| Flocculation sedimentation process is an indispensable key link in the process of water treatment, and the application of the flocculants is the core of the technology, which directly determines the effect of flocculation, the operation cost of the flocculation process and the treatment load of following process. Therefore, the development of new efficient and environment-friendly water treatment agent has become a new direction for the development of flocculants. As a new secure non-toxic flocculant, microbial flocculant has good application prospect and is characterized of its high efficiency and non-secondary pollution, But until now, most researches of microbial flocculant has been done in the laboratory, the applications on drinking water treatment are rare. Based on the practical requirements of agents on development and application of water treatment technology, bio-composite flocculant named as PAFC-CBF was prepared by mechanical mixing of compound bioflocculant(CBF) and polymeric aluminum ferric chloride(PAFC). The functional group and surface morphology of PAFC-CBF were determined by FTIR, XRD and SEM.Flocculating characteristic and mechanism were also studied. Researches on efficiency of compound bioflocculant based of the flocculation sedimentation process for the treatment of Songhua River were carried out.The results showed CBF had good removal effect on turbidity and chroma of surface water source water. Under the optimum removal conditions, the removal rate of turbidity was 91.99 % and the removal rate of chroma reached 73.33 %. In view of higher concentration of residual Al and difficulty to remove turbidity when treating source water with low temperature and low turbidity, CBF was used to treat the low temperature and low turbidity source water by orthogonal experiments. The results showed that the optimum flocculation condition was as follows: CBF dosage 20 mg/L, coagulation aid(Ca Cl2)dosage 1.5 m L /L, p H 8.0; hydraulic conditions of coagulation: the stir speed 160 r/min, the stir time 40 s, sedimentation time 30 min.A series of bio-composite flocculant named as PAFC-CBF was prepared by mechanical mixing of CBF and PAFC, which was a light brown liquid with a natural fermentation flavor and a little insolubles. Through analysis of FTIR, XRD and SEM, the results showed that CBF is successfully embedded into PAFC, formed a new flocculant with the common characteristic structure of both. Through considering cost of preservatives, the flocculation effect and inhibitive effects of bacteria, when adding 0.50 g/L potassium sorbate, or adding 0.125 g/L potassium sorbate+0.063 g/L of sodium propyl p-hydroxybenzoate, the shelf life of PAFC-CBF was efficiently prolonged to 12 months.The flocculation effects and flocculation characteristics of PAFC-CBF under different flocculation conditions were studied. The results showed PAFC-CBF had a good effect on the removal of water pollutants and CBF played an importantly coagulation-aid role and synergistic role on flocculation effect. On the basis of analysis of the flocculation characteristics, the flocculation mechanism of PAFC-CBF was expored. The flocculation mechanism was as followes: Firstly, adsorption and charge neutralization effect of polynuclear hydroxyl polymer of PAFC make colloid particles in water lose their stabilization, coagulate and form ideal primary particles. Active functional groups of CBF, such as-OH,-COOH and-NH2, combined with de-stable colloidal particles through hydrogen bonding, and formed the flocs, and the poly molecule chains in water rigid stretched through the repulsive force between th ese the groups distributions of biological poly molecular chain, and them played a bridging role. Ultimately, them promoted the formation of larger flocs with the characteristics of settling performance. PAFC-CBF fully played the role in synergy effect for pollutants removal based on several flocculation mechanisms.Effects of dosing sequence and dosing proportion on flocculation efficiency of the polymeric aluminum ferric chloride-compound bioflocculant dual-coagulant in the treatment of source water were researched. It is proved that the flocculation efficiency of PAFC-CBF and PAFC+CBF was better than PAFC and CBF+PAFC, relatively good flocculation effect was obtained at low dosage. The results indicated that the addition of CBF had great effect on the removal of organic matter without increase any organic matter. A set of flocculation sedimentation equipment was developed, and the effects of enhanced flocculation of CBF on treatment of source water were studied. The results showed that the combination of CBF and PAFC has a good removal effect for removal of turbidity, chroma, TOC, and UV254 in different seasons. The optimal concentration generally appeared in the CBF dosage 1-2 mg/L. Considering the factors of water quality, economic and technical factors, he optimal concentration was CBF 1 mg/L and PAFC 15 mg/L, removal rate of the turbidity, the chroma, TOC and UV254 was 70.37 %, 47.37 %, 38.56 % and 37.44 % respectively in low temperature period of the winter; the optimal concentration was CBF 2 mg/L and PAFC 15 mg/L, removal rate of the turbidity, the chroma, TOC and UV254 was 95.20 %, 83.33 %, 56.32 % and 48.61 % respectively in high temperature period of the summer; the optimal concentration was CBF 1 mg/L and PAFC 15-20 mg/L, removal rate of the turbidity, the chroma, TOC and UV254 was 87.62%-90.56%, 80.00%-83.33%, 37.53%-39.44% and 64.62%-65.82% respectively in the spring or autumn.Total bacteria number increased first and then decreased with variation of seasons. The highest total bacteria number occurred in summer. Based on the experimental results, combination of PAFC and CBF was more efficient for removal of total bacteria number at all seasons. Through analyzing 16 S r DNA sequence and phylogenetic tree, community structure changed obviously. At different period and different operation conditions, the great difference was showed for microbial community. It was proved that adding PAFC+CBF could control bacterial categories and number effectively, had good removal effect on the potential pathogenic bacteria. The flocculation enhanced technology of CBF can effectively improve the safety for water supply, and reduce the cost of subsequent disinfection. |
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