EFFECT OF SRT ON NUTRIENT REMOVAL IN SBR SYSTEM

The effect of solids retention time (SRT) on chemical oxygen demand (COD) degradation and nutrients removal was studied in a sequencing batch reactor (SBR). SRT of 10, 15, 20, 25, and 30 days was studied. A laboratory reactor of 6.6 L working volume with an 8-h-cycle time was used. In order to maintain relatively constant feed composition, a synthetic wastewater was employed. COD removal was unaffected by the variation of SRT (average removal of 83.6-94.4% for COD and total organic carbon (TOC). Removal of TKN and ammonium varied from 86.8 to 97.2% with SRT variation of 10-30 days. Phosphorus removal was strongly influenced by the SRT variation. Maximum phosphorus removal was observed between 20 and 25 days SRT (average of 90.6 and 97.2% Pioini removal, respectively). P removal decreased to 68.7% at 10 and 15 days SRT and was 44-47.3% (ortho-P and P total) at 30 days SRT. Maximum content of P in sludge solids was observed at 20 days SRT (6.2% g P/g VSS). In an SBR cycle, the P released in anaerobic phase was also maximum (62 mg/L) at 20 d SRT. The fraction of phosphorus in different phases (precipitated, adsorbed, P-organic, poly-P) was also determined for one cycle at each SRT studied.