Investigation On The Microbiological Characteristics Of Up-flow Microdilatancy BAC Process

The O3-BAC advanced treatment has been used extensively worldwide in China.However, potential microbilogical safety problems of the product water arise. Tosolve the problem, a technology reform is implemented. The up-flow BAC improvesthe removal efficiency of micro-pollutants, and ensure the microbilogical safety bythe postpositive sand filtration. To evaluate the up-flow BAC, a comprehensive studywas performed to determine the microbiological characteristics of up-flowmicrodilatancy BAC process. Specific studies include the design and operatingparameter, operating result, bioactivity of BAC and the microbilogical safety ofproduct water.The granular size, runtime, backwashing and temperature will affect theexpansion of BAC. Small granular size, raw GAC, no backwashing and hightemperature increase the expansion. According to the expansion curve, the sievefraction mesh12×40and mesh20×50is the most suitable used for up-flowmicrodilatancy BAC. At the hydraulic loading of water works, the expansion is5²0%. The turbidity of BAC effluent is increasing with the inflow. If the expansionof BAC is above20%, postpositive sand filtration is necessary. The granular size ofactived carbon affects the removal rate of DOC. The smaller actived carbon will leadhigh removal efficiency of DOC.The HPC, ATP and OUR distributes along the up-flow column. The HPC, ATPand OUR increases with temperature rises. Back wash also has effect on the HPC,ATP and OUR. The biocenosis of biological film will be abundant and stable as theBAC colomn performance a long period. The dominant microorganism species in thebiological film includes Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria,Gammaproteobacteria, Sphingobacteria and Flavobacteria. The biocenosis differs alot from different colomn. Howerver, there is no significant difference along thecolomn.The up-flow BAC with sand filtration postpositive process enhances the microbilogical safety of product water. The second-stage construction of Quehuawater works employs the up-flow BAC with postpositive sand filtration; the sandfiltration solves the problem, which numbers of particles and bacteria increases in thecarbon bed effluent. Compare with the first-stage construction effluent, the number ofparticles, HPC, coliform and total bacterial count of new process decreases. TheHPCs of carbon bed effluent in the northern water plants showed appreciable increaseafter homogenization when the temperature is higher. The dominant microorganismof raw water, up-flow BAC effluent, sand filtration effluent and disinfected productwater is Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. Thebiocenosis of procuct water after disinfection has a similar variation trend. Thedominant species is Gammaproteobacteria, and its abundance is45⁶0%. Themicrobial population of BAC bed effluent is abundance, which includesAlphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Flavobacteria,Actinobacteria, Sphingobacteria and Clostridia.The comparison between up-flow and down-flow is progressed. The backwashperiod of down-flow is very short, about3to4days. The loss of head of up-flowBAC changes rarely, the backwash period is14days. The turbidity of up-floweffluent is higher than those of down-flow. But the up-flow has high removal rate ofCOD_Mnby12%. The up-flow BAC have powerful removal efficiency of pollutants,because the OUR of up-flow BAC is higher than that of down-flow, and the OURremains high level along the whole column. The particles and HPCs increases afterup-flow BAC bed, the sand filtration postpositive will guarantee the microbilogicalsafety.