title: Roles of iron species and pH optimization on sewage sludge conditioning with Fenton's reagent and lime.
abstract: Conditioning sewage sludge with Fenton's reagent could effectively improve its dewaterability. However, drawbacks of conditioning with Fenton's reagent are requirement of acidic conditions to prevent iron precipitation and subsequent neutralization with alkaline additive to obtain the pH of the filtrate close to neutrality. In this study, roles of pH were thoroughly investigated in the acidification pretreatment, Fenton reaction, and the final filtrate after conditioning. Through the response surface methodology (RSM), the optimal dosages of H2SO4, Fe(2+), H2O2, and lime acted as a neutralizer were found to be 0 (no acidification), 47.9, 34.3 and 43.2 mg/g DS (dry solids). With those optimal doses, water content of the dewatered sludge cakes could be reduced to 55.8 ± 0.6 wt%, and pH of the final filtrate was 6.6 ± 0.2. Fenton conditioning without initial acidification can simplify the conditioning process and reduce the usage of lime. The Fe(3+) content in the sludge cakes showed a close correlation with the dewaterability of conditioned sludge, i.e., the water content of sludge cakes, SRF (specific resistance to filtration), CST (capillary suction time), bound water content, and specific surface area. It indicated that the coagulation by Fe(3+) species in Fenton reaction could play an important role, compared to traditional Fenton oxidation effect on sludge conditioning. Thus, a two-step mechanism of Fenton oxidation and Fe(III) coagulation was proposed in sewage sludge conditioning. The mechanisms include the following: (1) extracellular polymeric substances (EPS) were firstly degraded into dissolved organics by Fenton oxidation; (2) bound water was converted to free water due to degradation of EPS; (3) the sludge particles were disintegrated into small ones by oxidation; (4) Fe(3+) generated from Fenton reaction acted as a coagulant to agglomerate smaller sludge particles into larger dense particles with less bond water; (5) finally, the dewatered sludge cakes were obtained, with less small pores (1-10 nm) that contributed to water affinity, but with more large pores (>10 nm) that contributed to a permeable, rigid lattice structure. Morphology of the Fenton-conditioned sludge cake exhibited a porous structure. The estimated cost of the composite conditioner, Fenton's reagent and lime, is USD$ 43.8/t DS, which is less than that of ferric chloride and lime (USD$ 54/t DS). Furthermore, pH of the final filtrate using this composite conditioner is about 6.6. Comparatively, that using ferric chloride and lime is as high as 12.4.
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Wenbo
authors.initials: W
authors.lastname: Yu
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China. Electronic address: jkyang@mail.hust.edu.cn.
authors.forename: Jiakuan
authors.initials: J
authors.lastname: Yang
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Yafei
authors.initials: Y
authors.lastname: Shi
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Jian
authors.initials: J
authors.lastname: Song
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Shi
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiao
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Xu
authors.affiliation: Universtar Science & Technology (Shenzhen) Co., Ltd., Shenzhen, Guangdong 518057, PR China.
authors.forename: Shu
authors.initials: S
authors.lastname: He
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Sha
authors.initials: S
authors.lastname: Liang
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Xu
authors.initials: X
authors.lastname: Wu
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.
authors.forename: Jingping
authors.initials: J
authors.lastname: Hu
mesh_terms: D005290:Ferric Compounds; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D012722:Sewage / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D012722:Sewage; D006861:Hydrogen Peroxide; D007501:Iron
keywords: Fe(III) coagulation; Fenton's reagent; Sewage sludge conditioning; Sludge dewatering performance; pH optimization