Influence of pH on the dewatering of activated sludge by Fenton’s reagent
M.-C. Lu, C.-J. Lin, C.-H. Liao, W.-P. Ting and R.-Y. Huang
Department of Environmental Engineering and Health, Chia Nan University of Pharmacy and Science, Tainan,Taiwan 717
Abstract The specific filtration resistance, moisture, and SVI were used to evaluate the influence of pH on the filtration and dewatering efficiencies when applying Fenton’s reagent to treat the excess sludge. The excess sludge used in this study was obtained from the wastewater treatment plant of An-Ping Industrial Park in Tainan, Taiwan. Results show that initial pH has no significant effect on the filtration efficiency of sludge by using the Fenton (Fe2+/H2O2) system as the treatment process. However, the reduction of
specific resistance by Fenton-like (Fe3+/H2O2) process decreased suddenly to a level similar to that obtained from the control experiment at initial pH > 4.5. For the moisture of cake sludge, both Fenton and Fenton-like systems have the same tendency; the moisture of cake sludge increased slightly with increasing the initial pH. The SVI values for Fenton process decreased with increasing the initial pH, but the opposite result was obtained from the Fenton-like and control system; higher pH was not favora
ble for the sludge settling.
Keywords Dewatering; ferrous ions; filtration; hydrogen peroxide; sludge
Introduction
In conventional wastewater treatment plants, sludges are produced and require disposal. The sludges are principally of an organic nature, such as primary sludge and excess activat-ed sludge. Fresh or undigested sludges, such as primary or secondary sludges, are rather difficult to dewater as compared to digested sludges. Traditionally, sludge is usually condi-tioned to improve its dewatering properties, and then dewatered mechanically.
The Fenton system uses ferrous ions to react with hydrogen peroxide, producing hydroxyl radicals with powerful oxidizing abilities to degrade certain toxic contaminants (Spacek et al., 1995; Lipczynska-Kochany et al., 1995; Lu et al., 1997). The primary oxi-dant in this catalytic reaction is believed to be the hydroxyl radical, which is generated by conversion of hydrogen peroxide. The primary oxidant in this catalytic reaction is believed to be the hydroxyl radical, which is generated by conversion of hydrogen peroxide, as shown in Equation 1:
H2O2+Fe2+Æ◊OH +OH–+Fe3+(1) Moreover, the newly formed ferric ions may catalyze hydrogen peroxide, causing it to be decomposed into water and oxygen. Ferrous ions and radicals are also formed in the reactions. The reactions are as shown in Equations 2–5 (Pardieck et al., 1992; Spacek et al., 1995):
H2O2+ Fe3+´H++ FeOOH2+(2) FeOOH2+Æ ◊HO2+ Fe2+(3)
◊HO
2+ Fe2+Æ ◊HO2–+ Fe3+(4)
◊HO
degrade2+ Fe3+ÆO2 + Fe2++ H+(5)
Water Science and Technology
Vol 44 No 10 pp 327–332
© IWA
Publishing 2001
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