| Recent years, the production of the excess activated sludge has increased obviously with the sewage quantity augmenting gradually for treatment in China. The treatment of the excess activated sludge has been an urgent problem to be solved. The dewatering of the excess activated sludge has become the most important step in waste activated sludge(WAS) treatment process. At present, excess activated sludge has been conducted dewatering after the pre-conditioning in most of wastewater treatment plants. However, a lot of disadvantages emerged among the traditional sludge conditioning methods. Thus low-cost and environmental friendly new conditioning methods are needed urgently to develop. This study investigated the variation of WAS characteristics by using the sludge self-flocculating method. Meanwhile, the affecting factors and corresponding mechanism were also demonstrated. In addition, the effect of WAS storage time on sludge properties and self-flocculating traits was illustrated. Besides, we analyze the technical and economic of the engineering application. The test results can provide technical support for the design and operation management of sludge treatment of the sewage treatment plant of "twelfth five" water project.The efficiency of the first stirring self-flocculation and the secondary stirring self-flocculation were investigated by orthogonal experiment, it can be found some influence factors, such as sludge concentration, stirring intensity and mixing time could influence the efficiency, and the sludge concentration was the primary influence factor. The influence factors on sludge dewaterability, sludge settling properties and physicochemical properties were investigated for both the first stirring self-flocculation and the secondary stirring self-flocculation with single factor experiment method, and the influence of different factors on the effect of self-flocculation characteristics was analyzed. It was showed that the values of CST, SVI and PH decreased while the particle size and zeta potential increased during the first stirring and the secondary stirring. This shows that the floc flocculation, can improve the dewatering performance, settling characteristics and physical and chemical properties of sludge, while the sludge viscosity increased because of the overflow of intracellular material. The degree of improvement of each index increased firstly and then decreased with the sludge concentration, mixing intensity and mixing time during the first stirring and the secondary stirring. Within a certain range,the higher sludge concentration, mixing intensity and stirring time,the better self-flocculation effect of the first order stirring and two- stage stirring we will get; While once the sludge concentration is too high, although there were still beneficial to self-flocculation and the increasing of particle size, but the floc structure formed by first stirring and the secondary stirring was very loose, surface physicochemical properties were deteriorated and resulted in the weakness of dewaterability and settling performance. Therefore we could get the optimal parameters of the first stirring self-flocculation: Sludge concentration was 18000mg/L, stirring strength was 200 rpm, stirring time was 3.5min; and the optimal parameters of the secondary stirring self-flocculation: sludge concentration was 16000 mg / L, first stirring intensity was 400 rpm, first stirring time was 2.5min, secondary stirring intensity was 175 rpm, secondary stirring time was 5min. The effect of improvement of dewatering performance, settling properties and physicochemical properties of the two-stage stirred flocculation was better than the one-stage stirred flocculation. At the same time, the both of index of self-flocculation were analyzed, it could find that the variation of sludge CST, SVI, p H, Zeta potential and particle size became similar, all of them can be good indicators of sludge dewatering performance, the correlation coefficient R with CST was in a range of 0.65 to 0.95; But the change of sludge viscosity is different.A sludge concentration pilot test was carried out, the effectiveness of sludge concentration within 30 h and the change of sludge properties during that time was investigated. It was found that the reduce rate of water content slowed down gradually, and the change become stable after 14 h. Concentrated performance was too low, and the change of sludge properties was small, thereby the optimal sludge concentration time is 14 h. On this basis, the changes of sludge properties and characteristics of the secondary stirring self-flocculation were investigated within 72 h in this concentration pilot test. The results showed that during the sludge storage, the VFAs were produced and this resulting in the reduce of sludge p H and the rise of Zeta potential. At the same time, the EPS was consumed, resulting in the decline of flocculation capacity, the decrease of particle size, the deterioration of the dewatering performance and sedimentation performance. The Metabolism of sludge within the first 30 h was active, and sludge properties changed rapidly. While between 30 and 72 hours, the metabolic active was slowed down, and the properties of sludge became stabilized. When the storage time is less than 18 h, the changes of sludge floc structure and surface physicochemical properties is benefit to self-flocculation. When time for storage is longer than 18 h, sludge metabolic activity is too strong, the depletion of sludge EPS reduce the flocculation effect. Therefore, the best of the sludge storage time is 18 h. At the same time, the test result is applied in the Songhua river water special sewage treatment plant on the technical and economic analysis. We find that the test results compared with the traditional sludge treatment way can save running cost 431600 Yuan each year and reduce the sludge volume 638.75 tons. So it is economic and reasonableThis study analyzes the influencing factors and mechanism of sludge self-flocculation, provides a new idea of sludge conditioning. Provide theoretical support for reducing the drug consumption of sludge conditioning, optimizing the condition and control of sludge thickening and storage. The study will be useful to sludge treatment and resource reduction. |
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