Research On The Removal Efficiency Of Aqueous Nonylphenol By Immobilized Microalgae

Nonylphenol (NP) is a typical endocrine disruptor with estrogenic effects and it is widely distributed in aquatic environment. NP causes serious harm to physiology of various aquatic organisms, including reproduction, endocrine, immune, carcinogenesis and genetic toxicity. However, the technique research of NP removal in aquatic environment is limited. Cost-effective techniques are urgently required to remove NP from contaminated waters for reducing its ecological risks. The efficiency of NP removal and degradation with alginate-immobilized microalgae Scenedesmus obliquus (fresh water alga) and Phaeodactylum triconutum (marine water alga) were studied by the way of simulation in laboratory and used gas chromatography-mass spectrometry (GC-MS) method to measure the content of NP. To establish the optimal immobilized conditions, this study mainly explored the distribution and degradation of NP during the microalgae biological treatment process and compared the advantages and disadvantages of NP removal between immobilized microalgae and free microalgae cultures. This study provided the scientific basis for removal and purification research of NP in natural water.The followed conclusions all were showed in this study. (1) The optimal immobilized conditions by alginate-immobilized microalgae Scenedesmus obliquus and Phaeodactylum triconutum were 2% w/w (the same unit for all solutions, hereafter) sodium alginate,3% calcium chloride and the initial algae concentration was 1.0×106 cells/ml. The hardness, strength, stability and microalgae growth of algae beads were quite well under this condition and the beads were the most suitable for using to subsequent experiment. (2) There was no significantly influence on the removal and degradation percentage of NP by different algae beads usage. Therefore, this study found that it was most suitable for experiment research by selecting 160 algae beads (the initial concentration was about 1.0×106 cells/ml) in consideration of algae growth and cost. (3) The algal cell density and chlorophyll a content in alginate-immobilized microalgae Scenedesmus obliquus were increased in comparison with its free microalgal cultures; both free and immobilized algae could effectively remove NP in fresh water. At 72 h, the removal percentage of NP in low (10 μg/L) and high (100 μg/L) pollution load reached about 90%; At 120 h, the degradation percentage of NP in different groups reached about 80%. (4) The chlorophyll a content in alginate-immobilized microalgae Phaeodactylum triconutum were increased in comparison with its free microalgal cultures; both free and immobilized algae could effectively remove NP in sea water. At 96 h, the removal percentage of NP in low (1 μg/L) and high (10 μg/L) pollution load reached nearly 100%; At 168 h, the degradation percentage of NP in different groups reached above 95%.In addition, algae beads were easily harvested and recycled, such as the production of biodiesel. Immobilized beads are relatively larger in size compared to microalgae free cells culture, a simple filtration method (e.g. sieving) would be sufficient to separate the beads from water. Meanwhile, immobilization technology could improve chlorophyll a content in the microalgal and promote the microalgal growth. Hence, handling of microalgae biomass will become easier and feasible to be implemented in commercial scale. In short, the immobilized Scenedesmus obliquus and Phaeodactylum triconutum has a broad application prospect in the removal of NP from wastewater under photo-auto-trophic conditions.