Microwave-assisted chemical oxidation of biological waste sludge: Simultaneous micropollutant degradation and sludge solubilization

Beneficial effects of treating waste secondary sludge with thermally activated persulfate

“…During oxidative processes, the degradation efficiency of targeted organic contaminants that are sorbed on a solid matrix can be affected by their desorption as well as the properties of the matrix. 16 -18 Efficient oxidant contact with the contaminant in the complex sludge matrix can be considered a limiting factor for the performance of the chemical oxidation process; this has been clearly demonstrated for electrochemical treatment of organic contaminants in sludge. 19 Increase in process efficiency can be expected through desorption of the contaminant from the solid phase.…”

“…Actually, high degradation of the target contaminant was generally achieved in the early stages of oxidation, at which point the degree of solubilization of the sludge components was not high; prolonging the treatment time did not result in any substantial improvement in the degradation rates. 5,9,14 Furthermore, a high total solids concentration of sludge that was treated with a chemical oxidant could have initially exerted the aforementioned competition effect, 11,16 and this also could have resulted in a relatively low degradation rate of the target organics (Table 1). It is well known that because of its influence on desorption and solubilization processes, pH is an important factor in terms of the availability of organic pollutants and potential sludge catalytic components.…”

“…During ozone and calcium peroxide treatment of sludge, an enhancement in the degradation of antimicrobials and endocrine disrupters at high pH values has been attributed to desorption of the contaminants. 9,16 However, as shown in Table 1, even at acidic pH values, a high degradation rate of the organic contaminants can be achieved by hydrogen peroxide based oxidative treatment, which requires an acidic pH value to provide both the stability of the oxidant and the availability of the iron catalyst. 10,12,14,16 Furthermore, the pH exerts an influence on the electrostatic forces that exist between sludge particles, and in the case of weakly agglomerated sludge particles, oxidant contact with sludge contaminants can be enhanced.…”

“…To achieve more effective destruction of organic contaminants, thermally assisted oxidative treatment can be applied to sewage sludge as a means to enhance diffusion; however, this treatment causes a substantial increase in the concentration of solubilized organics. 13,16 Microwave (MW) heating can reduce the time of a thermally assisted oxidative treatment; 26 hence, it has the potential to reduce the operating costs/energy requirements associated with treating waste sludge. However, relatively high MW temperatures (>140 ∘ C) are required for MW-assisted oxidative treatment to achieve a large amount of target organic pollutant degradation in waste sludge.…”

“…However, relatively high MW temperatures (>140 ∘ C) are required for MW-assisted oxidative treatment to achieve a large amount of target organic pollutant degradation in waste sludge. 16 Furthermore, in the case of MW-assisted hydrogen peroxide oxidation, because of its higher reactivity compared with persulfate, hydrogen peroxide is consumed excessively by the native sludge enzyme catalase through a nonradical pathway; 27 therefore, inclusion of a preheating stage for sewage sludge treatment is necessary to eliminate the enzyme prior to treatment, and this prolongs the duration of the overall sludge treatment. 17 Unlike hydrogen peroxide, persulfate is not consumed by the sludge catalase during treatment, and it is effectively activated to produce the sulfate radical (SO 4…”