Inactivation of Chironomid Larva in Water with Bacillus thuringiensis subsp. Israelensis

The excessive propagation of Chironomid larva in waterworks is a difficult problem. The inactivation of Bacillus thuringiensis subsp. israelensis (Bti) on different instar Chironomid larva was studied using distilled water as test sample. Furthermore, batch experiments were performed to analyze the influence of pH value, liquid chlorine, and water temperature and ammonia nitrogen on inactivation efficiency of Chironomid larva with Bti. Based on it, removal effects on Chironomid larva in the actual raw water and pre-chlorination coagulation sedimentation water were evaluated. The results showed that Bti possessed good inactivation performance to all larval stages of Chironomid. The 24 h semi-lethal concentration of Bti to the third instar Chironomid larva was 0.423 mg/L. The inactivation rate at pH 9.2 was significantly higher than that at pH 4.4 and 7.1. The liquid chlorine had negative effects on inactivation, indicated by the decreased inactivation rate from 74.22% at liquid chlorine concentration of 0 mg/L to 15.5% at 2.5 mg/L when Bti concentration was 0.5 mg/L. Water temperature ranging from 15℃ to 35℃ did not affect the inactivation efficiency of Bti. At Bti concentration of 0.125 mg/L, the inactivation rate significantly increased from 17.32% at ammonia nitrogen concentration of 0 mg/L to 53.26% at 6 mg/L. The inactivation rate of Chironomid larva was significantly higher in actual raw water than that in pre-chlorination coagulation sedimentation water. It could conclude static immersion with Bti solution in sedimentation tank is an effective method to control Chironomid larva.