Field implementation of FeCl₃-conditioning and vacuum preloading for sewage sludge disposed in a sludge lagoon: a case study

Abstract

In China, sewage sludge from wastewater treatment plants is usually disposed in sludge lagoons in municipal solid waste landfills. The increasing amount of sewage sludge generated has become a serious environmental problem. A two-stage method called 'vacuum preloading combined with chemical conditioning' is proposed to treat the disposed sludge. This study presents a case study of full-scale field implementation of the method in a sludge lagoon at the Changan landfill, China. In the first stage, the chemical conditioner was injected into the sludge to improve its consolidation property. The effect of chemical conditioning on dewaterability of sludge was evaluated based on the vacuum filtration test. In the second stage, prefabricated vertical drains (PVDs) were installed in the sludge lagoon as a drainage path, and vacuum pressure was exerted on the conditioned sludge through the PVDs. After 4 months of vacuum preloading, the settlement of the 7 m thick sludge lagoon was approximately 2.91 m, and the volume of the sludge was reduced by 40%. The measurements of pore pressures in the PVDs showed that no attenuation took place for the distribution of vacuum pressure along the PVDs during the test, even when the axial strain of the PVD was 40%. The measurements of pore pressures away from the PVDs showed that pore water pressures in the sludge did not dissipate with respect to the hydrostatic pore water pressures. During the vacuum preloading of conditioned sludge, the degree of consolidation U p based on pore pressure was significantly lower than U s based on settlement.

Numerical Simulation of Vacuum Preloading for Chemically Conditioned Municipal Sludge

“…Lin et al [19] proposed a two-stage in-situ treatment method for vacuum preloading on conditioned sludge combined with chemical treatment to improve the sludge ground. Based on the pilot and field tests [19,29], it was proven that the combination of vacuum preloading and chemical treatment can successfully reduce the amount of sludge treatment, and a good curing effect was obtained. To further understand the consolidation characteristics of the conditioned sludge in the treatment process, the field and pilot tests were simulated with the developed model and the results were compared with the measured values.…”

“…In this study, a numerical analysis model for large deformation nonlinear shaft consolidation, which considers the large deformation and nonlinear characteristics of conditioned sludge in the consolidation process, was developed. The model was used to simulate the pilot and field tests [29] of chemically conditioned sludge under the conditions of vacuum preloading in a sludge lagoon at the Chang'an landfill, China, and the simulation results were compared with the measured values.…”

Insights into vacuum preloading consolidation of landfill sludge based on Fe2+-activated sodium persulfate

“…The test results expressed that the sludge water content signi cantly reduced, and the strength increased a little. Besides, Zhan et al (2015) combined the vacuum preloading method with FeCl 3 for the rst time. The sludge volume reduction exceeded 40%, showing the superiority of the experimental effect.…”

Consolidation Considering Clogging Effect under Uneven Strain Assumption

“…However, recent studies (Liu et al, 2017;Bao et al, 2014;Deng et al, 2018, Zhan et al, 2015 have reported that poor treatment quality was observed when dredged slurry was treated by the vacuum preloading method. In those cases, when the water discharge rate approached zero, the ground soil still showed low bearing capacity generally.…”