Study On Variation And Removal Of Organics During The Process Of Pre-pressure And Coagulation Sedimentation Treatment

In order to explore whether the pre-pressure and coagulation sedimentation process is superior to the existing process, leading to rupture of algal cells, water source of secondary pollution problem, this article focuses on and studies the variation and removal of dissolved organic matter (DOC), odor substances (GSM,2-MIB, etc.) and water organic molecular weight distribution, etc. after the pre-pressure treatment and the subsequent coagulation sedimentation process and powder activated carbon process to obtain the safe, efficient and economical treatment process of water containing algae. The main results are as follows:(1) The DOC concentration was not higher than the original of water containing algae under the pressure of 0.4,0.5,0.6,0.7,0.8 MPa. Pressure does not cause rupture of algal cells, but simply destroyed the airbag, sink in the algal cells at the same time, did not cause secondary pollution to the water. Water containing algae in 4 different ways of pressure:slow-pressure slow-release, slow-pressure quick-release, quick-pressure quick-release and quick-pressure slow-release, the results showed that the DOC in water did not increase bue decreased and this mean that no matter what can’t rupture algae cells, algal organic matter in the cell will not leak. While KMnO4 and NaClO pre-oxidation both increased the DOC, but the damage of algal cells after NaClO pre-oxidation was weaker than KMnO4 pre-oxidation. Thus, pre-pressure was safer than pre-oxidation process.(2) The organic molecular weight decreased after the pre-pressure treatment. The proportion of large molecular area of 200 kDa-500 kDa compared to the raw water had different degrees of reduction, while the proportion of small molecular area of 50 kDa-100 kDa had a certain increase, and with the increase of pressure, the highest peak would be reduced, this showed that some macro molecular substances’ molecular chain would fracture and became some small molecules because of pressure, caused by the change of the molecular weight distribution of organic matter in water. After 1.0mg·L-1 and 2.0mg·L-1 KMnO4 pre-oxidation, the relative molecular weight distribution of organic matter was basically the same as the raw water. While after 1.0mg·L-1 and 2.0mg·L-1 NaCIO pre-oxidation, its molecular weight distribution would be skewed to the left, but the highest peak did not significantly reduce, that small molecular weight substances would be increased, and the distribution curve was coincident.(3) After the KMnO4 pre-oxidation, with the increase of oxidant content, reduce the content of GSM and β-cyclocitral, while the NaCIO pre-oxidation was on the contrary, with the increase of the content of available chlorine, odor substance value also increased. The pre-pressure treatment did not increase the odor substances in only through physical interaction conditions. The concentration of β-cyclocitral respectively increased the content of 20.57% and 51.90% after 1.0mg·L-1 and 2.0mg·L-1 NaClO pre-oxidation.(4) After the pre-pressure treatment of water containing algae, coagulant dosage in the range of 20-45mg·L-1, with the coagulant dosage increased, turbidity, permanganate index, the concentration of DOC decreased gradually. After coagulation and sedimentation of pre-pressure, KMnO4 and NaClO pre-oxidation treatment, the effect of pre-pressure coagulation and sedimentation was far more than the other two treatments in the removal effect not only algae but also DOC. The pre-pressure removal rate of DOC can reach 30%, higher than that of NaCIO pre-oxidation of 15%～30%, higher than that of KMnO4 pre-oxidation about 10-20%.(5) When the content of organic matter in water is not high, considered adding a small amount of powder activated carbon of 2 mg·L-1, 5mg·L-1 can improve the removal rate of dissolved organic matter in water. With prolonged dosing time, the removal rate of DOC increased, indicating that Coagulation after a period of time, then powdered activated carbon can increase the removal rate of DOC. But then addition would make powder active carbon can not be removed well, the suspension of activated carbon will cause water turbidity increased. In general, you can powder activated carbon and coagulant at the same time.(6) The removal of water turbidity, DOC, odor substances had a very good effect after pre-pressure and coagulation sedimentation treatment, but the KMnO4 pre-oxidation adding powdered activated carbon treatment on the removal rate of DOC is higher. Therefore, the combined process of pre-pressure and KMMO4 pre-oxidation, coagulation and sedimentation in powdered activated carbon, the lowest turbidity can be reduced to about 0.6NTU, the removal rate of DOC was improved too. Therefore, after pre-pressure and dosing appropriate amount KMnO4 can also reduce the concentration of DOC.(7) In dynamic tests, compared with pre-pressure coagulation, raw water coagulation, pre-oxidation coagulation, pre-pressure combined with KMMO4 pre-oxidation coagulation process to remove algae and dissolved organic matter, the pre-pressure treatment process had great advantages. Dissolved organic matter was removed mainly in the process of coagulation and sedimentation, the average removal rate was 30%, after filtration and disinfection, the DOC value would have a slight rise. To further improve the removal of dissolved organic matter, then added a small amount of KMnO4 after pre-pressure of raw water.