Effect of sponge volume on the performance of down-flow hanging sponge system treating UASB reactor effluent.

ABSTRACT

The performance of down-flow hanging sponge (DHS) system treating UASB reactor effluent at different sponge volume of 38.2, 28.7, 19.1 and 9.6% was investigated. The hydraulic retention time (HRT) and flow rate were kept constant at 2.6 h and 0.46 m(3)/day, respectively. The results obtained indicated that reducing the sponge volume of the DHS system from 38.2 to 19.1% significantly decreased the removal efficiency of COD(total) from 80 +/- 8 to 62 +/- 14%; COD(soluble) from 71.2 +/- 10 to 53.7 +/- 18% and COD(particulate) from 86 +/- 10 to 62 +/- 15%. With further reduction of the sponge volume down to 9.6%, the removal efficiency was dropped to 54 +/- 15% for COD(total); 44.1 +/- 14% for COD(soluble) and 42 +/- 12% for COD(particulate). Likewise, the nitrification efficiency and fecal coliform (FC) removal was strongly affected by decreasing the sponge volume of the DHS system, i.e., the nitrification efficiency was dropped by a value of 48.3% when reducing the sponge volume of the DHS system from 38.2 to 19.1%. At sponge volume of 38.2%, the DHS system removes 2.6 +/- 0.3 log(10)/100 ml of FC which is significantly higher than that at sponge volume of 28.7, 19.1 and 9.6%. Accordingly, it is recommended to design and operate such a system at a bulk sponge volume not exceeding 38.2% of the total reactor volume and at an HRT of 2.6 h.