Impact of Conditioning Substances and Filtration Pressure on Dewatering Efficiency of Sewage Sludge

Tomasz Kamizela,Mariusz Kowalczyk

doi:10.3390/en14020361

Abstract

Sludge dewatering is a key element in sludge’s processing and management. Solid-phase separation, sludge volume reduction and the separation of a high-quality supernatant are the main tasks of the dewatering devices. The effectiveness of this task, in turn, results from the selection of the dewatering method and conditioning of the sludge before dewatering. The aim of the research was to determine the influence of conditioning substances (polyelectrolyte, fly ash and zeolite) on the efficiency of dewatering at variable filtration pressure. The use of polyelectrolyte in sludge conditioning was a solution that increased the efficiency of the filtration process. On the contrary, the use of structure-forming substances (fly ash and zeolite) slows the process but reduces the hydration of the filter cake. The same trends were obtained in dual conditioning combining dosing of polyelectrolyte and ash or zeolite. It was also shown that the dewatering efficiency of conditioned sludge with these two different substances (ash and zeolite) was the same. The use of zeolite in independent or dual conditioning was important for the quality of the supernatant.

Highlights

Municipal sewage sludge is a compressible material whose property can deteriorate the effects of drainage filtration
During the analysis of the results of the pressure filtration process, the greatest attention was focused on the parameter of filtration efficiency and the sludge dewatering effect directly related to efficiency
Much lower filtration efficiency was achieved during the dewatering of sludge conditioned with fly ash or zeolite

Summary

Introduction

Municipal sewage sludge is a compressible material whose property can deteriorate the effects of drainage filtration. 300–400 kPa, it is possible to obtain 35–40% of the dry matter content in the filter cake [1]. It is possible, depending on the type and characteristics of the sludge, that better dewatering effects can be obtained by increasing the pressure and filtration time [2]. Using variable pressure in the process of pressure filtration, a fundamental difference in final water content was obtained already at the stage of dewatering of raw sludge. Between the lowest (0.25 MPa) and the highest (0.75 MPa) applied pressure, a water content difference of up to 3.7% (80.4% for 0.25 MPa pressure and 76.7% for 0.75 MPa pressure) was obtained.

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