An integrated strategy to enhance performance of anaerobic digestion of waste activated sludge. (1st May 2021)

• Record Type: Journal Article
• Authors: Calderon, Angelica Guerrero; Duan, Haoran; Meng, Jia; Zhao, Jing; Song, Yarong; Yu, Wenbo; Hu, Zhetai; Xu, Kangning; Cheng, Xiang; Hu, Shihu; Yuan, Zhiguo; Zheng, Min
• Is Part Of: Water research. Volume 195(2021)
• Publication Date: 2021-05-01
• Subjects: Sludge pretreatment -- Enhanced anaerobic digestion -- Iron dosing -- Low pH -- Free nitrous acid; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.116977
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: A pretreatment method is developed to yield multiple benefits for AD process. Combined FeCl3 and nitrite pretreatment favors the formation of ppm-level FNA. Degradability of WAS is significantly enhanced after 24-hour pretreatment. Dosed Fe also improves biogas quality and vivianite recovery from digested sludge. Abstract: Anaerobic digestion (AD) is an essential process in wastewater treatment plants as it can reduce the amount of waste activated sludge (WAS) for disposal, and also enables the recovery of bioenergy (i.e. methane). Here, a new pretreatment method to enhance anaerobic digestion was achieved by treating thickened WAS (TWAS) with ferric (as FeCl3 ) and nitrite simultaneously for 24-hour at room temperature. Biochemical methane potential tests showed markedly improved degradability in the pretreated TWAS, with a relative increase in hydrolysis rate by 30%. A comparative experiment with the operation of two continuous-flow anaerobic digesters further demonstrated the improvement in biogas quantity and quality, digestate disposal, and phosphorus recovery in the experimental digester. The dosed FeCl3 (i.e. ~6 mM) decreased the pH of TWAS to ~5, which led to the formation of free nitrous acid (FNA, HNO2 ) at parts per million levels (i.e. ~6 mg N/L), after dosing nitrite at 250 mg NO2 − –N/L. This FNA treatment caused a 26% increase in methane yield and volatile solids destruction, 55% reduction in the viscosity of sludge in digester, and 24% less polymer required in further digestate dewatering. In addition, the dosed Fe(III) was reduced to Fe(II) which precipitated sulfide and phosphorus, leading to decreased hydrogen sulfide concentration in biogas, and increased percentage of vivianite in the total crystalline iron species in digested sludge. Our study experimentally demonstrated that combined dosing of FeCl3 and nitrite is a useful pretreatment strategy for improving anaerobic digestion of WAS. Graphical abstract: Image, graphical abstract