Efficient bio-refractory industrial wastewater treatment with mitigated membrane fouling in a membrane bioreactor strengthened by the micro-scale ZVI@GAC galvanic-cells-initiated radical generation and coagulation processes

Shihai Deng; Qi Wang; Qinqing Cai; Say Leong Ong; Jiangyong Hu

doi:10.1016/j.watres.2021.117943

Efficient bio-refractory industrial wastewater treatment with mitigated membrane fouling in a membrane bioreactor strengthened by the micro-scale ZVI@GAC galvanic-cells-initiated radical generation and coagulation processes

Water Res. 2022 Feb 1:209:117943. doi: 10.1016/j.watres.2021.117943. Epub 2021 Dec 7.

Authors

Shihai Deng¹, Qi Wang², Qinqing Cai¹, Say Leong Ong¹, Jiangyong Hu³

Affiliations

¹ Sembcorp-NUS Corporate Laboratory, Sembcorp-NUS Corporate Laboratory c/o FoE, National University of Singapore, Block E1A, #04-01, 1 Engineering Drive 2, Singapore 117576, Singapore; Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, Block E1A, #07-01, 1 Engineering Drive 2, Singapore 117576, Singapore.
² Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, Block E1A, #07-01, 1 Engineering Drive 2, Singapore 117576, Singapore.
³ Sembcorp-NUS Corporate Laboratory, Sembcorp-NUS Corporate Laboratory c/o FoE, National University of Singapore, Block E1A, #04-01, 1 Engineering Drive 2, Singapore 117576, Singapore; Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, Block E1A, #07-01, 1 Engineering Drive 2, Singapore 117576, Singapore. Electronic address: hujiangyong@nus.edu.sg.

PMID: 34923441
DOI: 10.1016/j.watres.2021.117943

Abstract

Micro-scale ZVI@GAC-based iron-carbon galvanic-cells (ZVI@GACs) were prepared with the Ca-Si-H/Ca-H formation process and first applied to initiate radical generation and coagulation processes in MBR for treating bio-refractory industrial wastewater (IWW). Batch tests revealed the H₂O₂ production (0.19-0.28 mg/L) and •OH generation (p-CBA decay, k₁ = 0.040 min^-1) in ZVI@GACs-dosed system (packing volume of 5%) under aeration. Adoption of ZVI@GACs into aerobic activated sludge process (ZVI@GACs/AS) enhanced TOC degradation (k₂) and phenolic compounds (PHENs) destruction (k₃). ZVI@GACs/AS at ZVI@GACs packing volume of 5%, 10% and 20% improved k₂ from 0.11 h^-1 (bare AS) to 0.17, 0.21 and 23 h^-1 and k₃ from 0.24 h^-1 to 0.36, 0.49 and 0.57 h^-1, respectively. The oxygen uptake rate (OUR) and 15-min acute bio-toxicity demonstrated that the bio-toxicity of IWW was reduced and the activity of biomass was enhanced in the ZVI@GACs/AS system. In MBR, ZVI@GACs at packing volume of 10% enhanced COD and PHENs removal by 14% and 22%, respectively. Membrane fouling cycle was prolonged by 71%. The accumulations of EPS-proteins, EPS-polysaccharides, SMP-proteins and SMP-polysaccharides were reduced by 6%, 67%, 27% and 60%, respectively. Fourier transform infrared spectroscopy (FTIR) confirmed the oxidation of SMP-polysaccharides in ZVI@GACs-MBR. The iron ions released from ZVI@GACs showed inhibition on the secretion of SMP-/EPS-proteins. Floc particle size distribution (PSD) and X-ray diffraction (XRD) spectrum confirmed that the coagulation effects of Fe(OH)₃ and FeOOH triggered by Fe³⁺ increased the sludge floc size and contributed to membrane fouling mitigation. Genus Enterococcus was enriched in MBR with the destruction of PHENs by the ZVI@GACs-initiated radical generation process. The findings of this study confirmed successful development and adoption of ZVI@GACs into MBR for bio-refractory IWW treatment. It also provided an in-depth understanding on the mechanisms of ZVI@GACs-MBR system.

Keywords: Bio-refractory industrial wastewater; Iron-carbon galvanic-cells (Fe(0)/C); Membrane bioreactor (MBR); Membrane fouling; Micro-scale ZVI@GACs; Soluble microbial products.