Why is the dissolved air flotation performance not good sometimes in the wastewater treatment process?
Dissolved Air flotation is mainly used to remove suspended impurities density of which is closed to that water. These impurities can not either settle naturally or float naturally. DAF has the advantages of high separation efficiency and simple structure. The dissolved air flotation will directly affect the effluent quality. The poor effect of the dissolved air flotation machine can mainly summarize as: No1. The outlet water from the DAF machine is not clear enough with color. No2. Suspended solids can still be observed in the DAF effluent . So, what caused the poor treatment effect of the dissolved air flotation equipment? Hope you can find the answer by reading the following aspects.
- Stability of influent flowrate
The influence of the stable flowrate on the treatment effect cannot be ignored. Changes in flowrate mean changes in the amount of pollutants, and it is necessary to adjust the dosage of chemicals in time to obtain better results.
When the wastewater flowrate is too large, the horizontal flow rate of the air flotation tank is accelerated, and the residence time is shortened, which is not conducive to the flotation and separation of flocs. Excessive flow rates can cause excessive turbulence in the separation zone and disrupt bubble-floc binding. Also when flowrate increased, the height of the outlet weir should be adjusted in time to prevent outlet water from entering the sludge bucket. - Air saturation water volume, reflux ratio and air saturation vessel pressure
The turbidity of the recycle water should be low. The lower the turbidity is, the more easily the air can be dissolved; the dissolved air water volume and the reflux ratio (dissolved air water volume/raw water volume) are determined according to the influent wastewater quality.
The higher the dissolved air water pressure is, the easier the oxygen is to dissolve in the water. The optimum pressure range is 4.0-5.0kg/cm2. The pressure of the dissolved air tank can be adjusted through the dissolved air water outlet valve. When the outlet valve is closed, the pressure rises, and when it is released, the pressure drops. If the raw water flocs increase, the reflux ratio can be appropriately increased, but the pressure of the dissolved air water must be taken into account as well as the normal operation of the reflux pump.
- Influence of flocculant and pH value on the effect of dissolved air flotation equipment
In general, the dosage of the chemicals is proportional to the COD concentration of the raw water. However, when we add chemicals to the dissolved air flotation equipment, it is not that the more flocculant is added, the better the flocculation effect will be. There is a suitable dosage value. If too much chemicals is added beyond the range of this value, then the flocculation effect will be reduced. In addition, we should also pay attention to the dosage order of the chemicals, which will also affect the effect. - Scraping frequency
The frequency of the scraper directly affects the thickness of the scum on the surface of the air flotation tank. When the frequency is slow, the thickness of the scum will be thicker and the water content will be less. so that the fluidity of the sludge layer is poor, it is easy to block the sludge discharge pipeline, and will lead to the subsequent sludge tank concentration is too high, which is not easy to improve. At the same time, the density of scum will increase, which increases the difficulty of solid-liquid separation, so that the incomplete separation will affect the effluent quality of the air flotation equipment. If this situation is found, the frequency of the skimmer can be adjusted according to the actual situation of the scum.
- Cleaning of DAF system
The cleaning of the DAF system is relatively easy to overlook. Generally, the industrial wastewater treated by DAF system contains certain oils, calcium elements, etc., as well as the chemicals added during the air flotation process. After long-term use, a layer of dirt will adhere to the air-floating wheels, bearings, air-floating swash plates, releasers and other components, causing the releaser to block, thereby reducing the air-floating efficiency. Therefore, after the user uses the DAF machine for a period of time, it is necessary to clean and inspect the equipment to ensure that it is in good condition.