The Research Of Conditions Of Startup And Running And Strategies Of Nituifiers Accumulation In CAST Process

As a kind of Sequencing Batch Reactors (SBR) process, Cyclic Activated SludgeTechnology (CAST) process was widely applied in practice for its advantages of simpleprocess, flexible operation mode, strong resistance to shock loading, wonderful nitrogenand phosphorus removal effect, etc. However, in practical application, the startup andrunning of Wastewater Treatment Plants (WWTPs) in a small town are difficult becauseof the longer Hydraulic Retention Time (HRT) caused by a large-scale of WWTP and theuncompleted collection systems. Additionally, enrichment of nitrobacteria is relativelyhard for activated sludge systems. Based on the startup and running of CAST process inBaihe WWTP, this research focused on the cultivation of activated sludge of CASTprocess and the enrichment of activated sludge system’s nitrifying bacteria under thecondition that the actual influent quantity is less than the designed inflow, it also studiedthe denitrification process of CAST process and its factors under the stable operation ofthe CAST process and denitrification capacity analysis of this WWTP.The main results of this study are as follows:1. By monitoring the quality and the amount of influent for half a year and observingtheir rule of this WWTP in this area, we found the sewage had following characteristicsin this area: firstly, beause it located in the mountains, collection of sewerage is faster, nobuffer structures such as regulating tank and equalization basin led to frequent influent;secondly, the process was kind of ruined by great quantitative and qualitative variation ofsewage water in this region for different periods in one day and different seasonsrespectively.2. This research monitored the quality of the influent and effulent, the concentrationof Mixed Liquor Suspended Solids (MLSS), Dissolved Oxygen (DO) in aeration tank, and observed the settling performance of the activated sludge, activated sludgemicroorganisms phase, etc. in the WWTP with a large number of experiments. Byanalyzing the experimental data and effect of the treatment, adjusting the operationscheme and accomplishing the cultivation of the activated sludge, this researchsummarized the factors that influenced the cultivation of the activated sludge under thegreater endogenous respiration time, and found out that the DO, SRT and HRT is themain influence factors, especially the SRT is vital for control of the concentration ofMLSS.3.Through the analysis of denitrification of CAST process in this WWTP, thisresearch found out that DO and Sludge Retention Time (SRT) are the main factors thatinfluenced the denitrification effect of CAST process, especially the effect of DO. Thestudy also found that the main denitrification of CAST process was SimultaneousNitrification and Denitrification (SND). It controlled the DO concentration in aerationtank as far as possible between0~2.0mg/L, and dissolved oxygen are close to zero duringabout50%aeration time,30%aeration time around1.0mg/L,20%at about2.0mg/L, wecould achieve a better denitrification effect.4. The regular time of a cycle in CAST process applied to the urban WWTP is4h,But for CAST process which was serious shortage of influent, we suggested that its timeof a cycle should be for6h, idle/water/aeration4h, precipitation1h, decanter1h, andadjusted the percentage of idle, water, and aeration time reasonably according to the waterquality and water inflow rate and removal of organic pollutants. According to the resultsof debugging and running, we found out that when the water temperature greater than15℃, the concentration of MLSS was about4000mg/L and SRT15d; When the watertemperature was less than15℃, the concentration of MLSS was about4500mg/L andSRT20d.5. The research shows that an enough exchange rate (λ≥0.17) should be ensured forthe startup of Cyclic Activated Sludge Technology (CAST) process under the longhydraulic retention time (HRT) condition, and the HRT should be less than35h, and thekey control indexes include sludge retention time (SRT)(approximately20d in this case)and the ratio of aeration time (more than0.5) that should be adjusted according to thewater quality and water inflow rate. Additionally, the endogenous respiration ratio could well indicate that status of the operation of WWTPs, i.e., ηen/C(the ratio of endogenousand organic removal respirations) and ηen/N(the ratio of endogenous and ammoniaremoval respirations) were in the range of5～10%and15～20%，respectively, indicatedthe good performance of WWTPs.