Biochar Addition in Membrane Bioreactor Enables Membrane Fouling Alleviation and Nitrogen Removal Improvement for Low C/N Municipal Wastewater Treatment

Abstract

Membrane bioreactors (MBRs) are frequently used to treat municipal wastewater, but membrane fouling is still the main weakness of this technology. Additionally, the low carbon-nitrogen (C/N) ratio influent has been shown to not only increase the membrane fouling, but also introduce challenges to meet the effluent discharge standard for nitrogen removal. Herein, the authors addressed the challenges by adding cost-effective biochar. The results suggested that the biochar addition can enable membrane fouling alleviation and nitrogen removal improvement. The reduced membrane fouling can be ascribed to the biochar adsorption capacity, which facilitates to form bigger flocs with carbon skeleton in biochar as a core. As a result, the biochar addition significantly altered the mixed liquor suspension with soluble microbial product (SMP) concentration reduction of approximately 14%, lower SMP protein/polysaccharide ratio from 0.28 ± 0.02 to 0.22 ± 0.03, smaller SMP molecular weight and bigger sludge particle size from 67.68 ± 6.9 μm to 113.47 ± 4.8 μm. The nitrogen removal is also dramatically improved after biochar addition, which can be due to the initial carbon source release from biochar, and formation of aerobic–anaerobic microstructures. Microbial diversity analysis results suggested more accumulation of denitrification microbes including norank_f__JG30-KF-CM45 and Plasticicumulans. Less relative abundance of Aeromonas after biochar addition suggested less extracellular polymer substance (EPS) secretion and lower membrane fouling rate.

Positive effects of lignocellulose on the formation and stability of aerobic granular sludge

“…In R1, the relative abundances of Thiothrix , Tessaracoccus , and Zoogloea decreased to 6.26, 0.44, and 3.68%, while the relative abundances of Candidatus_Competibacter , Plasticicumulans , norank_f__A4b , norank_f__norank_o__Saccharimonadales , and Micropruina increased to 18.79, 10.87, 9.02, 7.61, and 6.52%, respectively. The decrease in relative abundance of Zoogloea , along with the increased relative abundances of Plasticicumulans , norank_f__A4b , and norank_f__norank_o__Saccharimonadales , which were known for their ability to hydrolyze EPS ( Zhang et al, 2022 ; Jiang et al, 2023 ; Wang et al, 2023 ), collectively contributed to the reduction in EPS content during this stage. Interestingly, the relative abundance of Thiothrix increased to 19.25% in R2-2, however, no excessive filamentous bacteria were observed on the surface of granules in SEM images.…”

Uncovering the Dominant Contribution of Untreated Domestic Wastewater to Antimicrobials in the Lower Reach of the Lhasa River on the Tibetan Plateau

“…It was constructed in two phases, which were completed in 2011 and 2016, respectively . The total volume of treated wastewater discharged into the Lhasa River from the WWTP is approximately 2.3 m 3 /s …”