Unraveling oxidation behaviors for intracellular and extracellular from different oxidants (HOCl vs. H2O2) catalyzed by ferrous iron in waste activated sludge dewatering. (1st January 2019)

• Record Type: Journal Article
• Authors: Yu, Wenbo; Wen, Qianqian; Yang, Jiakuan; Xiao, Keke; Zhu, Yuwei; Tao, Shuangyi; Lv, Yang; Liang, Sha; Fan, Wei; Zhu, Suiyi; Liu, Bingchuan; Hou, Huijie; Hu, Jingping
• Is Part Of: Water research. Volume 148(2019)
• Page Start: 60
• Page End: 69
• Publication Date: 2019-01-01
• Subjects: Waste activated sludge -- Deep-dewatering -- Hypochlorite acid -- Oxidation intensity -- Extracellular and intracellular oxidation -- Cell lysis; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2018.10.033
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Cell lysis in sludge pretreatment by advanced oxidation process (AOP) has a great effect on sludge dewaterability. Cell lysis caused by reactive radicals (e.g. hydroxyl radical) was dependent on the reaction site of AOP. However, little is known about the accurate radical generation site of AOP in sludge pretreatment. In this study, two kinds of oxidation behaviors from different oxidants (HOCl vs. H2 O2 ) catalyzed by ferrous iron were comparatively investigated. Higher amount of living cells (84.3%) and hydroxyl radicals (9.86 × 10 −5 M), and more fragmentized sludge flocs (particle sizes of D50 was 50.1 vs. 57.3 μm of RS) were detected in sludge conditioned by Fe 2+ /H2 O2, which implied that Fenton reaction mainly happened at surface and outside of sludge flocs (such as EPS layer and liquid phase). Thus, it could be regarded as "extracellular oxidation". Fewer living cells (undetectable), fewer amount of hydroxyl radicals (undetectable in sludge), and more integrated sludge flocs (particle size of D50 was 56.1 vs. 57.3 μm of RS) were determined in sludge conditioned by Fe 2+ /Ca(ClO)2 . Hence, it could be regarded as "Intracellular oxidation". In addition, sludge pretreatment based on Fe 2+ /Ca(ClO)2 could achieve simultaneous deep-dewatering performance and total coliforms inactivation. Based on response surface methodology, the optimal dosages of Fe 2+ and Ca(ClO)2 were proposed as 106.1 and 234.5 mg/g volatile solids respectively, without any acidification of sludge. Under these optimal dosages, the water content of dewatered sludge cake was 51.9 ± 0.1 wt% and the pH of the final filtrate was 5.8 ± 0.2. Total coliforms of sludge could be inactivated in 10 s after Fe 2+ /Ca(ClO)2 addition. Graphical abstract: Highlights: Catalyzed hypochlorite achieved deep-dewatering and Escherichia coli inactivation. Optimal dosages of 106.1 mg Fe 2+ /g VS and 234.5 mg Ca(ClO)2 /g VS were proposed. Extracellular and intracellular oxidations were investigated in sludge pretreatment. Hypochlorite attacked inner cell components, resulting in intracellular oxidation. Fenton oxidation occurred at surface of sludge flocs as extracellular oxidation.