A node split method based on Partition-of-unity method and mesh modified has been developed for numerical simulation of crack growth. The crack tip could be represented by the enrichment function based on Partition-of-unity method. The crack besides the tip always locates on the edge of element by moving the nodes around crack, and the continuity of crack could be kept on. For an example of 2D quadrilateral mesh, mesh processing has been presented on different condition. The simulation results indicate that applying the node split method to simulate crack growth problem can achieve relatively good results even for sparse grid.

Using aluminium sulphate (AS) and chitosan as the main coagulant and coagulant-aid respectively, the high algae-laden water was treated by coagulation /flocculation/sedimentation (C/F/S). When the dosage ranges of AS and chitosan were 35~45 mg/L and 0.4~0.7 mg/L respectively, the removal rates of turbidity, algae cells and TOC were all enhanced apparently compared with adding AS alone. Especially the effective removal of organic matters has a significant sense. The compound action of AS and chitosan can reduce dosage of aluminum salt coagulant for meeting the treatment requirements, which means reduction of residual aluminium in treated water. The algae flocs generated by coagulation aid of chitosan were larger and more compact and had a faster settling velocity. So the application of chitosan can bring better environmental and economic benefits in water treatment.

Using polyaluminium chloride (PAC) and chitosan as the main coagulant and coagulant-aid respectively, the high algae-laden water was treated by coagulation/flocculation/dissolved air flotation (C/F/DAF). When the doses of PAC and chitosan were both moderate (7.0~8.4 mg Al2O3/L of PAC and 0.6~1.0 mg/L of chitosan), the removal rates of turbidity, algae cells and TOC were all increased apparently compared with adding PAC alone. Especially, the residual aluminum concentration reduced significantly in treated water with the aid of chitosan. The structrue and strength of flocs formed by coagulation aid of chitosan were improved obviously, which proved that addition of chitosan could enhance the flocculation performance of PAC. So, in C/F/DAF process for removing algae, using chitosan as coagulant-aid can improve the flotation performance and reduce residual aluminum concentration in treated water.

No abstract

Using chitosan-modified diatomaceous earth (DE) to treat micro-polluted water by coagulation/flocculation/sedimentation (C/F/S), the results indicated that the modified DE could apparently increase the removal rates of turbidity and UV254 in comparison with adding DE alone, and the optimal ratio between chitosan and DE was 1:40. With the compounding of polyaluminium chloride (PAC) and modified DE, the treatment effect was obviously improved by coagulation aid of modified DE under adding the same PAC dosage. The best removal rates of turbidity and UV254 reached 96.2% and 47.9% respectively with the PAC dosage of 35 mg/L and the modified DE dosage of 45 mg/L. The results indicated that the treatment effect of micro-polluted water improved with the enhanced coagulation of chitosan-modified DE.