Batch Kinetics Of Nutrients Uptake By Chlorella Vulgaris And Hormesis Of Growth Under The Stress Of Surfactants

Removal of nutrients has recently gained great attention due to eutrophicationcaused by excessive discharge into water bodies. The use of algae to eliminatenutrients was studied widely, because algae can take up nutrients easily. Algal growthand nutrient uptake may be influenced by potential toxic chemicals coexisting insewage, such as surfactants. The stress of surfactants on algal growth and nutrientuptake was still rare.With the understanding of the effects of initial nutrients concentrations ongrowth and nutrients removal rate. The effects of initial concentration of nitrogen andphosphorus on algal growth and nutrient uptake kinetics under the stress of surfactantswere researched in this article. In addition, the hormesis of algal growth under thestress of five quaternary ammonium salt surfactants was investigated. The followingconclusions have been gained:(1) With the increase of concentration of ammonia nitrogen, the growth ofChlorella vulgaris was promoted and then inhibited, the increase of concentration ofnitrate nitrogen and total phosphorus can promote the growth of C. vulgaris; Thegrowth rate of C. vulgaris under the stress of surfactants was observed to reduce tocertain degrees in surfactants treated groups. CPB, CTAC decreased algal growth ratemore evidently than LAS and Triton X-100did, while LAS-treated or TritonX-100-treated samples was only slightly lower;The maximum growth rates (μm) of0.31,0.35, and0.30d-1, and half-saturation constants (Km) of0.22,0.29, and0.02mg/L were determined by Monod model of ammonia nitrogen (NH4-N), nitratenitrogen (NO3-N) and total phosphorus (TP), respectively, which indicated that theeffect of phosphorus on the algal growth is more significant than that of nitrogen. KmNwas increased by cationic surfactants, which indicated that the effect of nitrogenconcentration on the promotion action of algae growth was decreased by cationicsurfactants.However, little inhibition on the absorption of KmNunder stress of anionicor nonionic surfactants. KmPwas increased by CTAC, which indicated that the effectof phosphorus concentration on the promotion action of algae growth was decreased.(2) The removal rate of NH4-N, NO3-N and TP by C. vulgaris was decreasedwith the increasing of initial nutrients concentration. The influence of surfactants onremoval rate:CPB>CTAC>LAS, Triton X-100； With the increasing of nutrientsconcentration, the uptake rate of NH4-N, NO3-N and TP was increased and then decreased. The uptake rate of nutrients was decreased by cationic surfactants(CPBand CTAC), little inhibition on the absorption of nutrientsunder stress of anionic(LAS)or nonionic surfactants(Triton X-100) was observed;the maximum removal rate (Vm)was28.63,29.00, and10.00μg/cell·d and the half-saturation constants (Ks) was8.59,17.40, and4.70mg/L of NH4+-N, NO3--N, and TP calculated by Michaelis-Mentenequations, respectively.CTAC and CPB display a significant inhibition on VmNand KsNbut almost no influence on VmPand KsP, while LAS or Triton X-100slightly affectedVmP, VmN, KsP,and KsN, which indicated that cationic surfactant enhance the affinity ofC. vulgaris to nitrogen.(3) The biomass of C. vulgaris was promoted by low concentration of quaternaryammonium cationic surfactants（QACs）, while inhibited by high concentration ofQACs, The growth inhibition rate of chlorella under the stress surfactants wasincreased with the increasing of QACs concentration.The low concentration of thesurfactant producing hormesis and the concentration was decreased with the increaseof carbon chain length of QACs, The toxicity of surfactants was increased with theincrease of carbon chain length of QACs；The intensity of photosynthesis of chlorellawas increased by low concentration of QACs (DTAB,CTAB), while decreased byhigh concentration of QACs (DTAB,CTAB).