Effect of Hydrogen Peroxide and Phosphate Addition on Biopolymers Formation and Changes in Head Loss in Biological Activated Carbon Process

Abstract

Objectives:The purpose of this study was to suggest a more efficient operation condition for the BAC(biological activated carbon) process by evaluating the change in the concentration of biopolymers in the effluent of the BAC process and the head loss of the BAC filter layer according to phosphate (PO4-P) and hydrogen peroxide (H2O2) input.Methods:During the experiment period (Feb. to Aug. 2020), the O3 dosage was fixed at 1 mg･O3/mg･DOC. Four columns with an inner diameter of 20 cm and a height of 250 cm were prepared. Empty bed contact time (EBCT) was fixed at 20 minutes and backwash was performed once a week. The four BAC columns are conventional BAC(control-BAC), enhanced BAC with hydrogen peroxide (H2O2+BAC), enhanced BAC with phosphate (PO4-P+BAC), and enhanced BAC with phosphate and hydrogen peroxide together (PO4-P+H2O2+BAC). In the case of enhanced BAC with PO4-P added, PO4-P was added with a concentration of 0.010 mg/L in the influent, and in BAC with H2O2, H2O2 was added with a concentration of 1 mg/L to the influent.Results and Discussion:According to the change of water temperature, the average head loss in control-BAC was 4.4 (25~28℃)~7.7 cm(8~12℃). In addition, PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC were 3.9~5.8 cm, 2.5~3.5 cm, and 2.6~3.5 cm, respectively. The head loss was reduced by the input of PO4-P and H2O2. During the low water temperature period, in control-BAC, the effluent biopolymers (BP) concentration was higher than the influent concentration, indicating that a large amount of EPS (extracellular polymeric substances) was produced and released from the attached biofilm. In PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC processes, the BP concentration ratio (Cout/Cin) was about 36~57% lower than that of the control-BAC during the low water temperature period. The BP concentration ratio was high when the water temperature (8~12℃) was low, and the BP concentration ratio gradually decreased as the water temperature increased. These results were very similar to those of the head loss change in the control-BAC process and the enhanced BAC process, and the BP concentration ratio and the head loss showed a very high correlation (r2=0.82~0.87). To evaluate the stability of the biofilm during the operation period, the total cell counts (TCC) in BAC treated waters were investigated. In control-BAC, PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC process, the average TCC was 46.8×106 cells, 30.3×106 cells, 21.8×106 cells, and 18.8×106 cells, respectively. Compared to the control-BAC, it was found to be 35~60% lower in the enhanced BAC processes. In addition, live cell count (LCC) ratio (LCC/TCC) was 0.84~0.89 in the enhanced BAC processes compared to 0.53 in the control-BAC. These results indicate that the biofilm stability of the enhanced BAC processes is higher than that of control-BAC.Conclusions:During the experiment, compared to the conventional BAC process, the enhanced BAC processes in which PO4-P and H2O2 were added showed a clear effect of reducing the head loss. In particular, the effect of reducing the head loss was higher when H2O2 was added than when PO4-P was added. A rapid head loss increase occurred in the conventional BAC process compared to the enhanced BAC processes in the low water temperature season is the result of the production of large amounts of EPS in the attached biofilm. The input of PO4-P or H2O2 reduces the head loss by improving the stability of the attached biofilm and reducing EPS production.