Influence of powdered activated carbon on gravity-driven ultrafiltration for decentralized drinking water treatment: Insights from microbial community and biofilm structure.

[Display omitted] • The link between microbial community, biofilm structure and flux was explored. • The presence of PAC reduced the abundance of metazoans, especially Nematoda. • The lower stable flux with PAC was due to increased EPS and decreased metazoans. • The presence of PAC promoted the nitrification within the biofilm. • The PAC/GDM system exhibited an excellent and long-lasting removal of organics. Gravity-driven membrane (GDM) filtration, an appealing approach for decentralized drinking water treatment, tolerates the development of membrane biofilms for the benefit of low energy consumption and stable flux. In this study, the effect of introducing powdered activated carbon (PAC) on the biofilm generated during long-term GDM filtration was investigated. The results indicated that the addition of PAC significantly enhanced the removal of dissolved organic compounds (DOC) (31 %), whereas only 15.7 % removal was achieved in the control GDM system without PAC. The improved permeate quality was attributed to the combined effects of adsorption and biodegradation of organic compounds by PAC. However, the presence of PAC reduced the permeability of the GDM system by 39 % compared to the control one, which was related to the synergetic effect of the increased extracellular polymeric substances (EPS) content and the decreased metazoan amounts (especially Nematoda) in the biofilm. A large number of substrates adsorbed by PAC facilitated the growth of bacteria and hence intensified the secretion of EPS. Meanwhile, the deposition of PAC on the membrane surface limited the movement space of metazoans, leading to a denser and flatter biofilm basal structure. Furthermore, fewer metazoans meant less predation on bacteria, which also contributed to bacterial reproduction. In addition, an enhanced removal efficiency of ammonia nitrogen was observed in the PAC/GDM system, corresponding to a much higher abundance of Nitrospira in bacterial community. This study links microbial community to hydraulic resistance of biofilm and has practical implications for the application of GDM processes. [ABSTRACT FROM AUTHOR]