Operation And Comparative Performance For Nitrogen And Phosphorus Removal Of A+A~2/O Process

Growing serious eutrophication of water body prompts municipal wastewater treatmentsystem to develop to the direction of multi–functional removal of organic compounds,nitrogen and phosphorus nutrients. The construction and operation of wastewater treatmentplant （WWTP） is the core of municipal wastewater treatment. The star-up, operation, andoptimization are the important parts of the operation and management of municipal WWTP.Though A2/O process is one of the most popular processes for simultaneous biologicalnitrogen and phosphorus removal, it has some inherent contradictions which are difficult toovercome, which makes the good nitrogen and phosphorus removal efficienciey cannot beachieved at the same time. Therefore, many researchers developed various kinds of modifiedA2/O processes; A+A²/O process is simple, feasible, and using more, among them. Anpre-anoxic tank to the front of anaerobic tank was added and influent port and proportionwere adjusted on the basis of conventional A2/O process, in order to eliminate the influence ofNOx-N to anaerobic phosphorus release.One WWTP in Guangzhou which was constructed in four different phases has threekinds of processes; the third phase is A+A²/O process with daily treated water of2010⁴m³/d.The work was carried on from the following five aspects: controlling parameters,characteristics of water quality for influent, nitrogen and phosphorus removal efficiency,operation problem and operation stability of A2/O process, using monitoring data of the wholeyear of2009as analysis data resource. Taking the second phase UNITANK process whichhas the same influent and similar influent quantity as A+A²/O process into account, thecomparative study on nitrogen and phosphorus removal efficiency, and operation stabilitybetween these two processes was also carried out.The operation results showed that: there is close links among process controllingparameters, and much useful information for operation through mutual effects was gained.There is fluctuation during the whole year on low-carbon influent, and it is appropriate toadopt biological treatment methods because of high biodegradability index, even there is arisk for nitrogen removal because of lower C/N ratiobetween4and6, C/P ratio wasfluctuative between30⁵0. The whole operation efficiency was better during2009, removalefficiencies for effluent indicator were high, the effluent met the first level B criteria specifiedin GB18918-2002, and the poor removal of TN was the direction of process optimization. Theresults of analysis on operational stability of A+A²/O process showed that, different effluentindexes have different ability for impact-resistance, that is, the sequence of CPin descending order was COD_cr＞BOD₅＞NH₄⁺-N＞TP＞SS＞TN. Effluent concentration valves per indexwere centralized in a comparatively small range, exception value was almost not emerged.Contrast analysis between A+A²/O process and UNITANK process was also carried outin this article, the results showed that: In the effect of process operation, removal efficiencyfor BOD₅/COD_cr, NH₄⁺-N/TN with A+A²/O process were better than UNITANK process, theremoval efficiencies of TP and SS with A+A²/O process were close to UNITANK process;In the effect of process operational stability, CPvalue for BOD₅, NH₄⁺-N/TN with A+A²/Oprocess was higher than UNITANK process, CPvalue for COD_cr, TP and SS was a litter lowerthan UNITANK process.