Pilot-scale Study On Anaerobic Fermentation Of Sewage Sludge For Volatile Fatty Acids

Bio-production of short-chain fatty acids (SCFAs) from anaerobic digestion can bean important way to realize the reduction and resource of sewage excesssludge.Meanwhile, volatile fatty acids can be use as the carbon source to satisfy theshortage of municipal wastewater treatment plant, which use biological nutrient removal(BNR) to removes TN and TP from wastewater. To solve the practical problems，apilot-scale study of fermentation and acidogenesis of sewage sludge was carried out in aself-mixing anaerobic fermentation column reactor in Bai Dang wastewater treatmentplant New District of SuZhou based on the bench·scale experimental study having beencarried out previously.In this dissertation, change rule of the dissolving out and hydrolysis of solubleorganic matter as well as the output ratio of volatile fatty acids during the startup ofpilot-scale test reactor was studied.After the stable operation of the reactor,furthermorestudies were carried out on sludge retention time and internal reflux,in order toinvestigate the the relationship between VFAs and consumed organic matter, to reveal theprinciple of the impact and to conclude of the best operating conditions of the process.Main results of this dissertation were shown as follows:①The results of laboratory test, which under the condition of the mediumtemperature and the unadjustment of pH,show that sludge retention time for8d forexcess sludge fermentation to produce volatile fatty acids would be the optimumcondition, it provides reference for the pilot-scale test reactor’s startup operationparameters.②The pilot-scale reactor was started successfully with a step-by-step culture．Thepilot-scale reactor was stable for various parameters after operated for80days or so, theefficiency of hydrolysis acidogenesis improved, what’s more the amount of volatile fattyacids start to accumulate.③The affect of sludge retention time on the hydrolysis and acidogenesis of excesssludge were studied in the pilot reactor, results show that the sludge retention time for10d for excess sludge fermentation produce the high mount of volatile fatty acids,and theproduction of volatile fatty acids was as far as0.36gVFAs/gVSS.④At the high amount production of volatile fatty acids of sludge solids retention time(10d), the effect of agitation on the hydrolysis and acidogenesis of excess sludgewere studied in the pilot reactor by adjust the internal reflux ratio,the results show thatinternal reflux mixing effectively improve the mass transfer effect of the reactor,andcontribute to the hydrolysis and acidogenesis of excess sludge.When the internal refluxratio was300%,the high amount production of volatile fatty acids was achieved,and thevalue was0.58gVFAs/gVSS.