This study investigated the effects of the light conditions on the productivity of scenedesmus dimorphus in the continuous mass cultivation system. To compare the algal productivity according to the light conditions, S. dimorphus was cultivated continuously under the wide range of light intensity(200-600 PPFD) and various light wavelength(white light and red-blue mixed light). After 100 days of cultivation under the different light intensity, the productivity of S. dimorphus increased as light intensity decreased. So, the productivity was maximized as 100 mg/L/d when light intensity was 200 PPFD. In case of light wavelength, the productivity of S. dimorphus was enhanced about 20% with the white light compared to that of the red-blue mixed light. Consequently, the optimal light conditions for the continuous mass cultivation of S. dimorphus were 200 PPFD as light intensity and white light as light wavelength.

This study investigated the effect of a co-culture of Scenedesmus dimorphus and nitrifiers using artificial wastewater on the removal of ammonium, nitrate and phosphate in the advanced treatment. To test the synergistic effect of the co-culture, we compared the co-culture treatment with the cultures using S. dimorphus-only and nitrifiers-only treatment as controls. After 6 days of incubation, nitrate was removed only in the co-culture treatment and total amount of N removal was 1.3 times and 1.6 times higher in the co-culture treatment compared to those in the S. dimorphus- and nitrifiers-only treatments, respectively. In case of total amount of P, co-culture treatment removed 1.2 times and 12 times more P than the S. dimorphus -and nitrifiers-only conditions, respectively. This indicates that the co-culture improved removal rates for ammonium, nitrate, and phosphate. This further implies that there was no need for denitrification of nitrate and luxury uptake of P processes because nitrate and phosphate can be removed from the uptake by S. dimorphus. In addition, co-culture condition maintained high DO above 7 mg/L without artificial aeration, which is enough for nitrification, implying that co-culture has a potential to decrease or remove aeration cost in the wastewater treatment plants.

VFAs like acetate are the major soluble metabolites of food waste leachates after digested. Therefore this study investigates the effect of acetate on growth rate and nutrient removal efficiency of Chlorella vulgaris to treat digested food waste leachates. The initial acetate concentration varied from 0 to 20 mM. As a result, Chlorella vulgaris growth rate was increased as high as the concentrations ranged from 0 to 20 mM. The same trend was observed with NH4-N and PO4-P consumption. The highest growth rate and the highest NH4-N, PO4-P removal rate were observed at acetate concentration of 20 mM. The microalgae growth rate and NH4-N, PO4-P removal rates were 1.5, 1.8, 2.3 times higher than the condition without acetate.

This study investigates the effect of sodium bicarbonate (NaHCO3) on growth of S. dimorphus. NaHCO3 concentration was varied from 0 to 2 g-C/L. As a result, the increase in concentration of NaHCO3 up to 1.5 g-C/L increased dry weight of algae. The highest specific growth rate of S. dimorphus was 0.36 day-1 which was obtained at concentration of 0.5 g-C/L NaHCO3. pH showed a large variation range at the concentrations lower than 0.5 g-C/L NaHCO3 whereas inorganic carbon, nitrate and phosphorus removal rates were almost same at the concentrations higher than 0.5 g-C/L NaHCO3 (0.75, 1, 1.25, 1.5, 2 g-C/L NaHCO3). Their average inorganic carbon, nitrate and phosphorus removal rate were 70 mg-C/L/d, 11.3 mg-N/L/d, and 1.6 mg-P/L/d, respectively. Thus, NaHCO3 didn’t effect on inorganic carbon, nitrate and phosphorus removal rate of S. dimorphus.

Microalgae is known as one alternative energy source of the fossil fuel with the small size of 5 ~ 50 µm and negative charge. Currently, the cost of microalgae recovery process take a large part, about 20 - 30% of total operating cost. Thus, the microalgae recovery method with low cost is needed. In this study, the optimum current for Scenedesmus dimorphus recovery process using electrocoagulation techniques was investigated. Under the electrical current, Al metal in anode electrode is oxidized to oxidation state of Al3+. In the cathode electrode, the water electrolysis generated OH- which combine with Al3+ to produce Al(OH)3. This hydroxide acts as a coagulant to harvest microalgae.Before applying in 1.5 L capacity electrocoagulation reactor, Scenedesmus dimorphus was cultured in 20 L cylindrical reactor to concentration of 1 OD.The microalgae recovery efficiency of electrocoagulation reactor was evaluated under different current conditions from 0.1 ~ 0.3 A. The results show that, the fastest and highest recovery efficiency were achieved at the current or 0.3 A, which the highest energy efficiency was achieved at 0.15 A.

미세조류는 광합성 반응을 통해 대기 중의 이산화탄소를 흡수하고, 산소를 배출하며, 체내에 카로티노이드, 피코시아닌 같은 유용물질을 생성할 수 있다. 또한, 미세조류의 대사특성은 하폐수처리, 바이오연료 생산, 이산화탄소 고정 및 유용물질 생산 등 다양한 분야로 적용이 가능하고, 전 세계적으로 연구가 활발히 진행되고 있다. 이러한 미세조류의 배양방법은 open system과 closed system이 존재하는데, 이 중 closed system은 미세조류 배양을 위한 다양한 조건들을 쉽게 조절할 수 있는 반면 운영 및 유지관리 비용이 든다. 따라서 본 연구에서는 저비용/고효율의 PBR(photo-bioreactor) 운전을 위한 최적운전 조건을 도출하기 위해, aeration rate와 pH가 미세조류 대량배양에 미치는 영향을 살펴보았다. 실험에 사용한 미세조류는 Scenedesmus dimorphus를 이용했고, NO3--N 100 mg/L, PO43--P 10 mg/L로 modified BBM 배지를 사용하였으며, 광도 40 ~ 100 ㎛ol/m²/s, 광주기 24(light) : 0(dark)로 설정하고 working volume 2 L인 photo bioreactor를 batch로 운전하였다. Aeration rate는 0.1 ~ 1 vvm, pH 7 ~ 10로 설정하여 실험을 진행하였다. Aeration rate이 Scenedesmus dimorphus 의 성장에 미치는 영향을 평가한 결과, 0.3 vvm과 0.5 vvm 에서 높은 성장량을 나타냈다. 무기탄소의 공급량이 많은 1 vvm 조건에서는 성장량이 다소 낮게 나타났는데, 이는 과도한 폭기로 인해 미세조류에 미치는 전단응력이 증가하여 성장에 저해를 유발한 것으로 사료된다. 폭기조건의 경제성을 고려하여 0.3 vvm을 유지하는 것이 적정조건으로 도출되었다. pH가 Scenedesmus dimorphus의 성장에 미치는 영향을 평가한 결과, pH 9에서 가장 높은 성장량을 나타냈다

미세조류는 세계적으로 고갈되고 있는 화석연료를 대체할 차세대 신재생 에너지로 주목을 받고 있으며, 일반적인 미세조류 배양 공정에서 회수비용은 약 20~30%로 많은 부분을 차지하고 있어, 경제적인 회수방안이 필요하다. 본 연구는 경제적인 미세조류 회수방안을 위해 스스로 침전하게 되는 autoflocculation(AF)법과 응집제(PAC) 주입법에 관한 연구를 진행하였다. AF는 미세조류가 자발적으로 floc을 형성하여 침전하는 것이며, 미세조류의 광합성에 의한 pH 상승으로 인해 액상에 존재하는 calcium, magnesium 이온 등과 결합하여 침전물을 형성하며, 형성된 침전물은 양전하를 띄어, 음전하를 가지는 미세조류와 반응하여 침전물을 형성하는 방법이다. 실험에 필요한 미세조류(Scenedesmus dimorphus)를 배양하기 위해 용량이 20L인 원통형 반응기를 사용하여 미세조류 농도가 2 OD가 될 때까지 배양한 후 실험하였으며, jar-test기를 이용하여 AF가 일어나는 최적 조건을 찾기 위해 pH 7~12, Mg2+ 주입농도 0~100 mg/L, 침전시간 5~20 min을 달리하였으며, PAC을 이용한 실험 시 pH 5~8, 주입농도 0~120 mg/L 로 달리하여 실험을 진행하였다. 응집효율은 미세조류 회수 후 광생물 반응기(PBR)에서 미세조류 재배양을 고려하여 85~90％의 응집효율이 적절할 것이라 판단하였고, 실험결과 AF가 일어나는 적정 pH는 11.5, Mg2+ 적정 주입농도는 100 mg/L로 나타났으며, 침전시간에 따른 응집효율 변화는 5~20 min에서 약 2% 응집효율 변화가 나타나 침전시간은 5 min이 적절할 것이라 판단하였다. 응집제(PAC)를 이용한 실험결과 적정 pH 범위는 6~8, 적정 주입농도는 60 mg/L로 나타났으며, 이상의 농도에서는 응집효율에서 큰 차이가 나타나지 않았다.