Studies On The Impact Of Surfactants To Duckweed In The Treatment Of Eutrophic Water

With population growth and rapid development of industry and agriculture, eutrophication in waters has become a worldwide environmental issue. Eutrophication is one of water pollutions which caused by receiving excessive nutrient substances such as nitrogen and phosphorus. Among various methods for treating eutrophic water, phytoremediation technology of aquatic plants shows great ecological significance and developmental potentials. Duckweed, a common aquatic plant with superior growth performance and wide applications, is capable of decomposing, absorbing and transforming nitrogen, phosphorus and organic matters. In recent years, sewage treatment using duckweed has become one of the hottest research areas in environmental protection. However, as a widely used fine chemical product in almost every industry, surfactant would be toxic to the aquatic plants of improving water quality when entering water. In this research, indoor culture method was applied to investigate the effects of different surfactants on duckweed growth and its absorption of nitrates and phosphates, which would be an important reference for assessing the surfactants’ecological harm and screening plants for ecological remediation. Major findings are listed as follows:With the absence of surfactant, Spirodela polyrrhiza grew well in simulated eutrophic water and showed great capability in nitrogen and phosphorus removal. The order of the effects of three surfactants to total phosphorus removal of Spirodela polyrrhiza was anionic surfactant LAS> cationic surfactant CTMAB> nonionic surfactant Tween-80. In concentration of0.1～1.0mg/L, the order of their effects to ammonia nitrogen removal of Spirodela polyrrhiza was Tween-80> CTMAB> LAS. And the Spirodela polyrrhiza’s absorption of total phosphorus could be more vulnerably affected than its absorption of ammonia nitrogen. Under10.0mg/L, the Spirodela polyrrhiza was significantly harmed by the presence of LAS and CTMAB, behaving negative absorption rate and growth. Thus this level of LAS and CTMAB had exceeded the tolerance limit of Spirodela polyrrhiza and could cause its death. Nonionic surfactant had relatively lowest toxicity to Spirodela polyrrhiza comparing to anionic and cationic surfactants.Under the stress of LAS, the activity of POD in Spirodela polyrrhiza increased first and then decreased with the increase of LAS concentration and in1.0mg/L reached maximum activity. When reaching10.Omg/L LAS, induced CAT enzyme activity increased dramatically in24hours, which was to eliminate the superoxide radicals in cells generated by the presence of surfactants and to maintain the cells’ balance. With the time increase, the CAT enzyme activity in Spirodela polyrrhiza tended to similarity under all levels of surfactants. Under low concentrations of active oxygen, the plant cell could eliminate that by elevating the activity of its protective enzyme; however, high concentrations of active oxygen could damage the adjustment and make the cell suffering serious peroxide harm.After7days’ cultivation in highly concentrated phosphorus solution,50mg/L LAS and10mg/L CTMAB respectively would cause the negative growth of Lemma aequinoctialis. Under same levels, the order of the effect of three different types of surfactants to total phosphorus removal of Lemma aequinoctialis was cationic surfactant CTMAB> nonionic surfactant OP-10> anionic surfactant LAS, and that to mass growth of Lemma aequinoctialis was CTMAB>LAS>0P-10.