The Anaerobic Degradation Characteristics Of Amino Acid Process Condensed Water Under Acidic PH Condition

Amino acid process condensed water（AAPCW）,which contains organic matters（mainly acetate）with characteristics of low molecular weight and low pH values（5.6-5.8）,was generated from the amino acid production processes including amino acid fermentation,product concentrating and crystallization.Mixing condensed water directly into the glycosylation process or cycling to the cooling water system for reuse were the main methods in amino acid fermentation industry.However,if the low molecular organic acid cannot be eliminated effectively,it will affect the whole fermentation process and reduce the repeated utilization of water resources.Therefore,how to purify the amino acid process condensed water with high efficiency but low cost has become the bottleneck problem of water resources regeneration and utilization in the amino acid fermentation industry.According to the water quality characteristics of AAPCW,the present study first put forward to establish an anaerobic system for the treatment of this kind of polluted water under acid pH condition,and produced methane which could used as an energy resource.Therefore,AAPCW was used as anaerobic fermentation substrate,and the researches such as the study of Biochemical Methane Potential（BMP）test under conditions of acid pH,start-up and running characteristics of reactor,organic shock loads test and dynamics of substrates degradation were carried out.Research results were as followed.（1）BMP test showed that anaerobic digestion could achieve a COD removal efficiency of more than 96% and an acetate removal efficiency of more than 98% under conditions of neutral and acid pH respectively（the reacting time were 132 and 156 hours respectively）.In addition,AAPCW was found to has a good alkalinity adaptive ability in the anaerobic degradation process,the methane-producing ability and activity were good even under the acid pH condition,methane gas production reached 340 m L CH₄/gCOD which significantly higher than neutral pH conditions,Maximum specific methane production rate（μmax·CH₄）reached 202.2m L CH₄/gVSS·d which amounted to 85% of neutral pH conditions.（2）The steady operation of UASB reactor under acid pH condition was achieved by using start-up strategies of gradually reducing the influent pH values.When the HRT was 6h,the removal efficiencies of COD and acetic acid reached 90% and 95% respectively,with steady effluent pH value of 6.35.The acid-tolerant methanogenic sludge aggregates could be cultivated in the UASB reactor with the value of SMAp H5.6 reaching to 209.8CH₄mL/gVSS·d,the methane yield and methane production rate were 1.9L/d and 320 m LCH₄/gCOD respectively,which indicated VFA could be converted to methane timely under the condition of acid influent water.As a result,the reactor pH could maintain stability.In addition,due to the decline of the reactor pH value,the concentration of coenzyme 420 increased from 0.0016mmol/L to 0.0046mol/L,which indicated a significant increase of hydrogenotrophic methanogenic activity,and the enhancement of hydrogenotrophic-methanogenesis was obviously in the reactor.（3）By testing the organic shock loads of reaction system though reducing the HRT from 24 h to 4 h,it could be showed that the anaerobic system had good resistance capability for hydraulic shock loading,which was caused by the method of gradual acclimation.It had good removal rates of pollutants and did not occur the phenomenon of propionic acid accumulation and sludge losses.When the HRT was 2h,the reactor pH values showed a descreasing trend and other anaerobic indicators showed some deterioration,due to the short contacting time between microorganism and substrates caused the acetic acid could not be converted to methane timely.（4）The dynamics model of anaerobic degradation in the UASB was analyzed.According to the result,the yield coefficient Y,death rate constant Kd,maximum specific growth rate μmax,half saturation constant KS and empirical coefficient β were 0.0222gVSS/gCOD,0.0053d^-1,0.0327d^-1,0.0412g/L and 0.0104gCOD/gbiomass in the Monod and Contois equation,respectively.The corresponding kinetic parameters Rmax obtained by the fitting analysis of Modified Stover-Kincannon matrix degradation kinetic model reached 24.0616gCOD/（L·d）,which suggested that UASB reactor had a high removal rate of substrates degradation under the acid pH condition.A comprehensive analysis and comparation of three common substrates degradation kinetic model which were used for anaerobic degradation of UASB,was carried out in this study.The results showed that Grau second-order and Modified Stover-Kincannon model were more suitable than Monod and Contois model in this study,and the linear correlation coefficient was 0.99.Meantime,the model of Grau second-order and Stover-Kincannon exhibited much more efficiency when predicting the performance of UASB reactor.