This study was designed to evaluate the toxicity to Closterium ehrenbergii using new indexes for nonionic and anionic surfactants. The new indexes were cell growth (A), normal zygospore forming ratio (Y) and asexual-sexual EC50 Ratio (R_EC50) . An anionic surfactant (Sodium dodecyl sulfate) was more toxic than nonionic surfactants (Polyethylene oxide oleate sorbitane, Polyethylene oxide oleate glyceryl, Polyethylene oxide oleate castor oil) . Nonionic surfactant toxicity tended to increase with decreasing the number of ethylene oxide (EO) groups. The Closterium ehrenbergii test by new indexes was good in sensitivity and agreement with other published results. In view of several inherent advantages including rapidity (4days in test), experimental simplicity (no skills), cost-effectiveness (low cost bioassay) and variety morpological responses (visiable) . The Closterium ehrenbergii test by new indexes offer promising potential for ecotoxicological applications.

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The nitrification rates under additional organic loading were measured with the sequencing batch reactor (SBR, 10l) . For the experiments, the settled wastewater of the sewage treatment plant in H city was used, and the temperature and MLSS were controlled at constant. Added organic matters were sodium acetate, ethanol and glucose. The nitrification rate under the condition of dissolution rate-determining (DO=0.3-0.5mg-O/l) were calculated from the change of NO₃-N concentration at SBR. Those under the condition of reaction rate-determining (DO>2mg-O/l) were calculated from the analogous data with another fully aerated reactor. In addition, total oxygen utilization rate (Rr) and oxygen utilization rate for oxidizing organic matter (C-Rr) were measured.
From those results, the relationship among the kinds and quantities of organic matters, nitrification rates and oxygen utilization rates (Rr, C-Rr) were analyzed.

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