EFFECT OF SLUDGE RETENTION TIME ON TREATING HIGH LOAD SYNTHETIC WASTEWATER USING AEROBIC SEQUENCINGBATCH REACTORS

The main aim of this study was to investigate the effect of sludge retention time on performance of aerobic synthetic batch reactor for treating a high load milk synthetic wastewater. For this purpose, four lab-scale sequencing batch reactors were operated under aerobic conditions with the same conditions at different sludge retention times (SRTs), feeding by high load milk synthetic wastewater. Operating volume, influent flow rate and influent organic loading rate for all reactors were adjusted to 5.5 L, 3.5 L/d and 1400 gCOD/m3d, respectively. The average effluent COD for reactor 1 to 4 with SRT of 5, 10, 15 and 20 d were 108, 97, 91 and 84 mg/L, respectively. COD removal was 94.99, 95.43, 95.86 and 96.16 percent respectively and slightly changed with SRT. However, the overall trend of COD removal vs. SRT showed an increasing rate with the correlation factor (R2) of 0.99. Reactor 2 with SRT of 10 d (SVI) had the maximum effluent TSSave (34mg/L) and turbidityave (5.89 mg/L) and the minimum sludge volume index (41mL/g). All reactors had SVIave of lower than 75 mL/g and effluent turbidityave 6 NTU which was lower than Iranian national discharge standards ( 50 NTU). SRT had directly influenced the biomass concentration, as the MLSSave of reactor 1 to 4 were found to be 1824, 2694, 3210 and 3864 mg/L, respectively. Best performance (minimum effluent COD, TSS and turbidity) was occurred in reactor 4 with SRT of 20 d.