Due to the high salinity of saline wastewater, the hydrolysis of polyaluminium chloride (PAC) is inhibited and the flocs are loose, which directly reduces the chemical oxygen demand (COD) removal rate. This article focuses on the influence mechanism of high-salt environment on the flocculation efficiency of polyaluminium chloride PAC, and systematically proposes a plan to improve salt resistance, providing technical support for the treatment of saline wastewater in the fields of chemical industry, seawater desalination, etc. Next, follow the editor of Xinhuan polyaluminium chloride manufacturer to learn more about it.
Mechanism of high salinity on the flocculation efficiency of polyaluminium chloride:
Salting-out effect and hydrolysis inhibition:
High concentration of salt ions (such as Na⁺, Cl⁻) compress the double electric layer of Al(OH)₃, the hydrolysis product of polyaluminium chloride PAC, through salting-out, reducing the ζ potential from +15mV to -5mV. Laser particle size analyzer measurements show that when the salinity is >3%, the production of Al₁₃ multi-core polymers is reduced by 70%, and the charge neutralization ability of the flocs is greatly attenuated.
Deterioration of floc structure:
Salt ions are embedded in the floc network to form "ion bridges", causing the floc fractal dimension (Df) to drop from 1.8 to 1.2, and the density to drop from 0.25g/cm³ to 0.1g/cm³. Scanning electron microscopy observations show that high-salt flocs have a lamellar structure, the specific surface area drops from 45m²/g to 20m²/g, and the adsorption sites are insufficiently exposed.
Challenges and measures of polyaluminium chloride in saline wastewater treatment:
The contradiction between the dosage of reagents and costs: In order to achieve a COD removal rate of >60%, the dosage of PAC needs to be increased from the conventional 80mg/L to 250mg/L, which directly pushes up the cost of reagents. Experimental data show that for every 1% increase in salinity, the unit consumption of PAC increases by 35%, and the annual loss exceeds 1,000 tons.
Load bottleneck of sedimentation equipment: Low-density flocs cause the surface load (q) of the sedimentation tank to increase from 0.5m³/(m²·h) to 2.0m³/(m²·h), far exceeding the design value. Actual measurements show that at this time, the removal rate of the sedimentation tank drops from 75% to 40%, and the effluent COD fluctuates between 80-120mg/L, with a significant risk of exceeding the standard.
Optimization of key parameters of process control:
1. Coordinated regulation of pH value and salinity: Through the online pH control system, the reaction pH is maintained at 6.0-7.0 to ensure that the proportion of Al₁₃ is >50%. Experiments show that under this condition, the dosage of polyaluminium chloride PAC is reduced by 30%, and the COD removal rate is stable > 60%.
2. Dynamic matching of stirring intensity and time: three-stage stirring is used in the mixing stage: the initial 30 seconds of high-speed stirring (180rpm) promotes the dispersion of polyaluminium chloride PAC, the middle 5 minutes of low-speed stirring (30rpm) ensures the growth of flocs, and the last 2 minutes of static sedimentation. This mode reduces the concentration of floc particle size distribution (D90/D10) from 4.0 to 1.5, and the effluent COD is stable < 50mg/L.
Through the above technical optimization, PAC can be used to treat saline wastewater, providing a reliable solution for the discharge of high-salt industrial wastewater. If you encounter any other problems during use, please feel free to contact the manufacturer of Xinhuan polyaluminium chloride. We will arrange professional technicians to communicate with you to help you solve the problem.
The main products of flocculant manufacturer Xinhuan Water Treatment are:
White polyaluminium chloride (food grade), drinking grade polyaluminium chloride, industrial grade polyaluminium chloride, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, petroleum recycling polyacrylamide, oil recovery polyacrylamide, polyacrylamide, polymer flocculant polymer flocculation coagulant, polymeric ferrous sulphate, polyferric aluminium chloride and other water treatment chemicals. Welcome customers to write to us to negotiate business! Tel/WhatsApp：+8619003830067 Email：joanna@xhwtm.com Contact:Joanna
