The Uptake Of Nitrogen And Phosphorus And Cell Responses Of Chlorella Vulgaris Under The Stress Of Quaternary Ammonium Compounds

The removal of nutrients is becoming an important priority for wastewatertreatment plants due to eutrophication caused by excessive discharge into theenvironment. Algae can take up nutrients for growth and assimilate them into cellularconstituents, thus achieving pollutants significant reduction in a moreenvironment-friendly way. However, some potential toxic chemicals, such assurfactants are discharged within the wastewater. Though surfactants usually coexistwith nitrogen and phosphorus in water treatment, the effect of surfactants on thesorption of nitrogen and phosphorus by algae is very limited.In this study, growth of Chlorella vulgaris and uptake of nitrogen andphosphorus, and effect of four kinds of QACs （typical cationic surfactants） on growthof Chlorella vulgaris and uptake of nitrogen and phosphorus were investgated. Underthe stress of cetyltrimethyl ammonium bromide （CTAB）, cell responses （includingvariance of chlorophyll fluorescence, cell viability, esterase activity and cellularmacromolecular composition） were investigated to explore the correspondingmechanisms in a six-day experiment by means of confocal laser scanner microscopy（CLSM）, spectrophotofluorimeter and fourier transform infrared spectrometry（FT-IR）.（1） With nitrogen source of NH4-N, growth of Chlorella vulgaris could bestimulated by low concentration of N （below10mg/L）. While it is higher than10mg/L, growth of Chlorella vulgaris was inhibited. With nitrogen source of NO3-N,growth of Chlorella vulgaris was stimulated with the increase of concentration of N.When it increased from5mg/L to20mg/L, growth rate of Chlorella vulgarisincreased from0.848×10⁶cells/（mL d） to0.914×10⁶cells/（mL d）. More NH4-N couldbe removed than NO3-N by Chlorella vulgaris, and the removal efficiency decreasedwith the increase of initial concentrarion. When initial concentration of N increasedfrom5mg/L to20mg/L, the removal efficiency of NH4-N and NO3-N decreased from98.8%and88.9%to48.4%and49.7%. The average removal rate of NH4-N washigher than that of NO3-N. With initial N concentrarion of10mg/L, removal rates ofNH₄-N and NO₃-N were1.608mg/（L·d） and1.277mg/（L·d）, respectively. Removalof TP by Chlorella vulgaris could be divided into two phases （fast adsorption andslow absorption）, and the removal efficiency was slightly effected by nitrogen sourceand the initial concentration. （2） Growth of Chlorella vulgaris could be significantly inhibited by QACs, andthe inhibition increased according the alkyl chain length. When concentration ofC10-TMAB, DTAB, TTAB and CTAB was8.0,1.2,1.0and0.6mg/L, growth ofChlorella vulgaris was totally inhibited. Meanwhile, uptake of NH4-N wassignificantly inhibited by QACs with the same trends of algal growth. Thus CTABhad the strongest inhibition ability, and when it ranged from0to0.6mg/L, removalefficiency of NH4-N decreased from98.5%to17.5%. Effect of the four tested kindsof QACs on the removal of TP was similar to NH4-N and algal growth. Effect ofQACs on the uptake rate of NH4-N was more significant than that on TP, and thesharp difference was disappeared with the increase of the alkyl chain length. In thetested concentration of C10-TMAB, the max inhibition efficiencies on uptake ofNH4-N and TP were70.3%and33.2%, while they were82.5%and83.0%for CTAB.（3） Cell responses of Chlorella vulgaris under the stress of CTAB, arepresentative for QACs, were investigated. The results suggest that QACs inwastewater inhibit nutrients uptake by algae significantly through declining algal cellactivities. When the concentration of CTAB increased from0to0.6mg/L, algal cellresponses showed a decline in photosynthesis activity as indicated by the increase ofChlorophyll autofluorescence from2.9to25.3a.u.; and a decrease of cell viabilityfrom88%to51%; and also a drop in esterase activity as indicated by the decrease influorescence of fluorescein diacetate stained cells from71.5to4.7a.u.. Additionally,FT-IR spectrum of algal cells showed distinct absorption bands over the wavenumbers ranging in4000-400cm^-1. These bands were attributed to C-H stretching ofmethyl and methylene groups of lipids (2970-2850cm^-1), N-H bending of amidesfrom proteins (amide II,-1540cm^-1), and P=O stretching of phosphodiester fromnucleic acid (DNA and RNA,-1245cm^-1). It confirmed that a transcription andtranslation response in algal cellular macromolecular composition was stimulated byCTAB.