Low-concentration acid-base wastewater treatment method

There is no cost-effective recovery method for low-strength wastewater containing acids (4%) and alkalis (2%). In order to avoid the harm of acid-base wastewater, it should be treated before discharge, and the main treatment method is neutralization. Adding alkaline substances to acidic wastewater or adding acidic substances to alkaline wastewater can neutralize the reaction to generate salt and water. So, what are the common methods for the treatment of low-concentration acid-base wastewater?

The treatment method of alkaline wastewater in BioCell Environment:
When conditions permit, use acid-base wastewater for neutralization, or use alkali slag to neutralize acid-containing wastewater, or use waste acid and flue gas to neutralize alkali-containing wastewater. This method saves neutralizer, has simple equipment and low treatment cost, but the flow and concentration of acid-base wastewater change with time, and the treatment effect is often unstable.

If alkaline wastewater or alkaline waste residue cannot be used, neutralizers are usually added to acidic wastewater or neutralized by filtration. Add alkaline agents such as lime (CaO), limestone (CaCO3), calcium carbide slag (containing Ca(OH)2), caustic soda (NaOH), sodium carbonate (Na2CO3) to acidic wastewater in the form of solution, emulsion or powder In the process, the wastewater is neutralized by sufficient reaction. This method is suitable for various acid wastewater, with strong adaptability, stable treatment effect, high discharge requirements, simple equipment, but large amount of sedimentation and difficult treatment. Filtration neutralization is to neutralize acidic wastewater and eliminate acidic substances by neutralizing the filter material layer (such as limestone, dolomite, marble, etc.). It is suitable for the treatment of clean wastewater containing hydrochloric acid, nitric acid and low-concentration sulfuric acid. The concentration of sulfuric acid should generally not exceed 2g/L, so as not to form calcium sulfate exceeding its saturation solubility, which will precipitate on the surface of the filter material and hinder the neutralization reaction. The BioCell environmental method has simple operation and management, low treatment cost, stable pH value of effluent, and low sediment production.

The disadvantage of this method is the limited concentration of sulfuric acid entering the neutralization filter. At present, there are two kinds of neutralization filters: ordinary neutralization filter and upflow expansion neutralization filter. Normal neutralization filters are generally gravity type. Due to the low filtration speed (generally 1-1.5 m/h, the maximum not exceeding 5 m), the filter material volume is large (generally 5-8 cm), if the concentration of sulfuric acid in the influent is high , the surface of the filter material will scale, and the treatment effect is not ideal. Due to the use of small particles (generally 0.5-3mm) and high filtration speed (generally 50-70m/h), the upflow expansion neutralization filter has higher treatment efficiency than ordinary neutralization filters, and can handle high sulfuric acid concentrated wastewater. In order to prevent small particles from overflowing from the upflow expansion neutralization filter and improve the utilization rate of large particles, an upflow expansion neutralization filter with variable filtration rate was developed. The filtration speed shall not be lower than 60 m/h at the bottom of the tank, and 15-20 m/h at the top of the tank. Treatment of acidic wastewater by neutralization method, such as calcium carbonate neutralization method, often produces a large amount of carbon dioxide, so that the pH of the effluent is between 5.5 and 6.0, which cannot meet the discharge standard. In this regard, carbon dioxide can be removed by steam stripping to increase the pH.

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