Effects Of Different Electron Acceptors And PH On Metabolism Of Polyphosphate Accumulating Organisms

The principle of Enhanced biological phosphorus removal (EBPR) process is by controlling the reaction conditions of the reactor, the phosphate accumulating bacteria release phosphorus in anaerobic stage, uptake excessive phosphorus in aerobic stage, through the mud to achieve phosphorus removal. The necessary conditions to maintain phosphorus removal is makeing phosphate accumulating bacteria to become the dominant bacterial. There are many factors affect the metabolism of PAOs, including carbon, carbon phosphorus ratio, pH, temperature, nitrate and so on.There have been many studies on the electron acceptor (oxygen, nitrate and nitrite) on the phosphorus uptake of bacteria. As we all know, oxygen can achieve effluent phosphorus removal as an electron acceptor. In recent years, denitrifying phosphorus removal was discovered, makes it possible to removal both nitrogen and phosphorus, denitrifying phosphorus removal can save carbon and energy sources, reduce the sludge production also, so nitrate have become popular; while if nitrite can be an electron is still in the controversial stage.There are few studies about the effect of electron acceptor on the phosphorus release of PAOs. In recent years, research has shown that inffluent wastewater directly after aeration, phosphate release occurred in the early, excessive phosphorus uptake later, phosphorus can also removal efficiently. No anaerobic stage SBR reactor saved stirring, reduced the hydraulic retention time. In most actual wastewater treatment plant, the operation results show that in the anaerobic phase, or anaerobic regions, the presence of nitrate will seriously affect the release of phosphorus.All of the above are based on the coexistence of a variety of bacteria in activated sludge systems, different operating parameters and conditions also led to different results. Thus, PAOs was incubated in an anaerobic-aerobic SBR reactor using synthetical sewage and the content has reached more than 85%. The efficient volume of reactor was 8L, and feed volume of each cycle which was 2L. Sludge retention time was about 8 d. The synthetic feed water contained PO4-P of 40 mg/L and COD of 800 mg/L which was given by acetate and propionate alternatively.Based on the enriched culture, the effects of three different types of electron acceptors (oxygen, natrite, nitrite) on the metabolism of PAOs was investigated, the effect of pH value was investigated alsl. The results showed that:In the short-term test of no anaerobic stage, the acetic acid uptake rate under aerobic conditions is almost the same with the normal cycle of acetic acid uptake rate. Using simulated wastewater, DO concentration in the aerobic section were 0.5-1.0, 2.0-2.5, 4.5-5.0 mg/L, respectively, the phosphorus uptake rates were 35.3mg/(L·h), 55.7mg/(L·h), 60.5mg/(L·h) in the previous 1 hour. There is no deterioration, and the effluent phosphorus concentration is below 0.5mg/L. Long-term tests of low DO concentrations (0.5-1.0mg/L) and high DO concentrations (4.5-5.0mg/L) did not affect the phosphorus removal.Different from the sewage treatment plants, phosphorus release was not inhibited by nitrate clearly. However, acetic acid uptake rate decreased with increasing nitrate content. When both the nitrates and phosphates were excessed, different initial NO₃^--N concentration of 20,40,80mg/L,the average denitrification rates were 20.15, 20.46, 20.15 mgNO₃^--N/( gMLSS?d) during the whole process of two hours, indicated that as a kind of heterotrophic bacteria, the denitrification capacity of PAOs has nothing to do with the nitrate concentration, less affected by the external environment.In an anaerobic-aerobic SBR reactor,the sudden accession of nitrite did not inhibit the phosphate release of PAO; instead, it causes large number release of phosphorus. With the nitrite concentration increased, the amount of phosphate release increased. Low concentration of NO₂^--N can be used as electron acceptor, but high concentrations of NO₂^--N inhibites. Lifted the inhibition of low concentration of nitrite, activity of phosphate accumulating bacteria recovered; lifted the inhibition of high concentrations of nitrite, phosphate accumulating bacteria can not be quickly restored to the original activity. NO₂^--N only affected the enzyme activity associated with uptake phosphorus; it not affected the enzyme activity associated with denitrification.In a certain pH range (7.0 to 9.0), the acetic acid under the same concentration of acetic acid uptake rate has nothing to do with the pH, they are all 9.33C-mmol/(L·h) around; PHV content is extremely low and unchanged basically, PHA synthesis capacity and glycogen content is essentially the same, that has nothing to do with the pH value, indicated that it has no sludge Glycogen (GAOs) almost. Long-term test results showed that the appropriate pH range of phosphorus accumulating organisms is between 7.0 and 8.0, and in this range of pH, metabolism of bacteria has been little affected, and GAOs will not generate.