[Toxicity and influencing factors of chlorine dioxide to chironomid larvae].

The toxic effect of chlorine dioxide to the different instar larvae of chironomid was studied using raw water as test sample. Furthermore, the effect of temperature and contact time on toxicity of chlorine dioxide was observed. It was found that chlorine dioxide possessed significantly toxic effect, and the LC50 value of chlorine dioxide to the 4th instar larvae was 0.41 mg/L(24 h). The toxicity of chlorine dioxide declined with the development of instar larvae. The 1st instar larvae was most sensitive to chlorine dioxide among the four instars, and the LC50 value of chlorine dioxide to the 4th instar was 1.78 times of that of the 1st instar larvae. Temperature was proved to have significant positive effect on chlorine dioxide toxicity, and the toxicity at 30 degrees C was 2.16 times of that at 15 degrees C. The toxicity of chlorine dioxide was significantly improved with the contact time increasing from 12 h to 24 h, while it did not make much difference with the contact time increasing to 36 h.

[Toxicity and influencing factors of liquid chlorine on chironomid larvae].

The excessive propagation of Chironomid larvae (red worm) in the sedimentation tanks is a difficult problem for the normal function of waterworks. The toxic effect of liquid chlorine on the different instar larvae of Chironomid was studied using distilled water as test sample. Furthermore, the effect of pH value, organic matter content, ammonia nitrogen, and algae content on toxicity of liquid chlorine was observed. The results show that the tolerance of Chironomid larvae to liquid chlorine is strengthened with the increase in instar. The 24h semi-lethal concentration (LC50) of liquid chlorine to the 4th instar larvae of Chironomid is 3.39 mg/L. Low pH value and high algae content are helpful to improve the toxic effect of liquid chlorine to Chironomid larvae. In neutral water body, the increase in organic matter content results in the decrease in the death rate of Chironomid larvae. The toxicity of liquid chlorine differs greatly in different concentrations of ammonia nitrogen. The death rate of the 4th instar larvae of Chironomid in raw water is higher by contrast with that in sedimentation tanks water for 24h disposal with various amount of liquid chlorine.

[Study on the combination of preozonation and post-ozonation-BAC process for drinking water treatment].

This study was conducted to illustrate the effectiveness of preozonation or O3-BAC or combination of these two process in controlling DBPs for treating a dam source water in South China through SBR and continuous flow (200 L/h) experiments and the variables in the treatment train included the point of preozonation with respect to coagulation; the point of ozonation with respect to BAC, the ozone dosage required for preozonation and the Br- content of raw water. Results indicated the reduction in DBP formation potential closely paralleled the reduction in UV absorbance, and trihalomethane and haloacetic acid formation potential can be removed under a dose of preozone at 0.5 - 1.0 mg/L, at the same time, ozone by-products (bromate and formaldehyde) can be controlled in low level. The continuous flow experiment results show that combination of preozonation and O3-BAC process has obviously positive effects on the removals of particles with a size above 2 microm, COD(Mn), and TOC. However, DBPs formation can be controlled by the removal of organic matters.