Chapter Two - Enhanced Sewage Sludge Dewaterability by Chemical Conditioning

Abstract

Dewatering is of paramount importance in sludge processing as it reduces sludge volume and the cost of transporting and disposal. For incineration, a sludge with moisture as low as possible is required (at least<50%); and for composting and sanitary landfill, a sludge with a moisture lower than 60% should be preferred. Sewage sludge is often regarded as “difficult to dewater” due to the complex colloidal nature and the strong hydrophilicity. Sludge-dewatering is still a major challenge for environmental researchers. Together with more stringent disposal regulations, this has caused an urgent demand for more efficient dewatering techniques. To enhance sludge dewaterability, various conditioning methods, including Fenton oxidation, Fe(II)-activated persulfate oxidation (Fe(II)-S2O82−), hydrothermal process, and enzymatic hydrolysis, have been proposed in this chapter. Among them, Fe(II)-activated persulfate oxidation is a newly emerging dewatering technique. The rapid disruption of EPS by (Fe(II)-S2O82−) oxidation through the generation of powerful sulfate radicals (SO4−), strengthened the dewatering characteristics, making it attractive for sludge-dewatering. Besides, the combinations of (Fe(II)-S2O82−) oxidation with mild-temperature process or electrolysis are also conducted to maximize the water removal from sludge. The outcome of the work has established some fundamentals that would be useful in the further exploration of novel combined techniques for waste-sludge dewatering. Besides, a newly developed elastic plate-filter press as well as its commercial applications status in sludge-dewatering is introduced.