An Improved Method for Dewatering Sewage Sludge Using Intermittent Vacuum Loading with Wheat Straw as Vertical Drains

Abstract

This paper presents an experimental investigation on the feasibility and effectiveness of an improved method for dewatering sewage sludge (SS) in landfills. Compared with traditional vacuum preloading with prefabricated vertical drains (PVDs), an improved intermittent vacuum loading with wheat straw vertical drains (WSVDs) was developed and a series of laboratory tests were conducted to evaluate the effects of WSVD type and intermittent loading period on the dewatering properties of SS. Tests results showed that the WSVD has a good elastic deformation characteristic during vacuum loading and unloading over PVD. The vacuum degree transmission tests on three types of WSVD showed that 5 cm crushed wheat straw is the optimum one. The surface settlement and water content of SS after the model test are similar for WSVD and PVD in the traditional vacuum consolidation method. There was a significant improvement when applying intermittent vacuum and optimum daily loading time of 10 hours was obtained. The cracks found in the sludge cake around the drainage body using improved method are suggested as the key factor since they are able to improve the vacuum transmission capacity and the permeability of SS. The improved method is expected to offer a feasible and cost-effective way to deal with high water content SS in landfills.