순환여과식 양식시스템 배출수 내 천연 및 합성 응집제의 투여량 및 pH 조건에 따른 응집 효율 평가 = Evaluation of Coagulation Efficiency of Natural and Synthetic Coagulants under Different Dosage and pH Conditions in Recirculating Aquaculture System Effluent

다국어 초록 (Multilingual Abstract)

This study evaluated the effects of coagulant type, dosage, and pH on the treatment of a resuspended sludge sample derived from the sedimentation tank of a freshwater eel （Anguilla japonica） recirculating aquaculture system （RAS）. Polyaluminum chloride （PAC） was used as a conventional inorganic coagulant and compared with natural or modified natural coagulants, including chitosan, alginate, starch, cationic starch, and an alginate–calcium complex. Jar tests were conducted using RAS sedimentation-tank sludge resuspended in distilled water and adjusted to an initial total suspended solids （TSS） concentration of 4,000 mg·L⁻¹. Coagulation performance was assessed based on TSS, turbidity, total dissolved solids （TDS）, chemical oxygen demand （COD）, total nitrogen （TN）, total phosphorus （TP）, and particle-size distribution. Coagulants showing relatively high treatment performance in the dosage experiment were subsequently evaluated at pH 5-9 using selected operating dosages. PAC and chitosan exhibited the highest overall treatment performance. At a dose of 80 mg·L⁻¹, chitosan effectively removed suspended solids, reducing TSS and turbidity to 0.0 mg·L⁻¹ and 4.0 FAU, respectively. PAC at 40 mg·L⁻¹ reduced TSS and TP to 32.2 and 11.4 mg·L⁻¹, respectively, demonstrating high efficiency in phosphorus removal. TDS increased with increasing PAC dosage, indicating the possible accumulation of dissolved inorganic components. In contrast, chitosan generally reduced TDS but was more sensitive to changes in pH. Alginate and starch alone showed limited removal of suspended solids and organic matter. Cationic modification improved the performance of starch, although relatively high dosages were required. The alginate–calcium complex performed better than alginate alone at specific dosages, but its treatment efficiency varied substantially with dosage. Because the dosage and pH experiments were conducted separately using different sample aliquots and only the initial TSS was standardized, comparisons between the two experiments were based on within-experiment trends rather than direct comparisons of absolute concentrations. In the pH experiments, treatment responses varied by coagulant and water-quality parameter across pH 5-8, whereas most measured residual concentrations increased markedly at pH 9. PAC showed the most stable treatment performance across pH 5-8, while chitosan exhibited a marked decrease in efficiency under alkaline conditions. These findings indicate that PAC is a practical option for RAS effluent treatment because of its high and stable treatment efficiency, whereas chitosan represents a promising environmentally friendly alternative when residual metal contamination is a concern. Nevertheless, field-scale application requires further assessment of chemical cost, coagulant preparation, sludge production, residual aluminum, biological safety, and long-term operational stability.

목차 (Table of Contents)

• I. 서 론 1
• II. 재료 및 방법 6
• II-1. 실험 재료 6
• II-2. 시료 조제 및 응집제 선정 6
• II-3. pH 조건별 실험 8
• II-4. 수질 및 입도 분석 8
• II-5. 통계 분석 9
• III. 결과 10
• III-1. 투여량 실험 결과 10
• 1. 입자성 고형물 지표 10
• 2. 용존 고형물 지표 15
• 3. 유기물 지표 18
• 4. 영양염 지표 20
• 5. 고형물 입도 지표 24
• III-2. pH 실험 결과 28
• 1. 입자성 고형물 지표 28
• 2. 용존 고형물 지표 33
• 3. 유기물 지표 35
• 4. 영양염 지표 37
• IV. 고찰 42
• 1. 투여량 조건에 따른 응집제별 처리 특성 42
• 2. pH 조건에 따른 응집 반응 및 처리 안정성 48
• 3. RAS 배출수 처리에서의 응집제 적용성 및 한계 51
• 요 약 54
• 감사의 글 57
• References 59
• Appendix 67