Environmental pollution is a matter of great concern. Among them, heavy metal pollution from industries is a threat to human health and the development of the ecosystem.
Metallic chromium and chromium 3 compounds (Cr3+) are not classified as hazardous to health, but thecompounds Substances containing chromium 6 (Cr6+) are extremely dangerous. Therefore, treating wastewater containing Chromium (Cr6+ ) is extremely necessary.
So where does Cr6+ come from?
Cr6+ is produced during chromium plating, zinc plating passivation, copper plating, chemical production, and leather production.
Type of wastewater
Cr concentration6+ (mg/L)
30 – 35
10 – 15
Hair dye production wastewater
1 – 2
Image of the chrome plating industry
So what methods are there to treat wastewater containing Chromium?
There are many types of chromium treatment methods in wastewater, mainly chemical methods, electrolysis methods, ion exchange methods, evaporation concentration methods, etc. Let’s learn A brief overview of some common methods.
Treatment of wastewater containing Chromium by chemical methods
This method uses the agents SO2/ NaHSO3/ FeSO4 (under acidic conditions) to convert Cr6 + to Cr3+ then use Na2CO3/ NaOH/ CaO (under alkaline conditions) to convert to Cr(OH)3 is a precipitate to remove chromium from water.
Cr6+ + 3e=> Cr3+
Cr3+ + 3OH– => Cr(OH)3
Image of chemical treatment diagram of chromium
Treatment of chromium-containing wastewater using ion exchange method
This method is based on the principle of exchanging positive ions on the surface of plastic beads with Cr+6 ions in solution when in contact with each other. Then we use another chemical to regenerate the plastic.
Image of Cr+6 treatment diagram by ion exchange method
Notes when handling Cr+6
In the process of treating chromium in wastewater, we need to pay attention to the pH value of wastewater, it directly affects the performance of the treatment process.
Depending on the type of wastewater, pollution concentration, and economics, choose the most optimal method.
Optimize waste flow to save chemicals and construction area
Technology line for treating wastewater containing Chromium by chemical methods
Diagram of wastewater treatment line containing Chromium
Explanation of the technology line is as follows:
Air conditioning tank
Wastewater enters the equalization tank to stabilize the flow and concentration of substances in the wastewater.
Normally, at factories with wastewater containing chromium, there is often a lot of grease generated. Therefore, when passing through the wastewater conditioning tank, it passes through a grease separator to remove grease.
After leaving the oil separator, wastewater will be pumped into the reaction tank to reduce Cr6+ to Cr3+. The reducing agent is NaHSO3 supplied by a metering pump.
Because the environment for the reduction reaction requires pH = 3, H2SO4 must be added to achieve the required pH. The reaction tank has 2 compartments: the first compartment supplies NaHSO3 and H2SO4, the tank is equipped with a stirrer to ensure even mixing of chemicals in the wastewater; The second compartment is the sedimentation compartment to both combine and settle large sized particles and have time for the reaction to occur more completely.
Wastewater and lime milk mixing tank
The waste streams are then pumped to a tank to mix the wastewater with lime milk to raise the pH of the wastewater to about 10 ¸ 11 to allow a reaction to convert the metal ions in the wastewater into precipitated hydroxide forms such as : Cr(OH)3, Ni(OH)2…
The mixing tank is cylindrical in shape. Inside there is a stirring paddle to quickly mix wastewater with lime milk.
Flocculation tank combined with sedimentation
After being mixed well with lime milk, wastewater will be pumped quantitatively to the flocculation and sedimentation tank. This is essentially a dual device, combining a cylindrical vortex reactor with a vertical settling tank.
First, wastewater is pumped into a cylindrical vortex reactor. Here, due to the effect of vortex currents, the precipitated flocs will combine together to form flocs that are larger in size, larger in volume and easier to settle.
To increase the effectiveness of the flocculation process, we add PAC-250 flocculation aid. Wastewater after leaving the cylindrical vortex reactor will automatically move to the vertical settling tank. Here, the precipitated flocs will settle to the bottom and be periodically discharged into the sludge tank.
Material filter tank
The filter tank consists of layers of materials: supporting gravel, quartz sand and activated carbon to remove dissolved organic compounds, trace elements, substances that are difficult or not to biodegrade and organic halogens for treatment. Manage targets to meet prescribed requirements.
Final pH adjustment tank
Finally, the wastewater after going through the treatment stages will be put into the final pH adjustment tank. Here we can use additional H2SO4 to adjust the wastewater pH to the required value. The wastewater is then discharged into the drainage ditch.
For advice and support on technology or construction issues related to chromium-containing wastewater treatment, please contact Hasy Environment immediately at number 0972221068 or website https://xulymoitruong360.com. With a team of experienced staff and testing machinery infrastructure, we are committed to bringing you the optimal processing model both technically and economically.
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