목적:인산염과 과산화수소 투입 유무에 따른 생물활성탄(biological activated carbon, BAC) 공정 유출수 중의 biopolymers 농도 및 BAC 공정 여층의 손실 수두 변화를 평가하여 보다 효율적인 BAC 공정의 운전 방안을 제시하고자 하였다. 방법: BAC 공정 시스템은 내경 20 cm, 높이 250 cm의 아크릴 컬럼 4개를 사용하여 공탑 체류시간은 20분, 역세척은 주 1회 실시하였다. 실험기간 동안 후오존은 1 mg·O₃/mg·DOC로 고정하여 투입하였다. 4개의 BAC 컬럼들은 기존 BAC (control-BAC), 인을 투입한 강화 BAC (PO₄-P+BAC), 과산화수소를 투입한 강화 BAC (H₂O₂+BAC) 및 인과 과산화수소를 함께 투입한 강화 BAC (PO₄-P+H₂O₂+BAC)이다. PO₄-P를 투입한 강화 BAC의 경우 유입수에 0.010 mg/L의 농도로 PO4-P를 추가로 보충하였으며, H₂O₂를 투입한 BAC에서는 H₂O₂를 유입수에 1 mg/L의 농도로 투입하였다. 결과 및 토의: 수온의 변화에 따른 control-BAC에서의 평균 손실 수두는 4.4 cm (25~28℃)~7.7 cm (8~12℃)였으며, PO₄-P+BAC, H₂O₂+BAC 및 PO₄-P+H₂O₂+BAC에서는 각각 3.9 cm~5.8 cm, 2.5 cm~3.5 cm 및 2.6 cm~3.5 cm로 나타났다. 인과 과산화수소의 투입으로 손실수두가 저감되었다. 수온이 낮은 시기에 control-BAC에서는 biopolymers (BP) 성분의 유출농도가 유입농도보다 높게 나타나 생물막에서 다량의 EPS (extracellular polymeric substances)가 생성되어 유출되는 것으로 나타났다. Control-BAC에 비하여 PO₄-P+BAC, H₂O₂+BAC 및 PO₄-P+H₂O₂+BAC에서는 수온 8~12℃ 기간에 BP의 잔존비(C<SUB>out</SUB>/C<SUB>in</SUB>)가 36~57% 정도 낮았다. BP 잔존비의 경우, 수온이 낮을수록 높게 나타났고, 수온이 상승할수록 점진적으로 감소하였다. 이러한 결과는 control-BAC와 강화 BAC 공정들에서의 손실 수두 변화결과와 매우 유사하였고, BP 농도 잔존비와 손실 수두는 매우 높은 상관관계(r²=0.82~0.87)를 나타내었다. 운전기간 동안의 생물막 안정도 평가를 위해 BAC 처리수 중의 평균 총 박테리아 개체수(total cell counts, TCC)를 조사한 결과, control-BAC, PO₄-P+BAC, H₂O₂+BAC 및 PO₄-P+H₂O₂+BAC 공정에서 각각 46.8×10<SUP>6</SUP> cells, 30.3×10<SUP>6</SUP> cells, 21.8×10<SUP>6</SUP> cells 및 18.8×10<SUP>6</SUP> cells로 나타나 control-BAC에 비해 강화 BAC 공정들 유출수에서 35~60% 정도 낮게 나타났다. 또한, TCC 중에서 활성 박테리아 개체수(live cell count, LCC) 비(LCC/TCC)의 경우도 control-BAC의 0.53에 비해 강화 BAC 공정들에서는 0.84~0.89 범위로 나타나 강화 BAC 공정들의 부착 생물막의 안정도가 높은 것으로 조사되었다. 결론: 운전기간 동안 기존 BAC (control-BAC) 공정에 비하여 인과 과산화수소를 투입한 강화 BAC 공정들에서 손실 수두 저감효과가 뚜렷하게 나타났다. 특히, 인을 투입한 경우보다 과산화수소를 투입한 경우에 손실 수두 저감효과가 높았다. 저수온기에 강화 BAC 공정들에 비하여 control-BAC에서의 급격한 손실 수두 증가는 생물막에서의 다량의 EPS 생성으로 인한 결과이며, 인이나 과산화수소 투입으로 부착 생물막의 안정도(stability) 향상 및 EPS 생성량을 저감시켜 손실 수두를 감소시킬 수 있었다.
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 (C<SUB>out</SUB>/C<SUB>in</SUB>) 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 46.8×10<SUP>6</SUP> cells, 30.3×10<SUP>6</SUP> cells, 21.8×10<SUP>6</SUP> cells, and 18.8×10<SUP>6</SUP> 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.