Research On The Physics And Biochemical Characteristics Of Thermal Pre-treatment Sludge

High solid sludge anaerobic digestion has been one of the most promising technologies for sludge disposal.In order to increase the advanced anaerobic digestion hydrolysis rate and gas production rate,sludge thermal hydrolysis is the most important pretreatment process of advanced anaerobic digestion.The dlivery resitance,dewatering performance and heat transfer performance of sludge are affected by the viscosity,specific resistance and thermal conductivity of sludge respectively.Besides,the COD of sludge filtrate,and the TS,VS,SS,VSS,and pH of sludge are all the conventional indexes affecting sludge anaerobic digestion with significant guidance.The effects of temperature,time and sludge solid content ratio on the viscosity,specific resistance and thermal conductivity of sludge after pretreatment were studied in this paper.The results show that the reaction temperature has a highly,general and less significant effect on the sludge specific resistance,thermal conductivity,and sludge viscosity separately.The sludge solid content ratio has a general effect on the sludge viscosity while little effect on the thermal conductivity and specific resistance.To obtain a smaller sludge viscosity and a large thermal conductivity,the hydrothermal reaction temperature and time should be controlled at 170? and 40 min.This research has discussd the influence law on the biochemical properties of sludge which are the COD of sludge filtrate,the TS,VS,SS,VSS and pH of the sludge.When the reaction temperature and time were less than 170? and 30 min,the COD increased rapidly,the TS,SS,VS and VSS decreased significantly while sludge pH decreased with the increase of temperature and prolongation of reaction time.When increasing the solid content ratio,the COD declined straightly while the sludge SS,VS and VSS raised,and the sludge solid content ratio had little effect on the pH value.For the anaerobic digestion of high solid sludge,the optimum condition of thermal hydrolysis pretreatment is 170?,30min,and 10%of solid content ratio to obtain larger filtrate COD,sludge TS,SS,VS and VSS.The influence of thermal hydrolysis on the sludge organic solids was discussed,and the change of organic removal rate of high soild ration and the reaction kinetic model of hydrolysis and dissolution were analyzed.The results show that the thermal hydrolysis has a certain effect on the dissolution of solid organic matter and the hydrolysis of organic matter in sludge,which the thermal hydrolysis temperature has more significant influence.With the time prolongation,the dissolution rate of organic matter gradually increased.The dissolution rate of high solid sludge COD closed to 40%,SS dissolution rate fluctuated between 30%and 40%,and the dissolution rate of SS was about 70%under the conditions of 170 ? and 30min.The hydrolysis of COD in the sludge transferd from the solid phase to the liquid phase,overcoming the sludge anaerobic digestion rate-limiting steps andimproving the anaerobic digestion of sludge performance.Compared with low concentration sludge,the solid matter in high solids sludge was not affected by the increase of sludge concentration.The dissolution of VSS during thermal hydrolysis coinsided with the first order reaction kinetics model and the reaction constant k had a linear positive correlation with sludge solid content.This work has great reference value for the design,operation and control of anaerobic digestion process equipment.