The Biological Phosphorus Removal Mechanism Of Reversed A~2/O Process Based On Anaerobic Environment

Enhanced biological phosphorus removal (EBPR) process can either alleviate eutrophication or recover phosphorus from wastewater. Great effort from the view of microbiology and biochemischry has been made clarify the mechanism of the process. It has been widely accepted that polyphosphate accumulating organisms (PAOs) cleave polyphosphate to produce energy for volatile fatty acids uptake (VFAs) and poly-hydroxyalkanoates (PHAs) synthesis during anaerobic pHase and use the PHAs as energy source to luxurily uptake pHospHate during the subsequent aerobic phase. That means the more phosphate released during anerobic phase the more phosphate can be uptaken during aerobic phase. By far, most wastewater treatment plants have been designed according to this theory.The configuration of reversed A2/O process has achieved better nutrient removal performance than traditional A/O process in many cases and it has been found to be energy saving. Those who had proposed the reversed A2/O process suggest that "the foundmental force that drive the PAOs to uptake phosphate luxurily is related to the anerobic hydraulic retention time and anaerobic degree of anerobic zones. To some extent, longer anerobic hydraulic retention time and deeper anaerobic degree lead to better motivation for phosphate uptake".In order to understand how the anaerobic environment affec the PAOs’ability to uptake phosphate, we studied the regular effects of anaerobic duration and anaerobic degree on the mataerial metabolism and energy metabolism of micorbes that perform phaosphorus uptake.When it coming to the effect of anerobic duration on biological phosphorus removal, we get three conclusions as follows:No matter how much VFAs the wastewater contains, proper longer anaerobic duration can always increase the PAOs’ phosphorus uptake motivation and removal efficiency, microbes’ energy level and activity. More released phosphorus and synthesized PHAs can not always lead to PAOs’ higher phosphorus removal ability.With the extention of anaerobic duration, PAOs’ motivation for phosphorus uptake always goes up and down simoutaneously with the microbes’ activity and energy level. When the other conditions remain unchanged, microbes’ higher activity and energy level almost always led to PAOs’ stronger motivation for phosphorus uptake. It is the microbes’ higher activity and energy level caused by proper longer anaerobic duration that led to PAOs’ stronger motivation for phosphorus uptake.The anaerobic duration the the microbes can endure should be limited in a proper range. Proper longer anaerobic duration can increase microbes’ activity and energy level but excessive longer anaerobic duration can impair microbes’ activity and energy level.How long anaerobic duration can cause the PAOs’ to exhibit the strongest motivation for phosphorus uptake depends on how much VFAs the wastewater contains which affect the PAOs, ability to endure anaerobic duration. As for domestic sewage, the anaerobic duration of4h can make the PAOs to show the best motivation for phosphorus uptake, energy level and activity.As far as the effect of anaerobic degree is concerned, we have three conclusions.No matter synthetic wastewater or domestic wastewater was used and no matter how much VFAs the wastewater contains, with a certain anaerobic duration, deeper anaerobic degree can always increase the released phosphorus and synthesized PHAs during anaerobic stage, the microbes’ energy level and activity and finally PAOs’ phosphorus uptake motivation and removal efficiency.When the sludge taken from wastewater treatment plants which is used to treat domestic sewage is used, higher VFAs content of the synthetic wastewater can increase the released phosphorus and synthesized PHAs during anaerobic stage, but can not correspondingly increase the phosphorus removal efficiency. That means more released phosphorus and synthesized PHAs can not always lead to PAOs’higher phosphorus removal ability.When the sludge taken from wastewater treatment plants which is used to treat domestic sewage is used, no matter how much VFAs the synthetic wastewater contains, microbes’ energy level and activity are always closely related to PAOs phosphorus removal ability, microbes’ higher energy level and activity usually lead to better phosphorus removal efficiency. It is the microbes’ higher energy level and activity caused by deeper anaerobic degree that makes the PAOs to uptake phosphorus more efficiently.