Research Of Inhibitor For Citric Acid Fermentation And Pretreatment In Anaerobic Effluent Recycling Process

Based on fermentation ecological engineering theory and "ethanol-methanedual-fermentation coupled" process, the process of recycling anaerobic effluent as cookingwater for citric acid fermentation was studied. Fermentation process of citric acid-producingstrain Aspergillus niger Wml-016was optimized in shake flasks. The effects of sporeinoculum level, seed age, initial pH，inoculum quantity, liquid volume in flask and rotationspeed were studied with single factor experiments, and the optimal fermentation conditionwas obtained as followed: above7xl05spores/mL，20-22h，5.5，15%，40mL/500mL and260r/min respectively. Stable citric acid yield and high repeatability were gained on the optimizedcultivation condition, which guaranteed the accuracy of results for late experiments.Anaerobic eflfuent had no effect on spore germination and liquefaction as cookingwater. More H2SO4was needed for adjusting pH because of alkalinity. Recycling anaerobiceffluent for citric acid fermentation caused lower citric acid yield and longer fermentationperiod, which indicated existence of inhibitors for citric acid fermentation. The quality ofanaerobic eflfuent was analysed as followed; turbidity295-324NTU; COD2856-3300mg/L;alkalinity1900-2830mg CaCOs/L; pH7.05-7.9; ammonia nitrogen120-230mg/L; lowconcentration of Cu2+, Fe3+，Mn2+and high concentration of Ca2+，K+，Na+.Some potential inhibitors were investigated by shake lfask experiment. The resultsshowed sludge in anaerobic eflfuent would inhibit citric acid fermentation, and the criticalinhibitory concentration of sludge was0.6g/L(dry weight). The ammonia nitrogen wouldinhibit citric acid fermentation, which was caused by excess of nitrogen source of medium butby maillard reaction. Cu2+, Fe3+and Mn2+didn’t cause inhibition at current concentration.Ca2+，K+and Na+had inhibitory effect on citric acid fermentation at current concentration,which reduced citric acid yield by4%，4%and8%respectively.Polymeric aluminium (PAC) combined anionic polyacrylamide (APAM) flocculationtreatment was high-eiffcient on sludge removal at concentration of300mg/L PAC and5mg/LAPAM, which decreased sludge quantity to0.27mg/L. Ammonia nitrogen was removed andalkalinity was reduced by air stripping treatment. Air stripping combined lime softening andflocculation treatment removed ammonia nitrogen, decreased hardness and alkalinity. Thecitric acid yield of treated sample was34.6%higher than the untreated sample and5.8%lessthan the deionized water sample.