Effect Of Different Ratios Of Acetic Acid To Propionic Acid On Phosphorus Removal In Sequencing Batch Reactor With Single-stage Oxic Process

It is widely accepted that biological phosphorus removal of wastewater can be achieved under cycling anaerobic and aerobic conditions in the traditional biological phosphorus removal technology. With the addition of wastewater to the anaerobic zone, the orthophosphate(PO4-P) level in the medium goes up due to the release from the biological phosphorus removal bacteria(bio-P bacteria). In the subsequent aerobic zone, PO4-P in the medium is taken up by the bio-P bacteria in a large excess of their metabolic requirements which is crucial to phosphorus removal. Treated wastewater can be separated from activated sludge in secondary clarifier. Part of the activated sludge called returned sludge goes back to anaerobic phase after secondary clarification and meanwhile phosphorus is finally removed from the treated wastewater by sludge wasting. Different from the traditional biological phosphorus removal theory, which believes the presence of anaerobic phase is essential, single-stage oxic theory deems that good phosphorus removal efficiency can be achieved under single-stage oxic condition. Due to its novelty, single-stage oxic technology has received lots of attention in recent years.At present, most researches on the single-stage oxic technology take acetate or glucose as carbon source and nobody has investigated the effect of propionic acid or the compound of propionic acid and acetic acid on the phosphorus removal of single-stage oxic technology.To investigate the effect of different concentration ratios of acetic acid to propionic acid on phosphorus removal in single-stage oxic process, two lab-scale sequencing batch reactors (SBRs) were operated (R1:propionic acid to acetic acid ratio=0.165; R2:propionic acid to acetic acid ratio=2.00) using synthetic wastewater. After a period of sludge acclimation (30d), R2showed a higher SOP removal efficiency than R1. In the long term, the average efficiency of phosphorus removal in R1and R2were77.95%and84.79%respectively. However, the research on the typical cycle revealed that the phosphorus removal amount per MLVSS in R1was higher than R2. The phosphorus removal amount per MLVSS in R1was8.66mg/g while in R2was8.03mg/g. When carbon source worked out, PHA instead of glycogen was the main energy source in both R1and R2. In the idle phase, though obvious phosphorus release was observed in both R1and R2, the content of phosphorus released in R2was higher than that in R1. The phosphorus release amount per MLVSS of R2was higher than R1. At the end of the aerobic phase, glycogen in R1didn’t decrease to the original level. Microorganism tends to degrade glycogen first to maintain its metabolism when glycogen and Poly-P compound co-exists in cell. As a result, glycogen in R1degraded obviously while that in R2seldom degraded, which maybe the reason why the phosphorus release amount per MLVSS of R2was higher than R1.