At present, water treatment flocculants are mainly divided into two categories: organic and inorganic, and organic flocculants mainly include organic polymers such as polyacrylamide.
Organic flocculants have many advantages, such as low dosage, strong flocculation ability, wide pH range, good precipitation effect, etc. However, the price of this substance is high, and the residual monomers are biologically toxic, and some have a “three-way” effect. (saccharification, carcinogenicity, mutagenicity), therefore, the safety of the use of organic flocculants has always been a technical bottleneck.
Inorganic flocculants commonly include iron-based and aluminum-based flocculants. Iron-based flocculants can form larger flocs and have good settling performance, but have high corrosiveness and low stability, and are prone to produce a large amount of sludge.
Aluminum-based flocculants have poor settling properties, small flocs, and complex production processes for some polymerized aluminum-based flocculants. The above flocculants have their own characteristics and have been widely used in various industrial wastewater treatment. However, with the increasingly strict environmental protection requirements, the requirements of industrial wastewater discharge standards are getting higher and higher, and higher requirements are also put forward for the technical upgrading of flocculants.
The new polysilicic acid flocculant is a uniform polymer formed by polycondensation and coordination bonding among various components such as polysilicic acid and metal ions.
This type of flocculant can provide a large amount of polyhydroxy complex ions, which can strongly adsorb dirt colloidal particles, and promote colloidal coagulation through adhesion, bridging, and cross-linking, and at the same time, physical and chemical changes occur, neutralizing colloidal particles and The surface charge of the suspended matter reduces the potential, so that the colloidal ions change from the original repulsion to the attraction, and the colloidal particles collide with each other, thereby forming a flocculent coagulation precipitation.
In this test, a new type of polysilicic acid flocculant was used to test a variety of industrial wastewater, with turbidity and COD as the inspection indicators. On the basis of the experiment, the design parameters of the flocculation process are summarized to provide effective technical support for the application of new polysilicic acid flocculants in industrial wastewater.
1.1 Experimental instruments and reagents
In this experiment, the potassium dichromate method was used to determine CODCr. The experimental instruments and reagents are shown in Table 1.
1.2 Experimental Procedure
(1) Measure the wastewater samples to be treated and pour them into beakers. A total of 5 kinds of water samples are: ethylene glycol chemical industry, coking industry, pharmaceutical industry, food processing, paper industry wastewater treatment plant tail water.
(2) Under the condition of stirring (200r/min), a certain amount of polysilicic acid flocculant was added respectively, and the reaction was stirred for 10min.
(3) When the stirring is completed, adjust the pH of the water sample to about 6.0~7.0 with alkali (if the pH value is higher than 6, no need to add alkali), and add anionic PAM (preparation concentration 1‰, molecular weight above 10 million), stir slowly (30r/min) for 1min, when large flocs appear, stop stirring and let stand for precipitation.
(4) After standing for precipitation for 30 minutes, the supernatant was taken and its COD was measured.
1.3 Experimental operation
(1) Determination of COD value of raw water sample: take 2 mL of raw water sample, add 1 mL of 0.009mol/L potassium dichromate reagent and 2 mL of 10g/L sulfuric acid-silver sulfate reagent, mix well, and use it as the reagent to be tested. The potassium hydrogen phthalate is used as the standard liquid to prepare standard series.
(2) If the chloride ion concentration in the water sample to be tested is high, mercury sulfate should be added to eliminate the interference.
(3) Dilute the high-efficiency coagulant standard solution at a dilution ratio of 1:100.
(4) Take 100mL water samples in 100mL conical flasks, add 1.0mL, 2.0mL, 4.0mL, 8.0mL and 10.0mL to the water samples respectively, and finally measure the COD value.
2 Experimental results
The relationship between the amount of dosing and COD removal was tested for the tail water of wastewater treatment plants in the ethylene glycol chemical industry, coking industry, pharmaceutical industry, food processing, and paper industry. The results are shown in Tables 2-6.
According to the above experimental test results, it can be seen that the new polysilicic acid flocculant has good COD degradation ability on the industrial wastewater tail water of the above-mentioned industries, the flocs are large and dense, the settling speed is fast, and the decolorization performance is good. mg~10mg/mgCOD.
For example, if the COD of industrial tail water is higher than 500mg/L, such as pharmaceutical wastewater, it is directly removed by dosing, the dosage of pharmaceuticals is large, and the operating cost is high.
It is more economical and reasonable to consider using a biochemical method to remove most of the COD, and then using a new type of polysilicic acid agent to strengthen the COD index of the effluent.
(1) The new polysilicic acid flocculant has good floc adhesion and aggregation, strong adsorption and bridging ability, large and dense flocs, fast settling speed, and good decolorization performance. It is suitable for advanced treatment of industrial wastewater tail water. It is used as a decarburization and decolorizing agent.
(2) According to the test of various industrial wastewater tail water, if the main goal is to degrade COD, it is suggested that the dosage of the flocculation process should be designed according to 5~10mg/mgCOD.