Water and resources recovery from sewage stand at the foreground of circular economy and technological innovation in the wastewater industry 4.0. The approach of up-concentration of municipal effluent upon arrival at the wastewater treatment facilities followed by anaerobic digestion allows closing cycles and is an alternative solution to conventional activated sludge processes, which have little or no reuse. Dissolved air flotation (DAF) has great potential as an up-concentration process, a first priority of the above-mentioned combo system. To bring the technology readiness level of DAF for up-concentration of sewage and A-sludge to a higher level to make it ready for the market, the knowledge gap in fluid mechanisms of flocculation and hydraulic performance in DAF will be addressed based on the computational fluid dynamics (CFD) modelling and integrated model framework of CFD and PBM (population balance model) and XDLVO (extended Derjaguin- Laudau- Verwey- Overbeek) forces, a totally complete bottom-up approach. Extensive validation experiments of fluid flow velocity, bubble and floc property (density, size distribution, interfacial force, etc.) and residence time distribution in bench- and pilot-scale DAF will be carried out together with the modeling work to build a simulation platform for reliable hydrodynamic prediction in DAF. Based on this platform, optimization of DAF will be carried out in terms of design and operation. A major reduction in the pretreatment flocculation times and an increase of floc stability will be achieved by optimizing contact zone, flocculator pipes and chemical dosage in sewage up-concentration. A major increase in the hydraulic loadings with flow pattern optimization will be pursued by modifying the configuration of contact and separation zone and by varying operations.