Pre-deposited biochar enhanced flux stabilization and pollutant removal in gravity-driven membrane system

The relatively unstable dissolved organic removal efficiency and low water flux during long-term filtration of gravity-driven membrane (GDM) are major barriers to its widespread application in decentralized water treatment. In this study, the role of pre-deposited biochar (BC) and iron-modified biochar (FBC) layers in GDM for treating surface water were firstly investigated, aiming to explore the feasibility of cost-effective agricultural waste as pre-deposition materials. Compared to the relatively low removal efficiency of GDM control group (DOC 18.1 %, UV₂₅₄ 10.6 %), both BC pre-deposited GDM (BC-GDM: DOC 36.0 %, UV₂₅₄ 39.9 %) and FBC pre-deposited GDM (FBC-GDM: DOC 31.9 %, UV₂₅₄ 32.4 %) show considerably enhanced removal efficacy. Also, pre-deposited BC/FBC layers accelerated the start-up process for NH₄⁺-N removal. The enhancement of functional bacteria such as Proteobacteria and Nitrospirota was accountable for pollutant removal efficacy. Regarding the flux stabilization, compared to the GDM control system, the final stable flux of BC-GDM increased by 3.61 % while FBC-GDM decreased by 9.55 %. The presence of BC layer increased the bacterial activity, porosity of the formed biofouling layer, thus favored the flux enhancement, resulting in a lower water production cost. Conversely, the presence of Fe in FBC may inhibit the microbial activity and diminish its pore structure, leading to reduced flux transport. Our study suggests simple pre-deposition of BC shows positive effect on ultra-low pressure GDM filtration, highlighting the potential application of low-cost agriculture waste in decentralized drinking water treatment.