Abstract
Conventional dewatering technologies, such as centrifuges, belt filter presses, and rotary vacuum filters, are not effective methods for treating sewage sludge with high water content. This study evaluated the field-scale feasibility of new technologies that use emulsion, ultrasonication, and microwaves to dewater sludge. Emulsion technology lowered the water content in sludge to 60%, but the overall process was too complex to incorporate into the design of commercial plants due to the requirement for oil- and methanol-recovery facilities. Ultrasonication had low dewatering and energy efficiency with long irradiation times, indicating that it would be difficult to implement in a field plant. The water content of sludge was reduced to 60% within 120 s using microwaves, but dewatering efficiency depended on the thickness and volume of the sludge. In a pilot-scale test, the average energy consumption was 0.54 kWh/kg of water removed, and the final water content of the sludge cake reached 60% within 30 min. Keywords : emulsion, energy efficiency, microwave, sludge dewatering, ultrasonication
Highlights
In recent years, the production of waste-activated sludge in municipal wastewater treatment plants has increased significantly
Treatment and disposal methods for municipal wastewater sludge include landfilling, ocean disposal, incineration, and composting, but direct landfills have been banned since July 2003 (MOE, 2003), and ocean disposal was outlawed in January 2012 (MOF, 2009)
Sludge dewatering is a fundamental step in sludge processing because it decreases sludge volume and the cost of transporting the sludge to its final disposal site
Summary
The production of waste-activated sludge in municipal wastewater treatment plants has increased significantly. The moisture content of municipal wastewater sludge must be reduced significantly before its incineration and composting. The water content of activated sludge can be decreased to approximately 80% with existing mechanical dewatering technologies. To this end, various methods have been proposed to improve sludge dewaterability, such as the addition of acids and surfactants, Fenton’s reagent pre-treatment, fungal treatment, ultrasonication, and microwave irradiation (Chen et al, 2001; Eskicioglu et al, 2007; Fakhru’l-Razi and Molla, 2007; Tony et al, 2008; Feng et al, 2009a; 2009b; Yu et al, 2009)
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