Research On The Condition Of Propionic Acid Degradation In Anaerobic Biological Treatment

Propionate is an important intermediate in the anaerobic degradation process. When an anaerobic reactor is overloaded, propionate tends to accumulate in the mixed liquor, resulting in the lowering of pH, and is very difficult to remove during recovery. Based on chemical free energy analysis, propionotrophic acetogenesis is thermodynamically unfavorable, unless the by product hydrogen can be readily removed by hydrogentrophic bacteria. Therefore, the degradation of propionate is one of the rate-limiting steps in anaerobic biological treatment process. It is well known that propionate degradation is affected by environmental factors such as pH, hydrogen partial pressure, VFA and temperature etc. The objectives of this work were (1) to show the characteristics of propionate degradation in the continuous anaerobic process, (2) to investigate influence of factors of the propionate concentration and pH on propionate degradation in the anaerobic process.Continuous experiments were conducted to investigate degradation characteristics of propionate-degrading sludge, a mesophilic methane production reactor was operated at a hydraulic retention time (HRT) of 10 days, corresponding to a propionate loading rate (LRHpr) of 667 mg/L·d or 1,334 mg/L·d. It was found that the anaerobic system have a greater impact if the propionate loading rate become higher. The system effluent COD reached 10,000mg/L, and the concentration of total VFA up to 1,800 mg/L at LRHpr1,334 mg/L·d, these two parameters are both bigger than value at LRHpr 667 mg/L·d. The propionate is more than acetate in the anaerobic system at LRHpr1,334 mg/L·d, and it has a opposite result at LRHpr 667 mg/L·d. Increase OLRHpr also reduce the methane production and the content of methane in the biogas.Batch experiments were conducted to investigate degradation characteristics of propionate-degrading sludge at propionate concentration from 500 mg/L to 3000 mg/L. The maximum accumulative methane production and methane-production rate were 25 mL and 3.5 mL-CH4/d, respectively at propionate concentration 1500mg/L, simultaneous the removal efficiencies for the propionate and COD were 97 % and 75% respectively.Another Batch experiments were conducted to investigate degradation characteristics of propionate-degrading sludge change pH from 5 to 10 at propionate concentration 1500 mg/L. As a result, the maximum accumulative methane production and methane-production rate were 57mL and 4.6mL-CH4/d, respectively at pH 7.0, simultaneous the removal efficiencies for the propionate and COD were 88 % and 88.5% respectively.