Evaluation Of The Flocculating And Fractal Characteristics Of Compound Biological Flocculants

Recently, biological flocculants (BFs) have been drawing an increasing attention in water treatment worldwide for their high efficiency and environmental-friendly natures. The introduction of compound bioflocculant is a milestone in the area of BFs. Based on a lots reference of this field, it is found that the study of the compound bioflocculant only rests on the regular flocculation characteristic, like activity distribution, component analysis and thermal stability, et al. The research emphasis of the compound bioflocculant is only put its development, so it is necessary to develop systemic research on flocculation characteristic of compound flocculant which is combined by BFs and chemical flocculants.Firstly, the flocculation stability, structure and mechanism of BFs were investigated in this subject; secondly, compound bioflocculants which were combined by BFs and AlCl₃, FeCl₃, respectively were prepared, then flocculation stability and optimal proportion of compound were studied, followed by an examination of optimum hydraulic conditions and cast quantity; lastly, prepared compound bioflocculants combined by BFs and chemical flocculants were used to water treatment and investigation of flocculation hydraulic conditions and cast quantity were performed to measure its treatment effect. Furthermore, in order to more precisely describe and explain the flocculation process and estimate the results, this study also focused on the fractal dimensions of the flocs during flocculation.There appeared slight flocculation instability in water treatment with different zymolysis batches of BFs produced at the same fermentation conditions through a lot of experiments. Results showed that the combined applications of the chemical coagulants and BFs could improve the stability of coagulation, and when the combination proportion of BFs to AlCl₃ was 5:1 and to FeCl₃ was 20:1, the effect of the treatment and stability of compounds were optimal, whatever high feculent or low feculent water. The optimal hydraulic conditions were as following: quickly mixing speed was 175r/min and time was 60s; slowly mixing speed was 60r/min and time was 180s in confecting kaoline water, using compound bioflocculants which were combined by BFs and FeCl₃. The best cast to feculent water (100NTU) was 5.25ml/L, 6.3 ml/L to 200NTU, 7.35ml/L to 300NTU, 8.4ml/L to 400NTU and 9.45ml/L to 500NTU using this compound in disposal different feculent water.On the basis of compound bioflocculants applications, it was found that charge neutralization should not be responsible for the flocculation, and the turbidity removal using BFs was worse than that using aluminum or ferric salts. But the optimum dosage could be maintained over a wide range (5-19ml/L). Additionally, when using BFs, the metallic elements were almost absent in the treated effluent. Adding small amounts of metallic ions (Al or Fe) into BFs in terms of compound bioflocculants could substantially improved the turbidity elimination, mainly due to the enhancement of cooperation of the charge neutralization and adsorption bridging flocculation. Additionally, The addition of the metallic ions promoted the formation of the crystal cores for particle flocculation, making the flocs more dense. The fractal dimension of D₂=1.2927 of the flocs generated with individual BFs was observed lower than that of D₂=1.5966 with addition of ferric salts.The uses of BFs in combination with FeCl₃ for domestic wastewater could achieve pollutant removal with the efficiency above 65% in terms of the considerable removal of corse particles such as suspended particeles. The quality of the effluent could meet the national standard of the discharge. By investigating the treatment effectiveness of mud wastewater using compound bioflocculants, the optimum dosage of BFs and AlCl₃, PAC and PAM was determined in the test for mud wastewater treatment. The flocculating efficiency was maintained as high as 98% on the basis of decrease of BFs and chemical flocculants. The combined use of BFs and chemical flocculants could accomplish much better performance than individual use of BFs and the amounts of both types of flocculants used was decreased, which could, in part dismish or reduce the risks of the inorganic flocculants brought to the human health. The substantial decrease of chemical coagulants could also reduce the residual toxic metals in the effluent. The experimental results obtained from industrial wastewater treatment using compound bioflocculants showed that the optimum dosage of the coagulants was BFs of 10 ml with FeCl₃ of 1.7 mL for gas wastewater and BFs of 12 ml with FeCl₃ of 2.8 mL for mill wastewater. The compound bioflocculants were shown able to effectively remove several pollutants with the efficiency above 55% from industrial wastewater.Analysis of flocculant structure based on fractal dimension of the flocs showed that whole change zone was in the range of 1.3 to 1.7 under any optimal experimental conditions during our study. It is further theoretically proved that fractal theory will have important control and forecast effect in flocculant research and production.