Optimizing emulsan production of A. venetianus RAG-1 using response surface methodology.

Statistical experimental design was used to optimize medium constituents for emulsan production by Acinetobacter venetianus RAG-1 in batch cultivation. The factors affecting emulsan production were screened by a two-level factorial design, and the optimal concentration of medium constituents for emulsan production were determined by the method of steepest path ascent and central composite experimental design. Experimental results showed that the optimal medium constituents were 9.16 g/L ethanol, 8.2 g/L KH(2)PO(4), 23.32 g/L K(2)HPO(4), 5.77 g/L (NH(4))(2)SO(4) and 0.354 g/L MgSO(4)*7H(2)O. Under this optimal composition, the predicted emulsan production was 72.198 mg/L, and experimental value was 73.312 mg/L for 80 h culture in the shake flasks, and the emulsan yield by A. venetianus RAG-1 was enhanced nearly 1.48-fold (from 49.5 to 73.312 mg/L). Based on the results, we identify the optimal medium constituents for emulsan production and could take advantage of strategy for scale up the fermentation of emulsan production.

Polyelectrolyte conditioning for iron-hydroxide-containing sludge produced from electroflocculation of fermentation wastewater.

The purpose of this study is to investigate the application of chemical conditioning method for the post-electroflocculation wastewater sludge treatment with polyelectrolytes of varying ionic characters, namely anionic, cationic and nonionic flocculating agents. Electroflocculation, a combination of the processes of electroflotation and electroprecipitation, was found effective to remove the organic and color components in monosodium glutamate fermentation wastewater. The settleability and dewaterability of the separated sludge, containing 15-20% of iron hydroxides, increased 35% and 60% due to polymer conditioning through a jar-test apparatus. The influence of shear conditions and polymer dose on the floc size, zeta potential, filterability and dewatering performance, and shear resistance of sludges was investigated. Experimental results showed that the anionic polymer acts as a better flocculating agent than both cationic and nonionic polymers, and the optimal polymer doses fall between 4.0 and 10.0 mg/g Fe sludge under corresponding shear rates of 200 300 rpm. This study also indicated that both charge neutralization and polymer bridging mechanisms operate in the sludge conditioning process.