slaked lime (calcium hydroxide), available in both solid form and as lime milk； 2. Bases include solid bases, flakes of base, and liquid base; solid bases and flakes of base have high concentrations, while the concentration of liquid base is generally 32% ； Advantages and disadvantages in use: 1. Lime is inexpensive, has a water-purifying effect, can precipitate certain cations thereby reducing salt content, and has low corrosivity ； The disadvantage is that it generates a lot of sludge ； 2. Liquid caustic produces less sludge and reacts more quickly; its disadvantages are high cost, no water purification effect, and corrosiveness.

Lime is a better choice; it is inexpensive, has low corrosivity, acts gently, settles quickly, and can reduce total salt levels, although it increases solid waste. The amount of liquid caustic and flake caustic used is small, but it increases the total salt content; therefore, the capacity of the biochemical system to handle such salt levels must be taken into consideration.

PH6 – the acidity level is very low; this is the normal value for tap water

The specific process is very important; it’s also necessary to know what the cationic and anionic components are in the acidic wastewater, what their properties are, what their concentrations are, in other words, how much of each component is present. Additionally, it’s important to determine the pH value at which neutralization occurs. By specifying all these process parameters, a more accurate and reasonable choice can be made. Generally, lime is used for neutralizing wastewater – after the lime is digested, the residue is removed and the resulting lime slurry is added to the wastewater. After neutralization, solid-liquid separation is carried out using methods such as pressure filtration, thickening, or centrifugation.