Dewatering municipal wastewater sludge using electro-coagulation combined with added free nitrous acid. (November 2022)

• Record Type: Journal Article
• Authors: Wang, Zehao; Song, Hongwei; Song, Lei; Yin, Zhenzhou; Hui, Kai; Gao, Wenjian; Xuan, Lili
• Is Part Of: Chemosphere. Volume 306(2022)
• Publication Date: 2022-11
• Subjects: Sludge dewaterability -- Electro-coagulation -- Free nitrous acid -- Re-flocculation; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2022.135484
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: An electro-coagulation (EC) process combined with added free nitrous acid (FNA) improves sludge dewaterability. Under optimal conditions(EC voltage of 25 V, EC process time of 60 min, FNA dosage of 1.13 mg/L, pH value of 4.5), specific resistance to filtration (SRF) and water content (WC) was decreased by 89.57%, and 18.90%respectively. The EC process disrupted the sludge structure, reducing sludge particles' size (D50) from 59.5 to 50.5 μm. After adding FNA, the sludge cells lysed, and the DNA concentrations and soluble chemical oxygen demand (SCOD) increased from 6.07 μg / ml and 29 mg/L to 364 μg / ml and 588 mg/L, respectively. The conversion of Fe(II) to Fe(III) was enhanced. The addition of FNA after EC further improved the sludge dewaterability. Combined conditioning using EC and FNA can effectively destroy tightly bound extracellular polymeric substances (TB-EPS) and release bound water. In addition, the pH value is kept low, which benefits sludge dewaterability and the removal of heavy metals. The concentrations of Zn and Mn in the sludge cake were reduced by 92.3% and 69.0%, respectively. The Bureau of Reference (BCR) sequential extraction method showed increases in the percentages of the residual fractions of Zn and Mn, showing that EC combined with FNA is an efficient and versatile means of sludge conditioning. Graphical abstract: Image 1 Highlights: EC + FNA produces Fe(III) to facilitate the re-flocculation of sludge. EC + FNA can destroy the structure of proteins and reduce the hydrophilic sites. EC + FNA spontaneously lowers pH value.