Views: 423 Author: Site Editor Publish Time: 2024-11-16 Origin: Site
To deal with the impact of low-turbidity and high-algae raw water on water treatment processes, the X Water Plant added dissolved air flotation (DAF) process facilities during the upgrade and renovation. Studies have shown that Wuxi Yosun Environmental's dissolved air flotation process can effectively reduce algae and turbidity in water, with an average algae removal rate of 92.16% and effluent turbidity stable below 1.0 NTU, showing good treatment results.
The raw water from the X Water Plant is taken from the F Reservoir. The water quality is generally stable, with turbidity between 2-6 NTU most of the time and algae content above 107/L all year round. The original mechanical stirring clarification process is ineffective in removing algae, resulting in a shortened filter backwash cycle.
| Time | Ptoject | Turbidity/NTU | Chroma/degree | Algae/(104·L-1) | COD Mn /(US·l－1) | Ammonia nitrogen/(mg·L -1) | Total nitrogen/(mg·L-1) | Total phosphorus/(mg·L-1) | Chloride ion/(mg·L-1) |
| 2021 | Maximum number | 23.00 | 45 | 27 600 | 3.96 | 0.400 | 1.00 | 0.016 | 25.00 |
| Minimum number | 1.93 | 4 | 2 930 | 1.17 | 0.001 | 0.36 | 0.010 | 2.00 | |
| Average number | 5.33 | 20 | 12 000 | 2.21 | 0.086 | 0.65 | 0.011 | 12.06 | |
| 2022 | Maximum number | 6.74 | 156 | 17 900 | 2.67 | 0.310 | 0.93 | 0.038 | 12.00 |
| Minimum number | 1.25 | 8 | 1 380 | 1.28 | 0.001 | 0.50 | 0.010 | 5.00 | |
| Average number | 2.91 | 16 | 6 252 | 1.72 | 0.093 | 0.74 | 0.018 | 7.43 |
After the pilot study, the flotation process showed effective removal of algae and turbidity, so it was decided to add the flotation process to replace the original sedimentation process in the X water plant. The removal rate of the flotation process can reach about 83%, significantly improving the water quality.
The success of the flotation water purification process depends on the steps of raw water coagulation, flocculation, and micro-bubble generation. The leading equipment of the flotation system includes centrifugal clean water pumps, air compressors, and dissolved air tanks. In the design, attention should be paid to the generation of bubbles and the formation of floccules to ensure sound treatment effects.
In actual operation, the flotation process monitored the removal effect of algae, turbidity, CODMn, and ammonia nitrogen. The algae removal rate reached 92.16%, and the turbidity removal rate was stable at more than 82.96%. However, the removal effects of CODMn and ammonia nitrogen were relatively weak, at 2.54%-38.46% and 8.33%-17.65%, respectively.
As shown in Figure 1, during the detection period, the original water algae were (2439~4590)×104/L, the original mechanical stirring clarification tank algae removal effect was poor, and the algae in the flotation tank effluent were reduced to (77~830)×104/L, the effluent algae content dropped significantly, and the average removal rate reached 92.16%, achieving effective treatment of low turbidity and high algae water.
Figure 1: Comparison of algae in the effluent of the clarification tank before and after the transformation
The turbidity of raw water is stable at 2 to 6 NTU all year round. The original mechanical stirring clarifier has a poor turbidity removal effect on this type of low-turbidity and high-algae raw water, with an average removal rate of only about 50%. After switching to the flotation process, the turbidity of the effluent is stabilized below 1.0 NTU and can be stabilized below 0.5 NTU when the water quality is good. The average removal rate reaches more than 82.96%, as shown in Figure 2.
Figure 2 Comparison of effluent turbidity of clarification tank before and after transformation
During the detection period, the average concentration of CODMn in the raw water was between 1.93 and 3.12 mg/L. The removal effect of CODMn by the flotation process was not noticeable or stable enough. The CODMn removal rate was 2.54% to 38.46%, as shown in Figure 3.
Figure 3 CODMn of water in and out of the flotation tank
During the detection period, the average ammonia nitrogen concentration in the raw water was between 0.24 and 0.36 mg/L. The flotation process had no noticeable effect on the removal of ammonia nitrogen, and the ammonia nitrogen removal rate was 8.33% to 17.65%, as shown in Figure 4.
Figure 4 Ammonia nitrogen in the inlet and outlet water of the flotation tank
In addition to affecting the filtration process, algae pollution also produces odor compounds, of which geosmin and 2-methylisoborneol are the two most common and complex to remove odor compounds. Since both compounds are saturated tertiary alcohol molecules, they are highly resistant to chemical oxidation and are challenging to remove by existing conventional water treatment processes. During the testing period, the geosmin concentration in raw water was 4.64 to 5.98 ng/L, and the concentration of 2-methylisoborneol was 24.9 to 61.5 ng/L.
As can be seen from Figure 5, the dissolved air flotation unit has a certain removal effect on geosmin and 2-methylisoborneol, but the performance is not stable. The removal rate of geosmin is 16.67% to 44.98%, and the removal rate of 2-methylisoborneol is 16.18% to 61.88%. Due to the high concentration of 2-methylisoborneol in the raw water, it is difficult to ensure that the odor level of the effluent meets the standard if only flotation treatment is used, and deep treatment processes such as biological activated carbon are required later.
a. Geosmin
b.2-MIB
Figure 5 Geosmin and 2-MIB in the inlet and outlet water of the flotation tank
Low algae removal efficiency: The original mechanical stirring clarification process has a poor algae removal effect, resulting in a shortened filter backwash cycle and even filter bed clogging. The average algae removal rate reached 92.16% by adding the DAF process, significantly improving the water quality.
Unsatisfactory turbidity removal effect: Before the transformation, the turbidity removal rate of the raw water was only about 50%, but after the DAF process was used, the effluent turbidity was stabilized below 1.0 NTU, and the average removal rate reached more than 82.96%, significantly improving the water treatment effect.
Insufficient ability to treat low-turbidity and high-algae water sources: The original process could not effectively treat low-turbidity raw water. Introducing the DAF process enabled the water plant to effectively respond to the challenges of low-turbidity and high-algae water sources and improve the overall treatment capacity.
Applying our dissolved air flotation system (DAF) technology in this water plant shows its practical treatment ability for low-turbidity and high-algae water sources. In the future, we should continue optimizing the flotation process and improving the equipment's standardization and intelligence level to cope with the increasingly severe water quality challenges.
