Study On Green Flocculant And Bacillus Thuringiensis Protector

Poly (γ-glutamic acid)(γ-PGA) is a water soluble polyamino acids which have excellent characters such as completely biodegradable, non-toxic to human and environment.γ-PGA and its derivates have potential applications in a wide range of industry and agriculture such as food, cosmetics, medicine and manure. Thus this natural and multifunctional biopolymer is worth researching and developing to a commercial material. In this paper, the effect ofγ-PGA as green flocculant and Bt protector are studied, which are applied in environment and agriculture.In the present study, the flocculation properties and mechanism of high molecular weightγ-PGA had been investigated. In kaolin suspension, flocculating activity ofγ-PGA was stimulated by adding cations and varied with the valency, variety and dosage of cations. The flocculating activity could keep highly for 48h and would descend when prolonging the flocculant solution age any longer resulted from decomposition ofγ-PGA. The Zeta potential of flocs was measured and the results indicated that flocculation occurred in high negative Zeta potential. During flocculation process, huge claviform flocs were formed in properγ-PGA dosage. We also examined re-suspension (under sonication) and re-flocculation of the sediment formed in the initial flocculation experiments. Re-suspension of the sediment formed in the initial flocculation experiments resulted in the formation of a stable dispersion. This result was attributed to breakage of the chain of high molecular weight polymer by physically severing during re-suspension. These results showed that in flocculating processγ-PGA molecule mainly formed bridge among kaolin particulates.γ-PGA could effectively reduce high temperature damage to insecticidal active components of Bacillus thuringiensis (Bt) broth during spray drying, and the best protective effect was obtained by adding 0.30%(w/v)γ-PGA in Bt broth.γ-PGA also could remarkably increase the resistance of Bt against ultraviolet (UV) irradiation, the insecticidal activity remaining of Bt containing 0.30%(w/v)γ-PGA could maintained 35.87% after 5h-irradiation. The potted plant experiment suggested that Bt sample containing 0.30%γ-PGA had a longer residual period, for its resistance against sunlight inactivating and rainwater scouring was effectively improved byγ-PGA.