A Contrastive Study Between A~2/O Technology And Parallel Connected A~2/O Technology On Nutrients Removal

Normal A²/O process is the most common nutrient removal technology at present,with connected anaerobic zone and anoxic zone.It means that the wastewater has to enter meaningless anaerobic zone in the nitrogen removal process and the same disadvantage exits in the phosphorus removal process to enter meaningless anoxic zone.This results in long retention time,large tank volume and high investment and operation cost.Parallel Connected A²/O process is a new technology with parallel connected anaerobic zone and anoxic zone,followed by aerobic zone.In theory,this new technology can modify the disadvantage of Normal A²/O process by improving anaerobic and anoxic time in the same volume and influent.To investigate the difference between Normal A²/O process and Parallel Connected A²/O process,a lab-scale experiment was conducted for one year to obtain the optimized running parameter of the new process.This study uses two parallel equipments to study on the the nutrients removal effect of the two technologies in three conditions(respectively the common condition, the condition of abundant carbon source and the condition of deficient carbon source), through regulating COD,TN and TP of the influent from municiple wastewater of Shanghai,with 15 days of each test condition.In the condition of 150～450mg/L COD influent with 13 hours' waterpower retention time,both the two systems perform good removal effect of COD.The outlet water absolutely meets the requirement of the first rank A of (GB18918-2002),which is less than 50 mg/L.In the concentration gradient of 170,250,330 and 450mg/L,comparing the nitrogen removal effect,two outcomes can be concluded:First,the nitrogen removal effect of the two systems are growing first and then lowing with the growing of COD concentration.The nitrogen removal rate reaches the highest when the influent COD is 330 mg/L,the Normal A²/O is 58.5%and the Parallel Connected A²/O is 66.7%. Both of them can meet the requirement of the first rank of (GB18918-2002).The nitrogen removal effect of Parallel Connected A²/O system is better than Normal A²/O system,because the anoxic time of Parallel Connected A²/O is two times of Normal A²/O.When the carbon source is relavent abundant,the denitrification of Parallel Connected A²/O is more sufficient than Normal A²/O.Second,as the influent COD(organic load)grows,phosphorus removal effect becomes better,when the influent COD is 330 mg/L,the Normal A²/O is 75.5%and the Parallel Connected A²/O is 75.6%.Both of them can meet the requirement of the first rank of (GB18918-2002). So it reflects that the growth of influent COD is good for phosphorus release.When influent TN is up to 50mg/L,Both the two systems perform bad removal rate of NH₄⁺-N,less than 75%.And the outlet concentration of NH₄⁺-N is more than 5mg/L in both the two systems,which are about 15mg/L.This reflect that the influent NH₄⁺-N concentration of 50mg/L beyond the nitrification ability.In the load of 0.18～0.24mg/L kgCOD/kgMLSS.d,the detrification of the two systems are bad.The increase of nitrogen and phophorus affects parallel A²/O much more than A²/O,it is to say,serious unsufficiency of carbon source affects parallel A²/O much more than A²/O.That is because the carbon source using efficiency of parallel A²/O is higher than A²/O,when unsufficient carbon source sivided into anaerobic zone and anoxic zone,none of the two zone can perform efficient phosphorus release and denitrification,which lead to worse nutrients removal effect of parallel A²/O system.Three outcomes can be abttained from the experiment:at the organic load of 0.30～0.48kgCOD/kgMLSS.d,the phosphorus release and denitrification of parallel A²/O is relovent sufficient for its anaerobic time and anoxic time is twice than Normal A²/O system,so Parallel Connected A²/O system possesses advantage to Normal A²/O system.At the organic load of 0.49～0.62kgCOD/kgMLSS.d,the nutrients removal rates of both systems are the same for sufficient carbon source.At the organic load of 0.18～0.24kgCOD/kgMLSS.d,none of phosphorus releases and denitrification can be good for seriously unsufficient carbon source divided into two influents.In this condition,the phosphorus removal of Parallel Connected A²/O system is worse than Normal A²/O system.The experiment reflects that the organic load of 0.18～0.24kgCOD/kgMLSS.d is fit for both the two systems.Therefore,Parallel Connected A²/O system is fit for abundant carbon source condition.