Investigation Of Municipal Sludge Biophysical Drying And Its Influence Factors

Bearing the properties of high moisture content and high viscosity, themechanically dewatered municipal sludge still has the moisture content ofover80%, which is difficult to be removed, hence, causing comparativelyhigher disposal cost, and has become a key issue.In this study, we investigated18sewage treatment plants in Kunshan city,based on which, the technics adopting “combined bio-physical drying” for thetreatment of sludge with organic content>45%was developed. Taking VSand O2as electron receptors, the biophysical drying makes use of themetabolic heat originates from microorganism in the sludge as energy,combined with the enforced ventilation to achieve the efficient removal ofwater in sludge.The impact of initial properties of sludge on biophysical drying was investigatedin a self-made dynamically rotating reactor. As shown in the results, the dynamicrotating process can effectively improve the homogeneity of sludge; pH stayedbetween6.3and7.5; the oxygen content of sludge decreased initially, and thenstabilized at19%. These are not the limiting factor of biophysical drying process.When the ratio of dewatered sludge: tree bark was7:3, ratio of dewatered sludge:tree bark: recycled sludge was9:3:0.5, the maximum temperature of59~67℃wasachieved in the first48h, and stayed72h at above50℃. After treatment of168h,the moisture content of sludge was decreased by43.5%~57.6%, from78.6%~74.1%to61.8%~60.9%.Parameters during the drying process are: ventilation, heating temperature,rotating frequency. Results shown, moisture content of sludge with150L/(kgVS h)ventilation and120h retention time was60.94%, decreased by52.26%The optimalrotating frequency was8times/day, with retention time of144h, thus the finalmoisture content of sludge was56.75%, decreased by55.59%.The key problem of improving drying of sludge through metabolism ofmicroorganism lies on the dimunition of heat loss in the sludge. In this study, we optimized the reaction parameters of biophysical drying, the retention time wasdecreased from168h to96h, and the moisture content of dewatered sludge can bedecreased to50%. The comparatively low organic consumption during rapid dryingof sludge endows it the further utilization of composting and incineration, hence,shows great economic feasibility.