Experimental instruments and reagents
Instrument: MY3000-6A-2 coagulation test mixer
722-s visible grating spectrophotometer
PHS-3C Precision pH Meter
Adjustable universal electric furnace
BS 210 S Analytical Balance
500mL full glass reflux device.
Reagent: 98% concentrated sulfuric acid, silver sulfate, aluminum sulfate, diatomaceous earth, distilled water, potassium dichromate standard solution (CK2Cr2O7=0.25mol/L), ferrous amine sulfate standard solution [C (NH4) 2Fe (SO4) 2 ≈ 0.1mol]:
Drugs: solid polyaluminum chloride, solid polyaluminum iron chloride, solid polyaluminum sulfate, solid polymeric ferric chloride.
The solid polyaluminum chloride flocculant studied in this paper is a light yellow solid, with a content of aluminum oxide (Al2O3) ≥ 28.0%, a salinity of 45.0% to 85.0%, a content of water insoluble matter ≤ 3.0%, and a pH value of 1% aqueous solution between 3.5 and 5.0. The drugs used above are analytical grade.
Analysis content and method
Study the flocculation effect of polyaluminum chloride on printing and dyeing wastewater, find out the addition amount and pH value, and discuss their impact on the flocculation effect of polyaluminum chloride.
The effects of stirring intensity, stirring time, and settling time on the flocculation efficiency of polyaluminum chloride were investigated.
To compare the flocculation effects of polyaluminum chloride and aluminum sulfate on printing and dyeing wastewater.
Compare the flocculation effects of polyaluminum chloride on different wastewater.
Compare the flocculation effects of polyaluminum chloride, polymeric ferric chloride, polymeric ferric aluminum sulfate, and polymeric aluminum ferric chloride on printing and dyeing wastewater.
Water quality analysis of printing and dyeing wastewater
Color: blue purple; pH：7.86； CODCr：415.7mg/L； Turbidity: 436.2 NTU
Results and Discussion
The amount of PAC flocculant added has little impact on the pH of the water sample, and the amount should be between 400 and 600 mg/L. At this time, PAC flocculant has a good treatment effect on CODCr and turbidity. If the addition amount is small, it cannot well destabilize the colloid, and is not sufficient to bridge and connect the colloidal particles, resulting in insufficient and large flocs formed, which cannot play a good adsorption and sweeping role, and the flocculation effect is not ideal. If there is too much, the adsorption surface of the colloidal particles will be covered by inorganic PAC polymers. When the two colloidal particles approach, they will be repelled by the mutual repulsion between the polymers and cannot aggregate, resulting in a "colloid protection" effect, which will reduce the flocculation effect and even re stabilize, i.e., "re stable.". In the experimental process, we found that the decolorization effect of PAC on printing and dyeing wastewater is also significant. The color of the raw water sample is blue-violet. After adding PAC, the color becomes significantly lighter, and when the flocculation effect is reached, the color is basically transparent. As can be seen from the above curve, the peak value occurs when the amount of PAC added is 500 mg/L. At this time, the effect is good, with a CODCr removal rate of 69.58% and a turbidity removal rate of 81.73%. Therefore, the optimal dosage of PAC is determined to be 500 mg/L.
Effect of pH value on CODCr and turbidity removal rate
Generally speaking, in flocculation reactions, the influence of pH value is very large, which affects the Zeta of the surface charge of the colloid（ ζ) The potential, the nature and action of the coagulant, etc. have a significant impact. Different coagulants have excellent coagulation regions. Properly adjusting the pH value can save a large amount of reagents, reduce costs, and fully exert the flocculation effect with good flocculation effect; On the contrary, if the pH value is not properly selected, the light ones may affect the coagulation effect, while the heavy ones may not form flocculation precipitation, or even cause the formed flocs to become colloidal solutions again. The hydrolytic polymerization form of PAC strongly depends on the pH value of the water body. At low pH values, the hydrolytic form of PAC is in the form of monomers, with polynuclear hydrolysates Al7 (OH) 174+and Al6 (OH) 153+in the neutral range, and at high pH values, it is Al (OH) 3, Al (OH) 4 -. Under neutral and weak alkaline conditions, the treatment effect of PAC flocculants on CODCr and turbidity is not affected to a large extent, but still has a high removal rate. Moreover, in the experimental process, pH value has little impact on the decolorization effect of PAC. Among them, the CODCr removal rate reached 72.63%, and the turbidity removal rate reached 87.14%. The optimal flocculation pH for PAC was determined to be 8.
Effect of stirring intensity and time on CODCr and turbidity removal rate
According to the experiment, for this water sample, the stirring strength has a certain impact on the flocculation effect of PAC, but it is not very significant. When the stirring intensity is small, the CODCr removal rate is only 5% lower than that under optimal flocculation conditions, and the turbidity removal rate is about 8% lower; When the stirring intensity is large, the CODCr and turbidity removal rates are poor, only 63.28% and 75.13%, respectively. From this, we can see that when the stirring strength is too small, it is not conducive to full contact between the flocculant and particles; When the stirring intensity is too high, it is easy to break large particles of solid into small particles, and break particles that can be precipitated into particles that cannot be precipitated, which also reduces the flocculation effect. Next, we discuss the impact of stirring time on CODCr and turbidity removal rates. Take three water samples, adjust the pH value of the solution to 8, and then add 0.1g/200mL PAC flocculant. Stir at 150r/min for 2min, 10min, and 20min, respectively. Allow to settle for 20min. Take the supernatant and investigate the effect of stirring time on CODCr and turbidity removal rate.
Experimental results
Using PAC as a flocculant, a process parameter optimization experiment was conducted for water sample treatment, and the optimal experimental conditions were obtained: the optimal mass concentration of polyaluminum chloride was 500 mg/L, the flocculation pH was 8, the flocculation stirring strength and action time were 150 r/min and 10 min, respectively, and the sedimentation time was 20 min. Through the treatment of coagulation, the CODCr in the effluent was reduced from 415.7mg/L to 113.8mg/L, with a removal rate of 73%; The turbidity decreased from 436.2 NTU to 56.1 NTU, with a removal rate of 87%, meeting the national secondary emission standard.
