Abstract: Before technical guideline of sludge treatment and disposal for municipal wastewater treatment plant [1]was implemented, tons of sewage sludge was directly poured into sludge lagoon in landfill, which took up designed landfill capacity of municipal solid waste. In order to restore storage capacity of landfill, treatment of sludge lagoon was undertaken. To investigate the feasibility of using vacuum preloading technique on sludge, two model tests were conducted. The experimental results showed that after vacuum preloading water content of sludge decreased sharply and its shear strength increased to 2-4 kPa. The consolidation coefficient of sludge displayed a nonlinear behavior in preloading process. Permeability and water content of sludge around prefabricated vertical drain decreased quickly in early stage, hindering consolidation of sludge away from prefabricated vertical drain. Therefore reducing spacing of prefabricated vertical drain could enhance treatment effect significantly. Pore pressure dissipation of sludge in preloading was different from that in soft clay, especially of the sludge distant from prefabricated vertical drain, which may reveal that pore pressure dissipation in sludge could not be explained by consolidation theory of Terzaghi. In vacuum preloading of sludge, intermittent inlet of boosted air could accelerate drainage rate in early stage; but overall its improvement was limited. Vacuum preloading method can be used as a technique of sludge reduction; but for the requirements of subsequent filling of municipal solid waste on the sludge lagoon, other in situ ground improvement methods should be adopted further to increase its shear strength.

Key words: sludge, vacuum preloading, model test, sludge reduction, in-situ treatment