Osmotic power is to produce electric power by using the chemical potential of two flows with the difference of salinity. Water permeates through a semipermeable membrane from a low concentration feed solution to a high concentration draw solution due to osmotic pressure. In a pressure retarded osmosis (PRO) process, river water and wastewater are commonly used as low salinity feed solution, whereas seawater and brine from the SWRO plant are employed as draw solution. During the PRO process using wastewater effluent as feed solution, PRO membrane fouling is usually caused by the convective or diffusive transport of PRO which is the most critical step of PRO membrane in order to prevent membrane fouling. The main objective of this study is to assess the PRO membrane fouling reduction by pretreatment to remove organic matter using coagulation-UF membrane process. The experimental results obtained from the pretreatment test showed that the optimum ferric chloride and PAC dosage for removal of organic matter applied for the coagulation and adsorption process was 50 mg/L as FeCl3 (optimum pH 5.5). Coagulation-UF pretreatment process was higher removal efficiency of organic matter, as also resulting in the substantial improvement of water flux of PRO membrane.

Pretreatment system of desalination process using seawater reverse osmosis(SWRO) membrane is the most critical step in order to prevent membrane fouling. One of the methods is coagulation-UF membrane process. Coagulation-UF membrane systems have been shown to be very efficient in removing turbidity and non-soluble and colloidal organics contained in the source water for SWRO pretreatment. Ferric salt coagulants are commonly applied in coagulation-UF process for pretreatment of SWRO process. But aluminum salts have not been applied in coagulation-UF pretreatment of SWRO process due to the SWRO membrane fouling by residual aluminum. This study was carried out to see the effect of residual matal salt on SWRO membrane followed by coagulation-UF pretreatment process. Experimental results showed that increased residual aluminum salts by coagulation-UF pretreatment process by using alum lead to the decreased SWRO membrane salt rejection and flux. As the salt rejection and flux of SWRO membrane decreased, the concentration of silica and residual aluminum decreased. However, when adjusting coagulation pH for coagulation-UF pretreatment process, the residual aluminum salt concentration was decreased and SWRO membrane flux was increased.

Large amounts of oily wastewater discharged from various industrial operations (petroleum refining, machinery industries and chemical industries) cause serious pollution in the aquatic environment. Although dissolved air flotation (DAF) separating oil pollutants using microbubbles represents current practice, bubble size cannot be selectively controlled, and lots of power is required to generate microbubbles. Therefore, to investigate performance of the DAF process, this study examined the distribution of different sizes of microbubbles resulting from changes in physical shear force via modifying shapes of a slit-nozzle without an additional power supply. Three types of slit-nozzles (different angle, shape and length of the slit-nozzle) were used to analyze the distribution of bubble size. At a slit angle of 60°, shear force was 4.29 times higher than a conventional slit, and particle size distribution (PSD) in the range between 2 and 20 μm more than doubled. Treatment efficiency of synthetic oily wastewater through the coagulation-DAF process achieved 90% removal of COD by injecting FeCl3 and PACl of 250 mg/L and 100 mg/L, respectively, and the same performance resulted using FeCl3 of 200 mg/L and PACl of 80 mg/L employing a slit-nozzle angle of 60°. This study shows that a coagulation-DAF process using a modified slit-nozzle can improve the pre-treatment of oily wastewater.

In the coagulation/sedimentation (C/S) process of the water treatment process, the inflow of massive algal bloom causes many problems including fouling of filter media. This study was conducted to find out the way to remove the algae’s harmful effects by addition of pre-treatment prior to C/S process. Many Jar-tests were conducted such as ① ACF (Algae Coagulation·Flotation) process using natural algae coagulant (Water Health®), ② ACF + C/S process and ③ C/S process with a variety of conditions using cultured algae. The average values of turbidity were ① 0.42 NTU for ACF process, ② 0.13 NTU for ACF + C/S process and ③ 0.25 NTU for C/S process. It was shown that the treatment efficiency of ACF process could get low turbidity results, and ACF + C/S process could achieve more efficient results than those of C/S process. Any negative effects of ACF process to the efficiency of C/S process were not observed in ACF + C/S process. In order to reduce the unfavorable effects of algae, it was found out that the introduction of ACF process in the forms of ① ACF or ② ACF + C/S could be one of the effective and alternative solutions.

A coagulation-flocculation (CF) process using aluminum sulfate as a coagulant was employed to treat highly suspended solids in tunnel wastewater. Response surface methodology (RSM) based on a Box-Behnken design was applied to evaluate the effects of three factors (coagulant dosage, pH and temperature) on total suspended solids (TSS) removal efficiency as well as to identify optimal values of those factors to maximize removal of TSS. Optimal conditions of coagulant dosage and pH for maximum TSS removal changed depending on the temperature (4 ~ 24°C). As temperature increased, the amount of coagulant dosage and pH level decreased for maximum TSS removal efficiency during the CF process. Proper adjustment of optimal pH and coagulant dosage to accommodate temperature fluctuations can improve TSS removal performance of the CF process.

본 연구는 Y 정수장의 세라믹 정밀여과막 공정을 위한 최적의 응집 조건을 도출하고자 수행되었다. 쟈테스트 결과 Y댐 원수의 pH를 7로 조정 시 응집효율이 가장 우수하였으며, 원수 탁도가 10 NTU 이하인 평상시 탁도 조건하에서 최적 응집제 주입량은 3 mg/L (as Al2O3)인 것으로 나타났다. 최적 응집제를 선정하기 위하여 응집제 종류(PAC, PACS (II), PAHCS)별로 미니모듈 실험장치를 이용하여 평가한 결과 PAC를 주입하고 원수 pH를 7로 조정한 경우 비여과유속 감소율이 가장 낮은 것으로 나타났다. 원수 탁도를 10~150 NTU로 변화시키며 미니모듈에서 비여과유속 감소율을 평가한 결과 원수탁도 10~30 NTU 조건에서는 응집제 주입량 증가에 따라 비여과유속 감소율이 크게 감소하였으나 원수탁도가 50 NTU 이상에서는 응집제 주입량을 증가시켜도 비여과유속 감소율에 큰 차이가 없는 것으로 나타났다. 따라서 Y 정수장을 위해서 는 원수탁도 10 NTU 이하에서는 PAC (11% as Al2O3) 30 mg/L, 10~50 NTU에서는 30~50 mg/L, 50 NTU 이상에서는 50 mg/L이 적절하다.

아크릴 폐수를 응집-여과-중화의 전처리 공정에 적용하여 막오염 인자를 최소화 한 후 UF/RO 공정에 적용하였다. 막의 형태 및 종류에 따라 한외여과 및 역삼투 모듈을 조합을 이루어 전처리 수를 온도 및 압력변화에 따라 적용하여 분리 특성을 고찰하였다. 투과 플럭스는 모듈 set 1의 UF모듈보다 모듈 set 4의 UF모듈의 투과량이 약 2~3배 더 많이 배출됨을 확인하였다. 최종적인 투과량은 관형모듈과 조합을 이룬 모듈 set 2와 모듈 set 3이 좋은 결과를 나타내었다. 모든 UF 모듈에서 TDS, T-N 및 COD의 제거 효율은 온도 및 압력변화에 영향을 받지 않고 제거 효율 또한 낮음을 알 수 있었다. RO모듈에서 TDS, T-N 및 COD가 우수한 제거 효율을 보였다. 아크릴 폐수의 최종적인 수질결과는 공장폐수의 배출 허용기준을 만족하였고, 막모듈 조합은 폐수의 재활용 가능성을 확인할 수 있었다.

In this study, solid-liquid separation conditions for coagulation and sedimentation experiments using inorganic coagulant (aluminum sulfate and Poly-Aluminum Chloride (PAC)) were optimized with brine wastewater discharged by the epoxy-resin process. When the turbidity and suspended solid (SS) concentration in raw wastewater were 74 NTU and 4.1 mg/L, respectively, their values decreased the lowest in a coagulant dosage of 135.0 - 270.0 mg Al3+/L. The epoxy resin was re-dispersed in the upper part of wastewater treated above 405.0 mg Al3+/L. The removal efficiencies of turbidity and SS via dosing with aluminum sulfate and PAC were evaluated at initial turbidity and SS of 74 - 630 NTU and 4.1 - 38.5 mg/L, respectively. They increased most in the range from 135.0 - 270.0 mg Al3+/L. The solid-liquid separation condition was quantitatively compared to the correlation of SS removal efficiency between the coagulant dosage and SS concentration based on the concentration of aluminum ions. The empirical formula,   , shows the relationship between SS removal efficiency (R) and coagulant dosage (D) at 38.5 mg/L; it produced high correlation coefficients (r2) of 0.9871 for aluminum sulfate and 0.9751 for PAC.

In this study, we have investigated to find optimal pre-treatment flocculation condition by analyzing the floc growth rate with mixing conditions and the membrane permeation flux for pre-treatment step of the membrane process. The higher mixing intensity showed a constant floc size index (FSI) values, and lower mixing intensity increased the degree of dispersion of the FSI values. Results of comparing the distribution characteristics of the FSI value and the permeation flux were more effective in increasing flux when the FSI values were 0.2 or higher. The degree of dispersion of FSI was relatively large in 40 rpm mixing condition compared to 120 rpm. In 40 rpm mixing condition, it decreased the permeation flux compared to 120 rpm because various sizes of flocs were distributed. Coagulation-UF membrane process enhanced 30%∼40% of the flux rate compare to UF alone process, and the coagulation-MF process increased up to 5% of the flux rate compare to MF alone process. Pre-treatment, that is, coagulation process, has been found to be less effects on relatively larger pore size for MF membrane. For UF membrane, the flux was a little bit same when applying only the rapid mixing process or rapid mixing with slow mixing processes together. In case of MF membrane, the flux was improved when rapid mixing process applied with slow mixing process together.

MEPC. 227(64)가 발의되면서 해상에서 선박 배출수의 오염에 대한 규제가 강화되었다. 특히 T-P에 대하여 유입수 대비 유출수의 제거율을 1.0 mg/L 또는 80%로 제한하고 있다. 이를 충족시키기 위해 SBR+MBR 공정을 적용하여 시험운전을 진행하였으며, 그에 따른 문헌조사 결과 생물학적 처리만으로 인의 목표 처리효율을 충족시키는 것에 한계가 있을 것으로 판단하여 응집제(PAC 5)를 도입하였다. 따라서 본 연구는 PAC 5를 이용한 응집공정 적용시 T-P의 제거율이 어떻게 변화하는지 연구하는 데에 그 목적이 있다. 실험에 사용된 원수는 실험을 위해 자체 제작한 화장실에서 발생된 오수를 사용하였으며 원수의 T-P 농도는 33.215 mg/L로 측정되었다. 실험은 총 3 사이클 동안 진행되었으며, SBR+MBR 공정을 거친 1차 유출수의 T-P 농도 및 제거율의 평균값과 PAC 5를 이용하여 응집공정까지 시행된 2차 유출수의 T-P 농도 및 제거율의 평균값을 비교하였다. 실험 결과 1차 유출수의 평균 T-P 농도는 15.05 mg/L로 유입수 대비 유출수가 70.8%의 제거율로 나타났고, 또한 2차 유출수의 경우 평균 농도 3.47 mg/L로 93.3%의 제거율로 나타났다. 실험을 통해 PAC 5를 적용한 응집공정을 실시하였을 때 T-P 평균 제거율이 22.5%가 상승한 것으로 확인되었다. 따라서 SBR+MBR 공정을 적용한 고도수처리장치에 있어서 PAC 5를 이용한 응집공정 적용은 긍정적인 것으로 판단된다.