| The rapid growth of algae in eutrophic waters is still a worldwide problem. In algae water treatment process, the fresh algae residue makes highly transportation and post processing costs because of the higher moisture content. After algae disruption, the release of algal toxins often brings new water quality problems during the treatment process. Traditional methods for removing algae not only are inefficient but also consume large amounts of energy, and there is the risk of secondary pollution. As a new water treatment technology, electro-flotation (EF) has received much concern for the treatment of algae-laden water. The reaction kinetic analysis of algae water separation by electro-flotation is often used to study separation mechanisms and predict separation results. After the algae water separation, the water quality analysis explains the situation of electro-flotation to affect the water quality. Therefore, this study firstly intends to optimize the separation parameters of algae water separation by discussing the algae removal, moisture content, slag water rate and algae damage. Secondly, a kinetic model was developed for discussing reaction mechanisms. Thirdly, the changes of water quality were studied after electro-flotation process. Finally, according to the experiment data, a device was built. The expected results would provide a new choice to the engineering application of algae water separation.1. The experimental studies on fast and secure algae water separation with electro-flotation.The OD value, residue and slag water volume, which were under different initial algal concentrations (1.5×109/L,1.5×108/L,1.5×107/L,1.5×106/L), electric current densities (1 mA/cm2,2 mA/cm2,3mA/cm2,4 mA/cm2) and run times (5,10,15,20 min), were measured to calculate the algae removal, moisture content and slag water rate. Then according to the results to evaluate the effects of the algae water separation and select the best separation parameters. The results show that the algae removal efficiency and the slag water rates increased with increasing of electric current densities, but the moisture content decreased. With the increase of initial concentration, algae removal increased the lead after fall. Then the moisture content decreased and the slag water rates increased. The algae removal efficiency and the slag water rates increased with the extension of time, but the moisture content decreased. Above all, the current density of 3mA/cm2 and the run time of 20min were found to be optimum to ensure the separation efficiency.The activity of algal cell under the above conditions was evaluated using two fluorochromes, fluorescein diacetate (FDA) and propidium iodide (PI). The results show that the proportion of dyed red algal cells increased with increasing of electric current densities. It means that the rate of damage algal cells increased. When the current density was 4mA/cm2, all algal cells were stained red and broken down. Extracellular MC-LR was monitored using high performance liquid chromatography (HPLC). The results show that the extracellular MC-LR concentration exhibited a slow decrease as the extension of time when the current density was from lmA/cm2-3mA/cm2. By contrast, the extracellular MC-LR concentration underwent a more gradual increase at 4mA/cm2.The results suggested that the intracellular MC-LR was released into the external. Above all, the current density of 3mA/cm2 and the run time of 20min were found to be optimum to ensure the secure separation.2. The preliminary study of reaction kinetics on algae water separation with electro-flotation. According to the reaction kinetics curves, the removal rate could be affected by the initial algal concentration, electric current density and run time. The larger value of the current density was, the faster removal rate was. And the longer run time was, the slower removal rate was. When the concentration was at low level, the removal rate gradually slowed down. When the concentration was at high level, the removal rate remained unchanged. Response curves under different conditions were fitted using origin 8.0 software. The results shown that, when the concentration was at low level (?8.1×108/L), the determination coefficients (R2) which got fit according to the first-order kinetic mode were relatively high. Alternatively, when the concentration was at high level (> 8.1×108/L), the determination coefficients (R2) which got fit according to the zero-order kinetic mode were relatively higher than the first-order kinetic mode's.The empirical kinetic model was fitted using multiple regression analysis with the Social Sciences (SPSS) version 13.0. Two comprehensive experience kinetic models, Ct=C0-C=C0-Coe(-0.01-0.041i)t (C?8.1×108/L) and Ct=C0(1.135-0.015it) (C?8.1×108/L), were developed. The experimental results showed that the reaction rate varied as a function of the run time and the electric current density. And electric current density is inversely proportional to run time. Moreover, the initial algal concentration affects the algae removal by reaction form. A kinetic analysis showed that the algae removal in a solution with low algal concentration appeared to be first-order with respect to the initial algal concentration, whereas a zero-order model was more appropriate to describe the algae removal in a solution with high algal concentration.3. The treatment and analysis of water samplesSampling from cyanobacteria-salvage yards in Lake Taihu was treated under the optimal parameters. The changes of water quality were analyzed before electro-flotation, after electro-flotation and after electro-flotation 24h, respectively. The evaluation indexes of water quality included temperature, color, smell and taste, pH, chemical oxygen demand, total phosphorus and ammonia nitrogen. The results show that the algae in the water completely removed. The immediate temperature after the electro-flotation was higher 0.6? than the temperature before the electro-flotation. The chromaticity reduced and there were no changes within 24h. The smell and taste disappeared and didn't occur again. The pH increased with the increased run time. The chemical oxygen demand (COD) decreased from 120mg/L to 60mg/L, and the removal efficiency was 50%. The total phosphorus (TP) decreased from 0.068mg/L to Omg/L, so it is completely removed. However, the ammonia nitrogen was on the rise and increased from O.lmg/L to 0.11mg/L and returned to the initial level before and after the treatment. Although the electro-flotation process caused the water temperature and pH value increased, there was no new pollution. The change of ammonia nitrogen was due to the transformation of total nitrogen in water body. Combined with the changes of odor and taste, the chemical oxygen demand and total phosphorus, it can be considered that the electric floating could improve water quality.4. Construction of the reactorIn order to reduce the load and power consumption of the circuit, the algae removal research was carried out in a way of distributed pulse electro-flotation. The algae removal, electric current and power consumption were contrasted under direct current, pulse and four-distribution, respectively. The research showed that the algae removal slightly changed when the distributive numbers of the electrodes were 4. But the electric current and power consumption obviously decreased. With the increasing of the distributive numbers, the electric current and power consumption decreased. Based on the principle of algae water separation, the distributed pulse electro-flotation system and the integrated algal slag removal system were designed, which were combined with experimental findings and the reaction kinetics. The systems were not only to ensure the safety of rapid algae water separation, but also to expand the scale of the employ. |
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