The overall goal of this project is to make resilient water treatment technologies that are the most economical for application in the global south and the highest performing for application in industrialized countries. Hydraulic flocculation requires no electricity, has no moving parts, and is a key component of resilient high performing treatment of surface water and of arsenic contaminated groundwater. The proposed research will create and test a mechanistically based model for turbulent flow hydraulic flocculation and to use that model as a basis for optimizing hydraulic flocculator design. The research performed under this project will be integrated into the AguaClara program at Cornell University. This integration ensures a high level of undergraduate involvement in the research and rapid transfer of the research results into scalable design algorithms and then to implementation partners in other countries who build AguaClara facilities for communities in need of safe drinking water. The hands-on research and design experience with an international context creates an engineering education that changes lives. The fundamental understanding resulting from this research will improve the performance of robust gravity powered, water treatment plants and will reduce costs.
The large range of relevant length scales (nm to m) and the turbulent and laminar flow regimes that occur in sequential processes used for water treatment have resulted in an empirical approach to design that does not correctly scale to the flows applicable to small communities (1,000 to 50,000 individuals). In the proposed research, theoretical analysis coupled with experimental evaluation will be used to identify the dominant parameters and mechanisms affecting the growth and breakup of flocculent particles, and their distribution of sedimentation velocities. Most previous work on flocculation has utilized mechanically-stirred reactors with poorly characterized and highly heterogeneous energy dissipation rates. This project will use well-characterized turbulent tube flow flocculators and turbulent serpentine baffled flow reactors (characterized by computational fluid dynamics (CFD)). Core components of the proposed model have already been created through studies of flocculation under laminar flow and reveal a composite dependence of flocculation on floc volume fraction, colloid surface coverage by coagulant (both dependent on influent turbidity and coagulant type and dose), and reactor conditions (energy dissipation rate, hydraulic residence time). Specialized instrumentation has also been constructed that permits non-destructive analysis of flocculent particle settling velocities, video monitoring of solids concentration over a wide range of time and spatial scales within experimental reactors, and automation of experiments which allows exploration of a greater range of parameter space than would otherwise be possible.
