Research On Optimization Of Sludge Alkaline Anaerobic Fermentation For Volatile Fatty Acids Production

With the increasing amount of sewage sluge produced by inlarged waste water quantity, sludge treatment as well as disposal has become an urgent problem. Meanwhile nitrogen and phosphorus removal efficiency in low C/N sewage treatment plants is restricted due to lack of carbon source. Anaerobic fermentation process can effectively transfer particulate organics in excess sludge to easily degradable organics, such as volatile fatty acids, whose addition can greatly improve the sewage nitrogen and phosphorus removal efficiency.In this study, the performance of anaerobic alkaline fermentation for acid production from activated excess sludge was investigated. A static fermentation experiment was carried out to study the influence of different alkali types on sludge hydrolysis and addification performance, and the influence of temperature and sludge retention time were subsequently investigated by running four continuous-flow stirred tank reactors. Finally, the optimum process conditions of the sludge anaerobic alkaline fermentation were put forward.First of all, by the static sludge fermentation experiment, the influence of different pHs and alkalis on soluble productions were studied, the results show that, the alkaline conditions are benifit to the sludge hydrolysis and acidification process, the concentration of dissolved productions has reached the maximum at pH10.0. At the same pH, NaOH is obviously more conducive to sludge hydrolysis process, while the effect of the two bases are almost the same for volatile fatty acid production. Therefore, pH10.0and the addition of Ca(OH)2were taken as optimum operating conditions for continuous flow experiments.Then, the experiment using CSTR was carried out to study the influence of different temperatures on the performance of sludge fermentation and acidification. Results found that under SRT8d and pH10.0adjusted by Ca(OH)2, high temperature is benefit to sludge hydrolysis and organic acidification, and the production of protein, carbohydrate and SCOD gradually increase with temperature upgrade from15℃to55℃, while volatile fatty acids production increases firstly and then decreases with temperature over35℃. The dissolved concentration of hydrolysis products reach the highest SCOD concentration of4193.8mg/L at temperature55℃, while volatile fatty acids production achieves its higher yields of1772.3and1995.1mg/L at25℃,35℃, respectively.Finally, the research on the influence of different sludge retention time on fermentation and acidification shows that with the sludge retention time lenthens from4d to10d, sludge hydrolysis degree increase gradually, and the highest SCOD concentration of3432.7mg/L is observed when the sludge retention time is10d, which is50%higher than that of the SRT4d. However, concentration of volatile fatty acid reaches the highest yield at SRT6-8d, and when sludge retention time increases to10d, volatile fatty acid concentration decreases.