Investigation On Coagulation Process Of Water Plants In A City Of South China And Study On The Application Of Al₁₃

Coagulation is widely applied in the water treatment process,and good coagulation performances are important in providing high quality drinking water.Factors which influenced the coagulation performances included the characteristics of source water,the characteristics of coagulants and the dosage of flocculants.Due to the constraints of research methods,most of the research objects are located in the improvement of coagulation efficiency and the preparation and hydrolysis of coagulants.Effects of the content and composition of dissolved organic matter,morphology and distribution of particulate matter in the source water and the morphological changes and composition of coagulants on the coagulation performances were not investigated well.For further information of the influence on coagulation performances by the characters of raw water,the coagulation process of four water plants in a city of southern China was investigated in this study followed by a series of coagulation experiments on its source water.Then the new compound flocculants was carried out for the case of poor coagulation effect.Finally,the application conditions of Al₁₃ and the co-optimization of composite coagulants were studied.The main research contents and results are as follows:?1?The results indicated that the characteristics of source water for A and B water treatment plant were low turbidity and high concentration of organic matter,and the characteristics of source water for C and D water treatment plant were high turbidity and low concentration of organic matter.The turbidity decreased with increasing the coagulation period,and the turbidity for water samples after settlementation was larger than 1.0 NTU.Concentrations of humic acid in water samples after coagulation process significantly?about 10%?decreased than raw water in A water treatment plant,and the concentrations of humic acid in water samples for other three water treatment plants were almost the same.The concentration of DOC after coagulation process significantly decreased,and the decrease of DOC in other three water treatment plant was not significant.?2?The results indicated that the Al₁₃ had significant advantages on the removal efficiency of turbidity.The removal efficiency for turbidity using Al₁₃ was high,and large concentration of organic matter in the source water could decrease the coagulation performances of Al₁₃.Compared to turbidity,the removal of organic matter need more coagulants.In order to improve the removal efficiency of organic matter,HCA was composited with Al₁₃ to prepare new coagulants,and the results indicated that the new coagulants could increase the removal efficiency of organic matter and floc size.?3?When the turbidity was adjusted to 30.0 NTU,the removal efficiency was larger using Al₁₃ as coagulant under smaller dosage condition?There were larger amount of positive charges?.The removal efficiency using composite coagulants increased first,and decreased when the ratio of HCA was large enough?10%?.Composite coagulants?The ratio of HCA was 5.0%?showed better coagulation performances when the coagulant dosage was larger than 0.05 mmol/L.When the turbidity was adjusted to 60.0 NTU,removal efficiency for turbidity using Al₁₃ and composite coagulant was larger than AlCl₃ under smaller dosage condition.When the coagulant dosage was larger than 0.05 mmol/L,the removal efficiency for turbidity increased with increasing the ratio of HCA.When the ratio of HCA was 10.0%,the removal efficiency for turbidity decreased due to repulsive between particles or steric hindrance.When the coagulant dosage was 0.04 mmol/L,the floc size increased first,and decreased when the ratio of HCA was 10.0%.After the regrowth period,the floc size using AlCl₃ as coagulant was larger than the flocs after growth period.Charge reversal occurred when the coagulant dosage was large enough,so the floc size formed by Al₁₃ or composite coagulants was smaller than flocs formed by AlCl₃.